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: Method for preparing an electrochemical generator

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

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

[0003] Zinc is used extensively in alkaline batteries and Leclanché® batteries. For industrial-sized rechargeable alkaline batteries, the first applications were in the military sector 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 is primarily composed of potassium hydroxide. However, the number of cycles obtained does not meet the usage requirements of industrial batteries for stationary applications, which must provide at least 2,000 deep charge and discharge cycles, corresponding to 80% depth of discharge or more.

[0004] Zinc is soluble in alkaline media in the form of zincates and readily forms, during the charging of zinc anode batteries, 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 charge and discharge cycles: thus, densification phenomena are observed which reduce the porosity of the electrode and consequently its ability to operate at current densities corresponding to practical battery use. Other Factors penalize the zinc anode, such as the precipitation of zinc oxide forming a layer that passively reduces the active surface of the electrode.

[0006] Much work has been carried out to understand the mechanisms of zinc deposition and dissolution in alkaline media, 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 objective of reducing the solubility of zincates, constitutes the bulk of the patents; - Mechanical processes are also described which allow the electrolyte alone or a zinc electrode dispersed in the electrolyte to circulate, to avoid dendritic growth by ensuring a homogeneous zinc deposition; - the use of pulsed currents, with or without polarity reversal, allowing the dendrites to be dissolved at least partially; - finally, the use of separators that limit the formation or suppress the diffusion of zincate ions from the anode to the cathode: these are for example multi-layered microporous separators or exchange membranes.

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

[0008] The loss of capacity in NiZn batteries during cycling has historically been primarily correlated with the formation of zinc dendrites, which ultimately create a short circuit. This dendrite formation was eliminated following work related to French patent FR 2 788 887 (filed on January 27, 1999, by SCPS), enabling more than 1,000 cycles at 80% depth of discharge and beyond. Subsequently, the loss of capacity in NiZn batteries was induced by the redistribution and densification of the active material, as well as the drying and passivation of the zinc electrodes. A new response to these limits of NiZn battery stability has been demonstrated with the work relating to the patent application filed by Sunergy on August 9, 2019 and published under number FR 3 099 851, allowing to exceed 2,000 cycles and more, at 100% depth of discharge.With increasing zinc electrode stability, the loss of capacity has been associated with the stability of the membrane's hydrophilic properties. A new response to this membrane stability limitation of NiZn batteries has been demonstrated in the work [reference missing]. relating to the patent application filed on February 17, 2022 under 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 battery, the membrane cannot be hydrophobic because it would block the passage of ions between the positive and negative electrodes. The membrane can be a selective ion barrier, as in the case of anionic or cationic exchange membranes. Since exchange membranes are thicker and more expensive, currently, commercially available membranes are generally hydrophobic polymer membranes that are modified by pretreatment 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 make it hydrophilic, is modified in situ in contact with the zinc electrode in the alkaline battery to become hydrophilic and allow the charging and discharging of the zinc-electrode-based battery. The advantage is a reduction in the cost of manufacturing the membrane, as the wetting agent treatment step is eliminated. The use of a hydrophobic membrane makes it possible to use membranes that are themselves more widely used in lithium-based battery technologies at lower costs.

[0011] To this end, tests are carried out on 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 antifoaming agents.

[0012] The objective pursued in patent application FR 2 201 375 is to improve the solid-liquid contact surface area for the active material of nickel and zinc electrodes and to prevent possible degradation of the membrane's hydrophilic properties. The hypothesis is that the wetting agents, whether soluble or suspended in the electrolyte, eventually adhere to the membrane's porosity, allowing the membrane to retain its hydrophilic properties for longer. The object of the present invention is to render a hydrophobic membrane hydrophilic by using an electrolyte containing an adequate amount of wetting agents and an antifoaming agent to control foam formation.

[0013] A review of the state of the art of zinc anode systems shows that several patents and studies mention 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 pre-coated with one or more wetting agents through a treatment specifically, to be able to be used with a zinc electrode in a rechargeable alkaline system.

[0014] In Chinese patent application CN110197904, an original hybrid redox flow system is described, with a zinc-based refillable electrolyte circulation and a solid-nickel-air hybrid double electrode on the positive side. In such a system, it is common to use a Nafion®-type membrane to restrict the flow between the negative and positive sides. This system also mentions the use of a hydrophobic diaphragm membrane in the nickel-air hybrid positive electrode. This membrane separates the nickel reactive layer from the air electrode reactive layer. Similar to the added impermeable-breathable membranes, the function of the hydrophobic diaphragm membrane is to limit the electrolyte's access to the air electrode's reaction zone, which requires triple solid-liquid-gas contact points to achieve oxygen reduction.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, reference is made to a protective barrier layer designed to be selective with respect to zincate ions, in order to protect the MnO2 cathode. The protective barrier layer is none other than a membrane, with regard to which it is recalled that polyolefin membranes are modified to be made hydrophilic prior to their implementation in the cell.

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

[0017] A review of the prior art of zinc anode systems shows that several patents and studies mention the use of wetting agents. For example, Rossler et al., in US patent 4,195,120, filed November 3, 1978, state that hydrogen evolution in cells having zinc anodes is reduced or eliminated by incorporating into the cell a wetting agent that is an ethylene oxide polymer, alkyl ester phosphate adduct. This wetting agent is added in such a way that, either directly or during wetting of the anode by the electrolyte, there is adsorption of the wetting agent onto the surface of the zinc anode material, which prevents hydrogen evolution. The wetting agent is desirablely 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 here 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. The wetting agent is added via the electrolyte. The wetting agent can be deposited on the zinc surface, while via the cathode, it can pass through the membrane and be deposited on the zinc. The desired action is on the zinc electrode, not the membrane.

[0018] In the Chinese patent application filed on December 18, 2019, and published under number CN111048846, it is stated that a wetting agent selected from sodium lauryl sulfate, sodium dodecylbenzene sulfonate, cetyltrimethylammonium bromide, octadecyltrimethylammonium chloride, tetrabutylammonium bromide, one or more compounds from tetrabutylammonium hydroxide, tetrabutylammonium chloride, and a perfluorinated surfactant improves the ability to increase the number of charge and discharge cycles from 100 to 600 by reducing the usual limitations: short-circuiting, dissolution, deformation, densification, passivation of the zinc electrode, and hydrogen evolution. The desired effect relates to the zinc electrode, not the separator.

[0019] A 1998 article by JiLing Zhu et al. (Journal of Power Sources 72 (1998) 231-235) discusses the effects of various types of perfluorinated ionic wetting agents, including the hydrocarbon-chain wetting agent CTAB, on the electrochemistry of zinc behavior. 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 produce more uniform and compact deposits and, consequently, reduce dendritic growth. The compounds designated FC-170C and CTAB are the most effective inhibitors.These ionic wetting agents remain bound to zinc during the high polarizations associated with hydrogen evolution, unlike non-ionic wetting agents. Cationic wetting agents can be adsorbed by the electrostatic attraction between the polar group of the molecules and the surface of the zinc electrode, so the rate of hydrogen evolution increases more slowly in the presence of compounds known as FC-135 or CTAB when the zinc electrode potential is more negative than -1.80 V. The shifts in the deposition start potential and the potential at the maximum cathode current indicate that zinc deposition is inhibited to some extent in the presence of wetting agents. This is because the wetting agents adsorb onto the surface of the zinc electrode to form a layer that has an inhibitory effect on the electroreduction process of zincate ions.Therefore, these wetting agents can slow the rate of zinc deposition from zincates during electrode charging and thus mitigate dendrite growth. Again, the objective is to improve the functioning 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 nonionic surfactant (PNE) as a corrosion inhibitor in the alkaline electrolyte (7.0 M KOH).

[0021] These prior art studies mentioning the addition of wetting agents are all related to the search for a reduction in hydrogen evolution coupled with zinc corrosion. In no case does this constitute a treatment intended to make a hydrophobic membrane, implemented in this state within a battery, hydrophilic by means of an in-situ action within said battery. The use of a hydrophobic membrane instead of a hydrophilic membrane aims to reduce the cost of the cells, as the lifespan of cells with a hydrophobic membrane can be comparable to that of cells using a hydrophilic membrane. Summary of the invention

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

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

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

[0025] Advantageous features of the zinc-anode alkaline electrochemical generator of statement 1 above are indicated in the following statements 2 to 17:

[0026] 2. A method according to statement 1, wherein the electrolyte is an aqueous solution alkaline.

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

[0028] 4. A method according to any one of statements 1 to 3, wherein the cathode is a cathode nickel.

[0029] 5. A method according to any one of statements 1 to 3, wherein the cathode is a cathode of manganese dioxide.

[0030] 6. A method according to any one of statements 1 to 3, wherein the cathode is a cathode of money.

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

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

[0033] 9. A process according to statement 8, wherein the ionic wetting agent is the bis(2-ethylhexyl) phosphate.

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

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

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

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

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

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

[0040] 16. A method according to any 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. A process according to the preceding statement, in which the agent(s) antifoam(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 process.

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

[0044] [Fig-1]: Curves of the capacitances measured during charging and discharging of element 1 (indicator) NiZn, 8Ah 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 during discharge of elements 2 and 3 (controls) NiZn 8 Ah cycling, 8A charge in 1 hour, 8A discharge IV, 100% depth of discharge; and

[0046] [Fig.3] : curves of the capacities measured during discharge of the 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 during discharge of element 5 (according to (Invention) NiZn 8Ah in cycling, charging 8A 1.92V up to 8Ah or stopping when the end-of-charge current rises again, discharging 8A1V, depth of discharge 100%. Detailed description of the invention

[0048] The zinc-anode battery is manufactured 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 that do not participate in the electrochemical reaction, but will, for example, provide electronic conduction, a mechanical link between the active elements and the collector, or a retention function for 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, carboxy-methyl cellulose..., which provide the function of binding 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 French patent FR 2 788 887.

[0050] A separator isolates the anodic and cathodic compartments: it is a felt, a porous or ion-exchange membrane, or a combination of felt and a porous membrane. The membrane is generally a hydrophobic polymer membrane which is modified, prior to its implementation, 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 battery, designed according to the main characteristics described below.

[0053] According to a preferred embodiment, a nickel-zinc accumulator is made 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 metallic foam as a collector. Some of these foams These are designated as "battery grade". Suppliers include, for example, Sumitomo Electric (Japan) and Corun (China). The foam thickness is chosen according to the desired surface capacitance of the nickel electrode: it is generally between 1.2 and 2 mm, but it can be laminated to precisely adjust the thickness to the desired surface capacitance.

[0055] The active material consists of nickel hydroxide which preferably also contains co-precipitated zinc and cobalt. The particles are preferably spherical or spheroidal in shape to increase the volumetric capacity. They may be coated with cobalt oxide and hydroxide which, during the formation of the accumulator, are transformed into conductive cobalt oxyhydroxide (Oshitani et al. J. Electrochem. Soc. 1989 136, 6, 1590).

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

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

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

[0060] The zinc electrode collector 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 an 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..., in the form of powders or filaments. - anti-corrosion agents: indium, bismuth, etc. - compounds that react with zincates: calcium hydroxides, barium hydroxides...

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

[0063] Depending on the technique chosen, it is possible to manufacture a high-viscosity paste that can be applied by pressure to both sides of the metal support to form a "sandwich" structure; to manufacture a medium-viscosity paste into which the collector is immersed and then removed, with excess paste being scraped off to adjust the electrode thickness using a scraper, followed by drying; or, finally, to use a dry powder mixed with a binder and compressed onto the metal support to form the electrode. 1. The electrolyte#

[0064] The electrolyte used is preferably a concentrated alkaline solution with a molarity 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 in mixtures.

[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 mixture, as described for example in patent no. US 5 215 836.

[0066] According to the present invention, the quantity of wetting agents added to the electrolyte is between 0.1 g / 1 and 50 g / 1 and preferably between 1 g / 1 and 25 g / 1 of electrolyte; the quantity of antifoaming 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] Wetting agents are selected, in particular, from the ionic wetting agent bis(2-ethylhexyl) phosphate and non-ionic wetting agents derived from alkyl polyglucosides, notably those of the Triton® brand. Antifoaming agents are selected from products belonging to the polyorganosiloxane chemical family. 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 made 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 the addition of silicate as described in the aforementioned French 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 0.2 bar low-pressure valve.

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

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

[0072] Element 1, with a nominal capacity of 8 Ah, is manufactured identically according to the general description provided above. Membrane A is used in element 1. Membrane A is a 25 µm thick microporous polypropylene membrane with an added wetting agent, making it hydrophilic. The pore size was measured at 37 ± 14 nm, and the porosity at 36 ± 1%. The breathability of this membrane A, expressed in Guerleys, is relatively high, exceeding 1000, enabling it to act as a gas barrier by limiting oxygen recombination on the surface of the zinc electrode, thus improving 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 the addition of silicate as described in the aforementioned patent FR 3 099 851 and a wetting and antifoaming agent as described in the aforementioned patent application FR 2 201 375. Element 1 was cycled to 100% depth of discharge at the IC regime with a current of 8 A up to IV. The 8 Ah charge is carried out at the IC regime up to 1.92 V, then at a constant voltage of 1.92 V up to 8 Ah, or it is stopped when the end-of-charge current rises again. [Fig. 1] illustrates this. The charging and discharging capacity of element 1. [Fig. 1] demonstrates a stable capacity for 3300 cycles, falling below 70% after 3800 cycles. Examples 2 and 3 (controls)

[0073] NiZn cells 2 and 3, with a nominal capacity of 8 Ah, are manufactured identically according to the general description provided above. Membrane B is used for cells 2 and 3. Membrane B is a 40 µm thick microporous polypropylene membrane pre-mixed with a wetting agent, making it a hydrophilic membrane. The breathability of this membrane B, expressed in Guerleys, is lower than that of membrane A, ranging from 450 to 750. The porosity is reported to be between 37% and 48%. This wide range of Guerleys and porosity suggests inhomogeneity defects in 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 10 M of hydroxyl anions with the addition of silicate, as described in the aforementioned patent FR 3 099 851.Element 2, mounted with membrane B, reaches zero capacitance after the formation stage, characterized by three charge cycles at C / 10 for 12 hours and discharge cycles at C / 5 until the battery voltage reaches 1.2V. As described in patent application FR 2 201 375, the addition to the electrolyte of four wetting agents, three of which are from the TRITON® brand (BG-10, CG-110, and X-100), plus bis(2-ethylhexyl) phosphate wetting agent, results in a total concentration of 21.3 g / L of the four wetting agents introduced into Element 2 (the same quantity for all four wetting agents). No antifoaming agent is added. After the addition of wetting agents in element 2, the result of the formation of element 2 is comparable to that of element 3. Element 3 mounted with membrane B, leads to a capacity greater 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]. Elements 2 and 3 were tested under constant current C regime at 100% depth of discharge, 8A Ih during charging and 8A IV during discharging.

[0074] Following the addition of wetting agents, element 2 leads to results comparable to element 3 during the first 600 cycles. After 600 cycles, element 2 outperforms element 3, clearly indicating a beneficial impact of the wetting agent additions on the lifespan 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 become functional and permitting a longer lifespan than element 3. This first experiment is therefore conclusive regarding the ability of wetting agents introduced into the electrolyte to bind to the membrane and restore its hydrophilic properties. Example 4 (present invention):

[0075] Element 2 in the aforementioned French patent application FR 2 201 375 describes the addition of wetting agents to 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 using an electrolyte containing an adequate amount of wetting agents while controlling foam formation. Element 4, with a nominal capacity of 8 Ah, is constructed identically according to the general description provided above. Element 4 uses membrane C. Membrane C is a 25 µm thick microporous polypropylene membrane without any added wetting agents to make it 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 3.5 E-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, and 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 pm. The electrolyte used is a concentrated alkaline solution with a molarity of 10M of hydroxyl anions with the 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, consists of three wetting agents: TRITON® BG-10 and TRITON® X-100, plus the wetting agent bis(2-ethylhexyl) phosphate (the same quantity for all four wetting agents). The total concentration of the three wetting agents is 10.8 g / L.An antifoaming 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 charging at the C / 10 regime for 12 hours and discharging at the C / 5 regime until The battery voltage was set to 1.2V. For cell 4, the initial charge was characterized by a very high voltage within the first few minutes, suggesting that membrane C presented too great a barrier to hydroxyl ion diffusion. Cell 4 was then placed in an oven at 45°C to accelerate membrane wetting. After 2 hours, the result was the same, and the cell was placed at 45°C for 15 hours. The initial charge was restarted, with the very high voltage removed, confirming that the membrane had become hydrophilic in situ to the cell. After this formation, cell 4 had a capacity greater than 8 Ah, similar to control cells 1 through 3, which used an initially hydrophilic membrane.

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

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

[0080] The NiZn 5 element with a nominal capacity of 8Ah is manufactured identically according to the general description provided above. Membrane D is used for element 5. Membrane D is a 20µm thick microporous polypropylene membrane without any added wetting agent to make it hydrophilic. Membrane D is therefore completely hydrophobic. The breathability of this membrane, expressed in Gerleys at 550, is lower than that of membrane C. The porosity is stated to be 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 (the same quantity for all 4 wetting agents). An antifoaming agent from the chemical family... Polyorganosiloxanes are added to the electrolyte, at a rate of 630mg per kilogram of electrolyte.

[0081] The formation process is similar to that of elements 1 to 3. It is characterized by three charge cycles at a C / 10 rate for 12 hours and discharge cycles at a C / 5 rate until the battery voltage reaches 1.2V. The charging voltage of the first cycle of the formation is similar and comparable to that of control elements 1 to 3, indicating that membrane D became hydrophilic in situ in element 5 more readily than membrane C. Element 5, after the formation, has a capacity greater than 8Ah and similar to that of control elements 1 to 3, which use a hydrophilic membrane prior to its implementation in the element.

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

[0083] Using a hydrophobic membrane that becomes hydrophilic in situ within the element by using an electrolyte derived from French patent application FR 2 201 375, instead of a pre-existing hydrophilic membrane, advantageously eliminates the pretreatment step(s) required for commercially available hydrophilic membranes. According to the present invention, it is therefore possible to achieve a significant reduction in membrane cost, as some of these hydrophobic membranes are used on a very large scale in lithium batteries and are less expensive to prepare.

[0084] Through 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 choice of concentrations of wetting agents and antifoaming agents can be favorably made over a wide range. The optimal concentrations depend in particular 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 conditions. It has thus been shown that the overall concentrations of wetting agents can range from approximately 0.1 to 50 g, and preferably from 1 to 25 g per liter of electrolyte, and those of antifoaming agents from approximately 10 to 3000 mg, preferably from 100 to 1000 mg per kilogram of electrolyte.

[0085] The preceding demonstrations concern the hydrophilization of an initially hydrophobic membrane. They therefore apply not only to generators nickel-zinc, 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 that have been provided as illustrations, but encompasses all variants thereof.

Claims

Demands

1. - Method of preparing an electrochemical generator, comprising the steps of: • assembling a hydrophobic membrane with a zinc cathode and anode, and then • adding an electrolyte which is an alkaline aqueous solution comprising at least one wetting agent and at least one antifoaming agent.

2. - Method according to claim 1, wherein the cathode is a nickel cathode.

3. - Method according to claim 1, wherein the cathode is a manganese dioxide cathode.

4. - Method according to claim 1, wherein the cathode is a silver cathode.

5. - A method according to any one of the preceding claims, comprising in situ activation of the hydrophobic membrane by impregnation with the electrolyte.

6. - A method according to any one of the preceding claims, wherein the electrolyte comprises at least one ionic wetting agent and at least one non-ionic wetting agent.

7. - A method according to claim 6, wherein the ionic wetting agent is bis(2-ethylhexyl) phosphate.

8. - A method according to claim 6 or 7, wherein the non-ionic wetting agent is selected from alkyl polyglucosides and polyethylene glycol and alkylphenol ethers.

9. - A method according to any one of the preceding claims, wherein the antifoaming agent is selected from polyorganosiloxanes.

10. - A method according to any one of the preceding claims, wherein the electrolyte has a molarity of between 4 M and 15 M of hydroxyl anions.

11. - A method according to the preceding claim, wherein the electrolyte has a molarity of between 7 M and 12 M of hydroxyl anions.

12. - A method according to any one of the preceding claims, wherein the wetting agent(s) has a concentration of between 0.1 g / l and 50 g / l of electrolyte.

13. - Method according to the preceding claim, wherein the wetting agent(s) has a concentration between 1 g / l and 25 g / l.

14. - A method according to any one of the preceding claims, wherein the antifoaming agent(s) is / are present in an amount between 10 mg and 3000 mg per kilogram of electrolyte.

15. - A method according to the preceding claim, wherein the antifoaming agent(s) is / are present in an amount between 100 mg and 1000 mg per kilogram of electrolyte.

16. - Electrochemical generator obtained by the process according to any one of claims 1 to 15.