CA1151727A

CA1151727A - Electro-chemical cells

Info

Publication number: CA1151727A
Application number: CA000382128A
Authority: CA
Inventors: Alan J. Parker; Pritam Singh; James Avraamides
Original assignee: Anumin Pty Ltd
Current assignee: Anumin Pty Ltd
Priority date: 1980-07-29
Filing date: 1981-07-21
Publication date: 1983-08-09
Also published as: US4377623A; DE3168482D1; MY8800018A; EP0045609A1; EP0045609B1

Abstract

ABSTRACT OF THE INVENTION

The invention relates to an electro-chemical cell having an electrolyte comprising water, a halogen other than fluorine, a halide other than fluoride, which is not oxidised by the halogen as a soluble salt, and a stable, saturated, organic nitrile or dinitrile containing from 2 to 5 carbon atoms or a mixture thereof, said electrolyte being composed such as to exist in two phases, a first phase being halogen and nitrile-rich and a second phase being water-rich and con-taining halide salt, the cell having an inert electrode in the halogen and nitrile-rich phase and an electrode, con-taining or contacting halogen oxidisable material, in the water-rich phase. The electro-chemical cell of the invention is particularly applicable to systems containing zinc as the halogen oxidisable material.
The use of the nitrile-rich phase reduces the degree of reaction between the halogen and the halogen oxidisable material.

Description

~ I `` 1151~Z7 ~he present inventi~n relate8 to electro-chemical cell~ in which, in the di~charge cycle, a halogen or polyhalide is reduced at an inert cathode and an oxidisable material is oxidised at an anode. In the charge cycle, if u~ed, the redox S processes are reversed. In particular, the invention relates to zinc-halogen cells where the oxidisable material i8 zinc.
In this description, the term halogen refers to iodine, bromine, - chlorine or iodine monochloride and excludes fluorine. Like-wise halide ion excludes fluoride.
In principle, zinc-halogen cells offer low costs, high current densitie6 and high voltage, but historically such cells suffer ~erlously from self discharge because halog~ns usually reach the zinc and react chemically with it. Also, in water the halogens are much less soluble and polyhalide ions are much less stable than in ~ome other 601vents so a totally agueous cell is impract~cal and the high conductivity of agueous solu-t$on~ cannot ~e utilized.
Many attempts have been made to make zinc-halogen cells to overco~e the historical problems but they suffer from high cost or self di wharge or high internal resistance or reguire com-plex methods of 6toring and circulating the electrolyte. Thus zinc-bromine cells ha~e been used as a totally agueous system with NaFion separators. Efficiencies are good but the separa-tors are very co~tly. Others have u~ed organic solvents such as carbon tetrachlori~e.

2-~, , , 1.151727 - 1;2-dichloroeth~ne and chloroform ~hich form two pha~e~ with water, dissolve large quantities of halogen but which have the halogen rich pha6e below the water-rich phase. Moreover, they are poor ~olvents for electrolytes, ~o give zinc-halogen cells S with high internal resi~tance. Wor~er~ at Exxon Corporation have used very low melting organic cation-polybromide salts, a6 water-Lmmiscible oils at carbon cathodes. These contain mo~t ofthe bromine aspolybromide and keep it from the zinc electrode in the aqueous phase. Such ~alts are expensive, however, and are u~ed as emulsion~ in water, requiring high ~peed pumps external to the battery. Zinc-chlorine batteries have been developed where chlorine is stored externally as solid chlorine hydrate at low temperatures, but refrigeration ~y~tems and external pumps are needed, which is a 6erious dis-advantage.
Almo~t inv~riably zinc-halogen cells are used in the bipolar mode and thi~ would 6eem to be most appropriate fGr the present invention Carbon, but not graphite, i5 a common inert elec-trode, but inert metal-coated electrodes, dimen6ionally etable ruthenium compounds and other well known inert electrodes are u~éd in the presence of halogens. We believe that carbon-pla~tic electrodes will prove to be very applicable to the present ~nvention because they have worked well in related zinc-bromine batteries used by worker~ at Exxon Corporation.
In view of the historical problem~ the pre~ent invention ; .

s I ~ 151727 provides solvent~ which form a second pha6e in the presence of water, in which halogens are soluble but stable, in which poly-halide ions are etable, polyhalide salt6 are ~oluble and mo~t salts are strong electrolytes ~o as to give highly conducting solution6. It is necessary that the solvent has an interface with a water-rich electrolyte solution which is highly conduc-ting. It is also desirable to avoid having to pump electrolyte or cool chlorine to form hydrate.
We have found that a zinc-halogen cell can be operated as a type of fuel cell, where particulate zinc is introduced from time to time as a slurry to contact a suitably designed inert anode and bromine is introduced continuously or intermittently as a liquid to contact an inert cathode, with removal of aqueous zinc bromide product from time to time. In such a fuel cell or primary battery, the advantage through gravity of having the particulate zinc lying on a horizontal dish-shaped anode at the bottom of a cell i~ apparent.
~ecause of our desire to have zinc in a lower water-rich phase in ~ome circumstance , it i8 preferable that the solvents have the additional property that they are less dense than water.
It has been found that those saturated organic nitriles con-taining from 2 to S carbon atoms which do not react with halogens, fill most of the above requirements and that cyanoe-thane, in particular, fills all the reguirements as a component of the halogen rich phase. ~hey are inert to halogens, water ~151727 is only slightly soluble in them, they form two phase systems with many aqueous electrolyte solutions and are less dense than water. They can dissolve at least 4 ~ bromine or 0.5 M
chlorine at 1 atmosphere. Cyanoethane has a high dielectric constant (27) and a very low viscosity (0.38 cp), polyhalide ions are stable in it and sodium, potassium, or zinc halides and polyhalides are moderately soluble in both phases, when it is present as a two phase system with water. When such nitriles are equilibrated with water, bromine, sodium or zinc bromide and concentrated sodium chloride, the two phases which form have comparable conductivity and the upper nitrile rich phase is bright red, containing typically 3 M bromine, whereas the lower water rich phase contains <0.15 M bromine. The large distribution coefficient of bromine between nitrile-rich phases and water-rich phases means that in such systems, zinc in the water-rich phases is only attacked very slowly by bromine.
Aq noted below, if certain polymeric porous separators are present, e,g. microporous polypropylene such as that identified by the trade mark ~"Celgard"), the distribution of bromi~e to the aqueous phase can be kept even lower and mixing or "levelling"
of the water-rich and nitrile-rich phases can be prevented, no matter what the configuration of the cell~
Thus the present invention provides an electro-chemical cell having an electrolyte comprising water, a halogen other than fluorine a halide other than fluoride which is not oxidised by r~;, ~.~ 5:17Z7 the halogen preferably the corresponding halide, as a soluble ~alt whose cation i8 not oxidised by haloqens, and a 6table saturated organic ~itrile or dinitrile containing from 2 to 5 carbon atoms or a mixture thereof, said electrolyte being S composed such as to exist in two phases, a first pha6e being halogen and nitrile-rich and a second phase being water-rich and containing halide salt, the cell having an inert electrode in the halogen and nitrile-rich phase and an eiectrode con-taining or contacting halogen oxidisable material, in the water-rich phase.
The electro-chemical cell can be multiplied to form a battery and the concept of a two pha6e electrolyte with halogen in a nitrile-rich phase i6 applicable to a variety of systems.
For example, it is applicable to a copper-bromine cell com-pri6ing a copper anode immersed in an aqueous 2 M sodium bro-mide solution with a second phase above it, containing 2 M
bromine $n cyanoethane and a carbon cathode. The cell had a microporous separator between the phases and operated at 30 mA cm 2 at about l volt. The halogen nitrile-carbon cathodic half cell can, in principle, be coupled with aqueous anodes familiar to electro-chemists such as metals ~zinc, mag-nesium, cadmium, lead) or oxidisable semi-conductors (Cu2S, CuFeS2, FeS) in the appropriate a~ueous phase6, but zinc ~eems to offer the best prospects for a useful battery.
~he two phase6 are either kept 6eparate naturally, i.e. with il ` ~ 151727 - *he more dense phase 1u6uallY water-rich) below the le~s den~e phase (usually nitrile-rich) or they are kept separate in ~ny cell configuration by a polymeric porous ~epar~tor which iB
not permeable to the hydrophilic and hydrophobic 601vents a~
de~cribea below.
While the diwovery of a halogen-nitrile-inert-cathode half cell is of general applicability for batteries when linked with a variety of anodic half cells containing water-rich electro-lytes, it will be described hereinafter with particular refe-rence to zinc-halogen cells.
Preferred nitriles for use in the present in~ention are cyano-ethane, l-cyanopropane and 2-cyanopropane. ~yanomethane is preferred in certain situations where 6ignificant water misci-bility is not a problem, but cyanomethane s more miscible with water and requires high ~salting out~ salt concentrations ~e.g.

3 M NaCl) and low or moderate temperatures to ensure two phases.
~ highly conducting nitrile ph2se i8 pos6ible with cyanomethane.
Acrylonitrile reacts with bromine.
The zinc-krominebattery is preerred over zinc-iodine or zinc-chlorlne because iodine i8 more expensive than bromi~e and chiorine is a gas, which is less soluble in the nitrile-rich phase and more difficult to contain than hromine. However, chlorine i~ cheaper than bromine and it is found that it o~fers higher voltage~ ~2.2Y) in a zinc-halogen cell. All three ~5 zinc-halogen batterie~ have been operat-d by u~ using nitrile-.. , _ _ . , . . , .. _,,, . . . . ~ . .. , . .. _ .. _ _ . . _ ... . . _ . _ .. . _ ~ `

ii ~ich phases to contain the halogens.
For the zinc-bromine battery, ~ufficient ions should be present (e.g. 0.5M) to complex with 60me bromine and form polybromide salts (e.g. NaBr3) which are soluble and conducting in the nitrile-rich phase. Sodium chloride ~8 the preferred major electrolyte for the aqueous phase because of its low cost, good conductance, salting out characteristics and high solu-bility in water. About ~ M solutions of NaCl are preferred, but higher concentrations may be used. KCl is preferred without bromide salts, for a zinc-chlorine battery. RCl forms polychlorides in the nitrile rich phase and enhances the solu-bility of chlorine. Preferably, the electrolyte contains suffi-cient halide ion such that more than 50~ of the halogen in the nitrile rich phase i6 in the form of polyhalide ions.
Carbon is preferred as the inert electrode and carbon in plastic i~ very ~uitable for related batteries.
I~ the battery i~ to operate in non horizontal configurations, or with a more dense phase on top of a less dense phase, a separator is essential. Microporous polypropylene is preferred a~ ~eparator material, but a variety of polymeric separators prevent the hydrophobic nitrile-rich and hydrophilic water-rich phases from mixing. Inclusion of such a separator has little effect on the ~ell current voltage performance. Examples of separators include ~Celgard~ products, e.g. ~Celgard" 5510.
Non-woven polymeric fabrics produced by the Xendall Company of 8.

., .

- 1 ~5~727 Boston, ~ass., U.S.A., such as their "Webril" trade mark M
and T series and "Webline" trade mark F series. The "Daramic"
trade mark separators, used by Exxon Corporation in their zinc-bromine cells, are very effective. It appears that the hydrophobic and hydrophilic properties o~ separators are important and phase separation is most effective when hydro-philic and hydrophobic phases are on opposite sides of the porous separator. Thus it is found that water flows through "wettable" polypropylene separators to air, or water at a lower level. Polypropylene materials are useful for cell construction. Electrode separations of 0.5 to 1 cm are commonly used in our experiments.
~ he zinc electrode is preferably zinc in contact with an inert conductor, such as carbon, but zinc plates can be used in primary battery use and as noted, we find that even stationary slurries of zinc powders in aqueous brine solutions in contact with carbon anodes give very effective cells, when coupled with halogen-nitrile-carbon cathodic half cells, containing halide salts, with or without a separator.
As noted, numerous cell configurations are possible with the aid of a separator. If the cell is to be recharged, we find that there are advantages in circulating the zinc halide water-rich phase during charging to improve electrodeposition of zinc. Some hydrogen is formed on charging, so that a vertical arrangement of electrodes and separator is preferred if the cell is to be recharged. The bipolar mode is preferred since ,_ .,~,, ~t allow6 easier collection of current from electrodes. If used a~ a fuel cell or pr~m~ry battery then the horizontal mode, with a zinc ~lurry in an electrolyte formulated so that the ~ater-rich phase i6 the denser ~nd zinc is at the bottom of the cell, i8 preferred. Some provision for introduction of zinc slurry, drainage of a zinc bromide water-rich solution and replenishment of bromine in the nitrile-rich phase i8 desirable in the fuel cell mode.
In one method of preparing the electrolyte, cyanoethane and water are equilibrated with sufficient bromine in the cyanoe-thane to form a ~-4 molar bromine solution in the nitrile-rich phase and with 2 M NaBr and 1 M zinc bromide in the water-rich phase. The nitrile-rich phase (containing dissolved water and zinc and sodium polybromides) is separated from the water-rich phase and placed in the cathode compartment of a zinc bromine cell, equipped with a ~Webril~ T polypropylene or ~Daramic~ porous polymeric separator. At the same time, the anode compartment is filled with a 3M sodium chloride solution ~n water. The cathode compartment contains a carbon electrode, the anode compartment a zinc-on-carbon electrode. ~he cell has an open circuit voltage of 1.8V and is then discharged at ~ 80~ Faradaic efficiency at currents between 30 - 120 mA
cm 2 at 1.4 - O.9 volts. ~n this method very little bromine appears to pass through the separator from the nitrile-rich to the water-rich phase. In another mode, halogen and ~olid 10.

iel ~1517Z7 i ~odium and zinc-halide are dissolved in the dry nitrile to give polyhalide salts and the nitrile solution is then placed in the cathodic compartment of a cell equippped with separator.
The anodic half cell contain~ zinc and s~dium halide in water.
5 Similar procedures were used with iodine replacing bromine and zinc and sodium iodides replacing zinc and sodium bromides, to give a zinc-iodine cell. We constructed a zinc-chlorine cell, with the chlorine maintained at a slight positive pres-sure. Potassium and zinc chloride replaced bromide salts in the above procedure. A saturated (0.5 - 1 M) chlorine solution formed in the nitrile-rich phase.
It should be noted that iodide cannot be used in the presence of chlorine or bromine since it would be oxidised to iodine.
Similarly, bromide cannot be used in the presence of chlorine since it would be oxidised to bromine.
The main reguirement of the electrolyte preparation is that ~table nitriles be chosen and concentrations of halogen and halide salts be such that two phases are formed, with both phases highly conducting (e.g. 0.04S cm 1) and the nitrile-rich phase containing sufficient halogen and polyhalide toprevent severe concentration polarization at the desired current densities. This is readily achieved by persons skilled in the art, if the principles outlined herein are followed.
Table 1 summarizes results from the simplest form of zinc bromine battery, with no separator and the cyanoethane rich 11 .

1 ~ ` 1151'727 pha~e above the water-rich pha~e. The compo~itions initially were made up with equal volumes of cyanoethane and water but at equilibration, the volumes of the two phases differ as ~hown, ~ue to mutual solubility of nitrile in water and vice versa. As reguired, the concentration of bromine i8 much greater in the nitrile-rich phase. In other experiments, ~Cl, NaN03 and LlBr were u6ed to encourage phase separation and enhance conductivity of the phases. The cells discharged at > 100 mA cm 2 of zinc with no apparent polarization. If a microporous polypropylene separator was included, there was little observed change in current voltage characteristics.
Increased temperature lowers the cell resistance but reduces the phase separation characteristics.
Table 2 records some data for typical zinc-bromine batteries, using nitrile solvents, together with results in the same cell, u~ing prior art electrolytes. Cyanoethane is slightly superior to l-cyanopropane and acetonitrile gives very desirable charac-teristic~, but requires high concentrations of NaCl ~3 M) to en~ure 2 phases. All the nitriles give superior cells to those containing prior art chloroform or dichloroethane as two phase ~ystems, with the organic phase bel~w the water-rich phase.
Table 3 compares the performance of a cyanoethane based zinc bromine cell with the same cell in which bromine i8 present a~ the water immiscible liguid N-methyl-N-methoxymethyl piperi-dinium polybromide salt. ~he latter i9 currently under inves-, ,j ,.

1, .

~ ~ ~ 1151727 tigation, ~s an electrolyte for 2inc bromine oell~, ~y other groups, ~ut the performance i~ le~8 satisfactory th~n when the bromine or polybromide iB present a6 a solution in . cyanoethane.
TABLE 1 : Phase separation, bromine di6tribution and conduc-tance of cyanoethane-water mixtures containing electrolytes lMx) at 25. No separator and the nitrile-rich phase is above the water-rich phase.d .
(ZnBr2~ a (Br2)~ a (MX) MX DBri org S cm ~
aq org aq M M . M

1.0 1.0 - - 7.2 6J0 0.038 0.065 1.5 1.0 - - - 1 pha6e 0.034 1.0 1.0 1.0 LiBr - 6.0 0.038 0.08 1.0 1.0 2.0 LiBr - 1 phase 1.0 1.0 4.0 LiBr - 1.5 1.0 1.0 1.0 NaCl19.3 1.4 0.039 0.09 1.0 1.0 3.0 NaC144.6 - - -~. Concentration is moles of solute per s~m of volumes of - bD~h phases, expre6Qed as moles litre b. Ratio of concentrations of bromine in organic versus agueous phase, at equilibrium.
c. Ratio of volumes of organic/aqueous phase, at equilibrium.
d. With 4 M bromine in these compositions~ the nitrile-rich phase becomes more dense and thus the lower phase.

, ,' ' 13.

,, . .. . . .. _ 1 ~1S17Z7 l o~ ~, o: ~ .~ o o o a ~ Z _I N O
~1 _i ~ N
~r JJ . ~
Z 0~ ~ ~ U __ -:~ m ~
C ~ ~ ~ ~ o o o~ 'D
_I ~ ~ ~ D O ~ -~
_~ ~ ~ ~ o o ~ o o h ~ Z ~ N
~ O :C ~ ~ O
J- ~ O

.a N ~ N N
~1 N _I ~ ` O O t` O O ~ t) ~) E~ ~.
~1 ~ z _1 0 0 N O ~ N
V
'~_1 O
O~
:~ ~1 ~ ~ o u~
N j~ ~` o ~I ~I
o m z ,~ O O _, ___ ",, ,,_, Q~ C
C ~:
~ ~ O t~
E ~ ~ ~
O C S~ ~ ~` o _1 0 ~ O, u~
. .. . o ~
Z~ Z; ~ O O ~ _ ___ ~ ~ .~ N ~
~i 8 ~ u .~
o ~ ~ ~ -~ C
~ ~ ,uO J'~ e~
~_~ ~ o ~ al ~ o ~ c ~0U . ~ ~ ~ U ~ ~ o C
-- ~ U O O ~ ~ . N
Z U ~ I N I O N I
c~0 ~ ~ ~u -, o I e P~ I
~ ~ U U 0 0US~ ~ ~ ~ ~
O .C U U C ~ tr. ~ U U ~S
U C~--I ~ ~ C O 10 tJ~ ~ 5 ~ tJ~ ~ d .. . U o ~ o' ~.~, ~, S ~ e ~ e N O 3 i i ~ s r ~ ~ ~ u~ ~o s O ul _e 8~ 0 ~e O U rl ~e ~ r~e ~3 d d ~ d ~d C
;~ ~

4.
,1 1~ ^
_ ~, . .,, _ _, ~ . _ _ _ _ , . . . . . . .
. ..

f ~IL51~Z7 . .
~i : ' ~ ~

. U Z N _I o 0 .C ~
h N ~ S _I m ~ ~ o~o ~ -~ m ~ ~
_I W ~o ~ ~ 0~ 0 ~ Z o~r o 0 0 ~
c~ U &- ~ ~
O IDu~ 0 3~ ~ ~ a E ~ m _~ ~r D O _1 ~ 0 U J~ 0~ ~ ~ X ~
~ z o_~ o ~ O -' S
U
~-1 0 o ~_1 . ~ 0 ~
~ ~ ~ u~ ~ Z
~4z z o r~ o ~0 ~ 3 ;~ 0 m .,, " ,, ~ 0 . ' O S O ~ S~ ~ O
O ~ ,, ~ O U
, ~ _~ U 10 ~ m U ~ ~ o ~ I a~ ~ u ~Z Z o ~
P~ 0 0 ~ N
u ~ ~ ~ z a) j~ .~ m .~ W e m m ~ W ~ ~i 0 _ o ~ oq ~ ~ ~ 3 ~ ~ ~ K
~ o ~ ~ 5 s ~ ~ 3 0 ~ ~ o ~ u, ~ ~ m ~ _~ ~ aU~ s 'o' ~ o Sv u o 1 ~ m w o t~ . . c ~ c 0 0~ C02 _~ U
. 1 N RN~l ~ ~1 111 ~1 ~ 0 ~ Z
ro- --I O ~ 1 C N ~ ~ ~ l U
o ~ ~ m ~ ~ ~ o ~, o ~ ~ . .
~a ~0 ~ a ~ ~ . .....
~ R ~) ~a 0 q~

15 .

., .
'~ - .. , !l ", ' 1 ~15~727 sI TABLE 3 : Comparison of the di~charge performance of a ~inc bromine battery with (NR4Br3)b or Zn~Br3)2 in CH3CH2CN in the cathode compartment. The battery comprises a porous carbon cathode, zinc anode, ~Webril~ non-woven polypropylene ~eparator.
Electrode separation 1 cm, electrode area, 3 cm2, temperature 25C,a Zn(Br3)2 in NR4Br3 CH3CH2CN Oil Concentration of Br2 4-5 M ca. 9 M
Solvents water/cyanoethane oil Sùpporting electrolyte S M ~aBr 5 M NaBr Open circuit voltage Ivolt6)1.819 1.783 Short circuit current (m Amps) 0.491 0.524 Short circuit voltage, ~volts) 0.404 0.260 Short circuit power ~m Watts cm 2) 101.2 70 Max, power output ~m Watt~ cm 2) 138 (2 Q)a 128 ~2 Q)a Conducti~ity of bromine-rich phase (S cm~ ) 0.07 0.042 Conducti~ity of water-rich phase (S cm~ ) ca 0.1 ca 0.1 a. Cell operated for 6 hours with the 5eparator in the vertical mode at this power density. It recharged when an external,potential of 1.9 volts was applied.
b. NR4 i~ the N-methyl-N-methoxymethyl piperidinium cation.

, 16.

..

,, . . . - --, ~ ~ 7Z7 ~ ~he present ~nvention will now be illu~trated ~y the following .' examples.

~his example illustrates an embodim~nt of the pre~ent invention with both ~olutions ~tationary in the horizontal mode. 0.1 mole of bromine and 0.2 mole each of zinc bromide and NaCl was dissolved in a mixture of 100 ml water and 100 ml cyanoe-thane. Two layers of approximately equal volume appeared.
The upper layer wa~ red, the lower pale yellow. A porous carbon felt electrode, ~arger than the zinc electrode, and partly in the organic phase and partly in the aqueous phase, and a zinc electrode separated by 1 cm wer~ placed in the upper red and lower yellow 601utions respectively and connected to current and voltage measuring devices. Both solutions were still and at 22C. The cell had an open circuit voltage of 1.76 V and a short circuit current of 210 mA cm 2 of zinc.
While chArging for 6 hours at 20 mA cm 2 the voltage was 1.96 V and zinc wa~ plated on the zinc electrode. Some dentrites were formed. A few gas bubbles were evolved, during charging at the zinc electrode. A little 1006e particulate zinc rested on the zinc electrode after 6 hours charging because of the horizontal configuratioD. The cell was discharged at 20 mA
cm 2 at 1;50 V over 6 hours. ~he coulombic efficiency ovex the discharge-charge cycle wa~ 774 ~i.e. 9C4 on charge, 86%
on discharge1.

17.

"

, il51727 ,¦ EXAMPLE II
~n an embodiment similar to that of Example I, the upper nitrile-rich layer flowed slowly past a glassy carbon electrode of the 6ame size as the zinc, but the lower water-rich layer remained Ctill. The voltage on charging at 10 mA cm 2 of zinc was 2.00 V and on discharging at 20 mA cm 2 was 1.55 V.
EXAMPLE III
A zinc chlorine cell was discharged in which the electrolyte was saturated chlorine under a slight positive pressure, 1 M
XC1 and 1 M zinc chloride in equal volumes of water and cyanoethane. Electrodes were zinc in the lower phase and carbon in the upper and there was no separator. The open cir-cuit voltage was 2.2 volt and the short circuit current was ~00 mA cm 2 of zinc. In a separate experiment, the distribu-tion coefficient for chlorine between cyanoethane and water contalning 2 M NaCl, 1 M ZnC12 and saturated chlorine at 1 atmospher was found to be S0. The concentration of chlorine in the organic phase was O.S M.
EXAMPLE IV
A zinc-halogen battery was operated in which the electrolyte was 1 M iodine monochloride, 4 M NaCl, 4 M NH4Cl and 1 M zinc chloride in equal volumes of water and cyanoethane. Electrodes were zinc and carbon at 0.75 cm separation. The open circuit voltage was 1.78 volt and the short circuit current on dis-charge was ca 230 mA cm 2 of zinc at 0.77 volt, rising to 18.

' 151~27 250 mA cm 2 at 0.88 volt after 5 minutes.
EXAM~LE V
A zinc-iodine cell was operated in a similar fashion to the Zn/Br2 battery with solutions containing cya~ethane, water, 0.5 M iodine, 1.0 ~ zinc iodide and gaturated potassium iodide. The electrodes were zinc and platinum. The open circuit voltage was 1.13 volt and the battery delivered 48 mA cm at 0.3 volt when short circuited. Coulombic charging efficiency was 71% at 25 mA cm 2 at a voltage of 1.64 V.
EXAMPLE VI
A battery was operated in which the two phase electrolyte was e~uilibrated 1 M bromine, 1 M zinc bromider and 1 M NaCl in equal volumes of water and cyanoethane. A carbon felt electrode of geometrical area 10 cm2 was in the upper bromine lS and ~itrile-rich layer and the other electrode was platinum gauze of about 15 cm effective area in a gently stirred suspenslon of zinc powder in the lower water-r~ch phase. The open circuit voltage was 1.70 V, the short circuit current wa~ lOS0 mA and when discharged at 356 mA the voltage was 1.16 volt. A stationary layer of zinc powder in the lower water-rich phase resting on a 10 cm2 dense carbon anode, with a ~Daramic~ separator between the two phases gave a comparable result.
EXAMPLE VII
The zinc-bromine batteries de~cribed in Example I, II and VI

19.

.
~, .. .

~ I ~lS1~27 were operated in ~arious configurations with a non-woven Webril~ polypropylene separator of thickne6s 0.005 inches, between the carbon electrode and the agueous phase. ~he performance was little chanqed at current densitie~ of 20 mA
cm from cells without separator. A ~CELGARD~ 511 micro porous ~ettable film polypropylene from Celanese Plactics Company behaved similarly to the Webril separator, as did a ~Daramic~ separator supplied by Exxon Corporation.
In separate experiments it was established that cyanoethane containing bromine and zinc tribromide did not pass through the ~Webril~ separator or ~Celgard" 511 separators into an aqueous solution.
EXAMPLE VIII
Zinc-bromine cells containing 4-5 M bromine, 3 M ~aCl and 0.5 M ZnBr2 in equal volumes of water and cyanoethane were opérated in the discharge mode with two 1 dm2 Celgard 511 microporou~ ~eparators with a 10 cm x 10 cm x 2 mm dense carbon cathode in the nitrile~rich phase, and two 10 cm x 10 cm x 2 mm zinc anodes in the water-rich phases on either side of the carbon. Separator and electrodes were in the vertical mode. Power densities of 50 mW cm 2 were obtained at 1.0 -1.2 ~olt and ~ 80% efficiency. Short term charging for inter-mittent periods at 20 mA cm at 2.1 volt proceeded satis-factorily with formation of zinc and bromine.
~XAMPLE IX

20.

' .

s 11 ~51727 i A three electrode system based on Example VIII, operat~ng inthe bipolar horizontal mode with carbon cathode and zinc powder ! on carbon an~de had an open circuit voltage of 3.5 V and a maximum power density of 40 mW cm 2. The carbon was ~omewhat porous which detracted from the long term performance of thi~
bipolar battery.
EXAMPLE X
The types of cells described in Examples VI and VII above were operated with little change in performance, by continuously dripping bromine into the cyanoethane rich phase containing a carbon cathode. Zinc powder half filled the anodic compart-ment which contained aqueous 2 M NaCl and zi~nc bromide solution.
The zinc powder contacted a carbon felt or a high conductivity compact carbon anode and was renewed intermittently as a zinc slurry ln 2 M NaCl. Zinc bromide solution was drained off from time to t~me in an amount equivalent to the 2 M brine slurry.
Modif~cations and variations such as would be apparent to a ~kllled addressee are deemed within the scope of the present lnvention.

_, , 21.

. .

Claims

We claim :

1. An electro-chemical cell having an electro-lyte comprising water, a halogen other than fluorine, a halide other than fluoride which is not oxidised by the halogen as a soluble salt, and a stable, saturated, organic nitrile or dinitrile containing from 2 to 5 carbon atoms or a mixture thereof, said electrolyte being composed such as to exist in two phases, a first phase being halogen and nitrile-rich and a second phase being water-rich and con-taining halide salt, the cell having an inert electrode in the halogen and nitrile-rich phase and an electrode, con-taining or contacting halogen oxidisable material, in the water-rich phase.

2. An electro-chemical cell according to claim 1, in which the electrolyte contains the halide corresponding to the halogen.

3. An electro-chemical cell according to claim 1, in which the organic nitrile is cyanoethane, 1-cyanopro-pane, 2-cyanopropane or acetonitrile.

4, An electro-chemical cell according to claim 1, in which the nitrile-rich phase in the cell is replenish-able with halogen by adding halogen to said phase during or after discharge.

5. An electro-chemical cell according to claim 1, which is a zinc-halogen cell in which the electrode in 22.

the water-rich phase contains or contacts zinc as the oxidi-sable material.

6. An electro-chemical cell according to claim 5, in which the electrode in the water-rich phase contains particulate zinc in contact with an inert anode.

7. An electro-chemical cell according to claim 5, in which particulate zinc in an anode compartment is replenishable by adding particulate zinc during or after discharge.

8. An electro-chemical cell according to claim 5, in which a solution of zinc halide salt in the water-rich phase has been removed and replaced by a solution of a halide salt containing less zinc halide in a water-rich phase.

9. An electro-chemical cell according to claim 5, which is a zinc-bromine cell containing bromine as the halogen in the electrolyte and bromide ions as the halide.

10, An electro-chemical cell according to claim 1, in which the electrolyte contains an amount of a stable salting out salt to enhance the separation of the electrolyte into two phases and enhance the conductance of the phases.

11. An electro-chemical cell according to claim 10, in which the salting out salt is a chloride taken from the group consisting of sodium chloride and potassium chlo-ride.

12. An electro-chemical cell according to claim 23.

1, in which the electrolyte contains sufficient halide such that more than 50% of the halogen in the nitrile-rich phase is in the form of polyhalide ions.

13. An electro-chemical cell according to claim 1, in which the two phases are separated by an inert porous polymeric separator which is substantially impermeable in the cell to water-rich phases and phases rich in saturated organic nitriles and dinitriles containing from 2 to 5 carbon atoms, but is permeable to small ions.

14. An electro-chemical cell according to claim 13, in which the separator is formed from micro-porous polyethylene or polypropylene.

15. An electro-chemical cell according to claim 13, in which the separator is formed from non-water wettable micro-porous polypropylene.

16. An electro-chemical cell according to claim 13, in which the separator is non-horizontally disposed.

17. An electro-chemical cell according to claim 1, in which the nitrile-rich phase is above the water-rich phase.

24.

24.