Manufacturing method of a zinc electrode using an aqueous manufacturing process

Description

Technical field

[0001] The invention relates to the field of electrochemical batteries and more particularly to a method of manufacturing a particular zinc electrode. Prior art

[0002] Metallic zinc negative electrodes for cells or batteries are particularly interesting because they have a high mass capacity (820 Ah / kg of zinc), can be subjected to charge / discharge cycles in aqueous electrolyte and are manufactured from an abundant, non-toxic and inexpensive raw material.

[0003] Zinc electrodes are used in several types of batteries that use an alkaline electrolyte. For example, zinc electrodes can be used in zinc-manganese dioxide batteries (commonly called "alkaline batteries") or zinc-air batteries (used, for example, in hearing aids). These two examples of batteries are not designed to be recharged and their zinc-based negative electrode works by electrochemical transformation of metallic zinc into zinc oxide (according to the reaction in Equation 1), or into zincate [Zn(OH) 4 ] 2-< in solution (according to the reaction in Equation 2)) Equation 1 Zn (s) + 2(OH) -< (aq) → ZnO (s) + H 2 O (l) + 2e Equation 2 Zn (s) + 4(OH) -< (aq) → [Zn(OH) 4 ] 2-< (aq) + 2e -<

[0004] Zinc electrodes are also used as negative electrodes in several types of rechargeable batteries using an alkaline electrolyte, for example Nickel-Zinc, Silver-Zinc or Zinc-Air batteries. To increase the number of charge-discharge cycles of these batteries, it is then preferable that the zinc electrode is mainly made of zinc oxide (ZnO), possibly mixed with metallic zinc (Zn). Indeed, in these examples of rechargeable batteries, the reactions given in equations 1) and 2) must also be able to work in reverse, according to the reactions of equations 3) and 4). Equation 3 ZnO (s) + H 2 O (l) + 2e -< → Zn (s) + 2(OH) -< (aq) Equation 4 [Zn(OH) 4 ] 2-< (aq) + 2e -< → Zn (s) + 4(OH) -< (aq)

[0005] When discharging such a battery, oxygen is reduced at the positive electrode and the metal is oxidized at the negative electrode: Discharge at the negative electrode: M → M n+< + ne Discharge at the positive electrode: O 2 + 2 H 2 O + 4 e → 4 OH -<

[0006] When a metal-air battery needs to be electrically recharged, the direction of the current is reversed. Oxygen is produced at the positive electrode and metal is redeposited by reduction at the negative electrode: Recharge at the negative electrode: M n+< + ne -< → M Recharge at the positive electrode: 4 OH → O 2 + 2 H 2 O + 4 e

[0007] The advantage of zinc-air systems lies in the use of a positive electrode with infinite capacity. Zinc-air electrochemical generators are therefore known for their high specific energies, which can reach several hundred Wh / kg. The oxygen consumed at the positive electrode does not need to be stored in the electrode and can be taken from the ambient air.

[0008] During recharging, the Zn 2+< metal ions are reduced at the negative electrode and are deposited in their Zn metallic form as soon as the potential at this electrode is sufficiently negative. A uniform and homogeneous deposition of the metal on the electrode is desired to ensure good resistance during the charge and discharge cycles of this electrode.

[0009] However, it has been found that under certain conditions, the metal is deposited as a loosely adherent foam on the surface of the electrode, which can then detach from the electrode, causing a loss of active material and consequently a loss of battery capacity. In other cases, it has been found that the metal can also be deposited in dendritic form. These dendrites can grow until they reach the positive electrode during charging, causing an internal short circuit preventing recharging.

[0010] To try to solve these problems, and produce a homogeneous zinc deposit during recharging, certain solutions have already been proposed: Lawrence Berkeley Laboratory (LBL) and MATSI Inc. have sought to increase the porosity in the electrode to reduce the high surface current densities responsible for dendrite formation. Using a porous zinc electrode can, to some extent, limit dendrite growth toward the outside of the electrode, because zinc growth during charging occurs inside the electrode. For example, Joseph F. Parker et al ("Rechargeable nickel-3D zinc batteries: An energy-dense, safer alternative to lithium-ion", Science 28 Apr 2017: Vol. 356, Issue 6336, pp. 415-418; DOI: 10.1126 / science.aak9991) describes a zinc electrode fabricated in a charged state as a sponge. However, this electrode should not be discharged beyond 40% of the theoretical zinc capacity in the electrode and loses more than 20% of its useful capacity after 80 charge / discharge cycles.the installation of a separator on the electrode has been proposed (see for example HL Lewis et al., “Alternative separation evaluations in model rechargeable silver-zinc cells”, Journal of Power Sources 80 (1999) 61-65, and EL Dewi et al., “Cationic polysulfoninun membrane as separator in zinc-air cell”, Journal of Power Sources 115 (2003) 149-152), the addition of additives in the electrolyte has also been considered (see for example CW Lee et al., “Effect of additives on the electrochemical behavior of zinc anodes for zinc / air fuel cells”, Journal of Power Sources 160 (2006) 161-164, and CW Lee et al., “Novel electrochemical behavior of zinc anodes in zinc / air batteries in the presence of additives”, Journal of Power Sources 159 (2006) 1474-1477), the addition of additives to the zinc electrode has also been described. Patent EP 1024545 proposes, for example, adding an electronic conductor that does not participate in the electrochemical reaction.This electronic conductor such as titanium nitride is added in powder form. It contributes to obtaining a more homogeneous and non-dendritic deposition of metallic zinc during charging. Patent application US2018 / 0086646 proposes the use of calcium zincate in the zinc electrode. During the charging phase, the zincate ions Zn(OH) 4 present in solution in the electrolyte are reduced to metallic zinc (equation 4)), decreasing the concentration of zincate ions in solution, particularly in the immediate vicinity of the metallic zinc redeposited on the electrode. This localized decrease in the concentration of zincate ions promotes the growth of metallic zinc in dendritic form. The addition of calcium zincate crystals Ca(OH) 2 .2Zn(OH) 2 .2H 2 O in the zinc electrode aims to locally increase the concentration of zincate ions.In application US2018 / 0086646, calcium zincate is obtained from a mixture of zinc oxide (ZnO), calcium hydroxide (Ca(OH) 2 ) and water in stoichiometric proportion in a large quantity of water, using a high-energy horizontal mixer containing zirconia microbeads. The solution proposed in this application, however, requires specific tooling which complicates the electrode manufacturing process. In addition, calcium zincate is not always distributed homogeneously within the electrode, which does not allow the formation of dendrites to be sufficiently effectively limited. Technical problem

[0011] There remains a need for new zinc electrodes that do not cause the formation of metallic zinc deposits that are detrimental to battery operation, particularly deposits in the form of foam or dendrites.

[0012] Such an electrode should make it possible to increase the number of electrical charge and discharge cycles of the zinc-air battery, and thus advantageously give the battery a longer lifespan. Summary of the invention

[0013] It is to the applicant's credit that he observed that by optimising the distribution and size of the calcium zincate crystals on the zinc electrode, it was possible to limit the formation of zinc deposits in the form of foam or dendrites.

[0014] The present invention provides a novel method of manufacturing a zinc electrode which enables the formation in situ calcium zincate crystals of controlled size within the zinc electrode, said crystals being distributed in a particularly homogeneous manner throughout the structure of the electrode. Statement of the invention

[0015] The present invention relates to a method for manufacturing a zinc electrode, comprising at least the following steps: a) preparing a mixture of zinc oxide (ZnO) and / or one of its precursors, calcium hydroxide (Ca(OH)2) and water (H2O), the molar ratio (ZnO / Ca(OH)2) being between 2 / 1 and 10 / 1, preferably 3 / 1 and 6 / 1 b) ripening the mixture prepared in step a), so as to form calcium zincate crystals Ca(OH)2.2Zn(OH)2.2H2O according to the reaction of equation 5) Equation 5: 2ZnO + Ca(OH)2 + 4H2O → Ca(OH)2.2Zn(OH)2.2H2O, c) adding solvent to the mixture from step b) so as to interrupt ripening by slowing down the growth of the calcium zincate crystals Ca(OH) 2 .2Zn(OH) 2 .2H 2 O, and d) manufacturing a zinc electrode using the mixture comprising calcium zincate crystals Ca(OH) 2 .2Zn(OH) 2 .2H 2 O from step c).

[0016] The presence of calcium zincate crystals Ca(OH) 2 .2Zn(OH) 2 .2H 2 O distributed uniformly in the structure of the electrode itself has the effect of acting as a reservoir making it possible to supply zincate ions in the vicinity of the electrode during the reduction phase, by decomposition according to the reaction of equation 6): Equation 6 Ca(OH) 2 .2Zn(OH) 2 .2H 2 O + 40H -< → 2[Zn(OH) 4 ] 2-< + Ca(OH) 2

[0017] In the context of the invention, the zinc electrode produced using the method described above consists mainly of zinc oxide ZnO, possibly mixed with metallic zinc. It is therefore produced in the discharged state and requires a first charge known as "formation" to precipitate the zinc in metallic form (active material in the redox reaction).

[0018] During the first charging phase (formation charge), several reactions allowing the formation of metallic zinc will take place: the reaction of transformation of zincate ions into metallic zinc, according to equation 4) previously described, which has the fastest kinetics; the reaction of dissolution of zinc oxide into zincate ions according to equation 7) described below, with slower kinetics; and the reaction of transformation of calcium zincate crystals into zincate ions according to equation 6) previously described, Equation 7 ZnO (s) + 2OH -< (aq) + H 2 O → [Zn(OH) 4 ] 2-< (aq)

[0019] It is to the applicant's credit to have observed that the size of the calcium zincate crystals made it possible to control the kinetics of their transformation into zincate ions during the reduction (charging phase). By controlling the size of the calcium zincate crystals, it is thus possible to ensure that their transformation into zincate ions occurs more quickly than the dissolution of the zinc oxide, but more slowly than the transformation of the zincate ions of the electrolyte into metallic zinc. In other words, the size of the calcium zincate crystals is controlled so that the kinetics of their transformation into zincate ions is between that of the dissolution of the zinc oxide and that of the transformation of the zincate ions of the electrolyte into metallic zinc. The calcium zincate crystals thus make it possible to compensate for the localized decrease in zincate ions in the vicinity of the metallic zinc precipitated on the electrode, thus preventing the formation of dendrites.The applicant has also developed a process for manufacturing a zinc electrode comprising calcium zincate crystals of controlled size and distributed homogeneously, in order to control the kinetics of their transformation into zincate ions.

[0020] The present invention also relates, according to another aspect, to a zinc electrode capable of being obtained from such a process.

[0021] The invention also relates, according to a third aspect, to a zinc-air battery using, as negative electrode, at least one zinc electrode as described previously. Step a

[0022] The method according to the invention therefore implements a first step of preparing a mixture of zinc oxide (ZnO) and / or one of its precursors, calcium hydroxide (Ca(OH) 2 ) and water (H 2 O).

[0023] The precursor of zinc oxide (ZnO) may, for example, be chosen from zinc peroxide (ZnO 2 ) or a zinc hydroxide, such as Zn(OH) 2 .

[0024] Preferably, the first step of the process according to the invention comprises the preparation of a mixture of zinc oxide (ZnO), calcium hydroxide (Ca(OH) 2 ) and water (H 2 O).

[0025] Zinc oxide (ZnO) and calcium hydroxide (Ca(OH)2) can be found in powder form.

[0026] Zinc oxide is introduced in molar excess into the mixture of step a). Zinc oxide is notably introduced in a ZnO / Ca(OH) 2 molar ratio of between 3 / 1 and 10 / 1.

[0027] Water (H2O) can be introduced in a mass ratio H2O / (ZnO+Ca(OH)2) between 1 / 5 and 1 / 20.

[0028] Such a quantity of water introduced into the mixture of step a) contributes to obtaining a controlled quantity of calcium zincate crystals having the desired sizes. In the case where the water is introduced in a mass ratio greater than 1 / 1, it is not possible to obtain a paste allowing the manufacture of a zinc electrode because the mixture is then too liquid. The kinetics of the reaction are slower and the size of the calcium zincate crystals is difficult to control. Finally, the zinc electrode obtained from a mixture having too large a quantity of water will contain fewer calcium zincate crystals.

[0029] The preparation of the mixture of step a) may comprise a first sub-step a.1). of mixing zinc oxide and calcium hydroxide, then a second sub-step a.2). of introducing water into the mixture thus produced of zinc oxide and calcium hydroxide.

[0030] In order to obtain a homogeneous mixture of solid reagents, the mixing of sub-step a.1) is carried out with stirring for a time of between 1 min and 10 min, preferably between 2 min and 7 min.

[0031] According to the method of the invention, the water introduced in sub-step a.2) may be, for example, demineralized water, distilled water, water on resin, deionized water and preferably deionized water.

[0032] Once water is added to the mixture preparation from step a), the formation of calcium zincate crystals begins. Step b

[0033] The method according to the invention thus implements a second step of ripening the mixture prepared in step a), so as to form calcium zincate crystals Ca(OH) 2 .2Zn(OH) 2 .2H 2 O according to the reaction of equation 5) Equation 5: 2ZnO + Ca(OH) 2 + 4H 2 O → Ca(OH) 2 .2Zn(OH) 2 .2H 2 O

[0034] Step b) of ripening allows the in-situ production of calcium zincate crystals of optimal size, in particular to prevent dendritic growth of zinc during charging.

[0035] The presence of controlled-size calcium zincate crystals is important to optimize zincate ion production kinetics and prevent dendrite formation.

[0036] Too small crystals, in particular those with a number average size of less than 10 µm, will tend to be consumed quickly and completely according to the reaction of equation 6) for the formation of zincate ions. In this case, the reaction of dissolution of zinc oxide into zincate ions according to equation 7), with slower kinetics, does not have time to take place and the zinc oxide remains inactive. In addition, if the calcium zincate crystals are completely consumed during the charging phase, the nucleation points for their growth during the subsequent discharging step according to the reaction of equation 8) described below, will have disappeared. Indeed, the reaction of equation 8) is initiated more efficiently and more homogeneously in the presence of residual calcium zincate crystals within the electrode. Equation 8 2Zn (s) + 4(OH) -< (aq) + Ca(OH) 2 + 2H 2 O → Ca(OH) 2 .2Zn(OH) 2 .2H 2 O + 4e -<

[0037] Conversely, if the calcium zincate crystals are too large, particularly if they have a number average size greater than 200 µm, the kinetics of the reaction in equation 6) is slowed down. Indeed, their low specific surface area (surface / volume ratio) slows down their dissolution. In this case, the decrease in zincate ion concentration in the electrolyte in the immediate vicinity of the electrode is no longer compensated, which again leads to the formation of dendrites.

[0038] According to a particular embodiment, the ripening step is carried out until crystals are obtained having a number average size of between 10 and 200 µm, preferably 20 and 100 µm, preferably 30 and 80 µm and preferably 40 and 60 µm.

[0039] The ripening step (step b) can be carried out with stirring at room temperature for a period of time allowing the growth of crystals of the desired size. In particular, the ripening step is carried out at a temperature of between 20 and 35°C, preferably between 20 and 25°C. Preferably, the ripening step is carried out for a time of between 3 min and 20 min, preferably between 5 min and 10 min.

[0040] The formation of calcium zincate crystals can be monitored throughout the ripening step b). In particular, the formation of calcium zincate crystals results in an increase in the viscosity of the mixture during step b). It is thus possible to monitor the formation of calcium zincate crystals by, for example, measuring the viscosity of the mixture from step b) continuously or by taking several samples at regular time intervals.

[0041] The calcium zincate crystals obtained using the process according to the invention can be characterized, for example, by scanning electron microscopy or by energy dispersive analysis, EDS or EDX for “energy dispersive X-ray spectrometry”.

[0042] Once the calcium zincate crystals have reached the desired size, ripening step b) is interrupted by adding a solvent to step c). Step c

[0043] The method according to the invention implements a third step of adding solvent to the mixture resulting from step b) so as to interrupt the ripening by slowing down the growth of the calcium zincate crystals Ca(OH) 2 .2Zn(OH) 2 .2H 2 O

[0044] The solvent in step c) neutralizes the precursors remaining after the ripening reaction in step b). Neutralizing the precursors helps to slow down the growth of the calcium zincate crystals, to enable the electrode to be manufactured. Adding the solvent thus helps to control the formation of the calcium zincate crystals, particularly in terms of size and number.

[0045] The short ripening step followed by a step of stopping the growth of calcium zincate by adding solvent allows to obtain an optimal mixture of zinc oxide, calcium hydroxide and calcium zincate.

[0046] The solvent added in step c) may generally be a water-miscible molecule having the hydroxyl function, i.e. an alcohol, and preferably, the solvent may be ethanol.

[0047] The solvent added in step c) is different from water and should not cause too great a decrease in the viscosity of the mixture from step b). In particular, the solvent may be introduced so as to decrease the viscosity of the mixture from step b) by between 1 and 5%, and preferably 2 and 3%. Step d

[0048] The method according to the invention finally comprises a step d) of manufacturing a zinc electrode using the mixture comprising calcium zincate crystals Ca(OH) 2 .2Zn(OH) 2 .2H 2 O obtained at the end of step c).

[0049] In addition to the calcium zincate crystals, the mixture from step c) also comprises zinc oxide (ZnO) or one of its precursors, water (H 2 O), and a residual content (for example less than 5%) of calcium hydroxide (Ca(OH) 2 ) and a solvent. This aqueous mixture, hereinafter referred to as "active mass", makes it possible to produce a zinc electrode comprising in situcalcium zincate crystals.

[0050] Advantageously, the zinc oxide and / or one of its precursors introduced into the mixture of step a) is not entirely consumed by the reaction of formation of calcium zincate crystals. It is then possible to manufacture a zinc electrode directly from the “active mass.”

[0051] The implementation of the method according to the invention allows a uniform distribution of calcium zincate crystals within the zinc electrode. This controlled distribution makes it possible to avoid the formation of non-homogeneous charge points which promote zinc deposition and the formation of dendrites.

[0052] In a first sub-step d.1), the active mass can be passed through a calender in order to smooth it, polish it and make it into a sheet of a predetermined thickness.

[0053] In a second sub-step d.2), the active mass in sheet form may be pressed through a grid or foam in order to give it its final shape and geometry. This sub-step d.2) is preferably carried out in less than four hours, in particular in less than two hours, and more preferably in less than one hour, to avoid hardening of the electrode during its shaping.

[0054] In a third sub-step d.3), the active mass can then be dried, for example in the open air or in a dry oven, in order to form a zinc electrode.

[0055] The zinc electrode thus obtained can then be integrated into an electrochemical battery. Binder

[0056] In order to ensure good cohesion of the zinc electrode obtained by a method as described in this present document, the method of manufacturing the zinc electrode may further comprise the addition of a binder at any of the steps of the method. Preferably, the binder is added at step b) of ripening.

[0057] The binder may be chosen from vinyl binders, acrylic binders, alkyd and glycerophthalic binders, preferably the binder may be chosen from siloxane, epoxy, polyurethane, linseed oil, beeswax or polytetrafluoroethylene (PTFE) and preferably the binder is PTFE.

[0058] In the case where the binder is added in step b) of ripening, the mixture may be stirred for a time of at least 3 min, and preferably a time of at least 5 min. In this way, the binder is distributed evenly throughout the mixture.

[0059] The binder can be added according to a binder / (water + zinc oxide + calcium hydroxide) mass ratio of between 10 and 90% and more particularly a mass ratio of 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85 or 90%, and preferably between 15 and 25%.

[0060] In the case where the binder used is PTFE, it can be introduced preferably in the form of an aqueous suspension at a concentration of between 40 and 80%, and preferably 60%. Other additives

[0061] The zinc electrode may also include any other additive usually used by those skilled in the art.

[0062] For example, to improve the percolation of the mixture, it is also possible to add to any of the steps of the zinc electrode manufacturing process an additive such as bismuth oxide, mercury oxide, indium hydroxide or any electronic conductor, or a mixture thereof.

[0063] Additionally, to protect the current collector from corrosion, metallic zinc (e.g. in the form of zinc powder) can also be added to the electrode.

[0064] Preferably, this addition is made in step a) or between step c) and step d), and preferably in step a) of preparing the mixture.

[0065] Zinc electrode and zinc-air battery

[0066] The invention also relates to a zinc electrode capable of being obtained by means of a method as described above, as well as a zinc-air battery comprising, as negative electrode, at least one zinc electrode.

[0067] In particular, the zinc electrode obtainable by means of a process as described above comprises from 20 to 45% by weight, preferably from 30 to 40% by weight of calcium zincate crystals.

[0068] In particular, the zinc-air battery includes: a negative terminal, a positive terminal, a negative electrode, connected to the negative terminal, a positive air electrode said negative electrode being a zinc electrode as previously described.

[0069] The positive electrode of the battery according to the invention may be an air electrode. An air electrode is a porous solid structure in contact with the liquid electrolyte. The interface between the air electrode and the liquid electrolyte is a so-called "triple contact" interface where the active solid material of the electrode, the gaseous oxidant, i.e., air, and the liquid electrolyte are simultaneously present. A description of the different types of air electrodes for zinc-air batteries is set out, for example, in the bibliographic article by V. Neburchilov et al., entitled "A review on air cathodes for zinc-air fuel cells", Journal of Power Sources 195 (2010) p. 1271-1291. Any type of air electrode may be used in the battery according to the present invention.In particular, the first positive air electrode of the battery may be an electrode obtained by agglomeration of a carbon powder consisting of carbon grains with a high specific surface area, as described in patent application WO 2000 / 036677. The air electrode, based on carbon particles, may further contain at least one oxygen reduction catalyst. This oxygen reduction catalyst is preferably chosen from the group consisting of manganese oxide and cobalt oxide.

[0070] In addition to the air electrode, the battery according to the invention may comprise a second positive electrode which is an oxygen-releasing electrode. Any type of electrode fulfilling this function known to those skilled in the art may be used in the battery according to the present invention. The second positive oxygen-releasing electrode may, for example, be a metal electrode stable in the electrolyte of the battery, such as a silver, nickel or stainless steel electrode.

[0071] When it comprises two positive electrodes, the battery according to the invention may comprise at least one switching means making it possible to connect to the positive terminal either the first positive air electrode or the second positive oxygen-releasing electrode and a means for charging the battery, which can be connected to the negative electrode and to the second positive oxygen-releasing electrode. Brief description of the drawings Fig. 1

[0072] [ Fig. 1 ] shows an illustration of the calcium zincate crystals Ca(OH)2.2Zn(OH)2.2H20 (1) formed during step b) according to the method of the present invention. Said crystals are formed in-situ in the mixture of zinc oxide (ZnO), calcium hydroxide (Ca(OH)2) and water (H2O) (2). Examples

[0073] A zinc electrode was prepared by means of the method according to the invention.

[0074] In the case of this example, the quantities presented in Table 1 of reagents were used. [Table 1] Reagent Quantity ZnO 150 g Ca(OH) 2 30 g Deionized water 30 mL PTFE 20 mL Ethanol 30 mL

[0075] Zinc oxide powder (Merck emsure) is mechanically mixed with calcium hydroxide (Merck) for five minutes in a mixer at 23°C. While keeping the mixer running, deionized water is added to the mixture at a constant speed over a period of thirty seconds, ensuring good homogeneity of the mixture. The addition of water initiates the formation of calcium zincate crystals.

[0076] The mixture is kept stirring for three minutes. Then, an aqueous suspension of PTFE at a concentration of 60% (Aldrich) is added over a period of one minute.

[0077] The mixture is again kept stirring for five minutes during which time the calcium zincate crystals continue to form and grow.

[0078] The ripening reaction is interrupted by adding ethanol over a period of ten seconds.

[0079] The resulting mixture is then passed through a calender, pressed and dried to form a zinc electrode in the discharged state.

Claims

1. A production method for a zinc electrode, comprising at least the following steps: a) preparation of a mixture of zinc oxide (ZnO) and / or one of the precursors thereof, calcium hydroxide (Ca(OH)2) and water (H2O), the molar ratio (ZnO / Ca(OH)2) being comprised between 3 / 1 and 10 / 1, the mass ratio H2O / (ZnO+Ca(OH)2) being comprised between 1 / 5 and 1 / 20, b) ripening of the mixture prepared in step a), so as to form calcium zincate crystals Ca(OH)2·2Zn(OH)2·2H2O according to the reaction from equation 5         Equation 5     2ZnO + Ca(OH)2 + 4H2O → Ca(OH)2·2Zn(OH)2·2H2O, c) addition of solvent to the mixture coming from step b) so as to interrupt the ripening by slowing the growth of the calcium zincate crystals Ca(OH)2·2Zn(OH)2·2H2O, and d) production of a zinc electrode by means of the mixture comprising calcium zincate crystals Ca(OH)2·2Zn(OH)2·2H2O from step c).

2. The method according to claim 1, characterized in that the ripening step b) is done at ambient temperature, in particular comprised between 20 and 35°C, preferably comprised between 20 and 25°C.

3. The method according to any one of the preceding claims, characterized in that the ripening step b) is executed for a time comprised between 3 minutes and 20 minutes, preferably between 5 minutes and 10 minutes.

4. The method according to any one of the preceding claims, characterized in that the solvent added in step c) is an alcohol, preferably ethanol.

5. The method according to any one of the preceding claims, characterized in that the crystals from step d) have an average size by number comprised between 10 and 200 µm, preferably 20 and 100 µm, preferably 30 and 80 µm and preferably 40 and 60 µm.

6. The method according to any one of the preceding claims, characterized in that the production of the electrode for step d) comprises at least the three following sub-steps: d.1) passage of the mixture obtained in step c) in a calender; d.2) pressing of the mixture from the sub-step d.1); d.3) drying of the mixture from the sub-step d.2);7. The method according to any one of the preceding claims, characterized in that a binder is added in any one of steps a) to d), and preferably a binder is added in step b).

8. The method according to claim 7, characterized in that the binder is polytetrafluoroethylene (PTFE).

9. The method according to any one of the preceding claims, characterized in that another additive is added in any one of steps a) to d), and preferably in step a).

10. The method according to claim 9, characterized in that the additive is selected from bismuth oxide, mercury oxide, indium hydroxide or an arbitrary electronic conductor, or a mixture thereof.

11. Zinc electrode obtainable by means of a production method according to any one of claims 1 to 10.

12. A zinc-air battery comprising at least one zinc electrode according to claim 11 as negative electrode.