Note: Descriptions are shown in the official language in which they were submitted.
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EI~ECTROCHEMICAh BUNDhE AND METHOD FOR MAKING SAME
FIEhD OF THE INVENTION
The present invention relates to electrochemical (EC)
equipment and, more specifically, to a current collecting
terminal which is used to connect a plurality of EC cells in
order to form an EC bundle. This invention also concerns a
method for making an EC bundle.
BACKGROUND OF THE INVENTION
In recent years, the field of electrochemical equipment
and, more specifically, that of energy storage devices
(i.e., batteries) has generally been characterized by a
certain effervescence. Tn fact, ever increasing and
evolving demand, research and development, and greater
competition in the market place are all factors that are
contributing to numerous innovations in this field.
Moreover, manufacturers and users of EC devices are also
envisioning alternate and diversified applications for these
products.
The automotive industry, for example, has been seeking
to commercialize a viable electrical vehicle for several
decades now. An important element of such a vehicle is its
battery. The battery must not only provide the requisite
level of energy production but must also be durable. As a
further example, the telecommunications industry also
requires relatively durable and powerful batteries such as
to provide a reliable and un-interruptible power source.
A number of advanced battery technologies have therefore
recently been developed, such as metal hydride (e.g., Ni-
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MH), lithium-ion, and lithium polymer cell technologies,
which would appear to provide the requisite level of energy
production and safety margins for many commercial and
consumer applications. Such advanced battery technologies,
however, often exhibit characteristics that provide
challenges for the manufacturers. In conventional battery
design, individual cells are hardwired together and to the
positive and negative power terminals of the battery. Such
advanced and complex~batteries, however, are relatively
difficult and expensive to manufacture. For example,
individual EC cells, which generally form the basis of
batteries, are usually connected to one another by welding
their respective components (i.e., electrodes and the like)
onto a current collecting terminal in order to form an EC
bundle (batteries generally comprising one or more EC
bundles). In addition to being tedious, such a process is
time-consuming, labor intensive, and costly.
Considering this background, it clearly appears that
there is a need in the industry to develop a simpler and
more cost-efficient method for connecting EC cells in order
to form an EC bundle.
SUN~1ARY OF THE INVENTION
Under a first broad aspect, the invention provides an
EC bundle having a plurality of cells. Each cell
respectively comprises: a pair of sheet-like electrodes; an
electrolyte separator interposed between the sheet-like
electrodes; and a sheet-like current collecting element.
The sheet-like current collecting element, which includes a
pair of generally opposite main faces, projects from~at
least one of the sheet-like electrodes and is electrically
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connected thereto. Moreover, the plurality of cells are
arranged into a stack such that their respective sheet-like
current collecting elements are in a side-by-side
relationship with their main faces generally facing one
another. The EC bundle further comprises a current
collecting terminal with a pair of arms in a spaced apart
relationship that define a recess which receives the sheet-
like current collecting elements and which establishes an
electrical connection with them. Each arm of the current
collecting terminal overlaps at least a portion of a main
face of one of the sheet-like current collecting elements.
Under a specific and non-limiting example of
implementation, the sheet-like current collecting elements
overlap the sheet-like electrodes from which they project,
and are electrically connected to one another via their
main faces; the latter preferably being in physical
contact with one another. Moreover, the sheet-like current
collecting elements can either project from a sheet-like
electrode that is an anode or a cathode.
The current collecting terminal, which is made from
ductile metallic material, is mechanically connected to the
sheet-like current collecting elements° by a crimping
process and/or by welding, soldering or adhesives. The
arms of the current collecting terminal diverge from one
another and can be of equal length or of unequal length,
with one arm being longer than the other. The latter form
of construction allows for providing an energy storage
device comprising at least a pair of EC bundles arranged
side-by-side such that the longer arms of their current
collecting terminals face one another and are in electrical
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connection with one another.
Under a second broad aspect, the invention provides an
energy storage device comprising at least one EC bundle as
broadly defined above.
Under a third broad aspect, the invention provides a
method for fabricating an EC bundle. The method comprises
providing a plurality of EC cells, each of which including:
a pair of sheet-like electrodes; an electrolyte separator
interposed between the electrodes; and a sheet-like current
collecting element. The sheet-like current collecting
element, which has a pair of generally opposite main faces,
projects from at least one of the sheet-like electrodes and
is electrically connected thereto. The plurality of cells
are then arranged into a stack such that the sheet-like
current collecting elements are in a side-by-side
relationship with their main faces generally facing one
another. The method also includes applying a current
collecting terminal on the sheet-like current collecting
elements for establishing an electrical connection with
them. The current collecting terminal has a pair of arms in
a spaced apart relationship defining therebetween a recess
which receives the current collecting elements. Each arm
of the current collecting terminal also overlaps at least a
portion of a main face of one of the sheet-like current
collecting elements.
BRIEF DESCRIPTION OF THE DRAWINGS
A detailed description of examples of implementation of
the present invention is provided hereinbelow with
reference to the following drawings, in which:
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Figure 1 is a perspective view of a typical EC cell;
Figure 2 is a perspective view of a plurality of
individual EC cells that are connected in order to form a
bundle according to a non-limiting example of
implementation of the present invention, several basic
components of the EC cells having been omitted from the
figure for the sake of clarity;
Figure 3 is a cross-sectional view of a current
collecting terminal as depicted in Figure 2, the current
collecting terminal being shown prior to being applied on
the currents collecting elements of the EC bundle;
Figure 4 is a perspective view of the current
collecting terminal depicted in Figure 3;
Figure 5 is a cross-sectional view of an EC bundle in
accordance with a first variant of the invention;
Figure 6 is a cross-sectional view of a plurality of
EC bundles similar to that depicted in. Figure 5, the EC
bundles being disposed in a side-by-side relationship and
being electrically connected;
Figure 7 is a cross-sectional view of a plurality of
EC bundles similar to that depicted in Figure 5, the EC
bundles being disposed in an alternating side-by-side
relationship and being electrically connected;
Figure 8 is a cross-sectional view of a plurality of EC
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bundles being electrically connected in series with current
collecting terminals in accordance with a second variant of
the invention; and
Figure 9 is a cross-sectional view of a plurality of EC
bundles being electrically connected in parallel with
current collecting terminals in accordance with a third
variant of the invention.
In the drawings, embodiments of the invention are
illustrated by way of example. It is to be expressly
understood that the description and drawings are only for
purposes of illustration and as an aid to understanding,
and are not intended to be a definition of the limits of
the invention.
DETAINED DESCRIPTION
With reference to Figure 1, there is shown an example
of a typical electrochemical (EC) cell 20. EC cell 20,
more specifically, comprises a negative sheet-like
electrode 22 (generally referred to as an anode), a
positive sheet-like electrode 24 (generally referred to as
a cathode), and an electrolyte 26 interposed between the
former and the latter. In addition, a sheet-like cathode
current collecting element 28 is positioned adjacent to the
cathode 24. Moreover, as shown in Figure 1, anode 22 is
slightly offset with respect to the current. collecting
element 28 such as to respectively expose the anode 22 and
the current collecting element 28 along first and second
ends 30, 32 of the EC cell. Each of the above components
will now be described in greater detail.
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In a preferred embodiment, anode 22 is a lithium or
lithium alloy metallic sheet or foil, which act both as a
cation source and as a current collector. Anode 22 may
also comprise an anode current collecting element distinct
from the active anode material. For instance, anode 22 may
be a composite comprising an anode current collecting
element preferably made of a thin sheet of copper, a
polymer, an electronic conductive filler, and an
intercalation material. Examples of the electronic
conductive filler include but are not limited to:
conductive carbon, carbon black, graphite, graphite fiber,
and graphite paper. Any intercalation material known to
those skilled in the art may be used and, in particular,
may be selected from the group consisting of: carbon,
activated carbon, graphite, petroleum coke, a lithium
alloy, nickel powder, and lithium intercalation compound.
The anode may further comprise a lithium salt. Other
materials can, however, also be used to form anode 22.
Although Figure 1 does not depict anode 22 as including a
structurally distinct current collecting element, it should
be expressly understood that an anode having such a feature
remains within the scope of the present invention. A
distinct current collector for the anode is typically made
of copper.
With respect to cathode ~4, the latter typically
comprises a. compound of a polymer, a lithium salt, and
electrochemically active material. Examples of suitable
electrochemically active material include : LiXVyOZ; LiCo02;
LiXMnyO~; LiNi02; LiFeP04; VxOY~ MnyOz; Fe (P04) s; or LiXTiyOz.
In a preferred embodiment, cathode 24 preferably comprises
lithiated vanadium oxide (LiXVyOZ) . Any other suitable
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active material can, however, be used to form the cathode
24.
Electrolyte 26, which is preferably but not necessarily
solid and made of polymer mixed with a lithium salt,
physically separates the anode 22 and the cathode 24 and
also acts as an ion transporting membrane.
Current collecting element 28, which serves the primary
function of conducting the flow of electrons between the
active material of cathode 24 and the terminals of a
battery (not shown), is typically constructed of material
such as copper, nickel, aluminum, and the like. In a
preferred embodiment, current collecting element 28 for
cathode 24 comprises an aluminum sheet or foil coated with
a thin protective layer having an electronic conductive
element such as carbon or graphite. This protective layer
prevents degradation of the current collecting element when
the latter is in contact with the cathode material.
Although Figure 1 depicts an EC cell in a mono-face
configuration (i.e., wherein a current collecting element
is associated with each anode/electrolyte/cathode element
combination), it should be specifically understood that the
present invention contemplates other EC cell configurations
as well. For example, a bi-face EC cell configuration
(i.e., wherein a common current collecting element is
associated with a pair of anode/electrolyte/cathode element
combinations) can also be used without departing from the
spirit of the invention.
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Energy storage devices, which are more commonly known
as batteries, generally include a plurality of EC cells
such as that shown in Figure 1. The EC cells are generally
grouped together and electrically connected to one another
in order to form one or more EC bundles.
Figure 2 depicts a specific embodiment of an EC bundle
70 according to the present invention. As shown, EC bundle
70 includes a plurality of individual EC cells 72 which are
disposed in a side-by-side relationship. Each of the
individual EC cells 72 includes, among others, an anode
current collecting element 74 and a cathode current
collecting element 76. Note that the anode current
collecting element can be structurally integral with its
corresponding electrode or distinct therefrom, as discussed
previously. The anode current collecting elements 74 of
the individual EC cells are all grouped together on. side 78
of the bundle while the cathode current collecting elements
76 are grouped together on side 80 of the same bundle. The
individual EC cells of a bundle are separated by a thin
insulating film of plastic material (not shown), such as
polypropylene, to prevent short circuiting between
individual cells.
In order to electrically connect the anode current
collecting elements 74 to one another, a current collecting
terminal 82 is positioned over these same anode current
collecting elements along the first side 78 of the EC
bundle. Current collecting terminal 82 includes a pair of
spaced-apart arms 86, 88 that diverge from one another and
which form a recess 90 therebetween. Recess 90 is shaped
such that it is capable of snugly receiving the anode
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current collecting elements 74 therein. Figure 2 further
shows that each of the arms 86, 88 of current collecting
terminal 82 also overlaps at least a portion of a main face
of the most exteriorly positioned anode current collecting
element 74. The cathode current collecting elements 76 are
also connected to one another in similar fashion via
current collecting terminal 84.-
Figure 2 also depicts that the anode current
collecting elements 74 are in electrical connection with
one another via their respective main faces; the latter
being in physical contact. Similarly, the cathode current
collecting elements 76 are in electrical connection with
one another via their respective main faces; the latter
being in physical contact.
As further shown, an insulation boot or tape 91, 93 is
positioned at the extremity of each arm 86, 88 and acts to
prevent any short-circuiting between the extremities of
arms 86 and 88 with opposing. electrode layers. As shown,
the arms of current collecting terminate 84 feature similar
insulation boots or tapes.
Although Figure 2 shows an EC bundle 70 comprising six
individual EC cells 72, it should be expressly understood
that an EC bundle comprising any number of individual EC
cells 72 remains within the scope of the present invention.
In order to obtain an EC bundle as depicted in Figure
2, current collecting terminals are respectively applied
onto the anode current collecting elements and the cathode
current collecting elements, and a pressure is exerted
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thereupon such as' to form a mechanical connection. The
current collecting terminals are thereby bent and assume a
shape such as that shown in Figure 2. Preferably, the
pressure is applied with a crimping tool to produce a
stronger mechanical connection between the current
collecting terminals with their associated current
collecting elements. Generally, the crimping pressure
alone is sufficient to bind the current collecting
terminals with their associated current collecting
elements. However, additional or other binding means
(e. g., ultrasonic welding, laser welding, arc welding,
pressure welding, soldering, adhesives, etc.) may be
required in certain circumstances to improve the mechanical
connections. The current collecting terminals will now be
described in greater detail.
Figures 3 and 4 depict, in isolation, an example of a
current collecting terminal 100 in accordance with the
present invention. As shown, the current collecting
terminal 100 preferably has an angled profile prior to use.
More specifically, current collecting terminal 100 has a
pair of plates which define arms 102, 104 that are
substantially perpendicular with respect to one another.
An insulation boot or tape 106 is also positioned at the
extremity of each arm; the purpose of which having being
discussed previously.
While current collecting terminal 100 is preferably
made of copper, it can, however, be made of any other
ductile and conductive material such as brass, gold,
silver, aluminum, and alloys thereof.
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Although Figures 3 and 4 show a current collecting
terminal as having a substantially right-angle shape, it
should be expressly understood that a current collecting
terminal featuring any other shape, prior to use, remains
within the scope of the present invention.
Once bundles such as those depicted in Figure 2 are
crimped, they can then be stacked side by side with an
insulating film separating each bundle and the various
current collecting terminals are connected together with
electrical leads, in series or in parallel depending on end
use, to form a battery or energy storage device . It should
be expressly understood that the final shape of current
collecting terminals 82 and 84 as depicted in Figure 2 may
vary to accommodate different electrical connections as
well as to provide thermal conduction between a bundle 70
and the casing of the energy storage device for example.
Figure 5 shows an alternative embodiment of an EC
bundle 120 according to the present invention. As shown,
EC bundle 120 also includes a plurality of individual EC
cells 122 whose anode current collecting elements and
cathode current collecting elements have been respectively
connected to one another via current collecting terminals
126, 128. In this particular embodiment, however, each of
the current collecting terminals 126, 128 features arms of
differing lengths. Current collecting terminal 126, for
example, includes a long arm 130 and a short arm 132.
Current collecting terminal 128 similarly features a long
arm 134 and a short arm 136. However, long arm 134 is
disposed on an opposite side o'f EC bundle 120 than is long
arm 130. The short arms 132 of current collecting terminal
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126 also features an insulation boot or tape 133.
Moreover, an insulation boot or tape 137 is also associated
with short arm 136 of current collecting terminal 128.
An advantage associated with the embodiment of Figure 5
is that a plurality of EC bundles 120 can be disposed in a
side-by-side relationship with their long arms preferably
touching one another thereby electrically connecting the EC
bundles. Such a disposition, which is shown in Figure 6,
obviates the need of placing each EC bundle within a
protective envelope and connecting the bundle via
electrical leads to an external connection. Thus, only a
single set of electrical leads is required as opposed to a
plurality of sets (i.e., one set for each bundle).
A further advantage is that higher current loads may
be conducted through the long arms 130, 134 of the current
collecting terminals 126 and 128 than through small gauge
wires extending from one end of the current collecting
terminals. In order to conduct high current loads through
wires connecting .the EC bundles in series, the wire gauge
would have to be increased substantially. This
configuration for the current collecting terminals permits
an efficient electrical connection of the EC bundles in
series without the use of large gauge wires between the EC
bundles when high current discharges are required such as
in automotive applications, for example. In high current
discharge applications, large gauge wires are used only to
connect the first and last EC bundles to the positive and
negative terminals (not shown) of the electrochemical
battery.
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It should be noted that the EC bundles 120 should be
disposed in such a manner that the negatively charged
current collecting terminals of each EC bundle are in
electrical connection with the positively charged current
collecting terminals of an adj acent EC bundle to connect a
set or pack of bundles. in series such that the main
electrical leads of the energy storage device are connected
only to the bundles at the end of a pack of bundles.
Although Figure 6 further shows that the long arm of
each EC bundle is in direct physical contact with the long
arm of the adjacent EC bundle, it should be specifically
understood that a mechanical separator may be positioned
between the long arms. An electrical connection can
therefore be maintained without, however, there being
direct physical contact between the long arms.
Figure 7 illustrates a variation of the alternative
embodiment in which the various bundles are stacked in an
alternating pattern. The negatively charged current
collecting terminals of each EC bundle are in electrical
connection with the positively charged current collecting
terminals of an adjacent EC bundle to connect the bundles
in series thereby forming a bundle stack connected in
series.
Figure 8 illustrates another embodiment in which the
current collecting terminal 150 also features arms of
differing lengths. However, in this particular embodiment,
the long arm 152 is folded backward. As illustrated, long
arm 152 is folded such that when electrically connecting
the EG bundles in series, the folded arms 152 of two
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adjacent current collecting terminals 150 are positioned
side by side and may be crimped, welded, ultra-sonically
welded or soldered together to ensure good electrical
contacts. This embodiment advantageously shortens the total
length of the long arms 152 thereby reducing the weight and
cost per current collecting terminal 150. It also removes
the extension of the long arms from in between each EC
bundle thereby decreasing the total volume of a stack of EC
bundles. This embodiment allows the connection of a
plurality of EC bundle in series, and which only have a
single set of electrical leads connecting the stack to the
positive and negative terminals of the electrochemical
battery. As previously mentioned, higher current loads may
be conducted through the long arms 152 of the Current
collecting terminals 150 than through small gauge wires.
Zarge gauge wires (not shown) can connect the first and
last Current collecting terminals 150 of a stack of EC
bundles to the positive and negative terminals (not shown)
of the electrochemical battery. Although not illustrated,
each EC bundle are separated by an insulating film to
prevent potential short-circuits between adjacent EC
bundles.
Figure 9 illustrates another embodiment of a current
collecting terminal 170~for electrically connecting the EC
bundles in parallel, Current collecting terminal 170
features two arms of similar length folded backward such
that when~electrically connecting a stack of EC bundles in
parallel, the folded arms 172 are positioned side by side
and may be crimped, welded, ultra-sonically welded or
soldered together to ensure good electrical contacts. This
embodiment also provides for a single set of electrical
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leads connecting the stack of EC bundles to the positive
and negative terminals of the electrochemical battery (not
shown) .
Of course, combinations of series and parallel
connections using the various configurations of current
collecting terminals are contemplated without departing
from the scope and spirit of the invention.
Although various embodiments have been illustrated,
this was for the purpose of describing, but not limiting,
the invention. Various modifications will become apparent
to those skilled in the art and are within the scope of
this invention, which is defined more particularly by the
attached claims.
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