A metallic zinc negative electrode with an oriented protective layer, a preparation method thereof, and an application thereof

Abstract

The present invention discloses a metallic zinc anode with an oriented protective layer, its preparation method and application. The preparation method of the metallic zinc anode with an oriented protective layer comprises the following steps: 1) preparing oriented flaky oxides; 2) adding the oriented flaky oxides, an electronically conductive agent and a binder into an organic solvent to obtain an oriented protective layer slurry; 3) coating the oriented protective layer slurry on a metallic zinc substrate and drying it under vacuum to obtain the metallic zinc anode plate. In the present invention, a crystal plane with high zinc affinity and lattice matching with the Zn(002) crystal plane is modified on the surface of the metallic zinc sheet, which can adsorb Zn<supgt;2+< / supgt; and make it stably exist on the surface of the oriented protective layer, and can induce Zn<supgt;2+< / supgt; to deposit in the (002) crystal plane direction to achieve an epitaxial growth interface, so as to inhibit the generation of zinc dendrites and extend the service life of the zinc secondary battery.

Description

Technical Field

[0001] The present invention belongs to the technical field of electrochemical energy storage materials, and particularly relates to a metal zinc negative electrode with an oriented protective layer, a preparation method thereof, and an application thereof. Background Art

[0002] Zinc secondary batteries are regarded as the most powerful alternatives to lead-acid batteries due to their low cost and safety, and are expected to become the main force of the next generation of large-scale storage batteries. Among them, the development of high-capacity, high-energy density, and long-life electrode materials has become the key.

[0003] Zinc secondary batteries (such as alkaline zinc-nickel batteries, alkaline zinc-silver batteries, neutral zinc-manganese batteries, zinc-nickel flow batteries, zinc-bromine batteries) use metallic zinc as the negative electrode, and its capacity can reach 820 mA h g -1 −1, and the redox potential is relatively low (−0.76 V vs. SHE), and a reversible redox reaction can be carried out in an aqueous solution. During the charge / discharge process, Zn 2+ is reversibly deposited / dissolved on the negative electrode to convert electrical energy and chemical energy. However, during the long-term charge and discharge process, the irregular Zn 2+ dissolution / deposition on the surface of the metal zinc negative electrode leads to the formation of zinc dendrites, and the uneven negative electrode surface leads to a decrease in the Coulomb efficiency (CE). Or Zn 2+ discharges at the tip of the dendrite, causing a short circuit; even worse, the cumulative growth of zinc dendrites will pierce the separator, resulting in a battery short circuit. In addition, the "dead zinc" caused by zinc dendrites can cause the loss of active substances, thereby reducing the battery capacity.

[0004] Currently, researchers have used methods such as elastic protective layers (CN111600025A), deposited three-dimensional network layers (CN 110444730B), composite nanofiber protective layers (CN113097496B), and ion-conductive coating layers (CN 113488653 A) to inhibit the growth of zinc dendrites and improve the life of the metal zinc negative electrode. However, these methods have cumbersome preparation steps and high manufacturing costs. Summary of the Invention

[0005] To solve the problems of zinc dendrites and dead zinc in the charge and discharge cycle of the metal zinc negative electrode, the purpose of the present invention is to provide a metal zinc negative electrode with an oriented protective layer, a preparation method thereof, and an application thereof. The metal zinc negative electrode has a high zincophilicity on its oriented substrate, can adsorb Zn 2+ and make it stably exist on the surface of the oriented protective layer, and it has a crystal plane that is lattice-matched with the Zn(002) crystal plane, and can induce Zn 2+ to deposit in the (002) crystal plane direction to achieve an epitaxial growth interface, so as to inhibit the generation of zinc dendrites and extend the service life of the zinc secondary battery.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] The metal zinc negative electrode with an oriented protective layer provided by the present invention includes a metal zinc substrate and an oriented protective layer located on the metal zinc substrate. The oriented protective layer includes oriented flaky oxides, an electronic conductive agent, and a binder. The contents of each component in the metal zinc negative electrode are as follows: the metal zinc substrate is 90.0 - 95.0 wt.%, the oriented flaky oxides are 7.0 - 3.5 wt.%, the electronic conductive agent is 2.0 - 1.0 wt.%, and the binder is 1.0 - 0.5 wt.%. The sum of the percentage contents of each component is 100%.

[0008] As a preferred solution, the two-dimensional lattice of the oriented crystal plane of the oriented protective layer matches the two-dimensional lattice of the Zn(002) crystal plane. The parameters of the oriented crystal plane of the oriented protective layer are as follows: the two-dimensional lattice is a hexagonal lattice, and the lattice side length ranges from

[0009] As a preferred solution, the metal zinc substrate is selected from one of pure zinc foil or zinc alloy foil, and its thickness is 0.01 - 3.00 mm. The electronic conductive agent is at least one of conductive carbon black, acetylene black, graphene, carbon nanotubes, carbon spheres, carbon fibers, and SuperP. The binder is at least one of polyvinylidene fluoride, polyvinyl butyral, polyethylene oxide, epoxy resin, polyamide-imide, styrene-butadiene rubber, polyacrylic acid, and polyvinyl alcohol.

[0010] The preparation method of the metal zinc negative electrode with an oriented protective layer provided by the present invention includes the following steps:

[0011] 1) Pour the solution of metal salt A into the solution of precipitating agent salt B, where the molar ratio of metal salt A to precipitating agent salt B is 1:(1 - 10). Stir and react at room temperature. After the reaction ends, filter and collect the obtained product, wash the product with water and ethanol until the pH of the filtrate is 7, and vacuum dry the product to obtain hydroxide precipitate C.

[0012] 2) Calcinate the hydroxide precipitate C obtained in step 1) in an atmosphere of air or oxygen or a mixture of both to obtain granular oxide D.

[0013] 3) Hydrolyze the granular oxide D obtained in step 2) in deionized water, centrifuge to collect the precipitate, wash the precipitate with water and ethanol until the pH of the supernatant is 7, and then vacuum dry the product to obtain flaky hydroxide E.

[0014] 4) Calcinate the flaky hydroxide E obtained in step 3) in a vacuum to obtain oriented flaky oxide F.

[0015] 5) Mix the oriented flaky oxide F obtained in step 4, the electronic conductive agent, and the binder in a ratio and add them to an organic solvent, stir evenly at room temperature to obtain a protective layer slurry, and then coat the protective layer slurry on the metal zinc substrate and dry it in vacuum to obtain a metal zinc negative electrode with an oriented protective layer.

[0016] As a preferred embodiment, in step 1), the precipitating agent salt B is one of the sodium salts, potassium salts, and ammonium salts corresponding to carbonate or bicarbonate; the metal salt A is one of the nitrates, sulfates, acetates, chlorides, and citrates corresponding to the elements in magnesium, aluminum, iron, cerium, and manganese, or one of the nitrates, acetates, and chlorides corresponding to calcium.

[0017] More preferably, in step 1), the molar ratio of the metal salt A to the precipitating agent salt B is 1:1.

[0018] As a preferred embodiment, in step 1), the stirring time is 5 - 60 min, the temperature of vacuum drying is 40 - 120 °C, the vacuum degree is 10 -2 ~10 -6 mbar, and the drying time is 6 - 24 h.

[0019] As a preferred embodiment, in step 2), the oxygen content in the atmosphere is 21 - 100 vol.%, the calcination temperature is 400 - 600 °C, and the calcination time is 1 - 3 h.

[0020] As a preferred embodiment, in step 3), the solid-liquid ratio of the granular oxide D to deionized water is 0.1 - 10.0 mg mL -1 , and the hydrolysis time is 1 - 5 h.

[0021] In the present invention, during the hydrolysis process of step 3), the concentration of the granular oxide D is relatively small, which is beneficial to the rapid nucleation of the granular oxide and its transformation into flaky hydroxide. The hydrolysis concentration controls the size of the diameter and thickness of the flakes.

[0022] As a preferred embodiment, in step 3), the temperature of vacuum drying is 40 - 120 °C, the vacuum degree is 10 -2 ~10 - 6 mbar, and the drying time is 6 - 24 h.

[0023] As a preferred embodiment, in step 4), the vacuum degree of vacuum calcination is 10 -2 ~10 -8 mbar, the calcination temperature is 300 - 700 °C, and the calcination time is 10 - 14 h.

[0024] In the present invention, in step 4), the flaky hydroxide is transformed into an oriented flaky oxide through topological decomposition.

[0025] As a preferred embodiment, in the step 5), the mass ratio of the oriented flaky oxide F, the electronic conductive agent and the binder is (5-8):(4.5-1):(0.5-1).

[0026] As a preferred embodiment, in the step 5), the mass ratio of the binder to the organic solvent is 1:(10-50); the organic solvent is at least one of N,N-dimethylpyrrolidone, ethanol, propanol, ether, acetonitrile, isopropanol, methanol, toluene, acetone and ethylene glycol.

[0027] As a preferred embodiment, in the step 5), the room temperature during stirring is 20-30°C, and the stirring time is 4-24 h.

[0028] As a preferred embodiment, in the step 5), the coating method is any one of blade coating, spin coating, dip coating, casting coating, biaxial stretching and uniaxial stretching.

[0029] As a preferred embodiment, in the step 5), the temperature of vacuum drying is 40-80°C, the vacuum degree is 10 -2 ~10 - 6 mbar, and the drying time is 12-24 h.

[0030] As a preferred embodiment, in the step 5), the thickness of the oriented protective layer of the metallic zinc negative electrode is 50-300 μm.

[0031] Application of the metallic zinc negative electrode with an oriented protective layer prepared by the above preparation method in a zinc secondary battery.

[0032] Advantages of the present invention:

[0033] 1) The present invention adopts an oriented protective layer, enabling Zn 2+ to deposit on the Zn(002) crystal plane, and this crystal plane orientation can inhibit the formation of dendrites during the deposition / dissolution process of the zinc negative electrode.

[0034] 2) The binding energy of the Zn(002) crystal plane on the oriented protective layer is relatively high, so the overpotential of the deposition / dissolution process of the zinc negative electrode is reduced to 20 mV, effectively improving the energy density of the battery.

[0035] 3) The dendrite-free negative electrode avoids the possibility of short circuit, ensures the safe use of the battery, and extends the service life of the zinc secondary battery to 1250 hours / 625 cycles.

[0036] 4) Compared with the prior art, the present invention is convenient to operate, has a low manufacturing cost, but has remarkable effects, and has high practical value and commercial prospects. Description of the Drawings

[0037] Figure 1Scanning electron micrographs of the o-MgO@Zn electrode prepared in Example 1, the c-MgO@Zn electrode prepared in Comparative Example 1, and the zinc foil in Comparative Example 2: (a) o-MgO@Zn electrode; (b) c-MgO@Zn electrode; (c) zinc foil.

[0038] Figure 2 Are the impedance spectrograms and nucleation process overpotential diagrams of the o-MgO@Zn electrode prepared in Example 1, the c-MgO@Zn electrode prepared in Comparative Example 1, and the zinc foil in Comparative Example 2.

[0039] Figure 3 Are the deposition / dissolution cycle performance diagrams of the o-MgO@Zn electrode prepared in Example 1, the c-MgO@Zn electrode prepared in Comparative Example 1, and the zinc foil in Comparative Example 2 in a symmetric cell.

[0040] Figure 4 Are the SEM images of the surface morphologies of the o-MgO@Zn electrode prepared in Example 1, the c-MgO@Zn electrode prepared in Comparative Example 1, and the zinc foil in Comparative Example 2 in a symmetric cell after 1250 hours of deposition / dissolution cycling: (a) o-MgO@Zn electrode; (b) c-MgO@Zn electrode; (c) zinc foil. Detailed implementation mode

[0041] The present invention will be further described below in conjunction with the accompanying drawings and embodiments. The raw materials or chemical reagents used in the embodiments and comparative examples of the present invention are all obtained through conventional commercial channels unless otherwise specified; the preparation methods adopted in the present invention are all conventional experimental methods in the art unless otherwise specified. The following embodiments are intended to illustrate the present invention rather than further limit the present invention.

[0042] Example 1

[0043] The pure zinc foil used in this example has a thickness of 0.1 mm and a zinc content of more than 99.9%.

[0044] 100 mL of 0.5 M sodium carbonate (Na2CO3) solution was quickly poured into 400 mL of 0.125 M magnesium nitrate (Mg(NO3)2) solution, stirred at room temperature for 10 minutes, the resulting precipitate was filtered and collected, washed with water and ethanol until the pH of the filtrate was 7, and then vacuum dried at 60 °C for 12 hours to obtain magnesium hydroxide (Mg(OH)2) precipitate. The magnesium hydroxide (Mg(OH)2) precipitate was calcined at 500 °C for 2 hours in an atmosphere with an oxygen content of 21 vol.%, to obtain magnesium oxide (MgO) particles. The magnesium oxide (MgO) particles were hydrolyzed in deionized water for 1 hour (the solid-liquid ratio of magnesium oxide particles to deionized water is 1 mg mL -1 ) and then the precipitate was collected by centrifugation, washed with water and ethanol until the pH of the filtrate was 7, vacuum dried at 60 °C for 12 hours, and the vacuum degree was 10-5 mbar to obtain flaky magnesium hydroxide (Mg(OH)₂). The flaky magnesium hydroxide (Mg(OH)₂) is vacuum calcined at 600 °C for 12 hours with a vacuum degree of 10 - 5 mbar to obtain oriented flaky magnesium oxide (o-MgO). The oriented exposed crystal plane is (111), the two-dimensional lattice is a hexagonal lattice, and the side length of the crystal plane is

[0045] Weigh oriented flaky magnesium oxide (o-MgO), acetylene black, polyvinylidene fluoride, and N,N-dimethylpyrrolidone at a mass ratio of 7:2:1:24, and stir at 25 °C for 12 hours to form a homogeneous slurry. The slurry is coated on pure zinc foil by doctor blading with a thickness of 100 μm, and dried in vacuum at 60 °C for 12 hours with a vacuum degree of 10 -5 mbar to fabricate the o-MgO@Zn electrode.

[0046] The obtained o-MgO@Zn electrode is cut into electrodes with a diameter of 16 mm. Take two electrodes as the positive and negative electrodes, and assemble a symmetric battery with a glass fiber membrane with a diameter of 18 mm as the separator and 3M zinc sulfate solution as the electrolyte.

[0047] Figure 1 (a) is the scanning electron micrograph of the electrode fabricated in this example, and its surface particles are uniform.

[0048] Figure 2 It includes the impedance spectrum diagram and the nucleation process overpotential diagram of this example. It can be seen from the figure that the battery composed of this electrode has the smallest impedance; the nucleation overpotential is the smallest, which is 43.4 mV.

[0049] Figure 3 It includes the electrochemical cycling performance curve of the battery in this example. The cycling current density is 1 mA cm -2 and the capacity is 1 mA h cm -2 The cycling life reaches 1250 hours, and the polarization voltage remains within 20 mV during the whole cycling process.

[0050] Figure 4 (a) is the scanning electron micrograph of the electrode after the Figure 3 electrochemical process shown in this example. It can be seen from the figure that the surface of the electrode is flat and no dendrites are formed.

[0051] Comparative Example 1

[0052] Comparative Example 1 is basically the same as Example 1, except that the oxide in the protective layer is commercially purchased magnesium oxide (c-MgO) with a purity of more than 98%.

[0053] The pure zinc foil used in Comparative Example 1 has a thickness of 0.1 mm and a zinc content of more than 99.9%.

[0054] Weigh commercial magnesium oxide (c-MgO), acetylene black, polyvinylidene fluoride, and N,N-dimethylpyrrolidone in a mass ratio of 7:2:1:24, and stir at 25 °C for 12 hours to form a homogeneous slurry. Coat the slurry on the pure zinc foil using a doctor blade coating method, with a thickness of 100 μm, and dry it in a vacuum at 60 °C for 12 hours, with a vacuum degree of 10 -5 mbar, to prepare the c-MgO@Zn electrode sheet.

[0055] Cut the obtained c-MgO@Zn electrode sheet into electrode sheets with a diameter of 16 mm. Take two electrode sheets as the positive and negative electrodes, use a glass fiber membrane with a diameter of 18 mm as the separator, and a 3M zinc sulfate solution as the electrolyte to assemble a symmetrical battery.

[0056] Figure 1 (b) is the scanning electron microscope image of the electrode sheet prepared in this comparative example, with uneven particle sizes and distributions on its surface.

[0057] Figure 2 It includes the impedance spectrum diagram and the nucleation process overpotential diagram of this comparative example. It can be seen from the figure that the battery composed of this electrode sheet has the largest impedance and the largest nucleation overpotential, which is 63.6 mV.

[0058] Figure 3 It includes the electrochemical cycling performance curve of the battery in this comparative example. The cycling current density is 1 mA cm -2 , and the capacity is 1 mA h cm -2 , and the polarization voltage is as high as 75 mV.

[0059] Figure 4 (b) is the scanning electron microscope image of the electrode after the Figure 3 electrochemical process shown. It can be seen from the figure that the deposition products on the electrode surface have a chaotic orientation and the electrode surface is uneven.

[0060] Comparative Example 2

[0061] Comparative Example 2 is quite different from Example 1 in that the zinc foil is not coated with a protective layer.

[0062] The pure zinc foil used in Comparative Example 2 has a thickness of 0.1 mm and a zinc content of more than 99.9%.

[0063] Cut the zinc foil into circular pieces with a diameter of 16 mm. Take two electrode sheets as the positive and negative electrodes, use a glass fiber membrane with a diameter of 18 mm as the separator, and a 3M zinc sulfate solution as the electrolyte to assemble a symmetrical battery.

[0064] Figure 1(c) is the scanning electron microscopy image of the electrode of this comparative example, with uneven particle sizes and distributions on its surface.

[0065] Figure 2 Including the impedance spectrogram and the nucleation process overpotential diagram of this comparative example. It can be seen from the figure that the battery composed of this electrode has a large impedance and a large nucleation overpotential, which is 61.7 mV.

[0066] Figure 3 Including the electrochemical cycling performance curve of the battery of this comparative example, with a cycling current density of 1 mA cm -2 , and a capacity of 1 mA h cm -2 . After cycling for 220 hours, the battery short-circuited.

[0067] Figure 4 (c) is the scanning electron microscopy image of the electrode after the Figure 3 shown electrochemical process. It can be seen from the figure that the deposition products on the electrode surface exist in the form of dendrites, perpendicular to the electrode surface.

[0068] Example 2

[0069] The pure zinc foil used in this example has a thickness of 0.15 mm and a zinc content of over 99.9%.

[0070] 200 mL of 0.5 M sodium carbonate (Na2CO3) solution was quickly poured into 400 mL of 0.125 M calcium chloride (CaCl2) solution, stirred at room temperature for 5 minutes, and the resulting precipitate was collected by filtration. The precipitate was washed with water and ethanol until the filtrate pH = 7, and then vacuum dried at 80 °C for 10 hours with a vacuum degree of 10 -2 mbar to obtain calcium hydroxide (Ca(OH)2) precipitate. The calcium hydroxide (Ca(OH)2) precipitate was calcined at 500 °C for 1 hour in an atmosphere with an oxygen content of 40 vol.%, to obtain calcium oxide (CaO) particles. The calcium oxide (CaO) particles were hydrolyzed in deionized water for 5 hours (the solid-liquid ratio of calcium oxide particles to deionized water is 10 mg mL -1 ), and then the precipitate was collected by centrifugation. The precipitate was washed with water and ethanol until the filtrate pH = 7, and vacuum dried at 80 °C for 10 hours with a vacuum degree of 10 - 2 mbar to obtain flaky calcium hydroxide (Ca(OH)2). The flaky calcium hydroxide (Ca(OH)2) was vacuum calcined at 500 °C for 13 hours with a vacuum degree of 10 -2 mbar to obtain oriented flaky calcium oxide (o-CaO), with the oriented exposed crystal plane being (111), the two-dimensional lattice being a hexagonal lattice, and the crystal plane side length being

[0071] Weigh oriented flaky calcium oxide (o-CaO), conductive carbon black, polyvinyl butyral, and ethanol at a mass ratio of 8:1:1:24, and stir them at 25 °C for 24 hours to form a homogeneous slurry. Coating the slurry on pure zinc foil by spin coating with a thickness of 150 μm, and drying it in vacuum at 80 °C for 12 hours with a vacuum degree of 10 -2 mbar to prepare the o-CaO@Zn electrode sheet.

[0072] Cut the obtained o-CaO@Zn electrode sheet into electrode sheets with a diameter of 16 mm. Take two electrode sheets as the positive and negative electrodes, and assemble a symmetrical battery with a glass fiber membrane with a diameter of 18 mm as the separator and a 3M zinc sulfate solution as the electrolyte.

[0073] The electrochemical cycling performance of this example is as follows: under a cycling current density of 1 mA cm -2 and a capacity of 1 mA h cm -2 conditions, perform charge-discharge cycling, and the cycling life reaches 1010 hours, and the polarization voltage remains within 35 mV during the whole cycle.

[0074] Example 3

[0075] The pure zinc foil used in this example has a thickness of 3 mm and a zinc content of more than 99.9%.

[0076] Quickly pour 500 mL of 0.5 M sodium carbonate (Na2CO3) solution into 400 mL of 0.125 M cerium chloride (CeCl3) solution, stir at room temperature for 60 minutes, filter and collect the obtained precipitate, wash the precipitate with water and ethanol until the pH of the filtrate is 7, and then dry it in vacuum at 120 °C for 6 hours with a vacuum degree of 10 -5 mbar to obtain cerium hydroxide (Ce(OH)4) precipitate. Calcinate the cerium hydroxide (Ce(OH)4) precipitate in an atmosphere with an oxygen content of 100 vol.% at 400 °C for 2 hours to obtain cerium oxide (CeO2) particles. Hydrolyze the cerium oxide (CeO2) particles in deionized water for 1 hour (the solid-liquid ratio of cerium oxide particles to deionized water is 0.1 mg mL -1 ), then centrifuge to collect the precipitate, wash the precipitate with water and ethanol until the pH of the filtrate is 7, and dry it in vacuum at 120 °C for 6 hours with a vacuum degree of 10 -5 mbar to obtain flaky cerium hydroxide (Ce(OH)4). Vacuum calcine the flaky cerium hydroxide (Ce(OH)4) at 300 °C for 14 hours with a vacuum degree of 10 -5 mbar to obtain oriented flaky cerium oxide (o-CeO2), the oriented exposed crystal plane is (111), the two-dimensional lattice is a hexagonal lattice, and the side length of the crystal plane is

[0077] Weigh oriented flaky cerium oxide (o-CeO2), graphene, polyethylene oxide, and isopropanol at a mass ratio of 7:2:1:50, and stir them at 30 °C for 4 hours to form a homogeneous slurry. Coating the slurry on pure zinc foil by dip coating with a thickness of 300 μm, and drying it in vacuum at 70 °C for 12 hours with a vacuum degree of 10 -5 mbar to prepare the o-CeO2@Zn electrode sheet.

[0078] Cut the obtained o-CeO2@Zn electrode sheet into electrode sheets with a diameter of 16 mm. Take two electrode sheets as the positive and negative electrodes, use a glass fiber membrane with a diameter of 18 mm as the separator, and 3M zinc sulfate solution as the electrolyte to assemble a symmetrical battery.

[0079] The electrochemical cycling performance of this example is as follows: at a cycling current density of 1 mA cm -2 , and a capacity of 1 mA h cm -2 under the condition of charge-discharge cycling, the cycling life reaches 1110 hours, and the polarization voltage remains within 29 mV throughout the cycling process.

[0080] Example 4

[0081] The pure zinc foil used in this example has a thickness of 0.2 mm and a zinc content of more than 99.9%.

[0082] Quickly pour 100 mL of 0.5 M sodium carbonate (Na2CO3) solution into 400 mL of 0.125 M manganese acetate (Mn(CH3COO)2) solution, stir at room temperature for 20 minutes, filter to collect the obtained precipitate, wash the precipitate with water and ethanol until the pH of the filtrate is 7, and then dry it in vacuum at 100 °C for 10 hours with a vacuum degree of 10 -3 mbar to obtain manganese hydroxide (Mn(OH)2) precipitate. Calcinate the manganese hydroxide (Mn(OH)2) precipitate at 500 °C for 2 hours in an atmosphere with an oxygen content of 40 vol.%, to obtain manganese dioxide (MnO2) particles. Hydrolyze the manganese dioxide (MnO2) particles in deionized water for 2 hours (the solid-liquid ratio of manganese dioxide particles to deionized water is 2 mg mL -1 ), then centrifuge to collect the precipitate, wash the precipitate with water and ethanol until the pH of the filtrate is 7, and dry it in vacuum at 100 °C for 10 hours with a vacuum degree of 10 -3 mbar to obtain flaky manganese hydroxide (Mn(OH)4). Calcinate the flaky manganese hydroxide (Mn(OH)4) in vacuum at 500 °C for 12 hours with a vacuum degree of 10 -3 mbar to obtain oriented flaky manganese dioxide (o-MnO2), the oriented exposed crystal plane is (111), the two-dimensional lattice is a hexagonal lattice, and the side length of the crystal plane is

[0083] Weigh oriented flaky manganese dioxide (o-MnO2), carbon nanotubes, epoxy resin, and acetone at a mass ratio of 7.5:1.5:1:40, and stir them at 30 °C for 8 hours to form a homogeneous slurry. Coating the slurry on pure zinc foil by casting, with a thickness of 200 μm, and drying it in vacuum at 60 °C for 20 hours, with a vacuum degree of 10 -3 mbar, to prepare the o-MnO2@Zn electrode sheet.

[0084] Cut the obtained o-MnO2@Zn electrode sheet into electrode sheets with a diameter of 16 mm. Take two electrode sheets as the positive electrode and the negative electrode, and assemble a symmetric battery with a glass fiber membrane with a diameter of 18 mm as the separator and 3M zinc sulfate solution as the electrolyte.

[0085] The electrochemical cycling performance of this example is as follows: under the conditions of a cycling current density of 1 mA cm -2 , and a capacity of 1 mA h cm -2 , perform charge-discharge cycling. The cycling life reaches 1110 hours, and the polarization voltage remains within 29 mV throughout the cycling process.

[0086] Example 5

[0087] The pure zinc foil used in this example has a thickness of 0.1 mm and a zinc content of more than 99.9%.

[0088] Quickly pour 1000 mL of 0.5 M sodium carbonate (Na2CO3) solution into 400 mL of 0.125 M aluminum sulfate (Al2(SO4)3) solution, stir at room temperature for 30 minutes, filter to collect the obtained precipitate, wash the precipitate with water and ethanol until the pH of the filtrate is 7, and then dry it in vacuum at 60 °C for 8 hours, with a vacuum degree of 10 -4 mbar, to obtain aluminum hydroxide (Al(OH)3) precipitate. Calcinate the aluminum hydroxide (Al(OH)3) precipitate at 600 °C for 1 hour in an atmosphere with an oxygen content of 21 vol.%, to obtain aluminum oxide (Al2O3) particles. Hydrolyze the aluminum oxide (Al2O3) particles in deionized water for 3 hours (the solid-liquid ratio of the aluminum oxide particles to deionized water is 5 mg mL -1 ), then centrifuge to collect the precipitate, wash the precipitate with water and ethanol until the pH of the filtrate is 7, and dry it in vacuum at 60 °C for 8 hours, with a vacuum degree of 10 -4 mbar, to obtain flaky aluminum hydroxide (Al(OH)3). Calcinate the flaky aluminum hydroxide (Al(OH)3) in vacuum at 700 °C for 10 hours, with a vacuum degree of 10 -4 mbar, to obtain oriented flaky aluminum oxide (o-Al2O3), the oriented exposed crystal plane is (001), the two-dimensional lattice is a hexagonal lattice, and the side length of the crystal plane is

[0089] Weigh oriented flaky alumina (o-Al2O3), carbon fiber, polyamide-imide, and ethylene glycol in a mass ratio of 5:4.5:0.5:24, and stir at 28 °C for 15 hours to form a homogeneous slurry. Coating the slurry on pure zinc foil by biaxial stretching with a thickness of 100 μm, and drying in vacuum at 60 °C for 18 hours with a vacuum degree of 10 -4 mbar to make the o-Al2O3@Zn electrode sheet.

[0090] Cut the obtained o-Al2O3@Zn electrode sheet into electrode sheets with a diameter of 16 mm. Take two electrode sheets as the positive and negative electrodes, use a glass fiber membrane with a diameter of 18 mm as the separator, and 3M zinc sulfate solution as the electrolyte to assemble a symmetric battery.

[0091] The electrochemical cycling performance of this example is as follows: at a cycling current density of 1 mA cm -2 , and a capacity of 1 mA h cm -2 Under the conditions, charge-discharge cycling is carried out, and the cycling life reaches 995 hours, and the polarization voltage remains within 48 mV during the whole cycle.

[0092] Example 6

[0093] The pure zinc foil used in this example has a thickness of 0.01 mm and a zinc content of more than 99.9%.

[0094] Quickly pour 600 mL of 0.5 M sodium carbonate (Na2CO3) solution into 400 mL of 0.125 M iron citrate (FeC6H5O7) solution, stir at room temperature for 45 minutes, filter to collect the obtained precipitate, wash the precipitate with water and ethanol until the pH of the filtrate is 7, and then dry in vacuum at 40 °C for 24 hours with a vacuum degree of 10 -6 mbar to obtain iron hydroxide (Fe(OH)3) precipitate. Calcinate the iron hydroxide (Fe(OH)3) precipitate at 400 °C for 3 hours in an atmosphere with an oxygen content of 100 vol.%, to obtain iron oxide (Fe2O3) particles. Hydrolyze the iron oxide (Fe2O3) particles in deionized water for 4 hours (the solid-liquid ratio of iron oxide particles to deionized water is 8 mg mL -1 ), then centrifuge to collect the precipitate, wash the precipitate with water and ethanol until the pH of the filtrate is 7, and dry in vacuum at 40 °C for 24 hours with a vacuum degree of 10 -6 mbar to obtain flaky iron hydroxide (Fe(OH)3). Calcinate the flaky iron hydroxide (Fe(OH)3) in vacuum at 400 °C for 14 hours with a vacuum degree of 10 -6 mbar to obtain oriented flaky iron oxide (o-Fe2O3), the oriented exposed crystal plane is (001), the two-dimensional lattice is a hexagonal lattice, and the side length of the crystal plane is

[0095] Weigh oriented flaky iron oxide (o-Fe2O3), SuperP, polyacrylic acid, and acetonitrile in a mass ratio of 6:3.5:0.5:10, and stir at 20 °C for 20 hours to form a homogeneous slurry. The slurry is coated on pure zinc foil by unidirectional stretching to a thickness of 50 μm, and dried in vacuum at 40 °C for 24 hours with a vacuum degree of 10 -6 mbar to prepare the o-Fe2O3@Zn electrode sheet.

[0096] The obtained o-Fe2O3@Zn electrode sheet is cut into electrode sheets with a diameter of 16 mm. Two electrode sheets are taken as the positive and negative electrodes, and a symmetric battery is assembled with a glass fiber membrane with a diameter of 18 mm as the separator and 3M zinc sulfate solution as the electrolyte.

[0097] The electrochemical cycling performance of this example is as follows: at a cycling current density of 1 mA cm -2 and a capacity of 1 mA h cm -2 under the condition of charge-discharge cycling, the cycling life reaches 982 hours, and the polarization voltage remains within 53 mV during the whole cycling process.

Claims

1. A metallic zinc negative electrode with an oriented protective layer, comprising a metallic zinc substrate and an oriented protective layer located on the metallic zinc substrate, wherein the oriented protective layer comprises oriented flaky oxides, an electronic conductive agent, and a binder; the contents of each component in the metallic zinc negative electrode are as follows: the metallic zinc substrate is 90.0 - 95.0 wt.%, the oriented flaky oxides are 7.0 - 3.5 wt.%, the electronic conductive agent is 2.0 - 1.0 wt.%, and the binder is 1.0 - 0.5 wt.%, and the sum of the percentage contents of each component is 100%; The flaky oxide is one of flaky magnesium oxide, flaky aluminum oxide, flaky iron oxide, flaky cerium oxide, flaky manganese oxide, and flaky calcium oxide; The two-dimensional lattice of the oriented crystal plane of the oriented protective layer matches the two-dimensional lattice of the Zn (002) crystal plane; the parameters of the oriented crystal plane of the oriented protective layer are: the two-dimensional lattice is a hexagonal lattice, and the lattice side length ranges from 0.01 to 10.00 Å.

2. The zinc metal negative electrode with an oriented protective layer according to claim 1, wherein, The metallic zinc substrate is selected from one of pure zinc foil or zinc alloy foil, and its thickness is 0.01 - 3.00 mm; the electronic conductive agent is at least one of conductive carbon black, acetylene black, graphene, carbon nanotubes, carbon spheres, and carbon fibers; the binder is at least one of polyvinylidene fluoride, polyvinyl butyral, polyethylene oxide, epoxy resin, polyamide-imide, styrene-butadiene rubber, polyacrylic acid, and polyvinyl alcohol.

3. A preparation method of the metallic zinc negative electrode with an oriented protective layer according to any one of claims 1 or 2, comprising the following steps: 1) Pour the solution of metal salt A into the solution of precipitating agent salt B, where, The molar ratio of metal salt A to precipitating agent salt B is 1:(1 - 10), and the reaction is stirred at room temperature. After the reaction ends, the obtained product is filtered and collected, washed with water and ethanol until the pH of the filtrate is 7, and the product is dried in vacuum to obtain hydroxide precipitate C; 2) The hydroxide precipitate C obtained in step 1) is calcined in an atmosphere of air or oxygen or a mixture of both to obtain granular oxide D; 3) After the granular oxide D obtained in step 2) is hydrolyzed in deionized water, the precipitate is collected by centrifugation, washed with water and ethanol until the pH of the supernatant is 7, and then the product is dried in vacuum to obtain flaky hydroxide E; 4) The flaky hydroxide E obtained in step 3) is calcined in vacuum to obtain oriented flaky oxide F; 5) The oriented flaky oxide F obtained in step 4), the electronic conductive agent, and the binder are mixed according to the ratio, added to an organic solvent, and stirred evenly at room temperature to obtain a protective layer slurry. The protective layer slurry is coated on the metallic zinc substrate and dried in vacuum to obtain a metallic zinc negative electrode with an oriented protective layer.

4. The preparation method of the metallic zinc negative electrode with an oriented protective layer according to claim 3, characterized in that, In step 1), the precipitating agent salt B is one of the sodium salts, potassium salts, and ammonium salts corresponding to carbonate or bicarbonate; the metal salt A is one of the nitrates, sulfates, acetates, chlorides, and citrates corresponding to the elements in magnesium, aluminum, iron, cerium, and manganese, or one of the nitrates, acetates, and chlorides corresponding to calcium.

5. The preparation method of the metallic zinc negative electrode with an oriented protective layer according to claim 3, wherein In the said step 1), the stirring time is 5 to 60 min, the temperature of vacuum drying is 40 to 120 °C, the vacuum degree is 10 -2 ~10 -6 mbar, and the drying time is 6 to 24 h.

6. The preparation method of the metallic zinc negative electrode with an oriented protective layer according to claim 3, characterized in that, In step 2), the oxygen content in the atmosphere is 21 - 100 vol.%, the calcination temperature is 400 - 600 °C, and the calcination time is 1 - 3 h.

7. The preparation method of the metallic zinc negative electrode with an oriented protective layer according to claim 3, characterized in that, In step 3), the solid-liquid ratio of granular oxide D to deionized water is 0.1~10.0 mg mL -1 , the hydrolysis time is 1~5 h; the temperature of vacuum drying is 40~120 °C, and the vacuum degree is 10 -2 ~10 -6 mbar, and the drying time is 6~24 h; in step 4), the vacuum degree of vacuum calcination is 10 -2 ~10 -8 mbar, the calcination temperature is 300~700 °C, and the calcination time is 10~14 h.

8. The preparation method of the metallic zinc negative electrode with an oriented protective layer according to claim 3, characterized in that, In the step 5), the mass ratio of the oriented flaky oxide F, the electronic conductive agent and the binder is (5-8):(4.5-1):(0.5-1); the mass ratio of the binder to the organic solvent is 1:10-1:50; the organic solvent is at least one of N, N-dimethylpyrrolidone, ethanol, propanol, ether, acetonitrile, isopropanol, methanol, toluene, acetone and ethylene glycol; when stirring, the room temperature is 20-30 °C and the stirring time is 4-24 h; the coating method is any one of blade coating, spin coating, dip coating, casting coating, biaxial stretching and uniaxial stretching; the temperature of vacuum drying is 40-80 °C, the vacuum degree is 10 -2 ~10 -6 mbar, the drying time is 12-24 h; the thickness of the oriented protective layer of the metallic zinc negative electrode is 50-300 μm.

9. Use of a metallic zinc negative electrode with an oriented protective layer prepared by the preparation method according to any one of claims 3 to 8 in a zinc secondary battery.

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