Alkaline electrochemical generator with zinc anode

Abstract

The present invention relates to electrochemical generators with zinc anodes and in particular storage batteries thereof. The present invention particularly relates to secondary generators with zinc anodes. More specifically, the present invention relates to electrochemical generators having zinc electrodes with a molar concentration of hydroxyl anions between 4M and 15M and an electrolyte which is an alkaline aqueous solution containing a) one or more wetting agents with an electrolyte concentration between 0.1g / l and 50g / l, and b) one or more antifoaming agents with an electrolyte concentration between 10mg and 1000mg per kg of electrolyte, the special electrochemical generators being those in which the electrolyte of the electrochemical generator contains an ionic wetting agent which is bis(2-ethylhexyl)phosphate, and / or the electrolyte contains one or more non-ionic wetting agents selected from alkyl polyglucosides and polyethylene glycols and alkylphenol ethers, and / or the antifoaming agent is selected from polyorganosiloxanes. The present invention also relates to a method for producing such a generator. [Selection diagram] Figure 3

Description

[Technical field]

[0001] The present invention relates to the field of alkaline electrochemical generators, and in particular to the field of storage batteries. The present invention relates to secondary generators with zinc anodes, in particular with zinc anodes such as nickel-zinc, zinc-manganese dioxide, silver-zinc, zinc-air, as well as fully soluble or partially soluble cathodes that obtain high cycle numbers with zinc electrodes, such as zinc-iodine, zinc-bromine, zinc-ferricyanide, zinc-manganese oxide. [Background technology]

[0002] Zinc is of particular interest as an anode material for electrochemical generators due to its energy properties (820 Ah / kg, 5845 Ah / I), electronegativity (1.65 V), low cost and ease of recycling. By comparison, the theoretical mass energies of nickel-zinc and zinc-air combinations are 334 Wh / kg and 1320 Wh / kg, respectively. In practice, the mass energy of a nickel-zinc battery can reach 80 Wh / kg in prismatic form, which is 2-3 times the mass energy of a lead-acid battery.

[0003] However, although zinc is widely used in alkaline and Leclanché batteries, its use is limited to a few cycles and is not used in industrial alkaline batteries, except for silver-zinc batteries, which are primarily used in military applications, and the more recent emergence of industrial nickel-zinc batteries.

[0004] Zinc is soluble as zincate in alkaline media and readily forms dendritic growths which can cause shorting of the counter electrode during charging of zinc anode batteries. Furthermore, the area of ​​the negative electrode where zinc is deposited changes during charge-discharge cycles. Thus, a densification phenomenon occurs that reduces the porosity of the electrode and, as a result, its ability to operate at current densities corresponding to the practical use of the battery. Other factors, such as the deposition of zinc oxide, which forms a layer that passivates and reduces the active surface of the electrode, have a detrimental effect on the zinc anode.

[0005] Much research has been carried out to understand the mechanisms of zinc precipitation and dissolution in alkaline media, and many patents have been filed proposing different solutions. - The majority of patents focus on the use of additives added to the electrolyte or mixed into the anode active material to reduce the solubility of the zincate. - Also described is a mechanical method that allows the circulation of the electrolyte alone or of zinc electrodes dispersed in the electrolyte to ensure homogeneous zinc deposition and avoid dendritic growth; - the use of a pulsed current, with or without polarity reversal, making it possible to at least partially dissolve the dendrites; and the use of separators that limit the diffusion of zincate ions from the anode to the cathode or inhibit their formation. These are, for example, multi-layer microporous separators or exchange membranes.

[0006] These various techniques, implemented alone or in combination, provide only part of the solution and, in some cases, increase the internal resistance, the cost of the battery or are complicated to implement. Moreover, some methods recommend the addition of lead or cadmium to the anode active material, which is largely unacceptable for obvious pollution reasons.

[0007] Progress has been made by adding additives to potassium-based electrolytes, such as the small nickel-zinc (NiZn) cylindrical accumulators available on the market, but the number of cycles achieved does not meet the needs of industrial and stationary batteries, which must ensure at least 1000 and 2000 deep charge-discharge cycles, respectively, corresponding to a discharge depth of at least 80%.

[0008] The first notable advance is the addition of a conductive ceramic, preferably titanium nitride (TiN), to the zinc electrode, an innovation described in patent FR 2 788 887 (filed January 27, 1999 by the company SCPS) (Patent Document 1), which allows more than 1000 cycles at a discharge depth of 80%. The second notable advance is the addition of SiO2 to the electrolyte, an innovation described in patent FR 3 099 851 (filed August 9, 2019 by the company Sunergy) (Patent Document 2), which allows more than 2000 cycles at a discharge depth of 80%.

[0009] The capacity loss of NiZn accumulators during cycling has historically been mainly correlated with the formation of zinc dendrites that eventually form short circuits. This dendrite formation was eliminated by the SCPC work related to the aforementioned patent FR 2 788 887, allowing more than 1000 cycles. The capacity loss of NiZn accumulators was then caused by redistribution, densification of the active material, drying and passivation of the zinc electrode. A new solution to these stability limitations of NiZn accumulators was shown by the Sunergy work related to the aforementioned patent FR 3 099 851, allowing more than 2000 cycles. With the improvement of the stability of the zinc electrode, the capacity loss became correlated with other parameters, such as the stability of the hydrophilicity of the membrane, in addition to the parameters already mentioned.

[0010] The aim of the present invention is to provide a new solution to the limited multi-cycle capability of batteries based on zinc electrodes by stabilizing the hydrophilic properties of the membrane while maintaining the progress that has made it possible to achieve more than 2000 cycles.

[0011] To achieve this, the test involves adding a wetting agent to the electrolyte in order to improve the solid-liquid contact surface of the active material of the nickel-zinc electrode and prevent the degradation of the hydrophilic properties of the membrane. The hypothesis is that some of the wetting agent dissolved or suspended in the electrolyte will eventually deposit in the pores of the membrane, allowing it to retain its hydrophilic properties for longer.

[0012] A survey of the state of the art in zinc anode systems reveals several patents and studies that refer to the use of wetting agents. For example, Rossler et al. in patent US 4 195 120, filed November 3, 1978, state that hydrogen evolution in batteries with zinc anodes is reduced or eliminated by incorporating into the cell a wetting agent, which is an ethylene oxide polymer of an alkyl phosphate ester. The wetting agent is added directly or during wetting of the anode with the electrolyte so that the wetting agent is adsorbed on the surface of the zinc anode material, thereby preventing hydrogen evolution. The wetting agent is preferably present in the cell in an amount of 0.001% to 5% by weight based on the zinc content of the cell. The wetting agents described herein are soluble or dispersible in water and alkaline electrolyte. The wetting agent is added directly to the zinc electrode or indirectly to the electrolyte or cathode. The wetting agent can be deposited on the surface of the zinc through the electrolyte or through a membrane through the cathode and deposited on the zinc.

[0013] In Chinese patent application CN111048846 (Patent Document 4) filed on December 18, 2019, one wetting agent selected from sodium lauryl sulfate, sodium dodecylbenzenesulfonate, cetyltrimethylammonium bromide, octadecyltrimethylammonium chloride, and tetrabutylammonium bromide, one or more compounds selected from tetrabutylammonium hydroxide and tetrabutylammonium chloride, and one perfluorosurfactant are used to reduce the usual limitations of short circuit, dissolution, deformation, densification, zinc electrode passivation, and hydrogen generation, thereby improving the ability to increase the number of charge and discharge cycles to 100 to 600 cycles.

[0014] In a 1998 paper by JiLing Zhu et al. (Journal of Power Sources 72 1998 231-235), the electrochemical effect of different types of perfluorinated ionic wetting agents, such as the hydrocarbon chain wetting agent CTAB, on the behavior of zinc, is mentioned. The results show that these agents can be used as substitutes for mercury to reduce the corrosion of zinc batteries. It is also shown that the deposition of zinc is improved to a certain extent in the presence of these agents. The morphology of the electrodeposited zinc shows that these agents lead to a more uniform and dense deposit, which in turn reduces dendritic growth. FC-170C and CTAB are the most effective inhibitors. These ionic wetting agents remain attached to the zinc during the strong polarization associated with hydrogen evolution, whereas non-ionic wetting agents do not. Cationic wetting agents are adsorbed due to electrostatic attraction between the polar groups of the molecule and the zinc electrode surface, so that the rate of hydrogen evolution increases more slowly in the presence of FC-135 or CTAB when the zinc electrode potential is less than -1.80 V. The potential difference between the onset of deposition and the maximum of the cathodic current indicates that the deposition of zinc is inhibited to some extent in the presence of wetting agents. This is because the wetting agents adsorb on the surface of the zinc electrode and form a layer that has an inhibitory effect on the electroreduction process of zincate ions. Thus, these wetting agents can slow down the rate of zinc deposition from the zincate during the charging of the electrode and suppress dendritic growth.

[0015] A 2015 paper by MA Deyab (Journal of Power Sources 292 (2015) 66-71) (Non-Patent Document 2) mentions the effect of polyoxyethylene (40) nonylphenyl ether as a non-ionic surfactant (PNE) as a corrosion inhibitor in alkaline electrolyte (7.0M KOH).

[0016] The state of the art research which refers to the addition of wetting agents is all related to the study of reducing hydrogen evolution associated with zinc corrosion. [Prior art documents] [Patent documents]

[0017] [Patent Document 1] French Patent No. 2788887 [Patent Document 2] French Patent No. 3099851 [Patent Document 3] U.S. Pat. No. 4,195,120 [Patent Document 4] China Patent Application Publication No. 111048846 [Non-patent literature]

[0018] [Non-Patent Document 1] JiLing Zhu et al.(Journal of Power Sources 72 1998 231-235) [Non-Patent Document 2] MA Deyab(Journal of Power Sources 292(2015) 66-71) Summary of the Invention [Problem to be solved by the invention]

[0019] SUMMARY OF THE PRESENT EMBODIMENT It is an object of the present invention to provide a rechargeable alkaline electrochemical generator having a zinc anode, which allows for improved battery capacity stability and extended cycle life. This goal is achieved, inter alia, by enhancing and stabilizing the hydrophilicity of the membrane, thereby lowering the surface tension and improving the contact of the electrolyte to the solid surface. [Means for solving the problem]

[0020] More specifically, the present invention relates to an alkaline electrochemical generator having a zinc anode according to the following statement 1: 1. An alkaline electrochemical generator having a zinc anode with an electrolyte that is an aqueous alkaline solution having a molar concentration of hydroxyl anion between 4M and 15M; a) one or more wetting agents having an electrolyte concentration of 0.1 g / l to 50 g / l, and b) An electrochemical generator containing one or more types of defoaming agent in an amount of 10 mg to 1000 mg per 1 kg of electrolyte.

[0021] Advantageous features of the alkaline electrochemical generator having the zinc anode of statement 1 above are given in statements 2 to 11 below. 2. An alkaline electrochemical generator having a zinc anode according to statement 1, comprising one or more ionic wetting agents and one or more non-ionic wetting agents.

[0022] 3. An alkaline electrochemical generator having a zinc anode according to statement 1 or 2 which contains an ionic wetting agent called bis(2-ethylhexyl) phosphate.

[0023] 4. An alkaline electrochemical generator having a zinc anode according to any one of claims 1 to 3, wherein the electrolyte contains one or more non-ionic wetting agents selected from alkyl polyglucosides and polyethylene glycols and alkyl phenol ethers, in particular octylphenol ethers.

[0024] 5. An alkaline electrochemical generator having a zinc anode according to any one of statements 1 to 4, wherein the antifoaming agent is selected from polyorganosiloxanes.

[0025] 6. An alkaline electrochemical generator having a zinc anode according to any one of statements 1 to 5, in which the molarity of the alkaline solution is 7 to 12 M.

[0026] 7. An alkaline electrochemical generator having a zinc anode according to any one of claims 1 to 6, wherein the concentration of one or more wetting agents in the electrolyte is between 1 g / l and 25 g / l.

[0027] 8. An alkaline electrochemical generator having a zinc anode according to any one of claims 1 to 7, wherein the concentration of the antifoaming agent per 1 kg of electrolyte is 100 mg to 500 mg.

[0028] 9. An alkaline electrochemical generator having a zinc anode according to any one of statements 1 to 8, wherein the electrolyte further comprises a silicate.

[0029] 10. An alkaline electrochemical generator having a zinc anode according to any one of statements 1 to 9, wherein the electrolyte further comprises a zincate salt.

[0030] 11. An alkaline electrochemical generator having a zinc anode according to any one of statements 1 to 10, wherein the electrolyte further comprises a borate, a phosphate and / or a fluoride.

[0031] According to another aspect, the present invention also relates to a method for producing an alkaline electrochemical generator having a zinc anode as described above, according to the following description 12. 12. A method for preparing an alkaline electrochemical generator having a zinc anode according to any one of statements 1 to 11, comprising the step of introducing lithium hydroxide, sodium hydroxide and / or potassium hydroxide during preparation of the electrolyte. Effect of the Invention

[0032] Further characteristics and advantages of the invention are explained in detail in the following description with reference to the attached schematic representation of the drawings. [Brief description of the drawings]

[0033] [Figure 1] Capacity curve during discharge for NiZn test example, cycle 8Ah, 8A 1 ​​hour charge, 8A 1V discharge, discharge depth 100%. [Diagram 2] Capacity curve during discharge for NiZn test example, cycle 8Ah, 8A 1 ​​hour charge, 8A 1V discharge, discharge depth 100%. [Diagram 3] Capacity curve during discharge for NiZn test example, cycle 8Ah, 8A 1 ​​hour charge, 8A 1V discharge, discharge depth 100%. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0034] <Detailed Description of the Invention> Zinc anode storage batteries are manufactured by methods known to those skilled in the art. The electrodes are in the form of plates made of current collectors and active materials. The active materials can incorporate compounds that do not participate in the electrochemical reaction but provide, for example, the function of electronic conduction, the mechanical connection between the active material and the current collector, and also the function of retaining the products of the electrochemical reaction.

[0035] In the case of zinc anodes, polymers that act as binders for the components of the electrode, such as PTFE, polyethylene glycol, polyvinyl alcohol, styrene butadiene polymers, carboxymethylcellulose, as well as calcium hydroxide, which limits the formation of soluble zincates, and conductive ceramics, such as those described in patent FR 2 788 887, can be used.

[0036] The separator separates the anode and cathode compartments. The separator can be a felt, a porous membrane, an ion exchange membrane, or a combination of a felt and a porous membrane. The membrane is generally a hydrophobic polymer membrane that is modified to be hydrophilic by the addition of one or more wetting agents.

[0037] Depending on the method of manufacture, zinc anode batteries can be prismatic, cylindrical, or, if the battery is of bipolar type, can take the form of a filter press type cell.

[0038] The invention is particularly applicable to the manufacture of nickel-zinc storage batteries designed according to the main characteristics described below. According to a preferred embodiment, a nickel-zinc accumulator battery is manufactured by combining a nickel electrode of the plasticized type with a zinc electrode also containing an organic binder.

[0039] 1) Nickel electrode Nickel electrodes are advantageously manufactured using nickel metal foams with very fine pores as the current collector. Some of these foams are designated as "battery grade". Suppliers include Sumitomo Electric (Japan) and Corun (China). The thickness of the foam is selected according to the desired surface capacity of the nickel electrode. The thickness is typically 1.2-2 mm, but can be layered to precisely adjust to the desired surface capacity.

[0040] The active material consists of nickel hydroxide, preferably with coprecipitated zinc and cobalt. The particles are preferably spherical or spheroidal in shape to increase the volumetric capacity. The particles may be coated with cobalt oxide and hydroxide particles which, upon formation of the storage battery, are converted to cobalt oxyhydroxide, which has electrical conductivity (Oshitani et al. J. Electrochem. Soc. 1989 136, 6, 1590).

[0041] Conductive additives (fibers, metal powders) can also be added to the nickel hydroxide powder. The paste is prepared by mixing the above mentioned components with deionized water to which carboxymethyl cellulose has been added. A polymer binder such as PTFE may be added in the form of a suspension at this stage of the manufacture or may be added after the current collector, particularly the nickel foam, has been filled with the active paste by immersion in the suspension.

[0042] Filling of nickel foam can be done in the laboratory by penetrating the paste into the thickness of the support using a scraper, or in the industrial stage by injecting the paste into the foam under pressure.

[0043] After drying, the electrode is compressed to ensure cohesion of the current collector, active material and additives, and cut to the desired size.

[0044] 2) Zinc electrode The zinc electrode current collector can be in the form of a perforated metal foil, a woven fabric, an expanded foil, or a metal foam. Copper is preferred for its electrical conductivity, but must be coated with a protective metal such as zinc, tin, or an alloy.

[0045] The zinc electrodes are manufactured in advance by preparing a paste of zinc oxide with various additives, including: electronic conductors such as metallic zinc in powder or filament form, carbon, copper, conductive ceramics, etc. Corrosion inhibitors such as indium and bismuth, These include compounds that react with zincates such as calcium hydroxide and barium hydroxide.

[0046] The liquid phase is deionized water or alcohol with the addition of carboxymethylcellulose as binder and thickener. Other binders, such as those described in patent application EP 1 715 536, can also be added.

[0047] Depending on the technology chosen, it is possible to produce a high viscosity paste that can be pressed onto both sides of a metal support to create a "sandwich" structure, or to produce a medium viscosity paste by dipping a current collector, removing excess paste and adjusting the electrode thickness with a scraper, followed by a drying operation. Finally, the dry powder mixed with a binder can be compressed onto a metal support to form an electrode.

[0048] 3) Electrolyte The electrolyte used is preferably a concentrated alkaline solution having a molar concentration of hydroxyl anion of 4 to 15 M (4 to 15 mol / L), preferably 4 to 12 M. Alkalinity is provided by potassium hydroxide, sodium hydroxide, lithium hydroxide, either individually or mixed.

[0049] The electrolyte may also contain zincates and silicates in various proportions, as described in patent FR 3 099 851. The electrolyte may also contain borates, phosphates, fluorides, either individually or as mixtures, as described in patent US 5 215 836.

[0050] According to the invention, the amount of wetting agent added to the electrolyte is between 0.1 g / l and 50 g / l, preferably between 1 g / l and 25 g / l, per liter of electrolyte, and the amount of antifoaming agent added to the electrolyte is between 10 mg and 1000 mg per kg of electrolyte.

[0051] The wetting agents are selected in particular from ionic wetting agents, non-ionic wetting agents based on bis(2-ethylhexyl)phosphate and alkylpolyglucosides, in particular from those of the Triton® brand. The antifoaming agents are selected from products based on polyorganosiloxane chemistry. These wetting agents and antifoaming agents can be used individually or in mixtures.

[0052] To clearly illustrate the function and definition of the invention, the NiZn test examples 1 to 11 with a nominal capacity of 8 Ah are manufactured in a similar manner according to the general description above. Test examples 1 to 4 have a zinc electrode with a different composition than test examples 5 to 11. All test examples have the same nickel electrode. The electrolyte used is a concentrated alkaline solution with a molar concentration of 10 M hydroxyl anion and addition of silicate, as described in patent FR 3 099 851. The electrolyte is modified for test examples 3, 4 and 8 to 11 by the addition of a wetting agent and an antifoaming agent. The test examples are equipped with a low pressure valve at 0.2 bar. The accumulator was charged for 1 hour at a constant current of 8 A, corresponding to the C rate, and discharged repeatedly, ending when the voltage reached 1 V. The parameters that distinguish test examples 1 to 11 and the number of cycles at which a capacity of more than 70% of the nominal capacity (Cn) was reached are summarized in table 1 below. [Table 1] Table 1: Characteristics of NiZn accumulator, nominal capacity 8 Ah, charging cycle 8A 1 ​​h, discharge to 100% 8A 1 ​​V, the symbol > indicates that the experiment is still in progress.

[0053] Example 1 (standard) NiZn test examples 1 to 4 with a nominal capacity of 8 Ah are produced in a similar manner according to the general description above. Test examples 1 to 4 have a zinc electrode of different composition than test examples 5 to 11. All test examples have the same nickel electrode. The electrolyte used is a concentrated alkaline solution of hydroxyl anion with a molar concentration of 10 M and the addition of silicate, as described in patent FR 3 099 851.

[0054] Two types of membranes, A and B, were used in these test examples. Membrane A is a 25 μm thick microporous polypropylene with added wetting agent. The air permeability of Membrane A is relatively high, exceeding 1000 Gurleys, and can limit oxygen recombination on the zinc electrode surface as a gas barrier for thermal stability. This membrane covers the zinc electrode with two overlapping layers of membrane, forming a 50 μm thick barrier. Membrane B is a 40 μm thick microporous polypropylene with added wetting agent. The air permeability of Membrane B is lower than Membrane A, ranging from 450 to 750 Gurleys. This wide range suggests that there is a defect in the homogeneity of the added wetting agent layer. Membrane B covers the surface of the zinc electrode with a single layer.

[0055] Test example 1 with membrane A showed 2240 cycles until the capacity was less than 70% of 8 Ah. Test example 2 with membrane B showed zero capacity after a cycle characterized by 12 hours of charging at C-rate / 10 and 3 discharges at C-rate / 5 until the battery voltage reached 1.2 V.

[0056] Test Example 3 is the same as Test Example 2 except that four wetting agents are added to the electrolyte, three of which are TRITON® BG-10, CG-110, and X-100, to which wetting agent bis(2-ethylhexyl)phosphate is added. The total concentration of the four wetting agents introduced into Test Example 2, resulting in Test Example 3, is 21.3 g / l. No antifoaming agent is added. The discharge capacity as a function of the number of cycles for storage batteries 1 and 3 is compared in Figure 1.

[0057] After the addition of the wetting agent, Example 2, which showed zero capacity, became Example 3, which achieved 2180 cycles, comparable to the results of Example 1. Thus, the wetting agent added to the electrolyte was able to deposit in situ on the membrane within the cell, enabling this previously incompatible membrane to function and achieve a similar lifetime as that obtained with Membrane A, which had no obvious defects in the wetting agent attachment. This first experiment therefore provided conclusive results on the ability of the wetting agent introduced into the electrolyte to anchor the membrane and restore its hydrophilicity.

[0058] However, it was found that there were two problems that were incompatible with sustained operation: first, a large amount of foam formed and could leak from the battery; second, the mass loss was obviously large. After 2000 cycles, the electrolyte mass of test example 1 was 8% and that of test example 3 was 44%. When the electrolyte mass loss exceeds about 20%, it is advisable to add water to avoid the capacity loss of the battery due to drying.

[0059] Example 2 (Invention) Test example 4, with a nominal capacity of 8 Ah, is produced in a similar manner according to the general description above. Test example 4 is the same as test example 1 with respect to the zinc-nickel electrode and membrane A. The electrolyte used is a concentrated alkaline solution of hydroxyl anion with a molar concentration of 10 M, with the addition of silicate, as described in patent FR 3 099 851, to which four wetting agents are added, three of which are TRITON® BG-10, CG-110 and X-100, plus the wetting agent bis(2-ethylhexyl)phosphate. The total concentration of the four wetting agents is 21.3 g / l. A polyorganosiloxane chemical antifoaming agent is added to the electrolyte in a proportion of 100 mg per kg of electrolyte. The accumulator is charged for 1 hour at a constant current of 8 A, corresponding to the C rate, and discharged repeatedly until the voltage reaches 1 V.

[0060] The discharge capacity as a function of the number of cycles of accumulators 1, 3 and 4 is compared in Figure 1. Although membrane A has no obvious wetting agent adhesion defects, the results obtained from more than 3500 cycles show that the wetting agent introduced into the electrolyte significantly improves the cycle life of this accumulator, since it has the ability to adhere to membrane A and maintain or restore its hydrophilicity. The addition of an antifoaming agent could significantly reduce the occurrence of foam. The mass loss after 2000 cycles was 21%, i.e. about three times that of test example 1, which was 8% without the use of a wetting agent. It was demonstrated that the larger mass loss could be compensated for by simply adding water, and that a higher number of cycles could be achieved by adding a wetting agent and an antifoaming agent to the electrolyte.

[0061] Example 3 (Standards and inventions) Test example 5 (reference) with a nominal capacity of 8 Ah is prepared in a similar manner according to the general description above. It is the same as test example 1 with regard to the nickel electrode and membrane A, but with a different composition of the zinc electrode. The electrolyte used is a concentrated alkaline solution of hydroxyl anion with a molar concentration of 10 M and the addition of silicate, as described in patent FR 3 099 851.

[0062] Test Example 6 (invention) is the same as Test Example 5, but four wetting agents are added to the electrolyte, three of which are TRITON® BG-10, CG-110, and X-100, to which wetting agent bis(2-ethylhexyl)phosphate is added. The total concentration of the four wetting agents is 21.3 g / l. A polyorganosiloxane chemical defoamer is added to the electrolyte at a rate of 100 mg per kg of electrolyte.

[0063] Test Example 7 (invention) is the same as Test Example 5, but with the addition of two wetting agents, namely TRITON® BG-10, CG-110, and X-100, to the electrolyte. The total concentration of the two wetting agents is 21.3 g / l. A polyorganosiloxane chemical defoamer is added to the electrolyte at a rate of 100 mg per kg of electrolyte.

[0064] These three types of batteries were repeatedly charged for 1 hour at a constant current of 8 A, which corresponds to the C rate, and discharged until the voltage reached 1 V. The discharge capacity as a function of the number of cycles for batteries 5, 6, and 7 is compared in Figure 2.

[0065] The addition of a wetting agent improved the number of cycles by 44% at 2500 cycles in Test Example 6 and 95% at 3400 cycles in Test Example 7 compared to Test Example 5. The addition of an antifoaming agent significantly reduced the formation of bubbles. The mass losses after 2000 cycles in Test Examples 5, 6 and 7 were 18%, 57% and 45%, respectively, which is about 2-3 times the rate without and with the addition of a wetting agent. The larger mass loss can be compensated for by simply adding water, demonstrating that a higher number of cycles can be achieved by adding a wetting agent and an antifoaming agent to the electrolyte.

[0066] Example 4 (Invention) To reduce foam formation associated with the addition of wetting agents, the amount of antifoam agent is doubled from 100 mg to 200 mg per kg of electrolyte. The amount of wetting agent is also reduced to reduce weight loss. Three new examples allow the evaluation of the effect of adding small amounts of wetting agent: 10.65 g / l, 7.1 g / l and 5.3 g / l for examples 8, 9 and 10 respectively.

[0067] Test Examples 8, 9 and 10 were the same as Test Example 5, except for the addition of a wetting agent and an antifoaming agent. These batteries were repeatedly charged for 1 hour at a constant current of 8 A, which corresponds to the C rate, and discharged until the voltage reached 1 V.

[0068] The number of cycles shown in Table 1 are 1740, 2120, 2220, 2520 and 2500 for Examples 5, 8, 9, 10 and 6, respectively, demonstrating that the wetting agent can be maintained at lower concentrations. This lower concentration and doubling of the mass of defoamer significantly reduced foam formation and mass loss, with mass losses of 11.8%, 9.3% and 13% for Examples 8, 9 and 10, respectively, after 2000 cycles.

[0069] Example 5 (Invention) Our analysis suggests that the stripping of the wetting agent from the membrane may be accelerated by strong oxygen recombination at the surface of the zinc electrode. In some cases, the heat release associated with this reaction can lead to a decrease in the accumulator voltage at the end of charge, which is commonly referred to in the state of the art as "delta V negativity."

[0070] To suppress this phenomenon, the structure of the zinc electrode in Test Example 11 was slightly modified.

[0071] Apart from this change, Example 11 is identical to Example 8 and similar to Examples 5 and 6, but with the addition of four wetting agents to the electrolyte, three of which are TRITON® BG-10, CG-110, and X-100, plus the wetting agent bis(2-ethylhexyl)phosphate. The total concentration of the four wetting agents in Example 11 is 10.65 g / l, which is half the concentration of Example 6. A polyorganosiloxane chemical defoamer was added to the electrolyte at a rate of 200 mg per kg of electrolyte, which is twice as much as in Example 6. The storage battery 11 was repeatedly charged for one hour at a constant current of 8 A, which corresponds to the C rate, and discharged until the voltage reached 1 V. The discharge capacity as a function of the number of cycles of the batteries 5, 6 and 11 is compared in FIG. This combination further improved the capacity stability of Example 11 as testing progressed beyond 3350 cycles. The mass losses after 2000 cycles for Examples 5, 6, and 11 were 18%, 57%, and 4%, respectively, indicating that the foam formation and mass loss associated with the addition of a wetting agent is improved, making the addition of water compatible with pushing to higher cycles.

[0072] Compared with the measurements of Example 8, the improved behavior of Example 11 (65% reduction in mass loss at 2000 cycles and over 55% increase in the number of cycles) revealed to the authors an enhanced stability with a reduction in the effects caused by oxygen recombination, i.e. an improved preservation of the wetting agent in both the electrolyte and the membrane.

[0073] Through extensive experimentation by the inventors of the present invention, it appears that the concentrations of the wetting agent and the defoamer can be advantageously selected within a wide range, of which only a limited number are shown in Table 1. The optimum concentrations depend, inter alia, on the properties of the membrane used, the alkalinity of the electrolyte, the composition and manufacture of the electrodes, the construction of the battery, and the cycling conditions. Thus, it has been shown that a total concentration of the wetting agent of about 0.1 to 50 g per liter of electrolyte and a total concentration of the defoamer of about 10 to 1000 mg per kg of electrolyte are advantageous.

[0074] At the zinc electrode, metallic zinc is formed during charging by the reduction of zincate ions present in solution. The zinc precipitate incorporates into its mass the particles present at the site of its nucleation.

[0075] Upon discharge of the zinc electrode, the zinc is converted to zincate ions and its surface is partially exposed and then covered again with the zinc oxide deposit characteristic of the discharged anodic material. During the exposure step, species deposited or trapped in the zinc are also released into the electrolyte and may be redeposited there or elsewhere, particularly on the membrane.

[0076] Such release into the electrolyte is advantageous when the affinity between zinc and the wetting agent is low, as is the case for non-ionic wetting agents, and it is believed that this mechanism provides the wetting agent to the membrane as it is in close proximity to the zinc electrode surface, stabilizing its hydrophilicity over time. This phenomenon is similar to the self-repair mechanism of membranes.

Claims

1. 1. An alkaline electrochemical generator having a zinc anode containing an electrolyte that is an aqueous alkaline solution having a molar concentration of hydroxyl anions of 4M to 15M, a) one or more wetting agents having an electrolyte concentration of 0.1 g / l to 50 g / l; and b) containing 10 mg to 1000 mg of one or more antifoaming agents per kg of electrolyte; It has the following characteristics: the electrolyte contains an ionic wetting agent which is bis(2-ethylhexyl)phosphate, and / or the electrolyte contains one or more non-ionic wetting agents selected from alkyl polyglucosides and polyethylene glycols and alkyl phenol ethers, and / or The antifoaming agents are selected from polyorganosiloxanes.

2. 10. An alkaline electrochemical generator having a zinc anode according to claim 1, comprising one or more ionic wetting agents and one or more non-ionic wetting agents.

3. 3. An alkaline electrochemical generator having a zinc anode according to claim 1 or 2, wherein the molarity of the alkaline solution is 7 to 12M.

4. 3. An alkaline electrochemical generator having a zinc anode according to claim 1, wherein the concentration of the one or more wetting agents in the electrolyte is from 1 g / l to 25 g / l.

5. 3. An alkaline electrochemical generator having a zinc anode according to claim 1 or 2, wherein the concentration of the antifoaming agent per 1 kg of electrolyte is 100 mg to 500 mg.

6. 3. The alkaline electrochemical generator having a zinc anode according to claim 1 or 2, wherein the electrolyte further comprises a silicate.

7. 3. The alkaline electrochemical generator having a zinc anode according to claim 1 or 2, wherein the electrolyte further comprises a zincate.

8. 3. The alkaline electrochemical generator having a zinc anode according to claim 1 or 2, wherein the electrolyte further comprises a borate, a phosphate and / or a fluoride.

9. 3. A method for preparing an alkaline electrochemical generator having a zinc anode according to claim 1 or 2, comprising the step of introducing lithium hydroxide, sodium hydroxide and / or potassium hydroxide during preparation of the electrolyte.

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