Liquid electrolyte for metal battery and preparation method thereof and metal battery

Abstract

The application discloses a liquid electrolyte for a metal battery, a preparation method of the liquid electrolyte and the metal battery. The liquid electrolyte comprises a solvent and a metal salt. The solvent comprises a crown ether, and the metal salt is a sodium salt or a zinc salt. In the application, the crown ether is added to the solvent of the liquid electrolyte, so that the cycle life of the metal battery is improved. Specifically, the coordination ability of the crown ether and sodium ions changes the solvation structure of the sodium ions. The complex of the crown ether / sodium ions attracts anions in the sodium salt, the content of the anions is increased, a stable SEI film is formed, the uniform nucleation and growth of sodium at the negative electrode are facilitated, the generation of sodium dendrites is reduced, and thus the long cycle life of the sodium metal battery is realized. The coordination ability of the crown ether and zinc ions changes the solvation structure of the zinc ions, the content of water in the solvation structure is reduced, the side reactions caused by water at the zinc negative electrode in the cycle process are reduced, the generation of the hydrogen evolution reaction is inhibited, and thus the long cycle life of the zinc metal battery is realized.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of metal batteries, in particular to a liquid electrolyte for metal batteries, a preparation method thereof and a metal battery. BACKGROUND

[0002] With the rapid development of electric vehicles and portable electronic products, the demand for portable, high-capacity and high-power energy storage devices continues to increase. Lithium ion batteries have been widely used in electronic devices, automobiles, mobile phones and other fields. However, the scarcity of lithium resources and the difficulty in reducing the cost of raw materials of lithium ion batteries hinder the further development of lithium ion batteries in the field of large-scale energy storage. Therefore, it is necessary to develop new high-energy density metal battery systems.

[0003] In order to reduce the cost of energy storage batteries, people began to develop low-cost secondary metal batteries mainly based on sodium and zinc. However, metal batteries mainly based on sodium and zinc have the problems of short cycle life, poor stability and safety. For example, sodium metal batteries have the advantages of abundant raw materials, low cost, wide distribution and other price advantages. In the current research of sodium metal batteries, researchers improve the cycle performance of sodium metal batteries by modifying the electrolyte. However, how to modify the organic electrolyte solution by adding simple electrolyte additives to improve the cycle stability and safety of sodium metal batteries is a problem to be solved at present; water-based zinc metal batteries have attracted widespread attention due to their poor safety. Providing low-cost and high-stability electrolyte to inhibit the generation of water and zinc by-products and hydrogen evolution reaction can improve the overall performance of zinc battery such as cycle performance, safety performance and other performance still needs further research.

[0004] Therefore, the prior art still needs to be improved and developed. SUMMARY

[0005] In view of the deficiencies of the prior art, the purpose of the present application is to provide a liquid electrolyte for metal batteries, a preparation method thereof and a metal battery, which aims to solve the problem that the cycle performance of existing sodium or zinc metal batteries still needs to be improved.

[0006] The technical scheme of the present application is as follows:

[0007] In a first aspect of the present application, a liquid electrolyte for metal batteries is provided, which comprises a solvent and a metal salt, wherein the solvent comprises a crown ether, and the metal salt is a sodium salt or a zinc salt.

[0008] Optionally, when the metal salt is a sodium salt, the solvent further comprises an alcohol ether organic solvent.

[0009] The mass content of the alcohol ether organic solvent in the solvent is 90-100%, and the mass content of the crown ether is 0-10%; wherein the mass content of the alcohol ether organic solvent is not 100%, and the mass content of the crown ether is not 0%.

[0010] Optionally, when the metal salt is a zinc salt, the solvent further comprises water;

[0011] The mass content of the alcohol ether organic solvent in the solvent is 90-100%, and the mass content of the crown ether is 0-10%; wherein the mass content of the alcohol ether organic solvent is not 100%, and the mass content of the crown ether is not 0%.

[0012] Optionally, the concentration of the sodium salt in the liquid electrolyte for metal batteries is 0.8-1.5 mol / L.

[0013] Optionally, the sodium salt is at least one of sodium hexafluorophosphate, sodium tetrafluoroborate, sodium bis(trifluoromethylsulfonyl)imide, sodium perchlorate, sodium bisfluorosulfonylimide, and sodium trifluoromethylsulfonate.

[0014] Optionally, the concentration of the zinc salt in the liquid electrolyte for metal batteries is 1-2.5 mol / L.

[0015] Optionally, the zinc salt is at least one of zinc sulfate, zinc chloride, zinc acetate, zinc perchlorate, zinc trifluoromethylsulfonylimide, and zinc trifluoromethanesulfonate.

[0016] In a second aspect, the application provides a preparation method of the liquid electrolyte for metal batteries as described above, and the preparation method comprises the following steps:

[0017] Mixing the solvent and the metal salt to obtain the liquid electrolyte for metal batteries.

[0018] The solvent comprises a crown ether, and the metal salt is a sodium salt or a zinc salt.

[0019] In a third aspect, the application provides a metal battery, wherein the metal battery comprises the liquid electrolyte for metal batteries as described above.

[0020] Optionally, the metal battery is a sodium metal battery or a zinc metal battery.

[0021] Beneficial effects: In the present application, the crown ether is added to the solvent of the liquid electrolyte for metal batteries, which can improve the cycle life and safety of metal batteries (such as sodium metal batteries or zinc metal batteries). Specifically, the coordination ability of the crown ether with metal ions in the liquid electrolyte changes the solvation structure of the metal ions. For sodium metal batteries, the coordination ability of the crown ether with sodium ions changes the solvation structure of the sodium ions, the crown ether / sodium ion complex attracts the anions in the sodium salt, increases the anion content, is conducive to the formation of a stable SEI film, and is conducive to the uniform nucleation and growth of sodium at the negative electrode, reduces the generation of sodium dendrites, reduces the occurrence of short circuits, thereby realizing long cycle life and high safety of sodium metal batteries. For zinc metal batteries, the coordination ability of the crown ether with zinc ions changes the solvation structure of the zinc ions, reducing the content of water in the solvation structure, thereby reducing the side reactions of water at the zinc negative electrode during the cycle process, inhibiting the occurrence of hydrogen evolution reaction, thereby realizing long cycle life and high safety of zinc metal batteries. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 The cycle performance test results of the half-batteries made with the liquid electrolyte for sodium metal batteries in Examples 1-3 and Comparative Example 1.

[0023] Figure 2 The cycle performance test results of the half-batteries made with the liquid electrolyte for sodium metal batteries in Example 2, Comparative Examples 1 and 2.

[0024] Figure 3 The cycle performance test results of the full batteries made with the liquid electrolyte for sodium metal batteries in Example 2 and Comparative Example 1.

[0025] Figure 4 The cycle performance test results of the half-batteries made with the liquid electrolyte for zinc metal batteries in Example 4 and Comparative Example 3.

[0026] Figure 5 The XRD test results of the surface products of the zinc foils after the half-batteries made with the liquid electrolyte for zinc metal batteries in Example 4 and Comparative Example 3 were cycled, respectively. DETAILED DESCRIPTION

[0027] The present application provides a liquid electrolyte for metal batteries, a preparation method thereof and a metal battery. In order to make the purpose, technical scheme and effect of the present application more clear and explicit, the present application will be further described in detail below. It should be understood that the specific examples described herein are only used to explain the present application and do not limit the present application.

[0028] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used in the description herein is for describing particular embodiments only and is not intended to be limiting of the application.

[0029] The metal battery liquid electrolyte provided by the embodiments of the present application comprises a solvent and a metal salt, wherein the solvent comprises a crown ether, and the metal salt is a sodium salt or a zinc salt. It can be understood that different metal salts are used in electrolytes of different metal batteries. When the metal salt used in the liquid electrolyte is a sodium salt, the liquid electrolyte is used in a sodium metal battery; and when the metal salt used in the liquid electrolyte is a zinc salt, the liquid electrolyte is used in a zinc metal battery.

[0030] In the embodiments of the present application, a crown ether is added to the solvent of the metal battery liquid electrolyte, which can improve the cycle life and safety of the metal battery (such as a sodium metal battery or a zinc metal battery). Specifically, the coordination ability of the crown ether with metal ions changes the solvation structure of the metal ions. For a sodium metal battery, the coordination ability of the crown ether with sodium ions changes the solvation structure of the sodium ions. The complex of the crown ether / sodium ion attracts anions in the sodium salt, increases the content of the anions, is conducive to the formation of a stable SEI film, and is further conducive to the uniform nucleation and growth of sodium at the negative electrode, reduces the generation of sodium dendrites, reduces the occurrence of short circuits of the battery, and thus realizes long cycle life and high safety of the sodium metal battery. For a zinc metal battery, the coordination ability of the crown ether with zinc ions changes the solvation structure of the zinc ions, reduces the content of water in the solvation structure, and thus reduces the side reactions of water during the cycle process at the zinc negative electrode, inhibits the occurrence of hydrogen evolution reactions, and thus realizes long cycle life and high safety of the zinc metal battery.

[0031] In an embodiment, when the metal salt is a sodium salt, the solvent further comprises an alcohol ether organic solvent. That is, in the embodiment, the liquid electrolyte comprises a solvent and a sodium salt, the solvent comprises an alcohol ether organic solvent and a crown ether, and the metal battery liquid electrolyte is used in a sodium metal battery. Further, in the solvent, the mass content of the alcohol ether organic solvent is 90-100%, and the mass content of the crown ether is 0-10%; wherein the mass content of the alcohol ether organic solvent is not 100%, and the mass content of the crown ether is not 0%. In specific implementation, in the solvent, the sum of the mass content of the alcohol ether organic solvent and the mass content of the crown ether is 100%. As an excellent additive, the crown ether can sufficiently improve the cycle life and stability of the sodium metal battery when the addition amount of the crown ether in the solvent is 0-10%. When the addition amount of the crown ether exceeds 10%, on the one hand, it is not conducive to reducing the cost, and on the other hand, a high content of the crown ether can easily lead to excessive polarization of the battery and affect the performance of the battery.

[0032] Compared with the ester solvent commonly used in metal ion batteries, the alcohol ether organic solvent has good cycle stability for the sodium metal battery itself, but due to the inevitable reaction of the alcohol ether organic solvent with sodium, an unstable SEI film is generated, which also affects its performance. Therefore, by adding a crown ether, a stable SEI film can be generated, which can on the one hand realize the effective and uniform nucleation of sodium, reduce the occurrence of battery short circuit, and has high safety performance; on the other hand, it can further prevent the inevitable reaction of the alcohol ether organic solvent with sodium. That is, in the present embodiment, the alcohol ether organic solvent (such as diethylene glycol dimethyl ether) is used in combination with the crown ether (such as 15-crown-5), which not only fully utilizes the advantages of the alcohol ether organic solvent, but also effectively avoids the disadvantages of the alcohol ether organic solvent. The combination of the two further improves the performance of the liquid electrolyte, so that the sodium metal battery realizes long service life and high safety and stability.

[0033] In an embodiment, the alcohol ether organic solvent is selected from at least one of diethylene glycol dimethyl ether, ethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, and ethylene glycol diethyl ether, but is not limited thereto.

[0034] In a further embodiment, the alcohol ether organic solvent is selected from diethylene glycol dimethyl ether.

[0035] In an embodiment, the concentration of the sodium salt in the liquid electrolyte for metal batteries is 0.8-1.5 mol / L. The sodium salt in this range can ensure that the liquid electrolyte maintains good electrical conductivity, and ensures the battery performance without using high-concentration sodium salt, thereby reducing the cost.

[0036] In a further embodiment, the concentration of the sodium salt in the liquid electrolyte for metal batteries is 1 mol / L.

[0037] In an embodiment, the sodium salt is selected from at least one of sodium hexafluorophosphate (NaPF6), sodium tetrafluoroborate, sodium bis(trifluoromethylsulfonyl)imide, sodium perchlorate, sodium bisfluorosulfonylimide, and sodium trifluoromethylsulfonate, but is not limited thereto. When the sodium salt is selected from NaPF6, the coordination ability of the crown ether (such as 15-crown-5) with sodium ions changes the solvation structure of sodium ions, and the complex of the crown ether / sodium ion attracts anions (PF6 - ). - ), resulting in an increase in the content of anions (PF6

[0038] In an embodiment, when the metal salt is a zinc salt, the solvent further comprises water. That is, in this embodiment, the metal battery liquid electrolyte comprises a solvent and a zinc salt, the solvent comprises water and a crown ether, and the metal battery liquid electrolyte is used in a zinc metal battery. Further, in the solvent, the mass content of the water is 90-100%, and the mass content of the crown ether is 0-10%; wherein the mass content of the water is not 100%, and the mass content of the crown ether is not 0%. In a specific implementation, in the solvent, the sum of the mass content of the water and the mass content of the crown ether is 100%. When the amount of the crown ether added in the solvent is 0-10%, the crown ether can have a good effect of improving the stability of the battery, and can sufficiently improve the cycle life and stability of the zinc metal battery. When the amount of the crown ether added exceeds 10%, on the one hand, it is not conducive to reducing the cost, and on the other hand, a high content of the crown ether can easily cause excessive polarization of the battery, thereby affecting the performance of the battery.

[0039] The addition of the crown ether in the aqueous zinc metal battery electrolyte can change the solvation structure of the zinc ion by the coordination ability of the crown ether and the zinc ion, reduce the content of water in the solvation structure, reduce the side reactions of water in the zinc negative electrode in the cycle process, inhibit the occurrence of hydrogen evolution, and thus make the zinc metal battery have a long cycle life.

[0040] In an embodiment, the crown ether is at least one selected from 15-crown-5, 12-crown-4, and 18-crown-6, but is not limited thereto.

[0041] In a further embodiment, the crown ether is 15-crown-5.

[0042] In an embodiment, in the metal battery liquid electrolyte, the concentration of the zinc salt is 1-2.5 mol / L. The zinc salt in this concentration range can ensure that the liquid electrolyte has good electrical conductivity, and can ensure the performance of the battery without using a high-concentration zinc salt, thereby reducing the cost. In addition, considering the solubility of the zinc salt, the concentration of the zinc salt should not be too high.

[0043] In a further embodiment, in the metal battery liquid electrolyte, the concentration of the zinc salt is 2 mol / L.

[0044] In an embodiment, the zinc salt is at least one selected from zinc sulfate, zinc chloride, zinc acetate, zinc perchlorate, zinc trifluoromethylsulfonylimide, and zinc trifluoromethanesulfonate, but is not limited thereto.

[0045] The embodiment of the present application also provides a preparation method of the metal battery liquid electrolyte as described above, which comprises the following steps:

[0046] Mixing the solvent and the metal salt to obtain the liquid electrolyte for the metal battery;

[0047] The solvent comprises a crown ether, and the metal salt is a sodium salt or a zinc salt.

[0048] In particular implementation, the solvent and the metal salt are mixed, and then stirring is performed until the solution becomes transparent to obtain the liquid electrolyte for the metal battery.

[0049] The preparation method provided by the embodiment of the present application is simple, easy to operate, and suitable for industrial large-scale production.

[0050] The embodiment of the present application also provides a metal battery, wherein the metal battery comprises the liquid electrolyte for the metal battery as described above.

[0051] In an embodiment, the metal battery is a sodium metal battery or a zinc metal battery. In the embodiment, the metal battery is different from the existing metal ion battery. The metal battery refers to a battery with a metal negative electrode, while the metal ion battery refers to a battery with a material capable of embedding and extracting metal ions as a negative active material. It can be understood that the sodium metal battery is different from the existing sodium ion battery. The sodium metal battery refers to a battery with a sodium metal negative electrode, while the sodium ion battery refers to a battery with a material capable of embedding and extracting sodium ions as a negative active material. The zinc metal battery is different from the existing zinc ion battery. The zinc battery refers to a battery with a zinc metal negative electrode, while the zinc ion battery refers to a battery with a material capable of embedding and extracting zinc ions as a negative active material.

[0052] In an embodiment, the sodium metal battery comprises a liquid electrolyte, and the liquid electrolyte comprises a solvent and a sodium salt. According to the mass percentage, the solvent comprises an alcohol ether organic solvent 90-100% and a crown ether 0-10%, wherein the alcohol ether organic solvent is not 100%, and the crown ether is not 0%.

[0053] In a further embodiment, the sodium metal battery comprises a liquid electrolyte, and the liquid electrolyte comprises a solvent and a sodium salt. According to the mass percentage, the solvent comprises diethylene glycol dimethyl ether 90-100% and 15-crown-5 0-10%, wherein the diethylene glycol dimethyl ether is not 100%, and the 15-crown-5 is not 0%.

[0054] In an embodiment, the sodium metal battery further comprises a positive electrode sheet and a negative electrode sheet, the negative electrode sheet adopts a sodium metal foil, and the positive electrode active material in the positive electrode sheet is selected from at least one of sodium vanadium phosphate (Na3V2(PO4)3, NVP) and sodium vanadium fluorophosphate (Na3V2(PO4)2F3, NVPF). In specific implementation, the positive electrode sheet can be prepared by coating the positive electrode active material on a positive electrode current collector, and further, the positive electrode active material, a conductive agent, and a binder can be mixed with a solvent in a mass ratio of 8:1:1 to form a positive electrode slurry, which is then coated on an aluminum foil to obtain the positive electrode sheet after drying. The cell process and specific type of the sodium metal battery are not limited by the present application. For example, the cell process can adopt a winding type or a stacking type, and the specific type can be a square can type, a cylindrical type, a soft package type, or a button cell, etc.

[0055] In an embodiment, the zinc battery comprises a liquid electrolyte, and the liquid electrolyte comprises a solvent and a zinc salt. The solvent comprises water 90-100% and crown ether 0-10% by mass percentage, wherein the water is not 100% and the crown ether is not 0%.

[0056] In a further embodiment, the zinc battery comprises a liquid electrolyte, and the liquid electrolyte comprises a solvent and a zinc salt. The solvent comprises water 90-100% and 15-crown-5 0-10% by mass percentage, wherein the water is not 100% and the 15-crown-5 is not 0%.

[0057] In an embodiment, the zinc battery further comprises a positive electrode sheet and a negative electrode sheet, the negative electrode sheet adopts a zinc metal foil, and the positive electrode active material in the positive electrode sheet is selected from vanadium disulfide (VS2). In specific implementation, the positive electrode sheet can be prepared by coating the positive electrode active material on a positive electrode current collector, and further, the positive electrode active material, a conductive agent, and a binder can be mixed with a solvent in a mass ratio of 8:1:1 to form a positive electrode slurry, which is then coated on a titanium foil to obtain the positive electrode sheet after drying. The cell process and specific type of the zinc metal battery are not limited by the present application. For example, the cell process can adopt a winding type or a stacking type, and the specific type can be a square can type, a cylindrical type, a soft package type, or a button cell, etc.

[0058] The following will be described in detail through specific embodiments.

[0059] Embodiment 1

[0060] Preparation of the liquid electrolyte for the sodium metal battery:

[0061] The diethylene glycol dimethyl ether (97.5 wt%) and 15-crown-5 (2.5 wt%) are mixed to obtain the solvent;

[0062] A certain amount of NaPF6 was added to the solvent, and stirring was performed using a magnetic stirrer until the solution became transparent, to prepare a liquid electrolyte for a sodium metal battery with a NaPF6 concentration of 1 mol / L.

[0063] Example 2

[0064] The preparation of the liquid electrolyte for a sodium metal battery differed from Example 1 in that a solvent was prepared by mixing diethylene glycol dimethyl ether (95 wt%) and 15-crown-5 (5 wt%).

[0065] Example 3

[0066] The preparation of the liquid electrolyte for a sodium metal battery differed from Example 1 in that a solvent was prepared by mixing diethylene glycol dimethyl ether (92.5 wt%) and 15-crown-5 (7.5 wt%).

[0067] Example 4

[0068] Preparation of a liquid electrolyte for a zinc metal battery:

[0069] A solvent was prepared by mixing deionized water (99 wt%) and 15-crown-5 (1 wt%);

[0070] A certain amount of ZnSO4 was added to the solvent, and stirring was performed using a magnetic stirrer until the solution became transparent, to prepare a liquid electrolyte for a zinc metal battery with a ZnSO4 concentration of 2 mol / L.

[0071] Comparative Example 1

[0072] The preparation of the liquid electrolyte for a sodium metal battery was substantially the same as in Example 1, except that a solvent was prepared by mixing diethylene glycol dimethyl ether (100 wt%) and 15-crown-5 (0 wt%).

[0073] Comparative Example 2

[0074] A certain amount of NaPF6 was added to propylene carbonate, and stirring was performed using a magnetic stirrer, to prepare a liquid electrolyte for a sodium metal battery with a NaPF6 concentration of 1 mol / L.

[0075] Comparative Example 3

[0076] The preparation of the liquid electrolyte for a zinc metal battery was substantially the same as in Example 4, except that a solvent was prepared by mixing water (100 wt%) and 15-crown-5 (0 wt%).

[0077] Test:

[0078] (1) The liquid electrolytes for a sodium metal battery in Examples 1-3 and Comparative Examples 1 and 2 were tested using a half-cell.

[0079] a. The half-cells were prepared as follows:

[0080] A copper current collector with a diameter of 14 mm was used as the working electrode, a sodium foil with a diameter of 14 mm was used as the counter / reference electrode, a glass fiber separator and a standard CR2032 battery shell were used to assemble the half-cell in an argon-filled glove box (H2O < 0.1 ppm, O2< 0.1 ppm) in the order of positive shell-copper current collector-electrolyte-separator-electrolyte-sodium foil-gasket-spring piece-negative shell, and finally sealed using a button cell sealer. During the assembly process, 60 μL of the liquid electrolyte for sodium metal batteries in Example 1 was added.

[0081] A copper current collector with a diameter of 14 mm was used as the working electrode, a sodium foil with a diameter of 14 mm was used as the counter / reference electrode, a glass fiber separator and a standard CR2032 battery shell were used to assemble the half-cell in an argon-filled glove box (H2O < 0.1 ppm, O2< 0.1 ppm) in the order of positive shell-copper current collector-electrolyte-separator-electrolyte-sodium foil-gasket-spring piece-negative shell, and finally sealed using a button cell sealer. During the assembly process, 60 μL of the liquid electrolyte for sodium metal batteries in Example 1 was added.

[0082] b. The above half-cells prepared using the liquid electrolyte for sodium metal batteries in Examples 1-3 and Comparative Example 1 were subjected to cycle performance tests, respectively. The test system used a new battery charge-discharge tester, and the test conditions were as follows: first using a constant current to deposit 6 mAh / cm2on the copper current collector, then using a current density of 2 mA / cm2, constant current deposition-electrolytic capacity of 3 mAh / cm2, and cycle performance test. 2 2 2

[0083] The results are shown in Table 1. Figure 1 The half-cell made from the liquid electrolyte for sodium metal batteries in Example 2 could be stably operated for 2400 h. The half-cell made from the liquid electrolyte for sodium metal batteries in Comparative Example 1 showed severe voltage oscillation after 300 h and failed. Although the half-cells made from the liquid electrolytes for sodium metal batteries in Examples 1 and 3 had better performance than that in Comparative Example 1, the half-cell made from the liquid electrolyte for sodium metal batteries in Example 2 containing diglyme (95 wt%) and 15-crown-5 (5 wt%) had the best cycle performance. The liquid electrolyte for sodium metal batteries in Example 2 containing diglyme (95 wt%) and 15-crown-5 (5 wt%) could effectively stabilize the sodium metal negative electrode deposition, thereby obtaining excellent electrochemical performance.​​​

[0084] c. The above half-cells prepared by using the liquid electrolyte for sodium metal battery in Example 2, Comparative Example 1 and 2 were respectively subjected to cycle performance test, and the test system used was a new battery charge-discharge tester, and the test conditions were: 6 mAh / cm2 was deposited on the copper current collector by using constant current for the first time 2 sodium metal, and then using a current density of 2 mA / cm2 2 , constant current deposition-electrolytic capacity of 3 mAh / cm2 2 , and cycle performance test was carried out. The test results are shown in Figure 2 , the half-cell prepared by Comparative Example 2 (using ester electrolyte) showed a sharp increase in polarization to 2.5 V at the beginning of the battery cycle, and reached 5 V after several cycles, which was the performance of the battery failure. At the same time, the voltage charge-discharge curves of the half-cells prepared by the liquid electrolyte for sodium metal battery in Example 2 and Comparative Example 1 were stable, and the polarization was very small (0.02 V), and it was known that the liquid electrolyte for sodium metal battery in Example 2 had the best effect in the later cycle, which could effectively stabilize the sodium metal negative electrode deposition, thereby obtaining excellent electrochemical performance. Figure 1

[0085] (2) The liquid electrolyte for sodium metal battery in Example 2 and Comparative Example 1 was tested by using a full battery.

[0086] a. Preparation of full battery:

[0087] The sodium foil with a diameter of 14 mm was used as the negative electrode, the active material with a diameter of 14 mm was used as the positive electrode (the current collector of the electrode piece used aluminum foil), Celgard 2325 separator and standard CR2032 type battery shell were used in the argon filled glove box (H2O<0.1 ppm, O2<0.1 ppm), and the full battery was assembled in the order of positive electrode shell-positive electrode-electrolyte-separator-electrolyte-sodium foil-gasket-spring piece-negative electrode shell in the argon filled glove box (H2O<0.1 ppm, O2<0.1 ppm), and finally sealed by using a button cell sealing machine, and the pressure was 50 Mpa, to obtain the full battery. During the assembly process, 60 μL of the liquid electrolyte for metal battery in Example 2 and Comparative Example 1 was added respectively.

[0088] b. The above full batteries prepared by using the liquid electrolyte for sodium metal battery in Example 2 and Comparative Example 1 were respectively subjected to cycle performance test, and the test system used was a new battery charge-discharge tester. The test conditions were: current density 0.2 A / g, voltage range 2.2-3.9 V.

[0089] The results are shown in Figure 3 ​As shown, the full battery made with the liquid electrolyte for sodium metal batteries in Example 2 still has a capacity retention rate of 91.1% after 600 stable running cycles. The full battery made with the liquid electrolyte for sodium metal batteries in Comparative Example 2 has a capacity drop to 0 mAh / g after 100 cycles, and the battery is invalid, which highlights the performance improvement of the liquid electrolyte for sodium metal batteries in Example 2 on the sodium metal battery.

[0090] (3) Test the liquid electrolyte for zinc metal batteries in Example 4 and Comparative Example 3 by using half cells

[0091] a. Preparation of half cells:

[0092] A zinc foil with a diameter of 12 mm is used as the working electrode, a zinc foil with a diameter of 12 mm is used as the counter / reference electrode, a glass fiber separator and a standard CR2032 type battery shell are used to assemble the battery, and the half cell is assembled in the order of positive shell-zinc foil-electrolyte-separator-electrolyte-zinc foil-gasket-spring sheet-negative shell. Finally, a button cell sealing machine is used to seal the half cell, and 170 μL of the liquid electrolyte for zinc metal batteries in Example 4 and Comparative Example 2 is added respectively during the assembly process of the half cell.

[0093] b. Cycle stability test of the half cells made with the liquid electrolyte for zinc metal batteries in Example 4 and Comparative Example 3 respectively. The test system uses a new battery charge-discharge tester, and the test conditions are a current density of 2 mA / cm 2 , a constant current deposition-electrolysis capacity of 2 mAh / cm 2 .

[0094] As shown in Figure 4 , the half cell made with the liquid electrolyte for zinc metal batteries in Example 4 can be stably run for a long time, and has better stability than the half cell made with the liquid electrolyte for zinc metal batteries in Comparative Example 3, which has obvious performance improvement.

[0095] (4) XRD test of the product after the half cells made with the liquid electrolyte for zinc metal batteries in Example 4 and Comparative Example 3 are cycled.

[0096] The half cells made with the liquid electrolyte for zinc metal batteries in Example 4 and Comparative Example 3 are cycled for 10 cycles under the conditions of a current density of 2 mA / cm 2 , a constant current deposition-electrolysis capacity of 2 mAh / cm 2 , and then disassembled, and the products generated on the surface of the zinc foil of the two are qualitatively analyzed by X-ray diffraction. The results are Figure 5As shown, by XRD test, the signal of the by-product Zn4(OH)6SO4·5H2O on the surface of the zinc foil after the half-cell test using the liquid electrolyte for zinc metal battery in Example 4 is obviously lower than that in Comparative Example 3, which indicates that the liquid electrolyte for zinc metal battery in Example 4 has a very obvious inhibitory effect on the generation of by-products of zinc metal battery, thereby improving the performance of the battery.

[0097] In summary, by adding the crown ether as an additive in the solvent of the liquid electrolyte for metal battery in the present application, the cycle life and safety of the metal battery (such as sodium metal battery or zinc metal battery) can be improved. Specifically, the coordination ability of the crown ether in the liquid electrolyte with metal ions changes the solvation structure of the metal ions. For the sodium metal battery, the coordination ability of the crown ether with sodium ions changes the solvation structure of the sodium ions, the complex of the crown ether / sodium ion attracts the anions in the sodium salt, increases the anion content, is conducive to the formation of a stable SEI film, and is conducive to the uniform nucleation and growth of sodium at the negative electrode, reduces the generation of sodium dendrites, reduces the occurrence of short circuit of the battery, thereby realizing the long cycle life and high safety of the sodium metal battery. For the zinc metal battery, the coordination ability of the crown ether with zinc ions changes the solvation structure of the zinc ions, reduces the content of water in the solvation structure, thereby reducing the side reactions of water at the zinc negative electrode during the cycle process, inhibiting the occurrence of hydrogen evolution reaction, thereby realizing the long cycle life and high safety of the zinc metal battery.

[0098] It should be understood that the application of the present application is not limited to the above examples, and those skilled in the art can make improvements or changes according to the above description, and all these improvements and changes shall belong to the protection scope of the appended claims of the present application.

Claims

1. A liquid electrolyte for a sodium metal battery, characterized by, The solvent is composed of crown ether and alcohol ether organic solvent, and the metal salt is sodium salt; In the solvent, the mass content of the alcohol ether organic solvent is 90-100%, and the mass content of the crown ether is 0-10%; wherein the mass content of the alcohol ether organic solvent is not 100%, and the mass content of the crown ether is not 0%; The alcohol ether organic solvent is selected from at least one of diethylene glycol dimethyl ether, ethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, and ethylene glycol diethyl ether.

2. The liquid electrolyte for sodium metal batteries according to claim 1, characterized in that, The concentration of the sodium salt in the liquid electrolyte for sodium metal batteries is 0.8-1.5 mol / L. 3.The liquid electrolyte for sodium metal batteries of claim 1, wherein, The sodium salt is selected from at least one of sodium hexafluorophosphate, sodium tetrafluoroborate, sodium bis(trifluoromethylsulfonyl)imide, sodium perchlorate, sodium bisfluorosulfonylimide, and sodium trifluoromethylsulfonate.

4. A method for preparing a liquid electrolyte for a sodium metal battery according to any one of claims 1 to 3, characterized in that, The method comprises the steps of: Mixing the solvent and the metal salt to obtain the liquid electrolyte for sodium metal batteries.

5. A sodium metal battery, characterized by, The sodium metal battery comprises the liquid electrolyte for sodium metal batteries according to any one of claims 1-3.

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