Process for manufacturing a zinc electrode by aqueous means

Abstract

The present invention relates to a method for manufacturing a zinc electrode with in-situ formation of calcium zincate crystals. The method comprises in particular the steps of preparing a mixture, growing the crystals, slowing down the growth and manufacturing the electrode.

Description

Title of the invention: Method for manufacturing a zinc electrode using an aqueous method 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 of 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 using 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 of equation 1), or into zincate [Zn(OH)4]2 in solution (according to the reaction of equation 2))

[0004] Equation 1 Zn(s) + 2(OH) (aq) —> ZnO(S) + H2O(i) + 2e

[0005] Equation 2 Zn(s) + 4(OH)(aq) -> [Zn(OH)4]2 (aq) + 2e

[0006] 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 for the zinc electrode to be mainly made of ZnO, possibly mixed with metallic zinc. Indeed, in these examples of rechargeable batteries, the reactions given in equations 1) and 2) must also be able to operate in the opposite direction, according to the reactions of equations 3) and 4).

[0007] To increase the number of charge-discharge cycles of these batteries, it is then preferable for the zinc electrode to be mainly made of ZnO, possibly mixed with metallic zinc. Indeed, in these examples of rechargeable batteries, the reactions given in equation 1) and 2) must also be able to operate in the opposite direction, according to the reactions of equations 3) and 4).

[0008] Equation 3 ZnO(S) + H2O(1) + 2e —> Zn(s) + 2(OH) (aq)

[0009] Equation 4 [Zn(OH)4]2 (aq) + 2e -> Zn(s) + 4(OH) (aq)

[0010] 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 —> Mn+ + ne - Discharge at the positive electrode: O2 + 2 H2O + 4 e —> 4 OH

[0011] 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: Mn+ + ne ->M - Recharge at the positive electrode: 4 OH —> O2 + 2 H2O + 4 e

[0012] 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.

[0013] During recharging, the Zn2+ metal ions are reduced at the negative electrode and are deposited in their Zn metal 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 performance during the charge and discharge cycles of this electrode.

[0014] However, it has been found that, under certain conditions, the metal is deposited in the form of a poorly adhering foam on the surface of the electrode, which foam 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.

[0015] 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 surface current densities responsible for dendrite formation, when they are high. The use of a porous zinc electrode allows, to a certain extent, to limit the growth of dendrites towards the outside of the electrode, because the growth of zinc 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 to 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 deposit 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 .2H2O 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, using a high-energy horizontal mixer containing zirconia microbeads.The solution proposed in this application, however, requires specific tools which complicate the electrode manufacturing process. In addition, the calcium zincate is not always distributed homogeneously within the electrode, which does not limit the formation of dendrites sufficiently effectively. Technical problem

[0016] There remains a need for new zinc electrodes that do not cause the formation of a deposit of metallic zinc harmful to the proper functioning of the battery, in particular deposits in the form of foam or dendrites.

[0017] Such an electrode must 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 service life. Summary of the invention

[0018] It is to the applicant's credit to have observed that by optimizing 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.

[0019] The present invention provides a novel method for manufacturing a zinc electrode which allows the in-situ formation of 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

[0020] The subject of the present invention is a method for manufacturing a zinc electrode, comprising at least the following steps: (a) the preparation of a mixture of zinc oxide (ZnO) and / or one of its precursors, calcium hydroxide (Ca(OH)2) and water (H2O), 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 the ripening by slowing down the growth of calcium zincate crystals Ca(OH)2 .2Zn(OH)2.2H2O, and d) manufacturing a zinc electrode using the mixture comprising calcium zincate crystals Ca(OH)2.2Zn(OH)2.2H2O from step c).

[0021] The presence of calcium zincate crystals Ca(OH)2.2Zn(OH)2.2H2O 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):

[0022] Equation 6 Ca(OH)2.2Zn(OH)2.2H2O + 4OH -> 2[Zn(OH)4]2 + Ca(OH)2

[0023] In the context of the invention, the zinc electrode produced by means of 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 called "formation" to precipitate the zinc in metallic form (active material of the redox reaction).

[0024] 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 presents 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,

[0025] Equation 7

[0026] ZnO(s) + 2OH (aq) + H2O [Zn(OH)4]2 (aq)

[0027] 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 method 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.

[0028] The present invention also relates, according to another aspect, to a zinc electrode capable of being obtained from such a process.

[0029] 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.

[0030] Step a

[0031] 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 (H2O).

[0032] The precursor of zinc oxide (ZnO) may, for example, be chosen from zinc peroxide (ZnO2) or a zinc hydroxide, such as Zn(OH)2.

[0033] 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 of water (H20).

[0034] Zinc oxide (ZnO) and calcium hydroxide (Ca(OH)2) can be in the form of powders.

[0035] The zinc oxide is preferably introduced in molar excess into the mixture of step a). The zinc oxide may in particular be introduced in a ZnO / Ca(OH)2 molar ratio of between 2 / 1 and 10 / 1, preferably 3 / 1 and 6 / 1.

[0036] Water (H2O) can be introduced in a mass ratio H2O / (ZnO+Ca(OH)2) of between 1 / 1 and 1 / 20 and, preferably, between 1 / 5 and 1 / 10.

[0037] The preparation of the mixture of step a) may comprise a first sub-step a1). 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.

[0038] In order to obtain a homogeneous mixture of solid reagents, the mixing of sub-step a1) is carried out with stirring for a time of between 1 min and 10 min, preferably between 2 min and 7 min.

[0039] According to the process 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.

[0040] Once water is added to the preparation of the mixture of step a), the formation of calcium zincate crystals begins.

[0041] Step b

[0042] The method according to the invention thus implements a second step of maturing 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

[0043] The ripening step b) makes it possible to manufacture in situ calcium zincate crystals of optimal size, in particular to prevent dendritic growth of zinc during charging.

[0044] The presence of calcium zincate crystals of controlled size is important to optimize the kinetics of zincate ion production and prevent the formation of dendrites.

[0045] Crystals that are too small, 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. Furthermore, 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.

[0046] Equation 8

[0047] 2Zn(s) + 4(OH)(aq) + Ca(OH)2 + 2H2O Ca(OH)2.2Zn(OH)2.2H2O + 4e

[0048] Conversely, if the calcium zincate crystals are too large, in particular having a number average size greater than 200 pm, the kinetics of the reaction of 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.

[0049] 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 pm, preferably 20 and 100 pm, preferably 30 and 80 pm and preferably 40 and 60 pm.

[0050] 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.

[0051] The formation of calcium zincate crystals can be monitored throughout the duration of 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 measuring, for example, the viscosity of the mixture from step b) continuously or by taking several samples at regular time intervals.

[0052] 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”.

[0053] Once the calcium zincate crystals have reached the desired size, ripening step b) is interrupted by adding a solvent to step c).

[0054] Step c

[0055] 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)2.2H2O

[0056] The solvent of step c) neutralizes the precursors remaining after the ripening reaction of step b). The neutralization of the precursors makes it possible in particular to slow the growth of calcium zincate crystals, to allow the electrode to be manufactured. The addition of the solvent thus makes it possible to control the formation of calcium zincate crystals, particularly in size and number.

[0057] The short ripening step followed by a step of stopping the growth of calcium zincate by adding solvent makes it possible to obtain an optimal mixture of zinc oxide, calcium hydroxide and calcium zincate.

[0058] The solvent added in step c) may generally be a molecule miscible with water having the hydroxyl function, i.e. an alcohol, and preferably, the solvent may be ethanol.

[0059] The solvent added in step c) should not cause too great a decrease in the viscosity of the mixture resulting from step b). In particular, the solvent may be introduced so as to reduce the viscosity of the mixture resulting from step b) by between 1 and 5%, and preferably 2 and 3%.

[0060] Step d

[0061] 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)2.2H2O obtained at the end of step c).

[0062] In addition to the calcium zincate crystals, the mixture resulting from step c) also comprises zinc oxide (ZnO) or one of its precursors, water (H2O), 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-situ calcium zincate crystals.

[0063] The implementation of the method according to the invention allows a uniform distribution of the 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.

[0064] In a first sub-step dl), 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.

[0065] In a second sub-step d.2), the active mass in sheet form may be pressed through a grid or a 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.

[0066] 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.

[0067] The zinc electrode thus obtained can then be integrated into an electrochemical battery.

[0068] Binder

[0069] 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.

[0070] 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.

[0071] In the case where the binder is added in step b) of curing, 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 uniformly throughout the mixture.

[0072] The binder may 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 of between 15 and 25%.

[0073] In the case where the binder used is PTFE, it can be introduced preferentially in the form of an aqueous suspension at a concentration of between 40 and 80%, and preferably 60%.

[0074] Other additives

[0075] The zinc electrode may also comprise any other additive usually used by those skilled in the art.

[0076] For example, to improve the percolation of the mixture, it is also possible to add to any of the steps of the process for manufacturing the zinc electrode an additive such as bismuth oxide, mercury oxide, indium hydroxide or any electronic conductor, or a mixture thereof.

[0077] Further, to protect the current collector from corrosion, metallic zinc (e.g., in the form of zinc powder) may also be added to the electrode.

[0078] Preferably, this addition is made in step a) or between step c) and step d), and preferably in step a) of preparing the mixture.

[0079] Zinc electrode and zinc-air battery

[0080] 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.

[0081] In particular, the zinc electrode capable of being obtained 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.

[0082] In particular, the zinc-air battery comprises: - 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 described above.

[0083] 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.

[0084] 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 stable metal electrode in the electrolyte of the battery, such as a silver, nickel or stainless steel electrode.

[0085] 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.l

[0086] [Fig.l] shows an illustration of calcium zincate crystals Ca(OH)2.2Zn(OH)2.2H2O (1) formed during step b) according to the process of 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

[0087] A zinc electrode was prepared by means of the method according to the invention.

[0088] In the case of the present example, the quantities presented in Table 1 of reagents were used.

[0089] [Tables 1] Reagent Quantity ZnO 150 g Ca(OH)2 30 g Deionized water 30 mL PTFE 20 mL Ethanol 30 mL

[0090] 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 at a constant speed to the mixture over a period of thirty seconds, ensuring good homogeneity of the mixture. The addition of water initiates the formation of calcium zincate crystals.

[0091] 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.

[0092] The mixture is again kept stirring for five minutes during which time the calcium zincate crystals continue to form and grow.

[0093] The ripening reaction is interrupted by adding ethanol over a period of ten seconds.

[0094] The resulting mixture is then passed through a calender, pressed and dried to form a zinc electrode in the discharged state.

Claims

Claims

1. A method of 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 3 / 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 the ripening by slowing down the growing calcium zincate crystals Ca(OH)2.2Zn(OH)2.2H2O, and d) manufacturing a zinc electrode using the mixture comprising calcium zincate crystals Ca(OH)2.2Zn(OH)2.2H2O from step c).

2. Method according to claim 1, characterized in that the ripening step b) is carried out at room temperature, in particular between 20 and 35°C, preferably between 20 and 25°C.

3. Method according to any one of the preceding claims, characterized in that the ripening step b) is carried out for a time of between 3 min and 20 min, preferably between 5 min and 10 min.

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

5. Method according to any one of the preceding claims, characterized in that the crystals of step d) have a number average size of between 10 and 200 pm, preferably 20 and 100 pm, preferably 30 and 80 pm and preferably 40 and 60 pm.

6. Method according to any one of the preceding claims, characterized in that the manufacture of the electrode of step d) comprises at least the following three sub-steps: dl). passing the mixture obtained in step c) through a calender, d.2). pressing the mixture of sub-step dl), d.3). drying the pressed mixture of sub-step d.2).

7. A method according to any preceding claim, ca-

8.

9.

10.

11.

12. characterized in that a binder is added in any one of steps a) to d), and preferably a binder is added in step b). Method according to claim 7, characterized in that the binder is polytetrafluoroethylene (PTFE). A method according to any one of the preceding claims, characterized in that another additive is added to any one of steps a) to d), and preferably one to step a). Method according to claim 9, characterized in that the additive is chosen from bismuth oxide, mercury oxide, indium hydroxide or an electronic conductor, or a mixture thereof. Zinc electrode obtainable by means of a manufacturing method according to any one of claims 1 to 10. Zinc-air battery comprising, as negative electrode, at least one zinc electrode according to claim 11.

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