Secondary alkaline electrochemical cells with zinc anode

Abstract

The invention relates to the field of alkaline electrochemical cells and more specifically to that of batteries. More specifically, the invention pertains to a secondary electrochemical cell with a zinc electrode, which is differentiated in that it comprises: a) an electrolyte which is an alkaline aqueous solution whose molarity is between 4 M and 15 M hydroxyl anions, comprising soluble silicates whose concentration expressed as silica (SiO.sub.2) is between 0.15 g/l and 80 g/l; and b) a zinc electrode containing a conductive ceramic at least partly consisting of hafnium nitride and/or carbide and/or magnesium carbide and/or nitride and/or silicide and/or niobium carbide and/or nitride and/or titanium carbide and/or nitride and/or silicide and/or vanadium nitride acid/or of double carbides and/or nitrides of any two metals selected among hafnium, magnesium, niobium, titanium and vanadium.

Claims

1. A secondary electrochemical cell comprising: a) a zinc negative electrode comprising a conductive ceramic selected from the group consisting of hafnium nitride, magnesium nitride, niobium nitride, titanium nitride, a vanadium nitride, hafnium carbide, magnesium carbide, niobium carbide, titanium carbide, magnesium silicide, titanium silicide, nitrides or carbides comprising two metals selected from the group consisting of hafnium, magnesium, niobium, titanium and vanadium, and combinations thereof; and b) an electrolyte comprising an alkaline aqueous solution whose molarity is between 4 M and 15 M hydroxyl anions provided by lithium hydroxide, sodium hydroxide, potassium hydroxide, or a combination thereof, said electrolyte comprising soluble silicates whose concentration expressed as silica (SiO.sub.2) is between 0.15 g/I and 80 g/I and which are provided by silica, fumed silica, microsilica, potassium silicate (K.sub.2O.sub.3Si), sodium silicate (Na.sub.2O.sub.3Si), potassium disilicate (K.sub.2O.sub.5Si.sub.2), sodium disilicate (Na.sub.2O.sub.5Si.sub.2), potassium meta-silicate, sodium metasilicate, potassium tetrasilicate (K.sub.2Si.sub.4O9), sodium ortho-silicate (Na.sub.4O.sub.4Si), or a combination thereof.

2. The secondary electrochemical cell according to claim 1, wherein the conductive ceramic comprises titanium nitride.

3. The secondary electrochemical cell according to claim 1, wherein the molarity of the alkaline solution is between 7 M and 13 M.

4. The secondary electrochemical cell according to claim 1, wherein the concentration of silicates in the electrolyte, expressed as silica, is between 20 g/I and 60 g/I.

5. The secondary electrochemical cell according to claim 1, wherein the electrolyte further comprises zincates from the zinc negative electrode.

6. The secondary electrochemical cell according to claim 1, wherein the electrolyte further comprises borates, phosphates, fluorides, or a combination thereof.

7. The secondary electrochemical cell according to claim 1, wherein the conductive ceramic comprises titanium nitride and the molarity of the alkaline solution is between 7 M and 13 M.

8. The secondary electrochemical cell according to claim 1, wherein the conductive ceramic comprises titanium nitride, the molarity of the alkaline solution is between 7 M and 13 M and the concentration of silicates in the electrolyte, expressed as silica, is between 20 g/I and 60 g/I.

Description

(1) More features and advantages of the invention will now be described in detail in the following statement given with reference to the attached figures, which schematically represent:

(2) FIG. 1: charging and discharging voltage of 4.6 Ah NiZn elements as a function of the percentage of the nominal capacity C=4.6 Ah of elements A and B;

(3) FIG. 2: voltage and pressure of the 3 Ah NiZn elements C and D with or without silicates for 3 training cycles;

(4) FIG. 3: measured capacity curves during discharge of the 8 Ah NiZn elements during cycling (8 A charge in 1 hour, discharge 8 A, 1 V, 100% depth of discharge).

(5) 1: anode with TiN and silicate-free electrolyte,

(6) 2: anode without TiN and electrolyte with silicate,

(7) 3: anode with TiO.sub.2 and electrolyte with silicate,

(8) 4: anode with TiN and electrolyte with silicate;

(9) FIG. 4: cumulative mass losses during cycling of the 8 Ah NiZn elements in FIG. 3,

(10) 1: anode with TiN and silicate-free electrolyte,

(11) 2: anode without TiN and electrolyte with silicate,

(12) 3: anode with TiO.sub.2 and electrolyte with silicate,

(13) 4: anode with TiN and electrolyte with silicate;

(14) FIG. 5: measured capacity curves during discharge of the 8 Ah NiZn elements during cycling (8 A charge in 1 hour, discharge 8 A, 1V, 100% depth of discharge),

(15) 5: anode without TiN and electrolyte with silicate,

(16) 6: anode with TiN and silicate-free electrolyte,

(17) 7: anode with TiN and electrolyte with silicate;

(18) FIG. 6: cumulative mass losses during cycling of the 8 Ah NiZn elements in FIG. 5,

(19) 5: anode without TiN and electrolyte with silicate,

(20) 6: anode with TiN and silicate-free electrolyte,

(21) 7: anode with TiN and electrolyte with silicate; and

(22) FIG. 7: measured capacity curves during discharge of the 8 Ah NiZn elements during cycling (8 A charge in 1 hour, discharge 8 A, 1 V, 100% depth of discharge).

(23) 8: anode with TiN and silicate-free electrolyte,

(24) 9: anode with TiN and electrolyte with 0.45 M silicate,

(25) 10: anode with TiN and electrolyte with 0.85 M silicate.

DETAILED DESCRIPTION OF THE INVENTION

(26) The zinc anode battery is made according to the methods known to the person skilled in the art. The electrodes are in the form of plates, consisting of a current collector and an active mass. The active mass can incorporate compounds that are not involved in the electrochemical reaction, but will, for example, perform an electronic conduction function or form a mechanical bond between the active substance and the collector, or carry out a retention function of a product of the electrochemical reaction.

(27) In the case of the zinc anode, in addition to polymers such as PTFE, polyethylene glycol, polyvinyl alcohol, styrene-butadiene rubber, carboxymethyl cellulose, etc., which act as a binder for the electrode constituents, calcium hydroxide can be used to limit the formation of soluble zincates, as well as conductive ceramics as described in patent FR 2 788 887.

(28) A separator isolates the anode and cathode compartments: it is a felt, a porous or ion-exchange membrane, felt and porous membrane can be combined.

(29) Depending on the manufacturing method, the zinc anode battery may be in the form of a prism, cylinder or in the form of a filter press cell if the battery is of the bipolar type.

(30) The present invention is in particular, and without limitation, applicable to the manufacture of a nickel-zinc battery designed according to the main characteristics described below.

(31) In accordance with a preferred method of manufacture, a nickel-zinc battery is produced by combining a plasticized type nickel electrode and a zinc electrode also containing an organic binder.

(32) 1) Nickel Electrode

(33) The nickel electrode can be advantageously produced by using a very fine-pored nickel metal foam. Some of these foams are referred to as “battery grade”. Such foams are supplied by, for example, Sumitomo Electric (Japan) and Corun (China). The foam thickness is chosen according to the desired surface capacity of the nickel electrode: it is generally between 1.2 and 2 mm, but it can be rolled to precisely adjust the thickness to the desired surface capacity.

(34) The active material consists of nickel hydroxide which preferably contains co-precipitated zinc and cobalt. The particles are preferably spherical or spheroidal in shape to increase the volume capacity. They can be coated with cobalt oxide and cobalt hydroxide which, while the battery is being made, are converted into conductive cobalt oxy-hydroxide (Oshitani et al. J. Electrochem. Soc. 1989 136, 6, 1590).

(35) One can also add conductive additives (fibres, metal powders) to the nickel hydroxide powder.

(36) A paste is prepared by mixing the constituents described above with permuted water to which carboxymethyl cellulose has been added. A polymeric binder, such as PTFE, may be added at this stage of manufacture as a suspension, or later after filling or covering the manifold, especially nickel foam, with the active paste by dipping it into the suspension.

(37) The nickel foam is filled for laboratory purpose using a doctor blade that is used to penetrate the paste into the thickness of the substrate, and for industrial purpose by injecting the paste under pressure into the foam.

(38) After drying, the electrode is compressed to ensure cohesion between the manifold, active material and additives and cut to the desired dimensions.

(39) 2) Zinc Electrode

(40) The zinc electrode collector can be in the form of perforated metal strip, woven wire cloth, expanded metal strip or metal foam. Copper may be preferred due to its conductivity, but must be covered with a protective metal: zinc, tin, or alloy.

(41) The zinc electrode is manufactured by first preparing a paste made of zinc oxide and various additives: electronic conductors: metallic zinc, carbon, copper, conductive ceramics . . . , in the form of powders or filaments. anti-corrosion agents: indium, bismuth, etc. compounds that react with zincates: calcium hydroxide, barium hydroxide, etc.

(42) The liquid phase is permuted water or alcohol, to which carboxymethyl cellulose has been added as a binder and thickener. Other binders can be added such as those mentioned in patent EP 1 715 536.

(43) Based on the technique chosen, it is possible to prepare a high-viscosity paste which can be applied by pressure to both sides of the metal support to form a “sandwich” structure, or to prepare a medium-viscosity paste in which the collector is immersed and then taken out while removing the excess paste to adjust the thickness of the electrode using a doctor blade, an operation which is followed by drying. Finally, it is possible to use a dry powder mixed with a binder and compress it on the metal support to form the electrode.

(44) 3) The Electrolyte

(45) The electrolyte used, to which the silicates are added, is preferably a concentrated alkaline solution whose molarity is between 4 and 12 M (4 and 12 mol/l) of hydroxyl anions. The alkalinity is provided by potassium, sodium and lithium hydroxides, used individually or as a mixture.

(46) The quantity of silicates added to the electrolyte, expressed as mass of silica per litre, is between 0.15 and 80 g/l and preferably between 20 and 60 g/l. The electrolyte may also contain zincates in varying proportions.

(47) The silicates are in particular provided by silica, fumed silica, silica fume or potassium and sodium silicates such as potassium and sodium di-silicates, potassium and sodium meta-silicates, potassium tetra-silicate and sodium ortho-silicate. These silicates can be used by themselves or as mixtures.

(48) The electrolyte may also contain borates, phosphates, and fluorides, used by themselves or in mixtures, as described for example in patent U.S. Pat. No. 5,215,836.

(49) Oxygen Recombination Processes

(50) In order to explain the approach that has been followed to arrive at the present invention, first the analysis of the loss of mass and the recombination of oxygen of NiZn elements will be described. Charging of the nickel electrodes is characterised by a parasitic oxygen change reaction, which takes place a little before reaching full charge of the nickel electrodes. In order to limit the drying out of the batteries resulting from expulsion of oxygen from the battery via the sealing valve, it is desirable to recombine the oxygen inside the battery in order to limit the drop in capacity. Oxygen can be recombined on the surface of the zinc electrode in two ways:

(51) (1) chemical oxidation expressed by the reaction 2Zn+O.sub.2+2H.sub.2O.fwdarw.2Zn(OH).sub.2, and

(52) (2) catalytic reduction on a conductive area, such as zinc metal or titanium nitride, expressed by the reactions:

(53) O.sub.2+2H.sub.2O+4e−.fwdarw.4OH— and/or O.sub.2+H.sub.2O+2e−.fwdarw.HO.sub.2.sup.−+OH.sup.− (while charging only).

(54) In order for these two reaction mechanisms to be efficient, they require triple phase contact points, solid-liquid-gas, where gas is the oxygen on the surface of the zinc electrodes. It is therefore essential to access oxygen on the surface of the zinc electrodes to ensure recombination.

(55) Different barriers can limit access of oxygen at the surface of the zinc anodes. Classified from the most restrictive to the least restrictive, their particularity is that they are of different physical states: liquid phase is the electrolyte at this surface; solid phase is the porous separator placed on the surface of the zinc electrode; gaseous phase consists of the hydrogen generated on the surface of the said anode. This evolution of hydrogen represents a indirect hindrance by increasing the amount of electrolyte at the interface when the electrolyte level is low.

(56) Two NiZn elements A and B with a nominal capacity of 4.6 Ah are made according to the general description given above and using identical electrode and electrolyte compositions. The electrolyte used is a concentrated alkaline solution of KOH with a molarity of 10 M hydroxyl anions without the addition of silicates.

(57) Titanium nitride is homogeneously introduced into the active mass of the zinc anode for element A. For element B, the same amount of TiN is preferentially deposited on the surface of the zinc electrodes. The elements are sealed, fitted with a valve which opens at pressures above 2 bar.

(58) Elements A and B are charged at C/10 between 100% and 180% state of charge and then discharged at C/5 with a cut-off voltage of 1.2 V, the example at 180% charge is given in Table 1 and FIG. 1. Mass losses (ΔM) of the elements are measured and a gas recombination rate (GCR) is calculated by converting the ampere-hour difference between the charge and the discharge into a mass of potentially lost water, Table 1 given below.

(59) For element A, the gas recombination rate decreases as the state of charge increases. This behaviour is not verified for element B, which is characterised by an overall mass loss that is twice as low and a gas recombination rate that increases at 180% state of charge compared to that calculated at 140%.

(60) This result corresponds to an increased catalytic activity of TiN with respect to oxygen, according to process (2), which we have sought to demonstrate here by showing accentuation of the phenomenon when the TiN is mainly located on the surface of the anode, therefore in greater quantity on its surface, compared with the case where the same overall quantity is distributed throughout the anode volume.

(61) The present invention is intended to enhance the catalytic activity of TiN on the recombination of oxygen in order to repel passivation mechanisms of the negative electrode and the drying mechanisms of the zinc anode elements.

(62) TABLE-US-00001 TABLE 1 Element Charge Charge Discharge Disch. ΔM TRG NiZn (%) (Ah) (Ah) (%) (g) (%) A 100% 4.603 4.497 97.7% 0.01 72% (TiN in the 120% 5.524 4.953 107.7% 0.12 38% thickness) 140% 6.444 4.999 108.6% 0.37 24% 180% 8.285 5.066 110.1% 0.87 20% ΣΔM: 1.37 B 100% 4 601 4.469 97.1% 0.00 100%  (TiN on 120% 5.524 4.992 108.5% 0.05 72% surfaces) 140% 6.444 5.100 110.8% 0.24 47% 180% 8.282 5.085 110.5% 0.33 69% ΣΔM: 0.62

(63) Seeking to define new methods of realisation that can resist passivation mechanism of the negative electrode and drying mechanism of the cell according to the present invention, its author carried out a comparative experiment conducted on identical 3 Ah NiZn C and D elements—excluding the electrolyte—realised according to the general description previously provided. Their zinc anodes contain TiN.

(64) The electrolyte used is a concentrated alkaline solution whose molarity is 10 M hydroxyl anions for element C. The electrolyte is modified for element D with an addition of 0.82 M silicates, provided by silica.

(65) Internal pressure of the elements is measured using a 0-10 bar pressure sensor and the elements are fitted with a safety valve which opens at pressures above approx. 0.85 bar.

(66) The 2 elements are initially formed by 3 cycles with charges at C/10 regime for 12 hours and discharges at C/5 regime up to a discharge cut-off voltage of 1.2V.

(67) Voltage and pressure of the C and D elements are given for the 3 cycles in FIG. 2.

(68) Pressure measurement of element D containing the silicate electrolyte is characterised by the absence of valve openings. Conversely, the internal pressure of element C, not containing silicate additions in the electrolyte, is characterised by valve openings, particularly in regions of the start of charge involving preferably an evolution of hydrogen at the zinc electrode. This result shows that the presence of silicates in the electrolyte reduces the formation of hydrogen and improves the recombination of oxygen.

(69) Without silicates, the low hydrogen overvoltage of TiN generates a limited production of hydrogen at the heart of the porous anode. The electrolyte contained in the porosity of the zinc electrodes is partially forced towards the electrode interface. Thickness of the electrolyte film at the electrode interface then increases, limiting the access of oxygen to the catalytic recombination areas of the TiN. Thus, recombination preferentially takes place on the Zn metal through the chemical recombination process (1), resulting in the drying and passivation phenomena by the formation of Zn (OH).sub.2, leading to a progressive drop in capacity.

(70) With silicates, the pressure measurement shows significant reduction in the evolution of hydrogen. Analysis of the phenomenon is used to conceive the hypothesis, such that it does not limit the scope of the invention stated here, according to which, by getting deposited on the zinc electrode's surface, the silicates decouple the TiN and the Zn metal, forming an insulating interface between the two, which makes it possible to reduce the evolution of hydrogen. Oxygen's access to TiN is thus improved, which enables recombination to take place preferentially according to the catalytic process (2), which does not result in the drying and passivation phenomena.

(71) In order to continue and illustrate highlighting the operation and definition of this invention, the NiZn elements 1, 2, 3 and 4 with a nominal 8 Ah capacity are identically produced, according to the general description given above.

(72) The elements are mounted with a 0.2 bar low pressure valve. The nickel hydroxide used for the cathodes of elements 1 to 4 contains 5% cobalt. The electrolyte used is a concentrated alkaline solution with a molarity of 10M hydroxyl anions for element 1. The electrolyte is modified for elements 2, 3 and 4 with an addition of silicates. The parameters that differentiate elements 1 to 4 are summarised in Table 2, below.

(73) TABLE-US-00002 TABLE 2 Characteristics of NiZn batteries, nominal capacity 8 Ah, charge 8 A 1 h, 100% discharge 8 A 1 V cycles. Silicates Co content in Number of cycles Element TiN in the in the Ni(OH).sub.2 of the at 90% residual Max. number (battery) zinc anodes electrolyte cathodes capacity of cycles 5 No 0.45M 8% 500 500 2 No 0.75M 5% 770 830 3 No 0.75M 5% 770 900 (with TiO.sub.2) 1 Yes No 5% 1.120 1.330 6 Yes No 8% 1.200 1.300 8 Yes No 8% 1.120 1.300 4 Yes 0.45M 5% 1.380 1.885 7 Yes 0.45M 8% 1.700 >1.840 9 Yes 0.45M 8% 1.940 2.640 10 Yes 0.85M 8% 1.740 2.680

(74) In element 3, titanium nitride is replaced by a titanium oxide compound.

(75) The batteries have been cycled at a constant current of 8 A, equivalent to the C regime, with a charge of one hour and a discharge that ends when the voltage reaches 1V.

(76) The discharged capacities and accumulated mass losses as a function of the number of cycles for batteries 1 to 4 are compared in FIGS. 3 and 4 respectively.

(77) It can be seen that the stability of the capacity of the batteries improves in the following sequence: Addition of silicate alone, batteries 2 and 3 (TiO.sub.2 does not have the same effect as TiN), Addition of TiN alone, battery 1 Addition of TiN and silicate, battery 4.

(78) The results are shown in Table 2. It can be seen that 90% of the initial capacity is maintained after 770, 770, 1,120 and 1,380 cycles for elements 2, 3, 1 and 4 respectively. After 90% of the residual capacity is passed, the capacities of the batteries drop rapidly except for 4 (TiN and silicates). Battery 4 (TiN and silicates) retains more than 75% of its initial capacity after 1,885 cycles, i.e. an improvement of 50% compared to battery 1, which retains 75% of its initial capacity after 1,260 cycles.

(79) Mass losses of batteries 2 (silicates without TiN) and 3 (silicates and TiO.sub.2) are the highest, suggesting insufficient oxygen recombination to limit the drying out of the batteries. Here, passivation of the zinc electrodes can be seen in accordance with the article by P. C. Foller indicating that for silica additions greater than 28-30 g/l, a silica deposit passivates the zinc surface. This deposit limits the recombination power of the zinc electrodes.

(80) In the context of the present invention, the author has also shown that the complexes formed between silicate and zincate ions in an alkaline medium, in particular even within porous zinc anodes, may have a stability that makes it possible to measure lower mobility, due to an increase in the steric effects of the zincates complexed by the silicates, than that of the smaller zincate ions by themselves. The limitation of mobility of the zincate ions by complexing with silicate ions is a parameter that can help to reduce the redistribution and densification phenomenon of zinc in the anodes.

(81) The formation of complexes between silicate and zincate ions in an alkaline medium, mentioned by several authors, has been described by Michel R. Anseau et al. (Inorg. Chem. 44, 8023-8032, 2005) in strongly alkaline media: zincates, in potash or soda solutions of 14 to 15 mol/l, react with monomeric, dimeric and cyclo-trimeric silicates to form very stable compounds.

(82) The mass losses of batteries 1 and 4 (with TiN) are significantly lower than those of batteries 2 and 3. It is interesting to note a different progressivity between these two batteries 1 (with TiN) and 4 (with TiN and silicates): from 0 to 900 cycles the mass loss increases very moderately and linearly in case of battery 4, whereas it accelerates from 300 cycles onwards in case of battery 1. This result is in line with an improvement in stability due to a decrease in densification of the zinc electrodes, as expected by the complexation of zincates with the silicates. between 900 and 1,260 for battery 1 and between 1,000 and 1,300 for battery 4, the mass loss increases sharply due to an increasingly significant evolution of oxygen at the end of charge. from 1,200 cycles onwards in case of battery 1, the mass loss becomes too great, resulting in a rapid drop in capacity due to the drying out of the cell and passivation of the electrodes. battery 4 shows a singular behaviour, characterised by a moderate overall loss of mass, with evolution of loss again decreasing beyond 1,300 cycles, in accordance with effective recombination of oxygen that sustainably limits its drying out and passivation of the electrodes.

(83) Thus, it can be seen that simple addition of titanium nitride to the anode, battery 1, or of silicates to the electrolyte, battery 2, provides satisfactory response to the stability of the zinc electrode, with suppression of dendritic formation and reduction in the densification of the zinc electrode.

(84) Addition of titanium nitride is, however, considerably more effective than the addition of silicates to the electrolyte. But this is a very significant improvement in operation that is measured during concomitant addition of titanium nitride to the zinc electrode and of silicates to the electrolyte, (battery 4), which corresponds to a greatly improved oxygen recombination power at the zinc electrodes, resisting the system drying out and zinc electrode passivation phenomena. Silicates provide a hitherto unidentified strengthening action of the catalytic reduction power of oxygen of a conductive ceramic such as titanium nitride.

(85) In the following comparison, NiZn 5, 6 and 7 batteries with a nominal 8 Ah capacity are made in the same way, following the general description given above.

(86) The elements are mounted with a 0.2 bar low pressure valve. The nickel hydroxide used for the cathodes of elements 5 to 7 contains 8% cobalt. Increasing the amount of cobalt increases the conductivity of the nickel hydroxide. The nickel electrode's charge is thus more efficient, with a decrease in the evolution of oxygen and thus a moderation of the cumulative mass losses.

(87) The electrolyte used is a concentrated alkaline solution with a molarity of 10M hydroxyl anions for element 6. The electrolyte is modified for elements 5 and 7 with significant addition of silicates. The anodes of element 5 do not contain TiN.

(88) The parameters that differentiate elements 5 to 7 are summarised in Table 2 above.

(89) The batteries 5 to 7 have been cycled at a constant current of 8A, equivalent to the C regime, with a charge of one hour and a discharge that ends when the voltage reaches 1V.

(90) The discharged capacities and accumulated mass losses as a function of the number of cycles for batteries 5 to 7 are compared in FIGS. 5 and 6 respectively.

(91) The results are shown in Table 2 above.

(92) Following the sequence without TiN and with silicate, battery 5, then with TiN and without silicate, battery 6, and finally with TiN and silicate, battery 7, the stability of the capacity of the batteries improves with a residual capacity at 90% of their initial capacity after 500, 1,200 and 1,700 cycles respectively, see Table 2. The number of cycles is lower for battery 5 (0.45M, i.e. 27 g/l of SiO.sub.2) than for batteries 2 and 3 (0.75M, i.e. 45 g/l of SiO.sub.2) suggesting a beneficial effect when adding silicates higher than 30 g/l expressed as SiO.sub.2,contrary to what is indicated by the state of the art which announces a drop in capacity by passivation following the precipitation of SiO.sub.2 or because of an excessively viscous electrolyte (article P. C. Foller).

(93) At 90% of the initial capacity, battery 7 shows an increase in the capacity's stability by 42% compared to battery 6. The evolution of mass losses of batteries 6 and 7 are similar to those of batteries 1 and 4, confirming the singular character of the oxygen's recombination power within batteries that combine titanium nitride in the zinc electrode and the addition of silicate in the electrolyte.

(94) Finally, NiZn elements 8, 9, and 10 with a nominal 8 Ah capacity are made in the same way, following the general description given above.

(95) The elements are fitted with a 0.2 bar low-pressure valve. The nickel hydroxide used for the cathodes of elements 8 to 10 is the same as that of elements 5 to 7 above. Elements 8 to 10 have zinc electrodes containing titanium nitride.

(96) Compared with elements 6 and 7, preparation of the active mass paste of the zinc electrode has been modified, without changing its chemical composition, by a procedure which increases the homogeneity of the constituents of this active mass.

(97) The electrolyte used is a concentrated alkaline solution with a molarity of 10M hydroxyl anions for element 8. The electrolyte is modified for elements 9 and 10 with significant additions of silicates at 0.45M and 0.85M respectively.

(98) The batteries 8 to 10 have been cycled at a constant current of 8 A, equivalent to the C regime, with a charge of one hour and a discharge that ends when the voltage reaches 1V.

(99) The discharged capacities as a function of the number of cycles performed for batteries 8 to 10 are compared in FIG. 7.

(100) The results are also shown in Table 2 above.

(101) Battery 8 (with TiN and without silicates) only delivers 70% of its initial capacity after 1,300 cycles, while battery 9 (with TiN and silicates at 0.45 M) still retains 70% of its initial capacity after 2,640 cycles, i.e. an increase of 103%. Battery 10 (with TiN and 0.85 M silicates) still retains 70% of its initial capacity after 2,680 cycles, i.e. an increase of 106% compared to battery 8.

(102) These various results show that the effect obtained by using titanium nitride in the anode and silicates in the electrolyte at the same time can be spectacular, with an increase of more than 100% in the number of cycles.

(103) They also reflect, as expected by the author of the present invention, a decrease in densification and changes in the shape of the zinc electrodes, linked to the formation of zincate-silicate complexes, which restricts their average free movement in the electrolyte, including within the anodes, and consequently reduces the redistribution of zinc.

(104) In addition, the combination of a conductive ceramic, such as TiN, and silicates modifies the recombination power of the zinc electrodes with respect to oxygen, promoting the recombination of oxygen according to the catalytic process (2) described above.

(105) The silicates no longer passivate the surface of the zinc electrodes, as observed in the absence of TiN. These phenomena limit the drying out of the batteries and significantly increase the cycle life.

(106) These are therefore new effects measured when combining a conductive ceramic, such as TiN, in the zinc anode and silicates in the electrolyte that are the subject of the present invention.

(107) Naturally, and as it largely results from what is given above, the invention is not limited to the particular methods of realisation that have been described by way of illustration and demonstration. The invention is not limited to the modes of realisation that have been provided, but embraces all the variants thereof.