Zinc electrode

Abstract

The present invention relates to a zinc electrode (100) having a solid metallic zinc layer (300) electrodeposited thereon, an electrochemical cell, and a method for zinc electrodeposition in an electrochemical cell. According to the present invention, a zinc electrode (100) is provided, comprising a current collector material (200) having a zinc layer (300) electrodeposited thereon, the zinc layer (300) appearing as a dense solid metal, having a nodular and / or layered microstructure, and being adherent with dense porosity.

Description

Summary of the Invention

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

[0002] Electrodeposition of zinc (Zn) onto a zinc electrode or current collector material is important for many applications, such as electrowinning, electrogalvanizing, zinc secondary batteries, and many others.

[0003] Zinc is one of the most commonly used battery anode materials due to its high capacity density of 820 Ah / kg (equivalent to approximately 5820 Ah / l). Except for zinc-carbon primary batteries, in which the zinc anode is in solid form, the zinc electrode in all battery systems is powdered to provide a large zinc-electrolyte interface and a good supply of electrolyte near the surface. Such electrodes provide space for dissolution product storage and allow for high reaction rates due to their high surface area, both by weight and volume.

[0004] Porosity of 60-80% of the zinc deposit is most commonly found in zinc electrodes in various battery systems. This translates to a 1.2 Ah / cm2 charge for the zinc active material in such applications. 3 (~1.46g / cm 3 equivalent to 2.2Ah / cm 3 (~2.7g / cm 3 This corresponds to a capacity of 1000 kJ / s.

[0005] However, high energy density alkaline primary batteries have a zinc volume of about 42-50% or a porosity of about 50-58% in these zinc deposits, which corresponds to 3-3.5 g / cm. 3 A high density Zn electrode is used.

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

[0007]

number

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

[0009] Although several zinc complexes can be formed, the predominant species in high molar potassium hydroxide (KOH) is the tetrahedral Zn(OH)4 2- The electrode is identified as a complex. 2 It also has a relatively high exchange current density.

[0010] The dissolution process at a zinc electrode in alkaline solution can be represented by equation [II]:

[0011]

number

[0012] When the solution near the surface becomes saturated with dissolved zinc species, a zinc oxide precipitate can form according to the following reaction [III]:

[0013]

number

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

[0015]

number

[0016] However, the morphology of the zinc deposit and its control play an important role in the quality and performance of the final zinc-deposited electrode and the use of such electrodes in various applications.

[0017] To date, zinc electrodes have been used primarily in non-rechargeable primary batteries such as alkaline or Zn-air batteries. Rechargeable systems using zinc anodes have been researched and developed for various applications, such as Zn-Ag batteries, Zn-MnO2 secondary alkaline batteries, Zn-NiOOH secondary nickel-zinc batteries, Zn-O2 secondary zinc-air batteries, and Zn-H2 hydrogen generation cells or electrolyzers that sequentially produce hydrogen and oxygen and store energy in between by deposition of zinc.

[0018] However, zinc batteries use zinc electrodes (anodes) with high surface areas to reduce overpotential. This is achieved by using small-particle zinc paste, also known as powdered zinc. Zinc electrodes for use in secondary batteries must have some sort of grid-like structure to hold the zinc ions in place. This is primarily ensured by additives and binders. The advantage of powdered zinc is that it has a slightly lower overpotential during discharge. Typically, zinc in powder, granular composition, or fiber form is used as the negative electrode in zinc batteries in gel form with binders and additives. Typical zinc particle sizes range from 20 to 50 μm.

[0019] A major problem associated with zinc-based secondary batteries is their limited cycle life, primarily due to the morphology of the zinc electrode, which is prone to change during charging or during the entire cycle. Morphology changes that lead to electrode performance degradation or failure can occur in multiple ways, including shape change, mossy zinc deposition, densification, and dendrite formation. Shape change is a phenomenon associated with a change in the geometric area of ​​the zinc electrode, in which zinc active material detaches from one location and aggregates in another. In such batteries, not all zinc ions are actually fixed in place, but rather flow through the electrolyte and are redeposited as metallic zinc in various locations. Densification is a phenomenon in which the electrode loses porosity and active surface area, resulting in reduced dynamic performance and easy passivation. Densification is often observed in conjunction with shape change. Dendrite formation occurs during charging and can penetrate the separator of an electrochemical cell, causing a short circuit and immediate cell failure.

[0020] Interest in developing secondary zinc or zinc-air batteries as high-energy power sources has prompted continued research into deposition from alkaline zincate solutions. The cycle life of such secondary zinc or zinc-air batteries has been found to be limited primarily due to the zinc electrode's tendency to passivate and become soluble in concentrated alkaline solutions, which are life-limiting factors. Furthermore, morphological changes during charging or recharging of the zinc electrode can occur, such as the formation of dendrites or loss of porosity. Another concern is the potential for the formation of moss and dense sponges, which can cause zinc particles to peel off from the electrode and potentially lead to short circuits within the cell.

[0021] The morphological zinc deposits that can occur during the electrochemical deposition of zinc to produce zinc deposit electrodes include a variety of types. Five main morphological types are typically described in the prior art: dense sponge, dendritic, nodular, lamellar, and mossy. It is generally assumed that dendrite growth is diffusion-controlled, while mossy growth is activation-controlled. Kinetically, there are preferred crystallographic directions and planes for dendrite growth. The two morphological types, mossy and dendritic, need to be prevented in battery applications. Mossy deposits can result in loss of active material or short circuits at the electrode edge. They can also lead to shape changes. Mossy zinc deposition favors low current density, high zincate concentration, and high temperature. Conditions favoring dendrite formation are high current density, low zincate concentration, and low temperature. It has also been shown that the generation of molecular hydrogen (H2) can lead to morphological changes favoring dendritic, mossy, or dense sponge morphologies. Furthermore, H2 evolution leads to electrolyte drying and pressure buildup in the electrochemical cell. H2 generation is the result of overpotential during charging due to excessively high current densities.

[0022] The causes and conditions for the occurrence of one or other morphological feature are currently the subject of research and have not yet been fully elucidated. A method for almost completely preventing such structures during the production of zinc-loaded electrodes is still unknown. The aforementioned structures, such as blocky or layered structures, can only be produced under very specific conditions and starting materials. For example, in the prior art, such structures can only be produced by electrolytic deposition of zinc onto a zinc substrate. However, such products cannot be used in galvanic cells or batteries.

[0023] However, prior art methods cannot produce uniform zinc layers over longer deposition times, let alone heavier zinc layers. In prior art methods, prolonged electrodeposition invariably results in changes in the zinc layer morphology. During prior art electrodeposition, the zinc layer undergoes a morphological change from a relatively dense, adherent layer to a non-adherent, mossy, or dense, sponge-like, non-dense, highly porous, or fibrous layer, which can lead to short circuits or other effects, such as overheating. In other cases, the formation of a dendritic layer can cause the electrodeposition process to stop or be interrupted. Dendrites can also cause short circuits. Additionally, passivation, which can occur during pre-discharge, can lead to the formation of mossy or fibrous deposits during a new deposition process. Such fibrous deposits are less dense and do not adhere to the electrode, resulting in short circuits.

[0024] Furthermore, secondary batteries or electrochemical reservoirs with zinc negative electrodes can be constructed with a metallic zinc electrode in the charged state and a ZnO layer on the current collector or zincate in the electrolyte in the discharged state. Naturally, primary batteries are fabricated in the charged state with zinc powder. Secondary NiZn batteries are often assembled in the discharged state, but may also be assembled in the charged state, for example, when using a 3D porous zinc electrode.

[0025] Prior art zinc electrodes vary in their structure and zinc content. In secondary systems, capacity density is related to the depth of discharge (DOD) or state of charge (SOC) available during cycling; that is, not all of the zinc is available for energy storage. In primary systems, approximately 95% of the zinc is used for discharge. However, prior art secondary systems only last a few cycles, approximately 10, with a DOD / SOC in the 90% range. The best reported results show 100-200 cycles at a DOD of 40% and several thousand cycles at a DOD of less than 1%.

[0026] In many cases of Zn-air and NiZn secondary batteries, the life (cycle count) limiting component is the zinc electrode, not the counter electrode. The reason zinc does not fully cycle is because the zinc electrode loses structure and interconnections between the active material portions. In most systems, the zinc electrode has two or three times higher capacity than the counter electrode. It should be noted that the high capacity of zinc metal makes a battery system competitive even with a zinc utilization rate of 30-40% of the cycle.

[0027] The present invention is therefore based on the object of providing an electrodeposited zinc electrode that overcomes the drawbacks of the prior art. In particular, the present invention provides a zinc electrode that allows for nearly 100% zinc utilization while providing nearly infinite cycles when used in practice.

[0028] This object is solved 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 respective dependent claims.

[0029] According to the present invention, there is provided a zinc electrode comprising a current collector material onto which is electrodeposited a zinc layer, the zinc layer appearing as a dense solid metal, having a nodular and / or lamellar microstructure and being deposited with dense porosity, where dense in the context of the present invention means densely packed without significant voids.

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

[0031] In the context of the present invention, "completely" means that approximately 100% of the zinc layer can be removed. In other words, the discharge process can partially (SOC>0) or completely (SOC=0) dissolve the zinc layer from the current collector material, and if the Zn layer is completely dissolved, the bare current collector material is available for further electrodeposition. However, discharge may only partially dissolve the Zn layer, and the Zn layer may be electrodeposited again. In principle, this Zn layer formation / electrodeposition and dissolution can be repeated almost indefinitely. In the context of the present invention, bare current collector material means the current collector material in its original state as originally used, i.e., free or almost free of residue.

[0032] According to another preferred embodiment, the zinc layer is electrodeposited onto a bare current collector material or onto a current collector material already electrodeposited with a zinc layer, which means that the electrodeposition of the electrode according to the invention can start or be carried out at an SOC≧0.

[0033] According to another preferred embodiment, the zinc layer has a coating density of 3.50 to 7.14 g / cm 3 It has a density of 4.50 to 7.14 g / cm 3 A density in the range of 5.00 to 7.00 g / cm is preferred. 3 Densities in the range 7.14 g / cm are particularly suitable. 3These densities are approximately the same as the actual density of metallic zinc. This indicates that the zinc deposits of the present invention have approximately the same actual density as metallic zinc. Mossy or dendritic zinc deposits do not achieve such densities. In some experiments, zinc deposits with higher densities could be produced by prior art techniques, but they were very thin and partially underwent morphological changes. Furthermore, in these tests, the zinc deposits were deposited only on reinforced zinc substrates as current collector materials, which is not meaningful for commercial use. 3.5 g / cm 3 A certain low porosity resulting in a density less than 100% can be achieved at certain deposition conditions, which may be favorable for achieving a low overpotential due to the high surface area.

[0034] The zinc electrode maintains the high capacity density of zinc, from 3.50 to 7.14 g / cm3 according to the present invention. 3 The deposition density of each is 2.87Ah / cm 3 ~5.85Ah / cm 3This corresponds to a capacity density of 0.5 . When used in batteries or other applications, such zinc electrodes of the present invention can provide nearly infinite charge / discharge cycles for the battery or other application. The zinc deposition of the present invention results in a dense, interconnected metal morphology. There is direct electrical connection of all portions of the zinc deposit to the current collector material. Therefore, there is no oxide barrier, as in powder / particle zinc electrode applications. A feature of the present invention is that, when used in cell systems or applications such as batteries, such zinc electrodes allow the system or application to start at a discharged state of charge (SOC) of 0. By using the zinc electrodes of the present invention, significantly higher energy densities can be achieved in applications by using a high SOC (up to about 80-100% of the ZnO / zincate of the system / application can be used for charging, and 100% DOD can be used for discharging). One feature of the present invention is that, when the zinc electrodes are used in batteries, for example, a large number of cycles (virtually infinite cycles) can be achieved by introducing a 100% DOD step during the cycling process. The volume change of zinc and / or partial mossy / dendritic deposits are completely removed, and the system, or more precisely the zinc electrodes, can be restarted with a uniform and smooth zinc deposit. Therefore, the capacity and capacity density values ​​described in this invention relate to 100% DOD, i.e., full utilization of the deposited zinc for energy storage, and the resulting high capacity density.

[0035] According to a preferred embodiment, neither the current collector material nor the zinc layer includes a binder, grid, foam, fabric, or additive to bond the zinc layer to the current collector material. Unlike the prior art, the electrodes of the present invention do not require a grid, foam, fabric, or binder, as in secondary Zn-air batteries or primary batteries, and therefore the electrodes of the present invention have a significantly higher energy density than the prior art. Furthermore, the electrodes of the present invention do not include additives, such as calcium hydroxide, that are typically present to immobilize zincates.

[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 active surface of the electrodes of the present invention is small, resulting in a large overvoltage. In the solid, non-powdered zinc deposits of the present invention, electrical connection between the zinc and the current collector material is always present, whereas in powdered deposits, passivating particles lose electrical connection with the current collector, resulting in reduced utilization of the active material. It is important to understand that the electrodes of the present invention are plated with pure, solid metallic zinc during charging or electrolytic deposition; no powdery deposits are produced or are already present. It is also understood that particulate zinc, when peeled from the substrate, forms mossy zinc deposits that have the same negative properties as powdered zinc. However, such powdery deposits are undesirable in the electrodes of the present invention, because the zinc deposits of the present invention, on the contrary, result in a dense, interconnected metal morphology. While the surface area may be smaller than that of powdered zinc, the particles can be coated with an oxide layer, and electrical conduction through the oxide of the particles is lower than that in the solid zinc layers described herein, so the discharge current is not significantly reduced.

[0037] One advantage of solid zinc is that the non-powder deposition allows for high zinc utilization during discharge and the ability to deposit zinc in the amount of several hundred mg / cm. 2 The ability to deposit thick, smooth layers of zinc over such electrodes is also a key advantage. Furthermore, with such electrodes, a virtually unlimited number of charge / discharge cycles can be achieved without permanent electrode shape change.

[0038] According to another preferred embodiment, the current collector material is selected from the group consisting of one or more of steel, low-carbon steel, nickel, nickel-plated steel, nickel-plated low-carbon steel, or nickel-phosphorus (NiP)-coated steel. Low-carbon steel has been found to be a preferred material due to its very low cost, lack of corrosion in alkaline environments, and lack of H2 evolution on its surface. The electrode may also comprise at least one polymer substrate or composite material with a nickel (Ni) or NiP surface coating. Alternatively, the electrode may comprise a structure made of carbon fiber or fibers with an electrically conductive surface coating. An optional additive for reducing self-discharge may be further applied to the electrolyte or deposited on the current collector material. In this case, the surface of the electrode is increased by depositing a dense, highly conductive zinc layer on such a high-surface-area substrate.

[0039] Furthermore, according to a 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, it has been found that cold-formed materials, particularly cold-formed or cold-rolled steel or low-carbon steel, are particularly suitable as current collector materials for producing electrodes according to the present invention. Cold-rolled low-carbon steel has been found to be a suitable material due to its very low cost, lack of corrosion in alkaline environments, and lack of surface H2 evolution during electrodeposition. These materials may have a crystalline or fine surface similar to that of pure zinc, which may facilitate the formation of a solid zinc layer. In this regard, it is surprising that the deposition of zinc on such current collectors can be achieved without the use of additives and / or binders. Naturally, additional additives or binders may be used, but it has been shown that they are not essential for the formation of electrodes according to the present invention.

[0041] According to another preferred embodiment, the zinc layer does not contain copper (Cu). For example, Cu may be added during the deposition of zinc. +It has been shown that the absence of ions such as ZnO is advantageous. Such ions promote H2 evolution during charging and cause mossy zinc deposits. If the presence of copper during deposition is avoided as much as possible, zinc-plated zinc electrodes will be substantially copper-free. However, it is also possible to use copper as a current collector material. However, in this case, the presence of Cu during deposition must be avoided to suppress H2 evolution during deposition. + Care must be taken to prevent decomposition of the ions. Thus, copper current collectors may be coated with Ni, NiP, or other iron (Fe) alloy coatings.

[0042] According to another preferred embodiment, the zinc layer has a thickness of 200 mg / cm 2 , preferably 300 mg / cm 2 , most preferably 400 mg / cm 2 The zinc electrode of the present invention has a mass of from a few micrograms to hundreds or thousands of milligrams per square centimeter (mg / cm 2 ) of zinc deposit mass. In principle, the mass of the zinc layer according to the present invention is nearly infinite, but it is clear that there are certain limitations to the realization of such a layer. So far, such layer masses of solid metallic zinc could not be produced by the prior art. The zinc electrode according to the present invention is therefore unique in terms of its compactness, morphology, and three-dimensionality. However, as mentioned above, in applications it is also possible to achieve higher layer masses, for example by continuously applying new zinc-containing electrolyte during electrodeposition. In such applications, it is possible to achieve layer masses of several thousand mg / cm. 2 cm 2 In terms of capacity per unit area, the present invention provides a coating composition of 200 to 400 mg / cm 2 The zinc layer has a capacity of 164~328mAh / cm 2 However, as mentioned above, this corresponds to a capacity density of several thousand mg / cm 2 Layer masses greater than 10 ...

[0043] According to another preferred embodiment, the zinc layer has a concentration of 0 to 10,000 mg / cm 2 , preferably 1 to 5000 mg / cm 2 , and more preferably 25 to 2000 mg / cm 2 has a mass of

[0044] According to another preferred embodiment, the zinc layer has a maximum of 10000 mg / cm 2 , preferably up to 5000 mg / cm 2 , more preferably up to 2000 mg / cm 2 has a mass of

[0045] According to yet another preferred embodiment, the mg / cm of zinc layer (300) 2 The mass of the unit is nearly unlimited.

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

[0047] According to another preferred embodiment, the zinc layer has a porosity of less than 50%. Because the electrode according to the present invention is very dense, with the density range of the zinc deposit being similar to the actual density of metallic zinc, 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 a porosity of less than 20% is even more preferred. Conventional zinc electrodes, let alone electrodes used in zinc-air batteries, do not achieve such low porosity values. Compared to typical electrode surfaces, the specific active surface of the zinc electrode according to the present invention is hundreds to thousands of orders of magnitude lower than the specific active surface in zinc-air battery applications due to the low porosity. For example, the surface area of ​​prior art zinc powder (e.g., in zinc-air batteries) is about 1 m 2 / g. According to the present invention, 1 cm 2 Layers of several micrograms to thousands of milligrams per layer can be achieved. For example, a layer mass of 200 mg / cm according to the present invention can be achieved. 2 In the case of zinc powder, the surface area is approximately 2000 cm2 Thus, even if a certain degree of porosity is present in the layer according to the invention, the active surface area is several orders of magnitude smaller than in conventional electrode layers of the prior art.

[0048] According to the present invention, there is provided an electrochemical cell for zinc electrodeposition comprising a zinc electrode according to one of the zinc electrode embodiments described above, the electrochemical cell further comprising 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 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 create a zinc-negative electrode using an electrochemical cell, the cell can be assembled in a discharged state (SOC=0) using only the anode current collector material as the negative electrode and the cathode current collector as the positive electrode. The two electrodes (negative and positive electrodes) are connected via an electrolyte containing zinc primarily in the form of ZnO and / or zincate, rather than powdered zinc. However, in the context of the present invention, an electrochemical cell includes an anode current collector material, a cathode current collector material, and a suitable electrolyte. For purposes of the present invention, an electrochemical cell is defined as a general term for various configurations used in electrochemistry or based on electrochemical processes. In this context, electrochemical cells include galvanic cells, electrolytic cells, and storage battery cells. The electrolyte can be liquid or solid, or both liquid and solid electrolytes can be present. Thus, an electrochemical cell can be defined as a configuration of two electrodes conductively connected via a zinc-containing electrolyte.

[0051] According to a preferred embodiment of the electrochemical cell, the zinc-containing cell is alkaline. It is contemplated that the zinc-containing electrolyte may comprise primarily zinc chloride or ammonium chloride, although an alkaline environment is still preferred.

[0052] According to a preferred embodiment of the electrochemical cell, the zinc layer, the zinc-containing electrolyte, the current collector material, and / or the 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 is Zn 2+ The zinc source includes a zinc source selected from the group consisting of one or more of zinc ions, ZnO, zincates, and / or zinc complexes. When the present invention refers to a zinc-containing source or zinc-containing electrolyte, it primarily refers to one of the above-mentioned substances, with ZnO and zincates being preferred. For the purposes of the present invention, a zinc complex is understood to be any type of zinc complex, but also a complex that contains zinc and can dissolve during (re)charging so that solid Zn can be further deposited on the current collector material or a current collector already plated with a zinc layer. The zinc source can have different viscosities and can be used as a paste or slurry, or as a solution. It is also possible to use several zinc sources in combination. However, in the context of the present invention, it is expressly intended that the zinc-containing source or zinc-containing electrolyte does not comprise zinc in the form of powdered zinc. Rather, the use or application of powdered zinc in the form of solid zinc powder is not suitable for the present invention.

[0054] According to another preferred embodiment of the electrochemical cell, the zinc source or at least one component of the zinc source becomes supersaturated after discharging the cell. This means that during discharging the cell, the components of the zinc source are not converted exactly stoichiometrically to the components actually used at the start, but at least one component is not or cannot be further converted, so this component is present in a supersaturated concentration. For example, ZnO may be used, which is converted to zinc via zincate, and then this zinc is plated during electrodeposition. In the reverse reaction, i.e., the discharge process, zinc is converted to zincate, but not all of the zincate above the saturation point returns to ZnO, so at that point the zincate becomes supersaturated.

[0055] According to yet another preferred embodiment of the electrochemical cell, the alkaline zinc-containing electrolyte comprises KOH. In this context, the electrolyte may further contain KOH in a minimum amount of 5-25 wt. % and a maximum amount of 35-60 wt. %; a KOH amount of 26-36 wt. % is preferred, and 30 wt. % KOH is particularly preferred.

[0056] According to another preferred embodiment, the zinc-containing electrolyte further comprises NaOH in a minimum range of 5-15 wt. % and a maximum range of 16-30 wt. % NaOH, with 20 wt. % NaOH being preferred and 18 wt. % NaOH being particularly preferred. NaOH may be used instead of or in combination with KOH.

[0057] According to yet another preferred embodiment of the electrochemical cell, the zinc-containing electrolyte, when applied in a new electrochemical cell, has a minimum ZnO / KOH ratio of 190.00 g ZnO per 1 L KOH, with a minimum ZnO / KOH ratio of 100.00 g ZnO per 1 L KOH being preferred, with a minimum ZnO / KOH ratio of 8.00 g ZnO per 1 L KOH being particularly preferred, and / or the zinc-containing electrolyte has a maximum ZnO / KOH ratio of 2380.00 g ZnO per 1 L KOH, with a maximum ZnO / KOH ratio of 2670.00 g ZnO per 1 L KOH being preferred, with a maximum ZnO / KOH ratio of 2980.00 g ZnO per 1 L KOH being particularly preferred. At the end of charging, the concentration can drop significantly, so the minimum zincate or dissolved ZnO (the ZnO does not remain as ZnO because it is below the saturation point) is approximately 0.1 M in 1 L of KOH or 8 g of ZnO in 1 L of KOH. For purposes of this invention, "applied to a new electrochemical cell" means that the cell is being filled for the first time or has completely fresh electrolyte. Thus, the application ratio is the ratio that exists before the start of the deposition process or charge cycle. It is understood that these parameters will change during a charge or discharge cycle.

[0058] According to yet another preferred embodiment of the electrochemical cell, the zinc-containing electrolyte has a minimum ZnO concentration of 0.01M per liter of KOH in HO electrolyte, with a preferred range of 0.1-0.8M per liter of KOH, and a maximum concentration of preferably 0.8-1.5M per liter of KOH.

[0059] According to yet another preferred embodiment of the electrochemical cell, the ZnO / KOH ratio is not affected by the KOH concentration.

[0060] According to another preferred embodiment of the electrochemical cell, the zinc-containing electrolyte further comprises Pb, Fe, Sn, CdMg, or other metals or alloys. The electrolyte may also contain an additive of at least one hydroxide of In, Pb, and / or Sn at a concentration of 10 to 500 ppm based on the amount of ZnO in the electrolyte. Such an additive may increase the hydrogenation voltage and reduce the self-discharge of the cell. The electrolyte may also contain at least one additive of electrolyte additives and / or surfactants, such as polyoxyethylene octadecenyl ether phosphate, polyethylene glycol, copolymers having acidic groups, modified styrene-maleic acid copolymer solutions, alkylolammonium salt solutions of low-molecular-weight polycarboxylic acid polymers, phosphate esters of alkylphenoxypolyethoxyethanol, polyether phosphate esters, or octylphenoxypolyethoxyethyl phosphate solutions, water, phosphoric acid, and polyethylene glycol octylphenyl ether. Such additives also used in alkaline primary batteries to reduce self-discharge may be used in the present invention, such as polyoxyethylene octadecenyl ether phosphate, polyethylene glycol, copolymers having acidic groups, modified styrene-maleic acid copolymer solutions, alkylolammonium salt solutions of low molecular weight polycarboxylic acid polymers, phosphate esters of alkylphenoxypolyethoxyethanol, polyether phosphate esters, polyether phosphate esters or octylphenoxypolyethoxyethyl phosphate solutions, water, phosphoric acid, and electrolyte additives and / or surfactants such as polyethylene glycol octylphenyl ether. Such additives affect the discharge or self-discharge behavior of electrochemical cells by affecting zinc passivation.

[0061] According to the present invention there is provided a method for zinc electrodeposition in an electrochemical cell according to one of the above-mentioned embodiments, the method comprising the steps of: using an electrochemical cell; applying 0-30 Hz, preferably 5-20 Hz, more preferably 10 Hz, 5%-80% duty cycle pulses for zinc deposition on the current collector material until a predetermined state of charge SOC and / or a predetermined mass of zinc layer is reached; Pulses having 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, with a duty cycle of 8% to 1% or less, preferably 5% to 2% or less, more preferably 5%, and / or a current of 10 mA / cm 2 Preferably less than 8 mA / cm 2 or less, more preferably 5 mA / cm 2 until a predetermined minimum current density is reached: Terminating the method; Includes:

[0062] According to another preferred embodiment of the method, the method applies pulses of about 0.01-500 Hz, preferably about 5-50 Hz, more preferably about 5-25 Hz, and especially preferably about 10 Hz.

[0063] According to another preferred embodiment of the method, the method comprises: using an electrochemical cell; applying 0-30 Hz, preferably 5-20 Hz, more preferably 10 Hz, 5%-80% duty cycle pulses for zinc deposition on the current collector material until a predetermined state of charge SOC and / or a predetermined mass of zinc layer is reached; A duty cycle of 8% to 1% or less, preferably 5% to 2% or less, more preferably 5%, and / or 10 mA / cm 2 Preferably less than 8 mA / cm 2 or less, more preferably 5 mA / cm 2 applying pulses of 0 to 30 Hz, preferably 5 to 20 Hz, more preferably 10 Hz, until a predetermined minimum current density is reached: Finishing the method Includes:

[0064] According to another preferred embodiment of the method, the method comprises: 2 , preferably 5 to 170 mA / cm 2 , and more preferably 5 to 125 mA / cm 2 and applying a pulse current density in the range of

[0065] The process parameters as duty cycle, frequency or current density are optimized for charging time, charging efficiency and structure (meaning deposition of a smooth solid zinc layer according to the present invention). However, according to the present invention, a low duty cycle (e.g. 5%) of 10 Hz and a low current density (5 mA / cm) are preferred. 2 ) produced thick zinc deposits (0.1-1000 mg / cm) at all ZnO / zincate concentrations. 2 ) but the charging time is very long. To shorten the charging time, a higher current density is required. For a high average current density, two options can be applied: (a) low duty cycle high current density or (b) high duty cycle low current density, where the average current density is the same in both (a) and (b). Option (a) with low duty cycle high current density has low electrical efficiency, while option (b) with high duty cycle low current density has good electrical efficiency.

[0066] As an example, using saturated zincate in 30% KOH, (a) 40% duty cycle 80 mAh / cm 2 , or (b) 80% duty cycle 40mA / cm 2 and both (a) and (b) are 100 mg Zn / cm 2 However, plating is less than 40mA / cm 2 Option (b) indicates that the zinc deposition is approximately 100 mg / cm 2 If the thickness exceeds 100 mg / cm, it will become mossy. However, if that thickness is desired, the 100 mg / cm deposited in option (b) 2 Zinc is more electrically efficient. Supersaturated zincates require low duty cycles and low current densities until they reach a saturation point, after which they can be used at 40 mA / cm. 2An 80% duty cycle (option (a)) of 40 mA / cm may be used. 2 Start with an 80% duty cycle (option (b)) and then reduce to a 40% duty cycle of 80mAh / cm 2 Switch to option (a) and use 100 mg / cm 2 More than one combination may be used.

[0067] The parameters given here are the basic parameters by which a zinc electrode according to the present invention can be obtained. However, it is understood that the pulsing parameters are influenced by the ZnO loading, meaning, for example, the zincate concentration (or other zinc source concentration), the degree of thickness / viscosity of the applied ZnO / KOH paste. Furthermore, these initial parameters can be influenced during the deposition process, for example, by the charging progress, temperature, zinc loading / cm 2 It is also clear that the temperature varies with the temperature. For zinc deposition, pulses of 0-30 Hz, preferably 5-20 Hz, and more preferably 10 Hz, with a 5%-80% duty cycle are applied to the desired zinc deposition mass in order to bring zincate ions closer to the electrode surface, allow OH to penetrate the inner structure, and avoid H2 evolution. All pulses are suitable for suppressing H2 evolution to prevent the formation of mossy or dendritic zinc deposits.

[0068] According to the present invention, there are several conditions that allow for metallic, solid, non-powder-like, and non-mossy zinc deposits during charging of the anode current collector material (negative electrode) in an electrochemical cell, although not all conditions need actually be present to produce a zinc electrode according to the present invention; in other words, not all conditions are essential but are merely advantageous when present.

[0069] Optionally, e.g., Cu + It is desirable to avoid ions such as ZnO, which promote H2 evolution during charging and contribute to mossy zinc deposits.

[0070] Additionally, it is desirable that the current collector surface be free of copper oxides or passivation, as such oxides promote H2 evolution during charging and contribute to mossy zinc deposits.

[0071] The deposition parameters must be selected so that H2 is not generated. H2 bubbles deposit zinc around them, forming mossy zinc. In fact, high currents are the cause of H2 generation. The use of high current densities has advantages mainly at the beginning of the deposition, depending on the substrate (current collector material or already deposited Zn layer). However, it is the pulses, not the high current density, that remove the H2 bubbles in the first place. When depositing on substrates made of materials with low H2 overpotential, i.e., good H2 generation substrates or catalysts, a current of 40 mA / cm2 for a duration of a fraction of a second is recommended to obtain an initial plating that inhibits the activity of the catalytic properties of the substrate. 2 An initial high-current pulse of 1000 Å is necessary. It is also advantageous to increase the number of nucleation sites on the substrate; otherwise, the substrate will dissolve the deposit during deposition. After the initial deposition, the current is preferably reduced; otherwise, mossy Zn will form.

[0072] The current collector material should be selected to have a high H2 overpotential to avoid H2 evolution at the start of plating on the bare current collector.

[0073] Another important condition is time. Thus, time is needed to allow the zincate ions consumed at the electrode / electrolyte interfacial layer to be replenished. This is achieved by lowering the duty cycle; for example, a very thick ZnO paste (in the context of this invention, thick means high viscosity and high ZnO concentration, as in other mentioned embodiments of the invention) between the Zn electrode and the separator requires a low duty cycle, e.g., 10%, while with lower ZnO or zincate concentrations, an 80% duty cycle is possible. However, as the zincate becomes depleted towards the end of the charge, a lower duty cycle is preferably applied.

[0074] According to another embodiment of the method, the method comprises: 2 The method further includes applying pulses of 0-30 Hz, preferably 5-20 Hz, and more preferably 10 Hz, with a 5%-80% duty cycle at a current density of 0-30 Hz, preferably 5-20 Hz, and more preferably 10 Hz, or higher. An initial Zn deposition step is performed before the main zinc deposition step. For current collector materials with low H2 overpotentials, such as nickel, such a step is essential to prevent H2 evolution that may occur during zinc deposition at the parameters described in the method of the present invention. In addition, this step can increase the number of nucleation sites, which is advantageous for uniform and improved zinc deposition in the next step. This increase in the number of nucleation sites applies not only to materials with low H2 overpotentials but also to materials with high H2 overpotentials, such as cold-rolled low-carbon steel. However, for cold-rolled low-carbon steel, such a step is not required. Preferably, such a step is applied in the method of the present invention when a bare current collector material is present, i.e., when zinc deposition is first applied to an electrochemical cell using a bare current collector material, or when the zinc layer has been completely stripped from the current collector material by a previous discharge cycle or step.

[0075] According to another embodiment of the method, if the electrochemical cell has previously been partially or fully discharged to form a surface passivation, the method further comprises applying a 5% to 10% duty cycle pulse at 1 to 100 kHz, preferably 30 to 70 kHz, and more preferably 50 kHz, for s seconds to m minutes. The surface passivation is preferably stripped prior to zinc deposition. Otherwise, plating onto the passivation will result in a mossy zinc deposit. However, as the zincate concentration decreases, the passivation will eventually dissolve. Stripping of the passivation is accomplished by applying a low duty cycle pulse of a fraction of a microsecond (μs) for a few seconds (e.g., 1 to 90 seconds, preferably 5 to 50 seconds, more preferably 30 seconds) to a few minutes during the initial charging or deposition process.

[0076] According to another embodiment of the method, the method further includes monitoring zinc electrodeposition for a sudden increase in cell current and / or a decrease in cell voltage, and if a sudden increase and / or decrease is present, immediately stopping zinc electrodeposition and terminating the method. Such a sudden increase and / or decrease indicates a short circuit and means that the zinc deposit is likely to be mossy or dendritic. Such unwanted deposition is remedied by full or partial discharge of the electrochemical cell, i.e., complete or partial removal of the zinc layer. Thereafter, new zinc deposition can be initiated (e.g., SOC=0 in the case of full discharge).

[0077] According to another embodiment of the method, the method comprises monitoring zinc electrodeposition for a predetermined cell current limit and / or a predetermined cell voltage limit indicative of a predetermined state of charge (SOC), and when the predetermined SOC is reached, monitoring the zinc electrodeposition for a duty cycle of 8% to 1% or less, preferably 5% to 2% or less, and more preferably 5% and / or 10 mA / cm 2 Preferably less than 8 mA / cm 2 or less, more preferably 5 mA / cm 2 It further comprises applying pulses of 0-30 Hz, preferably 5-20 Hz, more preferably 10 Hz, until a predetermined minimum current density is reached:

[0078] The parameters used to monitor zinc electrodeposition may vary depending on whether special cell designs or additional temperature control are required, and the parameters for different states of charge may be fixed or may be dynamically adjusted by performing occasional electrochemical impedance spectroscopy (EIS) during charging and adjusting pulse parameters accordingly to speed charging while avoiding short circuits.

[0079] Intermittent high-speed electrochemical impedance spectroscopy (EIS) can be performed to obtain information about the cell's condition and state of charge. For example, surface roughness can be indicated by EIS, with high roughness indicating undesirable mossy deposits and low roughness indicating solid Zn deposits. EIS can be performed before, immediately after, and every x hours after charging begins to indicate the presence of passivation, whether charging has started properly, and whether the Zn deposit maintains a good Zn solid structure. Surface roughness is indicated by the electrochemical double-layer capacitance. A higher capacity relative to the bare current collector capacity indicates a high surface area and the formation of mossy deposits. Measurements can be performed at several frequencies, but do not necessarily require continuous frequency scans. As long as the zinc deposit maintains a relatively low roughness and a solid, non-mossy structure, the capacity will remain approximately the same as that of the bare current collector.

[0080] Furthermore, the amount of electrolyte or the amount of zincate and / or ZnO in the cell can be determined by the cell resistance (real component of the impedance), which can be achieved by low frequency measurements. Furthermore, passivation can be detected by EIS.

[0081] In a different scenario, if the zinc electrode is part of an electrochemical cell containing a catalytic gas-evolving electrode that generates oxygen during zinc deposition and H2 during zinc dissolution, the recombination catalyst used as a safety device can also be used as a sensor. The temperature of the recombination catalyst can be monitored for uncontrolled zinc deposition and termination of charging. In either case, as H2 evolution begins and O2 is present, the temperature of the recombination catalyst begins to rise, indicating that charging should be terminated. The same occurs during discharge. If the temperature of the recombination catalyst rises, it indicates that the polarity has reversed and the cell has terminated electrolysis, releasing O2 and H2 simultaneously, indicating that discharge should be terminated.

[0082] Furthermore, in another example of a secondary zinc battery, oxygen can evolve at the positive electrode or hydrogen can evolve at the negative electrode in the event of overcharge, depending on which electrode has less active material. Gas passages can be implemented within the cell so that oxygen can recombine with hydrogen at the recombination catalyst or react with the zinc negative electrode.

[0083] However, it is also possible to adapt the duty cycle to the already charged capacity, 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, the duty cycle, can be determined as a function of current, state of charge, and temperature. This can be stored in a look-up table and used for discharging.

[0084] According to the present invention, there is provided an electrochemical cell for carrying out the method of the present invention.

[0085] The following methods, known to those skilled in the art, may be used to determine the properties and / or parameters of zinc electrodes according to the present invention and embodiments described herein.

[0086] Because the zinc layer is a solid metal, has only some surface roughness, and is largely free of inherent voids or closed pores, microscopic images are sufficient to determine the structure.

[0087] The structure of the zinc layer can therefore be analysed using microscopic images taken by an optical or electron microscope, for example a scanning electron microscope (SEM), and the results can be quantified by computer image analysis.

[0088] Scanning electron microscopy (SEM) is a technique for imaging the surface morphology of materials at high magnification. This technique provides detailed three-dimensional images that can be used to identify features such as cracks, pores, and grain boundaries in metal coatings.

[0089] Additionally or alternatively, other methods may be used, such as TEM or AFM. Transmission electron microscopy (TEM) generally offers even higher magnification than SEM and can provide detailed information about the internal structure of a coating, including nanoscale features. Atomic force microscopy (AFM) is a high-resolution imaging technique that uses a sharp tip to scan the surface of a sample. It is particularly useful for studying surface roughness and can provide information about both the surface topography and the mechanical properties of a coating.

[0090] The zinc layer may be analyzed using laser confocal microscopy, which provides a direct roughness value and is used to calculate the subsurface volume.

[0091] X-ray diffraction (XRD) can be used to analyze the crystalline structure of the coating, providing information about the crystallographic phases present in the coating, grain size, and preferred crystal orientation.

[0092] Various porosimetry techniques, such as mercury intrusion porosimetry and gas adsorption (e.g., BET), can be used to determine the porosity of a coating. These methods help to quantify the volume and size distribution of pores within the coating.

[0093] Cross-sectional analysis involves preparing a sample with a known coating and cutting it to expose the internal structure. This allows direct observation of the coating-substrate interface and assessment of porosity and thickness. More advanced techniques use an ion beam to prepare the cross-section (focused ion beam, FIB).

[0094] Electrochemical impedance spectroscopy (EIS) can be used to evaluate the corrosion resistance of metal coatings and indirectly infer information about porosity. Changes in impedance can provide insight into the coating's ability to withstand corrosion.

[0095] Microhardness tests, such as Vickers or Knoop hardness tests, can be performed on cross sections of coated samples. Variations in hardness across the coating can indicate porosity or compositional differences. The mossy layer is very soft compared to solid or bulk zinc.

[0096] Since zinc electrodes are mostly solid, have a relatively rough surface, 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.

[0097] In general, the following methods are known to those skilled in the art for determining the density of a zinc layer.

[0098] The Archimedes' principle method involves immersing a porous metal sample in a fluid (typically a liquid) and measuring the displacement of the fluid. According to Archimedes' principle, the buoyant force acting on an immersed object is equal to the weight displaced by the fluid. The density of the material can then be calculated based on the known density of the fluid.

[0099] Gas pycnometry is a technique in which gas is used to determine the pore volume in a material. By knowing the volume and mass of the sample, the density can be calculated.

[0100] X-ray computed tomography (CT) can provide a three-dimensional image of the internal structure of porous metals. By analyzing CT scans, researchers can estimate the volume of solid material and voids. Combining this information with the sample's mass allows for the calculation of density.

[0101] Ultrasonic techniques can be used to measure the speed of sound waves passing through a material. From the speed of sound and the known acoustic properties of the material, density can be inferred.

[0102] Optical and / or electron microscopes, combined with image analysis software, can be used to analyze the microstructure of porous metals. By quantifying the amount of solid metal and voids, researchers can estimate the overall density.

[0103] In the helium displacement method, helium is used to displace the air within the pores of the material, and the change in pressure or volume is then measured and the density calculated based on the ideal gas law.

[0104] Similar to Archimedes' principle, the buoyancy method involves immersing a sample in a liquid, but instead of measuring displaced fluid, the buoyancy method may directly measure the force exerted on the sample by buoyancy.

[0105] The mass of the zinc layer can be determined using a gravimetric method. This method is based on the fact that zinc is deposited on the current collector. The current collector is weighed before the start of deposition. After the zinc is deposited, it is weighed again, and the difference is the weight of the zinc coating.

[0106] The following well-known method may be used to determine the mass of the zinc layer.

[0107] A quartz crystal microbalance (QCM) is a sensitive mass measurement device that uses the change in the resonant frequency of a quartz crystal due to the addition of mass. Coatings can be deposited on the quartz crystal, changing the resonant frequency and allowing for accurate measurement of the added mass.

[0108] The coulometric method measures the amount of electricity passed during the deposition process. Knowing the electrochemical equivalent of the metal being deposited, the mass of the coating can be calculated.

[0109] In beta backscattering, beta particles are directed at the coating surface and the backscattered radiation is measured, the intensity of which is proportional to the thickness of the coating.

[0110] X-ray fluorescence (XRF) beta particles are directed at the coating surface and the backscattered radiation is measured, the intensity of which is proportional to the thickness of the coating.

[0111] Neutron activation analysis (NAA) involves irradiating a coated sample with neutrons and measuring the emitted gamma rays, the intensity of which is proportional to the amount of a particular metal in the coating.

[0112] Generally, all these methods belong to the common general knowledge of a person skilled in the art. Furthermore, a person skilled in the art may use all known methods to determine the parameters and / or properties of a zinc electrode, and is not limited to the methods described herein.

[0113] Additionally, all methodologies known in the relevant art for determining parameters and / or properties will yield the same results within a reasonable range of measurement accuracy.

[0114] Also, applications or embodiments of the present invention are described with reference to various subject matter. In particular, some applications or embodiments are described with reference to apparatus-type claims, while other applications are described with reference to method-type claims. However, those skilled in the art will understand from the above and following description that, unless otherwise specified, any combination of features belonging to one type of subject matter, as well as any combination of features relating to different types, is also intended to be disclosed herein. In particular, a combination of a feature relating to an apparatus-type claim with a feature relating to a method-type claim is considered to be disclosed. The present invention and its embodiments are described in further detail below in conjunction with the drawing(s). [Brief explanation of the drawings]

[0115] [Figure 1] 1 shows an image of the surface of a zinc deposit with a dense sponge-like micromorphology according to the prior art, adapted from RY Wang et al., Journal of The Electrochemical Society, 153 (5) C357-C364 (2006). [Figure 2]1 shows an image of the surface of a zinc deposit with dendritic micromorphology according to the prior art, adapted from RY Wang et al., Journal of The Electrochemical Society, 153 (5) C357-C364 (2006). [Figure 3] 1 shows an image of the surface of a zinc deposit with a moss-like micromorphology according to the prior art, adapted from RY Wang et al., Journal of The Electrochemical Society, 153 (5) C357-C364 (2006). [Figure 4] 1 shows an image of the surface of a zinc deposit with a nodular micromorphology according to the prior art, adapted from RY Wang et al., Journal of The Electrochemical Society, 153 (5) C357-C364 (2006). [Figure 5] 1 shows an image of the surface of a zinc deposit with a layered micromorphology according to the prior art, adapted from RY Wang et al., Journal of The Electrochemical Society, 153 (5) C357-C364 (2006). [Figure 6] 1 shows a classification table of Zn deposits according to the prior art, adapted from RY Wang et al., Journal of The Electrochemical Society, 153 (5) C357-C364 (2006).

[0116] [Figure 7] FIG. 1 shows a schematic diagram of a zinc electrodeposited anode electrode that develops a dendritic morphology according to the prior art. [Figure 8] FIG. 1 shows a schematic diagram of a zinc electrodeposited anode electrode that develops a fibrous / moss-like morphology according to the prior art. [Figure 9] FIG. 1 shows a schematic diagram of a zinc electrodeposited anode electrode that develops a solid metal (layered) morphology, according to an embodiment of the present invention. [Figure 10]1 shows a flowchart of the method steps for fabricating the zinc electrode described in this invention in an electrochemical cell, according to one embodiment of the present invention.

[0117] Figure 1 shows an image of the surface of a zinc deposit with a dense, sponge-like micromorphology. As shown, the dense, sponge-like deposit is a massive aggregate and highly branched dendrites developed over a long deposition time at a very high current density (cd). Furthermore, such deposits have finely dispersed pores and anisotropically oriented crystallinity. Depending on their appearance, such deposits can be perceived by the human eye as primarily a dark powder. However, because such dense, sponge-like deposits are non-adherent, for example, upon minor vibration or spontaneously, these layers can easily crumble or parts of the layer can easily peel off.

[0118] Figure 2 shows an image of the surface of a zinc deposit with dendritic micromorphology. The dendrites can be tree-like, leaf-like, or fern-like, and if deposition is slow, they can be hexagonal. The voids in such deposits are dispersed and exhibit isotropic crystallinity. Depending on their appearance, such deposits can be recognized by the human eye as metallic crystals. However, such deposits are non-adherent and, depending on their structure, can easily fracture. Another reason such deposits are unsuitable for certain applications is that the sharp edges of the dendrites can penetrate or damage the separator. Dendrites primarily form at very high current densities.

[0119] Figure 3 shows an image of the surface of a zinc deposit with a moss-like micromorphology. Fibrous moss deposits have a tangled, whisker-like appearance with typical diameters of 50–200 nm and lengths that can exceed 5 μm. Like dendrites and dense sponge deposits, moss deposits are non-adherent. However, they have extremely high porosity and isotropically oriented crystallinity. They primarily form at low current densities. Like dense sponge deposits, they primarily appear to the human eye as a dark, powdery layer. These moss deposits tend to peel or fracture, as can be expected from Figure 3. When such moss deposits peel off from the electrode or zinc deposit layer, these moss fibers appear as unattached cloud-like structures in the center of the electrochemical cell between the two electrodes.

[0120] Furthermore, Figure 4 shows an image of the surface of zinc deposits with a nodular micromorphology. The nodules are typically hexagonal in discrete clusters. Layer-by-layer growth of individual nodular deposits is evident in Figure 4. The nodular deposits have a granular nodular shape and exhibit predominantly anisotropically oriented crystallinity. Unlike the other deposits mentioned above, these deposits exhibit very dense porosity, meaning they are primarily non-porous. Furthermore, these deposits are adherent, meaning that flaking of portions of this layer is unusual and rare. To the human eye, such nodular deposits appear as gray metal. It is assumed that such deposits can occur at moderate or moderate current densities.

[0121] Figure 5 shows an image of the surface of a zinc deposit with a layered micromorphology. The layered deposit is a single-crystal growth and is typically found in the early stages of deposition. This type of Zn deposit is likely to be the densest and nearly nonporous. To the human eye, it appears as a shiny metallic layer, with a ridged or layered microstructure with epitaxially oriented crystallinity. Because this deposit is highly adherent, partial delamination is only possible with considerable force; therefore, spontaneous delamination of parts of the layer does not occur under normal circumstances. This layer is primarily observed at low current densities. Interestingly, however, despite this layer often appearing in the early stages of deposition, prior art techniques have not been able to achieve such layered deposits over long deposition times or for specific layer thicknesses. All of the processes and illustrated Zn electrodes described in the prior art have demonstrated thicker layered Zn deposits. The only methods or electrodes that demonstrate layered deposits with the characteristics described here use pure or treated zinc as the current collector material. However, if such an electrode were used in a battery, for example, it would be completely lost during discharge, making it completely useless for commercial applications.

[0122] A table of classifications of Zn deposits according to the prior art is shown in Figure 6. As can be seen from the table, various properties can be assigned to individual Zn deposits, such as macroscopic appearance, microstructure (under a microscope), adhesion, porosity, crystallinity, or growth current density.

[0123] In FIG. 7, a schematic diagram of a zinc electrode 100 with electrodeposited zinc that develops a dendritic morphology 310 is shown. As shown in this figure, Zn is deposited on an anode current collector material 200 during electrodeposition. Initially, the Zn layer 300 remains quite uniform, but as the layer thickness or duration of electrodeposition increases, the Zn layer begins to change shape. This results in the formation of dendrites that can fracture or damage other components of the electrical cell, such as the separator. Delamination of dendrite sections can also result in short circuits. The formation of such a dendrite layer can have several causes. One factor identified as having a significant impact on dendrite formation is the application of very high current carrying capacities during deposition.

[0124] Furthermore, FIG. 8 shows a schematic diagram of a zinc electrode 100 on which zinc has been electrodeposited, developing a mossy morphology 320. FIG. 8 illustrates that after the initial dense deposition of zinc (zinc layer 300) on the anode current collector material 200, a morphological change occurs. The subsequent deposit has a fibrous or mossy structure 320. This, like other non-dense structures such as dendritic zinc structures or dense sponge-like zinc, exhibits poor adhesion to the substrate. These mossy zinc deposits can easily peel off from the previously deposited zinc or current collector material. These peeled mossy Zn deposits are typically visible to the naked eye as cloud-like structures in the center of an electrochemical cell, i.e., between the electrodes. For example, flowing electrolyte can easily mechanically peel off these mossy zinc deposits, resulting in capacity loss or electrolyte clogging in fluid applications. The mossy zinc morphology can be caused by very low current carrying capacity during electrodeposition. Gassing, primarily due to hydrogen gas generated during electrodeposition, can also promote the formation of mossy zinc deposits.

[0125] FIG. 9 shows a schematic diagram of an anode electrode 100 with zinc electrodeposited thereon, developing a solid metallic (layered) morphology, according to an embodiment of the present invention. FIG. 9 shows a massive deposit of a solid metallic zinc layer 300 deposited directly onto the current collector material 200 of the anode electrode 100. This metallic zinc layer 300 has a layered and / or nodular morphology and exhibits a high density very close to that of pure metallic zinc. The layer 300 is dense throughout, adheres strongly to the substrate, and has a smooth surface 330. This dense layer 300 is substantially non-porous. To the eye, the layer surface 330 appears gray / shiny metal or metallic luster. The electrode 100 according to the present invention has a 200 mg / cm 2 The thickness of the layer may be well above 1000 nm.

[0126] FIG. 10 shows a flowchart of a method for fabricating the zinc electrode described herein in an electrochemical cell according to one embodiment of the present invention. 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 configurations used in electrochemistry or based on electrochemical processes. In this context, electrochemical cells include galvanic cells, electrolytic cells, and storage battery cells. An electrochemical cell includes at least two electrode or current collector materials, which always function as electronic conductors, and at least one electrolyte, i.e., an ionic conductor. The electrolyte may be a liquid or solid with a certain viscosity. Therefore, an electrochemical cell can be defined as a configuration of two electrodes conductively connected via a zinc-containing electrolyte.

[0127] In a first step S100, a cell is provided having a zinc-containing electrolyte, an anode current collector material, and a cathode current collector material. It is understood that the cell is designed so that two current collector materials (which may also be described as initial electrodes) are conductively connected via the zinc-containing electrolyte. This includes all components, such as the housing, current source, voltage source, and other measuring devices.

[0128] Furthermore, if deposition is performed for the first time and / or a fully discharged current collector material without a zinc layer is used, and in addition, the current collector has a low H overpotential, the optional step S200 can be performed. In that case, this step is essential to suppress H evolution at the current collector material in the further zinc deposition step (see S300), in other words, to prevent the catalytic activity of this current collector substrate. This step is also advantageous for increasing the nucleation surface on the substrate and improving layer formation. This step S200 can be performed, for example, at a current of 40 mA / cm 2 This is carried out by applying 5% to 80% duty cycle pulses at 0 to 30 Hz, preferably 5 to 20 Hz, and more preferably 10 Hz, at the above high current densities.

[0129] Another optional step S250 may be applied early in the zinc deposition process, involving a 5%-10% duty cycle pulse of 0.1 μs at 1-100 kHz for s seconds to m minutes (e.g., preferably 30 seconds or more). This step is advantageous for stripping any passivation that may have occurred during prior discharging of the cell or if the cell has been stored in a semi-discharged state for an extended period of time, and plating over the passivation would result in mossy zinc deposition.

[0130] However, actual zinc deposition then occurs in step S300. If a new cell with fresh electrolyte and a bare current collector with a high H2 overpotential is available, zinc deposition can begin immediately in step S300. Otherwise, steps S200 and / or S250 must precede step S300. In step S300, 1-30 Hz, preferably 5-20 Hz, and more preferably 10 Hz pulses with a 5%-80% duty cycle are applied for zinc deposition. This step continues until a predetermined mass of zinc deposit is reached or zinc deposition is stopped for other reasons, such as a predetermined charge stop or, in rare cases, the occurrence of a short circuit. The duty cycle depends on the amount of zinc source, which is often ZnO and / or zincate. As the zinc layer is depleted and the zincate level decreases, the duty cycle and current density are reduced (step S400).

[0131] Step S250 may be performed again if charging is interrupted at any step, as well as when storing a charged cell and initiating further charging. This step involves initialing a new zinc deposition process with a 5%-10% duty cycle pulse of 0.1 μs at 1-100 kHz for s seconds-m minutes (e.g., preferably 30 seconds or more). This step is advantageous for stripping any passivation that may have occurred during prior cell discharge or if the cell has been stored in a semi-discharged state for an extended period of time; plating over the passivation would result in mossy zinc deposition.

[0132] In optional steps S310 and / or S320, the cell may be monitored and inspected during zinc deposition. This may be done continuously or at intervals. If a voltage drop and / or current rise (short circuit) occurs during zinc electrodeposition, the deposition process is stopped (see step S500) because zinc moss deposits are highly likely to occur (S310). In such a case, the cell should be discharged, and after a passivation stripping step (S250), a new deposition may begin. However, if "no short circuit" means that moss deposits will not occur, monitoring may be stopped at a desired predetermined state of charge or state of charge (SOC) using current / voltage parameters (S320).

[0133] Then, in step S400, a duty cycle of 8% to 1% or less, preferably 5% to 2% or less, and / or 10 mA / cm 2 Preferably less than 8 mA / cm 2 or less, more preferably 5 mA / cm 2 Pulses of 0 to 30 Hz, preferably 5 to 20 Hz, more preferably 10 Hz, are applied until a predetermined minimum current density is reached:

[0134] After that step, or if a short circuit occurs, zinc deposition is terminated (S500), at which point the cell can be discharged again.

[0135] The zinc-loading electrode can also be removed from the cell for storage or transport purposes. In the event of a short circuit, the cell must be fully discharged and a new deposition process initiated to achieve zinc deposition according to the present invention.

[0136] It should be noted that the term "comprises" does not exclude other elements or steps, and "a" or "an" does not exclude a plurality. Furthermore, elements described in association with different embodiments may be combined.

[0137] It should also be noted that reference signs in the claims shall not be construed as limiting the scope of the claims. [Explanation of symbols]

[0138] 100 zinc electrodes 200 Current collector material 300 zinc layer 310 Dendritic zinc layer surface 311 Exfoliated dendrites 320 Mossy zinc layer surface 321 Exfoliated mossy zinc 330 Solid metal zinc layer surface (layered) S100~S500 Method steps S100~S500

Claims

1. A zinc electrode (100) comprising a current collector material (200) onto which a zinc layer (300) is electrodeposited, said zinc layer (300) appearing as a dense solid metal, having a nodular and / or layered microstructure, and being adherent with dense porosity.

2. 10. The zinc electrode (100) of claim 1, wherein the zinc layer (300) is partially or completely removed from the current collector material (200) during a discharge cycle, resulting in a bare current collector material (200) if completely removed.

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

4. The zinc layer (300) has a thickness of 3.50 to 7.14 g / cm ３ , preferably 4.50 to 7.14 g / cm ３ , more preferably 5.00 to 7.00 g / cm ３ The zinc electrode (100) of any one of claims 1 to 3, having a density of

5. 5. The zinc electrode (100) of any one of claims 1 to 4, wherein neither the current collector material (200) nor the zinc layer (300) includes a binder, grid, foam, woven structure, or additive to bond the zinc layer (300) to the current collector material (200).

6. The zinc electrode (100) of any one of claims 1 to 5, wherein the zinc layer (300) is formed from non-powdered zinc.

7. 7. The zinc electrode (100) of any one of claims 1 to 6, wherein the current collector material (200) is selected from the group comprising one or more of 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 claims 1 to 7, wherein the current collector material (200) is cold formed, preferably cold rolled.

9. 9. The zinc electrode (100) of any one of claims 1 to 8, wherein the zinc layer (300), the zinc-containing, zinc-containing electrolyte, the current collector material, and / or the cathode are free of copper, copper ions, and / or copper oxide.

10. The zinc layer (300) has a maximum of 10,000 mg / cm ２ , preferably 5000 mg / cm ２ , more preferably 2000 mg / cm ２ The zinc electrode (100) of any one of claims 1 to 9, having a mass of

11. The zinc layer (300) has a thickness of at least 25 mg / cm ２ The zinc electrode (100) of any one of claims 1 to 10, having a mass of

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

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

14. 14. The electrochemical cell of claim 13, wherein the zinc-containing electrolyte is alkaline.

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

16. The zinc-containing electrolyte is Zn ２＋ 16. The electrochemical cell of claims 13 to 15, comprising a zinc source selected from the group comprising one or more of ions, ZnO, zincates, or zinc complexes.

17. 17. The electrochemical cell of claim 16, wherein the zinc source or at least one component of the zinc source becomes supersaturated after discharging the cell.

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

19. 19. An electrochemical cell according to claims 13 to 18, wherein the zinc-containing electrolyte, when applied in a new electrochemical cell, has a minimum ZnO / KOH ratio of 190.00 g ZnO per litre of KOH, with a minimum ZnO / KOH ratio of 100.00 g ZnO per litre of KOH being preferred, with a minimum ZnO / KOH ratio of 8.00 g ZnO per litre of KOH being particularly preferred; and / or the zinc-containing electrolyte has a maximum ZnO / KOH ratio of 2380.00 g ZnO per litre of KOH, with a maximum ZnO / KOH ratio of 2670.00 g ZnO per litre of KOH being preferred, with a maximum ZnO / KOH ratio of 2980.00 g ZnO per litre of KOH being particularly preferred.

20. The zinc-containing electrolyte is H ２ 20. An electrochemical cell according to claims 13 to 19, having a minimum ZnO concentration of 0,01 M per litre of KOH in the electrolyte, with a range of 0,1 to 0,8 M per litre of KOH being preferred, and / or a maximum concentration of preferably 0,8 to 1,5 M per litre of KOH.

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

22. A method for zinc electrodeposition in an electrochemical cell according to any one of claims 13 to 21, comprising the steps of: S100, using the electrochemical cell; S300, applying 5-20 Hz 5%-80% duty cycle pulses for zinc deposition onto said current collector material (200) until a predetermined state of charge SOC and / or a predetermined mass of said zinc layer (300) is reached; S400, pulses having 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, with a duty cycle of 8% to 1% or less, preferably 5% to 2% or less, more preferably 5%, and / or 10 mA / cm ２ Preferably, 8 mA / cm or less ２ More preferably, 5 mA / cm or less ２ until a predetermined minimum current density is reached: S500, ending the method; A method comprising:

23. 1~300mA / cm ２ , preferably 3 to 170 mA / cm ２ , more preferably 5 to 125 mA / cm ２ 23. The method of claim 22 further comprising applying a pulse current density of

24. Before step S300, 40 mA / cm ２ 24. The method for producing a zinc electrode according to claim 22 or 23, further comprising the step S200 of applying 5% to 80% duty cycle pulses at 0 to 30 Hz, preferably 5 to 20 Hz, more preferably 10 Hz, at a current density of 0 to 30 Hz, more preferably 5 to 20 Hz, more preferably 10 Hz.

25. 25. The method for producing a zinc electrode according to any one of claims 22 to 24, further comprising a step S250 of applying 5% to 10% duty cycle pulses at 1 kHz to 100 kHz, preferably 30 to 70 kHz, more preferably 50 kHz for a duration of s seconds to m minutes if the electrochemical cell has previously been partially or fully discharged, prior to step S300.

26. 26. The method of producing a zinc electrode according to any of claims 22 to 25, further comprising S310 monitoring the zinc electrodeposition for a sudden rise in cell current and / or a drop in cell voltage, and if a sudden rise and / or drop is present, immediately stopping the zinc electrodeposition and terminating S500 the method.

27. 27. The method of producing a zinc electrode according to any of claims 22 to 26, further comprising S320 monitoring the zinc electrodeposition with respect to a predetermined cell current limit and / or a predetermined cell voltage limit indicative of said predetermined state of charge SOC, and applying steps S400 and S500 when said predetermined SOC is reached.

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