Note: Descriptions are shown in the official language in which they were submitted.
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This invention relates to primary and secondary non-aqueous fluid
cathode depolarized cells particularly cells containing sulfur dioxide
(S02) fluid cathode depolarizers.
Fluid cathode depolarized cells have generally contained inert carbon-
aceous cathode or porous metals upon which the fluid cathode depolarizers
are reduced during cell discharge. The porous metals were however somewhat
unsatisfactory particularly at high rates because of their relatively low
porosity when compared to the carbonaceous materials such as acetylene
black and were therefore less preferred. The carbonaceous materials, while
O satisfactory for primary cell application however suffered from degradation
in secondary cells in which they were repeatedly expanded and contracted
during the cell discharging and charging cycles respectively.
It is an object of the present invention to provide a fluld cathode
depolarized cell with a catalytic cathode which is both highly porous and
resistant to physical degradation.
It is a further object of the present invention to provide an effic-
iently rechargeable S02 containing cell having such catalytic cathode.
These and other objects, features and advantages of the present inven-
O tion will become more evident from the following discussion.
Generally the present invention comprises a non-aqueous fluid cathode
depolarized cell with a catalytic cathode comprised of one or more graphite
intercalated metal halides such as CuC12, CoC12, FeC13 and SbF5. Though
graphite has generally been regarded as an unsuitable material for use as a
cathode in fluid depolarized cells because of its tight lamellar structure,
the graphite intercalated metal halides of the present invention have been
found to be excellent porous cathode for fluid cathode depolarizer reduction
in primary cell applications. Furthermore, cathodes made of the graphite
intercalated metal halides of the present invention have been found to have
a high degree of resiliency even under repeated expansion and contraction
- during cycling in secondary cells. Thus the physical integrity of graphite
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intercalatedmetal halide cathodes is not seriously affected as compared to
prior art carbonaceous cathodes generally used in rechargeable fluid cathode
depolarized cells.
Some of the graphite intercalated~etal halides utilized in the cells
of the present invention are, for example, commercially available under the
Graphimet trademark (Alfa Division of Ventron Corp., Danvers, Mass.) and
are generally 10 - 50% metal halide by weight. As opposed to simple mix-
tures, the graphite intercalated metal halides are formed by reaction
between the graphite and the metal halide whereby the lamellar structure of
the graphite is opened to allow selective diffusion of molecules of proper
spatial geometry therein. In the past, such graphite intercalated metal
halides have been utilized as the actual active cathode materials of cells
(U.S. patent no. 4.041,220 issued to Michel B. Armand). However, because
of the very limited amount of reducible metal halide (50% or less) with
such materials the capacity of such cells was very low. In contrast there-
to the graphite intercalated metal halide cathode in the cell of the
present invention i6 substantially inactive and serves as the catalytic
site for the reduction of the high energy density fluid cathode depolari-
zer.
The fluid cathode depolarizers utilized in the cell of the present
invention include sulfur dioxide (SO2) which is utilizable in both primary
and secondary cells. In secondary or rechargeable cells the sulfur dioxide
is the sole electrolyte solvent since the further inclusion of organic
cosolvents, as used in primary cells, reduces the cycling efficiencies with
the production of generally irreversible reaction products. Thus, in the
totally inorganic SO2 containing rechargeable cells only electrolytes such
as gallium halide salts such as LiGaC14 or clovoborate salts such as
Li2B oCllo may be effectively utilized because of their solubility in SO2
alone with concomitant current carrying capability.
Other fluid cathode depolarizers include thionyl chloride which is
preferred in primary cell applications because of its high energy density
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and low vapor pressure. Other fluid cathode depolarizers generally util-
izable in primary cell applications include f]uid oxyhalides3 non-metallic
oxides and non-metallic halides and mixtures thereof such as phosphorous
oxychloride (POCl3), selenium oxychloride (SeOC12), sulfur trioxide (S03)
vanadium oxytrichloride (VOC13), chromyl chloride (CrO2Cl2), sulfuric oxy-
chloride (S02C12), nitryl chloride (NOC12), nitrogen dioxide (N02), sulfur
monochloride (S2C12) and sulfur monobromide (S2Br2). Each of the above can
be used together with thionyl chloride (SOC12) or sulfur dioxide (S02) as
fluid depolarizer/electrolyte solvent or separately.
The sulfur dioxide cathode depolarizer may be admixed with organic
solvents such as acetonitrile, propylene carbonate and the llke to enhance
solvation of salts in primary cell application. In such applications the
more common electrolyte salts such as LiBr and the like may be utilized.
It may be noted that metal halides such as FeCl3 are soluble in SO
and metal halides such as CuC12 are soluble in organic solvents. However,
with the intercalation of such metal halides with graphite they may be
effectively utilized in cells containing sulfur dioxide alone or sulfur
dioxide admixed with organic cosolvents.
The anode materials utilizable in the cells of the present inven-
tion are active metals (i.e., above hydrogen in the EMF series) and include
the alkali metals such as lithium (Li), sodium (Na) and potassium (K); the
alkaline earth metals such as calcium (Ca) and magnesium (Mg), and aluminum
(Al) and alloys of such metals particularly in the secondary cells of the
present invention.
In constructing the cathodes of the present invention the graphite
intercalated metal halides are generally admixed with small amounts,
typically about 10%, of a binder such as polytetrafluoroethylene (PTFE) and
then pasted onto a metal grid, such as of nickel, for support and as the
cathode current collector.
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In order to more fully illustrate the efficacy of the present inven-
tion the following examples are presented. It is understood however that
such examples are for illustrative purposes only and that specifics con-
tained therein are not to be oonstrued as limitations on the present
invention. Unless otherwise indicated all parts are parts by weight.
EXAMPLE 1 (PRIOR ART)
A cell was made with a carbon cathode weighing 2.6 gms (90% Shawinigan
black, 10% PTFE) pr~ssed in a 1.0" x 1.07" (2.5 x 2.7 cm) mold at 10,000
lb. on a ~li expanded metal grid to a thickness of 0.06". A nickel tab was
attached thereto and the cathode was placed in a microporous polypropylene
bag between two lithium-on-copper substrate layers within a prismatic cell.
The lithium capacity was 1.31 Ahr. The cell was then filled with lM
LiGaCl4 in S02 and placed on discharge at 6.6 mA (0.5 mA/cm ) and cycled
between 2 and 3.8 volts. After about 20 cycles the cell failed because of
cathod~ degradation and provlded a total of about 4 Ahrs.
EXAMPLE 2 (MODIFIED PRIOR ART)
A cell was made as in Example 1 but with the electrodes having the
dimensions 1.07" x 1.76" (2.7 x 4.5 cm) and the cathode being made oi
graphite (Vulcan 72X, trademark of Cabot Corporation) and 10% PTFE. Though
having a larger cathode, the cell failed almost immediately with a capacity
oI only about 6 mAhrs.
EXAMPLE 3
A cell was made as in Example 1 but with a cathode comprised of
graphite intercalated CoC12 (90% C and 10% CoC12) with lO~o PTFE binder.
The cell was placed on discharge at 6.6 mA (0.5 mA/cm ) and cycled between
2 and 3.~ volts. After the eighth cycle the discharge rate was increased
to l3.3 mA (1.0 mA/cm ). The cell was cvcled 196 times with a total
capacity of 15,6 Ahrs until the cell failed because of anode exhaustion.
**~Shawinigan Black is a trade maxk of Shawinigan
Pr6ducts Corporation]
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EXA~LE 4
A cell was made as in Example l but with a cathode comprlsed of
graphite intercalated CuCl2 (90% C, 10~, CuCl2) with 10% PTFE binder. The
cell was placed on discharge at 6.6 mA (0.5 mA/cm ) and cycled between 2.5
and 3.6 volts. After the third cycle the discharge rate was increased to
13.3 mA (1.0 mA/cm ). The cell was cycled 128 times with a total capacity
of about 6.9 Ahrs when the cell failed because of a short circuit.
EXA~PLE 5
A cell was made as in Example 1 but with a cathode comprised of
graphite intercalated FeC13 (85% C, 15% FeC13) with 10% PTFE binder. The
cell was placed on discharge at 6.6 mA (0.5 mA/cm ) and cycled between 2
and 3.6 volts. The cell failed after 8 cycles because of a short circuit
but delivered 3.4 Ahr.
EXAMPLE 6
A cell was made as in Example l but with a cathode comprised of
graphite intercalated SbF5 (50% C, 50% SbF5) with 10% PTFE binder. The
cell was placed on discharge at 6.6 mA (0.5 mA/cm ) and cycled between 2
and 3.6 volts. After 51 cycles and a cumulative capacity of 4.2 Ahr the
cell cycling was stopped because of capacity loss.
The cells in Examples 3-6 all exhiblted discharge voltages attri-
butable to S02 acting as the cathode depolarizer (i.e. about 2.8 volts).
Additionally the cells exhibited primary capacities during cycling well in
excess of the theoretlcal metal halide capacities indicating that catalytic
reduction of the S02 comprised the electrochemlcal reaction at the cathode.
It is understood that the above examples are illustrative in nature
with the changes in cell structure, components and relative component
ratios being possible without departing from the scope of the present
invenion as defined in the following claims.
