Zinc electrode

Abstract

The present invention relates to a zinc electrode (100) on which a solid metallic zinc layer (300) is electrodeposited, an electrochemical cell and a method for electrodeposition of zinc in an electrochemical cell. According to the present invention, a zinc electrode (100) is provided, where the zinc electrode (100) comprises a current collector material (200) having a zinc layer (300) electrodeposited thereon, where the zinc layer (300) is presented as a dense solid metal, comprises a giant and / or layered microstructure, and is adhered with dense pores.

Description

[0001] This invention relates to a zinc electrode having a solid zinc metal layer electrodeposited thereon, an electrochemical cell, and a method for zinc electrodeposition in the electrochemical cell.

[0002] Zinc (Zn) electrodes, or zinc electrodeposition on current collector materials, are important in many fields, such as electrowinning, zinc plating, and zinc rechargeable batteries.

[0003] Zinc is one of the most commonly used anode materials for batteries due to its high capacity density of 820 Ah / kg (approximately 5820 Ah / L). Except for zinc-carbon galvanic cells (where the zinc anode is in solid form), zinc electrodes in all battery systems are powdered to ensure good availability of electrolytes at the high zinc-electrolyte interface and near the surface. Such electrodes have space to store dissolved products and allow for high reaction rates due to their high surface area based on both weight and volume.

[0004] In zinc electrodes of various battery pack systems, a porosity of 60-80% for zinc deposits is most common. This equates to a capacity of 1.2 Ah / cm² for the zinc active material in such applications. 3 (equal to ~1.46g / cm³) 3 Up to 2.2 Ah / cm 3 (equal to ~2.7g / cm³) 3 ).

[0005] However, high-energy-density alkaline galvanic cells use 3-3.5 g / cm³. 3 The higher density Zn electrode, which is equivalent to about 42-50% of the zinc volume or about 50-58% of the porosity of these zinc deposits.

[0006] The standard potential of the zinc electrode is shown in equation [I].

[0007]

[0008] The oxidation of the zinc electrode during discharge can involve several basic steps, including the oxidation of zinc atoms on the surface (i.e., the breaking of metallic bonds), solvation in the solution, diffusion in the electrolyte, and precipitation of the zinc oxide (ZnO) solid phase when the solubility limit is reached. The deposition process during electrode (re)charging is the reverse of this.

[0009] It can form many zinc complexes, but the main component in high-molar potassium hydroxide (KOH) has been identified as tetrahedral. The electrode also exhibits a relatively high exchange current density, approximately 0.1–0.25 A / cm². 2 .

[0010] The dissolution process of the zinc electrode in alkaline solution can be represented by equation [II].

[0011]

[0012] When the solution near the surface is saturated with dissolved zinc, zinc oxide can precipitate according to the following reaction [III].

[0013]

[0014] Therefore, the overall reaction from zinc metal is shown in equation [IV].

[0015] Zn + 2OH - =ZnO + H₂O + 2e - [IV]

[0016] However, the morphology of zinc deposits and their control play a crucial role in the quality and performance of the final zinc-deposited electrode and in the use of such electrodes in a variety of applications.

[0017] To date, zinc electrodes have primarily been used in primary cells, rather than rechargeable batteries like alkaline or zinc-air batteries. Rechargeable systems using zinc negative electrodes have been researched and developed for various applications, such as Zn-Ag batteries, Zn-MnO2 rechargeable alkaline batteries, Zn-NiOOH rechargeable nickel-zinc batteries, Zn-O2 rechargeable zinc-air batteries, Zn-H2 hydrogen production batteries, or electrolyzers, which sequentially produce hydrogen and oxygen and store energy through zinc deposition.

[0018] However, zinc batteries use zinc electrodes (anodes) with high surface area to reduce overpotential. This high surface area is achieved by using a paste of finely powdered zinc (also known as powdered zinc). Zinc electrodes used in rechargeable batteries must have some kind of mesh-like structure to hold zinc ions in place. This holding is primarily ensured by additives and binders. The advantage of powdered zinc is its slightly lower overpotential during discharge. Typically, zinc in powder, granular composition, or fibrous form is used as the negative electrode in zinc batteries in gel form along with binders and additives, with typical zinc particle sizes ranging from 20 to 50 μm.

[0019] A major problem associated with zinc-based rechargeable batteries is limited cycle life, primarily due to the tendency of the zinc electrode morphology to change during zinc electrodeposition, either during charging or throughout the cycle. Morphological changes leading to electrode performance degradation or failure can occur in several ways: shape changes, moss-like zinc deposition, densification, and dendrite formation. Shape changes are a phenomenon related to alterations in the geometry of the zinc electrode, where the zinc active material leaves one location and accumulates at others. In such batteries, not all zinc ions are fixed in their positions but flow through the electrolyte and deposit back as metallic zinc at different locations. Densification is the phenomenon where the electrode loses porosity and active surface area, resulting in reduced kinetics and increased susceptibility to passivation. Densification is often observed alongside shape changes. Dendrite formation occurs during charging and can potentially penetrate the separator of the electrochemical cell, causing short circuits and transient battery failure.

[0020] Interest in developing rechargeable zinc batteries or zinc-air batteries as high-energy power sources has spurred ongoing research into deposition from alkaline zincate solutions. It has been found that the cycle life of such rechargeable zinc or zinc-air batteries is limited, primarily because the zinc electrode's passivation tendency and solubility in concentrated alkaline solutions are life-limiting factors. Furthermore, morphological changes such as dendrite formation or loss of porosity can occur during charging or discharging of the zinc electrode. Another point to consider is the potential formation of moss-like and thick, spongy deposits, which can cause zinc particles to detach from the electrode and lead to short circuits in the battery.

[0021] Morphological zinc deposits that may occur during the electrodeposition of zinc to create zinc-deposited electrodes include a variety of types. Typically, five main morphological types are described in the prior art: thick spongy, dendritic, boulder-like, layered, and moss-like. Dendritic growth is generally considered to be diffusion-controlled, while moss growth is activation-controlled. Kinetically, dendritic growth has a preferred crystal orientation and planarity. In battery applications, both moss-like and dendritic morphologies must be prevented. Moss-like deposits can lead to loss of active material at electrode edges or short circuits. It can also cause shape changes. Moss-like zinc is preferably deposited at low current densities, high zincate concentrations, and high temperatures. Conditions favorable for dendrite formation are high current densities, low zincate concentrations, and low temperatures. It has also been shown that the generation of molecular hydrogen (H2) can lead to morphological changes favorable to dendritic, moss-like, or thick spongy morphologies. Furthermore, H2 evolution leads to electrolyte drying and increased pressure in electrochemical cells. The generation of H2 is a result of excessive current density, which in turn generates overvoltage during charging.

[0022] The causes and conditions for the appearance of one or more morphological features are the subject of current research, but are not yet fully elucidated. It is unclear how to almost completely prevent such structures during the production of zinc-loaded electrodes. Structures resembling boulders or layered structures can only be produced under very specific conditions and with specific raw materials. For example, in the prior art, such structures can only be produced by electrodepositing zinc on a zinc substrate. However, this makes such products unsuitable for applications in galvanic cells or even battery packs.

[0023] However, existing methods cannot produce uniform zinc layers over long deposition times, let alone layers of greater mass. In known existing methods, the morphology of the zinc layer always changes with increasing electrodeposition time. During electrodeposition according to existing techniques, the zinc layer undergoes a morphological change from a fairly dense and adhesive layer to a moss-like or thick, spongy, non-dense, highly porous, or filamentous layer that no longer adheres, thus leading to short circuits or other effects such as overheating. In other cases, the formation of dendritic layers causes the electrodeposition process to stop or be interrupted. Dendrites can also cause short circuits. Furthermore, passivation may occur during previous discharge processes, leading to the formation of moss-like or filamentous deposits in new deposition processes. Such filamentous deposits have low density and do not adhere to the electrode, thus causing short circuits.

[0024] Furthermore, rechargeable batteries or electrochemical storage devices with zinc negative electrodes can be constructed using metallic zinc electrodes in the charging state, or using a ZnO layer on a current collector or zincates in the electrolyte in the discharging state. Of course, galvanic cells are manufactured using zinc powder in the charging state. In most cases, rechargeable NiZn batteries are assembled in the discharging state, but also in the charging state, for example, using 3D porous zinc electrodes.

[0025] Zinc electrodes in the prior art vary due to their structure and zinc content. For rechargeable systems, capacity density is related to the depth of discharge (DOD) or state of charge (SOC) usable during cycling. This means that not all of the zinc is used to store energy. In primary systems, approximately 95% of the zinc is used for discharge. However, prior art rechargeable systems can only withstand a few cycles (approximately 10 cycles) with a DOD / SOC in the 90% range. The best reported results show 100-200 cycles with a DOD of 40% and thousands of cycles with a DOD <1%.

[0026] In most Zn-air and NiZn rechargeable batteries, the zinc electrode, not the counter electrode, is the lifespan (cycle count) limiting component. Zinc does not cycle completely because the zinc electrode loses electrical connections between its structure and the active material portion. In most systems, the capacity of the zinc electrode is two to three times that of the counter electrode. It should be noted that due to the high capacity of zinc metal, even cycling with 30-40% zinc can produce competitive battery pack systems.

[0027] Therefore, the object of the present invention is to provide an electrodeposited zinc electrode that overcomes the shortcomings of the prior art. In particular, the present invention provides a zinc electrode that, when used in applications, achieves almost 100% zinc utilization while providing virtually unlimited cycling.

[0028] This objective is achieved by a zinc electrode having the features of claim 1, an electrochemical cell having the features of claim 13, and a method having the features of claim 22. Preferred embodiments of the invention are defined in the corresponding dependent claims.

[0029] According to the present invention, a zinc electrode is provided, wherein the zinc electrode comprises a current collector material on which a zinc layer is electrodeposited, wherein the zinc layer is a dense solid metal comprising a boulder-like and / or layered microstructure and adhered with dense pores. In the sense of the present invention, dense means densely packed without large gaps.

[0030] According to another preferred embodiment, during discharge cycling, the zinc layer is partially or completely removed from the current collector material, resulting in bare current collector material in the case of complete removal.

[0031] In the context of this invention, "completely" means that approximately 100% of the zinc layer can be removed. In other words, the zinc layer can be partially (SOC > 0) or completely (SOC = 0) dissolved from the current collector material by a discharge process, such that, in the case of complete zinc dissolution, the exposed current collector material can be used for further electrodeposition. However, the discharge can also partially dissolve the Zn layer, which can then be electrodeposited again. In principle, this formation / electrodeposition and dissolution of the Zn layer can be repeated almost indefinitely. In the context of this invention, exposed current collector material refers to current collector material in its initial state of use, i.e., with little or no residue.

[0032] According to another preferred embodiment, the zinc layer is electrodeposited on the bare current collector material or on a current collector material on which a zinc layer has already been electrodeposited. This means that electrodeposition of the electrode according to the invention can begin or occur when SOC ≥ 0.

[0033] According to another preferred embodiment, the zinc layer comprises 3.50 to 7.14 g / cm³.3 The density is preferably 4.50 to 7.14 g / cm³. 3 The density is preferably in the range of 5.00 to 7.00 g / cm³. 3 The density falls within a certain range. Ideally, the density is close to 7.14 g / cm³. 3 These densities are almost identical to the true density of metallic zinc. This indicates that the zinc deposits according to the present invention have almost the same density as metallic zinc. Moss-like or dendritic zinc deposits do not achieve such densities. In some experiments, zinc deposits with higher densities can be produced by existing technologies, but they have very low thicknesses and partially undergo morphological changes. Furthermore, in these tests, the zinc deposits were deposited only on a tempered zinc substrate used as a current collector, which is not meaningful for commercial applications. Under certain deposition conditions, densities less than 3.5 g / cm³ can be obtained. 3 Or even a specific low porosity. This may be advantageous for achieving a higher surface area, thereby reducing overpotential.

[0034] The zinc electrode maintains a high capacity density of zinc. According to the invention, the density is 3.50-7.14 g / cm³. 3 The depositional densities correspond to 2.87 Ah / cm³. 3 -5.85Ah / cm 3 The capacity density is high. When used in battery packs or other applications, such a zinc electrode according to the invention can provide virtually unlimited charge / discharge cycles for battery packs or other applications. The zinc deposition according to the invention results in a compact, interconnected metallic morphology. All portions of the zinc deposit are directly electrically connected to the current collector material. Therefore, there is no oxide barrier as in powdered / granular zinc electrode applications. The invention is characterized in that such a zinc electrode, when used in a battery system or application (e.g., a battery pack), starts up at a state of discharge (SOC) of 0. By using the zinc electrode according to the invention, much higher energy density can be achieved in applications due to the use of a high SOC (up to about 80-100% ZnO / zincate can be used for charging in the system / application, and 100% DOD can be used for discharging). One feature of the invention is that when the zinc electrode is used, for example, in a battery pack, a large number of cycles (virtually unlimited cycles) can be achieved by introducing a 100% DOD step during cycling. Zinc volume changes and / or some mossy / dendritic deposits can be completely removed, and the system, more precisely the zinc electrode, can begin uniform and smooth zinc deposition again. Therefore, the capacity and capacity density values ​​described in this invention relate to 100% DOD-deposited zinc being used entirely for energy storage, thus having a high capacity density.

[0035] According to a preferred embodiment, neither the current collector material nor the zinc layer contains adhesives, meshes, foams, fabric structures, or additives to bond the zinc layer to the current collector material. Unlike prior art, the electrode according to the invention does not require any meshes, foams, fabric structures, or adhesives, which is the case with rechargeable Zn-air batteries or galvanic cells; therefore, the electrode according to the invention has a much higher energy density compared to prior art. Furthermore, the electrode of the invention does not contain additives, such as calcium hydroxide, which is commonly used for zincate fixation.

[0036] According to another preferred embodiment, the zinc layer is made of non-powdered zinc. However, compared to powdered zinc electrodes and their applications, the electrode according to the invention has a smaller active surface area, resulting in a larger overvoltage. In the solid non-powdered zinc deposition according to the invention, zinc will always have an electrical connection with the current collector material, whereas in powdered deposition, the passivated particles will lose their electrical connection with the current collector, thus leading to lower utilization of the active material. Here, it is important to understand that in the electrode according to the invention, plating pure solid metallic zinc during charging or electrodeposition does not produce, nor does it already have, powdered deposits. Powdered zinc is also understood as a moss-like zinc deposit, which, when separated from the substrate, has the same negative properties as powdered zinc. However, such powdered deposition is undesirable in the electrode according to the invention; on the contrary, the zinc deposition according to the invention results in a dense, interconnected metallic morphology. Although the surface area may be smaller compared to zinc powder, the discharge current may not be so small because the particles may be covered by an oxide layer, and the conductivity through the particulate oxide is lower than that in the solid zinc layer described herein.

[0037] One advantage of solid zinc, non-powdered deposition, is the high zinc utilization rate during discharge and the deposition rate of hundreds of mg / cm³. 2 The ability to achieve a thicker, smoother zinc layer. Furthermore, such electrodes can achieve a virtually unlimited number of charge / discharge cycles without any permanent changes in electrode shape.

[0038] According to another preferred embodiment, the current collector material is selected from one or more of the following: steel, low-carbon steel, nickel, nickel-plated steel, nickel-plated low-carbon steel, or nickel-phosphorus (NiP) coated steel. Low-carbon steel is found to be a preferred material because it is very inexpensive, does not corrode in alkaline environments, and does not exhibit H2 precipitation on its surface. The electrode may also comprise at least one of a polymer substrate or composite material having a nickel (Ni) or NiP surface coating. Alternatively, the electrode may comprise a structure made of carbon fibers or fibers with a conductive surface coating. Optional additives to reduce self-discharge may also be applied to the electrolyte or deposited on the current collector material. In this case, the surface area of ​​the electrode is increased, but a dense, high-density, highly conductive zinc layer is deposited on such a high surface area substrate.

[0039] Furthermore, according to the preferred embodiment, the current collector material is cold-formed, preferably cold-rolled.

[0040] Furthermore, according to another preferred embodiment, the current collector material is cold-rolled steel, particularly cold-rolled low-carbon steel. Surprisingly, cold-formed materials (especially cold-formed or cold-rolled steel or low-carbon steel) have been found to be particularly suitable as current collector materials for the production of electrodes according to the invention. Cold-rolled low-carbon steel has been found to be a preferred material because of its very low cost, non-corrosiveness in alkaline environments, and the absence of H2 precipitation on its surface during electrodeposition. These materials can have a crystalline or microscopic surface similar to pure zinc, thus supporting the formation of a solid zinc layer. In this respect, it is surprising that zinc deposition on such current collectors can be achieved without any additives and / or binders. Of course, additional additives or binders can be used, but it has been shown that these are not essential for the formation of the electrodes according to the invention.

[0041] According to another preferred embodiment, the zinc layer is free of copper (Cu). It has been shown that if substances such as Cu are not present during the zinc deposition process... + The presence of these ions is beneficial. During charging, these ions promote the precipitation of H2, leading to a moss-like zinc deposition. If the presence of copper is avoided as much as possible during deposition, the zinc-plated electrode is practically copper-free. However, copper can also be used as the current collector. In this case, care must be taken to prevent Cu from being deposited during the deposition process. + The dissociation of ions suppresses the precipitation of H2 during the deposition process. Therefore, copper current collectors can be coated with Ni, NiP, or other iron (Fe-) alloy coatings.

[0042] According to another preferred embodiment, the mass of the zinc layer is 200 mg / cm³. 2 Preferably 300 mg / cm 2 The optimal value is 400 mg / cm³. 2 The zinc electrode according to the present invention can have a concentration ranging from several micrograms to hundreds or thousands of milligrams per square centimeter (mg / cm²). 2 The quality of the zinc deposit is virtually unlimited. However, certain limitations are clearly present in achieving such a layer. Until now, with the current level of technology, it has been impossible to produce such a quality of solid metallic zinc layer. Therefore, the zinc electrode according to the invention is unique in its density, morphology, and three-dimensionality. However, as mentioned above, even higher layer qualities can be obtained, for example, by continuously applying a new zinc-containing electrolyte during the electrodeposition process in the application. With such applications, even thousands of mg / cm³ can be achieved. 2 In capacitance / cm 2Regarding the 200 to 400 mg / cm² according to the present invention 2 Such a zinc layer corresponds to 164 to 328 mAh / cm³ 2 The volume density. However, as mentioned above, it is also possible to achieve a volume density exceeding 1000 mg / cm³. 2 The quality of the zinc layer is crucial for achieving even higher capacity densities. It is also clear that the required zinc layer quality will vary depending on the application and application type. For example, battery pack applications require a lower layer quality than H2 generator applications.

[0043] According to another preferred embodiment, the mass of the zinc layer is 0-10000 mg / cm³. 2 Preferred concentration: 1-5000 mg / cm³ 2 More preferably 25-2000 mg / cm³ 2 .

[0044] According to another preferred embodiment, the zinc layer has a mass of up to 10000 mg / cm³. 2 Preferred concentrations up to 5000 mg / cm³ 2 More preferably up to 2000 mg / cm³ 2 .

[0045] According to another preferred embodiment, the mass of the zinc layer (300) (in mg / cm³) 2 (Calculation) is almost unrestricted.

[0046] According to another preferred embodiment, the zinc layer has a mass of at least 25 mg / cm³. 2 .

[0047] According to another preferred embodiment, the porosity of the zinc layer is less than 50%. The electrode according to the invention is very dense, and the density range of its zinc deposit is similar to the range of the actual density of metallic zinc; therefore, the zinc deposit also has a low porosity of less than 50%. However, the porosity can be set even lower, up to 40%. A porosity of less than 30% is preferred, and particularly preferred is less than 20%. Conventional zinc electrodes do not achieve such low porosity values, let alone electrodes used in zinc-air batteries. Compared to ordinary electrode surfaces, the specific active surface area of ​​the zinc electrode according to the invention is hundreds to thousands of orders of magnitude lower than that in zinc-air battery applications due to the lower porosity. For example, the surface area of ​​zinc powder according to the prior art (e.g., in a zinc-air battery) is about 1 m². 2 According to the present invention, from several micrograms to several thousand milligrams / cm³ can be obtained. 2 The layer. According to the invention, the layer mass is, for example, 200 mg / cm³. 2 In this case, this would result in a zinc powder shell surface area of ​​approximately 2000 cm². 2The multiple is 2000. Therefore, even though a certain porosity still exists in the layer according to the invention, the active surface area is several orders of magnitude lower than that of conventional electrode layers in the prior art.

[0048] According to the present invention, an electrochemical cell is provided, the electrochemical cell comprising a zinc electrode according to one of the aforementioned embodiments of a zinc electrode for zinc electrodeposition, wherein the electrochemical cell further comprises a zinc-containing electrolyte and a cathode.

[0049] In the context of this invention, the current collector material of the zinc electrode is also referred to as the negative electrode, anode, anode current collector material, or anode current collector material. In the context of this invention, the cathode is also referred to as the positive electrode, counter electrode, counter current collector material, cathode current collector, or cathode current collector material.

[0050] To generate a zinc-loaded electrode using an electrochemical cell, the cell can be assembled in a discharged state (SOC = 0), with only the anode current collector material serving as the negative electrode side and the cathode current collector serving as the positive electrode side, and the two sides (negative and positive electrodes) connected by an electrolyte containing zinc primarily in the form of ZnO and / or zincates, but excluding powdered zinc. However, in the sense of this invention, an electrochemical cell includes an anode current collector material, a cathode current collector material, and a suitable electrolyte. For the purposes of this invention, an electrochemical cell is defined as a general term for various devices used in or based on electrochemical processes. Hereinafter, electrochemical cells include galvanic cells, electrolytic cells, and rechargeable batteries. The electrolyte can be liquid or solid, or both liquid and solid electrolytes may be present. Therefore, an electrochemical cell can be defined as a device with two electrodes electrically connected by a zinc-containing electrolyte.

[0051] According to the preferred embodiment of the electrochemical cell, the zinc-containing electrolyte is alkaline. Although it is also feasible for the zinc-containing electrolyte to mainly contain zinc chloride or ammonium chloride, an alkaline environment is still preferred.

[0052] According to a preferred embodiment of the electrochemical cell, the zinc layer, zinc-containing electrolyte, current collector material, and / or cathode are free of copper, copper ions, and / or copper oxides.

[0053] According to another preferred embodiment of the electrochemical cell, the zinc-containing electrolyte comprises a zinc source selected from one or more of the following: Zn 2+Zinc sources, ZnO, zincates, and / or zinc complexes. When this invention relates to zinc-containing sources or zinc-containing electrolytes, it primarily refers to one of the above-mentioned substances, preferably ZnO and zincates. For the purposes of this invention, zinc complexes are understood to be any kind of zincate complexes, but also include those containing zinc and dissociating during (re)charging, so that solid zinc can be further deposited on the current collector material or on a current collector already coated with a zinc layer. Zinc sources can have different viscosities and can be used as pastes, slurries, or solutions. Multiple zinc sources can also be used together. However, it should be explicitly mentioned that, in the sense of this invention, zinc-containing sources or zinc-containing electrolytes do not contain zinc in the form of powdered zinc. On the contrary, the use or application of powdered zinc in the form of solid zinc powder is not suitable for this invention.

[0054] According to another preferred embodiment of the electrochemical cell, after the battery discharges, the zinc source, or at least one component of the zinc source, is supersaturated. This means that during battery discharge, the components of the zinc source are not completely stoichiometrically converted back to the components actually used at the beginning, but at least one component is not or cannot be further converted, and therefore exists at a supersaturated concentration. For example, ZnO can be used, which is transferred to zinc via zincate and then electroplated during electrodeposition. In the reverse reaction (i.e., the discharge process), zinc is converted to zincate, but not all zincate above the saturation point is converted back to ZnO, so the zincate is now supersaturated.

[0055] According to another preferred embodiment of the electrochemical cell, the alkaline zinc-containing electrolyte contains KOH. In this case, the electrolyte may also contain a minimum amount of 5-25 wt% and a maximum amount of 35-60 wt% KOH, preferably 26 wt% to 36 wt% KOH, and most preferably 30 wt% KOH.

[0056] According to another preferred embodiment, the zinc-containing electrolyte further comprises a minimum of 5-15 wt% and a maximum of 16-30 wt% NaOH, preferably 20 wt% NaOH, and even more preferably 18 wt% NaOH. NaOH can be used in place of KOH or in combination.

[0057] According to another preferred embodiment of the electrochemical cell, when the zinc-containing electrolyte is applied to the new electrochemical cell, it has a minimum ZnO / KOH ratio of 190.00 g ZnO / L KOH, preferably 100.00 g ZnO / L KOH, and even more preferably 8.00 g ZnO / L KOH, and / or the zinc-containing electrolyte has a maximum ZnO / KOH ratio of 2380.00 g ZnO / L KOH, preferably 2670.00 g ZnO / L KOH, and even more preferably 2980.00 g ZnO / L KOH. At the end of charging, the concentration can be much lower, so the minimum amount of zincate or dissolved ZnO (since it is below the saturation point, ZnO will not remain as ZnO anyway) is approximately 0.1 M / L KOH or 8 g ZnO / L KOH. For the purposes of this invention, "applied to a novel electrochemical cell" means that the cell is being loaded for the first time or with a completely fresh electrolyte. Therefore, the applied ratios are those present before the deposition process or the start of the charging cycle. It should be understood that these parameters can change during charge or discharge cycles.

[0058] According to another preferred embodiment of the electrochemical cell, the zinc-containing electrolyte contains a minimum ZnO concentration of 0.01 M / L KOH in the H2O electrolyte, preferably in the range of 0.1 to 0.8 M / L KOH, and preferably a maximum concentration of 0.8 M to 1.5 M / L KOH.

[0059] According to another preferred embodiment of the electrochemical cell, the ZnO / KOH ratio is independent of the KOH concentration.

[0060] According to another preferred embodiment of the electrochemical battery, the zinc-containing electrolyte further comprises Pb, Fe, Sn, CdMg, or other metals or alloys. Alternatively, the electrolyte may contain a hydroxide additive comprising at least one of In-, Pb-, and / or Sn- hydroxides at a concentration of 10-500 ppm of ZnO in the electrolyte. Such additives increase hydrogen overvoltage, thereby reducing battery self-discharge. Alternatively, the electrolyte may include at least one of electrolyte additives and / or surfactants, such as polyoxyethylene octadecenyl ether phosphate, polyethylene glycol, copolymers having acidic groups, solutions of modified styrene-maleic acid copolymers, solutions of alkyl ammonium salts of lower molecular weight polycarboxylic acid polymers, phosphate esters of alkylphenoxypolyethoxyethanol, solutions of polyether phosphates or octylphenoxypolyethoxyethyl phosphate, water, phosphoric acid, and polyethylene glycol octylphenyl ether. Additives also used in alkaline galvanic batteries to reduce self-discharge can be used in this invention, such as electrolyte additives and / or surfactants, including solutions of polyoxyethylene octadecenyl ether phosphate, polyethylene glycol, copolymers having acidic groups, modified styrene-maleic acid copolymers, alkyl ammonium salts of lower molecular weight polycarboxylic acid polymers, phosphate esters of alkylphenoxypolyethoxyethanol, solutions of polyether phosphate or octylphenoxypolyethoxyethyl phosphate, water, phosphoric acid, and polyethylene glycol octylphenyl ether. Such additives affect zinc passivation, thereby affecting the discharge and self-discharge behavior of the electrochemical battery.

[0061] According to the present invention, a method for zinc electrodeposition in an electrochemical cell according to one of the foregoing embodiments is provided, wherein the method comprises:

[0062] -Use electrochemical cells;

[0063] - Apply a duty cycle pulse of 5%-80% at 0-30Hz, preferably 5-20Hz, more preferably 10Hz to deposit zinc onto the current collector material until a predetermined state of charge, SOC, and / or a predetermined quality of zinc layer is achieved.

[0064] - Apply a pulse with a lower limit of about 0.01 Hz, preferably about 0.05 Hz, more preferably about 0.1 Hz, and an upper limit of about 500 Hz, preferably about 100 Hz, more preferably about 50 Hz, until a duty cycle of ≤8%-1%, preferably ≤5%-2%, more preferably 5% and / or ≤10 mA / cm is achieved. 2 Preferred value ≤8mA / cm 2 More preferably ≤5mA / cm 2 The predetermined minimum current density; and

[0065] - End this method.

[0066] According to another preferred embodiment of the method, the method applies a pulse of about 0.01-500 Hz, preferably about 5-50 Hz, more preferably about 5-25 Hz, and even more preferably about 10 Hz.

[0067] According to another preferred embodiment of the method, the method includes:

[0068] -Use electrochemical cells;

[0069] - Apply a duty cycle pulse of 5%-80% at 0-30Hz, preferably 5-20Hz, more preferably 10Hz to deposit zinc onto the current collector material until a predetermined state of charge, SOC, and / or a predetermined quality of zinc layer is achieved.

[0070] - Apply a pulse of 0-30Hz, preferably 5-20Hz, more preferably 10Hz, until a duty cycle of ≤8%-1%, preferably ≤5%-2%, more preferably 5% is achieved and / or ≤10mA / cm is achieved. 2 Preferred value ≤8mA / cm 2 More preferably ≤5mA / cm 2 The predetermined minimum current density; and

[0071] - End this method.

[0072] According to another preferred embodiment of the method, the method further includes applying a pulse in the range of 1-300 mA / cm. 2 The preferred range is 5-170 mA / cm. 2 A more preferred range is 5-125 mA / cm. 2 The pulse current density.

[0073] For charging time, charging efficiency, and structure, optimization methods consider parameters such as duty cycle, frequency, or current density (which implies the deposition of a smooth solid zinc layer according to the invention). However, according to the invention, a low duty cycle of 10 Hz (e.g., 5%) is associated with a low current density (5 mA / cm²). 2 The combination will charge all ZnO / zincate concentrations to deposit bulk zinc deposits (tens to thousands of mg / cm³). 2 However, the charging time is long. To reduce the charging time, a higher current density is needed. Two options with higher average current densities can be applied:

[0074] (a) Low duty cycle, high current density or (b) High duty cycle, low current density, or both, where (a) and (b) have the same average current density. Option (a) with low duty cycle and high current density will have lower electrical efficiency, while option (b) with high duty cycle and low current density will have better electrical efficiency.

[0075] For example, using saturated zincate in 30% KOH: (a) 40% duty cycle 80 mAh / cm 2 Or (b) 80% duty cycle 40 mA / cm 2 Both (a) and (b) will have an electroplating density of <100mg Zn / cm³. 2 However, if the zinc deposition rate is approximately >100 mA / cm², 2 40mA / cm 2 Option (b) will result in a moss-like texture. However, if this is the desired thickness, 100 mg / cm² deposited with option (b) will achieve this. 2 Zinc will be more electrically efficient. Supersaturated zincates will require a lower duty cycle and lower current density until the saturation point is reached, at which point 40 mA / cm² can be used. 2 80% duty cycle (option (a)). A combination can be used from 40 mA / cm 2 Start with 80% duty cycle (option (b)), then switch to 40% duty cycle 80mA / cm midway. 2 (Option (a)) and exceeds 100 mg / cm 2 .

[0076] The parameters shown here are basic parameters used to obtain the zinc electrode according to the present invention. However, it should be understood that pulse parameters are affected, for example, by the zincate concentration (or other zinc source concentration) and ZnO loading (meaning the thickness / viscosity of the applied ZnO / KOH slurry). Furthermore, it is equally clear that these initial parameters will change during the deposition process, such as charging progress, temperature, and zinc loading / cm². 2 For zinc deposition, a duty cycle pulse of 5% to 80% at 0-30 Hz, preferably 5-20 Hz, more preferably 10 Hz, is applied until the desired quality of zinc deposition is achieved, to allow zincate ions to approach the electrode surface and cause OH- - It enters the substrate and prevents H2 precipitation. All pulses are designed to suppress H2 production to prevent the formation of moss-like or dendritic zinc deposits.

[0077] According to the present invention, during the charging of the anolyte (negative electrode) in an electrochemical cell, certain conditions exist that allow for the deposition of zinc in a non-powdered and non-moss-like form. However, for the zinc electrode prepared according to the present invention, not all conditions must actually exist; in other words, not all conditions are critical, but their presence is merely advantageous.

[0078] Optionally, the battery should not contain substances such as Cu. + These ions will promote H2 precipitation during charging, resulting in moss-like zinc deposition.

[0079] Furthermore, copper oxides or passivations should not be present on the surface of the current collector, as such oxides can promote H2 precipitation during charging, leading to moss-like zinc deposition.

[0080] Deposition parameters must be selected in a way that prevents H2 precipitation. H2 bubbles cause zinc to deposit around them, resulting in moss-like zinc. In fact, high current will cause H2 precipitation. Depending on the substrate (current collector material or already deposited Zn layer), using a high current density will primarily be beneficial at the start of deposition. However, it is the pulse that eliminates the H2 bubbles, not the high current density. If the deposition is on a substrate made of a material with a low H2 overpotential, meaning it is a good H2 precipitation substrate or catalyst, then 40 mA / cm² is required. 2 An initial high-current pulse is applied and sustained for tens of seconds to achieve an initial electroplating that inhibits the catalytic activity of the substrate. Furthermore, increasing the number of nucleation sites on such a substrate is also beneficial. Otherwise, the substrate will dissolve the deposit during zinc deposition.

[0081] After the initial deposition, the current should be reduced; otherwise, moss-like Zn will form.

[0082] A current collector material with a high H2 overpotential should be selected to avoid H2 precipitation, so that no H2 will be precipitated when electroplating begins on the bare current collector material.

[0083] Another important condition is time. Therefore, time should be allowed for the consumed zincate ions to be replenished at the electrode / electrolyte interface. This is achieved by reducing the duty cycle; for example, a very thick ZnO paste between the Zn electrode and the separator (thick in the sense of high viscosity and high ZnO concentration according to other embodiments mentioned in this invention) requires a low duty cycle, such as 10%, but a lower ZnO or zincate concentration allows for a duty cycle of 80%. However, a lower duty cycle should be applied when the zincate is depleted near the end of the charge.

[0084] According to another embodiment of the method, the method further includes applying a 5%-80% duty cycle pulse of 0-30Hz, preferably 5-20Hz, more preferably 10Hz, with a current density ≥40mA / cm². 2The first Zn deposition step is performed before the main zinc deposition step. This step is crucial for current collector materials with low H2 overpotentials, such as nickel, as it prevents H2 precipitation, which would otherwise occur during zinc deposition under the parameters described in the method according to the invention. Furthermore, this step can increase the number of nucleation sites, which facilitates more uniform and improved zinc deposition in the next step. This increase in the number of nucleation sites is real for materials with high H2 overpotentials and materials with low H2 overpotentials, such as cold-rolled low-carbon steel. However, in the case of cold-rolled low-carbon steel, this step is not crucial. Preferably, this step is applied in the method of the invention when there is an exposed current collector, i.e., when the method of depositing zinc in an electrochemical cell is first applied to an exposed current collector material, or when the zinc layer has been completely separated from the current collector material by a previous discharge cycle or step.

[0085] According to another embodiment of the method, the method further includes applying a 5%-10% duty cycle pulse of 1-100 kHz, preferably 30-70 kHz, more preferably 50 kHz, for a duration of s seconds to m minutes, after the electrochemical cell has been pre-discharged partially or fully discharged and passivation has already formed on the surface. The passivation on the surface should be separated before zinc deposition. Otherwise, the plating on the passivation will result in moss-like zinc deposition. However, the passivation will eventually dissolve when the zincate concentration decreases. At the start of charging or deposition, the passivation is separated by pulsed transmission of low duty cycle pulses of tens of microseconds (μs) over a period of several seconds (e.g., 1 to 90 seconds, preferably 5-50 seconds, more preferably 30 seconds) to several minutes.

[0086] According to another embodiment of the method, the method further includes monitoring zinc electrodeposition when a spike in battery current and / or a drop in battery voltage occurs, and immediately stopping zinc electrodeposition and ending the method if a spike and / or drop occurs. Such spikes and / or drops indicate a short circuit, meaning that the zinc deposit may be moss-like or dendritic. Such unwanted deposits are recovered by complete or partial discharge of the electrochemical cell, meaning complete or partial removal of the zinc layer. Afterward, new zinc deposition can begin (e.g., if fully discharged at SOC = 0).

[0087] According to another embodiment of the method, the method further includes monitoring zinc electrodeposition at a predetermined battery current limit and / or a predetermined battery voltage limit, indicating a predetermined state of charge (SOC), and if the predetermined SOC is reached, applying a pulse of 0-30 Hz, preferably 5-20 Hz, more preferably 10 Hz, until a duty cycle of ≤8%-1%, preferably ≤5%-2%, more preferably 5% is reached and / or ≤10 mA / cm² is reached. 2 Preferred value ≤8mA / cm 2More preferably ≤5mA / cm 2 The predetermined minimum current density.

[0088] The parameters used to monitor zinc electrodeposition can also be varied depending on whether a special battery design or additional temperature control is required. Furthermore, the parameters for different states of charge can be fixed, or these parameters can be dynamically adjusted by performing periodic fast impedance spectroscopy (EIS) during charging, thereby adjusting the pulse parameters to accelerate charging while avoiding short circuits.

[0089] Rapid electrochemical impedance spectroscopy (EIS) can be performed to obtain information about battery condition and state of charge. For example, EIS can indicate surface roughness; high roughness indicates moss-like deposits, which is undesirable, while low roughness indicates solid Zn deposits. EIS can be performed before charging begins, shortly after, and after every x charging time to indicate the presence of passivation, whether charging has started correctly, and whether the Zn deposit maintains a good solid Zn structure. Surface roughness is represented by electrochemical double-layer capacitance. Higher capacitance corresponds to a larger surface area compared to the capacitance of a bare current collector, implying a moss-like coating deposit. Measurements can be performed at multiple frequencies, but continuous frequency sweeps are not required. As long as the zinc deposit remains solid, non-moss-like, and has relatively low roughness, the capacitance will remain very similar to that of a bare current collector.

[0090] Furthermore, the amount of electrolyte or zincate and / or ZnO in the battery can be determined by the battery resistance (the real part of the impedance), which can be achieved through low-frequency measurement. Additionally, passivation can be detected by EIS.

[0091] In different scenarios, if the zinc electrode is part of an electrochemical cell that includes a catalyst gas evolution electrode that produces oxygen during zinc deposition and H2 during zinc dissolution, the composite catalyst, used as a safety device, can also be used as a sensor. The temperature of the reforming catalyst can be monitored to detect runaway zinc accumulation and the end of charging. In both cases, H2 will begin to evolve, and the temperature of the reforming catalyst will begin to rise due to the presence of O2, indicating that charging should be terminated. The same occurs under discharge conditions. If the temperature of the reforming catalyst rises, this is a signal that the battery polarity has reversed, electrolysis has ended, and O2 and H2 are released simultaneously, therefore discharging should be terminated.

[0092] Furthermore, in the case of another type of rechargeable zinc battery, under overcharge conditions, oxygen may be evolved at the positive electrode, or hydrogen may be evolved at the negative electrode, depending on which electrode has a less active material. Gas channels can be created in the battery so that oxygen can recombine with hydrogen at the recombination catalyst or react with the zinc negative electrode.

[0093] However, it's also possible to adapt the duty cycle to the already charged capacitor, thereby adapting to the thickness of the zinc layer on the electrode and the ZnO / zincate concentration during charging. Generally, the duty cycle can be increased during charging. For each type and size of electrochemical cell, the required charging parameters (duty cycle) can be determined as a function of current, state of charge, and temperature. This can be stored in a lookup table and then used for discharging.

[0094] According to the present invention, an electrochemical cell for carrying out the method of the present invention is provided.

[0095] The following methods, known to those skilled in the art, can be used to determine the properties and / or parameters of a zinc electrode according to the present invention and the embodiments described therein:

[0096] Since the zinc layer is a solid metal with only some surface roughness and almost no internal voids or closed pores, microscopic images are sufficient to determine its structure.

[0097] Therefore, the structure of the zinc layer can be analyzed using microscopic images taken by optical or electron microscopes, such as scanning electron microscopes (SEM). The results can be quantified through computational image analysis.

[0098] Scanning electron microscopy (SEM) is a technique for imaging the surface morphology of materials at high magnification. It provides detailed three-dimensional images that can be used to identify features such as cracks, pores, and grain boundaries in metallic coatings.

[0099] Alternatively or additionally, other methods such as TEM or AFM can be used. Transmission electron microscopy (TEM) typically offers higher magnification than SEM and is able to provide detailed information about the internal structure of coatings, including nanoscale features. Atomic force microscopy (AFM) is a high-resolution imaging technique that uses a tip to scan the sample surface. It is particularly useful for studying surface roughness and can provide information about the morphology and mechanical properties of coatings.

[0100] The zinc layer can also be analyzed using a laser confocal microscope, which directly provides roughness values ​​and can be used to calculate the volume beneath the surface.

[0101] X-ray diffraction (XRD) can be used to analyze the crystal structure of the coating and provide information about the crystalline phases present in the coating, grain size, and preferred orientation of the crystals.

[0102] Various porosity determination techniques, such as mercury porosimetry or gas adsorption methods (e.g., BET), can be used to determine the porosity of coatings. These methods help quantify the volume and size distribution of pores in the coating.

[0103] Cross-sectional analysis involves preparing samples with a known coating and then cutting them to expose the internal structure. This allows direct observation of the coating-substrate interface and assessment of porosity and thickness. More advanced techniques use ion beams to prepare cross-sections (focused ion beam, FIB).

[0104] Electrochemical impedance spectroscopy (EIS) can be used to assess the corrosion resistance of metallic coatings and indirectly infer their porosity. Changes in impedance can provide insights into the coating's ability to resist corrosion.

[0105] Microhardness testing, such as Vickers or Knoop hardness testing, can be performed on a cross-section of the coated sample. Variations in coating hardness may indicate differences in porosity or composition. Moss-like layers are very soft compared to solids or hard materials (bolders) such as zinc.

[0106] Because zinc electrodes are mostly solid with relatively rough surfaces and are deposited on a substrate of known weight and area, it is only necessary to measure the thickness of the zinc layer to determine the Zn density.

[0107] Generally, those skilled in the art know the following methods for determining the density of a zinc layer:

[0108] Archimedes' principle method involves immersing a porous metal sample in a fluid (usually a liquid) and measuring the volume of water displaced. According to Archimedes' principle, the buoyant force acting on an underwater object is equal to the weight of the fluid it displaces. The density of the material can then be calculated from the known density of the fluid.

[0109] The gas pycnometer method is a technique that uses gas to determine the pore volume in a material. Knowing the volume and mass of the sample, the density can be calculated.

[0110] X-ray computed tomography (CT) scans can provide three-dimensional images of the internal structure of porous metals. By analyzing CT scans, researchers can estimate the volume of solid materials and pore spaces. This information, combined with the sample's mass, allows them to calculate the density.

[0111] Ultrasonic technology can be used to measure the speed at which sound waves pass through a material. Density can be inferred from the speed of sound and the known acoustic properties of the material.

[0112] The microstructure of porous metals can be analyzed using optical and / or electron microscopy combined with image analysis software. By quantifying the amount of solid material and pore space, researchers can estimate the total density.

[0113] In the helium displacement method, helium gas is used to replace the air in the pores of the material. The change in pressure or volume is then measured, and the density is calculated according to the ideal gas law.

[0114] Similar to Archimedes' principle, the buoyancy method involves immersing the sample in a liquid. However, the buoyancy method directly measures the force exerted on the sample due to buoyancy, rather than measuring the displaced fluid.

[0115] The quality of the zinc coating can be determined using gravimetric analysis. Gravimetric analysis is based on the fact that zinc is deposited on the current collector. The weight of the current collector is measured before deposition begins. After zinc deposition, the weight is measured again, and the difference is the weight of the zinc coating.

[0116] The following well-known methods can also be used to determine the quality of the zinc coating:

[0117] A quartz crystal microbalance (QCM) is a highly sensitive mass measurement device that utilizes the change in the resonant frequency of a quartz crystal as its mass increases. When a coating is deposited on the crystal, it causes a change in the resonant frequency, allowing for precise measurement of the increased mass.

[0118] Coulometric method measures the amount of electricity passing through during the deposition process. By determining the electrochemical equivalent of the deposited metal, the quality of the coating can be calculated.

[0119] In the β backscattering method, β particles are aligned with the coating surface and the backscattered radiation is measured. The intensity of the backscattered radiation is proportional to the coating thickness.

[0120] X-ray fluorescence (XRF) beta particles were aligned with the coating surface, and backscattered radiation was measured. The intensity of the backscattered radiation is proportional to the coating thickness.

[0121] Neutron activation analysis (NAA) involves irradiating a coated sample with neutrons and then measuring the emitted gamma rays. The intensity of the gamma rays is proportional to the amount of a specific metal in the coating.

[0122] Generally, all of these methods are common knowledge to those skilled in the art. Furthermore, those skilled in the art can use all known methods to determine the parameters and / or properties of zinc electrodes, and are not limited to the methods described in this specification.

[0123] Furthermore, all methods known in the relevant technical field for determining parameters and / or properties produce the same results within appropriate limits of measurement accuracy.

[0124] It should also be noted that various aspects or embodiments of the invention have been described with reference to different subjects. Specifically, some aspects or embodiments have been described with reference to product claims, while others have been described with reference to method claims. However, those skilled in the art will understand from the above and below description that, unless otherwise stated, any combination of features related to different types of subjects is also considered to be disclosed herein, except for any combination of features belonging to one type of subject matter. In particular, combinations of features related to product claims and features related to method claims are considered to be disclosed. The invention and its embodiments will now be described in more detail with reference to one or more accompanying drawings.

[0125] Figure 1 shows an image of the surface of a zinc deposit with a thick, sponge-like microstructure, according to the prior art, which is derived from RY Wang et al., Journal of The Electrochemical Society, 153(5)C357-C364 (2006).

[0126] Figure 2 shows an image of the surface of a zinc deposit with a dendritic microstructure according to the prior art, which is derived from RY Wang et al., Journal of The Electrochemical Society, 153(5)C357-C364 (2006).

[0127] Figure 3 shows an image of the surface of a zinc deposit with a moss-like microstructure according to the prior art, which is derived from RY Wang et al., Journal of The Electrochemical Society, 153(5)C357-C364 (2006).

[0128] Figure 4 shows an image of the surface of a zinc deposit with a boulder-like microstructure according to the prior art, which is derived from RY Wang et al., Journal of The Electrochemical Society, 153(5)C357-C364 (2006).

[0129] Figure 5 shows an image of the surface of a zinc deposit with a layered microstructure according to the prior art, which is derived from RY Wang et al., Journal of The Electrochemical Society, 153(5)C357-C364 (2006).

[0130] Figure 6 shows a table of zinc deposits classified according to the prior art, which is derived from RY Wang et al., Journal of The Electrochemical Society, 153(5)C357-C364 (2006).

[0131] Figure 7 shows a schematic diagram of an anode electrode with a dendritic morphology formed by electrodepositing zinc according to the prior art.

[0132] Figure 8 shows a schematic diagram of an anode electrode with a filamentous / moss-like morphology formed by electrodepositing zinc according to the prior art.

[0133] Figure 9 shows a schematic diagram of an anode electrode with a solid metal (layered) morphology formed by electrodepositing zinc according to an embodiment of the present invention.

[0134] Figure 10 shows a flowchart of method steps according to an embodiment of the present invention for producing a zinc electrode as described in the present invention in an electrochemical cell.

[0135] Figure 1 shows an image of the surface of a thick, sponge-like zinc deposit. It can be seen that the thick, sponge-like deposit consists of large, boulder-like clumps and highly branched dendrites formed after very high current densities (cd) and long deposition times. Furthermore, such deposits exhibit finely dispersed pores and anisotropic crystallinity. Based on their appearance, such deposits can be perceived primarily as a black powder by the human eye. However, such thick, sponge-like deposits are non-adhesive, which leads to the fragmentation of these layers or the easy separation of some layers, for example, under slight vibration or spontaneous conditions.

[0136] Figure 2 shows an image of the surface of a zinc deposit with a dendritic microstructure. Dendrites are tree-like, leaf-like, or fern-like structures, and can be hexagonal if deposition is slow. The porosity of such deposits is dispersed, and they exhibit isotopically oriented crystallinity. Based on their appearance, such deposits can be visually identified as metallic crystals. However, such deposits are non-adhesive and, due to their structure, can be easily fractured. Another reason making such deposits unsuitable for certain types of applications is that the dendrite spikes can penetrate or damage the diaphragm. Dendrites primarily form at very high current densities.

[0137] Figure 3 shows an image of the surface of a zinc deposit with a moss-like microstructure. The filamentous moss deposits have an appearance of entangled crystalline tendrils, typically 50-200 nm in diameter and exceeding 5 μm in length. Like dendrites and heavy sponge deposits, moss-like deposits are non-adhesive. However, they possess extremely high porosity and isotropic crystallinity. They primarily form at low current densities. Like heavy sponge deposits, they are primarily visible to the naked eye as a black, powdery layer. As can be anticipated from Figure 3, these moss-like deposits are easily separated or broken. When such moss-like deposits separate from the electrodes or the Zn deposition layer, these moss-like filaments appear as a cloud-like structure in the middle of the electrochemical cell between the two electrodes, without being connected to either electrode.

[0138] Furthermore, Figure 4 shows an image of the surface of zinc deposits with a boulder-like microstructure. The boulders are typically hexagonal in the discontinuous assemblage. Layer-by-layer growth on individual boulder-like deposits can be seen in Figure 4. The boulder-like deposits have a granular boulder-like shape and exhibit predominantly anisotropic crystallinity. Unlike the other deposits mentioned above, these deposits have very dense pores, meaning they are primarily non-porous. Furthermore, these deposits are adherent, meaning partial separation of the layer is atypical and rare. To the human eye, such boulder-like deposits appear as gray metal. It is speculated that such deposition can occur at moderate or adequate current densities.

[0139] Figure 5 shows a surface image of a zinc deposit with a layered microstructure. The layered deposit is epitaxially grown and is typically found at the beginning of deposition. This type of Zn deposit is likely the densest and has almost no porosity. It appears to the naked eye as a shiny metallic layer with ridged or layered microstructures and crystallinity consistent with the epitaxial orientation. This deposit is highly adhesive, and only with considerable force can the layer be partially separated; therefore, spontaneous partial separation does not occur under normal conditions. The presence of this layer is primarily observed at low current densities. However, it is interesting that, although the layer often appears at the beginning of deposition, such layered deposition is not achievable in the prior art over a longer deposition time or within a certain thickness. For all methods described in the prior art and the Zn electrodes shown therein, relatively thick layered Zn deposits have so far been shown. The only method or electrode that has shown such layered deposits with the properties described herein uses pure zinc or treated zinc as the current collector material. However, this is meaningless for commercial applications because, for example, when such an electrode is used in a battery pack, it completely disappears during discharge.

[0140] Figure 6 shows a table illustrating the classification of Zn deposits according to existing techniques. As can be seen from the table, various properties (e.g., naked-eye appearance, microstructure (under a microscope), adhesiveness, porosity, crystallinity, or growth current density) can be attributed to individual Zn deposits.

[0141] Figure 7 shows a schematic diagram of a zinc electrode 100, where electrodeposited zinc forms a dendritic morphology 310. As shown in the figure, during electrodeposition, Zn is deposited on the anode current collector material 200. Initially, the Zn layer 300 remains very uniform, but as the layer thickness or electrodeposition duration increases, the shape of the Zn layer begins to change. This forms dendrites, which can break off or damage other components of the battery, such as the separator. Short circuits can also occur due to the separation of dendrite portions. There are several reasons for the formation of such dendritic layers. One reason considered to have a significant impact on dendrite formation is the application of very high current capacity during deposition.

[0142] Furthermore, Figure 8 shows a schematic diagram of the zinc electrode 100, where electrodeposited zinc forms a moss-like morphology 320. Figure 8 illustrates the shape change that occurs after the initial dense deposition of zinc (zinc layer 300) on the anode current collector material 200. Subsequent deposits exhibit filamentous or moss-like structures 320. This structure, along with dendritic zinc structures or other non-dense structures (such as thick, spongy zinc), demonstrates poor adhesion to the substrate. These moss-like zinc deposits can be easily separated from the deposited zinc or current collector material. These separated moss-like Zn deposits are typically visible as a whitish, cloud-like structure in the center of the electrochemical cell (i.e., between the electrodes), and are sometimes visible to the naked eye. For example, flowing electrolytes can easily mechanically separate these moss-like zinc deposits, which can lead to capacity loss or blockage of the electrolyte in flowing applications. Moss-like zinc morphologies may occur due to the very low current capacity during electrodeposition. In addition, gas generation (primarily due to hydrogen produced during electrodeposition) can favor the formation of moss-like zinc deposits.

[0143] Figure 9 shows a schematic diagram of an anode electrode 100 with a solid metallic (layered) morphology formed by electrodeposited zinc according to an embodiment of the present invention. Figure 9 shows a large deposit of a solid metallic zinc layer 300 directly on the current collector material 200 of the anode electrode 100. This metallic zinc layer 300 has a layered and / or boulder-like morphology and exhibits a high density very close to that of pure metallic zinc. The layer 300 is generally dense and firmly adheres to the substrate, and has a smooth surface 330. This dense layer 300 has almost no porosity. To the naked eye, the layer surface 330 presents a gray / sparkling metallic or metallic luster. The electrode 100 according to the present invention can have a density well exceeding 200 mg / cm³. 2 The thickness of the zinc coating.

[0144] Figure 10 shows a flowchart of a method according to one embodiment of the present invention for producing a zinc electrode as described in the present invention in an electrochemical cell. The electrochemical cell includes an anode current collector material, a cathode current collector material, and a suitable electrolyte. For the purposes of this invention, an electrochemical cell is defined as a general term for various devices used in or based on electrochemical processes. In this document, electrochemical cells include galvanic cells, electrolytic cells, and rechargeable batteries. An electrochemical cell contains at least two electrodes or current collector materials (which always act as electronic conductors) and at least one electrolyte (i.e., an ionic conductor). The electrolyte can be liquid or solid and has a certain viscosity. Therefore, an electrochemical cell can be defined as a device with two electrodes electrically connected by a zinc-containing electrolyte.

[0145] In the first step S100, a battery is provided having a zinc-containing electrolyte, an anode current collector material, and a cathode current collector material. It should be understood that the battery is designed such that the two current collector materials (which can also be described as starting electrodes) are electrically connected through the zinc-containing electrolyte. This also includes all components such as the casing, current source, voltage source, and other measuring devices.

[0146] Furthermore, in the case of initial deposition and / or using a fully discharged current collector material without a zinc layer, and where the current collector also has a low H2 overpotential, optional step S200 can be implemented. This step is then mandatory to suppress H2 precipitation from the current collector material in the subsequent zinc deposition step (see S300), in other words, to block the catalytic activity of the current collector substrate. Furthermore, this step is beneficial for increasing nucleation sites on the substrate, thereby enhancing layer formation. Step S200 is performed, for example, by applying a 5%-80% duty cycle pulse of 0-30 Hz, preferably 5-20 Hz, and more preferably 10 Hz, using a high current density ≥40 mA / cm². 2 .

[0147] Another optional step S250 can be applied, which includes a 5%-10% duty cycle pulse of tens of μs at the start of the zinc deposition process, lasting from s seconds to m minutes (e.g., preferably ≤30 seconds). This step is beneficial for separating some passivation deposits that may have appeared during the previous discharge of the battery, or if the battery has been stored in a half-discharged state for a long time, because the plating of passivation deposits leads to moss-like zinc deposition.

[0148] However, then, in step S300, actual zinc deposition occurs. If a new battery with a fresh electrolyte and a bare current collector with a high H2 overpotential is available, zinc deposition can begin immediately in step S300. In all other cases, steps S200 and / or S250 must occur before step S300. In step S300, a 5%-80% duty cycle pulse of 1-30 Hz, preferably 5-20 Hz, more preferably 10 Hz, is applied for zinc deposition. This step continues until a predetermined zinc deposition quality is achieved, or zinc deposition stops for other reasons, such as a predetermined charging stop or, in rare cases, a short circuit. The duty cycle depends on the amount of zinc source, which in most cases is ZnO and / or zincates. As the zinc layer is depleted, the zincate level decreases, and the duty cycle and current density decrease (see step S400).

[0149] If charging is interrupted at any step, or if a charged battery is stored and further charging begins, step S250 can be performed again. Step S250 includes a 5%-10% duty cycle pulse of tens of μs at 1-100 kHz at the start of a new zinc deposition process, lasting from s seconds to m minutes (e.g., preferably ≤30 seconds). This step is beneficial for separating some passivation that may have appeared during the battery's previous discharge, or if the battery has been stored in a half-discharged state for a long time, as the plating of passivation deposits leads to moss-like zinc deposition.

[0150] In optional steps S310 and / or S320, the battery can also be monitored and inspected during zinc deposition. This can be done continuously or intermittently. If a voltage drop and / or current rise (short circuit) occurs during zinc electrodeposition, the deposition process is stopped (see step S500) because moss-like zinc deposition is likely occurring (S310). In such a case, the battery should be discharged, and then a new deposition can begin after the passivation separation step (S250). However, if "no short circuit" means no moss-like deposition has occurred, monitoring can also be performed using current / voltage parameters to track the desired predetermined state of charge or state of charge (SOC) and stop at the desired predetermined zinc layer quality (S320).

[0151] Subsequently, in step S400, a pulse of 0-30Hz, preferably 5-20Hz, more preferably 10Hz, is applied until a duty cycle of ≤8%-1%, preferably ≤5%-2%, and / or ≤10mA / cm is achieved. 2 Preferred value ≤8mA / cm 2 More preferably ≤5mA / cm 2 The predetermined minimum current density.

[0152] After this step, or in the event of a short circuit, zinc deposition is terminated (S500). At this point, the battery can be discharged again.

[0153] The zinc-loaded electrode can also be removed from the battery for storage or transportation purposes. In the event of a short circuit, the battery should be fully discharged, and a new deposition process should begin to achieve zinc deposition according to the invention.

[0154] It should be noted that the term "comprising" does not exclude other elements or steps, and "a(a)" or "an(an)" does not exclude multiple. Furthermore, elements described in conjunction with different embodiments can be combined.

[0155] It should also be noted that the reference numerals in the claims should not be interpreted as limiting the scope of the claims.

[0156] Figure Labels

[0157] 100 Zinc Electrode

[0158] 200 Current collector materials

[0159] 300 zinc coating

[0160] 310 Dendritic zinc layer surface

[0161] 311 Separated dendrites

[0162] 320 Moss-like zinc layer surface

[0163] 321 Separated moss-like zinc

[0164] 330 Solid zinc layer surface (layered)

[0165] S100-S500 Method Steps S100 to S500

Claims

1. A zinc electrode (100) comprising a current collector material (200) on which a zinc layer (300) is electrodeposited, wherein the zinc layer (300) is a dense solid metal comprising a boulder-like and / or layered microstructure and adhered with dense pores.

2. The zinc electrode (100) according to claim 1, wherein the zinc layer (300) is partially or completely removed from the current collector material (200) during discharge cycling, thereby creating bare current collector material (200) in the case of complete removal.

3. The zinc electrode (100) according to claim 1 or 2, wherein the zinc layer (300) is electrodeposited on the bare current collector material (200) or electrodeposited on the current collector material (200) on which the zinc layer (300) has been electrodeposited.

4. The zinc electrode (100) according to any one of the preceding claims, wherein the density of the zinc layer (300) is 3.50-7.14 g / cm³. 3 The preferred value is 4,50-7,14 g / cm³. 3 More preferably 5.00-7.00 g / cm³ 3 .

5. The zinc electrode (100) according to any one of the preceding claims, wherein neither the current collector material (200) nor the zinc layer (300) contains adhesives, meshes, foams, fabric structures or additives to bond the zinc layer (300) to the current collector material (200).

6. The zinc electrode (100) according to any one of the preceding claims, wherein the zinc layer (300) is made of non-powdered zinc.

7. The zinc electrode (100) according to any one of the preceding claims, wherein the current collector material (200) is selected from one or more of the following: steel, low carbon steel, nickel, nickel-plated steel, nickel-plated low carbon steel or NiP-coated steel.

8. The zinc electrode (100) according to any one of the preceding claims, wherein the current collector material (200) is cold-formed, preferably cold-rolled.

9. The zinc electrode (100) according to any one of the preceding claims, wherein the zinc layer (300), the zinc-containing material, the zinc-containing electrolyte, the current collector material and / or the cathode are free from copper, copper ions and / or copper oxides.

10. The zinc electrode (100) according to any one of the preceding claims, wherein the zinc layer (300) has a mass of up to 10,000 mg / cm³. 2 5000mg / cm 2 More preferably 2000 mg / cm 2 .

11. The zinc electrode (100) according to any one of the preceding claims, wherein the zinc layer (300) has a mass of at least 25 mg / cm³. 2 .

12. The zinc electrode (100) according to any one of the preceding claims, wherein the porosity of the zinc layer (300) is less than 50%, preferably less than 40%, and more preferably less than 30%.

13. An electrochemical cell comprising a zinc electrode for zinc electrodeposition according to any one of claims 1-12, the cell further comprising: - Zinc-containing electrolyte -cathode.

14. The electrochemical battery according to claim 13, wherein the zinc-containing electrolyte is alkaline.

15. The electrochemical cell according to claim 13 or 14, wherein the zinc-containing electrolyte and / or current collector material (200) and / or the cathode are free of copper.

16. The electrochemical cell according to claims 13 to 15, wherein the zinc-containing electrolyte comprises a zinc source selected from the group consisting of one or more of the following: Zn 2+ Ions, ZnO, zincates, or zinc complexes.

17. The electrochemical cell according to claim 16, wherein after the cell is discharged, the zinc source or at least one component of the zinc source is supersaturated.

18. The electrochemical cell according to claims 13 to 17, wherein the zinc-containing electrolyte comprises KOH.

19. The electrochemical cell according to claims 13 to 18, wherein the zinc-containing electrolyte, when applied to a new electrochemical cell, has a minimum ZnO / KOH ratio of 190.00 g ZnO / L KOH, preferably a minimum ZnO / KOH ratio of 100.00 g ZnO / L KOH, and more preferably a minimum ZnO / KOH ratio of 8.00 g ZnO / L KOH, and / or wherein the maximum ZnO / KOH ratio of the zinc-containing electrolyte is 2380.00 g ZnO / L KOH, preferably a maximum ZnO / KOH ratio of 2670.00 g ZnO / L KOH, and more preferably a maximum ZnO / KOH ratio of 2980.00 g ZnO / L KOH.

20. The electrochemical cell according to claims 13 to 19, wherein the zinc-containing electrolyte contains a minimum ZnO concentration of 0.01 M / L KOH in the H2O electrolyte, preferably in the range of 0.1 to 0.8 M / L KOH, and / or wherein the maximum concentration is preferably 0.8 to 1.5 M / L KOH.

21. The electrochemical cell according to claim 20, wherein the ZnO / KOH ratio is independent of the KOH concentration.

22. A method for zinc electrodeposition in an electrochemical cell according to any one of claims 13 to 21, wherein the method comprises: -S100, using the electrochemical cell; -S300, apply a 5%-80% duty cycle pulse of 5-20Hz to deposit zinc onto the current collector material (200) until a predetermined state of charge (SOC) and / or a predetermined quality of zinc layer (300) are achieved; -S400, applying a pulse with a lower limit of about 0.01 Hz, preferably about 0.05 Hz, more preferably about 0.1 Hz and an upper limit of about 500 Hz, preferably about 100 Hz, more preferably about 50 Hz, until a duty cycle of ≤8%-1%, preferably ≤5%-2%, more preferably 5% and / or ≤10 mA / cm is achieved. 2 Preferred value ≤8mA / cm 2 More preferably ≤5mA / cm 2 The predetermined minimum current density; and -S500, end the method.

23. The method for producing a zinc electrode according to claim 22, wherein the method further comprises applying a pulse of 1-300 mA / cm 2 Preferred 3-170mA / cm 2 More preferably 5-125 mA / cm 2 The pulse current density.

24. The method for producing a zinc electrode according to claim 22 or 23, wherein prior to step S300, the method further comprises step S200, which applies a pulse with a duty cycle of 5%-80% at 0-30 Hz, preferably 5-20 Hz, more preferably 10 Hz, and a current density ≥40 mA / cm². 2 .

25. The method for producing a zinc electrode according to any one of claims 22 to 24, wherein prior to step S300, the method further comprises step S250, which, in the case of a previously partially or fully discharged electrochemical cell, applies a 5%-10% duty cycle pulse of 1 kHz-100 kHz, preferably 30-70 kHz, more preferably 50 kHz, for a duration of s seconds to m minutes.

26. The method for producing a zinc electrode according to any one of claims 22 to 25, wherein the method further comprises S310, which monitors zinc electrodeposition when a spike occurs in the battery current and / or a drop occurs in the battery voltage, and immediately stops zinc electrodeposition and terminates method S500 if either a spike or a drop occurs.

27. The method for producing a zinc electrode according to any one of claims 22 to 26, wherein the method further comprises S320, which monitors zinc electrodeposition at a predetermined battery current limit and / or a predetermined battery voltage limit, indicates a predetermined state of charge (SOC), and applies steps S400 and S500 if the predetermined SOC is reached.

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