Electrolyte for improving calendar aging of aqueous zinc metal battery and application of electrolyte

Abstract

The invention discloses an electrolyte for improving calendar aging of an aqueous zinc metal battery and application of the electrolyte. According to the preparation method of the electrolyte, acetate is introduced into an original zinc salt electrolyte so as to regulate and control a solvation structure in which anions participate in the electrolyte, meanwhile, generation of dead zinc and dendritic crystals in the circulation process is remarkably reduced, and then the capacity loss caused by aging of the zinc metal battery is effectively relieved. The method is simple in process and convenient to prepare, meets the green chemical requirement, and can be directly used for aqueous zinc metal batteries. The electrolyte can be prepared only by dissolving acetate with a certain concentration into the original zinc salt electrolyte under the condition of room temperature. When the obtained electrolyte is applied to the zinc metal battery, compared with the traditional electrolyte, the capacity loss is reduced by about 50 times at most. According to the method, the calendar life of the zinc metal battery is remarkably prolonged, and important theoretical support and technical guidance are provided for developing the high-performance and long-life zinc metal battery.

Description

Technical Field

[0001] The present invention belongs to the technical field related to zinc metal battery optimization, and more specifically, relates to a method for preparing an electrolyte for improving calendar aging of zinc metal batteries and its application. Background Art

[0002] As the demand for battery energy density in electric vehicles, portable devices, and energy storage devices continues to increase, researchers have gradually turned their attention to zinc metal, which has high theoretical capacity and good electrochemical stability, as anode materials. Zinc metal has a high theoretical capacity (820mAh g -1 ) and a low redox potential (-0.76V vs. SHE), showing great potential in the next generation of high energy density battery technology. Although zinc metal anode has significant advantages in cycle stability and energy density, its long-term stability still faces many challenges. In particular, during long-term open circuit storage (i.e., no charge and discharge state), the zinc metal anode will suffer from significant calendar aging effects. This process is usually accompanied by problems such as capacity decay and decreased battery efficiency, which seriously affects the service life and reliability of the battery. To solve this problem, it is particularly important to develop an electrolyte that improves the calendar aging of zinc metal batteries. Summary of the Invention

[0003] In view of the deficiencies and improvement needs in the existing technology, the calendar aging effect of the zinc metal negative electrode in the existing technology and the rapid generation rate of "dead zinc" and dendrites during the cycle are solved.

[0004] The technical solution of the present invention is an electrolyte for improving calendar aging of aqueous zinc metal batteries. The electrolyte is a mixed solution of acetate and one or more of zinc bromide, zinc chloride, zinc sulfate or zinc trifluoromethanesulfonate; the acetate is one or more of zinc acetate and ammonium acetate.

[0005] Furthermore, when the acetate is zinc acetate, the concentration is 1 to 7 mol / kg; when the acetate is ammonium acetate, the concentration is 1 to 20 mol / kg; when the acetate includes zinc acetate and ammonium acetate, the concentrations of zinc acetate and ammonium acetate are 1 to 10 mol / kg and 1 to 30 mol / kg, respectively, and the molar ratio of zinc acetate to ammonium acetate is in the range of 3:1 to 1:5.

[0006] Furthermore, when the electrolyte is a mixed solution of acetate and zinc bromide, the concentration of zinc bromide is 1 to 5 mol / kg;

[0007] When the electrolyte is a mixed solution of acetate and zinc chloride, the concentration of zinc chloride is 1 to 10 mol / kg;

[0008] When the electrolyte is a mixed solution of acetate and zinc sulfate, the concentration of zinc sulfate is 1 to 10 mol / kg;

[0009] When the electrolyte is a mixed solution of acetate and zinc trifluoromethanesulfonate, the concentration of zinc trifluoromethanesulfonate is 1 to 5 mol / kg.

[0010] Furthermore, when the electrolyte includes two or more of zinc bromide, zinc chloride, zinc sulfate or zinc trifluoromethanesulfonate, the zinc ion concentration is 1 to 30 mol / kg;

[0011] Furthermore, when the electrolyte is a mixed solution of acetate and multiple zinc salts, the acetate concentration is 1 to 40 mol / kg, and the zinc ion concentration is 1 to 30 mol / kg;

[0012] An aqueous zinc metal battery comprises a positive electrode, a negative electrode, a separator and the electrolyte of the present invention.

[0013] The present application introduces acetate into the electrolyte of a zinc metal battery to regulate the solvation structure in which anions participate, promotes the rapid migration and uniform deposition of zinc ions during the charge and discharge process, significantly reduces the formation of "dead zinc" and dendrites during the cycle, thereby reducing the uneven electroplating and specific surface area of zinc in the electrolyte, and effectively alleviates the capacity loss of the zinc metal battery during further static aging. The present application proposes a comprehensive strategy for improving the calendar cycle life of acetate electrolytes and non-acetate electrolytes, ensuring the comprehensiveness of the method, low cost and simple operation. The capacity loss caused by calendar aging of the non-acetate electrolyte improved by the present application is reduced by nearly 50 times. The method of the present application is applied to a Zn||ZnI2 full battery. In the absence of a negative electrode, under the test conditions of aging for 6 hours per cycle, the improved zinc metal battery is cycled 120 times and the capacity retention rate is still 96.17%. The present application uses Raman spectroscopy to characterize the solvation structure in which anions participate. Raman spectroscopy can accurately measure the vibration modes of molecules or ions in solution. These vibration modes are closely related to the solvation structure and have high accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 The graph is a graph showing the change in calendar aging capacity loss versus electroplating capacity in a Zn||Cu half-cell using the electrolyte in Comparative Example 1 and the electrolyte in Example 1.

[0015] Figure 2 The graph is a graph showing the change in calendar aging capacity loss versus electroplating capacity in a Zn||Cu half-cell using the electrolyte in Comparative Example 2 and the electrolyte in Example 2.

[0016] Figure 3The graph is a graph showing the change in calendar aging capacity loss versus electroplating capacity in a Zn||Cu half-cell using the electrolyte in Comparative Example 3 and the electrolyte in Example 3.

[0017] Figure 4 The zinc electroplating morphology was characterized by scanning electron microscopy using the electrolyte in Comparative Example 1 and the electrolyte in Example 1.

[0018] Figure 5 The zinc electroplating morphology was characterized by scanning electron microscopy using the electrolyte in Comparative Example 2 and the electrolyte in Example 2.

[0019] Figure 6 The zinc electroplating morphology was characterized by scanning electron microscopy using the electrolyte in Comparative Example 3 and the electrolyte in Example 3.

[0020] Figure 7 The zinc electroplating roughness was characterized by laser confocal microscopy using the electrolyte in Comparative Example 2 and the electrolyte in Example 2.

[0021] Figure 8 This is a solvation structure diagram obtained by Raman characterization using the electrolytes of Comparative Example 3 and Example 3.

[0022] Figure 9 This is a graph of discharge surface capacity-cycle number after aging of the full battery using the Zn||ZnI2 electrolyte of Comparative Example 3 and Implementation 3.

[0023] Specific example method

[0024] The present invention utilizes a mixed solution formed by dissolving a certain concentration of acetate in the original zinc salt electrolyte to regulate the solvation structure in which anions participate, thereby promoting the rapid migration and uniform deposition of zinc ions during the charge and discharge process, significantly reducing the generation of "dead zinc" and dendrites during the cycle process, thereby reducing the uneven electroplating and specific surface area of zinc in the electrolyte, and effectively alleviating the capacity loss of the zinc metal battery during further static aging.

[0025] The concentration of the added acetate is preferably 1 to 7 mol / kg;

[0026] For an electrolyte that is already acetate, the electrolyte preparation method includes introducing a quaternary ammonium salt containing acetate into the original electrolyte to increase the ion concentration of acetate in the electrolyte and change the solvation structure in which anions in the electrolyte participate;

[0027] Assembled into different types of aqueous zinc metal batteries, including a positive electrode, a negative electrode, a separator and the above-mentioned improved electrolyte.

[0028] Comparative Example 1

[0029] The test electrolyte was prepared by adding 2 mol of zinc bromide (ZnBr2) to 1 kg of deionized water. The mixture was stirred thoroughly until 2 mol of ZnBr2 was completely dissolved. The mixture was allowed to stand to obtain a ZnBr2 aqueous zinc metal electrolyte with a molar concentration of 2 m (m is the molar concentration, unit: mol / kg).

[0030] Comparative Example 2

[0031] The test electrolyte was prepared by adding 2 mol of zinc trifluoromethanesulfonate (ZnTf2) to 1 kg of deionized water. The mixture was stirred thoroughly until 2 mol of ZnTf2 was completely dissolved. After standing, the solution was obtained to obtain an aqueous zinc metal battery electrolyte with a molar concentration of 2 m ZnTf2.

[0032] Comparative Example 3

[0033] The test electrolyte was prepared by adding 1 mol of zinc acetate (ZnAc2) to 1 kg of deionized water, stirring thoroughly until 1 mol of ZnAc2 was completely dissolved. The mixture was allowed to stand to obtain an aqueous zinc metal battery electrolyte with a molar concentration of 1 M ZnAc2.

[0034] Example 1

[0035] Preparation of the test electrolyte: Preparation of the test electrolyte: Add 1 mol of ZnBr2 and 1 mol of zinc acetate (ZnAc2) to 1 kg of deionized water, stir thoroughly until 1 mol of ZnBr2 and 1 mol of ZnAc2 are completely dissolved, and then stand to obtain acetate-modified aqueous zinc metal battery electrolyte (containing 1M ZnBr2 and 1M ZnAc2);

[0036] Example 2

[0037] Test electrolyte configuration: Test electrolyte configuration: Add 1 mol of ZnTf2 and 1 mol of ZnAc2 to 1 kg of deionized water, stir thoroughly until 1 mol of ZnBr2 and 1 mol of ZnAc2 are completely dissolved, and then stand to obtain acetate-modified aqueous zinc metal battery electrolyte (containing 1 m ZnTf2 and 1 m ZnAc2)

[0038] Example 3

[0039] Test electrolyte configuration: Test electrolyte configuration: Add 2 mol of ZnAc2 and 3 mol of betaine (TAA) to 1 kg of deionized water, stir thoroughly until 2 mol of ZnAc2 and 3 mol of TAA are completely dissolved, and then stand to obtain a full acetate modified aqueous zinc metal battery electrolyte (containing 2m ZnAc2 and 3m TAA)

[0040] Example 1 and Comparative Example 1 were applied to a zinc-copper half-cell at 1 mA cm-2 The current density and 1, 2, 4, and 6 mAh cm -2 The electroplating capacity was tested by discharging, standing for 12 hours, and then charging. By adjusting the electroplating capacity, the difference in electroplating morphology was controlled, thereby affecting the capacity loss caused by aging. The capacity loss was calculated as the difference between the zinc deposition capacity during the discharge process and the zinc stripping capacity during the charging process. Figure 1 As shown in FIG, the electrolyte of this method can improve the capacity loss by 4.04 times. The electrolyte of Example 2 and Comparative Example 2 can improve the capacity loss by 49.28 times. Figure 2 As shown, the effect is significant; for the full acetate electrolyte, the electrolyte of Example 3 and Comparative Example 3 can also improve the capacity loss by 1.62 times, as shown in FIG. Figure 3 As shown. By the method designed in this application, the calendar aging behavior is significantly improved;

[0041] The electrolytes of Comparative Example 2 and Example 2 were applied to a zinc-copper electrolytic cell at 1 mA cm -2 Current density and 4 mAh cm -2 The electroplating capacity was electroplated on a copper substrate. The morphology after electroplating was characterized by scanning electron microscopy (SEM). Figure 4 As shown in the figure, the electroplated morphology of zinc metal is more compact and smooth when the electrolyte of Comparative Example 2 and Example 2 is used. Figure 5 As shown in the figure, this method can significantly improve the electroplating morphology of zinc metal. The roughness of the electroplated morphology was characterized using a laser confocal microscope. Figure 7 As shown in FIG. 2 , in which the capacity loss is higher, the electroplating roughness of the zinc metal is higher; whereas, in the comparative example 3 , in which the capacity loss is lower, the electroplating roughness of the zinc metal is lower. For the full acetate electrolyte, when the electrolytes of Example 3 and Comparative Example 3 are used, the electroplating morphology of the zinc metal is as follows: Figure 6 As shown, the electroplating morphology is smoother and more uniform by using the electrolyte of this method.

[0042] The electrolytes obtained in Comparative Example 3 and Example 3 were subjected to Raman spectroscopy characterization tests. The Raman detection wavenumber range was 800 cm -1 to 3600cm -1 , the laser wavelength is 532nm. The electrolyte obtained by using Example 3 contains more contact ion pair (CIP) solvation structures, such as Figure 8 This structure is believed to help promote uniform deposition of metal.

[0043] The above-mentioned Example 3 and Comparative Example 3 were applied to the assembly of a full-cell aqueous zinc metal battery: commercial zinc iodide powder, conductive carbon black and binder (PTFE) were mixed evenly at a ratio of 50:47:3 and added to anhydrous ethanol. After drying in a vacuum drying oven at 60°C for 2 hours, a positive electrode sheet was obtained. The positive electrode shell, positive electrode sheet, diaphragm, electrolyte, brass, gasket, shrapnel and brass foil were assembled in this order and compacted with a tablet press to obtain an aqueous zinc metal battery (in the form of a full-cell without a negative electrode). The assembled battery was subjected to an aging cycle test program cycle of constant current and constant voltage charging to 1.6V at 25°C - standing for 6 hours - discharging to 0.6V. The electrochemical properties of each battery are shown as follows: Figure 9 The Zn||ZnI2 full battery using the electrolyte of Example 3 maintained a capacity retention rate of 96.17% after 120 cycles, while the Zn||ZnI2 full battery of Comparative Example 3 could only cycle 50 times under the same conditions, with a capacity retention rate of 78.21%.

Claims

1. An electrolyte for improving calendar aging of aqueous zinc metal batteries, the electrolyte being a mixed solution of acetate and one or more of zinc bromide, zinc chloride, zinc sulfate, or zinc trifluoromethanesulfonate; the acetate being one or more of zinc acetate and ammonium acetate.

2. The electrolyte for improving calendar aging of aqueous zinc metal batteries according to claim 1, characterized in that: When the acetate is zinc acetate, the concentration is 1 to 7 mol / kg; when the acetate is ammonium acetate, the concentration is 1 to 20 mol / kg; when the acetate includes zinc acetate and ammonium acetate, the concentrations of zinc acetate and ammonium acetate are 1 to 10 mol / kg and 1 to 30 mol / kg respectively, and the molar ratio of zinc acetate to ammonium acetate is in the range of 3:1 to 1:

5.

3. The electrolyte for improving calendar aging of aqueous zinc metal batteries according to claim 1, characterized in that: When the electrolyte is a mixed solution of acetate and zinc bromide, the concentration of zinc bromide is 1 to 5 mol / kg.

4. The electrolyte for improving calendar aging of aqueous zinc metal batteries according to claim 1, characterized in that: When the electrolyte is a mixed solution of acetate and zinc chloride, the concentration of zinc chloride is 1 to 10 mol / kg.

5. The electrolyte for improving calendar aging of aqueous zinc metal batteries according to claim 1, characterized in that: When the electrolyte is a mixed solution of acetate and zinc sulfate, the concentration of zinc sulfate is 1 to 10 mol / kg.

6. The electrolyte for improving calendar aging of aqueous zinc metal batteries according to claim 1, characterized in that: When the electrolyte is a mixed solution of acetate and zinc trifluoromethanesulfonate, the concentration of zinc trifluoromethanesulfonate is 1 to 5 mol / kg.

7. The electrolyte for improving calendar aging of aqueous zinc metal batteries according to claim 1, characterized in that: When the electrolyte includes two or more of zinc bromide, zinc chloride, zinc sulfate or zinc trifluoromethanesulfonate, the zinc ion concentration is 1 to 30 mol / kg.

8. The electrolyte for improving calendar aging of aqueous zinc metal batteries according to claim 1, characterized in that: When the electrolyte is a mixed solution of acetate and multiple zinc salts, the acetate concentration is 1 to 40 mol / kg, and the zinc ion concentration is 1 to 30 mol / kg.

9. An aqueous zinc metal battery using the electrolyte according to claim 1, comprising a positive electrode, a negative electrode, a separator and the electrolyte according to claim 1.

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