Note: Descriptions are shown in the official language in which they were submitted.
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BATTERY CONNECTIONS AND METALLIZED FILM COMPONENTS IN ENERGY
STORAGE DEVICES HAVING INTERNAL FUSES
FIELD OF THE INVENTION
[001] The present disclosure relates to improvements in the structural
components and physical
characteristics of lithium battery articles. Standard lithium ion batteries,
for example, are prone to
certain phenomena related to short circuiting and have experienced high
temperature occurrences
and ultimate firing as a result. Structural concerns with battery components
have been found to
contribute to such problems. Improvements provided herein include the
utilization of thin
metallized current collectors (aluminum and/or copper, as examples), high
shrinkage rate materials,
materials that become nonconductive upon exposure to high temperatures, and
combinations
thereof Such improvements accord the ability to withstand certain
imperfections (dendrites,
unexpected electrical surges, etc.) within the target lithium battery through
provision of ostensibly an
internal fuse within the subject lithium batteries themselves that prevents
undesirable high
temperature results from short circuits. Battery articles and methods of use
thereof including such
improvements are also encompassed within this disclosure.
[002] Of particular interest and importance is the provision of a lithium
battery cell that includes
needed tabs leads to allow for conductance from the internal portion thereof
externally to power a
subj ect device, which may be a non-trivial provision because of the thin
nature of the electrodes, and
potentially that the two sides of the electrode material may not be conductive
with each other. In
this disclosure, provided are tabs that exhibit sufficient safety levels in
combination with the internal
fuse characteristics noted above while simultaneously displaying pull strength
to remain in place
during utilization as well as complete coverage with the thin film metallized
current collectors for
such an electrical conductivity result. Such tabs are further provided with
effective welds for the
necessary contacts and at levels that exhibit surprising levels of amperage
and temperature resistance
to achieve the basic internal fuse result with the aforementioned sufficient
conductance to an
external device. With such a tab lead component and welded structure, a
further improvement
within the lithium battery art is provided the industry.
[003] Additionally, the internal fuse developments disclosed herein,
exhibiting extremely thin
current collector structures, further allow for the potential for repetitive
folds thereof within a single
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cell. Such a fold possibility provides the capability of connecting two sides
of a current collector,
which might otherwise be electrically insulated by a polymer layer situated
between the two
conducting layers, without the need for excessive internal weight and/or
battery volume
requirements. Ostensibly, the folded current collector retains the internal
fuse characteristics while
simultaneously permitting for such a power increase, potentially allowing for
any number of power
increases within any number of sized batteries without the need for the
aforementioned excessive
weight and volume requirements, creating new battery articles for different
purposes with targeted
high power levels and as high safety benefits as possible.
BACKGROUND ART
[004] Lithium batteries remain prevalent around the world as an electricity
source within a
myriad of products. From rechargeable power tools, to electronic cars, to the
ubiquitous cellular
telephone (and like tablets, hand-held computers, etc.), lithium batteries (of
different ion types) are
utilized as the primary power source due to reliability, above-noted
rechargeability, and longevity of
usage. With such widely utilized power sources, however, comes certain
problems, some of which
have proven increasingly serious. Notably, safety issues have come to light
wherein certain
imperfections within such lithium batteries, whether due to initial
manufacturing issues or time-
related degradation problems, cause susceptibility to firing potentials during
short circuit events.
Basically, internal defects with conductive materials have been found to
create undesirable high heat
and, ultimately, fire, within such battery structures. As a result, certain
products utilizing lithium
batteries, from hand-held computerized devices (the Samsung Galaxy Note 7, as
one infamous
situation) to entire airplanes (the Boeing 787) have been banned from sales
and/or usage until
solutions to compromised lithium batteries used therein and therewith have
been provided (and even
to the extent that the Samsung Galaxy Note 7 has been banned from any
airplanes in certain
regions). Even the Tesla line of electric cars have exhibited notable problems
with lithium battery
components, leading to headline-grabbing stories of such expensive vehicles
exploding as fireballs
due to battery issues. Widespread recalls or outright bans thus remain today
in relation to such
lithium battery issues, leading to a significant need to overcome such
problems.
[005] These problems primarily exist due to manufacturing issues, whether
in terms of
individual battery components as made or as such components are constructed as
individual batteries
themselves. Looked at more closely, lithium batteries are currently made from
six primary
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components, a cathode material, a cathode current collector (such as aluminum
foil) on which the
cathode material is coated, an anode material, an anode current collector
(such as copper foil) on
which the anode material is coated, a separator situated between each anode
and cathode layer and
typically made from a plastic material, and an electrolyte as a conductive
organic solvent that
saturates the other materials thereby providing a mechanism for the ions to
conduct between the
anode and cathode. These materials are typically wound together into a can, as
shown in Prior Art
FIG. 1, or stacked. There are many other configurations that are and may be
utilized for such battery
production purposes, including pouch cells, prismatic cells, coin cells,
cylindrical cells, wound
prismatic cells, wound pouch cells, and the list goes on. These battery cells,
when made correctly
and handled gently, can provide energy for various applications for thousands
of charge-discharge
cycles without any appreciable safety incident. However, as alluded to above,
certain events and, in
particular, certain defects can cause internal shorting between the internal
conductive materials
which can lead to heat generation and internal thermal runaway, known to be
the ultimate cause of
fire hazards within such lithium batteries. Such events may further be caused
by, as noted above,
.. internal defects including the presence of metallic particles within the
battery, burrs on the current
collector materials, thin spots or holes in the separator (whether included or
caused during
subsequent processing), misalignments of battery layers (leaving "openings"
for unwanted
conductivity to occur), external debris penetrating the battery (such as road
debris impacting a
moving vehicle), crushing and/or destabilizing of the cell itself (due to
accidents, for instance),
charging the cell in a confined space, and the like. Generally speaking, these
types of defects are
known to cause generation of a small electronic conductive pathway between the
anode and cathode.
When such an event occurs, if the cell is then charged, such a conductive
pathway may then cause a
discharge of the cell therethrough which ultimately generates excessive heat,
thereby compromising
the battery structure and jeopardizing the underlying device being powered
thereby. Combined with
the presence of flammable organic solvent materials as battery electrolytes
(which are generally of
necessity for battery operability), such excessive heat has been shown to
cause ignition thereto,
ultimately creating a very dangerous situation. Such problems are difficult to
control once started, at
the very least, and have led to significant injuries to consumers. Such a
potential disastrous situation
is certainly to be avoided through the provision of a battery that delivers
electrical energy while not
.. compromising the flammable organic electrolyte in such a manner.
[006] The generation of excessive heat internally may further create
shrinkage of the plastic
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separator, causing it to move away from, detach, or otherwise increase the
area of a short within the
battery. In such a situation, the greater exposed short area within the
battery may lead to continued
current and increased heating therein, leading to the high temperature event
which causes significant
damage to the cell, including bursting, venting, and even flames and fire.
Such damage is
particularly problematic as the potential for firing and worse comes quickly
and may cause the
battery and potentially the underlying device to suffer an explosion as a
result, putting a user in
significant danger as well.
[007] Lithium batteries (of many varied types) are particularly susceptible
to problems in
relation to short circuiting. Typical batteries have a propensity to exhibit
increased discharge rates
with high temperature exposures, leading to uncontrolled (runaway) flaring and
firing on occasion,
as noted above. Because of these possibilities, certain regulations have been
put into effect to
govern the actual utilization, storage, even transport of such battery
articles. The ability to effectuate
a proper protocol to prevent such runaway events related to short circuiting
is of enormous
importance, certainly. The problem has remained, however, as to how to
actually corral such issues,
particularly when component production is provided from myriad suppliers and
from many different
locations around the world.
[008] Some have honed in on trying to provide proper and/or improved
separators as a means to
help alleviate potential for such lithium battery fires. Low melting point
and/or shrinkage rate
plastic membranes appear to create higher potentials for such battery firing
occurrences. The
general thought has then been to include certain coatings on such separator
materials without
reducing the electrolyte separation capabilities thereof during actual
utilization. Thus, ceramic
particles, for instance, have been utilized as polypropylene and/or
polyethylene film coatings as a
means to increase the dimensional stability of such films (increase melting
point, for example).
Binder polymers have been included, as well, as a constituent to improve
cohesion between ceramic
particles and adhesion to the plastic membrane (film). In actuality, though,
the thermal increase
imparted to the overall film structure with ceramic particle coatings has been
found to be relatively
low, thus rendering the dominant factor for such a separator issue to be the
actual separator
material(s) itself.
[009] As a result, there have been designed and implemented, at least to a
certain degree,
separator materials that are far more thermally stable than the polyethylene
and polypropylene
porous films that make up the base layer of such typical ceramic-coated
separators. These low
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shrinkage, dimensionally stable separators exhibit shrinkage less than 5% when
exposed to
temperatures of at least 200 C (up to temperatures of 250, 300, and even
higher), far better than the
high shrinkage rates exhibited by bare polymer films (roughly 40% shrinkage at
150 C), and of
ceramic-coated films (more than 20% at 180 C) (such shrinkage measurement
comparisons are
5 provided in Prior Art FIG. 2). Such low shrinkage rate materials may
change the mechanism of
thermal degradation inside a target cell when a short occurs. Generally
speaking, upon the
occurrence of a short within such a battery cell, heat will always be
generated. If the separator does
not shrink in relation to such a short circuit event, heat will continue to be
generated and "build up"
until another material within the battery degrades. This phenomenon has been
simulated with an
industry standard nail penetration test. For instance, even with a separator
including para-aramid
fiber and exhibiting a shrinkage stability up to 550 C., the subject test
battery showed a propensity
to short circuit with unique internal results. Such a cell was investigated
more closely subsequent to
such treatment wherein the cell was opened, the excess electrolyte was
evaporated, the cell filled
with epoxy and then sectioned perpendicular to the nail, which was left in the
cell. Scanning
electron microscope images were then undertaken using backscattered electron
imaging (BEI),
which enabled mapping of the different battery elements to show the effect of
such a nail penetration
activity. These are shown in Prior Art FIGS. 3A and 3B.
[010] In Prior Art FIG. 3A, it is noted that the copper layers consistently
come closer to the nail
than the aluminum layers. It is also noted that the high stability separator
is still intact between the
electrodes. Prior Art FIG. 3B shows a higher magnification of the end of one
aluminum layer,
showing that it ends in a layer of cracked grey matter. This was investigated
with BEI, which
showed the resultant matter to actually be aluminum oxide, an insulating
ceramic. Such evidence
led to the proposed conclusion that when the separator itself is thermally
stable, the aluminum
current collector will oxidize, effectively breaking the circuit (and
stopping, as a result, any short
circuit once the insulating aluminum oxide is formed). Once the circuit is
broken, the current stops
flowing and the heat is no longer generated, reversing the process that, with
less stable separators,
leads to thermal runaway.
[011] This possible solution, however, is limited to simply replacing the
separator alone with
higher shrinkage rate characteristics. Although such a simple resolution would
appear to be of great
value, there still remains other manufacturing procedures and specified
components (such as
ceramic-coated separator types) that are widely utilized and may be difficult
to supplant from
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accepted battery products. Thus, despite the obvious benefits of the
utilization and inclusion of
thermally stable separators, undesirable battery fires may still occur,
particularly when ceramic
coated separator products are considered safe for such purposes. Thus, it has
been determined that
there is at least another, solely internal battery cell structural mechanism
that may remedy or at least
__ reduce the chance for heat generation due to an internal short in addition
to the utilization of such
highly thermal stable separator materials. In such a situation, the occurrence
of a short within such a
battery cell would not result in deleterious high temperature damage due to
the cessation of a
completed internal circuit through a de facto internal fuse creation. Until
now, however, nothing has
been presented within the lithium battery art that easily resolves these
problems. The present
disclosure provides such a highly desirable cure making lithium battery cells
extremely safe and
reliable within multiple markets.
[012] Of further and particular interest is the consideration of
properly allowing for conduction
of electrical charge from the subject lithium ion battery to an external
source. This is generally
accomplished through the utilization of a tab that is contacted and affixed to
a current collector or,
potentially, in some way to both anode and cathode current collectors to
provide the needed
conductance property with an external source. The tab ostensibly functions as
a contact with such
internal battery components and extends outside of the battery cell casing
with contact points for
such conductivity purposes. The tab must thus remain in place and not
disengage from the current
collector(s) and allow for unabated access to the external source without,
again, dislodgement
internally or disengagement therewith externally. As there have been no
disclosures within the
lithium ion battery art regarding such thin film current collectors, there is
likewise nothing that has
attempted to improve upon or optimize such tab connection issues, either.
Certainly, standard types
of tabs are well known and connect with large current collectors of standard
battery cells; however,
such do not provide any considerations as to protecting the effects of thin
film current collectors
(internal fuse, for instance) while still providing a dimensionally stable
result overall to protect from
battery failure due to structural compromises. As such, nothing has been
discussed or disclosed
within the current lithium ion battery art or industry to such an effect. The
present disclosure,
however, overcomes such paradigms and provides a result heretofore unexplored
and/or understood
within the pertinent industry.
DISCLOSURE OF TECHNOLOGY
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[013] A distinct advantage of this disclosure is the ability through
structural components to
provide a mechanism to break the conductive pathway when an internal short
occurs, stopping or
greatly reducing the flow of current that may generate heat within the target
battery cell. Another
advantage is the ability to provide such a protective structural format within
a lithium battery cell
that also provides beneficial weight and cost improvements for the overall
cell manufacture,
transport and utilization. Thus, another advantage is the generation and
retention of an internal fuse
structure within a target battery cell until the need for activation thereof
is necessitated. Another
advantage is the provision of a lower weight battery through the utilization
of a thin film base
current collector that prevents thermal runaway during a short circuit or like
event. Still another
advantage is the ability to utilize flammable organic electrolytes materials
within a battery without
any appreciable propensity for ignition thereof during a short circuit or like
event. Another distinct
advantage is the ability to provide a sufficient conducting tab component
welded, or otherwise in
contact with, the internal fuse current collector, particularly in contact
with both the upper surface
and lower surface thereof simultaneously. Yet another advantage is the ability
to create folds within
the thin current collector components disclosed herein in order to allow for
cumulative power
generation in series of multiple current conductance internal structures to
provide robust on-demand
battery results without needing excessive weight or volume measurements.
[014] Accordingly, this inventive disclosure can encompass an energy
storage device
comprising an anode, a cathode, at least one polymeric or fabric separator
present between the anode
and the cathode, an electrolyte, and at least one current collector in contact
with at least one of the
anode and the cathode; wherein either of the anode or the cathode are
interposed between at least a
portion of the current collector and the separator, wherein the current
collector comprises a
conductive material coated on a polymeric material substrate, and wherein the
current collector stops
conducting at the point of contact point of contact point of contact of an
exposed short circuit at the
operating voltage of the energy storage device, wherein the voltage is at
least 2.0 volts. One example
would be a current density at the point of contact of 0.1 amperes/mm2 with a
tip size of 1 mm2 or
less. Of course, for larger cells, the required threshold current density may
be higher, and the cell
may only stop conducting at a current density of at least 0.3 amperes/mm2,
such as at least 0.6
amperes/mm2, or even at least 1.0 amperes/mm2. Such a coated polymeric
material substrate should
.. also exhibit an overall thickness of at most 25 microns, as described in
greater detail below.
Methods of utilizing such a beneficial current collector component within an
energy storage device
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(whether a battery, such as a lithium ion battery, a capacitor, and the like)
are also encompassed
within this disclosure. Furthermore, such a thin film current collector
battery article may also be
provided with at least one tab contacted with a base thin film collector
through between 2 and 50
uniformly spaced and sized welds leading along the length of the current
collector, wherein the at
least one tab is laid upon the thin film such that the at least one tab has an
exposed top surface and a
bottom surface in contact with a covered surface of the thin film current
collector, wherein the welds
exhibit placement of conductive material passing through the tab from its
exposed top surface to the
covered surface of the thin film current collector. Further encompassed herein
is the utilization of
multiple current collectors as disclosed above and folded to provide separate
power generation
regions that are connected in series within a single battery article.
[015] Another aspect of the present invention can be an energy storage
system including an
anode, a cathode, at least one separator present between the anode and the
cathode, and an
electrolyte. At least one thin film current collector can be in contact with
at least one of the anode
and the cathode. The current collector can comprise a conductive material
coated on a non-
conductive material substrate. The current collector can stop conducting at
the point of contact of a
short circuit at an operating voltage of the energy storage device. The
voltage can be at least 2.0
volts. At least one tab can be attached to the at least one thin film current
collector. A connection
means can be configured to attach the tab to the collector. The connection
means can exhibit
electrical contact with an exposed surface of the tab and the thin film
current collector. Either of the
anode or the cathode can be interposed between at least a portion of the thin
film current collector
and the separator.
[016] In some or all embodiments of the preset invention, the connection
means can be selected
from the group consisting of welds, tape, staples, interposing metal strips, z-
folded metal strips,
conductive adhesives and clamps.
[017] In some or all embodiments of the preset invention, the connection
means can consist of
between 2 and 50 connections distributed throughout the current collector so
as to allow uniform
current flow from the electrode materials to the tabs.
[018] In some or all embodiments of the preset invention, the current
collector can be folded to
allow face-to-face contact between opposing sides of the current collector.
[019] In some or all embodiments of the preset invention, the separator can
be polymeric,
nonwoven, fabric or ceramic.
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[020] In some or all embodiments of the preset invention, the non-
conductive material substrate
can be a polymer film.
[021] In some or all embodiments of the preset invention, the electrolyte
can be a flammable
organic electrolyte.
[022] In some or all embodiments of the preset invention, the tab can be a
first tab in contact
with an upper surface of the current collector, and a second tab in contact
with a lower surface of the
current collector. The first tab and the second tab can be parallel.
[023] In some or all embodiments of the preset invention, the tab can be
folded over the current
collector so a first prong of the tab is in contact with an upper surface of
the current collector, and a
second prong of the tab is in contact with a lower surface of the current
collector. The first prong
and the second prong can be parallel.
[024] In some or all embodiments of the preset invention, the current
collector can have a
double folded configuration to create two electrically isolated layers.
[025] In some or all embodiments of the preset invention, the current
collector can be a plurality
of current collectors connected in series, with the tab attached to a final
current collector of the
plurality of current collectors.
[026] Some or all embodiments of the present invention can include a second
tab attached to a
first current collector of the plurality of current collectors. The tab and
the second tab can be
parallel.
[027] Additionally, much larger current densities may be supported for a
very short period of
time, or in a very small tipped probe. In such a situation, a larger current,
such as 5 amperes, or 10
amperes, or even 15 amperes, may be connected for a very short time period
[for example, less than
a second, alternatively less than 0.1 seconds, or even less than 1 millisecond
(0.001 seconds)].
Within the present disclosure, while it may be possible to measure a larger
current, the delivery time
for such a current is sufficiently short such that the total energy delivered
is very small and not
enough to generate enough heat to cause a thermal runaway event within the
target battery cell. For
example, a short within a conventional architecture cell has been known to
generate 10 amperes for
seconds across 4.2 volts, a result that has delivered 1200 joules of energy to
a small local region
within such a battery. This resultant measurement can increase the temperature
of a 1-gram section
30 of the subject battery by about 300 C., a temperature high enough to
not only melt the conventional
separator material present therein, but also drive the entire cell into a
runaway thermal situation
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(which, as noted above, may cause the aforementioned compromise of the
electrolyte materials
present therein and potential destruction of not only the subject battery but
the device/implement
within which it is present and the surrounding environment as well. Thus, it
is certainly a possibility
that the ability to reduce the time for short circuit duration, as well as the
resulting delivered energy
5 levels associated within such a short to a low joules measurement,
thermal runaway (and the
potential disaster associated therewith) may be avoided, if not completely
prevented. For instance,
the reduction of short circuit residence time within a current collector to 1
millisecond or less can
then subsequently reduce the amount of delivered energy to as low as 0.04
joules (as opposed to
1200 joules, as noted above, leading to excessive, 300 degrees Celsius or
greater, for example,
10 within a 1-gram local region of the subject battery). Such a low level
would thus only generate a
temperature increase of 0.01 C. within such a 1-gram local region of battery,
thus preventing
thermal runaway within the target cell and thus overall battery.
[028] Therefore, it is another significant advantage of the present
disclosure to provide battery a
current collector that drastically limits the delivery time of a current level
applied to the target
current collector surface through a probe tip (in order to controllably
emulate the effect of an internal
manufacturing defect, a dendrite, or an external event which causes an
internal short within the
subject battery) to less than 1 second, preferably less than 0.01 seconds,
more preferably less than 1
millisecond, and most preferably, perhaps, even less than 100 microseconds,
particularly for much
larger currents. Of course, such a current would be limited to the internal
voltage of the cell, which
might be 5.0 V, or 4.5 V, or 4.2 V or even less, such as 4.0 V or 3.8 V, but
with a minimum of 2.0
V.
[029] Such a novel current collector component is actually counterintuitive
to those typically
utilized and found within lithium (and other types) of batteries and energy
storage devices today.
Standard current collectors are provided are conductive metal structures, such
as aluminum and/or
copper panels of thicknesses that are thought to provide some type of
protection to the overall
battery, etc., structure. These typical current collector structures are
designed to provide the
maximum possible electrical conductivity within weight and space constraints.
It appears, however,
that such a belief has actually been misunderstood, particularly since the
thick panels prevalent in
today's energy storage devices will actually not only arc when a short occurs
but contribute greatly to
runaway temperatures if and when such a situation occurs. Such a short may be
caused, for
example, by a dendritic formation within the separator. Such a malformation
(whether caused at or
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during manufacture or as a result of long-term usage and thus potential
degradation) may allow for
voltage to pass unexpectedly from the anode to the cathode, thereby creating
an increase in current
and consequently in temperature at the location such occurs. Indeed, one
potential source of short
circuit causing defect are burrs that form on the edges of these thick typical
current collectors when
they are slit or cut with worn blades during repetitive manufacturing
processes of multiple products
(as is common nowadays). It has been repeatedly analyzed and understood,
however, that the
standard current collector materials merely exhibit a propensity to spark and
allow for temperature
increase, and further permitting the current present during such an occurrence
to continue through
the device, thus allowing for unfettered generation and movement, leaving no
means to curtail the
current and thus temperature level from increasing. This problem leads
directly to runaway high
temperature results; without any internal means to stop such a situation, the
potential for fire
generation and ultimately device immolation and destruction is typically
imminent. Additionally,
the current pathway (charge direction) of a standard current collector remains
fairly static both
before and during a short circuit event, basically exhibiting the same
potential movement of electric
charge as expected with movement from cathode to anode and then horizontally
along the current
collector in a specific direction. With a short circuit, however, this current
pathway fails to prevent
or at least curtail or delay such charge movement, allowing, in other words,
for rapid discharge in
runaway fashion throughout the battery itself. Coupled with the high
temperature associated with
such rapid discharge leads to the catastrophic issues (fires, explosions,
etc.) noted above.
[030] To the contrary, and, again, highly unexpected and counterintuitive
to the typical
structures and configurations of lithium batteries, at least, the utilization
of a current collector of the
instant disclosure results in an extremely high current density measurement
(due to the reduced
thickness of the conductive element) and prevention of charge movement (e.g.,
no charge direction)
in the event of a short circuit. In other words, with the particular
structural limitations accorded the
disclosed current collector component herein, the current density increases to
such a degree that the
resistance level imparts an extremely high, but contained, high temperature
occurrence in relation to
a short circuit. This resistance level thus causes the conductive material
(e.g., as merely examples,
aluminum and/or copper) to receive the short circuit charge but, due to the
structural formation
provided herein, the conductive material reacts immediately in relation to
such a high temperature,
localized charge. Combined with the other structural considerations of such a
current collector
component, namely the actual lack of a dimensionally stable polymeric material
in contact with such
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a conductive material layer, the conductive material oxidizes instantly at the
charge point thereon,
leaving, for example, aluminum or cupric oxide, both nonconductive materials.
With such
instantaneous nonconductive material generation, the short circuit charge
appears to dissipate as
there is no direction available for movement thereof. Thus, with the current
collector as now
described, an internal short circuit occurrence results in an immediate
cessation of current,
effectively utilizing the immediate high temperature result from such a short
to generate a barrier to
further charge movement. As such, the lack of further current throughout the
body of the energy
storage device (in relation to the short circuit, of course) mutes such an
undesirable event to such a
degree that the short is completely contained, no runaway current or high
temperature result occurs
thereafter, and, perhaps most importantly, the current collector remains
viable for its initial and
protective purposes as the localized nonconductive material then present does
not cause any
appreciable reduction in current flow when the energy storage device (battery,
etc.) operates as
intended. Furthermore, the relatively small area of nonconductive material
generation leaves
significant surface area, etc., on the current collector, for further
utilization without any need for
repair, replacement, or other remedial action. The need to ensure such a
situation, which, of course,
does not always occur, but without certain precautions and corrections, as now
disclosed, the
potential for such a high temperature compromise and destruction event
actually remains far higher
than is generally acceptable. Thus, the entire current collector, due to its
instability under the
conditions of a short circuit, becomes a two-dimensional electrical fuse,
preventing the potentially
disastrous high currents associated with short circuits by using the
instantaneous effect of that high
current to destroy the ability of the current collector to conduct current at
the point of the short
circuit.
[031] Such advantages are permitted in relation to such a novel
resultant current collector that
may be provided, with similar end results, through a number of different
alternatives. In any of these
alternative configurations, such a current collector as described herein
functions ostensibly as an
internal fuse within a target energy storage device (e.g., lithium battery,
capacitor, etc.). In each
instance (alternative), however, there is a current collector including a
polymeric layer that is
metallized on one or both sides thereof with at least one metallized side in
contact with the anode or
cathode of the target energy storage device. One alternative then is where the
total thickness of the
entire metallized (coated) polymeric substrate of the current collector is
less than 20 microns,
potentially preferably less than 15 microns, and potentially more preferably
less than 10 microns, all
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with a resistance measurement of less than 1 ohm/square potentially preferably
less than 0.1
ohms/square, and potentially more preferably less than 50 ohms/square. Typical
current collectors
may exhibit these features but do so at far higher weight than those made with
reinforcing polymeric
substrates and without the inherent safety advantages of this presently
disclosed variation. For
example, a copper foil at 10 microns thick may weight 90 grams/m2. However, a
copperized foil
may weigh as little as 50 grams/m2, or even as little as 30 gram/m2, or even
less than 20 grams/m2,
all while delivering adequate electrical performance required for the cell to
function. In this
alternative structure, however, the very thin component also allows for a
short to react with the metal
coat and in relation to the overall resistance levels to generate, with an
excessively high temperature
due to a current spike during such a short, a localized region of metal oxide
that immediately
prevents any further current movement therefrom.
[032] Another possible alternative for such a novel current collector
is the provision of a
temperature dependent metal (or metallized) material that either shrinks from
a heat source during a
short or easily degrades at the specific material location into a
nonconductive material (such as
aluminum oxide from the aluminum current collector, as one example and as
alluded to above in a
different manner). In this way, the current collector becomes thermally weak,
in stark contrast to the
aluminum and copper current collectors that are used today, which are quite
thermally stable to high
temperatures. As a result, an alloy of a metal with a lower inherent melting
temperature may
degrade under lower shorting current densities, improving the safety
advantages of the lithium-based
energy device disclosed herein. Another alternative is to manufacture the
current collector by
coating a layer of conductive material, for example copper or aluminum, on
fibers or films that
exhibit relatively high shrinkage rates at relatively low temperatures.
Examples of these include
thermoplastic films with melt temperatures below 250 C., or even 200 C., and
can include as non-
limiting examples polyethylene terephthalate, nylon, polyethylene or
polypropylene. Another
possible manner of accomplishing such a result is to manufacture a current
collector by coating a
layer of conductive material, for example copper or aluminum, as above, on
fibers or films that can
swell or dissolve in electrolyte when the materials are heated to relatively
high temperatures
compared to the operating temperatures of the cells, but low compared to the
temperatures that
might cause thermal runaway. Examples of such polymers that can swell in
lithium ion electrolytes
include polyvinylidene fluoride and poly acrylonitrile, but there are others
known to those with
knowledge of the art. Yet another way to accomplish such an alternative
internal electrical fuse
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generating process is to coat onto a substrate a metal, for example aluminum,
that can oxidize under
heat, at a total metal thickness that is much lower than usually used for
lithium batteries. For
example, a very thin aluminum current collector as used today may be 20
microns thick. A coating
thickness of a total of less than 5 microns would break the circuit faster,
and one less than 2 microns,
or even less than 1 micron would break the circuit even faster. Even still,
another way to accomplish
the break in conductive pathway is to provide a current collector with limited
conductivity that will
degrade in the high current densities that surround a short, similar to the
degradation found today in
commercial fuses. This could be accomplished by providing a current collector
with a resistivity of
greater than 5 mOhm/square, or 10 mOhm/square, or potentially preferably
greater than 20
mOhm/square, or, a potentially more preferred level of greater than 50
mOhm/square. These
measurements could be on one side, or on both sides of a material coated on
both sides. The use of
current collectors of different resistivities may further be selected
differently for batteries that are
designed for high power, which might use a relatively low resistance compared
to cells designed for
lower power and higher energy, and/or which might use a relatively high
resistance. Still another
way to accomplish the break in conductive pathway is to provide a current
collector that will oxidize
into a non-conductive material at temperatures that are far lower than
aluminum, thus allowing the
current collector to become inert in the area of the short before the
separator degrades. Certain
alloys of aluminum will oxidize faster than aluminum itself, and these alloys
would cause the
conductive pathway to deteriorate faster or at a lower temperature. As
possible alternatives, there
may be employed any type of metal in such a thin layer capacity and that
exhibits electrical
conductivity, including, without limitation, gold, silver, vanadium, rubidium,
iridium, indium,
platinum, and others (basically, with a very thin layer, the costs associated
with such metal usage
may be reduced drastically without sacrificing conductivity and yet still
allowing for the protections
from thermal runaway potentials during a short circuit or like event). As
well, layers of different
metals may be employed or even discrete regions of metal deposited within or
as separate layer
components may be utilized. Certainly, too, one side of such a coated current
collector substrate
may include different metal species from the opposing side, and may also have
different layer
thicknesses in comparison, as well.
[033] One way to improve the electrical properties of the cell would be
to ensure that a coated
current collector includes two conductive coated sides, ostensibly allowing
for conductivity from the
coating on one side to the coating on the other side. Such a result is not
possible for a non-coated
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polymer film, for instance. However, it has been realized that such a two-
sided conductivity
throughput can be achieved by, as one non-limiting example, a nonwoven
including a certain
percentage of conducting fibers, or a nonwoven loaded with conductive
materials, or a nonwoven
made from a conductive material (such as carbon fibers or metal fibers), or,
as noted above, a
5 nonwoven containing fibers coated with a conductive material (such as
fibers with a metal coating
on the surface). Another type of novel thin current collector material
exhibiting top to bottom
conductivity may be a film that has been made conductive, such as through the
utilization of an
inherently conductive material (such as, for example, conductive polymers such
as polyacetylene,
polyaniline, or polyvinylpyrrolidine), or via loading with a conductive
material (such as graphite or
10 graphene or metal particles or fibers) during or after film manufacture.
Additionally, another
possible two-sided thin current collector material is a polymer substrate
having small perforated
holes with sides coated with metal (aluminum or copper) during the
metallization process. Such a
conductivity result from one side to the other side would not need to be as
conductive as the
conductive coatings.
15 [034] Thus, such alternative configurations garnering ostensibly
the same current collector
results and physical properties include a) wherein the total thickness of the
coated polymeric
substrate is less than 20 microns with resistance less than 1 ohm/square, b)
the collector comprising
a conductive material coated on a substrate comprising polymeric material,
wherein the polymeric
material exhibits heat shrinkage at 225 C of at least 5%, c) wherein the
collector metallized
polymeric material swells in the electrolyte of the battery, such swelling
increasing as the polymeric
material is heated, d) wherein the collector conductive material total
thickness is less than 5 microns
when applied to a polymeric substrate, e) wherein the conductivity of the
current collector is
between 10 mOhm/square and 1 ohm/square, and f) wherein the metallized
polymeric substrate of
the collector exhibits at most 60% porosity. The utilization of any of these
alternative configurations
within an energy storage device with a separator exhibiting a heat shrinkage
of less than 5% after 1
hour at 225 C. would also be within the purview of this disclosure. The
overall utilization (method
of use) of this type of energy storage device (battery, capacitor, etc.) is
also encompassed herein.
[035] While the primary advantage of this invention is enhanced safety
for the cell, there are
other advantages, as alluded to above, including reduced weight of the overall
energy storage device
through a reduced amount of metal weight in relation to such current collector
components. Again,
it is completely counterintuitive to utilize thin metallized coated polymeric
layers, particularly of
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low dimensionally stable characteristics, for current collectors within such
battery articles. The
present mindset within this industry remains the thought that greater amounts
of actual metal and/or
insulator components are needed to effectuate the desired protective results
(particularly from
potential short circuit events). It has now been unexpectedly realized that
not only is such a
paradigm incorrect, but the effective remedy to short circuiting problems
within lithium batteries,
etc., is to reduce the amount of metal rather than increase and couple the
same with thermally
unstable base layers. Thus, it has been not only realized, again, highly
unexpectedly, that thin metal
layers with such unstable base layers provide the ability to combat and
effectively stop discharge
events during short circuits, the overall effect is not only this far safer
and more reliable result, but a
significantly lower overall weight and volume of such component parts. Thus,
the unexpected
benefits of improved properties with lowered weight and volume requirements
within energy storage
products (batteries, etc.), accords far more to the industry than initially
understood.
[036] As a further explanation, aluminum, at a density of 2.7 g/cm3, at 20
microns thick would
weigh 54 g/m2. However, the same metal coated at 1 micron on a 10-micron thick
polypropylene
film (density 0.9 g/cm3) would weigh 11.7 g/m2. This current collector
reduction in weight can
reduce the weight of the entire target energy storage device (e.g., battery),
increasing mobility,
increasing fuel mileage or electric range, and in general enhance the value of
mobile electric
applications.
[037] Additionally, because of the high strength of films, the above
example can also be made
thinner, a total thickness of 11 microns compared to 20 microns, for example,
again reducing the
volume of the cell, thereby effectively increasing the energy density. In this
way, a current collector
of less than 15 microns, preferably less than 12, more preferably less than
10, and most preferably
less than 8 microns total thickness, can be made and utilized for such a
purpose and function.
[038] With the bulk resistivity of aluminum at 2.7x10-8 ohm-m and of copper
at 1.68x10-8 ohm-
m, a thin coating can be made with less than 1 ohm/square, or less than 0.5
ohms/square, or even
less than 0.1 ohms/square, or less than 0.05 ohms/square. The thickness of
these conductive
coatings could be less than 5 microns, preferably than 3 microns, more
preferably less than 2
microns, potentially most preferably even less than 1 micron. It is extremely
counterintuitive, when
standard materials of general use in the market contain 10 microns or more of
metal, that suitable
performance could be obtained using much less metal. Indeed, most of the metal
present in typical
storage devices is included to give suitable mechanical properties for high
speed and automated
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processing. It is one of the advantages of this invention to use a much lower
density polymer
material to provide the mechanical properties, allowing the metal thickness to
be reduced to a level
at which the safety of the cell is improved because of the inability of the
current collector to support
dangerously high current densities that result from internal electrical shorts
and result in thermal
runaway, smoke and fire.
[039] Additionally, these conductive layers can be made by multiple layers.
For example, a
layer of aluminum may be a base layer, coated by a thin layer of copper. In
this way, the bulk
conductivity can be provided by the aluminum, which is light, in expensive and
can easily be
deposited by vapor phase deposition techniques. The copper can provide
additional conductivity
and passivation to the anode, while not adding significant additional cost and
weight. This example
is given merely to illustrate and experts in the art could provide many other
multilayer conductive
structures, any of which are excellent examples of this invention.
[040] These thin metal coatings will in general result in higher resistance
than in an aluminum
or copper current collector of normal practice, providing a distinguishing
feature of this invention in
comparison. Such novel suitable current collectors can be made at greater than
10 mohm/square,
preferably greater than 20 mohm/square, more preferably greater than 50
mohm/square, and
potentially most preferably even greater than 100 mohm/square.
[041] Additionally, cells made with the thermally weak current collectors
described above could
be made even more safe if the separator has a high thermal stability, such as
potentially exhibiting
low shrinkage at high temperatures, including less than 5% shrinkage after
exposure to a
temperature of 200 C. for 1 hour, preferably after an exposure of 250 C. for
one hour, and
potentially more preferably after an exposure to a temperature of 300 C. for
one hour. Existing
separators are made from polyethylene with a melt temperature of 138 C. and
from polypropylene
with a melt temperature of 164 C. These materials show shrinkage of >50% at
150 C., as shown
in FIG. 2; such a result is far too high for utilization with a thin current
collector as now described
herein. To remedy such a problem, it has been realized that the utilization of
certain separators that
shrink less than 50% at 150 C., or even less than 30%, or less than 10%, as
measured under NASA
TM-2010-216099 section 3.5 are necessary. Even ceramic coated separators show
significant
shrinkage at relatively modest temperatures, either breaking entirely or
shrinking to more than 20%
at 180 C. It is thus desirable to utilize a separator that does not break
during the test, nor shrink to
more than 20% at an exposure of 180 C. (at least), more preferably more than
10%, when measured
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under the same test standard. The most preferred embodiment would be to
utilize a separator that
shrinks less than 10% when exposed to a temperature of 200 C., or 250 C., or
even 300 C.
[042] For any of these metallized substrates, it is desirable to have a
low thickness to facilitate
increase the energy density of the cell. Any means can be used to obtain such
thickness, including
calendering, compressing, hot pressing, or even ablating material from the
surface in a way that
reduces total thickness. These thickness-reducing processes could be done
before or after
metallization. Thus, it is desirable to have a total thickness of the
metallized substrate of less than
25 microns, preferably less than 20 microns, more preferably less than 16
microns, and potentially
most preferably less than 14 microns. Commercial polyester films have been
realized with
thicknesses of at most 3 microns, and even lower at 1.2 microns. These types
could serve as suitable
substrates and allow the total thickness of the current collector to be less
than 10 microns, preferably
less than 6 microns, and more preferably less than 4 microns. Such ultra-thin
current collectors
(with proper conductivity as described above and throughout) may allow much
higher energy density
with improved safety performance, a result that has heretofore gone
unexplored.
[043] It is also desirable to have low weight for these metallized
substrates. This could be
achieved by the use of low density polymer materials such as polyolefins or
other low-density
polymers including polyethylene, polypropylene, and polymethylpentene, as
merely examples. It
could also be achieved by having an open pore structure in the substrate or
even through utilization
of low basis weight substrates. Thus, the density of the polymer used in the
substrate material could
be less than 1.4 g/cm3, preferably less than 1.2 g/cm3, and potentially more
preferably less than 1.0
g/cm3. Also, the areal density of the substrate material could be less than 20
g/m2, preferably less
than 16 g/m2, and potentially most preferably less than 14 g/m2. Additionally,
the areal density of
the metal coated polymer substrate material could be less than 40 g/m2,
preferably less than 30 g/m2,
more preferably less than 25 g/m2, and potentially most preferably less than
20 g/m2.
[044] Low weight can also be achieved with a porous polymer substrate.
However, the porosity
must not be too high for these materials, as such would result in low strength
and high thickness,
effectively defeating the purpose of the goals involved. Thus, such base
materials would exhibit a
porosity lower than about 60%, preferably lower than 50%, and potentially more
preferably lower
than 40%. Since solid materials can be used for this type of metal coated
current collector, there is
no lower limit to the porosity.
[045] High strength is required to enable the materials to be processed
at high speeds into
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batteries. This can be achieved by the use of elongated polymers, either from
drawn fibers or from
uniaxially or biaxially drawn films.
[046] As presented below in the accompanying drawings the descriptions
thereof, an energy
storage device, whether a battery, a capacitor, a supercapacitor and the like,
is manufactured and
thus provided in accordance with the disclosure wherein at least one current
collector that exhibits
the properties associated with no appreciable current movement after a short
is contacting a cathode,
an anode, or two separate current collectors contacting both, and a separator
and electrolytes, are all
present and sealed within a standard (suitable) energy storage device
container, is provided. The
cathode, anode, container, electrolytes, and in some situations, the
separator, components are all
standard, for the most part. The current collector utilized herewith and
herein, however, is, as
disclosed, not only new and unexplored within this art, but counterintuitive
as an actual energy
storage device component. Such is, again, described in greater detail below.
[047] As noted above, in order to reduce the chances, if not totally
prevent, thermal runaway
within a battery cell (particularly a lithium ion rechargeable type, but
others are possible as well, of
course), there is needed a means to specifically cause any short circuit
therein to basically exist
within a short period of time, with reduced residence time within or on the
subject current collector,
and ultimately exhibit a resultant energy level of de minimis joule levels
(i.e., less than 10,
preferably less than 1, and most preferably less than 0.01). In such a
situation, then, and as alluded to
earlier, the electrical pathway from anode to cathode, and through the
separator, with the thin
conductive current collector in place, and organic flammable electrolyte
present, it has been
observed that the low-weight, thin current collector allows for such a
desirable result, particularly in
terms of dissipation of rogue charges at the collector surface and no
appreciable temperature
increase such that ignition of the electrolyte component would be imminent.
Surprisingly, and
without being bound to any specific scientific explanation or theory, it is
believed that the
conductive nature of the thin current collector material allows for short
circuit electrical charges to
merely reach the thin conductive current collector and immediately create a
short duration high-
energy event that reacts between the metal at the current collector surface
with the electrical charge
itself, thereby creating a metal oxide to form at that specific point on the
current collector surface.
The metal oxide provides insulation to further electrical activity and current
applied dissipates
instantaneously, leaving a potential deformation within the collector itself,
but with the
aforementioned metal oxide present to protect from any further electrical
charge activity at that
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specific location. Thus, the remaining current collector is intact and can
provide the same capability
as before, thus further providing such protections to any more potential short
circuits or like
phenomena. In the case of thermal runaway in prior art battery products, the
anode, cathode, current
collectors and separator comprise the electrical pathway, which generate heat
and provide the spark
5 to ignite the cell in reaction to a short circuit, as an example. The
further presence of ion
transporting flammable electrolytes thus allows for the effective dangers with
high temperature
results associated with such unexpected electrical charges. In essence, the
heat generated at the prior
art current collector causes the initial electrochemical reactions within the
electrolyte materials,
leading, ultimately to the uncontrolled ignition of the electrolyte materials
themselves. Thus, the
10 disclosed inventive current collector herein particularly valuable when
utilized within battery cells
including such flammable electrolytes. As examples, then, such electrolytes
generally include
organic solvents, such as carbonates, including propylene carbonate, ethylene
carbonate, ethyl
methyl carbonate, di ethyl carbonate, and di methyl carbonate, and others.
These electrolytes are
usually present as mixtures of the above materials, and perhaps with other
solvent materials
15 including additives of various types. These electrolytes also have a
lithium salt component, an
example of which is lithium hexafluorophosphate, LiPF6. Such electrolytes are
preferred within the
battery industry, but, as noted, do potentially contribute to dangerous
situations. Again, this
inventive current collector in association with other battery components
remedies these concerns
significantly and surprisingly.
20 [048] One way that this current collector will exhibit its
usefulness is in the following test. A
current source with both voltage and current limits can be set to a voltage
limit similar to the
operating voltage of the energy storage device in question. The current can
then be adjusted, and the
current collector tested under two configurations. In the first, a short strip
of the current collector of
known width is contacted through two metal connectors that contact the entire
width of the sample.
The current limit of the current source can be raised to see if there is a
limit to the ability of the
material to carry current, which can be measured as the total current divided
by the width, achieving
a result in A/cm, herein designated as the horizontal current density. The
second configuration
would be to contact the ground of the current source to one of the full width
metal contacts, and then
touch the tip of the probe, approximately 0.25 mm2, to a place along the strip
of the current
collector. If the current is too high, it will burn out the local area, and no
current will flow. If the
current is not too high for the current collector, then the full current up to
the limit of the current
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source will flow. The result is a limit of current in A/mm2, herein designated
as the vertical current
density. In this way, a current collector which can reach a high current under
both configurations
would be similar to the prior art, and a current collector which could support
the horizontal current
when contacted under full width, but would not support a similar vertical
current under point contact
would be an example of the invention herein described.
[049] For example, it may be desirable for a current collector to be able
to support horizontal
current density 0.1 A/cm, or 0.5 A/cm, or 1 A/cm or 2 A/cm or even 5 A/cm. And
for a current
collector that could support a horizontal current density as above, it would
be desirable not to
support a vertical current density of 0.1 A/mm2, or 0.5 A/mm2, or 1 A/mm2 or 2
A/mm2 or even 5
A/mm2.
[050] As alluded to above, there is also generally present within lithium
ion battery cells a tab
weld to join the internal components, particularly the current collectors,
together to connect to a tab
lead for transfer of charge to an external source. In this situation, with the
current collectors of
extremely thin types, it is paramount such a tab lead effectively contact the
internal foil collectors
and remain sufficiently in place to contact an external source as well.
Additionally, due to the
effectiveness of the aforementioned and unexpectedly good thin film current
collectors to permit the
needed operations of the battery cell itself, as well as the ability to
provide the internal fuse
characteristics to prevent runaway current during a possible problem (dendrite
formation, etc.), such
a tab must not exhibit any degree of displacement or ineffectiveness to combat
the same potential
runaway charge issues themselves. In other words, the effectiveness of the
internal fuse results must
not be undone or compromised by tab issues. Surprisingly, it has been
determined that such needed
characteristics are permissible with such tab components.
[051] To that level, then, it was realized that the thin film collectors
actually allow for an
effective and strong weld of the tab thereto and with the ability to actually
allow for conductance at
both film sides. The tab itself is actually thicker than each individual
current collector and when
placed in contact with one another the weld may be undertaken to a depth that
is partially through
the tab material in relation to the shape and depth of the weld itself. The
surprising result, however,
is that the weld may actually pass through the tab in a thin "stream" or like
formation, thus allowing
for conductance through such a weld material to the tab. In this manner, the
limited, though
effective, conduction path is generated in order to not only allow for the
needed conductance at the
weld location to the tab (and then out of the battery cell casing to an
external source), but also there
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is provided a means to limit the actual amperage and temperature generated by
such a conductive
flow at each weld location. Such a result allows for the aforementioned
control of runaway
conductivity from the metallized film current collectors should a short
(dendrite formation, etc.)
occur since the electrical charge will stop at the actual current collector
surface and no other pathway
for a runaway charge is provided. The welds may thus be provided along the
length of the tab
component running along the current collector with as many as five, as one
example, spaced
uniformly from one another, thus allowing for effective conductivity from the
foil collector(s) to the
tab through the battery casing to the external source. The limited number of
welds thus reduces, as
well, the number of possible runaway charge sites, albeit with each exhibiting
limited amperage, but
with multiples such levels show increases in some situations, certainly.
However, for high power or
high current batteries, the number of welds per tab can be increased to
accommodate the high
amount of current needed for the battery to be effective in its application.
In this case, it is possible
to require a larger number of welds, potentially as many as 10, or 20, or even
50 welds per tab. In
rare circumstances in very high power or very high current cells, even more
than 50 welds may be
necessary. The welds provide a base strength, additionally, to prevent
movement of the tab during
utilization. Stability and rigidity and needed to ensure proper operation of
the battery overall. The
limited welds do provide a certain level of reliability in this respect, while
the addition of pull tape
thereover as applied to the current collector films also aids in protecting
from such potential
problems as well.
[052] In effect, the thin film current collectors are unexpectedly good for
the prevention of
runaway charges during a short. However, the need for tab leads in sufficient
contact with such
collectors in order to allow for effective conductivity external the battery
cell requires a structural
situation that allows for such thin current collector film utilization with
standard tab components.
As noted above, the ability to determine proper dimensions of both current
collector film(s) and tabs
with suitable welds for effective attachment and contact for electrical
current to pass through
effectively for battery operation, while still exhibiting the proper low
potential for runaway charge
has proven difficult, particularly in view of the specific and accepted thick
monolithic current
collector components of the state of the art today. This unexpectedly
effective result, particularly
with the tab contact and pull strength characteristics determined as noted
above, accords a full
.. lithium ion battery that may be provided with reduced weight or greater
internal capacity for other
components without sacrificing battery power generation capability while
simultaneously providing
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complete protection from runaway charges during short circuit events.
[053] Such lithium ion battery thin films may require certain unique
processing steps due to
their unique qualities. However, many processing steps that are well known in
the art may also be
employed. In general, the process to produce a lithium ion battery with the
inventive films
comprises the steps of:
[054] a. Providing an electrode having at least one metallized substrate
with a coating of an ion
storage material;
[055] b. Providing a counterelectrode;
[056] c. Layering the electrode and counterelectrode opposite each other
with a separator
component interposed between the electrode and the countelectrode;
[057] d. Providing a package material including an electrical contact
component, wherein the
contact includes a portion present internally within the package material and
a portion
present external to the package material;
[058] e. Electrically connecting the electrical contact with the metallized
substrate;
[059] f. Introducing at least one liquid electrolyte with ions internally
within the package
material; and
[060] g. Sealing the package material.
[061] The metallized substrate can be any substrate as described within
this disclosure.
[062] The ion storage material can for example be a cathode or anode
material for lithium ion
batteries, as are well known in the art. Cathode materials may include lithium
cobalt oxide LiCoO2,
lithium iron phosphate LiFePO4, lithium manganese oxide LiMn204, lithium
nickel manganese
cobalt oxide LiNixMnyCoz02, lithium nickel cobalt aluminum oxide
LiNixCoyAlz02, or mixtures of
the above or others as are known in the art. Anode materials may include
graphite, lithium titanate
Li4Ti5012, hard carbon, tin, silicon or mixtures thereof or others as are
known in the art. In addition,
the ion storage material could include those used in other energy storage
devices, such as
supercapacitors. In such supercapacitors, the ion storage materials will
include activated carbon,
activated carbon fibers, carbide-derived carbon, carbon aerogel, graphite,
graphene, graphene, and
carbon nanotub es .
[063] The coating process can be any coating process that is generally
known in the art. Knife-
over-roll and slot die are commonly used coating processes for lithium ion
batteries, but others may
be used as well, including electroless plating. In the coating process, the
ion storage material is in
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general mixed with other materials, including binders such as polyvinylidene
fluoride or
carboxymethyl cellulose, or other film-forming polymers. Other additives to
the mixture include
carbon black and other conducting additives.
[064] Counterelectrodes include other electrode materials that have
different electrochemical
potentials from the ion storage materials. In general, if the ion storage
material is a lithium ion
anode material, then the counterelectrode would be made form a lithium ion
cathode material. In the
case where the ion storage material is a lithium ion cathode material, then
the counterelectrode
might be a lithium ion anode material. In the case where the ion storage
material is a supercapacitor
material, the counterelectrode can be made from either a supercapacitor
material, or in some cases
from a lithium ion anode or lithium ion cathode material. In each case, the
counterelectrode would
include an ion storage material coated on a current collector material, which
could be a metal foil, or
a metallized film such as in this invention.
[065] In the layering process, the inventive electrode is layered with the
counterelectrode with
the electrode materials facing each other and a porous separator between them.
As is commonly
known in the art, the electrodes may be coated on both sides, and a stack of
electrodes formed with
the inventive electrode and counterelectrodes alternating with a separator
between each layer.
Alternatively, as is also known in the art, strips of electrode materials may
be stacked as above, and
then wound into a cylinder.
[066] Packaging materials may include hard packages such as cans for
cylindrical cells,
flattened hard cases or polymer pouches. In each case, there must be two means
of making electrical
contact through the case that can be held at different voltages and can
conduct current. In some
instances, a portion of the case itself forms one means, while another is a
different portion of the
case that is electrically isolated from the first portion. In other instances,
the case may be
nonconducting, but allow two metal conductors to protrude through the case,
often referred to as
tabs.
[067] Connecting the means to make electrical contact with the metallized
substrate can include
commonly used methods, such as welding, taping, clamping, stapling, riveting,
or other mechanical
means. Because the metal of the metallized substrate can be very thin, in
order to enable an
interface that allows for high current flow, a face-to-face contact is
generally required, giving high
surface area between the means of making electrical contact through the case
and the metallized
substrate. To carry sufficient current, this surface area should be higher
than 1 square millimeter
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(102 square meters) but may need to be higher than 3 square millimeters, or
even 5 square
millimeters or more preferably 10 square millimeters.
[068] The liquid electrolyte is typically a combination/mixture of a polar
solvent and a lithium
salt. Commonly used polar solvents include, as noted above, propylene
carbonate, ethylene
5 carbonate, dimethyl carbonate, diethyl carbonate, but other polar
solvents, including ionic liquids or
even water may be used. Lithium salts commonly utilized within this industry
include, without
limitation, LiPF6, LiPF4, LiBF4, LiC104 and others. The electrolyte may also
contain additives as are
known in the art. In many cases, the electrolytes can be flammable, in which
the safety features of
the inventive metallized substrate current collectors can be advantageous
preventing dangerous
10 thermal runaway events, which result in fire and damage both to the cell
and external to the cell.
BRIEF DESCRIPTION OF THE DRAWINGS
[069] FIG. 1 is a Prior Art depiction of the architecture of a wound cell,
such as an 18650 cell.
[070] FIG. 2 is a Prior Art depiction of the shrinkage as a function of
temperature as measured
15 by Dynamic Mechanical Analysis of several lithium ion battery
separators, as measured according to
NASA/TM-2010-216099 "Battery Separator Characterization and Evaluation
Procedures for
NASA's Advanced Lithium Ion Batteries," which is incorporated herein by
reference, section 3.5.
Included are first generation separators (Celgard PP, Celgard tri-layer), 2'
generation separators
(ceramic PE) and 3rd generation separators (Silver, Gold, Silver AR).
20 [071] FIG. 3A is a Prior Art depiction of a scanning electron
micrograph (SEM) of the cross
section of a pouch cell that has undergone a nail penetration test. The layers
are aluminum and
copper as mapped by BEI (backscattered electron imaging). The nail is vertical
on the left side. In
each case, the aluminum layer has retreated from the nail, leaving behind a
"skin" of aluminum
oxide, an insulator.
25 [072] FIG. 3B is a Prior Art depiction of a zoom in on one of the
layers from the image shown
in FIG. 3A. It shows a close up of the aluminum oxide layer, and also reveals
that the separator had
not shrunk at all and was still separating the electrodes to the very edge.
[073] FIG. 4 is a depiction of the invention, where the thin layer of
conductive material is on the
outside, and the center substrate is a layer that is thermally unstable under
the temperatures required
for thermal runaway. This substrate can be a melting layer, a shrinking layer,
a dissolving layer, an
oxidizing layer, or other layer that will undergo a thermal instability at a
temperature between 1000
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C. and 500 C.
[074] FIG. 5A is a Prior Art depiction of a thick aluminum current
collector, generally between
12-20 microns thick.
[075] FIG. 5B is a depiction of the current invention, showing a 14-micron
thick substrate with
.. 1 micron of aluminum on each side. In the case of the inventive current
collector, it is not capable
of carrying the high currents associated with a short circuit, while the thick
current art is and does.
[076] FIGS. 6 and 6A show images of comparative examples 1-2, each after
having been
touched by the tip of a hot soldering iron. The comparative examples do not
change after touching
with a hot soldering iron.
[077] FIGS. 7, 7A, and 7B show images of examples 1-3, each after having
been touched by the
tip of a hot soldering iron. The examples 1-3 all exhibit shrinkage as
described in this disclosure for
substrates to be metalized.
[078] FIGS. 8, 8A, and 8B show images of examples 4-6, each after having
been touched by the
tip of a hot soldering iron. The example 4 exhibits shrinkage as described in
this disclosure for
substrates to be metalized. Example 5 has a fiber that will dissolve under
heat in lithium ion
electrolytes. Example 6 is an example of a thermally stable substrate that
would require a thin
conductive layer to function as the current invention.
[079] FIGS. 9, 9A, and 9B are SEMs at different magnifications in cross
section and one
showing the metalized surface of one possible embodiment of one current
collector as now disclosed
as described in Example 9. The metal is clearly far thinner than the original
substrate, which was 20
microns thick.
[080] FIGS. 10 and 10A are optical micrographs of a Comparative Examples 3
and 4 after
shorting, showing ablation of the area around the short but no hole.
[081] FIGS. 11 and 11A are optical micrographs of two areas of Example 14
after shorting,
showing clear holes in the material caused by the high current density of the
short.
[082] FIG. 12 shows a depiction of the size and shape of a current
collector utilized for
Examples noted below.
[083] FIG. 13 depicts a side perspective view of a single layer current
collector with welded tab
as one potentially preferred embodiment.
[084] FIG. 14 depicts a side perspective view of a single layer current
collector with taped tab as
another potentially preferred embodiment.
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[085] FIG. 15 depicts a side perspective view of a single layer current
collector with stapled tab
as another potentially preferred embodiment.
[086] FIG. 16 depicts a side perspective view of a single layer current
collector with a single
rounded fold therein and a taped tab as another potentially preferred
embodiment.
[087] FIG. 17 depicts a side perspective view of a single layer current
collector with a double
rounded fold therein and a taped tab as another potentially preferred
embodiment.
[088] FIG. 18 depicts a side perspective view of a single layer current
collector with two parallel
welded tabs as another potentially preferred embodiment.
[089] FIG. 19 depicts a side perspective view of a single layer current
collector with a single
folded welded tab as another potentially preferred embodiment.
[090] FIG. 20 depicts a side perspective view of a single layer current
collector with a double
rounded fold therein and a welded tab as another potentially preferred
embodiment.
[091] FIG. 21 depicts a side perspective view of a plurality of single
layer current collectors
each with a double rounded fold therein and a welded tab as another
potentially preferred
.. embodiment.
[092] FIG. 22 depicts a side perspective view of a plurality of single
layer current collectors
each with a double rounded fold therein and two opposing welded tabs as
another potentially
preferred embodiment.
[093] FIG. 23 depicts a side perspective view of a plurality of single
layer current collectors in
contact with a multiple Z-folded clamped tab as another potentially preferred
embodiment.
DETAILED DESCRIPTION OF THE TECHNOLOGY
[094] The following descriptions and examples are merely representations of
potential
embodiments of the present disclosure. The scope of such a disclosure and the
breadth thereof in
terms of claims following below would be well understood by the ordinarily
skilled artisan within
this area.
[095] As noted above, the present disclosure is a major shift and is
counterintuitive from all
prior understandings and remedies undertaken within the lithium battery (and
other energy storage
device) industry. To the contrary, the novel devices described herein provide
a number of beneficial
results and properties that have heretofore been unexplored, not to mention
unexpected, within this
area. Initially, though, as comparisons, it is important to note the stark
differences involved between
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prior devices and those currently disclosed and broadly covered herein.
Short Circuit Event Examples
Comparative Example 1
[096] A cathode for a lithium iron phosphate battery was obtained from GB
Systems in China.
The aluminum tab was removed as an example of a commercial current collector,
and the thickness,
areal density and resistance were measured, which are shown in Table 1, below.
The aluminum foil
was then touched with a hot soldering iron for 5 seconds, which was measured
using an infrared
thermometer to have a temperature of between 500 and 525 F. There was no
effect of touching the
soldering iron to the current collector. The thickness, areal density and
resistance were measured.
The material was placed in an oven at 175 C. for 30 minutes and the shrinkage
measured. A
photograph was taken and included in FIG. 6. FIG. 5 provides a representation
of the traditional
current collector within such a comparative battery.
Comparative Example 2
[097] An anode for a lithium iron phosphate battery was obtained from GB
Systems in China.
The copper tab was removed as an example of a commercial current collector,
and the thickness,
areal density and resistance were measured, which are shown in Table 1, below.
The copper foil
was then touched with a hot soldering iron in the same way as Example 1. There
was no effect of
touching the soldering iron to the current collector. The thickness, areal
density and resistance were
measured. The material was placed in an oven at 175 C. for 30 minutes and the
shrinkage
measured. A photograph was taken and included in FIG. 6. As in Comparative
Example 1, FIG. 5
provides a representation of the internal structure of such a battery. The
thickness of the current
collector is significant as it is a monolithic metal structure, not a thin
type as now disclosed.
Example 1
[098] Polypropylene lithium battery separator material was obtained from
MTI Corporation.
The material was manufactured by Celgard with the product number 2500. The
thickness, areal
density and resistance were measured, which are shown in Table 1, below. The
separator was then
touched with a hot soldering iron in the same way as Example 1. Touching the
thermometer to the
current collector created a small hole. The diameter was measured and included
in Table 1. The
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thickness, areal density and resistance were measured. The material was placed
in an oven at 175
C. for 30 minutes and the shrinkage measured. A photograph was taken and
included in FIG. 7.
Example 2
[099] Ceramic coated polyethylene lithium battery separator material was
obtained from MTI
Corporation. The thickness, areal density and resistance were measured, which
are shown in Table
1, below. The separator was then touched with a hot soldering iron in the same
way as Example 1.
Touching the soldering iron to the current collector created a small hole. The
diameter was
measured and included in Table 1. The thickness, areal density and resistance
were measured. The
material was placed in an oven at 175 C. for 30 minutes and the shrinkage
measured. A photograph
was taken and included in FIG. 7A.
Example 3
[0100] Ceramic coated polypropylene lithium battery separator material
was obtained from MTI
Corporation. The thickness, areal density and resistance were measured, which
are shown in Table
1, below. The separator was then touched with a hot soldering iron in the same
way as Example 1.
Touching the soldering iron to the current collector created a small hole. The
diameter was
measured and included in Table 1. The thickness, areal density and resistance
were measured. The
material was placed in an oven at 175 C. for 30 minutes and the shrinkage
measured. A photograph
was taken and included in FIG. 7B.
Example 4
[0101] Aluminized biaxially oriented polyester film was obtained from
All Foils Inc., which is
designed to be used for helium filled party balloons. The aluminum coating
holds the helium longer,
giving longer lasting loft for the party balloons. The thickness, areal
density and resistance were
measured, which are shown in Table 1, below. The film was then touched with a
hot soldering iron
in the same way as Example 1. Touching the soldering iron to the current
collector created a small
hole. The diameter was measured and included in Table 1. The thickness, areal
density and
resistance were measured. The material was placed in an oven at 175 C. for 30
minutes and the
shrinkage measured. A photograph was taken and included in FIG. 8. Compared to
the
commercially available aluminum current collector of Comparative Example 1,
this material is 65%
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thinner and 85% lighter, and also retreats away from heat, which in a lithium
ion cell with an
internal short would have the effect of breaking the internal short.
Example 5
5 [0102] Dreamweaver Silver 25, a commercial lithium ion battery
separator was obtained. It is
made from a blend of cellulose and polyacrylonitrile nanofibers and polyester
microfibers in a
papermaking process, and calendered to low thickness. The separator was then
touched with a hot
soldering iron in the same way as Example 1. Touching the thermometer to the
current collector did
not create a hole. The thickness, areal density and resistance were measured.
The material was
10 placed in an oven at 175 C. for 30 minutes and the shrinkage measured.
Compared to the prior art,
comparative examples #3-5, these materials have the advantage that they do not
melt or shrink in the
presence of heat, and so in a lithium ion battery with an internal short, will
not retreat to create an
even bigger internal short. Such is seen in FIG. 8A.
15 Example 6
[0103] Dreamweaver Gold 20, a commercially available prototype lithium
ion battery separator
was obtained. It is made from a blend of cellulose and para-aramid nanofibers
and polyester
microfibers in a papermaking process, and calendered to low thickness. The
separator was then
touched with a hot soldering iron in the same way as Example 1. Touching the
thermometer to the
20 current collector did not create a hole, as shown in FIG. 8B. The
thickness, areal density and
resistance were measured. The material was placed in an oven at 175 C. for 30
minutes and the
shrinkage measured. The advantages of this separator compared to the prior art
separators are the
same as for Example 2.
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TABLE 1
Example Material Thickness Areal Resistance Shrinkage Solder
Density (175 C) Tip
Hole
Size
Comp Aluminum 30 p.m 80 g/m2 <0.1 0% No
hole
Example 1 mOhm/square
Comp Copper 14 p.m 125 g/m2 <0.1 0% No
hole
Example 2 mOhm/square
Example 1 PP 24 p.m 14 g/m2 Infinite Melted 7.5
p.m
Example 2 PP ceramic 27 p.m 20 g/m2 Infinite Melted 2
tm/1
11m
Example 3 PE ceramic 27 p.m 20 g/m2 Infinite Melted 5
p.m/2
11m
Example 4 Aluminized 13 p.m 12 g/m2 6.3 33% 2
p.m
PET Ohm/square
Example 5 Fiber blend 27 p.m 16 g/m2 Infinite 2% No
hole
Example 6 Fiber blend 23 p.m 16 g/m2 Infinite 0% No
hole
[0104] Comparative Examples 1-2 are existing current collector
materials, showing very low
resistance, high areal density and no response at exposure to either a hot
solder tip or any shrinkage
at 175 C.
[0105] Examples 1-3 are materials that have infinite resistance, have
low areal density and melt
on exposure to either 175 C. or a hot solder tip. They are excellent
substrates for metallization
according to this invention.
[0106] Example 4 is an example of an aluminized polymer film, which
shows moderate
resistance, low areal density and shrinks when exposed to 175 C. or a hot
solder tip. It is an
example of a potential cathode current collector composite film according to
this invention. In
practice, and as shown in further examples, it may be desirable to impart a
higher level of metal
coating for higher power batteries.
[0107] Examples 5-6 are materials that have infinite resistance, have
low areal density, but have
very low shrinkage when exposed to 175 C. or a hot solder tip. They are
examples of the polymer
substrate under this invention when the thickness of the metallized coating is
thin enough such that
the metallized coating will deteriorate under the high current conditions
associated with a short.
Additionally, the cellulose nanofibers and polyester microfibers will oxidize,
shrink and ablate at
temperatures far lower than the melting temperatures of the metal current
collectors currently in
practice.
[0108] Example 5 additionally is made from a fiber, polyacrylonitrile,
that swells on exposure to
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traditional lithium ion carbonate electrolytes, which is also an example of a
polymer substrate under
this invention such that the swelling will increase under heat and create
cracks in the metalized
coating which will break the conductive path, improving the safety of the cell
by eliminating or
greatly reducing the uniform conductive path of the current collector on the
exposure to heat within
the battery.
Example 7
[0109] The material utilized in Example 5 was placed in the deposition
position of a MBraun
Vacuum Deposition System, using an intermetallic crucible and aluminum
pellets. The chamber
was evacuated to 3x10-5 mbar. The power was increased until the aluminum was
melted, and then
the power set so the deposition rate was 3 Angstroms/s. The deposition was run
for 1 hour, with
four samples rotating on the deposition plate. The process was repeated three
times, so the total
deposition time was 4 hours. The samples were measured for weight, thickness
and resistance (DC
and 1 kHz, 1 inch strip measured between electrodes 1 inch apart), which are
shown in Table 2
below. Point resistance was also measured using a Hioki 3555 Battery HiTester
at 1 kHz with the
probe tips 1" apart. The weight of added aluminum was calculated by the weight
added during the
process divided by the sample area. This is divided by the density of the
material to give the average
thickness of the coating.
Example 8
[0110] A nonwoven polymer substrate was made by taking a polyethylene
terephthalate
microfiber with a flat cross section and making hand sheets at 20 g/m2 using
the process of Tappi
T206. These hand sheets were then calendered at 10 m/min, 2000 lb s/inch
pressure using hardened
steel rolls at 250 F. This material was metalized according to the process of
Example 7, and the
same measurements taken and reported in Table 8.
Example 9
[0111] Material according to Example 5 was deposited according to the
process of Example 7,
except that the coating was done at a setting of 5 Angstroms/second for 60
minutes. The samples
were turned over and coated on the back side under the same procedure. These
materials were
imaged under a scanning electron microscope (SEM), both on the surface and in
cross section, and
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the images are presented in FIGS. 9, 9A, and 9B.
Example 10
[0112] Materials were prepared according to the procedure of Example 9,
except the deposition
on each side was for only 20 minutes.
Example 11
[0113] The polymer substrate of Example 8 was prepared, except that the
sheets were not
calendered. The deposition of aluminum is at 5 Angstroms/second for 20 minutes
on each side.
Because the materials were not calendered, the porosity is very high, giving
very high resistance
values with a thin coat weight. Comparing Example 11 to Example 8 shows the
benefits of
calendering, which are unexpectedly high.
TABLE 2
Sample Added DC 1 kHz 1 kHz point
Average
weight Resistance Resistance resistance
coating
thickness
Units g/m2
Ohms/square Ohms/square Ohms
Microns
Example 7 3.5 0.7 0.5 0.1
1.3
Example 8 2.0 7 7 0.4
0.7
Example 9 2.2 0.2
0.8
Example 10 0.8 1.7
0.3
Example 11 0.8 100
0.3
Example 12
[0114] The aluminum coated polymer substrate from Example 9 was coated
with a mixture of
97% NCM cathode material (NCM523, obtained from BASF), 1% carbon black and 2%
PVDF
binder in a solution of N-Methyl-2-pyrrolidone. The coat weight was 12.7
mg/cm2, at a thickness of
71 microns. This material was cut to fit a 2032 coin cell, and paired with
graphite anode coated on
copper foil current collector (6 mg/cm2, 96.75% graphite (BTR), 0.75% carbon
black, 1.5% SBR
and 1% CMC). A single layer coin cell was made by placing the anode, separator
(Celgard 2320)
and the NCM coated material into the cell, flooding with electrolyte (60 uL,
1.0M LiPF6 in
EC:DEC:DMC=4:4:2 vol+2w. % VC) and sealing the cell by crimping the shell. To
obtain
adequate conductivity, a portion of the aluminum coated polymer substrate from
Example 9 was left
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uncoated with cathode material and folded over to contact the shell of the
coin cell, completing the
conductive pathway. The cell was formed by charging at a constant current of
0.18 mA to 4.2 V,
then at constant voltage (4.2 V) until the current dropped to 0.04 mA. The
cell was cycled three
times between 4.2 V and 3.0 V at 0.37 mA, and gave an average discharge
capacity of 1.2 mAh.
Example 13
[0115] A cell was made according to the procedure and using the
materials from Example 12,
except the separator used was Dreamweaver Silver 20. The cell was formed by
charging at a
constant current of 0.18 mA to 4.2 V, then at constant voltage (4.2 V) until
the current dropped to
0.04 mA. The cell was cycled three times between 4.2 V and 3.0 V at 0.37 mA,
and gave an average
discharge capacity of 0.8 mAh. Thus in this and the previous example, working
rechargeable
lithium ion cells were made with an aluminum thickness of less than 1 micron.
Comparative Example 3
[0116] The aluminum tab of Comparative Example 1, approximately 2 cmx4 cm
was connected
to the ground of a current source through a metal connector contacting the
entire width of the
sample. The voltage limit was set to 4.0 V, and the current limit to 1.0 A. A
probe connected to the
high voltage of the current source was touched first to a metal connector
contacting the entire width
of the sample, and then multiple times to the aluminum tab, generating a short
circuit at 1.0 A. The
tip of the probe was approximately 0.25 mm2 area. When contacted across the
entire width, the
current flowed normally. On initial touch with the probe to the tab, sparks
were generated,
indicating very high initial current density. The resultant defects in the
current collector only
sometimes resulted in holes, and in other times there was ablation but the
current collector remained
intact. In all cases the circuit remained shorted with 1.0 A flowing. A
micrograph was taken of an
ablated defect, with no hole, and is shown in FIG. 10. The experiment was
repeated with the current
source limit set to 5.0, 3.0, 0.6 A, 0.3 A and 0.1 A, and in all cases the
result was a continuous
current at the test current limit, both when contacted across the entire width
of the current collector
and using the point probe of approximately 0.25 mm2 tip size.
Comparative Example 4
[0117] The copper tab of Comparative Example 2 of similar dimensions was
tested in the same
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way as Comparative Example 3. When contacted across the entire width, the
current flowed
normally. On initial touch with the probe to the tab, sparks were generated,
indicating very high
initial current density. The resultant defects in the current collector only
sometimes resulted in
holes, and in other times there was ablation but the current collector
remained intact. In all cases the
5 circuit remained shorted with 0.8 A flowing. A micrograph was taken of an
ablated defect, with no
hole, and is shown in FIG. 10A. The experiment was repeated with the current
source limit set to
5.0, 3.0, 0.6 A, 0.3 A and 0.1 A, and in all cases the result was a continuous
current at the test
current limit, both when contacted across the entire width of the current
collector and using the point
probe of approximately 0.25 mm2 tip size.
Example 14
[0118] The inventive aluminum coated polymer substrate material of
Example 7 of similar
dimensions was tested using the same method as Comparative Examples 3-4. When
contacted
across the entire width, the current flowed normally. In each case of the
touch of the probe to the
inventive current collector directly, the sparks generated were far less, and
the current ceased to flow
after the initial sparks, leaving an open circuit. In all cases, the resultant
defect was a hole.
Micrographs of several examples of the holes are shown in FIGS. 11 and 11A.
The experiment was
repeated with the current source limit set to 5.0, 3.0, 0.6 A, 0.3 A and 0.1
A, and in all cases the
result a continuous flow of current when contacted through the full width
connectors, and no current
flowing through the inventive example when contacted directly from the probe
to the inventive
current collector example.
[0119] The key invention shown is that, when exposed to a short circuit
as in Comparative
Examples 3-4 and in Example 14, with the prior art the result is an ongoing
short circuit, while with
the inventive material the result is an open circuit, with no ongoing current
flowing (i.e., no
appreciable current movement). Thus, the prior art short circuit can and does
generate heat, which
can melt the separator, dissolve the SEI layer, and result in thermal runaway
of the cell, thereby
igniting the electrolyte. The open circuit of the inventive current collector
will not generate heat and
thus provides for a cell, which can support internal short circuits without
allowing thermal runaway,
and the resultant smoke, heat and flames.
Examples 15 and 16 and Comparative Examples 5 and 6
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[0120] Two metallized films were produced on 10 micron polyethylene
terephthalate film in a
roll to roll process. In this process, a roll of the film was placed in a
vacuum metallization
production machine (an example of which is TopMet 4450, available from Applied
Materials), and
the chamber evacuated to a low pressure. The roll was passed over heated boats
that contain molten
aluminum at a high rate of speed, example 50 m/min. Above the heated boats
containing molten
aluminum is a plume of aluminum gas, which deposits on the film, with the
deposition rate
controlled by speed and aluminum temperature. A roll approximately 500 m long
and 70 cm wide
was produced through multiple passes until the aluminum coating was .about.300
nm. The coating
process was repeated to coat the other side of the film, with the resultant
product utilized herein as
Example 15 (with the inventive current collector of FIG. 4 a depiction of that
utilized in this
Example). Example 16 was thus produced in the same way, except the metal in
the boat was copper
(and with the depiction of FIG. 5B representing the current collector utilized
within this inventive
structure). The basis weight, thickness and conductivity of each film were
measured, and are
reported below in Table 3. The coating weight was calculated by subtracting
13.8 g/m2, the basis
weight of the 10 micron polyethylene terephthalate film. The "calculated
coating thickness" was
calculated by dividing the coating weight by the density of the materials (2.7
g/cm3 for aluminum,
8.96 g/cm3 for copper), and assuming equal coating on each side.
[0121] Comparative Example 5 is a commercially obtained aluminum foil 17
microns thick.
Comparative Example 6 is a commercially obtained copper foil 50 microns thick.
Comparative
.. Example 7 is a commercially obtained copper foil 9 microns thick.
TABLE 3
Sample Bases Coating Thickness DC
Calculated
Weight Weight Resistance
coating
thickness
Units g/m2 g/m2 Microns Ohms
Microns
Example 15 17 3 11 0.081
0.5
Example 16 24 10 11 0.041
0.5
Comparative 46 17
Example 5
Comparative 448 50
Example 6
Comparative 81 9
Example 7
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[0122] Example 15, Example 16, Comparative Example 5 and Comparative Example 6
were
subjected to a further test of their ability to carry very high current
densities. A test apparatus was
made which would hold a polished copper wire with radius 0.51 mm (24 AWG
gauge) in contact
with a current collector film or foil. The film or foil under test was
grounded with an aluminum
contact held in contact with the film or foil under test, with contact area >1
square centimeter. The
probe was connected in series with a high power 400W resistor of value 0.335
ohms, and connected
to a Volteq HY3050EX power supply, set to control current. The current
collector to be measured
was placed in the setup, with the polished wire in contact with the surface of
the current collector at
zero input current. The current was increased in 0.2 ampere increments and
held at 30 seconds for
each increment, while the voltage across the resistor was measured. When the
voltage dropped to
zero, indicating that current was no longer flowing, the sample was shown to
fail. Each of Example
15, Example 16, Comparative Example 5 and Comparative Example 6 were tested.
Example 15
failed at a 7 A (average of two measurements). Example 16 failed at 10.2 A
(average of two
measurements). Neither of Comparative Example 5 nor Comparative Example 6
failed below 20 A.
Both Example 15 and Example 16 showed holes in the current collector of radius
>1 mm, while
neither of the Comparative Examples 5 or 6 showed any damage to the foil. In
this example test, it
would be advantageous to have a current collector that is unable to carry a
current of greater than 20
A, or preferably greater than 15 A or more preferably greater than 12 A.
[0123] In another test, meant to simulate using these inventive current
collectors as a tab
connecting the electrode stack of a cell to the electrical devices in use
(either inside or outside the
cell), Examples 15 and 16 and Comparative Examples 5 and 6 were subjected to a
current capacity
test along the strip. To prepare the samples for the test, the current
collectors were cut into the shape
shown in FIG. 12, which consists of a strip of material that is four
centimeters by on centimeter (4
cmxl cm), with the ends of the strip ending in truncated right isosceles
triangles of side 4 cm. Each
of the triangles of the test piece was contacted through a piece of aluminum
with contact surface
area >1 cm. One side was connected through a 400 W, 0.335 ohm resistor, and
this circuit was
connected to a Volteq HY3050EX power supply. The voltage was measured across
the resistors to
measure the current, and the piece was shown to fail when this voltage dropped
to zero. For each
test, the piece was connected with the power supply set to zero current, and
then increased in 0.2 A
increments and allowed to sit for 30 seconds at each new voltage, until the
sample failed and the
current flowing dropped to zero. The test was configured so that the
metallized current collectors
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could be measured with contact either on one side, or on both sides of the
metallized current
collector. The currents at failure are shown below in Table 4. For materials
tested in a 4 cmxl cm
strip, it would be advantageous to provide an internal fuse by limited the
amount of current that can
flow to be below 20 A, or preferably below 15 A, or more preferably below 10
A, each with either
single or double-sided contact.
TABLE 4
Sample Single Sided Failure Double Sided
Failure
Voltage Voltage
Units V V
Example 15 2.7 4.5
Example 16 24 10
Comparative Example 5 No failure below 20 A No failure below
20 A
Comparative Example 6 No failure below 20 A No failure below
20 A
Examples 17-19 and Comparative Example 8
[0124] Cells were made by coating standard foil current collectors and the
metallized PET film
current collectors from Examples 15 and 16 with electrode materials. NMC 523
cathode materials
were prepared using BASF NMC523 (97%), carbon black (2%) and PVDF (1%) in NMP
solvent,
and coated on the aluminum current collector (15 micron aluminum current
collector) and Example
were at a basis weight of 220 g/m2, corresponding to a cathode loading density
of 3.3 mAh/cm2.
15 Anode materials were prepared by using graphite BTR-918S (94%), carbon
black (5%) and PVDF
(1%) in NMP solvent, and coating on the copper current collector (18 micron
copper current
collector) at 118 g/m2, corresponding to an anode loading density of 4.0
mAh/cm2. Four double
sided cathodes were prepared, and three double sided anodes and two single
sided anodes. These
were stacked with Celgard 2500 separator to form small pouch cells, which were
then filled with
electrolyte and sealed with designed capacity 1 Ah. Four types of cells were
made by different
combinations of foil materials, and the capacity measured at C/10 and C/5
(that is, 0.1 A and 0.2 A).
The cells were formed by charging at 100 mA to 4.2 V, and held at 4.2 V until
the current dropped
to 10 mA. The fully formed cells were then weighed, and tested for capacity by
discharging at C/10,
then charging at C/10 and discharging at C/5. These results are shown in Table
5, below.
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TABLE 5
Sample Cathode Anode Cell Weight C/10 C/5
Capacity
Current Current Capacity
Collector Collector
Units Grams mAh
mAh
Comparative Al Foil Cu Foil 27 924
615
Example 8
Example 17 Example 15 Cu Foil 26.8 1049
751
Example 18 Al Foil Example 16 24.7 1096
853
Example 19 Example 15 Example 16 24.7 1057
848
[0125] Thus, it has been shown that the Examples provided above exhibit
the desirable thickness,
metal coating, and conductivity results needed to prevent thermal runaway
within an electrolyte-
containing battery, thereby providing not only a much safer and more reliable
type, but one that
requires far less internal weight components than ever before, without
sacrificing safety, but, in fact,
improving thereupon.
[0126] As noted above, the ability to not only provide such a thin
current collector (as an internal
fuse within a lithium battery article) but also the necessary benefits of a
tabbed structure to ensure
generated voltage is transferred external of the subject battery cell, is
accorded within this
disclosure. Additionally, the ability to further utilize the beneficial thin
structures of the current
collector as above lends itself to any number of myriad configurations within
the confines of the
subject battery article itself, potentially generating cumulative power levels
all with the beneficial
internal fuse component(s) in place. Such are discussed in greater detail
within FIGS. 12-22.
[0127] FIG. 13 shows a single thin film current tab/collector 600 with a
metallized film layer 614
and a lower non-metal layer 616. A conducting tab 610 (to lead to the external
power transfer
component of a battery) is provided as well, aligned perpendicularly to the
collector, and connected
thereto with welds 612.
[0128] FIG. 14 shows a similar current collector 620 but with a tab 622
present with tape 624
.. connecting the tab 622 to the collector 634 for such a conductive purpose.
As above, the tab/current
collector 620 has a metallized film layer 626 and a lower non-metal layer 632.
The tape component
622 is provided on the outer surface 628 of the tab and leading to the non-
metal layer 626 of the
current collector, provided a shear strength adhesive quality for the tab to
remain secured and in
suitable manner for conduction purposes.
[0129] FIG. 15 provides a different tab/collector 640 showing a different
manner of connecting a
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tab 642 to a single thin current collector 648 (with a metallized film layer
644 and a lower non-metal
layer 650), connecting the two components through the utilization of
conducting staple components
646.
[0130] Such flat current collector structures allow for a typical
battery structure with a compact
5 battery structures (such as in FIG. 1, for instance). FIG. 16 shows a
single fold 710 tab/current
collector 700 with a single taped tab 702 attached thereto the metallized film
surface 712 (which
covers, as above, the non-metal layer 708). In this manner, the single fold
710 current collector 704
imparts the capability of an increase in power generation within the battery
cell as a result, albeit
with the need for a slight increase in battery size from the flat structure.
10 [0131] FIG. 17 depicts a double folded 732 tab/current collector
720 utilizing the same thin
structure collector 724. Such a double fold 732 thus further provides the
ability to connect the two
sides 726, 728 of the current collector 724 that might otherwise be
electrically insulated by the
polymer film situated between the two electrically conducting layers. The tab
722 attaches at the
collector surface 730 for such a double fold 732 conductivity purpose.
15 [0132] FIG. 18 likewise includes a flat tab/current collector 750
with the same type of upper 758
and lower surface 762 as above. The tab 752, 754, in this instance, is
provided as two parallel
structures with contact with both the top 758 and lower surfaces 760 of the
current collector 762.
Such a tab 752, 754 includes welds 756 for connection to and with both
surfaces 758, 760.
[0133] FIG. 19 shows a similar structure 780 to FIG. 16, but with a
single folded tab 794 in place
20 that is in contact with both surfaces 788, 790 of the current collector
792 through welds 786 with
two extended prongs 782, 784 of the folded tab 794 leading therefrom.
[0134] FIG. 20 shows a welded 804 tab 802 to a double folded 810
tab/current collector 800, thus
exhibiting the same ability to connect electrically isolated layers 808, 812
as above as part of the
collector 806, but with safer welds 804 in place to more reliably and more
potentially effective for
25 power transfer purposes.
[0135] FIG. 21 thus shows a composite tab/multiple collectors structure
820 with a plurality (here
five) of such double rounded folded 856 current collectors 826, 828, 830, 832,
834 with metallized
film layers 858, 860, 862, 864, 866 and lower non-metal layers 846, 848, 850,
852, 854, connected
in a series for even more ability to connect electrically isolated layers for
conductivity through a
30 single tab 822 with welds 824 connecting for conductance with the top
double rounded folded
collector 826. The welded tab 822 stays in place strongly for improved
reliability purposes, as well.
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[0136] A second, opposite, welded 906 tab 904 is provided in FIG. 22
with such a multiple
multi-rounded fold 938 current collector array 908, 910, 912, 914, 916 in
place, as well. Such a
tabs/collectors structure 900 allows for increased power generation without
necessitating weight of
volume increases for the subject battery cell through the two tabs 902, 904
configured and connected
.. with the two outer collectors 908, 916, as noted previously. Metallized
film layers 940, 942, 944,
946, 948 are, as above, provided with opposing non-metal layers 928, 930, 932,
934, 936 are present
as with such other collector examples.
[0137] Referring to FIG. 23, as yet another non-limiting example
tab/collector structure 960, a
multi-Z-fold 972 tab 962 clamped to a series of parallel flat thin current
collectors 964, 966, 968,
970 (here four) (as described above), with metallized film layers 974, 978,
982, 986 and lower non-
metal layers 976, 980, 982, 984, again, to provide a different manner of
generating cumulative
power in a series, albeit with flat thin current collectors 964, 966, 968, 970
(acting as multiple
internal fuses).
[0138] Such structures of FIGS. 13-23 thus allow for different external
connections to the
internal fuse components of a standing lithium battery.
[0139] Having described the invention in detail it is obvious that one
skilled in the art will be
able to make variations and modifications thereto without departing from the
scope of the present
invention. Accordingly, the scope of the present invention should be
determined only by the claims
appended hereto.
