Zinc negative electrode coating and preparation method and application thereof

Abstract

The invention relates to a zinc negative electrode coating and a preparation method and application thereof, and belongs to the technical field of zinc metal batteries. The zinc negative electrode coating provided by the invention comprises the following components in percentage by mass: 85%-90% of an active material and 10%-15% of a binder, and the active material comprises at least one of sodium hexafluoroaluminate and potassium hexafluoroaluminate. Researches find that at least one of sodium hexafluoroaluminate or potassium hexafluoroaluminate is used as an active material of the zinc negative electrode coating; the zinc cathode has the effects of remarkably improving contact at a zinc cathode-electrolyte interface, promoting desolvation of zinc ions on the surface of the zinc cathode, reducing zinc nucleation overpotential, promoting zinc nucleation on the surface of the zinc cathode, promoting uniform deposition of zinc on the surface of the zinc cathode, inhibiting growth of zinc dendrites and the like; and the cycle performance of the battery can be remarkably improved.

Description

Technical Field

[0001] This invention belongs to the field of zinc metal battery technology, specifically relating to a zinc negative electrode coating, its preparation method, and its application. Background Technology

[0002] Against the backdrop of the current global green energy transition, developing renewable energy power generation is an inevitable path. Developing low-cost, environmentally friendly distributed electrochemical energy storage technologies that match renewable energy power generation has become a hot topic. Among electrochemical energy storage technologies, lithium-ion batteries (LIBs) currently hold an absolute dominant position, but their high cost, high pollution, and susceptibility to spontaneous combustion limit their application in future distributed energy storage technologies. Aqueous zinc metal batteries (ZMBs) possess high specific capacity (820 mAh·g). -1 With its advantages such as suitable redox potential (-0.76 V vs. SHE.), environmentally friendly electrolyte with no risk of spontaneous combustion, and low manufacturing cost, it is considered to have great potential in future distributed energy storage technologies.

[0003] However, three major problems still seriously hinder the application of aqueous zinc metal batteries: zinc dendrite growth, hydrogen evolution reaction, and corrosion reaction; among them, zinc dendrite growth is the main problem. The essence of zinc dendrite growth is the uneven zinc deposition on the surface of the zinc anode. According to the order of occurrence, the entire zinc deposition process can be divided into four steps: (1) mass transfer, (2) desolvation, (3) charge transfer, and (4) electrocrystallization (nucleation and growth). Promoting one or more of these processes can often achieve the effect of suppressing zinc dendrite growth. However, the current zinc anode has problems such as high activation energy of zinc ion desolvation and high overpotential of zinc nucleation. Therefore, it is of great significance to develop a zinc anode coating that can effectively suppress zinc dendrite growth and improve the cycle performance of the battery. Summary of the Invention

[0004] The purpose of this invention is to overcome the problems existing in the prior art and provide a zinc anode coating that promotes zinc ion desolvation and zinc nucleation, as well as its preparation method and application.

[0005] This invention is achieved through the following technical solution: In a first aspect, the present invention provides a zinc anode coating comprising, by weight percentage, 85%-90% of active material and 10%-15% of binder, wherein the active material comprises at least one of sodium hexafluoroaluminate and potassium hexafluoroaluminate.

[0006] Sodium hexafluoroaluminate, also known as cryolite, has the chemical formula Na3AlF6, and potassium hexafluoroaluminate, also known as potassium cryolite. This invention, through research, has found that using at least one of sodium hexafluoroaluminate and potassium hexafluoroaluminate as a zinc anode coating can significantly improve the contact at the zinc anode-electrolyte interface, promote the desolvation of zinc ions on the zinc anode surface, reduce the zinc nucleation overpotential and promote zinc nucleation on the zinc anode surface, promote uniform zinc deposition on the zinc anode surface and inhibit zinc dendrite growth, thereby significantly improving the battery cycle performance.

[0007] Furthermore, the zinc anode coating comprises, by weight percentage, 88% active material and 12% binder.

[0008] Further, the active material is sodium hexafluoroaluminate. Further, the binder includes at least one of polyvinylidene fluoride and carboxymethyl cellulose.

[0009] Furthermore, the thickness of the zinc negative electrode coating is 10 μm to 50 μm.

[0010] In a second aspect, the present invention provides a zinc negative electrode, comprising a zinc substrate layer and a zinc negative electrode coating disposed on at least one side surface of the zinc substrate layer.

[0011] Furthermore, the zinc substrate layer comprises zinc foil with a thickness of 80 μm to 150 μm.

[0012] The zinc negative electrode coating of the present invention has a good improvement effect on zinc foil of different thicknesses.

[0013] Thirdly, the present invention provides a method for preparing the zinc negative electrode, comprising the following steps: S1. Mix the active material and binder evenly in a solvent to obtain a coating slurry; S2. The coating slurry obtained in step S1 is coated onto the surface of the zinc substrate and dried to obtain the zinc negative electrode.

[0014] Furthermore, in step S1, the solvent includes N-methylpyrrolidone.

[0015] Further, in step S1, the concentration of the coating slurry is 0.3 g / mL - 0.5 g / mL.

[0016] Furthermore, in step S2, the drying temperature is 40℃-80℃, and the drying time is 1h-3h.

[0017] Furthermore, in step S2, the coating includes one or more of the following: scraping, spin coating, and spray coating.

[0018] Fourthly, the present invention provides a zinc metal battery, including the zinc negative electrode.

[0019] The present invention has the following beneficial effects: (1) The zinc anode coating of the present invention contains at least one of cryolite and potassium cryolite. It is a zinc anode protective coating with excellent hydrophilicity, high fluorine content and good electronic insulation. At the same time, it can reduce the transmission resistance at the interface between the zinc anode and the electrolyte, the difficulty of zinc ion desolvation on the surface of the zinc anode and the zinc nucleation overpotential on the surface of the zinc anode. It can promote the uniform deposition of zinc on the surface of the zinc anode, inhibit the growth of zinc dendrites and improve the cycle performance of the battery.

[0020] (2) The present invention uses a simple coating method to cover the surface of the zinc substrate with a zinc anode coating containing cryolite and potassium cryolite, which has excellent hydrophilicity, high fluorine content and good electronic insulation. This physically blocks the direct contact between the zinc anode and the electrolyte, inhibits the hydrogen evolution reaction and corrosion reaction on the surface of the zinc anode, and thus improves the cycle performance of the battery.

[0021] (3) The zinc metal battery assembled using the zinc negative electrode of the present invention has excellent cycle stability. For example, the assembled Zn||Zn symmetric battery has excellent cycle stability at a current density of 0.5 mA·cm⁻¹. -2 The surface capacity is 0.5 mAh·cm³. -2 Under certain conditions, it can stably undergo stripping / deposition cycles for over 600 h; assembled into a Zn||MnO2 full cell, it can achieve a current density of 2 A·g -1 Under conditions of charging cutoff voltage of 1.8 V and discharging cutoff voltage of 0.8 V, the capacity retention rate is as high as 77.6% after 1000 stable cycles. Attached Figure Description

[0022] Figure 1 The voltage-time diagrams are for the symmetrical cell obtained from the zinc anode and zinc foil in Example 1; (a) is Example 1, and (b) is the zinc foil. Figure 2 The graphs show the charge-discharge cycle performance of the full cell obtained from the zinc anode and zinc foil in Example 2; (a) is Example 2, and (b) is the zinc foil. Figure 3 The charge-discharge cycle performance of the full cells obtained with zinc anodes in Comparative Examples 1-3 is shown in the diagrams; (a) is Comparative Example 1, (b) is Comparative Example 2, and (c) is Comparative Example 3. Figure 4 The contact angles of the zinc negative electrode and zinc foil in Example 2 are shown in (a) and (b) are the zinc foil in Example 2. Figure 5The following are electrochemical impedance diagrams and desolvation activation energy fitting diagrams of the symmetrical battery obtained with zinc anode and zinc foil in Example 2: (a) Electrochemical impedance diagram of the symmetrical battery obtained in Example 2; (b) Electrochemical impedance diagram of the symmetrical battery obtained with zinc foil; (c) Desolvation activation energy fitting diagram. Figure 6 The graphs show the zinc nucleation overpotential test results of a half-cell using the zinc anode coating of the present invention and a half-cell not using the zinc anode coating of the present invention; (a) shows the half-cell using the zinc anode coating of the present invention, and (b) shows the half-cell not using the zinc anode coating of the present invention. Figure 7 In-situ optical microscope photographs of the zinc electrodeposition test process for Example 4, the zinc negative electrode, and the zinc foil surface; (a) is Example 4, and (b) is the zinc foil. Detailed Implementation

[0023] To better illustrate the objectives, technical solutions, and advantages of this invention, the invention will be further described below with reference to specific embodiments. Those skilled in the art should understand that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0024] Unless otherwise specified, the experimental methods used in the examples are conventional methods; the materials and reagents used are commercially available unless otherwise specified.

[0025] Example 1 A zinc anode includes a zinc foil and a zinc anode coating disposed on one side surface of the zinc foil. The zinc anode coating comprises, by weight percentage, 88% sodium hexafluoroaluminate and 12% polyvinylidene fluoride. The zinc foil has a thickness of 80 μm, and the zinc anode coating has a thickness of 30 μm.

[0026] The method for preparing the zinc negative electrode coating includes the following steps: S1. Cryolite and polyvinylidene fluoride are ground and mixed at a mass ratio of 88:12, and then N-methylpyrrolidone (NMP) is added and stirred evenly to obtain a coating slurry with a concentration of 0.4 g / mL. S2. The coating slurry obtained in step S1 is poured evenly and slowly onto a clean, dry, and polished zinc foil negative electrode with a thickness of 80 μm. Using a four-corner coater at a specific height on one side, it is uniformly and unidirectionally coated once. Then, it is vacuum dried at 60 ℃ for 2 h to obtain a zinc negative electrode with a coating thickness of 30 μm.

[0027] Example 2 A zinc anode includes a zinc foil and a zinc anode coating disposed on one side surface of the zinc foil. The zinc anode coating comprises, by weight percentage, 88% sodium hexafluoroaluminate and 12% polyvinylidene fluoride. The zinc foil has a thickness of 120 μm, and the zinc anode coating has a thickness of 30 μm.

[0028] The method for preparing the zinc negative electrode coating includes the following steps: S1. Cryolite and polyvinylidene fluoride are ground and mixed at a mass ratio of 88:12, and then N-methylpyrrolidone (NMP) is added and stirred evenly to obtain a coating slurry with a concentration of 0.4 g / mL. S2. The coating slurry obtained in step S1 is poured evenly and slowly onto a clean, dry, and polished zinc foil negative electrode with a thickness of 120 μm. Using a four-corner coater at a specific height on one side, it is uniformly and unidirectionally coated once. Then, it is vacuum dried at 60 ℃ for 2 h to obtain a zinc negative electrode with a zinc negative electrode coating thickness of 30 μm.

[0029] Example 3 A zinc anode includes a zinc foil and a zinc anode coating disposed on one side surface of the zinc foil. The zinc anode coating comprises, by weight percentage, 88% sodium hexafluoroaluminate and 12% polyvinylidene fluoride. The zinc foil has a thickness of 100 μm, and the zinc anode coating has a thickness of 50 μm.

[0030] S1. Cryolite and polyvinylidene fluoride are ground and mixed at a mass ratio of 88:12, and then N-methylpyrrolidone (NMP) is added and stirred evenly to obtain a coating slurry with a concentration of 0.4 g / mL. S2. The coating slurry obtained in step S1 is poured evenly and slowly onto a clean, dry, and polished zinc foil negative electrode with a thickness of 100 μm. Using a four-corner coater at a specific height on one side, it is uniformly and unidirectionally coated once. Then, it is vacuum dried at 60 ℃ for 2 h to obtain a zinc negative electrode with a zinc negative electrode coating thickness of 50 μm.

[0031] Example 4 A zinc anode includes a zinc foil and a zinc anode coating disposed on one side surface of the zinc foil. The zinc anode coating comprises, by weight percentage, 88% sodium hexafluoroaluminate and 12% polyvinylidene fluoride. The zinc foil has a thickness of 150 μm, and the zinc anode coating has a thickness of 30 μm.

[0032] The method for preparing the zinc negative electrode coating includes the following steps: S1. Cryolite and polyvinylidene fluoride are ground and mixed at a mass ratio of 88:12, and then N-methylpyrrolidone (NMP) is added and stirred evenly to obtain a coating slurry with a concentration of 0.4 g / mL. S2. The coating slurry obtained in step S1 is poured evenly and slowly onto a clean, dry, and polished zinc foil negative electrode with a thickness of 150 μm. Using a four-corner coater at a specific height on one side, it is uniformly and unidirectionally coated once. Then, it is vacuum dried at 60 ℃ for 2 h to obtain a zinc negative electrode with a coating thickness of 30 μm.

[0033] Comparative Example 1 A zinc anode includes a zinc foil and a zinc anode coating disposed on one side surface of the zinc foil, wherein the zinc anode coating is polyvinylidene fluoride, the zinc foil has a thickness of 120 μm, and the zinc anode coating has a thickness of 30 μm.

[0034] The method for preparing the zinc negative electrode coating includes the following steps: S1. Polyvinylidene fluoride is added to N-methylpyrrolidone (NMP) and stirred until homogeneous to obtain a coating slurry with a concentration of 0.4 g / mL; S2. The coating slurry obtained in step S1 is poured evenly and slowly onto a clean, dry, and polished zinc foil negative electrode with a thickness of 120 μm. Using a four-corner coater at a specific height on one side, it is uniformly and unidirectionally coated once. Then, it is vacuum dried at 60 ℃ for 2 h to obtain a zinc negative electrode with a zinc negative electrode coating thickness of 30 μm.

[0035] Comparative Example 2 A zinc anode includes a zinc foil and a zinc anode coating disposed on one side surface of the zinc foil, the zinc anode coating comprising 88% AlF3 and 12% polyvinylidene fluoride by mass percentage, the zinc foil having a thickness of 120 μm and the zinc anode coating having a thickness of 30 μm.

[0036] The method for preparing the zinc negative electrode coating includes the following steps: S1. AlF3 and polyvinylidene fluoride are ground and mixed at a mass ratio of 88:12, and then N-methylpyrrolidone (NMP) is added and stirred evenly to obtain a coating slurry with a concentration of 0.4 g / mL. S2. The coating slurry obtained in step S1 is poured evenly and slowly onto a clean, dry, and polished zinc foil negative electrode with a thickness of 120 μm. Using a four-corner coater at a specific height on one side, it is uniformly and unidirectionally coated once. Then, it is vacuum dried at 60 ℃ for 2 h to obtain a zinc negative electrode with a zinc negative electrode coating thickness of 30 μm.

[0037] Comparative Example 3 A zinc anode includes a zinc foil and a zinc anode coating disposed on one side surface of the zinc foil. The zinc anode coating comprises 88% CaF2 and 12% polyvinylidene fluoride by weight percentage. The zinc foil has a thickness of 120 μm, and the zinc anode coating has a thickness of 30 μm.

[0038] The method for preparing the zinc negative electrode coating includes the following steps: S1. CaF2 and polyvinylidene fluoride are ground and mixed at a mass ratio of 88:12, and then N-methylpyrrolidone (NMP) is added and stirred evenly to obtain a coating slurry with a concentration of 0.4 g / mL. S2. The coating slurry obtained in step S1 is poured evenly and slowly onto a clean, dry, and polished zinc foil negative electrode with a thickness of 120 μm. Using a four-corner coater at a specific height on one side, it is uniformly and unidirectionally coated once. Then, it is vacuum dried at 60 ℃ for 2 h to obtain a zinc negative electrode with a zinc negative electrode coating thickness of 30 μm.

[0039] Characterization and Testing 1. Cycle life The zinc anode from Example 1 was used to prepare a Zn||Zn symmetric cell for cycle life testing. The preparation method of the Zn||Zn symmetric cell was as follows: the zinc anode from Example 1 was cut into several plates with a diameter of 16 mm and named "NAF / Zn". Two NAF / Zn cells were assembled with 100 μL of electrolyte containing 2 mol / L zinc sulfate, glass fiber separator, spring sheet, gasket, positive electrode and negative electrode battery case to obtain the NAF / Zn||NAF / Zn symmetric cell.

[0040] Zinc foil was cut into several electrode pieces with a diameter of 16 mm and named "Bare Zn". The same method was used to make a Bare Zn||Bare Zn symmetrical cell with two Bare Zn electrodes.

[0041] The resulting NAF / Zn||NAF / Zn symmetric cells and Bare Zn||Bare Zn symmetric cells were tested at a current density of 0.5 mA·cm⁻¹. -2 The surface capacity is 0.5 mAh·cm³. -2 Under the conditions of stripping / deposition cycle testing, the voltage-time plot results are as follows: Figure 1 (a) and Figure 1 As shown in (b), from Figure 1 As can be seen in (a), the NAF / Zn||NAF / Zn symmetric battery made of zinc anode with zinc anode coating of the present invention has a cycle life of more than 650 h, which suggests that the growth of zinc dendrites on the zinc anode surface is suppressed. Figure 1As shown in (b), the cycle life of the battery without the zinc anode coating of the present invention is only about 330 h, which suggests that zinc dendrite growth is severe.

[0042] 2. Capacity retention performance The zinc anode from Example 2 was used to prepare a Zn||MnO2 full cell for charge-discharge cycle testing. The preparation method of the Zn||MnO2 full cell was as follows: the zinc anode from Example 2 was cut into several plates with a diameter of 16 mm and named "NAF / Zn". One NAF / Zn was assembled with one MnO2 positive electrode, 100 μL of electrolyte containing 2 mol / L zinc sulfate and 0.2 mol / L manganese sulfate, glass fiber separator, spring sheet, gasket, positive and negative electrode battery case to obtain the NAF / Zn||MnO2 full cell.

[0043] A 120 μm thick zinc foil was cut into several electrodes with a diameter of 16 mm and named “Bare Zn”. The same method was used to assemble a Bare Zn||MnO2 full cell.

[0044] Using the same method, the zinc anodes of Comparative Examples 1-3 were used to prepare Zn||MnO2 full cells. The full cell obtained in Comparative Example 1 was denoted as PVDF / Zn||MnO2 full cell, the full cell obtained in Comparative Example 2 was denoted as AlF3 / Zn||MnO2 full cell, and the full cell obtained in Comparative Example 3 was denoted as CaF2 / Zn||MnO2 full cell.

[0045] The full cells obtained from Example 2, Comparative Examples 1-3, and Bare Zn were subjected to a current density of 2 A·g. -1 Charge-discharge cycle tests were conducted under the conditions of a charging cutoff voltage of 1.8 V and a discharging cutoff voltage of 0.8 V. The test results of Example 2 are as follows: Figure 2 As shown in (a), the test results for Bare Zn are as follows: Figure 2 As shown in (b), the test results of Comparative Example 1 are as follows: Figure 3 As shown in (a), the test results of Comparative Example 2 are as follows: Figure 3 As shown in (b), the test results of Comparative Example 3 are as follows: Figure 3 As shown in (c). From Figure 2As shown in (a), the full battery made with the zinc anode containing the zinc anode coating of the present invention exhibits a capacity retention rate as high as 77.6% after 1000 charge-discharge cycles, demonstrating excellent cycle performance and capacity retention. In contrast, the Bare Zn||MnO2 full battery exhibits a capacity retention rate of only 15.6% after 1000 charge-discharge cycles, showing very poor cycle performance and capacity retention. The full batteries obtained with zinc anodes in Comparative Examples 1-3 have capacity retention rates of only 25.8%, 41.9%, and 29.5% after 1000 charge-discharge cycles, respectively. It is evident that the addition of cryolite to the zinc anode coating of the present invention has a significantly improved effect compared to other fluorinated compounds, and can significantly improve the battery's capacity retention rate.

[0046] 2. Contact Angle Test Contact angle tests were performed on the zinc anode and 120 μm thick zinc foil of Example 2. The test method was as follows: one drop of electrolyte containing 2 mol / L zinc sulfate was dropped onto the surface of both the zinc anode and the 120 μm thick zinc foil of Example 2, and the contact angle value was read 30 seconds after dropping. The results are as follows. Figure 4 As shown.

[0047] The smaller the contact angle, the more fully the electrolyte contacts the zinc negative electrode, and the less resistance there is to interfacial transport between the zinc negative electrode and the electrolyte in an aqueous zinc metal battery. Figure 4 (a) is the contact angle of the zinc negative electrode in Example 2, where the contact angle between the zinc negative electrode coating and the electrolyte is only 45°. o Based on the surface, it can be inferred that the interface transmission is relatively smooth. Figure 4 (b) is the contact angle of the zinc foil, which is as high as 91° between the zinc foil and the electrolyte. o This suggests that interface transmission is quite difficult.

[0048] 3. Electrochemical impedance spectroscopy The zinc anode from Example 3 was used to prepare a Zn||Zn symmetric cell according to the aforementioned preparation method. Electrochemical impedance spectroscopy (EIS) tests were performed sequentially at temperatures of 42°C, 47°C, 52°C, and 57°C. The desolvation activation energy (Ea) was calculated to verify the promoting effect of the zinc anode coating of the present invention on the desolvation behavior of zinc ions on the zinc anode surface. The results are as follows: Figure 5 (a) and Figure 5 As shown in (c), the zinc ion desolvation activation energy on the zinc anode surface using the zinc anode coating of the present invention is only 46.43 kJ·mol⁻¹. -1 The desolvation of zinc ions is relatively easy, which is beneficial for the uniform deposition of zinc and the suppression of zinc dendrites.

[0049] Using the same method, 100 μm thick zinc foil was assembled into a symmetrical cell. Electrochemical impedance spectroscopy (EIS) was performed sequentially at temperatures of 42 ℃, 47 ℃, 52 ℃, and 57 ℃. The desolvation activation energy (Ea) was calculated using fitting, and the results are as follows: Figure 5 (b) and Figure 5 As shown in (c), the zinc ion desolvation activation energy on the zinc anode surface of the zinc foil symmetric battery without the coating of the present invention is as high as 99.87 kJ·mol⁻¹. -1 The efficiency is much higher than that of the zinc anode in Example 3, making desolvation very difficult and the interfacial electrochemical process slow.

[0050] 4. Zinc nucleation overpotential test To test the promoting effect of the zinc anode coating of the present invention on zinc nucleation on the zinc anode surface, a zinc anode coating with a thickness of 10 μm was prepared on the surface of copper foil. The specific preparation method is as follows: S1. Weigh 1 g of cryolite with a mass fraction of 88% and polyvinylidene fluoride with a mass fraction of 12%, grind and mix them, and then add 2.5 mL of N-methylpyrrolidone (NMP) and stir evenly to obtain the coating slurry; S2. The coating slurry obtained in step S1 is poured evenly and slowly onto a clean, dry, and polished copper foil with a thickness of 80 μm. Using a four-corner coater at a specific height on one side, it is uniformly and unidirectionally coated once. Then, it is vacuum dried at 60 ℃ for 2 h to obtain a copper positive electrode with a zinc negative electrode coating thickness of 10 μm.

[0051] The copper positive electrode was cut into several plates with a diameter of 16 mm and named "NAF / Cu". A Zn||NAF / Cu half cell was obtained by assembling one NAF / Cu with one Bare Zn, 100 μL of electrolyte containing 2 mol / L zinc sulfate, glass fiber separator, spring, gasket, positive and negative electrode battery case.

[0052] Cut copper foil into several electrode pieces with a diameter of 16 mm, and use the same method to make a Zn||Bare Cu half cell with one copper foil and one zinc foil.

[0053] The obtained Zn||NAF / Cu half-cells and Zn||Bare Cu half-cells were subjected to scanning at a voltage range of 1.0 to -0.4 V and a scan rate of 0.5 mV·s. -1 Cyclic voltammetry (CV) tests were performed under specific conditions to obtain the nucleation overpotential for zinc nucleation on the surface of the copper cathode, thus reflecting the difficulty of zinc nucleation on the surface of the zinc anode. The results are as follows: Figure 6 (a) and Figure 6 As shown in (b), Figure 6(a) shows that after the zinc anode coating of the present invention is applied to the surface of the copper cathode, the nucleation overpotential of zinc on the surface of the metallic copper cathode is only 51 mV, reflecting that the nucleation overpotential and nucleation difficulty of zinc on the surface of the metallic zinc anode should also be low, which is beneficial to the uniform deposition of zinc and the suppression of zinc dendrites. Figure 6 In (b), the nucleation overpotential of zinc on the surface of the copper cathode without the coating of the present invention is 65 mV, which reflects that the nucleation overpotential and nucleation difficulty of zinc on the surface of the zinc anode should also be relatively high, indicating that the deposition of zinc on the surface of the zinc anode is greatly hindered.

[0054] 5. In-situ optical microscope photographs The zinc negative electrode from Example 4 was cut into several square electrode sheets with a side length of 10 mm and named "NAF / Zn". Two NAF / Zn electrodes were assembled with approximately 500 μL of an electrolyte containing 2 mol / L zinc sulfate, and the current density was 1 mA·cm⁻¹. -2 Zinc electrodeposition was performed under a deposition time of 30 min, and the entire process was observed using an in-situ optical microscope to verify the inducing effect of the zinc anode coating of this invention on uniform zinc deposition on the zinc anode surface and its inhibitory effect on zinc dendrite growth. The results are as follows: Figure 7 As shown in (a), it can be seen in 7(a) that the zinc deposition is very uniform within 30 min, with no protrusions or dendrites.

[0055] Similarly, a 150 μm thick zinc foil was cut into several square electrodes with sides of 10 mm, and named "Bare Zn". Two Bare Zn electrodes were assembled with approximately 500 μL of electrolyte containing 2 mol / L zinc sulfate, and the current density was 1 mA·cm⁻¹. -2 Zinc electrodeposition was performed under a deposition time of 30 min, and the entire process was observed using an in-situ optical microscope. The results are as follows: Figure 7 As shown in (b), zinc deposition is uneven within 30 minutes, with protrusions forming.

[0056] In summary, compared with existing technologies, the Zn||Zn symmetric battery assembled with the zinc anode coating of the present invention achieves a current density of 0.5 mA·cm⁻¹. -2 The surface capacity is 0.5 mAh·cm³. -2 Under these conditions, it can stably undergo peeling / deposition cycles for over 600 hours, which is higher than the approximately 380 hours without the coating; the assembled Zn||MnO2 full cell can achieve a current density of 2 A·g -1After 1000 stable cycles under conditions of a charging cutoff voltage of 1.8 V and a discharging cutoff voltage of 0.8 V, the capacity retention rate reached 77.6%, which is higher than the 15.6% without the coating and the 25.8%, 41.9%, and 29.5% of some previously reported coatings of the same thickness (30 μm) prepared according to the same method, such as PVDF, AlF3, and CaF2, respectively. This invention discloses the application of cryolite, a common and inexpensive fluoride compound with extremely strong hydrophilicity (even strong water absorption), slight solubility in water, and a high fluorine content of up to 54.55%, as a coating on the surface of the zinc anode of aqueous zinc-metal batteries, showing significant application prospects.

[0057] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A zinc negative electrode coating, characterized in that, The active material comprises 85%-90% active material and 10%-15% binder by weight percentage, wherein the active material comprises at least one of sodium hexafluoroaluminate and potassium hexafluoroaluminate.

2. The zinc negative electrode coating according to claim 1, characterized in that, The active material is sodium hexafluoroaluminate, and the binder includes at least one of polyvinylidene fluoride and carboxymethyl cellulose.

3. The zinc anode coating according to claim 1, characterized in that, The thickness of the zinc anode coating is 10μm to 50μm.

4. A zinc negative electrode, characterized in that, The zinc substrate layer includes a zinc negative electrode coating as described in any one of claims 1-3, which is disposed on at least one side surface of the zinc substrate layer.

5. The zinc negative electrode according to claim 4, characterized in that, The zinc substrate layer includes zinc foil with a thickness of 80 μm to 150 μm.

6. A method for preparing a zinc negative electrode according to any one of claims 4-5, characterized in that, Includes the following steps: S1. Mix the active material and binder evenly in a solvent to obtain a coating slurry; S2. The coating slurry obtained in step S1 is coated onto the surface of the zinc substrate and dried to obtain the zinc negative electrode.

7. The method for preparing the zinc negative electrode according to claim 6, characterized in that, In step S1, the concentration of the coating slurry is 0.3 g / mL - 0.5 g / mL.

8. The method for preparing the zinc negative electrode according to claim 6, characterized in that, In step S2, the drying temperature is 40℃-80℃ and the time is 1h-3h.

9. The method for preparing the zinc negative electrode according to claim 6, characterized in that, In step S1, the solvent includes N-methylpyrrolidone; and / or, in step S2, the coating includes one or more of blade coating, spin coating, and spray coating.

10. A zinc metal battery comprising the zinc negative electrode as described in any one of claims 4-5.

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