Note: Descriptions are shown in the official language in which they were submitted.
1~ 3~
.
The present invention relates to electrochemical cells,
more particularly to primary electrochemical cells having an
oxidizable active anode material, an inert ca~hode current
collector, and an electrolyte solution comprising ~ solu~le
cathode and an electrolyte sa~t.
Primary electrochemical cells are a class of vol~aic
cells. Voltaic cells are those electrochemical cells in which
chemical changes produce electrical energy, in aistinction' to
electrolysis cells in which electrical energy ~rom an outside
source produces chemical changes within the cell. Primary cells
are those voltaic cells which cannot be conveniently recharged,
which usually are aiscarded after a single exhaustion of the;r
component elements, or which require replacement of their
exhausted chemical constituents to bring them back to t~eir
original condition. These cells are distinguishe~ from ano~her
class of voltaic cells, namely, secondary cells, in which the
exhausted cell may be recharged by passing electrical current
~rom an outside source through it in the reverse direction to
the discharge current.
In a primary cell, chemical energy is convertea to
electrical energy with a reduction in the free energy o~ the
system. ~n the course o~ the cell,reaction,,negative char~e
lea~es the anode and enters the catho~e through a ariven
external circuit. Thus, the catho~e, where reauction is
occurring, is the positive electro~e alld the anode, where
`-~ ' ` C 113~4 C
oxida~tion is occurring, is the negative electrode. By virtue
of the established electromotive series, it is possible to select
suitable cathodes and anodes to obtain a theoretically high
potential It would be desirable if the cell could be designed
such that the theoretical potential could be obtained under load
and the loss in free energy would manifest itself entirely ~as
electrical energy outside the cell. However, this ideal is
never attained in practice because the internal resistance of a
cell is not zero and the reactions within the cell are never
completely reversible. Moreover, problems of incompatibility
of the cathode and anode with each other or with the electrolyte,
polarization, and other well ~nown prablems prevent performance
at theoretical values. There is a present neea for batteries
which have high initial electromotive force, greatly exten~ea
storage and operating life, improved total current output,
reduced power to weight ratios, and improved constancy of
~oltage with time of storage ana discharge.
A number of promising electrochemical cells have
undergone development in recent years. ~mong these is a class
of cells, usable in hearing aids and other medically-related
aevices, wh~ch employ soluble or liquia cathodes as opposed to
the more conventional solid cathode cells. In such solu~le
cathode cells, the active catho~e material is usually a solvent,
or one of a number of cosolvents, for the electrolyte salts
During discharge, the solvent or cosolvents are electrochemically
reduced on an inert cathode current collector which typically
comprises a screen having pressed thereon a mixture of an inert
conductive material such as carbon black, ~raphite, or the like.
~13~
The anode for these cells is usually lithium metal although
other active metals such as sodium, potassium, rubidium,
calcium, magnesium, strontium, barium and cesium may be used
either singly or in combination.
In U.S. Patent 3,567,515, issued March 2, 1971, Maricle
and Mohns describe a cell of this general type. They disclose
an electrochemical cell comprising an anode of a metal capable
of reducing sulfur dioxide, a cathode current collector of a
material substantially inert to sulfur dioxide but on which
sulfur dioxide is reducible and an electrolyte salt substan-
tially inert to sulfur dioxide and to the anode metal, wherein
the anode and cathode current collector are immersed in the
sulfur dioxide solution. The sulfur dioxide solution is used
as the soluble cathode or material which undergoes electro-
chemical reduction.
In U.S. Patent 3,578,500, issued May 11, 1971, Maricle
and Hoffman disclose a variation of the above cell which uses
certain compounds as soluble cathodes together with sulfur
dioxide. The disclosed solvents are, in general, liquid
organic and inorganic compounds which have electron rich
centers, i.e., contain one or more atoms having at least one
unshared pair of electrons, and which lack acidic hydrogen
atoms. A large number of compounds are listed as possible
cosolvents with sulfur dioxide, among these is sulfuryl
chloride. The disclosed cells typically have open circuit
potentials of four volts or less. Example XVII shows a cell
employing a lithium anode, a nickel plaque cathode and an
electrolyte comprising one molar LiC104 in propylene carbonate
and sulfur dioxide together with sulfuryl chloride. The cell
gave an open circuit potential of 3.5V.
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.,
113~
In U.S. Patent 3,926,669, issued December 16, 1975, to
Auborn, there is disclosed another electrochemical cell of this
~eneral class which employs a covalent inorganic oxyhalide or
thiohalide as the soluble cathode and solvent for the electro-
lyte solution. Sulfuryl chloride is disclosed as a suitable
soluble cathode either alone or in admixture with other materials.
The examples show a variety of cells employing lithium anodes
and different cathode materials, which exhibit open circuit
potentials of from 2.05 to 3.74V. It is stated at column 5,
lines 40 to 59, that the disclosed electrochemical cells
specifically exclude sulfur dioxide and other oxidants as
cathode materials or as solvent or cosolvent materials, because
there is no need for sulfur dioxide where the thiohalide or
oxyhalide is employed.
In U.S. Patent 4,020,240, issued April 26, 1977, to
Schlaikjer,there is disclosed another electrochemical cell of
this general type, employing an electrolyte salt containing a
clovoborate anion. The disclosed cells are said to have
characteristics of high potential and current capabilities at
low temperatures, and to be resistant to anode passivation
during long-time storage at elevated temperatures. The
disclosed electrolyte salts are said to be useful in electro-
chemical cells utilizing a wide variety of soluble cathode
materials. Among these are sulfur dioxide, sulfuryl chloride
and sulfur trioxide. It is broadly disclosed that these as
well as the other compatible solvents can be used alone or in
combination. The cell in Example 3 employed a lithium anode,
a thionyl chloride solvent with Li2BloCllo as the electrolyte
salt and showed an open circuit potential of about
3.62 + 0.05V.
--5--
113~
In our copending application, Canadian Serial No.
341~130 filed December 4, 1979, there is disclosed a primary
voltaic electrochemical cell having an oxidizable anode
material, an inert cathode current collector, and an electro-
lyte soltulon consisting essentially of at least one electrolyte
salt and a solvent mixture consisting essentially of sulfur
dioxide and sulfur trioxide, wherein the sulfur trioxide is the
sole active cathode material. These cells are capable of
producing open circuit potentials (OCP) of 4.6V and above.
Accordingly, the present invention provides a primary
electrochemical cell comprising: an oxidizable active anode
material; an inert cathode current collector; and an electro-
lyte solution, in contact with the anode and the cathode
current collector, consisting essentially of at least one
soluble electrolyte salt and a solvent mixture selected from
the group consisting of (a) cosolvents sulfur trioxide and
sulfuryl chloride, and (b) trisolvents sulfur trioxide,
sulfur dioxide and sulfuryl chloride; wherein the sulfur
trioxide is the sole active cathode material.
Some embodiments of the invention will now be
described, by way of example, with reference to the accompany-
ing drawings in which:-
FIGURE 1 shows the discharge curve for a cell according to
the present invention prepared in Example 3;
FIGURE 2 shows the construction of an AA size cell according
to the present invention prepared in Example 4; and
FIGURE 3 shows the potential as a function of time for this
cell while being discharged at 40 microamps.
~ c - ~
1139;~4
This invention relates to a primary electrochemical
cell having: an oxidizable active anode material; an inert
cathode current collector; and an electrolyte solution,- in
¦ contact with the anode and the cathode current collector,
consisting essentially of at least one soluble electrolyte salt
and a solvent mixture selected from the group consisting of
ta) cosolvents sulfur trioxide (SO3~ ana sulfuryl chloriae
(SO2Cl23, and (b) trisolvents sulfur trioxi~e (SO3), sulur
~ dioxide (SO2) and sulfuryl chloride (SO2C12); whereln ~he
sulfur trioxide is the sole active cathode materialt The
electrolyte salt provides an effective aegree of co~ductivity to
provide an operable ^ell.
The cells produced according to the presen~ invention,
\ and those produced in our above-identified copending application,
are the only known operable and practical soluble cathode cells
that will discharge on inert cathode current collectors at 4.5V
or higher versus lithium For the purposes of the present
invention, the cell is defined as having sulfur trioxide as the
! sole reaucible cathode material. The o-~her solvents, sulfur
dioxide or sulfuryl chloride, function primarily to promote
solubility of the electrolyte salt and to prevent the sulur
- trioxide from poly~erizing (freezing). They aO not function
as active, reducible cathoae materials. No solvents ot~er
than sulfur dioxide and sulfuryl çhlori~e are known t~ be
effective with sulfur trioxide- Solvents ~uch as POCl3 ana
S2O5C12 have been found too corrosive when mixe~ with sulfur
trioxide. Likewise, metal based halides and oxyhalides such
{
364
as SeOC12, VOC13, CrO2C12, and the li~e have been rejected!
because of toxicity, reactivity, expense, lack of ability to
dissolve electrolyte salts, or, usually, a combination of
these reasons. Thus, the present invention is limitea to the
named solvent mixtures.
The anode is preferably lithium metal, although
other oxidizable anode materials contemplatea fox use in a
cell of this invention include other alkali metals such as
sodium, potassium, cesium and rubidium; Group IIA and B elements,
which are the alkaline earth metals such as beryllium, magnesium,
calcium, strontium, barium, zinc and cadmium; the Group IIIA
and IIIB metals such as the rare earths, scandium, yttrium,
aluminum, gallium, indium and thallium; the ~roup IVA metals
such as tin ana lead; and transition meta-s such as titanium,
vanadium, manganese, iron, cobalt and copper.
The inert cathode current collector i5 any matexial
which is inert to the other components of the system ana
sufficiently electrically conductive to draw off the current
that is being produced by the cell. Typically, the current
collector is a nickel, nickel alloy or stainless steel gria
or screen having applied to it an inert and electrically
conductive material such as carbon blac~, graphite or other
electrically conductive material of high surface area. These
materials preferably contain binding agents which hola them
together and maintain them in position on the screen
The salts utilized as electrolytes accor~ing to the
present invention must provide M n ions, such as Li~, and
anions which are stable to oxidation and Lewis acid addition
~139364
by S03. The salts will be present in amounts effective to
provide sufficient conductivity to the cell to operate as
a primary voltaic electrochemical cell. Typically, the
salts will be employed in amounts effective to make the
solutions from 0.01 to 2.OM. Specific conductivities above
1 x 10 5 ohm lcm 1 will typically be employed. Preferably,
the conductivities should be above 1 x 10 40hm lcm 1
Among the useful electrolyte salts are those which
provide at least one anion of the general formula S03X ,
MX4 , M'X6 and M"C16 , where M is an element selected from
the group consisting of aluminum and boron; M' is a Group VA
or VB metal selected from the group consisting of phosphorous,
arsenic and antimony, niobium and tantalum; M" is a Group IVA
or IVB element selected from the group consisting of silicon,
tin, zirconium, hafnium and titanium; and X is chlorine or
fluorine. Preferred salts provide at least one anion selected
from the group consisting of: S03Cl, S03F, BF4 , BC14 ,
AlC14 , AlF6 , PF6 , AsF6 , SbF6 , SbC16 , NbF6 ~ TaF6
SiF6 , SiC16 , SnF6 , ZrF6 , HfF6 ~ TiC16 , TiF6
WF6 , MoF6 , and PbC16 . U.S. Patent 3,926,669 discloses
electrolyte salts of this type.
Also suitable as electrolyte salts, are the
clovoborates disclosed in U.S. Patent 4,020,240. Among these
are metal clovoborates having a metal cation selected from the
qroup consisting of lithium, sodium, potassium, rubidium,
cesium, magnesium, calcium, strontium and..barium, or combinations
thereof, and a clovoborate anion which has a formula (BmXn) k
wherein m, n and k are integers with m ranging from 6-20,
n ranging from 6-18 and k ranging from 1-4, B is boron, and
X is selected from the group consisting of H, F, Cl, Br, I,
OH and combinations thereof.
Examples of suitable soluble salts yielding Li and
anions are Li2B12C112, LiCl, LiF, LiBF4, LiAsF6, LiSbF6, and
LiPF6. The nature of the solubilization of electrolyte salts
with concomitant useful conductivity in this invention does
not seem to be the same for the various classes of salts and
the precise interaction for all is not presently known. The
solubility of Li2B12C112 in the solvent mixtures of this
invention increases with the presence of SO2. Generally,
our experience with Li2B12C112 suggests that as the weight
percentage of SO3 and So2C12 increases, the solubility of
this salt declines. Solubility in pure liquid SO2 results
from the ability of the solvent to polarize or interact with
large multi-electron anions and in such fashion contribute
significantly to solvation energy. This propensity of
polarizability by liquid SO2 is apparently operative with the
Li2B12C112 electrolyte salt and allows for the observed
solubility and conductivity when the weight percentages of
SO3 and SO2C12 are carefully adjusted.
The ability of the disclosed halogenmetallate com-
plexes, MX4 , M'X6 and M"X6 to act as electrolytes in the
SO3-So2C12 is not entirely understood at this time. For
example, LiAsF6 is insoluble in liquid SO2C12 and in liquid SO3
separately, yet a novel mixture of the two solvents effects
dissolution of the salt. In fact, a 0.5M LiAsF6 solution has
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113~;~6~
been prepared in 50 wt.~ S03 and S02C12 which has a specific
conductivity of 1.0 x 10 Q lcm 1 The nature of the solvent
interaction may rest with the ability of the electron
deficient S03 molecules to form fluoride bridges with the
A~F6 anion and thereby render the salt soluble in this
solvent system, i.e.,
~ S~3 ~
F ~F F
The electrolyte solution consists essentially of at
least one soluble electrolyte salt as described above and a
solvent mixture selected from the group consisting of (a)
cosolvents sulfur trioxide and sulfuryl chloride, and (b~ tri-
solvents sulfur trioxide, sulfuryl chloride, and sulfur
dioxide. The cosolvent or trisolvent mixture will always be
present in more than a major amount, and cannot contain other
materials which adversely affect the operation of the cells
as improved by the sulfur trioxide liquid cathode system of
this invention.
The solvents sulfur trioxide, sulfur dioxide and
sulfuryl chloride may be utilized in all weight percentages
depending on the volumetric amount of sulfur trioxide needed
and the desired conductivity of the solution once the electro-
lyte salt is added. However, they are preferably employed in
weight ratios sufficient to fully dissolve the electrolyte salt
employed. In the case of the cosolvent system, the typical
weight percentages of the S03 will be from 10 to 90% and the
sulfuryl chloride will be from 90 to 10~. In the case of the
--11--
trisolvent system, the typical wei~ht percentages of the SO2
will be from 1 to 25~, the SO3 will be from 10 to 90~, ana the
sulfuryl chloriae will be from 9 to 89~, The cosolvent system
of sulfur trioxide and sulfuryl chloride, and the trisolvent
system of sulfur trioxide, sulfuryl chloride and sulfur
dioxide, exhibit specific conauctivities of less than 1 x 10 7
ohm~l cm~l before aadition o~ ~he electrolyte salt.
It is preferre~ that the sulfur ~ioxide be dried ~y
, conaensing it onto P4Olo at -78~C and ~istilling it from this
mixture to yiel~ uid SO2 free of H2O Typical specific
conductivities for liquid SO2 collected using the aforementioned
treatment are less than 1 x 10-6 ohm~l cm~l. The sulfur trioxiae
can be obtained from MCB Manufacturing Chemists, a dis~ributor
~ c~,k)
of Allied Chemical Corporation's SUL~AN~stabilized sulfur -
trioxide and is pre~erably fractionally distilled to proviaeSO3 essentially ree from H2S04 and commercial stabilizers.
The sulfuryl chloride is also preferably fractionally distilled
from lithium metal to remove hydrolysis impurities.
The new electrochemical cells of the present invention
provide a number of advantages over prior art cells ana those
described in our above-identified paten~ ap,plication. In
general, the cells of this invention are high performance cells
wi~h improved sa~ety-and reliability over our earlier sulfur
trioxide-sulfur aioxide liquid cathode cells. The cells of the
present invention are safer by virtue of the vapor pressure
reducing effect of the sul~uryl chloride which allows for more
secure hermetic seals.
An advantage of the trisolvent system SO3-SO2C12-SO2
arises from the higher con~uctivity a)ld hi~her solubility of
electrolyte salts in this mixture as well as a relatively low
vapor pressure. The trisolvent system shows a higher conduc-
tivity for LiAs~6 and Li2B12C112 electrolyte salts than
S03-S02C12 mixtures. This trisolvent combines the conauctivity
and solubility advantages of the SO3-5O2 system with the
improved lithium stability of the S03-S02C12 system ~urther
advantages of this invention are that both the self-discharge
of the cell and the rate of corrosion of the anoae due to
hy~rolysis impurities, are relatively low for lithium an~ like
active ~etal anode cells employing the cathode systems of
this invention.
The following examples are for the purpose of further
illustrating and explaining the present invention, ana are not
to be taken as limiting in any regara, Unless o~herwise
inaicatea, all parts and percentages are by weight.
Example 1
This example illustrates the preparation and aischarge
of a cell according to the invention employing a lithium metal
anode, an electrolyte solution consisting essentially of a
cosolvent mixture of sulfur trioxide and sulfur~l chloride and
LiAsF6 as the electrolyte salt, wherein sulfur trioxiae is the
sole cathode material.
The LiAsF6 was used as received from U.S.S. Fluorine
~hemicals, Decat~r, Georgia. The electrolyte solution contained
50 wt.% SO3 ana 50 wt.% SO2C12. Sufficient LiAsF6 was addea
to the cosolvents to make the solution 0.5M. The solution was
mildly heated for a few minutes to aissolve ~he electrolyte salt.
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1~'3~
The specific conductivity of the resulting solution was
1 x 10 3 Q~l cm~l. The liquid cathode containing the
electrolyte was transferred to a glass pressure cell which
contained a lithium anode supported on nickel screen, a Li
reference and a cathode current collector comprise~ of carbon
black and ~inder-supported on nickel screen. The initial open
circuit potential was 4.75V. The cell discharged f~r two ~ays
above 4V at a rate of 0.2 mA/cm2.
Example 2
This example describes the preparation and discharge
of a cell according to this invention which comprises a lithium
metal anode, an electrolyte solution consis~ing essentially vf
a cosolvent mixture of sulfur trioxide ana su~furyl chloride
and Li2B12C112 as the electrolyte salt, wherein sulfur trioxiae
is the sole cathode material.
The Li2Bl2Cl12 was prepared by ~nown chemical
literature procedures (U.S. Patent 3,551,1~0, Substitutea
Dodecaborates; and norg. Chem., 3, 159 [1964]) The
~i2B12C112 is essentially insoluble in SO3 and in SO2Clz
se~arately but shows sufficient solubility ana conducti~ity
in a cosolvent mixture of 50 wt.% SO3 an~ 50 wt.~ SO2C12 to be
useful as an electrolyte. The conductivity of ~ O.OlM solution
Li2~12C112 in the SO3-SO2C12 solvent mixture is 3 x 10 5 Q~l cm 1
A flooded cell constructed as explained in Example 1, showea
an open circuit potential of 4.56V with this electrolyte. This
cell was dischaxged for 1500 hours to a depth o~ 120 mAhr
(milliamp hours) and average cell volta~e of ~.35V.
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1~3~
Example 3
This example illustrates the preparation ana discharge
of a cell accor`ding to the present invention havin~ a lithium
metal anode, an eletrolyte solution which consists essentially
of a trisol~ent mixture of sulfur trioxide, sulfuryl chlori~e
and sulfur dioxide, and Li2B12C112 as the electrolyte salt,
wherein su-fur trioxide is the sole cathode material.
A Q.OlM Li2B12C112 solution in 45 wt.% S03, 46 wt.%
S02C12 and 9 wt.% S02, displayea a conductivity of 1 x lQ 4
~ 1 cm~l. An electrochemical cell as preparea in Example 1 and
composed of a Li anode, Li reference and carbon cathode curren~
collector with the described solution trisolvents and electrolyte
salt showed an open circuit potential of 4.6V. Figure 1 shows
the aischarge curve for this cell preparea with ~loodea flag
electrodes. The cell was discharged at a rate of 15 ~A~cm2 o~
lithium to a t~tal depth of 63 mAhr. Inspection ana aisassembly
revealed that the termination of discharge resuited from
cathode failure caused by the accumulation of discharge products.
Example 4
2Q This example illustrates the preparation an~ ~ischarqe
o~ a limited electrolyte cell having a lithium anode, an
electrolyte solution consisting essentially o* a triso~vent
mixture of S03, S02C12 and S02 and Li2B12C112 as the electrolyte
salt, wherein the sole reducible cath~de material is the sulur
trioxide.
A O.Ql~ Li2B12C112 solution in ~0- wt.~ S03, 35 wt
S02C12 and 15 wt.% S02 was utilized as the electrolyte The
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(~ (
1~3~64
electrochemic~l cell ~esign is shown in Figure 2. A conventiona
size "~" battery can with the cathode current collector ana
anodè as shown was protected within a glass pressure vessel
and fillea to the top of the can with the electrolyte solution.
A load simulating a total drain of 40 ~A was imposed_ The
ensuing potential as a function of time is shown in Figure 3.
The above disclosure is for the purpose of explaining
the present invention to those skilled in the art, ana is not
intended to descrlbe all those obvious modifications and
variations of the invention which will become apparent upon
reading. Applicants do intend, however, to incluae all such
obvious modifications and variations withinthe scope o~ the
invention which is defined by the following claims~
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