Note: Descriptions are shown in the official language in which they were submitted.
1188360 M-3573
This invent~ OD relates to non-aqueous rechar~eable cells and more
particularly to such cells having lithium anodes and sulfur dioxide electro-
lyte solvents.
The rechargeabllity of non-aqueous cells has been generally
hampered by the presence within such cells of mater~als which ~eart either
upon ~tanding or during cell discharge and which are not capable of be~ng
completely regenerated from ~heir reaction products during cell charginK.
Organic electrolyte solvents utili~.ed in non-aqueous rell~ such as propylene
carbonate which ~or~s anode metal carbonates and propylene ga5 are the most
common of the :Lncompletely regenerable material~. Ho~everg such organic
electrolyte soLvents are generally indispensible for proper operation of the
non-aqueous cells particularly cells having sulfur dioxlde electrolyte
solvent/cathode depolarizers, since sulfur dioxide alone i6 a poor solvent
for electrolyte salt6 except for certain esoteric salts such as clovobora~es
and gallium halldes as descrlbed in ~.S. PatentR Nos. 4,020,240 and 4,177,329
respectively. More common salts such as metal halides; e.g., LiBr and
tetrachloroaluminat~ e.g., LiAlC14 are ei~her insoluble iD S02 alone or
form complexes therewith whereby cell performance is drastically deterior
ated. Utilization of the aforemeneloned esoteric 6alts ln order to provide
a totally inorganic cell has been e~fective in ~ncreasing the rechargeable
efficiency ~f 6uch cells. Ho~ever9 fiome of the e60teric salts, while
effective, are nevertheless exceedingly costly whereby construction of an
economical cell ~herewith has been generally precluded. Further~ore 7
durlng the increased cycle lif~ in such cells a second cource o~ deteriora-
tion of the eells was discover2d. In cells containing the inorganic sulfur
dio~ide electrolyte and lnert carbon cathodes said cathode6 tended to lose
their structural inte~rity. The formAtion and depletion of cell react~on
products with~n the cathode causes detrimental expansion and contraction of
the carbon cathode which expansion and contraction could not be accommodated
without structural damage to the cathode.
-2-
1~88360 M-3573
It i8 an object of the pre6ent lnventiDD tc prcvlde an improved
toeally inor~anic non-aqueous cell which is readily and efficiently recharge-
able.
It iR a further object of the present invention to provide such
cell with readily obtainable and economical comp~nents.
These and other ob~ects, features and advan~a~es ~f the pre~ent
lnvention will be more readily apparent fr~m the followlng discussion and
the drawings in which:
Flgure 1 is a discharge-charge graph of cells made in a~cordance
with the present invention and
Figure 2 is a discharge~charge graph of another embodiment of a
cell made in accordance with the present invention.
Generally, the present invention comprl~es ~n efficiently recharge-
able totally in~rganic non-aqueous cell consaining an anode of an alkali or
alkaline earth metal preferably lithium, including alloys and mixtures, a
totally inorganic electrolyte comprified of sulfur dioxide with an electro-
lyte salt soluble therein dissolved therein, and an insolu~le (in said
sulfur dioxide) metal h~lide cathode which dischar~es during cell operation
in preference to the S02. Metal salts such as FeC13 whlch are coluble in
S02 are accordingly generally not with$n the purview ~f the present lnven-
tion. In order to prevent such S02 discharge snd for greater cell capacity
it ls preferred that the metal halide provides a potential greater than that
obtainable from the S02 as a cathode depolarl~er. Howeve~, even with metal
halides of lower potential the S02 electrolyte solvent is substantially
prevented from being discharged in preference to the meta~ halide because
the insoluble metal halide cathode does not provide a catalytic surface for
the discharge of the S02 as compared to inert carbon cathodes.
In a preferred embodiment of the present invent~on the cell is
comprised of a li~hium anode ~nd a coppe~ chloride ~CuC12) cathode. It has
been discovered that the previously unsuitable but economical salts such as
. LiAlC14 (which ~hlle soluble in the S02 de~rimentally complexed therewith)
1188360 M-3573
co~ld be effectively utlllzed in the cells Df the present invention. This
utility is believed to be attributable ts the fact that S02 in the cell is
not discharged and that its complexing with the salt does nDt a~ a result
affect cell capacity or performance. It is therefore preferred from an
economic standpoint, to utilize tetrachloroaluminate ~alts such as LiAlC14
as the electrolyte salt. This does not however preclude the util~zation of
other salts such aB LiGaC14, Li2BloCllo and the like as electrolyte salts
provided that they are soluble in the S02 without the necessity for organic
cosolvents. Preferably such 6alts are anode ~etal salts.
Though metal halides such as copper chloride have been utilized as
cathodes in non-aqueous cells, such cells have invariably contained organic
solvents in which the halides ~uch as copper chlorlde were at least partial-
ly soluble. As a result such cells were con6idered to be unsatisfactory
because of the inherent problem of self discharge caused by the solvated
metal halide. However9 the ~ery deficiency of S02, ehat lt is a poor sol-
vent without or~anic cosolvents, renders the present invention operable
since the metal halides such as copper chloride are substan~ially totally
insoluble in S02 alone.
~he metal halide cathode is preferably made from a compressed
~o mixture of the metal halide~ conductive materials such as graphite or carbon
and a binder such as polytetrafluoroethylene. The preferred percentage of ~he
metal halide is between 60% to 80% by wei~ht with ~he remainder being the
conductive material ~about 30 to 10%) and binder ~about 10%). The higher
the intended rate the greater the amount of conductive materials.
In order to more clearly illustrate the efficacy of the present
invention, the ~ollowing examples are presented. It is understood that such
examples are for illustrati~e purposes only and that spec~fics contained
therein are not to be construed as limitations on the present invention.
Unless otherwise indicated all parts and percenta~es are by wei~ht.
M-3573
EXAMPLE_l
Flat cells ~ere made with each having two an~de layers of lith$um
foil (1 x 1.6 x 0.020" or 2.54 x 4.06 x O.Q5 cm) pressed onto a copper foil
(0.020" or 0.05 cm), ab~ut 25 grams of 0.5 M L-lGaCl~-SO2 electrolyte, and
four grams of a compressed (20,000 psi or 1406 Kg/cm ) mi~ture of 60~ CuCl2,
30% graphite and 10% polytetrafluoroethylene ~PTFE) on an expanded nickel
grid as the cathode (l x 1.6 x 0.065" Dr 2.54 x 4.06 x 0.16 cm). The anode
layers and cathode were individually heat sealed inside sheets Df micrD-
porous polypropylene and the anode layerc placed one ~n each 6ide of the
cathode. Two cells were each dlscharged at a ra~e of 2~A/cm2 or 40 ~A and
thereafter charged in a cycling regimen with a 2 volt cutoff for charging.
The theoretical capacity of the cells was 480mAhrs (limiting cathode capa-
city. Anode capacity was about 1800 mAhrs.). Figure 1 depicts the cycling
efficiency of the cell~ wlth one cell ~hown by the solid line after the 4th
cycle and the broken line indicating the ;~econd cell after the 70th cycle ~a
~h~rt circuit in the first cell prematurely ended itB cycling life after
about 60 cycles).~ The 6econd cell was cycled lOl times but wl~h di~ini~hed
capacity snd delivered about 67 times the CuC12 capacity on voltage cycling
and lô anode turnovers. The average discharge voltage i6 rel~tively high at
about 3.3 volts as compared to the discharge voltage of S02 of abDut 2.9
v~lts.
E~AMPLE 2
=
A cell was made as in Example 1 but with a 1 M LlAlC14-S02 elec-
troly~e and a 2 gram cathode. The cell was discharged at the same rate of
2ma/cm2 and charged at lma/cm2 with discharge-charge cycling being on a
timed basis of 4.9 hr. discharge and 9.~ hr. charge. The cell underwent 23
cycles and Figure 2 depicts the curves for the first cycle (solid line) and
twenty-first cycle (broken line~ with the cell actually lmproving over
contlnued cycling~
--5--
118836~ M-3573
It is u~derstood that ~he above examples are for illustrative
purposes only ~nd that changes m~y be made in cell constructiQn and compo-
nents without departing from ~he scope of the present invention as defined
in the following claims.
