Preparation method of electrolyte and application of electrolyte in zinc-sulfur secondary battery

Abstract

The invention belongs to the technical field of aqueous secondary batteries, and particularly relates to a preparation method of an electrolyte and application of the electrolyte in a zinc-sulfur secondary battery, the electrolyte is composed of ultrapure water, an amide organic solvent, a soluble zinc salt electrolyte and an iodine-containing additive; wherein the iodine elementary substance or zinc iodide of the iodine-containing additive can serve as a redox medium to promote electrochemical oxidation of ZnS in the charging process of the zinc-sulfur secondary battery; the mixed system of the amide organic solvent and the ultrapure water is adopted, so that the wettability of the sulfur electrode can be effectively improved, the sulfur conversion reaction kinetics can be improved, the water activity in the electrolyte can be reduced, the hydrogen evolution side reaction can be inhibited, the dendritic crystal formation of the zinc metal negative electrode can be prevented, and the cycling stability of the zinc-sulfur secondary battery can be remarkably enhanced; the electrolyte provided by the invention is low in cost, efficient and environment-friendly, and has important significance on large-scale application of high-performance zinc-sulfur secondary batteries.

Description

Technical Field

[0001] The present invention belongs to the technical field of aqueous secondary batteries, and particularly relates to a method for preparing an electrolyte and application of the electrolyte in zinc-sulfur secondary batteries. Background Art

[0002] Aqueous batteries are a type of battery that uses water as the main electrolyte or reaction product. They use the chemical properties of water to store and release energy through electrochemical reactions. They have the advantages of high safety, environmental friendliness, high conductivity and low cost. They are widely used in new energy vehicles, consumer electronic devices and energy storage systems. The electrochemical reaction process of aqueous batteries is complex, and the electrolyte and electrode materials are the key factors that determine their performance. Zinc-ion batteries are a new type of secondary aqueous battery developed in recent years. They have the advantages of high energy density, high power density, efficient and safe discharge process, non-toxic and cheap battery materials, and simple preparation process. They have high application value and development prospects in fields such as large-scale energy storage.

[0003] The positive electrode is a key component that determines the energy density of aqueous zinc-ion batteries. Since sulfur is an abundant, inexpensive, and readily available resource on Earth, and possesses an extremely high theoretical capacity (1675 mAh / g), zinc-sulfur secondary batteries are considered a key candidate for next-generation energy storage devices due to their affordability, non-toxicity, environmental friendliness, and non-flammability. However, zinc-sulfur secondary batteries face numerous challenges in practical applications, including poor electrode wettability of the positive electrode sulfur, slow solid-solid conversion reaction kinetics, severe hydrogen evolution side reactions at the negative electrode, and zinc dendrite growth. Summary of the Invention

[0004] In response to the problems existing in the prior art, the present invention provides a method for preparing an electrolyte and its application in a zinc-sulfur secondary battery. The electrolyte is prepared by adding an iodine-containing additive and a soluble zinc salt electrolyte to a mixed solution system of an amide organic solvent and ultrapure water as the electrolyte solvent. The electrolyte is applied to a zinc-sulfur secondary battery to improve the wettability of the battery's positive sulfur electrode, inhibit the hydrogen evolution side reaction at the negative electrode, prevent the formation of dendrites of the negative zinc metal, and improve the battery life.

[0005] To solve the above problems, the present invention provides a method for preparing an electrolyte and its application in a zinc-sulfur secondary battery. The electrolyte is prepared from ultrapure water, an amide organic solvent, a soluble zinc salt electrolyte, and an iodine-containing additive. The method for preparing the electrolyte comprises the following steps: S1. Mixing an amide organic solvent with ultrapure water, and ultrasonically dispersing the mixture until uniform, to obtain an electrolyte solvent; S2. Add the iodine-containing additive to the electrolyte solvent described in S1, disperse it by ultrasonication until it is completely dissolved, then add the soluble zinc salt electrolyte, continue ultrasonic dispersion, and obtain the electrolyte after the electrolyte is completely dissolved.

[0006] Preferably, the mixing volume ratio of the amide organic solvent and ultrapure water in S1 is 1-5:1-20; the ultrasonic dispersion time is 10-60 min, and the temperature is 20-40°C.

[0007] Preferably, the ultrasonic dispersion in S2 is carried out for 10 to 60 minutes at a temperature of 20 to 40°C.

[0008] Preferably, the concentration of the iodine-containing additive in the electrolyte is 0.1-1 mol / L, and the concentration of the soluble zinc salt electrolyte is 0.1-10 mol / L.

[0009] Preferably, the amide organic solvent is one or a combination of two or more of formamide, acetamide, N-methylformamide, N-methylacetamide, N-ethylacetamide, N-ethylformamide, N,N-dimethylformamide, N,N-dimethylacetamide, N,N-dimethylpropionamide, N-methylpyrrolidone, N-ethylpyrrolidone, N-propylpyrrolidone, N-butylpyrrolidone and hexamethylphosphoramide in any volume ratio.

[0010] Preferably, the iodine-containing additive is elemental iodine or zinc iodide.

[0011] Preferably, the soluble zinc salt is one or a combination of two or more of zinc sulfate, zinc chloride, zinc nitrate, zinc acetate, zinc perchlorate, zinc gluconate, zinc trifluoromethanesulfonate and zinc bistrifluoromethanesulfonyl imide in any mass ratio.

[0012] The electrolyte is applied to zinc-sulfur secondary batteries, which can significantly improve the electrochemical performance of the zinc-sulfur secondary batteries. By introducing elemental iodine or zinc iodide, it can act as a redox medium to promote the electrochemical oxidation of ZnS during the charging process of the zinc-sulfur battery. The use of a mixed system of amide organic solvents and ultrapure water can effectively improve the wettability of the sulfur electrode and enhance the kinetics of the sulfur conversion reaction. At the same time, it can also reduce the water activity in the electrolyte, inhibit the occurrence of hydrogen evolution side reactions, and prevent the formation of dendrites at the zinc metal negative electrode, thereby significantly enhancing the cycle stability of the zinc-sulfur secondary battery.

[0013] Preferably, the positive electrode of the zinc-sulfur secondary battery is a sulfur / carbon composite material, and the negative electrode is a zinc foil. The specific preparation method of the battery is as follows: S1. Treatment of zinc foil: Cut zinc foil with a thickness of 10-150 μm into circular electrodes with a diameter of 12 mm and place them in an ethanol solution for ultrasonic cleaning for 30 min. Rinse them with deionized water and dry them in a forced air oven at 60°C. Seal them for later use. S2. Treatment of sulfur / carbon composite materials: Sulfur powder, conductive carbon black, polytetrafluoroethylene (PTFE) binder, and isopropyl alcohol solvent were mixed in a ratio of 7:2:1:3 to prepare a slurry. The slurry was then coated on the surface of the current collector, dried at 60°C, and cut into circular electrodes with a diameter of 10 mm. This was the positive electrode material for the zinc-sulfur secondary battery. S3. Select glass fiber, non-woven fabric or proton exchange membrane as the battery separator; S4. Battery assembly: Place the components in the order of positive electrode shell, sulfur / carbon composite material, diaphragm, electrolyte, zinc foil, gasket, shrapnel, and negative electrode shell for assembly. Finally, use a battery packaging machine to package the battery to obtain the required zinc-sulfur secondary battery.

[0014] In the preparation method of the zinc-sulfur secondary battery of the present invention, in actual application, the thickness and size of the zinc foil of the negative electrode material and the size of the circular electrode piece of the positive electrode material can be adjusted according to the actual required battery specifications.

[0015] Compared with the prior art, the technical solution of the present invention has the following beneficial effects: (1) The technical solution of the present invention uses a mixed system of an amide organic solvent and water as an electrolyte solvent, introduces an iodine-containing additive and a soluble zinc salt electrolyte, and prepares the resulting electrolyte for use in zinc-sulfur secondary batteries. This can effectively improve the wettability of the sulfur electrode of the zinc-sulfur secondary battery, accelerate the zinc ion transport at the electrode interface, thereby improving the sulfur conversion reaction kinetics and reducing the charge and discharge polarization of the zinc-sulfur secondary battery; the amide organic molecules interact with the water molecules to form strong hydrogen bonds, which can reduce the number of active water molecules, thereby increasing the overpotential of the hydrogen evolution reaction, making it difficult for the hydrogen evolution reaction to occur within the normal operating voltage range; (2) In the technical solution of the present invention, the polar groups in the amide organic solvent react with the zinc ion (Zn² + ) interaction, partially replacing Zn² + Solvation of water molecules in the sheath, thereby regulating Zn² + It can also adsorb on the surface of the zinc metal anode to form a uniform protective layer, enhancing the stability of the electrode-electrolyte interface, thereby helping to achieve uniform zinc deposition and avoiding the uncontrolled growth of zinc dendrites caused by local high current density. (3) The technical solution of the present invention introduces iodine or zinc iodide additives into the electrolyte. During the charging process of the zinc-sulfur secondary battery, I - / I3 - The electrode couple can act as a redox medium to promote the oxidation of ZnS. First, the iodide ions I - Electrochemical oxidation occurs to generate I3 - , then I3 -It will react chemically with ZnS to generate I - and S; (4) The specific capacity, rate and polarization of zinc-sulfur secondary batteries are key parameters that affect their performance. They are interrelated and have an important impact on the overall performance of the battery. The electrolyte of the present invention is applied to zinc-sulfur secondary batteries, which can improve the electrolyte's wetting performance on the electrodes and expand the battery's discharge specific capacity. During the battery charge and discharge process, the electrode potential deviates less from the equilibrium potential, has smaller polarization and higher energy conversion efficiency, and good rate performance can achieve large current charge and discharge, and the battery has a large number of cycles and a long service life.

[0016] The technical solution of the present invention is further described below in conjunction with specific embodiments and drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 The electrolytes prepared in Examples 1 to 3 and Comparative Example 1 were used in zinc-sulfur secondary batteries, and the specific capacity change curve of the battery at 0.1C was obtained; Figure 2 The electrolytes prepared in Example 4, Example 5, and Example 5.1 were used in zinc-sulfur secondary batteries, and the specific capacity change curve of the battery at 0.1C; Figure 3 The electrolytes prepared in Example 4, Example 5, and Example 5.1 are used in zinc-sulfur secondary batteries, showing the relationship between the specific capacity and the number of cycles at 0.1-2C. Figure 4 The electrolytes prepared in Example 4, Example 5, and Example 5.1 were used in zinc-sulfur secondary batteries, and the cycle number of the batteries at 2C was measured; Figure 5 The specific capacity change curve of the battery at 0.1C is shown for using the electrolytes prepared in Example 6, Example 7, and Examples 7.1 to 7.4 in a zinc-sulfur secondary battery. DETAILED DESCRIPTION

[0018] Example 1 A method for preparing an electrolyte, wherein the electrolyte is prepared from ultrapure water, an organic solvent of N,N-dimethylformamide (DMF), zinc acetate, and zinc iodide. The preparation method is as follows: S1. Mix N,N-dimethylformamide (DMF) organic solvent and ultrapure water in a volume ratio of 2:8, and ultrasonically disperse at 20°C for 10 minutes to obtain an electrolyte solvent after uniform dispersion; S2. Add zinc iodide to the electrolyte solvent described in S1, ultrasonically disperse it at 20°C for 15 minutes until it is completely dissolved, then add zinc acetate, and continue ultrasonically dispersing it for 30 minutes. After the zinc acetate is completely dissolved, the electrolyte is obtained, wherein the concentration of zinc iodide in the electrolyte is 0.2 mol / L, and the concentration of zinc acetate is 1 mol / L.

[0019] Example 2 Example 2 was set up under Example 1, and the DMF organic solvent in Example 1 was replaced by N-methylpyrrolidone (NMP) organic solvent. Other conditions were the same as those described in Example 1 to prepare an electrolyte.

[0020] Example 3 Example 3 was set up under Example 1, and the DMF organic solvent in Example 1 was replaced by formamide (FA) organic solvent. Other conditions were the same as those described in Example 1 to prepare an electrolyte.

[0021] Comparative Example 1 was set up under Examples 1 to 3. The preparation method and conditions of the electrolyte of Comparative Example 1 were the same as those described in Examples 1 to 3, except that the electrolyte of Comparative Example 1 did not contain an amide organic solvent component.

[0022] The four electrolytes prepared in Examples 1 to 3 and Comparative Example 1 were respectively applied to zinc-sulfur secondary batteries; the positive electrode of the zinc-sulfur secondary battery was a sulfur / carbon composite material, and the negative electrode was a zinc foil. The specific preparation method of the battery was as follows: S1. Treatment of zinc foil: Cut a 100 μm thick zinc foil into circular electrodes with a diameter of 12 mm and place them in an ethanol solution for ultrasonic cleaning for 30 min to remove oil and impurities on the surface. Rinse them with deionized water and dry them in a forced air oven at 60°C. Seal them and set aside. S2. Treatment of sulfur / carbon composite materials: Sulfur powder, conductive carbon black, PTFE binder, and isopropyl alcohol solvent were mixed in a ratio of 7:2:1:3 to prepare a slurry. The slurry was then coated on the surface of the current collector, dried at 60°C, and cut into circular electrode pieces with a diameter of 10 mm, which became the positive electrode material for the zinc-sulfur secondary battery. S3. Battery assembly: Place the components in the order of positive electrode shell, sulfur / carbon composite material, glass fiber, electrolyte, zinc foil, gasket, shrapnel, and negative electrode shell for assembly. Finally, use a battery packaging machine to package the battery to obtain the required zinc-sulfur secondary battery.

[0023] Among them, the electrolytes were respectively prepared in Examples 1 to 3 and Comparative Example 1, and finally four types of batteries were obtained. Charge and discharge tests were carried out under 0.1 C (rate) conditions. During the test, the charge and discharge polarization of the battery was calculated by the difference in the platform voltage of the charge and discharge curve. Generally, the smaller the polarization, the higher the discharge specific capacity; The test results are as follows Figure 1 As shown in the figure, it can be seen that at 0.1C, compared with Comparative Example 1, the electrolyte prepared by the technical solutions of Examples 1 to 3 contains an amide organic solvent, so the obtained zinc-sulfur secondary battery has a larger specific capacity; compared with Examples 2 to 3, the zinc-sulfur secondary battery prepared in Example 1 using DMF organic solvent has the largest specific capacity, followed by NMP and FA organic solvents; the larger specific capacity indicates that the electrolyte has better wettability on the sulfur electrode and has a higher active material utilization rate; it can be seen that when the organic solvent is DMF, the polarization of the zinc-sulfur secondary battery is the smallest, followed by NMP and FA organic solvents; therefore, when the amide organic solvent in the electrolyte is DMF, the electrode potential of the prepared zinc-sulfur secondary battery deviates less from the equilibrium potential during the charge and discharge process, the electrode reaction kinetics are faster, the utilization rate of the active material is higher, and the energy conversion efficiency is higher.

[0024] In the technical solution of the present invention, the prepared electrolyte is applied to zinc-sulfur secondary batteries. On the positive electrode of the battery, the introduction of amide organic solvent DMF can improve the wettability of the electrolyte to the sulfur electrode, thereby improving the interfacial charge transfer efficiency; it can also effectively block the direct contact between water and the sulfur electrode, inhibiting the by-products such as SO4 in the sulfur conversion process. 2- The generation of iodine can avoid the rapid attenuation of battery capacity; at the same time, the synergistic effect between amide organic solvents and iodine-containing additives can activate efficient polar I - / I3 ⁻ The catalytic electrode pair reduces the activation energy barrier of ZnS during the battery charging process, improves the conversion kinetics of sulfur, and releases a higher reversible capacity; on the negative electrode of the battery, there is a strong hydrogen bond interaction between the amide organic solvent and the water molecules, which can reduce the number of active water molecules, thereby increasing the hydrogen evolution overpotential, making it difficult for the hydrogen evolution reaction to occur within the normal operating voltage range; in addition, the polar groups in the amide organic solvent interact with Zn²⁺, partially replacing the water molecules in the Zn²⁺ solvation sheath, thereby regulating the solvation structure of Zn²⁺ and optimizing its deposition kinetics. At the same time, it can also be adsorbed on the surface of the zinc metal negative electrode to form a uniform protective layer, enhancing the stability of the electrode-electrolyte interface, thereby helping to achieve uniform zinc deposition and avoiding the uncontrolled growth of zinc dendrites caused by local high current density.

[0025] Example 4 A method for preparing an electrolyte, wherein the electrolyte is prepared from ultrapure water, an organic solvent of N,N-dimethylformamide (DMF), zinc acetate, and zinc iodide. The preparation method is as follows: S1. Mix N,N-dimethylformamide (DMF) organic solvent and ultrapure water in a volume ratio of 1:9, and ultrasonically disperse at 30°C for 10 minutes to obtain an electrolyte solvent after uniform dispersion; S2. Add zinc iodide to the electrolyte solvent described in S1, ultrasonically disperse it at 40°C for 15 minutes until it is completely dissolved, then add zinc acetate, and continue ultrasonically dispersing it for 15 minutes. After the zinc acetate is completely dissolved, the electrolyte is obtained. The concentration of zinc iodide in the electrolyte is 0.5 mol / L, and the concentration of zinc acetate is 0.5 mol / L.

[0026] Example 5 Example 5 was set up under Example 4, and the volume ratio of DMF organic solvent to ultrapure water was replaced with 2:8. Other conditions were the same as those described in Example 4 to prepare an electrolyte.

[0027] Example 5 was followed by setting Example 5.1, except that the volume ratio of DMF organic solvent to ultrapure water was changed to 3:7. Other conditions were the same as those described in Example 5, to prepare an electrolyte.

[0028] The three electrolytes prepared in Examples 4, 5, and 5.1 were respectively used in the preparation of zinc-sulfur secondary batteries to obtain three different batteries, wherein the positive electrode of the zinc-sulfur secondary battery was a sulfur / carbon composite material and the negative electrode was a zinc foil. The specific preparation and assembly methods are as follows: S1. Treatment of zinc foil: Cut a 150 μm thick zinc foil into circular electrodes with a diameter of 12 mm and place them in an ethanol solution for ultrasonic cleaning for 30 minutes to remove oil and impurities on the surface. Rinse them with deionized water and dry them in a forced air oven at 60°C. Seal them and set aside. S2. Treatment of sulfur / carbon composite materials: Sulfur powder, conductive carbon black, PTFE binder, and isopropyl alcohol solvent were mixed in a ratio of 7:2:1:3 to prepare a slurry. The slurry was then coated on the surface of the current collector, dried at 60°C, and cut into circular electrode pieces with a diameter of 10 mm, which became the positive electrode material for zinc-sulfur secondary batteries. S3. Battery assembly: Place the components in the order of positive electrode shell, sulfur / carbon composite material, proton exchange membrane, electrolyte, zinc foil, gasket, shrapnel, and negative electrode shell for assembly. Finally, use a battery packaging machine to package the battery to obtain the required zinc-sulfur secondary battery.

[0029] First, the three different batteries were charged and discharged under 0.1C conditions. The results are as follows: Figure 2 As shown in the figure, it can be seen that when the technical scheme of Example 5.1 is adopted, that is, when the DMF organic solvent and ultrapure water are mixed in a volume ratio of 3:7, the specific capacity of the battery is the largest and the charge and discharge polarization is the smallest. Secondly, when the technical schemes of Example 5 and Example 4 are adopted, that is, when the DMF organic solvent and ultrapure water are mixed in a volume ratio of 2:8 and 1:9, the specific capacity of the battery gradually decreases; this shows that in the electrolyte, a high concentration of amide organic solvents has a more significant improvement on the performance of aqueous zinc-sulfur secondary batteries.

[0030] Secondly, the three different batteries were tested for rate and cycle number at 0.1~2 C and 2C conditions respectively; Among them, the rate test results are as follows Figure 3 As shown in the figure, it can be seen that when the charge and discharge test is carried out under the conditions of 0.1~2C, when the technical solution of Example 5.1 is adopted, that is, when the DMF organic solvent and ultrapure water are mixed at a volume ratio of 3:7, the discharge specific capacity of the battery in the range of 0.1~0.2C is the highest compared with the technical solutions of Examples 4 and 5. This shows that a high concentration of amide organic solvents can make the zinc-sulfur secondary battery have better rate performance and can achieve large current charge and discharge, that is, fast charge and discharge; Among them, the cycle test results are as follows Figure 4 As shown in the figure, it can be seen that when the technical solution of Example 5.1 is adopted, that is, when the DMF organic solvent and ultrapure water are mixed in a volume ratio of 3:7, under 2C conditions, after 500 cycles, the battery has the highest capacity retention rate compared with the technical solutions of Examples 4 and 5. This shows that a high concentration of amide organic solvents can make the zinc-sulfur secondary battery have better cycle performance, better cycle stability, higher reliability in the repeated charge and discharge process, lower probability of failure during actual use, and longer battery life.

[0031] Example 6 A method for preparing an electrolyte, wherein the electrolyte is prepared from ultrapure water, N-methylpyrrolidone organic solvent, zinc sulfate and iodine element, and the preparation method is specifically as follows: S1, N-methylpyrrolidone organic solvent and ultrapure water are mixed in a volume ratio of 0.5:9.5, and ultrasonically dispersed at 40° C. for 15 min to obtain an electrolyte solvent after uniform dispersion; S2. Add iodine to the electrolyte solvent described in S1, ultrasonically disperse it at 40°C for 10 minutes until it is completely dissolved, then add zinc sulfate and continue ultrasonically dispersing it for 50 minutes. After the zinc sulfate is completely dissolved, the electrolyte is obtained; the concentration of iodine in the electrolyte is 1 mol / L, and that of zinc sulfate is 10 mol / L.

[0032] Example 7 Example 7 was set up under Example 6, and the zinc sulfate in Example 6 was replaced by zinc chloride. The remaining conditions were the same as those described in Example 6 to prepare an electrolyte.

[0033] Under Example 7, Examples 7.1, 7.2, 7.3, and 7.4 were set respectively, and the zinc chloride in Example 7 was replaced by zinc perchlorate, zinc nitrate, zinc trifluoromethanesulfonate, and zinc bistrifluoromethanesulfonyl imide respectively; the remaining conditions were the same as described in Example 7, and 4 different electrolytes were prepared respectively.

[0034] The six electrolytes prepared in Examples 6, 7, and 7.1, 7.2, 7.3, and 7.4 were respectively applied to the preparation of zinc-sulfur secondary batteries to obtain six different batteries, wherein the positive electrode of the zinc-sulfur secondary battery was a sulfur / carbon composite material and the negative electrode was a zinc foil. The specific preparation and assembly methods are as follows: S1. Treatment of zinc foil: Cut a 100 μm thick zinc foil into circular electrodes with a diameter of 12 mm and place them in an ethanol solution for ultrasonic cleaning for 30 min to remove oil and impurities on the surface. Rinse them with deionized water and dry them in a forced air oven at 60°C. Seal them for later use. S2. Treatment of sulfur / carbon composite materials: Sulfur powder, conductive carbon black, PTFE binder, and isopropyl alcohol solvent were mixed in a ratio of 7:2:1:3 to prepare a slurry. The slurry was then coated on the surface of the current collector, dried at 60°C, and cut into circular electrode pieces with a diameter of 10 mm, which became the positive electrode material for zinc-sulfur secondary batteries. S3. Battery assembly: Place the components in the order of positive electrode shell, sulfur / carbon composite material, non-woven fabric, electrolyte, zinc foil, gasket, shrapnel, and negative electrode shell for assembly. Finally, use a battery packaging machine to package the battery to obtain the required zinc-sulfur secondary battery.

[0035] The six batteries were charged and discharged at 0.1C. The results are as follows: Figure 5 As shown; As can be seen from the figure, when different soluble zinc salts are used as electrolytes, they all have a stable charge and discharge platform. The discharge specific capacity of the six different batteries is from high to low: zinc sulfate, zinc perchlorate, zinc trifluoromethanesulfonate, zinc nitrate, zinc chloride, and bistrifluoromethanesulfonyl imide zinc; Among them, the specific capacity of the electrolyte with zinc sulfate as the electrolyte is higher, and the specific capacity of the electrolyte with zinc bis(trifluoromethanesulfonylimide) as the electrolyte is lower. This is because the degree of dissociation of zinc salts is different. The interaction between the organic anions and zinc ions in zinc bis(trifluoromethanesulfonylimide) is stronger and not easy to dissociate, which makes the zinc ion conductivity of the electrolyte low, which is not conducive to the electrode reaction kinetics of the sulfur positive electrode and the zinc negative electrode, thereby reducing the specific capacity of the zinc-sulfur secondary battery; batteries with high specific capacity can significantly improve energy density, reduce battery size and weight, reduce material cost, and can extend cycle life and improve safety after optimized design.

[0036] Example 8 A method for preparing an electrolyte, wherein the electrolyte is prepared from ultrapure water, a mixed solution of N,N-dimethylformamide and N-methylpyrrolidone organic solvent, a mixture of zinc sulfate and zinc chloride, and elemental iodine. The preparation method is specifically as follows: S1. N,N-dimethylformamide and N-methylpyrrolidone organic solvent are mixed in a volume ratio of 3:2, the obtained mixed solution is mixed with ultrapure water in a volume ratio of 1:20, and ultrasonically dispersed at 40° C. for 10 minutes to obtain an electrolyte solvent after uniform dispersion; S2. Adding elemental iodine to the electrolyte solvent described in S1, ultrasonically dispersing it at 20° C. for 40 min until it is completely dissolved, adding a mixture of zinc sulfate and zinc chloride, and continuing ultrasonically dispersing it for 20 min, wherein the zinc sulfate and zinc chloride are mixed in a mass ratio of 5:2, and the electrolyte is obtained after the mixture of zinc sulfate and zinc chloride is completely dissolved; the concentration of elemental iodine in the electrolyte is 0.8 mol / L, and the concentration of the mixture of zinc sulfate and zinc chloride is 7 mol / L.

[0037] The electrolyte is applied to the preparation of zinc-sulfur secondary batteries, and the resulting batteries have good performance parameters.

[0038] Example 9 A method for preparing an electrolyte, wherein the electrolyte is prepared from ultrapure water, a mixed solution of N-ethylacetamide, N-ethylformamide, and an organic solvent of N,N-dimethylpropionamide, a mixture of zinc acetate, zinc perchlorate, and zinc gluconate, and zinc iodide. The preparation method is specifically as follows: S1, N-ethylacetamide, N-ethylformamide, and N,N-dimethylpropionamide were mixed in a volume ratio of 5:1:2, the obtained mixed solution was mixed with ultrapure water in a volume ratio of 4:1, and ultrasonically dispersed at 20° C. for 60 min to obtain an electrolyte solvent after uniform dispersion; S2. Add zinc iodide to the electrolyte solvent described in S1, and after complete dissolution by ultrasonic dispersion at 30°C for 50 min, add a mixture of zinc acetate, zinc perchlorate and zinc gluconate, wherein the zinc acetate, zinc perchlorate and zinc gluconate are mixed in a mass ratio of 7:3:4, and then continue ultrasonic dispersion for 10 min. After the mixture of zinc acetate, zinc perchlorate and zinc gluconate is completely dissolved, the electrolyte is obtained; the concentration of elemental iodine in the electrolyte is 0.3 mol / L, and the concentration of the mixture of zinc acetate, zinc perchlorate and zinc gluconate is 0.2 mol / L.

[0039] The electrolyte is applied to the preparation of zinc-sulfur secondary batteries, and the obtained batteries have a long service life.

[0040] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any way. Any simple modification, change and equivalent variation made to the above embodiment based on the essence of the invention technology shall still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A method for preparing an electrolyte, characterized in that: The steps include: S1. Mixing an amide organic solvent with ultrapure water, and ultrasonically dispersing the mixture until uniform, to obtain an electrolyte solvent; S2. Add the iodine-containing additive to the electrolyte solvent described in S1, perform ultrasonic dispersion until it is completely dissolved, then add the soluble zinc salt electrolyte, continue ultrasonic dispersion, and obtain the electrolyte after the electrolyte is completely dissolved.

2. The method for preparing the electrolyte according to claim 1, wherein: The mixing volume ratio of the amide organic solvent and ultrapure water in S1 is 1-5:1-20; the ultrasonic dispersion time is 10-60 minutes, and the temperature is 20-40°C.

3. The method for preparing the electrolyte according to claim 1, wherein: The ultrasonic dispersion in S2 is carried out for 10 to 60 minutes at a temperature of 20 to 40°C.

4. The method for preparing the electrolyte according to claim 1, wherein: The concentration of the iodine-containing additive in the electrolyte is 0.1-1 mol / L, and the concentration of the soluble zinc salt electrolyte is 0.1-10 mol / L.

5. The method for preparing the electrolyte according to claim 2, wherein: The amide organic solvent is one or a mixture of two or more of formamide, acetamide, N-methylformamide, N-methylacetamide, N-ethylacetamide, N-ethylformamide, N,N-dimethylformamide, N,N-dimethylacetamide, N,N-dimethylpropionamide, N-methylpyrrolidone, N-ethylpyrrolidone, N-propylpyrrolidone, N-butylpyrrolidone and hexamethylphosphoramide.

6. The method for preparing the electrolyte according to claim 4, wherein: The iodine-containing additive is elemental iodine or zinc iodide.

7. The method for preparing the electrolyte according to claim 4, wherein: The soluble zinc salt is one or a mixture of two or more of zinc sulfate, zinc chloride, zinc nitrate, zinc acetate, zinc perchlorate, zinc gluconate, zinc trifluoromethanesulfonate and zinc bistrifluoromethanesulfonyl imide.

8. Application of an electrolyte in a zinc-sulfur secondary battery, characterized in that: The electrolyte prepared by the method according to any one of claims 1 to 7 is applied to a zinc-sulfur secondary battery.

9. Use of the electrolyte according to claim 8 in a zinc-sulfur secondary battery, characterized in that: The positive electrode of the zinc-sulfur secondary battery is a sulfur / carbon composite material, and the negative electrode is a zinc foil. The preparation method of the battery comprises the following steps: S1. Treatment of zinc foil: Cut zinc foil with a thickness of 10-150 μm into circular electrodes with a diameter of 12 mm and place them in an ethanol solution for ultrasonic cleaning for 30 min. Rinse them with deionized water, dry them at 60°C, and seal them for later use. S2. Treatment of sulfur / carbon composite materials: Sulfur powder, conductive carbon black, polytetrafluoroethylene binder, and isopropyl alcohol solvent were mixed in a ratio of 7:2:1:3 to prepare a slurry. The mixture was then coated on the surface of the current collector, dried at 60°C, and cut into circular pole pieces with a diameter of 10 mm. This was the positive electrode material for the zinc-sulfur secondary battery. S3. Select glass fiber, non-woven fabric or proton exchange membrane as the battery separator; S4. Assembling the battery: placing the components in the order of positive electrode shell, sulfur / carbon composite material, separator, electrolyte, zinc foil, gasket, shrapnel, and negative electrode shell for assembly, and finally packaging the battery using a battery packaging machine to obtain the zinc-sulfur secondary battery.

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