ELECTROCHEMICAL CELL AND ELECTROLYTIC SOLUTION THEREFOR

PILE ELECTROCHIMIQUE ET SOLUTION ELECTROCHIMIQUE CONNEXE

English Abstract

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ABSTRACT OF THE DISCLOSURE
An electrochemical cell having an oxidizable anode
containing lithium and a cathode current collector. The
cell includes an electrolytic solution in contact with
the anode and the cathode current collector. The solu-
tion includes a solvent which is also a reducible liquid
cathode material, specifically SOCl2, and an electrolyte
solute consisting of the reaction products of a salt of
an oxyacid, specifically Li2SO3, constituting a Lewis
base and a Lewis acid, specifically AlCl3, dissolved in
the solvent.

Claims

22020
THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. An electrochemical cell comprising
an oxidizable anode material;
a reducible cathode material; and
an electrolyte solute in an electrolytic solution,
the solute consisting of the reaction products
of a salt of an oxyacid constituting a Lewis
base and a Lewis acid dissolved in the solvent
of the electrolytic solution.
2. An electrochemical cell in accordance with Claim 1
wherein
the salt of an oxyacid constituting a Lewis base
has a cation selected from the group consisting of
alkali metals, alkaline earth metals, ammonium,
alkyl ammonium, pyridinium, alkyl pyridinium,
scandium, yttrium, and the rare earths, and has an
oxygen containing anion selected from the group
consisting of orthoborates, metaborates, aluminates,
<IMG> , polythionates, thiosulfates,
molybdates, phosphomolybdates, tungstates, C1O3-,
ClO4-, BrO3-, BrO4, lO3-, and IO4-; and
the Lewis acid is selected from the group consisting of
AlCl3, AlBr3, AlI3, BCl3, BF3, BBr3, BI3, PF5, AsF5, SbF5,
SbCl5, SnCl4, TiCl4, ZrCl4, GaCl3, GaF3, GaBr3,
GaI3, InCl3, InF3, InBr3, InI3, TlCl3, TlF3, SiF4, and
GeCl4.
3. An electrochemical cell comprising
an oxidizable anode material;
a cathode current collector; and

-22020
an electrolytic solution, in contact with the anode
material and the cathode current collector,
comprising a reducible liquid cathode material
and an electrolyte solute consisting of the
reaction products of a salt of an oxyacid
constituting a Lewis base and a Lewis acid
dissolved in the liquid cathode material.
4. An electrochemical cell in accordance with Claim 3
wherein
the salt of an oxyacid constituting a Lewis base
has a cation selected from the group consist-
ing of alkali metals, alkaline earth metals,
ammonium, alkyl ammonium, pyridinium, alkyl
pyridinium, scandium, yttrium, and the rare
earths, and has an oxygen containing anion
selected from the group consisting of orthobo-
rates, metaborates, aluminates, <IMG>
polythionates, thio-
sulfates, molybdates, phosphomolybdates,
tungstates, CIO3-, ClO4-, BrO3-, BrO4-, IO3-,
and IO4-; and
the Lewis acid is selected from the group consisting
of AlCl3, AlBr3, AlI3, BCl3, BF3, BBr3, BI3,
PF5, AsF5, SbF5, SbCl5, SnCl4, TiCl4, ZrCl4,
GaCl3, GaF3, GaBr3, GaI3, InCl3, InF3, InBr3,
InI3, TlCl3, TlF3, SiF4, and GeCl4.
5. An electrochemical cell in accordance with Claim 4
wherein
the reducible liquid cathode material is selected
from the group consisting of fluid oxyhalides,

D-22020CN
11384/W/S
fluid non-metallic oxides, fluid non-metallic
halides, and mixtures thereof; and
the oxidizable anode material is selected from the
group consisting of alkali metals, alkaline earth
metals, scandium, yttrium, and rare earths.
6. An electrochemical cell in accordance with claim 5
wherein
the reducible liquid cathode material is selected
from the group consisting of oxyhalides of sulfur,
phosphorus and selenium;
the salt of any oxyacid constituting a Lewis base is
lithium sulfite;
the Lewis acid is aluminum chloride; and
the oxidizable anode material is lithium metal.
7. An electrochemical cell in accordance with claim 6
wherein
the reducible liquid cathode material is thionyl
chloride.
8. An electrolytic solution including in combination
a liquid electrochemically reducible solvent selected
from the group consisting of fluid oxyhalides,
fluid non-metallic oxides, fluid non-metallic
halides, and mixtures thereof; and
an electrolyte solute consisting of the reaction
products of a salt of an oxyacid constituting a
Lewis base and a Lewis acid dissolved in the
solvent.

D-22020CN
11384/W/S
9. An electrolytic solution in accordance with claim 8
wherein
the salt of an oxyacid constituting a Lewis base has
a cation selected from the group consisting of
alkali metals, alkaline earth metals, ammonium,
alkyl ammonium, pyridinium, alkyl pyridinium,
scandium, yttrium, and the rare earths, and has an
oxygen containing anion selected from the group
consisting of orthoborates, metaborates,
aluminates, <IMG>,
polythionates, thiosulfates, molybdates, phospho-
molybdates, tungstates, ClO3-, ClO4-, BrO3-,
BrO4-, IO3-, and IO4-; and
the Lewis acid is selected from the group consisting
of AlCl3, AlBr3, AlI3, BCl3, BF3, BBr3, BI3, PF5,
AsF5, SbF5, SbCl5, SnCl4, TiCl4, ZrCl4, GaCl3,
GaF3, GaBr3, GaI3, InCl3, InF3, InBr3, InI3,
TlCl3, TlF3, SiF4, and GeCl4.
10. An electrolytic solution in accordance with claim 9
wherein
the liquid electrochemically reducible solvent is
selected from the group consisting of fluid
oxyhalides, fluid non-metallic oxides, fluid
non-metallic halides, and mixtures thereof.
11

D-22020CN
11384/W/S
11. An electrolytic solution in accordance with claim 10
wherein
the liquid electrochemically reducible solvent is
selected from the group consisting of oxyhalides
of sulfur, phosphorus, and selenium;
the salt of an oxyacid constituting a Lewis base is
lithium sulfite; and
the Lewis acid is aluminum chloride.
12. An electrolytic solution in accordance with claim 11
wherein
the liquid electrochemically reducible solvent is
thionyl chloride.
12

Description

1:~6~3~3
`-220~:0 ~1--
ELEC'.l.'ROC~lEMIC~I. CELL AND ELECT OLYTIC SOLUT OP THEREPOR
This invention relates to electrochemical cells.
More particularly, it is concerned with elec~rochemical
cells employing non-aqueous electrslytic solutions and
to electrolytic solutions cherefor.
A particularly effectiJe clas~ of elec~rochemica]
cells which employs soluble or liqui~ cathcde materials
has undergone rapid development in recent years~ In
these cells the active cathode material is usually a
fluid solvent for an electrolyte solute which provi~es
conductivity. The active anocle for these cells ;~.~
usual:Ly lithium or other hiyhly electropositi.-~e me-tal.
During discharge the sol~ent is electrochemicall~7 re~
duced on a cathode current collector to yi.elcl ions, e~g.,
halide i.ons, which react wit~ positive metal ions from
the. anode to form insoluble metal salts, e.g., metal
halides.
One particular type of elect.rochemical cell of the
foregoing class which contains a lithium anode emplo~s
a reducible liquid cathode of thion~l chloride. Typi-
cally the electrolyte solute dissolvea n the thionyl
chloride solvent is lithium tetrachloroaluminate. This
salt is prepared from the Lewis acia alum.num chloride
and the Lewis base lithium chloride. A Le~Jis acid is
any compound capable of entering into a chemical reac~
tion by acceptinct an eletron pair to ~orm a covalent
bon~, and a Lewi.~ base i~ any compound capable of
entering i.nto a chemical reaction by ~onati.n~ arl

5 $3 ~ ~
.-22020 ~2-
electron pair to form a covalent bond. Lithium/thionyl
chloride elect~-ochemical cells have proven to have
outstanding weight and volume energy density, long shelf
lire, and unusually high power density when comparcd
with other cells presently available.
Under unfavorable circumstances during prolonged
stora~e or ~torage under extreme conditions, corrosion
of the lithium anode in a cell causes a film of lithium
chloride to grow on the anode sufficient to cause signl-
Eicant polarization at the onse-t of discharge of the
cell~ After operating at a reduced potential for a
period of time, a cell may recover depending upon the
~severity of the condition. This initial polarization is
~ef~rred to as voltage delay and has been found particu-
larl~ troublesome in cells which are required to operate
at current densities higher than 1 mA/cm .
Various attempts have been made to overcome the
problem of vol.tage delay upon startup. In one techni~ue
desc.ci.bed in U.S. Patent No. 4,020,240 to Carl R.
Schlai~jer dated April 26, 1977, a lithium clovoborate
salt such as Li2 BloCllo is enmployed as the electrolyte
solute. In another l:echnique described by J. P~ Gabano
in pa~er -,~27, presented at the Electrochemical Societ~ -
~all ~ee-ki.ng, .ittsburgh, October 15-20, 1978, the
electrolyte solute is a salt prepared by dissolving
li.thium oxide in thionyl chloride containing aluminum
chloride~ It is postulated that the salt produced by
the reaction is Li2 (AlC130 AlC13). Although the
solutes of SchlaiXjer and ~abano provide cells having
i.rnproved startup characteristics, either they are ex-
pensive, diEficu3.t to puri:Ey or l.ess conduct1ve than

-220~0 ~-
presently used materials.
Accordingly, the present invention provides an
electrochemical cell eomprising an oxidizable
anode material; a reducible cathode material; and
an eleetrolyte solute in an electrolytic solution,
the solute consisting of the reaction products of a
salt of an oxyacid constituting a Lewis base and a
Lewis acid dissolved in the solvent of ~he electrolytic
solution.
Some e~odiments of the invention will now be
described, by way of example, w.ith reference to the
accompanying drawings in which:5 FIG. 1 is a graph illustrating the conductivity of an
electroly~ic solution in accordance with the
presen-t inven-tion in comparison with other
solutions;
FIG. 2 is an elevational view partially in cross
2~ section of an electrochemical cell in aecGrdance
with the present invention;
FIG. 3 is a graph illustrating the startup charac-ter-
istics of electrochemical cells of previously
known type; and5 FIG. 4 i.s a graph illustrating the startup character-
istics o~ eleetrochemical cells in accordance
with the present invention.
For a better understanding of the present invention,
together.with other and further objects, advantages, and

,~ ~ 1 6
22020 -~-
capabilities thereof, reference is made to the following
discussion and appended claims in connection with the
above described drawings.
The present invention relates to non-aqueous elec-
trolytic solutions containing an electrolyte salt pro-
duced by the react~on of a salt of an oxyacid which
cons'itutes a L,ew;s base with a Lewis acid. 5alts of
oxyac~ds which may be em~loyed in electroly-tic solutions
of the invention pro~ide a cation of an alkali metal,
alkaline earth matal, ammonium, alkyl ammonium, pyridini-
um, alkyl pvridinium, scandium, yttrium, or a rare earth.
Suitable oxyacid salts provide an anion such as orthob~-
xa5:e, metaborate, aluminate, C03 , SiO3 , GeO
~n3 ~ N03 , P03 , P04 , AsO3 , As04 , S03 , SO~ ,
SeO4 , TeO4 , TeO4 , S204 ~ S26 ~ P
thiosulfate, molybdate, phosphomalybdate, tungstate,
_
C103 , C104 , BrO3 , BrO4 , I03 , and I04 Th~ oxyacid
sa~t is reacted wi.th a Lewis acid such as AlC13, AlBr3,
AlI3~ BC13~ BF~ BBr3~ BI3~ PF5~ AsF5~ ~bF5~ SbC15,
SnC14~ TiC14~ ZrC14~ Ga~l3~ GaF3~ GaBr3~ GaI3, InC~3,
In~3~ IrlBr3, InI3~ TlC13, TlE'39 SiF4~ ana GeC14-
The solute is produced by the reac-tion obtained by
dissolving the salt of an oxyacid and a Lewis acid in a
solvent. The solvent may be an electrochemically redu-
cible liquid such as an oxyhalide of sulfur, phosphorus,
or selenium. It may also be a fluid non-metallic oxide,
or a fluid non-me~allic halide, or mixtures thereo-f~
Qther classes of solvellt which may be utilized include
30 aliphatic ether~;, alicylic ethers, este.rs, cyclic es~ers,
j
'. ` ~
,

? ~ f3 1~
-22020 ~5-
cyclic lactone.q, anhydrides, nitriles, amides, and
ureas~
Electrochemical cells utilizing electrolytic solu~
tions in accordance with th~ present invention May also
employ oxidizable anode materials other than lithl-lm.
The anode material may be another alkali metal, an alka-
line earth metal, scandium, yttrium, or a rare earth.
.More specifically, an electrolytic solu~ion parti-
cularly useful in electrochemical cells employiny ].ithium
and thionyl. chloride was obtained by reacting aluminum
chloride (AlC13), a Lewis acid, with lithi.um sul~ite
(Li2503), which constitutes a Lewis base. A 1 M solution
of AlC13 in SOC12 was stirred while bei.ng hea-ted under
reflux with enough solid Li2S03 -..o provide a stoich.o-
metxic ratio of AlC13 to Li2S03 of 2 to 1.1. The con-
ductivity of the solution was tested at various tempera-
tures and the curve of conductivity versus temperature
i9 plotted in FIG~ 1. Curves illustrating the conducti-
vity of a l.OM soluti.on of LiAlC14 in SOC12, a 0.5 ~
solution of Li.~BloCllo in SOCl2, and a 4 M solution of
AlC13 in SOCl~ are also shown in FIG. 1. Also shown
i~ a curve illll.strating the.conductivity of a 0.5 M Li2
~.~].C130AlCl3) solution in ~OCl~. It is postulaked that
this is the salt produced by dissolving Li20 in SOCl2
~5 containing AlCl3 in accordance with the teaching3 in the
aforementioned al~ticle by Gabano. As can be seen from
the curves of FIG. ~ the conductivity of applicants'
solution cornpares favorably with that of lithium
tetrachloroaluminate and is significantly highe~ tharl
that of solutiGns contai.nillg Lithium clo~oborate ~n~ the
sal.ts prepared in accordance with the technique of:
Gabano.

i 1 6~8 ~. 3
~-22020 -6-
The properties of the electrolytic so:lution of -the
present inventlon indicate that a soluble lithium salt
is a product of the reaction of the Li2SO3 and AlC13 in
SOC12~ It may be that the Li2So3~ actiny as a Lewis
base, forms an adduct salt wi-th the AlC13, a Lewis acid.
Several electrochemical cells as illustrated in FIG.
2 were constructed. Some were filled with an electrolytic
solution containing lithium tetrachloroaluminate as a
solute and some were filled with an electroly~ic solution
in accordance with the present invention. The cells were
about the size of commercial AA cells, approximately
1-7/8 inches long and 1/2 inch in diameter. The cases 10
were of stainless steel. Anodes 11 of lithium metal were
pressed to the inside walls of the cases 10. Concentric
bobbin cathodes 13 of Shawinigan (trade mark) carbon black
and Teflon (trade mark) formed as an aqueous dispersion
and dried were placed in the cases encircled by separators
12 of insulating material. After being filled with an
electrolytic solution, each case was sealed with a ~over
15 having a conductive lead 16 to the cathode 13 through
a glass-to~metal seal 17,
Some of the cells were filled with a 1.8 M solution
of LiAlC14 in SOC12. Other cells were illed with an
electrolytic solution in accordance with the present
2S invention. The solution was prepared by refluxing a
solution of AlC13 in SOC12 with excess Li2SO3 for sixteen
days. The mixture was then filtered and diluted such
that the concentration of aluminum was reduced to about
3 M. For both electrolytic solutions the SOC12 solvent
was the reducible liquid cathode material of the cells.
Three cells containing LiAlC14 as a solute and three
cells with Li2SO3 and LiC13 were stored for four days at
.~, .
- . . . , ~ . . . . .. .. .
.

~ ~ 3 ~; 5 ~
22020 -7~
72 C, The startup charactsristi.cs o~ these cells at
room temperature under a load of $0 ohms and current
densities at about 408 mA/crn were recorded. The result-
ing curves of output voltage versus time for the cells
employing LiAlC14 in SOC12 are shown in FIG~ 3. Output
voltage ve.rsus time for the three cells containing the
reaction products of Li2S03 and LiC13 in SOC12 are shown
in FIG. 4. As indicated by FIGS. 3 and 4 electrochemical
cells employing an electrolvtic solution in accordance
with the present invention operate at full operating
- potential immediately upon startup withou~ the voltage
delay problem encountered with previously known de~ices.
While there has been shown and described what are
considered preferred embodiments of the present inven.tion,
it will be obvious to those skilled in the art that va~i-
ous changes and modifications may be made therein withoutdeparting from the invention as de-ined by the appende~ ..
claims. .
' . ~ , '
.. ' ' '
'~ .