Aqueous zinc-ion battery and method for protecting the zinc negative electrode thereof

Abstract

The application discloses a water-based zinc ion battery and a protection method of a zinc negative electrode thereof, and realizes preferential growth of a (002) crystal surface (2theta=36°) during zinc electrodeposition through electrolyte regulation, thereby inhibiting generation of zinc dendrites and by-products and stabilizing the zinc negative electrode in the zinc ion battery. a The electrolyte solvent is water or a mixture of water and an organic solvent, the solute is zinc salt (ZnX b ) and trace amounts of other metal salts (M c ) and polybasic organic acid, wherein the organic solvent is one or more of methanol, ethanol, isopropanol, acetone and dimethylformamide; M= one or more of Bi 3+ , Al 3+ , Cu 2+ , Fe 2+ , Fe 3+ , Co 2+ , Ni 2+ , Pt 4+ and Pd 2+ . The zinc negative electrode working under the electrolyte exhibits excellent deposition-dissolution reversibility, and the zinc sheet after circulation exhibits the characteristics of significantly enhanced (002) surface preferential orientation, no dendrites and no by-products. The method is simple and low in cost, and can significantly improve the cycle stability of the zinc negative electrode in the water-based zinc ion battery.

Description

Technical Field

[0001] This invention relates to aqueous zinc-ion batteries and methods for protecting their zinc anodes, specifically to a method for protecting the anode by adjusting specific components of the electrolyte to improve the reversibility of zinc dissolution and deposition in zinc-ion batteries, belonging to the field of electrochemistry. Background Technology

[0002] Against the backdrop of limited fossil fuel reserves and rising carbon dioxide emissions leading to global warming, renewable and clean energy is receiving increasing attention. However, renewable energy sources, such as solar and wind power, are characterized by intermittency, volatility, randomness, and geographical dependence, requiring highly safe, low-cost, and long-life energy storage technologies to ensure stable energy output. Compared to traditional mechanical, electromagnetic, thermal, and chemical energy storage, electrochemical energy storage (i.e., various secondary battery energy storage) is considered to play a crucial role in the future energy storage market due to its flexible configuration, rapid response, and short construction period. Currently, lithium-ion batteries dominate electrochemical energy storage (approximately 88%). However, lithium is expensive ($19.2 / kg). Furthermore, lithium-ion batteries use organic electrolytes, posing serious safety hazards; leaks or overheating can easily lead to fires and explosions. Therefore, there is an urgent need to develop low-cost, highly safe electrochemical energy storage technologies.

[0003] Zinc metal is abundant in my country (ranking first in the world) and has advantages such as low cost ($2.4 / kg), non-toxicity, and high theoretical capacity (5851 mAh / mL; 820 mAh / g). Its relatively low redox potential (-0.76 V vs SHE) allows zinc-ion batteries to directly use aqueous electrolytes. The ionic conductivity of aqueous electrolytes is about two orders of magnitude higher than that of organic electrolytes (~1000 mS / cm). -1 vs~1-10mS cm -1 Therefore, aqueous zinc-ion batteries can be charged and discharged quickly. Furthermore, thanks to the relatively stable chemical and physical properties of zinc metal, aqueous zinc-based batteries pose no risk of explosion or fire, making them highly safe and promising for applications in portable devices, electric vehicles, and large-scale energy storage.

[0004] However, current aqueous zinc-ion batteries face key challenges such as dendrite formation and side reactions, which can easily lead to electrode failure or low cycle life. Zinc dendrites can easily puncture the separator, causing battery open circuits, and can also cause uneven electrode thickness, leading to electrode deformation. Side reactions (including water corrosion and hydrogen evolution reaction) not only reduce zinc utilization and battery coulombic efficiency, but the generation of hydrogen also affects the battery's safety and electrochemical performance. Therefore, effectively suppressing the occurrence of zinc dendrites and side reactions is a crucial problem that must be solved in the development of zinc-ion batteries. Summary of the Invention

[0005] The purpose of this invention is to improve the cycle stability of the zinc-ion battery anode by avoiding zinc dendrite formation and side reactions. This invention provides a zinc anode protection method that improves the reversibility of zinc anode dissolution and deposition in zinc-ion batteries through electrolyte composition regulation. Specifically, by adjusting the composition and concentration of the electrolyte in the battery system, the deposition behavior of zinc is guided at the electrode / solution interface on the zinc anode side of the zinc-ion battery, causing zinc to preferentially grow along the (002) crystal plane. The (002) plane of zinc has a denser surface atomic arrangement, providing a good interface for nucleation and effectively suppressing side reactions such as hydrogen evolution and water corrosion, thus exhibiting excellent zinc deposition and dissolution reversibility. Battery cycle performance results show that the zinc anode preferentially deposits along the (002) crystal plane in the regulated electrolyte, suppressing zinc dendrite formation and side reactions, exhibiting efficient and reversible deposition / dissolution performance; the method is simple and low-cost.

[0006] This invention provides a method for protecting the zinc anode in a zinc-ion battery. Zinc-based materials are used as the active material of the zinc anode. During zinc electrodeposition, zinc preferentially grows along the (002) crystal plane, thereby inhibiting the formation of zinc dendrites and by-products.

[0007] Furthermore, in the above technical solution, the zinc electrodeposition of zinc in the zinc anode of the stable zinc-ion battery is preferentially grown along the (002) crystal plane by electrolyte regulation; the solvent of the electrolyte is water or a mixture of water and organic solvent, and the solute is zinc salt, as well as trace amounts of other metal salts that promote hydrogen evolution reaction and polybasic organic acids containing two or more carboxyl groups.

[0008] This invention provides a zinc-ion battery electrolyte, characterized in that: the solvent of the electrolyte is water or a mixture of water and an organic solvent, and the solute is a zinc salt, as well as trace amounts of other metal salts that promote hydrogen evolution reaction and polybasic organic acids containing one or more carboxyl groups.

[0009] This invention provides a zinc-ion battery, characterized in that: a zinc-based material is used as the zinc negative electrode active material, the electrolyte solvent is water or a mixture of water and organic solvent, and the solute is a zinc salt, as well as trace amounts of other metal salts and polybasic organic acids containing one or more carboxyl groups.

[0010] Furthermore, in the above technical solution, the zinc negative electrode is a zinc sheet, zinc foil, zinc powder, zinc mesh, porous zinc, or zinc alloy.

[0011] Furthermore, in the above technical solution, the organic solvent is one or more of methanol, ethanol, isopropanol, acetone, and dimethylformamide; the volume ratio of the organic solvent to water is 0 to 1.

[0012] Furthermore, in the above technical solution, the solute is zinc salt ZnX. a , where X=Cl- SO4 2- NO3 - CH3COO - CF3SO3 - ClO4 - One or more of the following, where a = 1~2; the zinc salt Zn a X b The concentration is 0.1~5 M.

[0013] Furthermore, in the above technical solution, the trace amount of other metal salt is M. b X c X=Cl - SO4 2- NO3 - CH3COO - CF3SO3 - ClO4 - One or more of them, M=Bi 3+ Al 3+ Cu 2+ Fe 3+ Co 2+ Ni 2+ Pt 4+ Pd 2+ One or more of the following, b=1~2, c=2~4; the metal salt M b X c The concentration is 0.1~50 mM.

[0014] Furthermore, in the above technical solution, the polybasic organic acid is one or more of pyromellitic acid, terephthalic acid, phthalic acid, isophthalic acid, thiophene dicarboxylic acid, and naphthalene dicarboxylic acid; the concentration of the polybasic organic acid is 0.1~50 mM.

[0015] This invention provides an electrolyte preparation method that optimizes electrolyte composition to improve the reversibility of zinc anode deposition and dissolution, comprising the following steps:

[0016] (1) A certain amount of polybasic organic acid is dissolved in a certain amount of organic solvent or water, wherein the organic acid is one or more of pyromellitic acid, terephthalic acid, and phthalic acid; the concentration of the polybasic organic acid is 1~100 mM.

[0017] (2) Add a certain amount of zinc salt ZnX a Dissolves in aqueous solution, where X = Cl - SO4 2- NO3 - CH3COO - CF3SO3 - ClO4- One or more of the following, where a = 1~2; the zinc salt ZnX a The concentration is 0.1~6 M.

[0018] (3) Other metal salts M b X c When dissolved in an aqueous solution, its X=Cl - SO4 2- NO3 - CH3COO - CF3SO3 - ClO4 - One or more of them, M=Bi 3+ Al 3+ Cu 2+ Fe 3+ Co 2+ Ni 2+ Pt 4+ Pd 2+ One or more of the following, b=1~2, c=2~4; the metal salt M b X c The concentration ranges from 0.1 to 100 mM.

[0019] (4) Add the solution from step (1) to the solution from step (3) and stir until a clear liquid is formed.

[0020] (5) Add the solution from step (2) to the clarified solution from step (4), and then add an appropriate amount of deionized water to adjust the composition of the solution to a specific range.

[0021] Based on the above technical solution, the preferred solvent ratio, i.e., the volume ratio of organic solvent to water, is 0~1.

[0022] Based on the above technical solution, the preferred solute ratio is zinc salt ZnX a Concentrations range from 0.1 to 5 M, metal salt M b X c The concentration is 0.1~50 mM, and the concentration of polybasic organic acids is 0.1~50 mM.

[0023] The reversibility of zinc anode deposition and dissolution in the electrolyte prepared in this invention was evaluated using a zinc symmetric cell, as follows:

[0024] Two zinc anodes are placed in their corresponding positions within the battery mold, with a separator between them to isolate electron transport. Electrolyte is then added, and the zinc anode symmetrical battery is encapsulated using a button cell sealing machine. The encapsulated battery is then connected to an electrochemical charge-discharge apparatus and charged at a specified current density (0.1~20 mA / cm²). 2 Cyclic stability tests were performed under these conditions.

[0025] Beneficial results:

[0026] This invention utilizes a regulated electrolyte to induce strong preferential growth of zinc on the (002) crystal plane (2θ=36°) during zinc deposition. XRD test results show that the strongest peak of the zinc sheet after cycling corresponds to the (002) crystal plane of zinc (the strongest XRD peak of the initial zinc (2θ=43°) corresponds to the (101) crystal plane), and there is no XRD peak of the byproduct Zn4(OH)6SO4·5H2O (XRD results are shown in Figure 1). Figure 2 (As shown); Scanning electron microscopy (SEM) images of the zinc surface after 1900 hours of cycling showed no zinc dendrites or byproducts (SEM results are shown in the image). Figure 1 (As shown). The zinc-symmetric cell exhibits excellent reversibility of zinc deposition and dissolution, with symmetrical, stable, and flat voltage-time curves; at 0.5 mA / cm²... 2 At current densities, the cycle life can reach 2000 hours (the voltage-time curve of the battery cycle test is shown in Figure 1). Figure 3 (As shown).

[0027] The method provided by this invention is time-saving, simple in steps, low in cost, and highly repeatable. Attached Figure Description

[0028] Figure 1 These are scanning electron microscope images of the zinc surface after battery cycling in Examples 1-9.

[0029] Figure 2 The image shows the X-ray diffraction (XRD) pattern of the zinc foil after battery cycling in Example 1.

[0030] Figure 3 The voltage-time curve is the battery cycle test result from Example 1.

[0031] Figure 4 A scanning electron microscope image of the zinc surface after battery cycling in Comparative Example 1.

[0032] Figure 5 The X-ray diffraction (XRD) pattern of the zinc foil after battery cycling in Comparative Example 1 is shown. Detailed Implementation

[0033] The following embodiments will further illustrate the present invention, but are not intended to limit the invention.

[0034] The electrolyte preparation method in the following embodiments includes the following steps:

[0035] (1) Dissolve a certain amount of polybasic organic acid in a certain amount of organic solvent or water.

[0036] (2) Add a certain amount of zinc salt ZnX aDissolves in aqueous solution;

[0037] (3) Other metal salts M b X c Dissolves in aqueous solution;

[0038] (4) Add the solution from step (1) to the solution from step (3) and stir until a clear liquid is formed.

[0039] Add the solution from step (2) to the clarified solution from step (4), and then add an appropriate amount of deionized water to adjust the composition of the solution to a specific range.

[0040] Example 1

[0041] Weigh 200 mg of terephthalic acid powder, 90 mg of NiSO4·6H2O powder, and 10 g of ZnSO4·7H2O powder, and dissolve them separately in 20 mL of propanol, 20 mL of deionized water, and 20 mL of deionized water, respectively. Mix the three solutions according to the electrolyte preparation steps described above, and finally add 40 mL of deionized water to obtain the optimized electrolyte composition. Assemble a zinc-ion symmetric cell using commercial zinc foil and this electrolyte. At 0.5 mA / cm²... 2 At the current density, after 1900 hours of battery cycling, the zinc surface exhibits a preferred orientation of (002) plane. The zinc surface morphology is shown in [reference needed]. Figure 1 The X-ray diffraction (XRD) spectra of zinc after 1900 hours of battery cycling are shown below. Figure 2 The battery achieved a stable cycle time of 1900 hours. The voltage-time curve for the battery cycle test is shown below. Figure 3 .

[0042] Example 2

[0043] Weigh 150 mg of naphthalene dicarboxylic acid powder, 50 mg of FeCl2·4H2O powder, and 4 g of ZnCl2 powder, and dissolve them separately in 20 mL of isopropanol, 20 mL of deionized water, and 15 mL of deionized water. Mix the three solutions according to the electrolyte preparation steps described above, and finally add 20 mL of deionized water to obtain the optimized electrolyte composition. Assemble a zinc-ion symmetric cell using a zinc-aluminum alloy sheet and this electrolyte. The measured value is 0.5 mA / cm². 2 At a current density of [value missing], after 1000 hours of battery cycling, the zinc surface exhibits a preferred orientation of (002) plane. The zinc surface morphology is shown in [details missing]. Figure 1 .

[0044] Example 3

[0045] Weigh 80 mg of trimesic acid powder, 50 mg of Bi(NO3)3·5H2O powder, and 8 g of Zn(NO3)2·6H2O powder, and dissolve them separately in 10 mL of dimethylformamide, 20 mL of deionized water, and 20 mL of deionized water, respectively. Mix the three solutions according to the electrolyte preparation steps described above, and finally add 35 mL of deionized water to obtain the optimized electrolyte composition. Assemble a zinc-ion symmetric cell using zinc powder supported on a stainless steel mesh and this electrolyte. At 2 mA / cm²... 2 At a current density of [value missing], after 500 hours of battery cycling, the zinc surface exhibits a preferred orientation of (002) plane. The zinc surface morphology is shown in [details missing]. Figure 1 .

[0046] Example 4

[0047] Weigh 90 mg of isophthalic acid powder, 30 mg of Co(CH3COO)2·4H2O powder, and 3 g of Zn(CH3COO)2·2H2O powder, and dissolve them separately in 20 mL of ethanol, 20 mL of deionized water, and 40 mL of deionized water. Mix the three solutions according to the electrolyte preparation steps described above, and finally add 35 mL of deionized water to obtain the optimized electrolyte composition. Assemble a zinc-ion symmetric cell using zinc powder supported on a stainless steel mesh and this electrolyte. At 2 mA / cm²... 2 At a current density of [value missing], after 500 hours of battery cycling, the zinc surface exhibits a preferred orientation of (002) plane. The zinc surface morphology is shown in [details missing]. Figure 1 .

[0048] Example 5

[0049] Weigh 250 mg of phthalic acid powder, 70 mg of CuSO4·5H2O powder, and ZnSO4·7H2O powder, and dissolve them separately in 20 mL of methanol, 20 mL of deionized water, and 40 mL of deionized water. Mix the three solutions according to the electrolyte preparation steps described above, and finally add 25 mL of deionized water to obtain the optimized electrolyte composition. A zinc-ion symmetric battery was assembled using commercially available zinc sheets and this electrolyte, achieving a speed of 2 mA / cm². 2 At a current density of [value missing], after 500 hours of battery cycling, the zinc surface exhibits a preferred orientation of (002) plane. The zinc surface morphology is shown in [details missing]. Figure 1 .

[0050] Example 6

[0051] Weigh 150 mg of thiophene dicarboxylic acid powder, 20 mg of Fe2(SO4)3·7H2O powder, and 10 g of ZnSO4·7H2O powder, and dissolve them separately in 15 mL, 20 mL, and 20 mL of deionized water, respectively. Mix the three solutions according to the electrolyte preparation steps described above, and finally add 50 mL of deionized water to obtain the optimized electrolyte composition. Assemble a zinc-ion symmetric cell using a zinc-aluminum alloy sheet and this electrolyte. The measured value is 10 mA / cm². 2 At a current density of [value missing], after 500 hours of battery cycling, the zinc surface exhibits a preferred orientation of (002) plane. The zinc surface morphology is shown in [details missing]. Figure 1 .

[0052] Example 7

[0053] Weigh 100 mg of terephthalic acid powder, 50 mg of PtCl4·5H2O powder, and 4 g of ZnCl2 powder, and dissolve them separately in 20 mL of acetone, 20 mL of deionized water, and 15 mL of deionized water. Mix the three solutions according to the electrolyte preparation steps described above, and finally add 70 mL of deionized water to obtain the optimized electrolyte composition. Assemble a zinc-ion symmetric cell using a zinc-copper alloy sheet and this electrolyte. The measured value is 0.5 mA / cm². 2 At a current density of [value missing], after 1000 hours of battery cycling, the zinc surface exhibits a preferred orientation of (002) plane. The zinc surface morphology is shown in [details missing]. Figure 1 .

[0054] Example 8

[0055] Weigh 30 mg of isophthalic acid powder, 50 mg of PtCl4·5H2O powder, and 4 g of ZnCl2 powder, and dissolve them separately in 20 mL of acetone, 20 mL of deionized water, and 15 mL of deionized water. Mix the three solutions according to the electrolyte preparation steps described above, and finally add 65 mL of deionized water to obtain the optimized electrolyte composition. Assemble a zinc-ion symmetric cell using a zinc-copper alloy sheet and this electrolyte. The measured value is 2 mA / cm². 2 At a current density of [value missing], after 500 hours of battery cycling, the zinc surface exhibits a preferred orientation of (002) plane. The zinc surface morphology is shown in [details missing]. Figure 1 .

[0056] Example 9

[0057] Weigh 70 mg of trimesic acid powder, 40 mg of AlCl3·6H2O powder, and 4 g of ZnCl2 powder, and dissolve them separately in 20 mL of methanol, 20 mL of deionized water, and 15 mL of deionized water. Mix the three solutions according to the electrolyte preparation steps described above, and finally add 40 mL of deionized water to obtain the optimized electrolyte composition. Assemble a zinc-ion symmetric cell using commercially available zinc foil and this electrolyte, and achieve a speed of 10 mA / cm². 2 At a current density of [value missing], after 500 hours of battery cycling, the zinc surface exhibits a preferred orientation of (002) plane. The zinc surface morphology is shown in [details missing]. Figure 1 .

[0058] Comparative Example 1

[0059] 115.0 g of ZnSO4·7H2O powder was weighed and dissolved in an appropriate amount of ultrapure water to prepare a 2 M ZnSO4 solution. A zinc-ion symmetric cell was assembled using commercially available zinc foil and the 2 M ZnSO4 solution, connected to an electrochemical charge-discharge apparatus, and set to 0.5 mA / cm². 2 The cycling current density and 1-hour charge-discharge cycle were measured. After 80 hours of cycling, the battery failed due to trigger voltage protection circuit breaker failure. The zinc foil surface showed obvious dendrites after cycling; surface morphology images are shown below. Figure 4 After 80 hours of cycling, the zinc foil contained a high amount of byproducts, and the zinc crystal orientation was consistent with the initial (101) orientation of the zinc foil. The X-ray diffraction (XRD) pattern of the zinc foil after 80 hours of cycling is shown below. Figure 5 .

[0060] Comparative Example 2

[0061] Weigh 54.5 g of ZnCl2 powder and dissolve it in an appropriate amount of ultrapure water to prepare a 2 M ZnCl2 solution. Assemble a zinc-ion symmetric cell using commercially available zinc foil and the 2 M ZnCl2 solution, connect it to an electrochemical charge-discharge apparatus, and set the flow rate to 0.5 mA / cm². 2 The cycle current density and charge-discharge cycle of 15 min were measured. After 40 h of cycling, the battery failed due to the trigger voltage protection circuit breaking. After 40 hours of cycling, the zinc foil showed a dendritic morphology and (101) plane orientation similar to Comparative Example 1.

Claims

1. A method for protecting the zinc negative electrode in a zinc-ion battery, characterized in that: Using zinc-based materials as zinc anode active materials, zinc preferentially grows along the (002) crystal plane during electrodeposition, suppressing the formation of zinc dendrites and by-products; In a stable zinc-ion battery, zinc electrodeposition at the zinc anode is achieved through electrolyte regulation, with preferential growth along the (002) crystal plane. The electrolyte is a solvent of water or a mixture of water and organic solvent, and the solute is a zinc salt, as well as trace amounts of other metal salts that promote the hydrogen evolution reaction and polybasic organic acids containing one or more carboxyl groups. The trace amounts of other metal salts are M. b X c X=Cl - SO4 2- NO3 - CH3COO - CF3SO3 - ClO4 - One or more of them, M=Bi 3+ Al 3+ Cu 2+ Fe 3+ Co 2+ Ni 2+ Pt 4+ Pd 2+ One or more of the following, b=1~2, c=2~4; the metal salt M b X c Concentrations range from 0.1 to 50 mM; The polybasic organic acid is one or more of the following: pyromellitic acid, terephthalic acid, phthalic acid, isophthalic acid, thiophene dicarboxylic acid, and naphthalene dicarboxylic acid; the concentration of the polybasic organic acid is 0.1~50 mM.

2. A zinc-ion battery electrolyte, characterized in that: The electrolyte is a solvent of water or a mixture of water and an organic solvent, and the solute is a zinc salt, as well as trace amounts of other metal salts and polybasic organic acids containing one or more carboxyl groups; the trace amounts of other metal salts are M. b X c X=Cl - SO4 2- NO3 - CH3COO - CF3SO3 - ClO4 - One or more of them, M=Bi 3+ Al 3+ Cu 2+ Fe 3+ Co 2+ Ni 2+ Pt 4+ Pd 2+ One or more of the following, b=1~2, c=2~4; the metal salt M b X c Concentrations range from 0.1 to 50 mM; The polybasic organic acid is one or more of the following: pyromellitic acid, terephthalic acid, phthalic acid, isophthalic acid, thiophene dicarboxylic acid, and naphthalene dicarboxylic acid; the concentration of the polybasic organic acid is 0.1~50 mM.

3. A zinc-ion battery, characterized in that: Zinc-based materials are used as the active material for the zinc negative electrode, and the electrolyte is the electrolyte described in claim 2.

4. The protection method according to claim 1, characterized in that: The zinc negative electrode is zinc sheet, zinc foil, zinc powder, zinc mesh, porous zinc or zinc alloy.

5. The battery according to claim 3, characterized in that: The zinc negative electrode is zinc sheet, zinc foil, zinc powder, zinc mesh, porous zinc or zinc alloy.

6. The protection method according to claim 1, characterized in that: The organic solvent is one or more of methanol, ethanol, isopropanol, acetone, and dimethylformamide; the volume ratio of the organic solvent to water is 0 to 1.

7. The electrolyte according to claim 2, characterized in that: The organic solvent is one or more of methanol, ethanol, isopropanol, acetone, and dimethylformamide; the volume ratio of the organic solvent to water is 0 to 1.

8. The battery according to claim 3, characterized in that: The organic solvent is one or more of methanol, ethanol, isopropanol, acetone, and dimethylformamide; the volume ratio of the organic solvent to water is 0 to 1.

9. The protection method according to claim 1, characterized in that: The solute is zinc salt ZnX. a , where X=Cl - SO4 2- NO3 - CH3COO - CF3SO3 - ClO4 - One or more of the following, a=1~2; the zinc salt ZnX a The concentration is 0.1~6M.

10. The electrolyte according to claim 2, characterized in that: The solute is zinc salt ZnX. a , where X=Cl - SO4 2- NO3 - CH3COO - CF3SO3 - ClO4 - One or more of the following, a=1~2; the zinc salt ZnX a The concentration is 0.1~6M.

11. The battery according to claim 3, characterized in that: The solute is zinc salt ZnX. a , where X=Cl - SO4 2- NO3 - CH3COO - CF3SO3 - ClO4 - One or more of the following, a=1~2; the zinc salt ZnX a The concentration is 0.1~6M.

12. The electrolyte according to claim 2, characterized in that... The preparation method includes the following steps: (1) A certain amount of polybasic organic acid is dissolved in a certain amount of organic solvent or water, wherein the organic acid is one or more of pyromellitic acid, terephthalic acid, and phthalic acid; the concentration of the polybasic organic acid is 1~100 mM; (2) Add a certain amount of zinc salt ZnX a Dissolves in aqueous solution, where X = Cl - SO4 2- NO3 - CH3COO - CF3SO3 - ClO4 - One or more of the following, where a = 1~2; the zinc salt ZnX a Concentrations range from 0.1 to 6 M; (3) Other metal salts M b X c When dissolved in an aqueous solution, its X=Cl - SO4 2- NO3 - CH3COO - CF3SO3 - ClO4 - One or more of them, M=Bi 3+ Al 3+ Cu 2+ Fe 3+ Co 2+ Ni 2+ Pt 4+ Pd 2+ One or more of the following, b=1~2, c=2~4; the metal salt M b X c Concentrations range from 0.1 to 100 mM; (4) Add the solution from step (1) to the solution from step (3) and stir until a clear liquid is obtained; (5) Add the solution from step (2) to the clarified solution from step (4), and then add an appropriate amount of deionized water to adjust the composition of the solution to a specific range.

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