Method for preparing an electrochemical generator

Abstract

The invention relates to the field of electrochemical generators, particularly alkaline generators, and more especially to batteries. It is specifically related to secondary generators with a zinc anode. It relates in particular to a method for preparing an electrochemical generator, comprising the steps of: assembling a hydrophobic membrane with a cathode and an anode, and then adding an electrolyte comprising at least one wetting agent and at least one antifoaming agent. The invention also relates to an electrochemical generator obtained by the method according to the invention. Figure for the abstract: Figure 3

Description

Title of the invention: Process for preparing an electrochemical generator

[0001] The present invention relates to the field of electrochemical generators, in particular alkaline ones, and more particularly that of accumulators. It relates especially to secondary generators with a zinc anode such as nickel-zinc, zinc-manganese dioxide, silver-zinc, zinc-air, as well as those comprising a totally soluble or partially soluble cathode such as zinc-iodine, zinc-bromine, zinc-ferricyanide, zinc-manganese oxide and is intended to obtain with the zinc electrode a high number of cycles. State of the art

[0002] The energy characteristics of zinc (820 Ah / kg, 5845 Ah / l), its electronegativity (1.65V), its low cost and its ease of recycling, make it a particularly interesting anode material for electrochemical generators: thus, the theoretical mass energies of the nickel-zinc and zinc-air couples are respectively 334 Wh / kg and 1,320 Wh / kg. In practice, the mass energy of nickel-zinc accumulators can reach 80 Wh / kg in prismatic format, i.e. two to three times that of lead accumulators.

[0003] Zinc finds widespread use in alkaline batteries and Leclanché® batteries. For industrial-sized rechargeable alkaline batteries, the first applications were in the military field with silver-zinc batteries whose use is limited to a few cycles. More recently, small industrial cylindrical and prismatic nickel-zinc (NiZn) batteries have appeared on the market following progress made by adding additives to the electrolyte, which consists mainly of potash. However, the number of cycles obtained does not meet the usage needs of industrial batteries for stationary applications, which must at least ensure 2,000 deep charge and discharge cycles, corresponding to 80% depth of discharge and more.

[0004] Zinc is soluble in an alkaline medium in the form of zincates and easily forms, when charging zinc anode accumulators, dendritic growths which cause short circuits between electrodes of opposite polarities.

[0005] Furthermore, the areas of the negative electrode where zinc is deposited evolve during the charge and discharge cycles: thus, densification phenomena are observed which reduce the porosity of the electrode and consequently its capacity to operate at current densities corresponding to practical use of batteries. Other factors penalize the zinc anode, such as the precipitation of zinc oxide forming a layer that passivates and reduces the active surface area of ​​the electrode.

[0006] Much work has been carried out to understand the mechanisms of deposition and dissolution of zinc in an alkaline medium and a large number of patents proposing various solutions have been filed: - the use of additives added to the electrolyte or incorporated into the anodic active material, with the aim of reducing the solubility of zincates, constitutes the bulk of the patents; - mechanical processes are also described which allow the circulation of the electrolyte alone or a zinc electrode dispersed in the electrolyte, to avoid dendritic growth by ensuring a homogeneous zinc deposition; - the use of pulsed currents, without or with polarity inversion, allowing the dendrites to be at least partially dissolved; - finally, the use of separators which limit the formation or eliminate the diffusion of zincate ions from the anode to the cathode: these are, for example, microporous separators in multiple layers or exchange membranes.

[0007] These various techniques can be implemented in isolation or in combination, but they only provide part of the solution, and depending on the case increase the internal resistance, increase the cost of the battery, or are complex to implement. Furthermore, some recommend the addition of lead or cadmium to the active mass of the anode, which is hardly acceptable for obvious pollution reasons.

[0008] The loss of capacity of NiZn accumulators during cycling is historically correlated mainly with the formation of zinc dendrites which ultimately form a short circuit. This formation of dendrites was eliminated following work relating to patent FR 2 788 887 (filed on January 27, 1999 by the company SCPS) allowing the performance of more than 1,000 cycles at 80% depth of discharge and beyond. Subsequently, the loss of capacity of NiZn accumulators was induced by the redistribution, densification of the active material, drying and passivation of the zinc electrodes. A new response to these limits of the stability of NiZn accumulators has been demonstrated with the work relating to the patent application filed by the company Sunergy on August 9, 2019 and published under number FR 3 099 851, making it possible to exceed 2,000 cycles and more, at 100% depth of discharge.With the increase in the stability of the zinc electrode, the loss of capacity was associated with the stability of the hydrophilic properties of the membrane. A new answer to this limitation of the stability of the membrane of NiZn accumulators was demonstrated with the work relating to the patent application filed on February 17, 2022 under the number . FR 2 201 375 by the company Sunergy, allowing to exceed 3,000 cycles and beyond, at 100% depth of discharge.

[0009] In an alkaline accumulator, the membrane cannot be hydrophobic because it would block the passage of ions between the positive and negative electrodes. The membrane can be an ion-selective barrier, as in the case of exchange membranes, anionic or cationic. Since exchange membranes are thicker and more expensive, currently, the commercial membranes used are generally hydrophobic polymer membranes which are modified by a pre-treatment to become hydrophilic.

[0010] The object of the present invention is the use of a hydrophobic membrane. The hydrophobic membrane, which has not undergone any prior treatment to be made hydrophilic, is modified in situ in contact with the zinc electrode in the alkaline accumulator to become hydrophilic and allow the zinc electrode-based accumulator to operate in charge and discharge. The advantage is a reduction in the cost of producing the membrane, since the wetting agent treatment step is eliminated. The use of a hydrophobic membrane makes it possible to use membranes themselves used more widely in lithium-based accumulator technologies at lower costs.

[0011] To do this, tests concern the use of a hydrophobic membrane in NiZn accumulators using electrolytes developed in the work relating to the aforementioned patent application FR 2 201 375 and containing wetting and anti-foaming agents.

[0012] The objective pursued in patent application FR 2 201 375 is to improve the solid-liquid contact surface for the active material of nickel and zinc electrodes and to prevent possible degradation of the hydrophilic properties of the membrane. The hypothesis is that the wetting agents soluble or suspended in the electrolyte end up in part by sticking in the porosity of the membrane, allowing the membrane to retain its hydrophilic properties for longer. The object of the present invention is to make a hydrophobic membrane hydrophilic by using an electrolyte having an adequate quantity of wetting agents and antifoam to control the formation of foam.

[0013] A review of the state of the art of zinc anode systems shows that there are several patents and studies mentioning the use of a hydrophobic membrane. For example, Celgard Inc., Charlotte, NC (US) in US patent 7,981,549 filed on July 19, 2011 clearly shows that the hydrophobic microporous membrane must be previously coated with one or more wetting agents through a specific treatment, in order to be used with a zinc electrode in a rechargeable alkaline system.

[0014] In the Chinese patent application CN110197904 concerning an original hybrid flow redox system with on the zinc side, a circulation of the rechargeable electrolyte and on the positive side a double solid hybrid electrode, nickel and air. In such a system, it is common to associate a Nafion® type membrane to limit the passage between the negative side and the positive side. In this system, the use of a hydrophobic membrane-diaphragm in the solid hybrid nickel-air positive electrode is mentioned. This membrane separates the nickel reactive layer from the air electrode reactive layer. Just like the added impermeable-breathable membranes, the function of the hydrophobic membrane-diaphragm is to limit the access of the electrolyte to the reaction zone of the air electrode which requires solid-liquid-gas triple contact points to achieve the reduction of oxygen.If the electrolyte access is too great, the air electrode is flooded and the triple contact areas disappear.

[0015] In the patent application published under number US2021 / 399305, mention is made of a protective barrier layer which is designed to be selective with respect to zincate ions, to protect the MnO2 cathode. The protective barrier layer is none other than a membrane about which it is recalled that the polyolefin membranes are modified to be made hydrophilic prior to their implementation in the cell.

[0016] In the publication of Bi Yang (Journal of Power Sources 251 (2014) 14-19), it is mentioned that the hydrophobic Celgard® membrane can only be used in an alkaline battery after undergoing a special treatment by soaking in a lubricant for 24 hours before its implementation in the battery.

[0017] A review of the state of the art of zinc anode systems shows that there are several patents and studies mentioning the use of wetting agents. For example, Rossler et al. in U.S. Patent 4,195,120, filed November 3, 1978, states that hydrogen evolution in cells having zinc anodes is reduced or eliminated by incorporating into the cell a wetting agent which is an ethylene oxide, alkyl ester phosphate adduct polymer. This wetting agent is added in such a manner that, directly or upon wetting of the anode by the electrolyte, there is adsorption of the wetting agent to the surface of the zinc anode material, which prevents hydrogen evolution. The wetting agent is desirably present in the cell in an amount of 0.001% to 5% by weight of the zinc component of the cell. The wetting agent described herein is soluble or dispersible in water and alkaline electrolyte.The wetting agent is added either directly to the zinc electrode or indirectly to the electrolyte or cathode. Via the electrolyte, the wetting agent can be deposited on the zinc surface, while via the cathode, the wetting agent can pass through the membrane to be deposited on the zinc. The desired action is on . the zinc electrode, not on the membrane.

[0018] In the Chinese patent application filed on December 18, 2019 and published under the number CN111048846, it is mentioned that a wetting agent selected from sodium lauryl sulfate, sodium dodecyl benzene sulfonate, cetyl trimethyl ammonium bromide, octadecyl trimethyl ammonium chloride, tetrabutyl ammonium bromide, one or more compounds from tetrabutyl ammonium hydroxide, tetrabutyl ammonium chloride, a perfluorinated surfactant makes it possible to improve the ability to increase the number of charge and discharge cycles from 100 to 600 by reducing the usual limitations, short circuit, dissolution, deformation, densification, passivation of the zinc electrode and hydrogen evolution. The desired effect concerns the zinc electrode, not the separator.

[0019] A 1998 article by JiLing Zhu et al. (Journal of Power Sources 72 (1998) 231-235) mentions the effects of different types of perfluorinated ionic wetting agents including the hydrocarbon chain wetting agent CTAB on the electrochemistry examined on the behavior of zinc. The results show that these wetting agents can be used as a substitute for mercury to reduce corrosion in zinc batteries. It is also shown that zinc deposition in the presence of these wetting agents can be improved to some extent. The morphology of the electrodeposited zinc shows that these agents can provide more uniform and compact deposits and, therefore, reduce dendritic growth. The compounds called FC-170C and CTAB are the most effective inhibitors.These ionic wetting agents remain attached to zinc during strong polarizations that are associated with hydrogen evolution, which is not the case for non-ionic wetting agents. Cationic wetting agents can be adsorbed by the electrostatic attraction between the polar group of the molecules and the zinc electrode surface, so that the hydrogen evolution rate increases more slowly in the presence of compounds called FC-135 or CTAB when the zinc electrode potential is more negative than -1.80 V. The shifts in the deposition onset potential and the potential at the maximum of the cathodic current indicate that zinc deposition is inhibited to some extent in the presence of wetting agents. The reason is that the wetting agents adsorb onto the zinc electrode surface to form a layer that has an inhibiting effect on the electroreduction process of zincate ions.Therefore, these wetting agents can slow down the rate of zinc deposited from zincates during electrode charging and, thus, attenuate dendrite growth. Once again, the intended purpose concerns the operation of the zinc electrode.

[0020] A 2015 article by MA Deyab (Journal of Power Sources 292 (2015) 66-71) mentions the effects of polyoxyethylene (40) nonylphenyl ether as a surfactant non-ionic (PNE) as a corrosion inhibitor in alkaline electrolyte (7.0 M KOH).

[0021] These state-of-the-art researches mentioning the addition of wetting agents are all related to the search for a reduction in the evolution of hydrogen coupled with the corrosion of zinc. In no case is it a treatment intended to make a hydrophobic membrane implemented in this state in an accumulator hydrophilic, by an in situ action in said accumulator. The use of a hydrophobic membrane instead of a hydrophilic membrane aims to reduce the cost of the elements, the lifetime of the elements with a hydrophobic membrane being able to be comparable to that of the elements using a hydrophilic membrane. Summary of the invention

[0022] The aim of the invention is to enable the production of rechargeable alkaline electrochemical generators with a zinc anode incorporating a hydrophobic membrane, therefore without prior treatment which would have been intended to make it hydrophilic.

[0023] This aim is achieved by electrolytes such as those described in patent application FR 2 201 375 (filed on February 17, 2022 by the company Sunergy) and which contain wetting and antifoaming agents making it possible to confer in situ hydrophilic properties to the membrane on the accumulator.

[0024] More specifically, the invention relates to any alkaline electrochemical generator with a zinc anode according to the following statement 1: 1. Method for preparing an electrochemical generator, comprising the steps of: • assemble a hydrophobic membrane with a cathode and an anode, then • add an electrolyte comprising at least one wetting agent and at least one antifoam agent.

[0025] Advantageous characteristics of the alkaline electrochemical generator with zinc anode of the aforementioned statement 1 are indicated in the following statements 2 to 17:

[0026] 2. Method according to statement 1, in which the electrolyte is an aqueous solution alkaline.

[0027] 3. Method according to statement 1 or 2, in which the anode is a zinc anode.

[0028] 4. Method according to one of statements 1 to 3, in which the cathode is a cathode of nickel.

[0029] 5. Method according to one of statements 1 to 3, in which the cathode is a cathode of manganese dioxide.

[0030] 6. Method according to one of statements 1 to 3, in which the cathode is a cathode of money.

[0031] 7. Method according to one of the preceding statements, comprising in situ activation of the hydrophobic membrane by impregnation of the electrolyte.

[0032] 8. Method according to one of the preceding statements, in which the electrolyte comprises at least one ionic wetting agent and at least one non-ionic wetting agent.

[0033] 9. Method according to statement 8, in which the ionic wetting agent is the bis(2-ethylhexyl) phosphate.

[0034] 10. Method according to statement 8 or 9, in which the non-ionic wetting agent is selected from alkyl polyglucosides and polyethylene glycol and alkylphenol ethers.

[0035] 11. Method according to one of the preceding statements, in which the antifoaming agent is chosen from polyorganosiloxanes.

[0036] 12. Method according to one of the preceding statements, in which the electrolyte has a molarity between 4 M and 15 M of hydroxyl anions.

[0037] 13. Method according to the preceding statement, in which the electrolyte has a molarity between 7 M and 12 M hydroxyl anions.

[0038] 14. Method according to one of the preceding statements, in which the agent(s) wetting agent(s) has / have a concentration between 0.1 g / l and 50 g / l of electrolyte.

[0039] 15. Method according to the preceding statement, in which the agent(s) wetting agent(s) has / have a concentration between 1 g / l and 25 g / l.

[0040] 16. Method according to one of the preceding statements, in which the agent(s) antifoam(s) is / are present in an amount between 10 mg and 3000 mg per kilogram of electrolyte.

[0041] 17. Method according to the preceding statement, in which the agent(s) an- timousse(s) is / are present in an amount between 100 mg and 1000 mg per kilogram of electrolyte.

[0042] According to another aspect, the invention also relates to an electrochemical generator obtained by the aforementioned method.

[0043] Other characteristics and advantages of the invention will now be described in detail in the following description which is given with reference to the appended figures, which schematically represent:

[0044] [Fig-1]: curves of the capacities measured in charge and discharge of element 1 (witness) NiZn, 8Ah in cycling, charge 8A 1.92V up to 8Ah or stop when the end of charge current rises, discharge 8A IV, depth of discharge 100%;

[0045] [Fig.2]: curves of the capacities measured in discharge of elements 2 and 3 (controls) NiZn 8 Ah in cycling, charge 8A in 1 hour, discharge 8A IV, depth of discharge 100%; and

[0046] [Fig.3]: curves of the capacities measured in discharge of element 4 (according to the invention) NiZn 8Ah in cycling, charge 8A 1.92V up to 8Ah or stop when the end of charge current rises, discharge 8A1V, depth of discharge 100%.

[0047] [Fig.4]: curves of the capacities measured in discharge of element 5 (according to the invention) NiZn 8Ah in cycling, charge 8A 1.92V up to 8Ah or stop when the end of charge current rises, discharge 8A1V, depth of discharge 100%. Detailed description of the invention

[0048] The zinc anode accumulator is produced according to methods known to those skilled in the art. The electrodes are in the form of plates, consisting of a current collector and an active mass. The active mass may incorporate compounds which do not participate in the electrochemical reaction, but will ensure, for example, an electronic conduction function or a mechanical connection between the active elements and the collector, or even a function of retention of a product of the electrochemical reaction.

[0049] In the case of the zinc anode, in addition to polymers such as PTFE, polyethylene glycol, polyvinyl alcohol, styrene-butadiene polymer, carboxymethyl cellulose, etc., which provide the binding function for the constituents of the electrode, calcium hydroxide can be used to limit the formation of soluble zincates, as well as conductive ceramics as described in the aforementioned patent FR 2 788 887.

[0050] A separator isolates the anodic and cathodic compartments: it is a felt, a porous or ion exchange membrane, felt and porous membrane can be combined. The membrane is generally a hydrophobic polymer membrane which is, prior to its implementation, modified to become hydrophilic by the addition of one or more wetting agents.

[0051] Depending on the manufacturing method, the zinc anode accumulator can be prismatic, cylindrical, or in the form of a filter-press type cell if the battery is bipolar.

[0052] The present invention is particularly applicable to the manufacture of a nickel-zinc accumulator, designed according to the main characteristics described below.

[0053] According to a preferred embodiment, a nickel-zinc accumulator is produced by combining a plasticized nickel electrode and a zinc electrode also containing an organic binder. 1. Nickel electrode

[0054] The nickel electrode can advantageously be made using a very fine-pored nickel metal foam as the collector. Some of these foams are designated as "battery grade". Suppliers include, for example, Sumitomo Electric (Japan) and Corun (China). The thickness of the foam 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.

[0055] The active material consists of nickel hydroxide which preferably contains in in addition to 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 hydroxide, which, during battery formation, transform into conductive cobalt oxy-hydroxide (Oshitani et al. J. Electrochem. Soc. 1989 136, 6, 1590).

[0056] Conductive additives (fibers, metal powders) can also be added to the nickel hydroxide powder.

[0057] A paste is conventionally prepared by mixing the constituents described above and deionized water to which carboxymethylcellulose has been added. A polymer binder, such as PTFE, may be added at this stage of manufacture in the form of a suspension, or later after filling the collector, in particular the nickel foam, with the active paste by dipping it into the suspension.

[0058] The filling of the nickel foam can be carried out on a laboratory scale using a scraper which forces the paste into the thickness of the support, and on an industrial scale by injecting the paste into the foam under pressure.

[0059] After drying, the electrode is compressed to ensure cohesion between the collector, active mass and additives and cut to the desired dimensions. 1. Zinc electrode

[0060] The collector of the zinc electrode can be in the form of perforated metal strip, woven fabric, expanded metal strip or metal foam. Copper is preferred because of its conductivity, but must be covered with a protective metal: zinc, tin, or alloy.

[0061] The zinc electrode is preferably manufactured by first preparing a paste consisting of zinc oxide and various additives: - electronic conductors: metallic zinc, carbon, copper, conductive ceramics, etc., in the form of powders or filaments. - anti-corrosion agents: indium, bismuth, etc. - compounds that react with zincates: calcium hydroxides, barium hydroxides, etc.

[0062] The liquid phase is deionized water or alcohol, to which carboxymethylcellulose has been added as a binder and thickener. Other binders may be added, such as those mentioned in the patent application published under number EP 1 715 536.

[0063] It is possible, depending on the technique chosen, to manufacture a high viscosity paste which can be applied by pressure on both sides of the metal support to form a "sandwich" structure, to manufacture a medium viscosity paste in which the collector is immersed, then removed by removing the excess paste to adjust the thickness of the electrode using a scraper, an operation which is followed by a drying. Finally, it is possible to use a dry powder mixed with a binder and compress it onto the metal support to form the electrode. 1. The electrolyte

[0064] The electrolyte used is preferably a concentrated alkaline solution with a molarity of between 4 and 15 M (4 and 15 mol / l), preferably between 7 and 12 M of hydroxyl anions. The alkalinity is provided by potassium, sodium and lithium hydroxides, taken individually or as a mixture.

[0065] The electrolyte may also contain zincates and silicates in varying proportions, as mentioned in patent no. FR 3 099 851. The electrolyte may also contain borates, phosphates, and fluorides, taken separately or in a mixture, as described for example in patent no. US 5 215 836.

[0066] According to the present invention, the amount of wetting agents added to the electrolyte is between 0.1 g / l and 50 g / l and preferably between 1 g / l and 25 g / l of electrolyte; the amount of antifoam agents added to the electrolyte, expressed in mg per kg of electrolyte, is between 10 mg and 3000 mg, preferably between 100 mg and 1000 mg.

[0067] The wetting agents are selected in particular from the ionic wetting agent, bis(2-ethylhexyl) phosphate and non-ionic wetting agents from alkyl polyglucosides, in particular those of the Triton® brand. The antifoaming agents are selected from products which refer to the chemical family of polyorganosiloxanes. These wetting and antifoaming agents can be used separately or in mixtures. Examples

[0068] In order to illustrate the demonstration of the operation and the definition of the present invention, NiZn elements from 1 to 5, with a nominal capacity of 8Ah are produced in an identical manner according to the general description provided above.

[0069] All elements have similar zinc and nickel electrodes. The electrolyte used is a concentrated alkaline solution with a molarity of 10M of hydroxyl anions with an addition of silicate as described in the aforementioned patent FR 3 099 851. The membrane is hydrophilic for elements 1 to 3 and hydrophobic for elements 4 and 5. The elements are mounted with a low pressure valve of 0.2 bar.

[0070] The parameters that differentiate elements 1 to 5, such as the nature of the membrane, the quantity of wetting and antifoaming agent in the electrolyte are indicated in Table 1. Element NiZn Membrane Wetting agents (g / D) Antifoam agents (mg / kg electrolyte) Name Character Guerley Thickness (pm) 1 A Hydrophil e >1000 25 10.8 210 2 B Hydrophil e 450-750 40 0 ​​0 3 B Hydrophil e 450-750 40 21.3 0 4 C Hydropho be 620 25 10.8 630 5 D Hydropho be 550 20 10.8 630

[0071] Table 1: characteristics of NiZn accumulators, nominal capacity 8Ah. Example 1 (witness):

[0072] Element 1 with a nominal capacity of 8Ah is produced in an identical manner according to the general description provided above. Membrane A is used in element 1. Membrane A is a microporous polypropylene with a thickness of 25 μm with an added wetting agent allowing it to be hydrophilic. The pore size was measured at 37 ± 14 nm, the porosity at 36 ± 1%. The breathability of this membrane A, expressed in Guerley is relatively high, greater than 1000, allowing it to be a gas barrier by limiting the recombination of oxygen at the surface of the zinc electrode, for better thermal stability. This membrane is deposited on the zinc electrode in two layers one on top of the other creating a barrier with a total thickness of 50 μm.The electrolyte used is a concentrated alkaline solution with a molarity of 10M of hydroxyl anions with an addition of silicate as described in the aforementioned patent FR 3 099 851 and wetting and antifoaming agent as described in the aforementioned patent application FR 2 201 375. Cell 1 was cycled at 100% depth of discharge at the IC rate with a current of 8A up to IV. The 8Ah charge is carried out at the IC rate up to 1.92V, then at constant voltage at 1.92V up to 8Ah or it is stopped when the end of charge current rises again. [Fig.l] illustrates the charge and discharge capacity of cell 1. [Fig.l] demonstrates a stable capacity for 3300 cycles and becoming less than 70% after 3800 cycles. Examples 2 and 3 (witnesses).

[0073] NiZn cells 2 and 3 with a nominal capacity of 8Ah are produced identically according to the general description provided above. Membrane B is used for cells 2 and 3. Membrane B is a microporous polypropylene with a thickness of 40 μm previously added with a wetting agent allowing it to be a hydrophilic membrane. The breathability of this membrane B, expressed in Guerley, is lower than that of membrane A, between 450-750. The porosity is announced between 37% and 48%. This wide range of Guerley and porosity suggests defects in the homogeneity of the membrane. This membrane B is deposited on the surface of the zinc electrode in a single layer. The electrolyte used is a concentrated alkaline solution with a molarity of 10M of hydroxyl anions with an addition of silicate as described in the aforementioned patent FR 3 099 851.Cell 2, mounted with membrane B, leads to zero capacity after the formation step characterized by 3 charge cycles at the C / 10 rate for 12 hours and discharge at the C / 5 rate until the battery voltage reaches 1.2V. As described in patent application FR 2 201 375, an addition to the electrolyte of 4 wetting agents, three of which are of the TRITON® brand, BG-10, CG-110, X-100 plus the wetting agent bis(2-ethylhexyl) phosphate, leads to the total concentration of 21.3 g / l of the 4 wetting agents introduced into cell 2 (same quantity for the 4 wetting agents). No antifoam agent is added. After the addition of wetting agents in cell 2, the result of the formation of cell 2 is comparable to that of cell 3. Cell 3 mounted with membrane B, leads to a capacity higher than 8Ah after formation without any addition of wetting agent, demonstrating that membrane B is hydrophilic.The discharged capacities as a function of the number of cycles for accumulators 2 and 3 are compared in [Fig.2]. Cells 2 and 3 were tested at the constant current C regime at 100% depth of discharge, 8A Ih in charge and 8A IV in discharge.

[0074] Following the addition of the wetting agents, element 2 leads to results comparable to element 3 during the first 600 cycles. After 600 cycles, element 2 becomes better than element 3, clearly indicating a beneficial impact of the addition of the wetting agents on the lifetime of the elements. It is assumed that the wetting agents added to the electrolyte of element 2 were therefore able to deposit in situ in the cell on membrane B, allowing this previously dysfunctional membrane to be functional and to allow a lifetime greater than that of element 3. This first experiment is therefore conclusive on the capacity of the wetting agents introduced into the electrolyte to attach to the membrane and to restore its hydrophilic properties. Example 4 (present invention):

[0075] Element 2 present in the aforementioned patent application FR 2 201 375, describes an addition of wetting agents in the electrolyte to consolidate and maintain the hydrophilic properties of the membrane. Element 4 aims to verify whether it is possible to make a hydrophobic membrane hydrophilic by using an electrolyte having an adequate quantity of wetting agents while controlling the formation of foam. Element 4 with a nominal capacity of 8Ah is produced in an identical manner according to the general description provided above. Element 4 uses membrane C. Membrane C is a microporous polypropylene with a thickness of 25 μm without added wetting agent allowing it to become hydrophilic. Membrane C is therefore completely hydrophobic.The values ​​in the table below giving the contact angle of a water droplet with the surface of the membranes, the ionic conductivity and the diffusion of hydroxyl ions of membranes A, B and C clearly indicate that membrane C is hydrophobic. Membrane A Membrane B Membrane C Contact angle (°C) 62 + 5 60+1 100 + 5 Ionic conductivity (mS / cm) 2.6 E-10 3.1 E-10 3.5E-15 Diffusion of OH- ions (m2 / S) 2.2 E-02 1.6 E-02 0

[0076] The pore size of membrane C was measured at 25 ± 11 nm, the porosity at 43 ± 2%. The breathability of this membrane C, expressed in Guerley is relatively low, at 620, compared to membrane A. This membrane is deposited on the zinc electrode in two layers one on top of the other creating a barrier with a total thickness of 50 μm. The electrolyte used is a concentrated alkaline solution with a molarity of 10M of hydroxyl anions with an addition of silicate as described in the aforementioned patent FR 3 099 851. The addition of the wetting and antifoaming agents as described in the aforementioned patent application FR 2 201 375 are 3 wetting agents TRITON®BG-10 and TRITON®X-100 plus the wetting agent bis(2-ethylhexyl) phosphate (same quantity for the 4 wetting agents). The total concentration of the 3 wetting agents is 10.8 g / l.An antifoam agent from the polyorganosiloxane chemical family is added to the electrolyte, at a rate of 630 mg per kilogram of electrolyte.

[0077] The formation is similar to that of elements 1 to 3, characterized by 3 cycles of charge at the C / 10 regime for 12 hours and discharge at the C / 5 regime until the battery voltage reaches 1.2V. For element 4, the first charge is characterized by a very high voltage from the first minutes of the charge suggesting that membrane C constitutes too great a barrier for the diffusion of ions hydroxyl. Element 4 is placed in an oven at 45°C to accelerate the wetting of the membrane. After 2 hours, the result is the same and the element is placed at 45°C for 15 hours. The first charge is restarted with the removal of the very high voltage attesting that the membrane has become hydrophilic, in situ to the element. Element 4, after formation, has a capacity greater than 8 Ah and similar to control elements 1 to 3 which use an initially hydrophilic membrane.

[0078] It has also been shown that the wetting and in situ activation of certain hydrophobic membranes could be carried out at room temperature for similar concentrations of wetting agents, and for comparable durations of less than or equal to 3 days.

[0079] Cell 4 was cycled at 100% depth of discharge at IC rate with a current of 8A up to IV. The 8 Ah charge is carried out at IC rate up to 1.92V, then at constant voltage at 1.92V up to 8 Ah or it is stopped when the end of charge current rises again. [Fig. 3] illustrates the charge and discharge capacity of cell 4, demonstrating a stable capacity for more than 1200 cycles, the experiment still being in progress. The result of this cell 4 clearly demonstrates that it is possible to use a hydrophobic membrane with the electrolyte described in the aforementioned patent application FR 2 201 375. Example 5 (present invention):

[0080] The NiZn 5 element with a nominal capacity of 8Ah is produced in an identical manner according to the general description provided above. Membrane D is used for element 5. Membrane D is a microporous polypropylene with a thickness of 20 μm without an added wetting agent allowing it to become hydrophilic. Membrane D is therefore completely hydrophobic. The breathability of this membrane, expressed in Guerley at 550, is lower than that of membrane C. The porosity is announced at 36%. This membrane D is deposited on the surface of the zinc electrode in two layers. The electrolyte used is a concentrated alkaline solution with a molarity of 10M of hydroxyl anions with an addition of silicate as described in the aforementioned patent FR 3 099 851. The addition of wetting agents as described in the aforementioned patent application FR 2 201 375 concerns 3 wetting agents, TRITON®BG-10 and TRITON®X-100, and the wetting agent bis(2-ethylhexyl) phosphate. The total concentration of the 3 wetting agents is 10.8 g / l (same quantity for the 4 wetting agents). An antifoam agent from the chemical family of polyorganosiloxanes is added to the electrolyte, at a rate of 630 mg per kilogram of electrolyte.

[0081] The formation is similar to that of elements 1 to 3. The formation is characterized by 3 cycles of charge at the C / 10 regime for 12h and discharge at the C / 5 regime until the battery voltage reaches 1.2V. The charge voltage of the first cycle of formation is similar and comparable to those of control cells 1 to 3, indicating that membrane D became hydrophilic in situ in cell 5 more easily than membrane C. Cell 5, after formation, has a capacity greater than 8Ah and similar to those of control cells 1 to 3 which use a hydrophilic membrane prior to its implementation in the cell.

[0082] Cell 5 was cycled at 100% depth of discharge at IC rate with a current of 8A up to IV. The 8Ah charge is carried out at IC rate up to 1.92V, then at constant voltage at 1.92V up to 8Ah or it is stopped when the end of charge current rises again. [Fig.4] illustrates the charge and discharge capacity of cell 5, demonstrating a stable capacity for more than 240 cycles, the experiment still being in progress. The result of this cell 5 clearly demonstrates that it is possible to use a hydrophobic membrane with the electrolyte described in the aforementioned patent application FR 2 201 375.

[0083] Using a hydrophobic membrane which becomes hydrophilic in situ in the element using an electrolyte derived from patent application FR 2 201 375, instead of a previously hydrophilic membrane advantageously makes it possible to eliminate the step(s) of prior treatment of commercial hydrophilic membranes. It is therefore possible according to the present invention to benefit from a significant reduction in the cost of the membrane, some of these hydrophobic membranes being used on a very large scale in lithium accumulators, and being of a lower preparation cost.

[0084] Through the numerous experiments conducted by the authors of the present invention, of which those presented in Table 1 constitute only a part, it appears that the choices of concentrations of wetting agents and antifoaming agents can be made favorably in wide ranges. The optimal concentrations are in particular dependent on the characteristics of the hydrophobic membranes used, the alkalinity level of the electrolyte, the formulations and embodiments of the electrodes, the accumulator configurations and the cycling regime conditions. It has thus been shown that the overall concentrations of wetting agents can be between approximately 0.1 and 50 g and preferably between 1 and 25 g per liter of electrolyte, and those of antifoaming agents between approximately 10 and 3000 mg, preferably between 100 and 1000 mg per kilogram of electrolyte.

[0085] The preceding demonstrations concern the hydrophilization of an initially hydrophobic membrane. They therefore apply not only to nickel-zinc generators, but also to other generators, in particular zinc-manganese dioxide generators and silver-zinc generators.

[0086] The invention is therefore not limited to the examples which have been provided as illustrations, but embraces all variants thereof.

Claims

[Claim 1] Claims Method for preparing an electrochemical generator, comprising the steps of: • assemble a hydrophobic membrane with a cathode and an anode, then • add an electrolyte comprising at least one wetting agent and at least one antifoaming agent. The method of claim 1, wherein the electrolyte is an aqueous alkaline solution. A method according to claim 1 or 2, wherein the anode is a zinc anode. Method according to one of claims 1 to 3, in which the cathode is a nickel cathode. A method according to any one of claims 1 to 3, wherein the cathode is a manganese dioxide cathode. Method according to one of claims 1 to 3, in which the cathode is a silver cathode. Method according to one of the preceding claims, comprising the in situ activation of the hydrophobic membrane by impregnation of the electrolyte. Method according to one of the preceding claims, in which the electrolyte comprises at least one ionic wetting agent and at least one non-ionic wetting agent. The method of claim 8, wherein the ionic wetting agent is bis(2-ethylhexyl) phosphate. A method according to claim 8 or 9, wherein the non-ionic wetting agent is selected from alkyl polyglucosides and polyethylene glycol and alkylphenol ethers. Method according to one of the preceding claims, in which the antifoaming agent is chosen from polyorganosiloxanes. Method according to one of the preceding claims, in which the electrolyte has a molarity of between 4 M and 15 M of hydroxyl anions. Method according to the preceding claim, in which the electrolyte has a molarity of between 7 M and 12 M of hydroxyl anions. Method according to one of the preceding claims, in which the wetting agent(s) has / have a concentration of between 0.1 g / l and 50 g / l of electrolyte. Method according to the preceding claim, in which the wetting agent(s) has / have a concentration of between 1 g / l and 25 g / l. A method according to any preceding claim, wherein the antifoam agent(s) is / are present in an amount of between 10 mg and 3000 mg per kilogram of electrolyte. Method according to the preceding claim, in which the antifoam agent(s) is / are present in an amount of between 100 mg and 1000 mg per kilogram of electrolyte. Electrochemical generator obtained by the method according to one of claims 1 to 17.

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