An aqueous zinc-ion battery electrolyte, its preparation method, and a zinc-ion battery

Abstract

The present invention discloses an aqueous zinc-ion battery electrolyte, a preparation method thereof, and a zinc-ion battery, relating to the technical field of secondary batteries. The aqueous zinc-ion battery electrolyte of the present invention comprises a solvent, a zinc salt, and a compounding additive, and the compounding additive comprises a first additive, a second additive, and a third additive; wherein, the first additive is at least one of small molecule carboxylates, small molecule phosphonates, and small molecule sulfonates; the second additive is a small molecule organic compound containing a polar functional group, and the polar functional group is at least one of a mercapto group, a carbon-sulfur double bond, a pyridine group, and a triazole group; the third additive is a high molecular compound, and the high molecular compound has at least one of a hydroxyl group, an ether group, and an amide group. By adding the compounding additive to the aqueous zinc-ion battery electrolyte, the generation of by-products on the surface of the metallic zinc negative electrode can be inhibited, the flatness of the negative electrode can be improved, and its cycle life can be prolonged.

Description

Technical Field

[0001] The present invention relates to the technical field of secondary batteries, and in particular, to an aqueous zinc-ion battery electrolyte, a preparation method thereof, and a zinc-ion battery. Background Art

[0002] As a sustainable electrochemical system using an aqueous electrolyte, the aqueous zinc-ion battery has attracted increasing attention in the energy storage battery industry in recent years due to its safety, environmental friendliness, and low cost. Compared with zinc-ion batteries (LIBs) using flammable organic electrolytes, the aqueous zinc battery has greatly solved the safety problem. Metal zinc is rich in source, cheap in price, has a low redox potential (-0.76 V vs. SHE), and a relatively high theoretical capacity (820 mAh / g), making it an excellent candidate for the negative electrode. Despite these advantages, the metal zinc negative electrode still has the problem of easy dendrite formation. In addition, the electrolyte will corrode the metal zinc negative electrode, and the formed electrochemically inert and irreversible by-products will accumulate on the surface of the metal zinc negative electrode, resulting in increased polarization and poor electrode surface uniformity, further reducing the battery performance. Therefore, it is urgent to develop a suitable solution to solve the problems of dendrite growth and corrosion of the metal zinc negative electrode. Among many solutions, adjusting the composition of the electrolyte is a low-cost and scalable method.

[0003] CN111900497A discloses an aqueous zinc-ion battery electrolyte and its application. The aqueous zinc-ion battery electrolyte disclosed therein contains solvent water, a high-concentration electrolyte salt, and a zinc salt; the high-concentration electrolyte salt is potassium bis(fluorosulfonyl)imide and / or potassium trifluoromethanesulfonate, and its molality is not less than 10 mol / kg. The above method is difficult to fundamentally reduce the by-products that continuously increase on the surface of the metal zinc negative electrode during cycling.

[0004] CN113948779A proposes a zinc-ion battery electrolyte containing an additive, a preparation method thereof, and a zinc-ion battery. The zinc-ion battery electrolyte disclosed therein contains an additive, an electrolyte salt, and a solvent; the additive will produce a precipitate as the pH value of the electrolyte increases, and the precipitate does not dissolve with the change of pH. When the electrolyte is applied to a battery, based on the change of the environmental pH at the interface between the electrode material and the electrolyte, an inorganic solid protective film can be formed on the surface of the electrode material to prevent the material from directly contacting the electrolyte, thereby avoiding the erosion and dissolution of the material by the electrolyte and improving the cycle stability of the positive and negative electrode materials. Although the above method forms a protective film and has a certain inhibitory effect on corrosion and dendrite growth, it still cannot avoid the phenomenon of by-products generated by corrosion during the initial cycling process, which has an adverse effect on the flatness of the protective film. The uneven deposition of metal zinc on the protective film will also lead to dendrite growth. In addition, as the battery operates, a thicker and thicker precipitate film will be generated on the electrode surface, resulting in increased battery polarization and affecting the cycle performance. Summary of the Invention

[0005] The main object of the present invention is to provide an aqueous zinc-ion battery electrolyte, a preparation method thereof, and a zinc-ion battery, so as to solve the problems in the prior art that the negative electrode of the aqueous zinc-ion battery is easily corroded by the electrolyte, the surface flatness is low, dendrites are easily formed, and the electrochemical performance is poor.

[0006] To achieve the above object, according to the first aspect of the present invention, an aqueous zinc-ion battery electrolyte is provided. The electrolyte includes a solvent, a zinc salt, and a compounding additive. The compounding additive includes a first additive, a second additive, and a third additive. Among them, the first additive is a small molecule organic acid salt, and the small molecule organic acid salt is at least one of a small molecule carboxylate, a small molecule phosphonate, and a small molecule sulfonate. The second additive is a small molecule organic compound containing a polar functional group, and the polar functional group is at least one of a mercapto group, a carbon-sulfur double bond, a pyridine group, a thiophene group, and a triazole group. The third additive is a polymer compound, and the polymer compound has at least one of a hydroxyl group, an ether group, and an amide group.

[0007] The first additive and the second additive can synergistically regulate the deposition-dissolution equilibrium of by-products such as basic zinc sulfate on the negative electrode surface, reduce its deposition amount, and have little influence on the acidity and alkalinity of the electrolyte, and will not corrode the negative electrode material. The first additive and the third additive can synergistically improve the problem that by-products are easily generated on the negative electrode surface. By adding the above compounding additive to the aqueous zinc-ion battery electrolyte, the problems that the negative electrode is easily corroded and the surface flatness is low can be effectively alleviated, which helps to improve the electrochemical performance of the aqueous zinc-ion battery.

[0008] Further, in the aqueous zinc-ion battery electrolyte, the concentration of the zinc salt is 0.5-4 mol / L; the concentration of the first additive is 0.05-0.4 mg / mL, the concentration of the second additive is 1-12 mg / mL, and the concentration of the third additive is 0.5-8 mg / mL.

[0009] Further, in the aqueous zinc-ion battery electrolyte, the concentration of the zinc salt is 1-3 mol / L; the concentration of the first additive is 0.05-0.4 mg / mL, the concentration of the second additive is 2-8 mg / mL, and the concentration of the third additive is 1-4 mg / mL.

[0010] Further, the mass ratio of the first additive to the second additive is 1:(20-30); and / or, the mass ratio of the first additive to the third additive is 1:(10-20).

[0011] Further, the small molecule organic acid salt is at least one of sodium ethylenediaminetetraacetate, sodium 2-hydroxyphosphonoacetate, sodium hydroxylethylidene diphosphonate, sodium aminotrimethylenephosphonate, sodium diethylenetriamine pentamethylenephosphonate, sodium ethylenediaminetetramethylenephosphonate, sodium C1-C9 alkylsulfonate, and sodium polydithiodipropanesulfonate; and / or, the small molecule organic compound containing a polar functional group is at least one of 2-mercaptopyridine, thiourea, vinylthiourea, thioacetamide, thiophene, and benzotriazole; and / or, the polymer compound is at least one of polyvinyl alcohol, polysaccharide, polyethylene glycol, and polyacrylamide.

[0012] Further, the number average molecular weight of the polymer compound is 1,000 - 90,000.

[0013] Further, the zinc salt is at least one of zinc sulfate, zinc acetate, zinc chloride, zinc nitrate, zinc trifluoromethanesulfonate, and zinc bis(trifluoromethylsulfonyl)imide; and the solvent is water.

[0014] According to the second aspect of the present invention, there is provided a method for preparing an aqueous zinc ion battery electrolyte according to the first aspect of the present invention. The preparation method is as follows: adding a zinc salt to a solvent, and then adding a compounding additive to obtain a transparent solution, which is the aqueous zinc ion battery electrolyte.

[0015] According to the third aspect of the present invention, there is provided a zinc ion battery, which includes a positive electrode plate, a negative electrode plate, a separator, and the aqueous zinc ion battery electrolyte according to the first aspect of the present invention.

[0016] Further, the above positive electrode plate includes a current collector, positive electrode active materials, a conductive agent, and a binder located on one or both sides of the current collector. The current collector is one of a titanium foil, a stainless steel mesh, a stainless steel foil, a graphite film, a carbon cloth, and a carbon paper; the negative electrode plate is a metal zinc sheet.

[0017] By applying the technical solution disclosed in the present invention, adding a compounding additive to the aqueous zinc ion battery electrolyte significantly improves the corrosion phenomenon on the surface of the negative electrode and the deposition phenomenon of by-products, and enhances the electrochemical performance of the zinc ion battery. The compounding additive is easily available and can be industrially applied. Description of the Drawings

[0018] Figure 1 It is a surface scanning electron microscope image of the metal zinc sheet before immersion;

[0019] Figure 2 It is a surface scanning electron microscope image of the metal zinc sheet immersed in the aqueous zinc ion battery electrolyte of Example 2 for 3 days;

[0020] Figure 3 It is a surface scanning electron microscope image of the metal zinc sheet immersed in the aqueous zinc ion battery electrolyte of Comparative Example 1 for 3 days;

[0021] Figure 4 It is the surface scanning electron microscope image of a metallic zinc sheet immersed in the electrolyte of the aqueous zinc-ion battery in Comparative Example 3 for 3 days;

[0022] Figure 5 It is the surface scanning electron microscope image of a metallic zinc sheet immersed in the electrolyte of the aqueous zinc-ion battery in Comparative Example 12 for 3 days;

[0023] Figure 6 It is the surface scanning electron microscope image of a metallic zinc sheet immersed in the electrolyte of the aqueous zinc-ion battery in Comparative Example 15 for 3 days. Detailed implementation manners

[0024] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be described clearly and completely below. For those not specified in the embodiments, they are carried out according to conventional conditions or the conditions recommended by the manufacturer. Those reagents or instruments not specified by the manufacturer can be obtained as conventional products available for purchase on the market.

[0025] As described in the background art of the present invention, in the existing aqueous zinc-ion batteries, water has high activity, and the metallic zinc negative electrode is easily corroded, resulting in an uneven surface of the negative electrode and prone to dendrite generation; in addition, the deposition of corrosion products will increase polarization and affect the electrochemical performance of the aqueous zinc-ion battery. To solve the above technical problems, in a typical implementation manner of the present invention, an electrolyte for an aqueous zinc-ion battery is provided. The electrolyte includes a solvent, a zinc salt, and a compounding additive. The compounding additive includes a first additive, a second additive, and a third additive; wherein, the first additive is a small molecule organic acid salt, and the small molecule organic acid salt is at least one of a small molecule carboxylate, a small molecule phosphonate, and a small molecule sulfonate; the second additive is a small molecule organic compound containing a polar functional group, and the polar functional group is at least one of a mercapto group, a carbon-sulfur double bond, a pyridine group, a thiophene group, and a triazole group; the third additive is a high molecular compound, and the high molecular compound has at least one of a hydroxyl group, an ether group, and an amide group.

[0026] The first additive can convert side reaction deposits on the surface of the metallic zinc anode, such as zinc basic sulfate and zinc oxide, into water-soluble complexes and enter the liquid phase. The second additive can undergo a coordination reaction with zinc ions in the liquid phase to form a more stable coordination solvation structure. The compounding of the two additives can reduce the content of side reaction deposits on the surface of the metallic zinc anode, reduce polarization, improve the flatness of the surface of the metallic zinc anode, and reduce the probability of dendrite growth. The third additive can adsorb on the surface of the metallic zinc anode to form a protective film, preventing side reactions caused by the electrolyte from occurring on the surface of metallic zinc, and improving the cycle stability of the aqueous zinc-ion battery. The compounding of the first additive and the third additive helps to inhibit the aggregation of deposits on the surface of the zinc anode, prevent fresh metallic zinc from being corroded by the electrolyte again, and improve the electrochemical performance of the aqueous zinc-ion battery. The compound additive composed of the above three additives can significantly reduce the corrosion rate of the metallic zinc anode, reduce the deposit content, improve the flatness of the metallic zinc anode, and improve the cycle stability of the aqueous zinc-ion battery.

[0027] In a preferred embodiment of the present invention, in the electrolyte of the aqueous zinc-ion battery, the concentration of the zinc salt is 0.5 - 4 mol / L; the concentration of the first additive is 0.05 - 0.4 mg / mL, the concentration of the second additive is 1 - 12 mg / mL, and the concentration of the third additive is 0.5 - 8 mg / mL.

[0028] Increasing the concentration of the zinc salt can provide more zinc ions and improve the ionic conductivity. However, too high a concentration of zinc ions will affect the viscosity of the electrolyte and reduce the ionic migration rate. In addition, the concentration of the zinc salt has a certain influence on the coordination reaction between the additive and the deposits on the surface of the metallic zinc anode. By making the above limitations on the concentration of the zinc salt and the first additive, the second additive, and the third additive, the electrochemical performance of the aqueous zinc-ion battery can be improved.

[0029] In a preferred embodiment of the present invention, in the electrolyte of the aqueous zinc-ion battery, the concentration of the zinc salt is 1 - 3 mol / L; the concentration of the first additive is 0.05 - 0.4 mg / mL, the concentration of the second additive is 2 - 8 mg / mL, and the concentration of the third additive is 1 - 4 mg / mL.

[0030] By making the above limitations on the concentration of each component in the electrolyte of the aqueous zinc-ion battery, the corrosion rate of metallic zinc is lower, its surface flatness is higher, and the aqueous zinc-ion battery composed of this electrolyte has higher cycle stability.

[0031] In a preferred embodiment of the present invention, the mass ratio of the first additive to the second additive is 1:(20 - 30); and / or, the mass ratio of the first additive to the third additive is 1:(10 - 20).

[0032] Further optimizing the mass ratio of the first additive to the second additive can enable their synergistic effect. On the one hand, it can remove by-products such as basic zinc sulfate and make zinc ions re-enter the aqueous solution. On the other hand, these zinc ions can stably exist in the solution instead of redepositing and aggregating near metallic zinc, which helps reduce polarization and improve the flatness of the metallic zinc negative electrode. Further optimizing the mass ratio of the first additive to the third additive can reduce the amount of side reaction products and form a uniform protective film on the exposed surface of metallic zinc, significantly enhancing the long-cycle stability and cycle life of the metallic zinc negative electrode.

[0033] In a preferred embodiment of the present invention, the small molecule organic acid salt is at least one of sodium ethylenediaminetetraacetate, sodium 2-hydroxyphosphonoacetate, sodium hydroxyethanediphosphonate, sodium aminotrimethylenephosphonate, sodium diethylenetriaminepenta(methylene phosphonate), sodium ethylenediaminetetramethylenephosphonate, sodium C1-C9 alkyl sulfonate, sodium polydithiopropanesulfonate; and / or, the small molecule organic compound containing polar functional groups is at least one of 2-mercaptopyridine, thiourea, vinylthiourea, thioacetamide, thiophene, benzotriazole; and / or, the high molecular compound is at least one of polyvinyl alcohol, polysaccharide, polyethylene glycol, polyacrylamide, and the polysaccharide includes cellulose materials such as sodium carboxymethylcellulose.

[0034] The complex formed by the above small molecule organic acid salt and zinc ions has high stability and certain solubility; the above small molecule organic compound containing polar functional groups has a stronger coordination effect with zinc ions, which can stabilize zinc ions near the metallic zinc negative electrode and reduce the probability of forming precipitates such as basic zinc sulfate due to local changes in zinc ion concentration; the above high molecular compound can form an adsorption film on the surface of metallic zinc, effectively reducing the activity of water at the interface and slowing down the metal corrosion rate.

[0035] In a preferred embodiment of the present invention, the number average molecular weight of the high molecular compound is 1000 - 90000.

[0036] The number average molecular weight of the high molecular compound is higher than 1000, and it is easy to form a film; the number average molecular weight of the high molecular compound is not higher than 90000, and the steric hindrance generated after it adsorbs and forms a film on the surface of the metallic zinc negative electrode is relatively small, which helps reduce the overpotential of the aqueous zinc ion battery and further improve the cycle stability of the aqueous zinc ion battery.

[0037] In a preferred embodiment of the present invention, the first additive is at least one of sodium ethylenediaminetetraacetate, sodium hydroxyethanediphosphonate, sodium polydithiopropanesulfonate, the second additive is at least one of thiophene, benzotriazole, 2-mercaptopyridine, and the third additive is at least one of sodium carboxymethylcellulose, polyacrylamide, polyethylene glycol.

[0038] When the types of the first additive, the second additive, and the third additive meet the above limitations, the symmetric battery assembled from the aqueous zinc-ion battery electrolyte has a current density of 0.5 mA / cm 2 , and the cycle life measured under the condition of a cycle capacity of 0.5 mAh / cm 2 can exceed 900 h.

[0039] In a preferred embodiment of the present invention, the first additive is at least one of sodium ethylenediaminetetraacetate, sodium hydroxyethyldiphosphonate, and sodium polydithiopropanesulfonate, the second additive is 2-mercaptopyridine, and the third additive is at least one of sodium carboxymethyl cellulose, polyacrylamide, and polyethylene glycol; in addition, when the third additive is sodium carboxymethyl cellulose, its number average molecular weight is 50,000 - 90,000, when the third additive is polyacrylamide, its number average molecular weight is 8,000 - 60,000, and when the third additive is polyethylene glycol, its number average molecular weight is 1,000 - 60,000.

[0040] When the types of the three additives meet the above limitations, the symmetric battery assembled from the aqueous zinc-ion battery electrolyte has a current density of 0.5 mA / cm 2 , and the cycle life measured under the condition of a cycle capacity of 0.5 mAh / cm 2 can reach 930 h, having excellent cycle stability and being suitable for industrial application.

[0041] Typical but not limiting, the zinc salt is at least one of zinc sulfate, zinc acetate, zinc chloride, zinc nitrate, zinc trifluoromethanesulfonate, zinc bis(trifluoromethylsulfonyl)imide, or zinc tetrafluoroborate; the solvent is water. The preparation methods of the above zinc salts are relatively mature, with low cost and easy to obtain.

[0042] In another typical embodiment of the present invention, a preparation method of the aqueous zinc-ion battery electrolyte in the above embodiment is provided. The preparation method is: adding a zinc salt to a solvent, and then adding a compound additive to obtain a transparent solution, which is the aqueous zinc-ion battery electrolyte. Optionally, during the preparation process, it can be mixed evenly by stirring, or it can be mixed evenly by ultrasonic treatment. In addition, the zinc salt can also be added to the solvent simultaneously with the compound additive, or added to the solvent after the compound additive.

[0043] In yet another typical embodiment of the present invention, a zinc-ion battery is provided. The zinc-ion battery includes a positive electrode plate, a negative electrode plate, a separator, and the aqueous zinc-ion battery electrolyte in the above embodiment.

[0044] Typical rather than limiting, the positive electrode plate in the above embodiments includes a current collector, positive electrode active material, conductive agent, and binder located on one or both sides of the current collector. The current collector is one of titanium foil, stainless steel mesh, stainless steel foil, graphite film, carbon cloth, and carbon paper; the negative electrode plate is a metal zinc sheet.

[0045] The following further describes the present application in detail with specific embodiments, and these embodiments should not be construed as limiting the scope claimed by the present application.

[0046] Information on some components in the examples and comparative examples is as follows:

[0047] First additive: sodium ethylenediaminetetraacetate (EDTA-4Na), tetrasodium hydroxyethylethylenediphosphonate (HEDP-4Na), sodium bis(propylsulfonyl) disulfide (SPS);

[0048] Second additive: thiophene, benzotriazole (BTA), 2-mercaptopyridine (2-MP);

[0049] Third additive: sodium carboxymethyl cellulose (CMC-Na, number average molecular weight of 90,000), polyacrylamide (PAM, number average molecular weight of 40,000), polyethylene glycol (PEG, number average molecular weight of 2,000).

[0050] Examples 1-7

[0051] Examples 1-7 are examples of the aqueous zinc ion battery electrolyte of the present invention. The preparation methods of Examples 1-7 are as follows: Add zinc sulfate, a zinc salt, to water as a solvent, and then add the first additive, the second additive, and the third additive to obtain a mixed solution. Stir until a homogeneous and transparent solution is formed to obtain the aqueous zinc ion battery electrolyte described in Examples 1-7. The specific formulations of Examples 1-7 are shown in Table 1.

[0052] Performance testing

[0053] (1) Surface morphology effect: Immerse a metal zinc sheet in the aqueous zinc ion battery electrolyte of Examples 1-7 for 3 days, and observe its surface morphology. Different symbols are used to represent different surface morphologies: ◎, the surface is flat and good without obvious by-products; △, the surface flatness is average and there are a small amount of by-products; ×, the surface flatness is very poor and there are a large number of by-products.

[0054] (2) Assemble the aqueous zinc ion battery electrolytes in Examples 1-7 into a symmetric battery (the positive and negative electrode materials are both metal zinc) for charge and discharge testing. The current density is 0.5 mA / cm 2 , and the cycle capacity is 0.5 mAh / cm 2 , and test the cycle life and overpotential of the battery.

[0055] The test results of the surface topography effect and the electrochemical performance of the battery are recorded in Table 1.

[0056] Table 1

[0057]

[0058] From the above test results, it can be seen that adding the first additive, the second additive, and the third additive described in the present invention to the aqueous zinc-ion battery electrolyte can significantly improve the surface topography of the metallic zinc sheet. Figure 1 It is the surface scanning electron microscope image of the metallic zinc sheet before immersion. Figure 2 It is the surface scanning electron microscope image of the metallic zinc sheet immersed in the aqueous zinc-ion battery electrolyte of Example 2 for 3 days. As can be seen from the figure, its surface is extremely flat. Therefore, it is difficult to form dendrites, has a relatively high cycle life, which can reach more than 900 h, and its overpotential is small, indicating that there are fewer by-products on the surface of the metallic zinc. In addition, from the above test results, it can be seen that when the first additive is at least one of sodium ethylenediaminetetraacetate, sodium hydroxyethyldiphosphonate, and sodium polydisulfide propane sulfonate, the second additive is 2-mercaptopyridine, and the third additive is at least one of sodium carboxymethyl cellulose, polyacrylamide, and polyethylene glycol, the cycle life of the battery can reach more than 930 h, having excellent cycle stability and being suitable for application in zinc-ion batteries.

[0059] Examples 8-13

[0060] Examples 8-13 are examples of the aqueous zinc-ion battery electrolyte of the present invention. Their preparation methods are the same as those of Example 2, and the difference from Example 2 is only that the concentrations of each component are different, as shown in Table 2 specifically.

[0061] The performance test methods of Examples 8-13 are the same as the above methods, and the test results are shown in Table 2.

[0062] Table 2

[0063]

[0064] Comparing the test results of Comparative Example 1, Examples 8-9 and Examples 10-11, it can be found that when the mass ratio of the first additive to the second additive is 1:(20-30) and the mass ratio of the first additive to the third additive is 1:(10-20), the surface morphology of metallic zinc after immersion in the above aqueous zinc-ion battery electrolyte is the best, and it has a relatively high cycle life, which can reach more than 900 h. Comparing the test results of Comparative Example 1, Examples 8-11 and Examples 12-13, it can be found that in the aqueous zinc-ion battery electrolyte, the concentration of zinc salt is 1-3 mol / L; when the concentration of the first additive is 0.05-0.4 mg / mL, the concentration of the second additive is 2-8 mg / mL, and the concentration of the third additive is 1-4 mg / mL, the cycle life of the symmetric battery is relatively higher, all of which can reach more than 750 h. That is to say, the above electrolyte is more suitable for application in aqueous zinc-ion batteries, broadening the application field of zinc-ion batteries.

[0065] Comparative Examples 1-16

[0066] Comparative Examples 1-16 are aqueous zinc-ion battery electrolytes, and their preparation methods are the same as those of Example 2. The difference from Example 2 is only that the types and concentrations of additives are different, as shown in Table 3 specifically.

[0067] The performance test methods of Comparative Examples 1-16 are the same as the above test methods, and the test results are shown in Table 3.

[0068] Table 3

[0069]

[0070] From the above test results, it can be seen that in the aqueous zinc-ion battery electrolytes of Comparative Examples 2-4, only the first additive is added in addition to the zinc salt. Compared with Comparative Example 1, its cycle life is significantly higher and the overpotential is relatively lower. This result shows that the first additive helps to remove the deposits on the surface of the metallic zinc sheet, but its improvement effect on the surface state of the metallic zinc sheet is limited, and when its addition amount is too large, the cycle life will instead decrease, probably because adding the first additive alone will further corrode the metallic zinc sheet. Figure 3 is the surface scanning electron microscope image of the metallic zinc sheet immersed in the aqueous zinc-ion battery electrolyte of Comparative Example 1 for 3 days. It can be seen from the figure that the surface corrosion phenomenon is relatively serious and the surface of the metallic zinc sheet is extremely uneven. Figure 4 is the surface scanning electron microscope image of the metallic zinc sheet immersed in the aqueous zinc-ion battery electrolyte of Comparative Example 3 for 3 days. It can be seen from the figure that the surface flatness of the metallic zinc sheet is still relatively low.

[0071] From the test results of Comparative Examples 5-7, it can be seen that in addition to zinc salts, adding only the second additive can also improve the cycle life. This is because the second additive can complex with zinc ions, improve the stability of zinc ions, and increasing the amount of the second additive can improve the cycle performance. However, when the amount of the second additive is too large, it is difficult to further improve its improvement effect.

[0072] From the test results of Comparative Examples 8-10, it can be seen that in addition to zinc salts, adding only the third additive also helps to improve the cycle performance. Because the polymer compound disclosed in the present invention has good film-forming properties and can adsorb on the surface of the metallic zinc negative electrode to form a protective film, preventing the metallic zinc sheet from being further corroded by the electrolyte. However, it brings a large steric hindrance, resulting in a significant increase in battery polarization, and it increases significantly with the increase of the addition amount, ultimately leading to excessive battery polarization and reducing the cycle life.

[0073] From the test results of Comparative Examples 11-13, it can be seen that by adding the first additive and the second additive, the cycle life of the battery can be significantly improved, indicating that they have a synergistic effect. They not only remove the original oxides on the surface of the metallic zinc negative electrode and the by-product basic zinc sulfate formed due to side reactions, but also stabilize the solvation structure of zinc ions, slowing down the rate of re-formation of basic zinc sulfate to a certain extent, ultimately reducing battery polarization and extending the cycle life of the battery; in addition, the second additive may have a certain adsorption effect on the electrode surface, which also helps to slow down the corrosion rate. Figure 5 FIG. is the surface scanning electron microscope image of the metallic zinc sheet immersed in the electrolyte of the aqueous zinc-ion battery of Comparative Example 12 for 3 days. It can be seen from the figure that its surface flatness is relatively high.

[0074] From the test results of Comparative Examples 14-16, it can be seen that the first additive and the third additive also have a synergistic effect. After the by-products on the surface of the metallic zinc sheet are removed, the third additive can adsorb on the exposed surface of the metallic zinc sheet to prevent it from being corroded again, thereby improving its cycle life. However, when the amount of the third additive is further increased, the steric hindrance on the surface of the metallic zinc sheet increases, resulting in an increase in battery polarization, which will instead reduce the cycle life of the battery. Figure 6 FIG. is the surface scanning electron microscope image of the metallic zinc sheet immersed in the electrolyte of the aqueous zinc-ion battery of Comparative Example 15 for 3 days. It can be seen from the figure that adding the first additive and the third additive simultaneously in the aqueous zinc-ion battery electrolyte can significantly alleviate the corrosion phenomenon on the surface of the zinc sheet and improve the flatness of the metallic zinc sheet.

[0075] The above are only the preferred embodiments of the present invention and are not used to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. An aqueous zinc-ion battery electrolyte, characterized in that, It includes a solvent, a zinc salt and a compound additive. The compound additive includes a first additive, a second additive and a third additive; the first additive is a small molecule organic acid salt, and the small molecule organic acid salt is at least one of small molecule carboxylate, small molecule phosphonate and small molecule sulfonate; the second additive is a small molecule organic compound containing a polar functional group, and the polar functional group is at least one of a mercapto group, a carbon-sulfur double bond, a pyridine group, a thiophene group and a triazole group; the third additive is a high molecular compound, and the high molecular compound has at least one of a hydroxyl group, an ether group and an amide group; in the aqueous zinc ion battery electrolyte, the concentration of the zinc salt is 0.5 - 4 mol / L; the concentration of the first additive is 0.05 - 0.4 mg / mL, the concentration of the second additive is 1 - 12 mg / mL, and the concentration of the third additive is 0.5 - 8 mg / mL.

2. The aqueous zinc-ion battery electrolyte according to claim 1, wherein In the aqueous zinc ion battery electrolyte, the concentration of the zinc salt is 1 - 3 mol / L; the concentration of the first additive is 0.05 - 0.4 mg / mL, the concentration of the second additive is 2 - 8 mg / mL, and the concentration of the third additive is 1 - 4 mg / mL.

3. The aqueous zinc ion battery electrolyte according to claim 1 or 2, characterized in that, The mass ratio of the first additive to the second additive is 1:(20 - 30); and / or, the mass ratio of the first additive to the third additive is 1:(10 - 20).

4. The aqueous zinc-ion battery electrolyte according to claim 1, wherein The small molecule organic acid salt is at least one of sodium ethylenediaminetetraacetate, sodium 2-hydroxyphosphonoacetate, sodium hydroxyethyldiphosphonate, sodium aminotrimethylenephosphonate, sodium diethylenetriaminepenta(methylene phosphonate), sodium ethylenediaminetetramethylenephosphonate, sodium C1-C9 alkyl sulfonate, sodium polydithiopropanesulfonate; and / or, the small molecule organic compound containing a polar functional group is at least one of 2-mercaptopyridine, thiourea, vinylthiourea, thioacetamide, thiophene, benzotriazole; and / or, the high molecular compound is at least one of polyvinyl alcohol, polysaccharide, polyethylene glycol, polyacrylamide.

5. The aqueous zinc-ion battery electrolyte according to claim 1, characterized in that, The number average molecular weight of the high molecular compound is 1000 - 90000.

6. The aqueous zinc-ion battery electrolyte according to claim 1, wherein The zinc salt is at least one of zinc sulfate, zinc acetate, zinc chloride, zinc nitrate, zinc trifluoromethanesulfonate, zinc bis(trifluoromethylsulfonyl)imide; the solvent is water.

7. A method for preparing an aqueous zinc-ion battery electrolyte according to any one of claims 1 to 6, characterized in that, The preparation method is: adding the zinc salt into the solvent, and then adding the compound additive to obtain a transparent solution, which is the aqueous zinc ion battery electrolyte.

8. A zinc-ion battery, characterized in that, It includes a positive electrode plate, a negative electrode plate, a separator and an electrolyte, and the electrolyte is the aqueous zinc ion battery electrolyte according to any one of claims 1 to 6.

9. The zinc ion battery according to claim 8, characterized in that, The positive electrode plate includes a current collector, a positive electrode active material, a conductive agent and a binder. The current collector is one of a titanium foil, a stainless steel mesh, a stainless steel foil, a graphite film, a carbon cloth and a carbon paper; the negative electrode plate is a metal zinc sheet.

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