Note: Descriptions are shown in the official language in which they were submitted.
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This invention relates to high energy electro-
chemical power cells. More particularly, it relates to
cells having an oxidizable anode material and a liquid
active cathode material and a solid current collector.
- Recently there has been a rapid growth in portable
electronic products requiring electrochemical cells to
supply the energy. Examples are calculators, cameras and
digital watches. These products, however, have highlighted
the deficiencies of the existing power ce'ls Sor demanding
1~ applications. For example, digital watches were developed
using the silver oxide cell, and although these watches have
become popular, it is now generally recognized that the
least developed component of the digital watch system is the
power cell. In particular, the energy density of the silver
cells is such that thin, stylish watches with reasonable
operating life are difficult to make. Additionally, these
cells have poor storage characteristics, low cell voltages,
and leakage problems.
In an effort to develop a cell that a~dresses one
or more of the foregoing problems, substantial work has been
done with cell chemistries using a lithium anode. The
cathode and electrolyte material consisting of a solvent and
solute vary. Indeed the literature is replete with examples
of lithium anode cells with different cathodes and elec-
trolytes. The ~lectrical characteristics of these cellssuch as energy per unit volume, called energy density; cell
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voltage; and internal impedance vary greatly.
Among all of the known combinations of lithium
anodes with different cathodes and electrolytes, those
believed to have among the highest energy density and lowest
internal impedance use certain inorganic liquids as the
active cathode depolarizer. This type of cell chemistry i5
commonly referred to as "liquid cathode".
Early liquid cathode cells used liquid sulfur
dioxide as the active cathode depolarizer as described in
U.S. Patent No. 3,567,515 issued to Maricle, et al. on March
2, 1971. Since sulfur dioxide is not a liquid at room
temperature and at atmospheric pressure, it proved to be
quite a difficult chemistry with which to work. More
importantly, sulfur dioxide cells are unsafe for most
i5 consumer applications due to their propensity to explode
under certain circumstances.
A major step forward in the development of liquid
cathode cells was the discovery of a class of inorganic
materials, generally called exyhalides, that are liquids at
room temperature and also perform the function of being the
active cathode depolarizer. Additionally~ these materials
may also be used as the electrolyte solvent. Liquid cathode
cells using oxyhalides are described in U.S. Patent No.
3,926,669 issued to Auborn on December 16, 1975, and in
British Patent No. 1,409,307 issued to Blomgren et al. on
October 18, 1975. At least one of the oxyhalides, thionyl
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chloride (SOC12), in addition to having the general charac-
teristics described above, also provides substantial addi-
tional energy density.
As described in the Auborn and Blomgren patents,
the anode is lithium metal or alloys of lithium and the
electrolyte solution is an ionically conductive solute
dissolved in a solvent that is also an active cathode
depolarizer.
The solute may be a simple or double salt which
will produce an ionically conductive solution when dissolved
in the solven~. Preferred solutes are complexes of inor-
ganic or organic Lewis acids and inorganic ionizable salts.
The requirements for utility are that the salt, whether
simple or complex, be compatible with the solvent being
employed and that it yield a solution which is ionically
conductive. According to the Lewis or electronic concept of
acids and bases, many substances which contain no active
hydrogen can act as acids or acceptors or electron doublets.
In the U.S. Patent No. 3,542,602 it is suggested that the
complex or double salt formed between a Lewis acid and an
ionizable salt yields an entity which is more stable than
either of the components alone.
Typical Lewis acids suitable for use in the -
present invention include aluminum chloride, antimony
pcn~ckl~ e, zirconium tetrachloride, phosphorous pent-
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chloride, boron fluoride, boron chloride and boron bromide.
Inoniæable salts useful in combination with the
Lewis acids include lithium fluoride, lithium chloride,
lithium bromidej lithium sulfide, sodium fluoride, sodium
chloride, sodium bromide, potassium fluoride, potassium
chloride and potassium bromide.
The double salts formed by a Lewis acid and an
inorganic ionizable salt may be used as such or the indivi-
dual components may be added to the solvent separately to
form the salt. One such double salt, for example, is that
formed by the combination of aluminum chloride and lithium
chloride to yield lithium aluminum tetrachloride.
In addition to an anode, active cathode depo-
larizer and ionically conductive electrolyte, these cells
require a current collector.
According to Blomgren, any compatible solid, which
is substantially electrically conductive and inert in the
cell, will be useful as a cathode collector since the
function of the collector is to permit external electrical
contact to be made with the active cathode material. It is
desirable to have as much surface contact as possible
between the liquid cathode and the current collector.
Therefore, a porous material is preférred since it will
provide a high surface area interface with the liquid
cathode material. The current collector may be metallic
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and may be present in any physical form such as metallic
film, screen or a pressed powder. Examples of some sui-tab:e
metal current collectors are provided in ~able II of the
Auborn Patent. The current collector may also be made
S partly or completely of carbon. Examples provided in the
Blomgren Patent use graphite.
Electrical separation of current collector and
anode is required to insure that cathode or anode reactions
do not occur unless electrical current flows through an
external circuit. Since the current collector is insoluble
in the electrolyte and the anode does not react spontan-
eously with the electrolyte, a mechanical separator may be
used. Materials useful for this function are described in
the Auborn Patent.
Although the varied cells described in the Blom-
gren and Auborn Patents may be feasib~e, much of the recent
interest is in cells using thionyl chloride as the active
cathode depolarizer and electrolyte solvent. This results
from thionyl chloride's apparent ability to provide greater
energy density and current delivery capability than other
o~yhalide systems. Yet even though thionyl chloride cells
have proven to be the best performer among the oxyhalides,
they have not lived up to expectations on energy density or
internal impedance. Furthermore, the thionyl cloride cell
is equally if not more dangerous than the sulfur dioxide
cell. As a result, all known efforts to co~mercialize cells
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using this chemistry have failed.
The present invention is based on the discovery that a substantially
safer lithium or calcium anode, thionyl chloride active cathode depolarizer
cell with the added benefits of higher energy density and lower internal
impedance can be made by adding copper to the cell.
Thus, it is an object of this invention to provide an improvement
to the known lithium/thionyl chloride cell that renders the cell safer.
It is another object to provide a lithium/thionyl chloride cell
having higher energy densities than those reported in the literature.
Finally, it is the object of this invention to provide a lithium/
thionyl chloride cell with low internal impedance.
These and other objects of the invention may be achieved by an
electrochemical cell comprising an anode made from either lithium or calcium;
a current collector spaced from said anode; an electrolyte solution disposed
between said current collector and anode; and an additive consisting primarily
of copper in intimate contact with said electrolyte. The electrolyte solution
includes an active cathode depolarizer which may be either phosphoryl chloride,
thionyl chloride, or sulfuryl chloride.
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As mentioned previously, the basis of this inven-
tion is the discovery that the addition of elemental copper
to the cell provides substantial improvements in both
performance and safety. While the theoretical explanation
of this phenomenon is not clear, and applicant does not
intend to be limited to any theory of invention, at least
one explanation of the results involves a reaction with the
copper and elemental s-ulfur. Some of the several different
reactions that could occur in the prior art cells ~there is
no conclusive evidence as to which reaction or reactions
actually occur) are as follows:
3 SOC12 + 8 Li Li2S03 * 6 LiCl + 2S (1)
4 SOC12 + 8 Li ~i2S2 4 2 2 (2)
4 SOC12 + 8 Li 4 ~iCl + SO2 + S (3)
These reactions all release the same amount of
electrical energy~ However, equation (1) requires less
thionyl chloride. Thus the energy density of this reaction
is higher. That is, more electrical energy can be derived
from a given volume of chemicals with the reaction of
equation (l) than with the reaction of e~uations (2~ or (3).
One possible explanation of the difference in
energy of the cell of this invention is that the copper
first acts as a catalyst to force the reaction to be a
higher energy density reaction such as the reaction of
equation (1), and second, combines with the elemental sulfur
to form copper sulfide.
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The significance of the copper sulfur reaction
relates to safety. It is widely believed that the elemental
sulfur in contact with lithium will explode above a certain
temperature and that this temperature may be easily reached
by short circuiting, reverse charging, or other electrical
conditions, as well as exposure to high ambient tempera-
tures. However, copper sulfide does not react explosively
with lithium at any temperature likely to be experienced by
batteries. Experimental evidence tends to support this in
that batteries made pursuant to this invention do not
explode under circumstances that would cause prior art
batteries to explode.
Test results showing the effect of varying per-
centages of copper on energy density and internal impedance
are provided in Table I. This data is given by way of ~-
examples to enable those persons skilled in the art to more
clearly understand and practice the invention. They are
intended to be illustrative and representati~e but not
limiting to the scope of the invention.
Each of the entries in Table I represents a test
cell having a nominal internal volume of .035 cu inches
constructed in a typ;cal button configuration with single
disc shaped current collector, anode and separator. The
electrolyte is a 1.5 molar solution of lithium aluminum
tetrachloride in thionyl chloride. The anode is a .680 inch
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diameter disc o .020 inch thick lithium. The separator is
a commercially available ceramic paper. The current col-
lector is acetylene black. Particulate copper is dispersed
in the acetylene black which is then compacted into a
pellet. The only variable in the cell is the ratio by
weight of carbon to copper.
TABLE I
Ratio ~ Life Load Current Internal
10 C:Cu Cu - mah voltage Impedance
1:1 50 110 3.29 54.8 5.16
2:1 33 170 3.30 55.0 5.56
3:1 25 180 3.29 54~8 5.65
1~ 4:1 20 200 3.28 54.6 5.86
6:1 14 210 3.28 54.6 5.86
8:1 11 205 3.24 54.0 6.6
10:1 9.1 195 3.24 54.0 6.6
12:1 7.7 195 3.22 53.6 7.0
16:1 5.9 195 3.22 53.6 7.~2
-- 0 190 3.15 52.5 8.57
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The foregoing results were taken from samples that
were tested shortly after their construction. The trends
generally indicated by the data in Table I are accentuated
as the batteries are stored at elevated temperatures.
It is understood that the preferred embodiment
described above does not limit the scope of the invention.
Certainly copper in either a more or less finely divided
state would be useful, and other battery geometrics such as
spiral wound may also be employed with the present inven-
tion.
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