Negative-electrode-free sodium ion battery electrolyte as well as preparation method and application thereof

Abstract

The embodiment of the invention relates to a negative-electrode-free sodium-ion battery electrolyte and a preparation method and application thereof, and the negative-electrode-free sodium-ion battery electrolyte comprises a non-fluorinated conventional ether substance, a fluoroether substance and a sodium salt; the mass percent of the non-fluorinated conventional ether substance, the fluoroether substance and the sodium salt is (5%-85%): (5%-85%): (5%-30%); wherein the non-fluorinated conventional ether substances comprise linear ether and / or cyclic ether. Compared with the traditional carbonic ester electrolyte, the negative-electrode-free sodium ion battery electrolyte provided by the embodiment of the invention has the advantages that the transmission rate of sodium ions can be improved, the sodium ions can be subjected to reversible deposition with high coulombic efficiency on a pure current collector, and the overall oxidation stability of the electrolyte is improved; the prepared sodium ion battery without the negative electrode can stably operate under high working voltage and has excellent electrochemical performance.

Description

Technical Field

[0001] The present invention relates to the field of sodium ion battery materials, and in particular to a negative electrode-free sodium ion battery electrolyte and a preparation method and application thereof. Background Art

[0003] Sodium-ion batteries have similar working principles to lithium-ion batteries, and sodium resources are abundant and low-cost. They are considered to be an effective supplement to lithium-ion batteries, especially suitable for large-scale energy storage applications. However, they are limited by their low energy density (~100Wh / kg) and the difficulty in processing hard carbon negative electrode materials, resulting in low compaction density and peeling force of the pole pieces, which further increases the difficulty of process processing requirements. At present, the large-scale commercial value of sodium-ion batteries has not yet been realized.

[0004] In recent years, negative electrode-free sodium-ion batteries have received much attention from academia and industry. Since negative electrode-free sodium-ion batteries do not use hard carbon as the negative electrode material, the negative electrode only uses conventional copper or aluminum foil used in the lithium / sodium-ion battery industry. Since the negative electrode of negative electrode-free sodium-ion batteries does not need to be coated with graphite active materials, the overall mass of the battery cell is effectively reduced, the energy density is effectively improved, and the process difficulty can be reduced. The material processing and battery cell preparation of negative electrode-free sodium-ion batteries can be fully realized based on existing process technologies. However, negative electrode-free sodium-ion batteries also face severe challenges, such as disordered deposition of sodium ions, low initial efficiency, and poor cycle stability, which have become problems that need to be urgently solved for negative electrode-free sodium-ion batteries.

[0005] As an important component of anode-free sodium-ion batteries, the electrolyte can react with most ester solvents to cause dendrite growth and dead sodium generation due to the low potential and strong reducing property of the in-situ deposited metallic sodium. These problems will cause the battery performance to decay rapidly. Therefore, traditional carbonate electrolytes are not suitable for anode-free sodium-ion batteries. Summary of the invention

[0006] The purpose of the present invention is to provide a negative electrode-free sodium ion battery electrolyte and a preparation method and application thereof in view of the defects of the prior art.

[0007] To achieve the above-mentioned objectives, in a first aspect, the present invention provides an electrolyte for a negative electrode-free sodium ion battery, wherein the electrolyte for a negative electrode-free sodium ion battery comprises conventional non-fluorinated ether substances, fluoroether substances and sodium salts; the mass percentages of the conventional non-fluorinated ether substances, fluoroether substances and sodium salts are: 5%-85%: 5%-85%: 5%-30%; wherein the conventional non-fluorinated ether substances comprise linear ethers and / or cyclic ethers.

[0008] Preferably, the cyclic ether includes at least one of 1,3-dioxolane, tetrahydrofuran, and 2-methyltetrahydrofuran.

[0009] Preferably, the linear ether includes at least one of dimethoxypropane, dimethoxymethane, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether.

[0010] Preferably, the fluoroether substances include: 1,1,2,2-tetrafluoroethyl methyl ether, 1,1,2,2-tetrafluoroethyl ethyl ether, bis(2,2,2-trifluoroethyl) ether, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, perfluoropropyl vinyl ether, 1,1,2,3,3,3-hexafluoropropyl methyl ether, methyl 2,2,3,3,3-pentafluoropropyl ether, difluoromethyl At least one of 2,2,3,3-tetrafluoropropyl ether, allyl 1,1,2,3,3,3-hexafluoropropyl ether, 1,1,2,3,3,3-hexafluoropropyl difluoromethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 2-(heptafluoropropoxy)hexafluoropropyl trifluorovinyl ether, 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether, and 1,2-bis(1,1,2,2-tetrafluoroethoxy)ethane.

[0011] Preferably, the sodium salt includes any one or more of sodium tetrafluoroborate, sodium hexafluorophosphate, sodium perchlorate, sodium bis(trifluoromethylsulfonyl)imide, and sodium bis(trifluoromethylsulfonyl)imide.

[0012] In a second aspect, the present invention provides a method for preparing a negative electrode-free sodium ion battery electrolyte as described in any one of the first aspects above, the preparation method comprising:

[0013] The water value and oxygen value of the glove box filled with argon are adjusted to within the preset value range;

[0014] After dehydrating the non-fluorinated conventional ether substance and the fluorinated ether substance, respectively, a water content test is performed, and when the water content of the non-fluorinated conventional ether substance and the fluorinated ether substance is not greater than a preset water content, the non-fluorinated conventional ether substance and the fluorinated ether substance are mixed and stirred to obtain a mixture;

[0015] Sodium salt is added to the mixture, mixed and allowed to stand, and an acidity test is performed. When the acidity value is not greater than a preset acidity value, the negative electrode-free sodium ion battery electrolyte is obtained; the mass percentages of non-fluorinated conventional ether substances, fluoroether substances and sodium salt in the negative electrode-free sodium ion battery electrolyte are: 5%-85%: 5%-85%: 5%-30%; wherein the non-fluorinated conventional ether substances include linear ethers and / or cyclic ethers.

[0016] Preferably, the preset value range is less than or equal to 0.01 ppm.

[0017] Preferably, the preset water content is 30 ppm.

[0018] Preferably, the preset acidity value is 50 ppm.

[0019] In a third aspect, the present invention provides a negative electrode-free sodium ion battery, comprising a positive electrode plate, a negative electrode plate, a separator, and the negative electrode-free sodium ion battery electrolyte described in any one of the first aspects or the negative electrode-free sodium ion battery electrolyte prepared by any one of the preparation methods described in the second aspect.

[0020] The negative electrode-free sodium ion battery electrolyte of the embodiment of the present invention comprises a conventional non-fluorinated ether substance, a fluorinated ether substance and a sodium salt, wherein the conventional non-fluorinated ether substance belongs to a polar solvent molecule, and the active solvent molecular structure of a strong electron donor can achieve a high dissociation degree of the sodium salt and a high Na+ content of the electrolyte. + Conductivity. Compared with traditional carbonate electrolytes, it can promote the rapid migration of sodium ions, improve the rate performance of sodium ion batteries, and form a uniform solid electrolyte interface film on the surface of sodium metal, inhibit the growth of sodium dendrites, and enhance the cycle stability; due to the strong electron-withdrawing effect of fluorine atoms, fluoroether substances can improve the antioxidant capacity of the electrolyte, make up for the disadvantage of low oxidation stability of non-fluorinated conventional ethers, improve the overall oxidation resistance of the electrolyte, and make the electrolyte adaptable to high-voltage positive electrodes. In addition, the SE I film formed by the participation of fluoroether solvents is rich in sodium fluoride components, which greatly increases the content of inorganic components NaF, Na2CO3, and NaCl in the solid electrolyte membrane, improves its density, and further reduces the growth of sodium metal dendrites. In addition, the high bond energy of carbon-fluorine bonds can improve the high temperature tolerance of the electrolyte; sodium salts can provide a sodium ion source, participate in the formation of solid electrolyte membranes, and are the core carriers of battery operation. In summary, this electrolyte can increase the transmission rate of sodium ions, enable the reversible deposition of metallic sodium ions on pure current collectors with high Coulombic efficiency, and improve the overall oxidative stability of the electrolyte, so that the prepared negative electrode-free sodium ion battery can operate stably at a high operating voltage and has excellent electrochemical performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 A flow chart of a method for preparing a negative electrode-free sodium ion battery electrolyte provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0022] In order to make the purpose, technical scheme and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0023] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments.

[0024] An electrolyte for a sodium ion battery without a negative electrode provided in an embodiment of the present invention may specifically include conventional non-fluorinated ether substances, fluorinated ether substances and sodium salts. The mass percentages of conventional non-fluorinated ether substances, fluorinated ether substances and sodium salts may specifically be: 5%-85%: 5%-85%: 5%-30%, preferably 10-80%: 10%-80%: 10%-20%.

[0025] Among them, the non-fluorinated conventional ether substances specifically include linear ethers and / or cyclic ethers. The linear ethers specifically include: at least one of dimethoxypropane, dimethoxymethane, ethylene glycol dimethyl ether (DEM), diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether, preferably ethylene glycol dimethyl ether (DEM). The cyclic ethers specifically include: at least one of 1,3-dioxolane (DOL), tetrahydrofuran (THF), and 2-methyltetrahydrofuran (2-Me-THF), preferably 1,3-dioxolane (DOL).

[0026] Fluorinated ether substances specifically include: 1,1,2,2-tetrafluoroethyl methyl ether, 1,1,2,2-tetrafluoroethyl ethyl ether, bis(2,2,2-trifluoroethyl) ether, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (HFE), perfluoropropyl vinyl ether, 1,1,2,3,3,3-hexafluoropropyl methyl ether, methyl 2,2,3,3,3-pentafluoropropyl ether, difluoromethyl 2,2,3,3-tetrafluoropropyl ether, allyl 1, At least one of 1,2,3,3,3-hexafluoropropyl ether, 1,1,2,3,3,3-hexafluoropropyl difluoromethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 2-(heptafluoropropoxy)hexafluoropropyl trifluorovinyl ether, 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether, and 1,2-bis(1,1,2,2-tetrafluoroethoxy)ethane (BTFEE), preferably 1,2-bis(1,1,2,2-tetrafluoroethoxy)ethane (BTFEE).

[0027] The sodium salt specifically includes any one or more of sodium tetrafluoroborate (NaBF4), sodium hexafluorophosphate (NaPF6), sodium perchlorate (NaClO4), sodium bis(trifluoromethylsulfonyl)imide (NaTFS I), and sodium bis(trifluoromethylsulfonyl)imide (NaFS I), preferably sodium tetrafluoroborate (NaBF4), sodium hexafluorophosphate (NaPF6), and sodium bis(trifluoromethylsulfonyl)imide (NaFS I).

[0028] The negative electrode-free sodium ion battery electrolyte of the embodiment of the present invention comprises a conventional non-fluorinated ether substance, a fluorinated ether substance and a sodium salt, wherein the conventional non-fluorinated ether substance belongs to a polar solvent molecule, and the active solvent molecular structure of a strong electron donor can achieve a high dissociation degree of the sodium salt and a high Na+ content of the electrolyte. + Conductivity. Compared with traditional carbonate electrolytes, it can promote the rapid migration of sodium ions, improve the rate performance of sodium ion batteries, and form a uniform solid electrolyte interface film on the surface of sodium metal, inhibit the growth of sodium dendrites, and enhance the cycle stability; due to the strong electron-withdrawing effect of fluorine atoms, fluoroether substances can improve the antioxidant capacity of the electrolyte, make up for the disadvantage of low oxidation stability of non-fluorinated conventional ethers, improve the overall oxidation resistance of the electrolyte, and make the electrolyte adaptable to high-voltage positive electrodes. In addition, the SE I film formed by the participation of fluoroether solvents is rich in sodium fluoride components, which greatly increases the content of inorganic components NaF, Na2CO3, and NaCl in the solid electrolyte membrane, improves its density, and further reduces the growth of sodium metal dendrites. In addition, the high bond energy of carbon-fluorine bonds can improve the high temperature tolerance of the electrolyte; sodium salts can provide a sodium ion source, participate in the formation of solid electrolyte membranes, and are the core carriers of battery operation. In summary, this electrolyte can increase the transmission rate of sodium ions, enable the reversible deposition of metallic sodium ions on pure current collectors with high Coulombic efficiency, and improve the overall oxidative stability of the electrolyte, so that the prepared negative electrode-free sodium ion battery can operate stably at a high operating voltage and has excellent electrochemical performance.

[0029] The present invention also provides a method for preparing a negative electrode-free sodium ion battery electrolyte, the process of which is as follows: Figure 1 As shown, the following steps are included:

[0030] Step 110, adjusting the water value and oxygen value in the glove box filled with argon gas to within a preset value range;

[0031] Specifically, the preset value range is less than or equal to 0.01 ppm.

[0032] Step 120, after dehydrating the non-fluorinated conventional ether substance and the fluorinated ether substance, respectively, a water content test is performed, and when the water content of the non-fluorinated conventional ether substance and the fluorinated ether substance is not greater than a preset water content, the non-fluorinated conventional ether substance and the fluorinated ether substance are mixed and stirred to obtain a mixture;

[0033] Specifically, the preset water content is 30ppm. The water removal process can be specifically achieved by molecular sieves. In the present application, the type of molecular sieve is specifically a sodium type molecular sieve of McLean 4A with a pore size of 2mm-3mm. The water content is determined using a Karl Fischer moisture tester. It is only necessary to inject the non-fluorinated conventional ether substances and fluoroether substances after dehydration into the titration cup of the Karl Fischer moisture tester through a syringe cleaned and dried by ethanol, and read the reading after the reading stabilizes. The temperature for mixing and stirring the non-fluorinated conventional ether substances and fluoroether substances is room temperature.

[0034] It should be noted that the materials involved in this embodiment are the same as above and will not be described again here.

[0035] Step 130, adding sodium salt to the mixture, mixing and standing, and performing an acidity test, when the acidity value is not greater than a preset acidity value, obtaining a negative electrode-free sodium ion battery electrolyte;

[0036] Specifically, the preset acidity value is 50ppm. The mass percentages of conventional ether substances, fluorinated ether substances and sodium salts in the negative electrode-free sodium ion battery electrolyte are: 5%-85%: 5%-85%: 5%-30%. Among them, the non-fluorinated conventional ether substances include linear ethers and / or cyclic ethers.

[0037] In this process, before adding sodium salt to the mixture, the mixture needs to be frozen at -10°C in an auxiliary refrigerator or other freezing equipment configured in the glove box for more than 6 hours to avoid increasing acidity due to temperature increase during the salt addition and mixing process.

[0038] The acidity test specifically uses the triethylamine titration method. The details are as follows:

[0039] First, place a conical flask dried in a blast drying oven at 105°C in a glove box, add about 15g-20g of the mixed solution by reduction method, then add 30mL of ethyl methyl carbonate (EMC) and 2-3 drops of methyl red-acetonitrile indicator, at this time, the solution is rose red.

[0040] Secondly, add triethylamine-EMC standard solution until the solution changes from rose red to bright yellow, record the amount of standard solution consumed, and thus calculate the content of hydrofluoric acid in the mixed solution.

[0041] In summary, the preparation process of the negative electrode-free sodium ion battery electrolyte provided by the embodiment of the present invention is simple and can be completed using conventional equipment. The addition of fluoroether improves the overall oxidation resistance of the electrolyte, and can also increase the inorganic components in the solid electrolyte membrane, especially the content of sodium fluoride inorganic matter, so that sodium ions are more easily electroplated and stripped on the surface of metallic sodium, which helps to improve the electrochemical performance of the battery.

[0042] The negative electrode-free sodium ion battery electrolyte provided by the embodiment of the present invention can be applied to a negative electrode-free sodium ion battery, wherein the negative electrode-free sodium ion battery comprises a positive electrode plate, a negative electrode plate, a separator and a negative electrode-free sodium ion battery electrolyte.

[0043] The positive electrode sheet includes a positive current collector, a positive active material, a conductive agent and a binder, wherein the positive current collector includes any one or two of aluminum foil and carbon-coated aluminum foil. The positive active material includes at least one of sodium vanadium phosphate, sodium iron pyrophosphate, sodium vanadium fluorophosphate, sodium ferromanganate, sodium nickel iron manganate, and sodium ferrophosphate. The conductive agent includes any one or at least two of superconducting carbon, acetylene black, Ketjen black, conductive graphite, carbon nanotubes, graphene, carbon fiber, and SP (Super-P). The binder includes any one or at least two of polyvinylidene fluoride, polytetrafluoroethylene, polyacrylic acid, sodium alginate, carboxymethyl cellulose, sodium carboxymethyl cellulose, and styrene-butadiene rubber.

[0044] The negative electrode plate includes a negative electrode current collector, which may specifically include one or both of aluminum foil and carbon-coated copper foil.

[0045] The diaphragm includes any one or at least two of Celgard2500 diaphragm, Celgard2325 diaphragm and glass fiber diaphragm.

[0046] In order to better understand the technical solution provided by the present invention, the following uses a number of specific examples to illustrate the specific process of preparing a negative electrode-free sodium ion battery electrolyte using the method provided in the above embodiment of the present invention, as well as the electrochemical properties of the prepared negative electrode-free sodium ion battery electrolyte.

[0047] Example 1

[0048] In the first step, the water and oxygen levels in the glove box filled with argon were adjusted to ≤ 0.01 ppm.

[0049] In the second step, non-fluorinated conventional ether substances: ethylene glycol dimethyl ether and fluoroether substances: 1,2-bis(1,1,2,2-tetrafluoroethoxy)ethane were dehydrated using McLean 4A sodium molecular sieve with a pore size of 2mm-3mm. Then, 0.5mL of each solution was taken from a syringe cleaned and dried with ethanol and injected into a titration cup of a Karl Fischer moisture tester for water content testing. When the water content of ethylene glycol dimethyl ether was 28ppm and the water content of 1,2-bis(1,1,2,2-tetrafluoroethoxy)ethane was 25ppm, ethylene glycol dimethyl ether and 1,2-bis(1,1,2,2-tetrafluoroethoxy)ethane were mixed and stirred to obtain a mixture.

[0050] The third step is to place the mixture in an auxiliary refrigerator configured in the glove box, freeze it at -10°C for 6 hours, take it out and add sodium tetrafluoroborate to the mixture, mix it and let it stand for acidity test, the actual measured acidity result is 45.2ppm, and a negative electrode-free sodium ion battery electrolyte is obtained, wherein the mass ratio of ethylene glycol dimethyl ether, 1,2-bis(1,1,2,2-tetrafluoroethoxy)ethane and sodium tetrafluoroborate in the negative electrode-free sodium ion battery electrolyte is 85%:5%:10%.

[0051] Afterwards, the prepared negative electrode-free sodium ion battery electrolyte was used to assemble button cells for testing, as follows:

[0052] First, the positive electrode sheet was prepared: the positive electrode active material sodium nickel iron manganese oxide, the conductive agent SP, and the binder polyvinylidene fluoride were added into N-methyl-2-pyrrolidone in a mass ratio of 8:1:1 and mixed and ground until there was no granularity. The mixed slurry was coated on a carbon-coated aluminum foil, dried at 80°C for 12 hours, and then rolled and cut into sodium nickel iron manganese oxide positive electrode discs with a diameter of 10 mm.

[0053] Secondly, preparation of negative electrode plates: use carbon-coated aluminum foil as the negative electrode current collector and cut it into plates with a diameter of 14 mm using a die-cutting machine.

[0054] Then, the above-mentioned electrode pieces were assembled into CR2032 button cells in an argon-filled glove box. The assembly order was: negative electrode shell, negative electrode current collector, separator, positive electrode piece, electrolyte, gasket, spring, positive electrode shell, wherein the amount of electrolyte was 200 microliters.

[0055] Finally, the CR2032 button battery was left to stand for 8 hours, and the charge and discharge test was performed on the Blue Electric Battery Test System (CT2001A) at 25°C. The test conditions were: the test voltage range was 1.5-3.8V, 0.1C constant current charging was performed first, the cut-off voltage was 3.8V, and then 0.1C constant current discharge was performed after standing for 10 minutes, the cut-off voltage was 1.5V, and the number of cycles was set to 50cl s. After the cycle test, the battery was taken out, and the electrochemical impedance spectroscopy (EIS) test was performed on the cycled battery using the Chenhua electrochemical workstation. The test conditions were 0.01-100KHz and the amplitude was 5mV / s. After that, the test results were fitted by Zview fitting software.

[0056] Wherein, first coulombic efficiency = first discharge capacity / first charge capacity. 50c ls capacity retention rate = 50c ls discharge capacity / first cycle discharge capacity.

[0057] Example 2

[0058] In the first step, the water and oxygen levels in the glove box filled with argon were adjusted to ≤ 0.01 ppm.

[0059] In the second step, non-fluorinated conventional ether substances: ethylene glycol dimethyl ether and fluoroether substances: 1,2-bis(1,1,2,2-tetrafluoroethoxy)ethane were dehydrated using McLean 4A sodium molecular sieve with a pore size of 2mm-3mm. Then, 0.5mL of each solution was taken from a syringe cleaned and dried with ethanol and injected into a titration cup of a Karl Fischer moisture tester for water content testing. When the water content of ethylene glycol dimethyl ether was 28ppm and the water content of 1,2-bis(1,1,2,2-tetrafluoroethoxy)ethane was 25ppm, ethylene glycol dimethyl ether and 1,2-bis(1,1,2,2-tetrafluoroethoxy)ethane were mixed and stirred to obtain a mixture.

[0060] The third step is to place the mixture in an auxiliary refrigerator equipped in the glove box, freeze it at -10°C for 6 hours, take it out and add sodium tetrafluoroborate to the mixture, mix it and let it stand for acidity test, the actual measured acidity result is 42.3ppm, and a negative electrode-free sodium ion battery electrolyte is obtained, wherein the mass ratio of ethylene glycol dimethyl ether, 1,2-bis(1,1,2,2-tetrafluoroethoxy)ethane and sodium tetrafluoroborate in the negative electrode-free sodium ion battery electrolyte is 80%:10%:10%.

[0061] The testing process is the same as in Example 1.

[0062] Example 3

[0063] In the first step, the water and oxygen levels in the glove box filled with argon were adjusted to ≤ 0.01 ppm.

[0064] In the second step, non-fluorinated conventional ether substances: ethylene glycol dimethyl ether and fluoroether substances: 1,2-bis(1,1,2,2-tetrafluoroethoxy)ethane were dehydrated using McLean 4A sodium molecular sieve with a pore size of 2mm-3mm. Then, 0.5mL of each solution was taken from a syringe cleaned and dried with ethanol and injected into a titration cup of a Karl Fischer moisture tester for water content testing. When the water content of ethylene glycol dimethyl ether was 28ppm and the water content of 1,2-bis(1,1,2,2-tetrafluoroethoxy)ethane was 25ppm, ethylene glycol dimethyl ether and 1,2-bis(1,1,2,2-tetrafluoroethoxy)ethane were mixed and stirred to obtain a mixture.

[0065] The third step is to place the mixture in an auxiliary refrigerator configured in the glove box, freeze it at -10°C for 6 hours, take it out and add sodium tetrafluoroborate to the mixture, mix it and let it stand for acidity test, when the actual measured acidity result is 39.8ppm, a negative electrode-free sodium ion battery electrolyte is obtained, wherein the mass ratio of ethylene glycol dimethyl ether, 1,2-bis(1,1,2,2-tetrafluoroethoxy)ethane and sodium tetrafluoroborate in the negative electrode-free sodium ion battery electrolyte is 70%:20%:10%.

[0066] The testing process is the same as in Example 1.

[0067] Example 4

[0068] In the first step, the water and oxygen levels in the glove box filled with argon were adjusted to ≤ 0.01 ppm.

[0069] In the second step, non-fluorinated conventional ether substances: ethylene glycol dimethyl ether and fluoroether substances: 1,2-bis(1,1,2,2-tetrafluoroethoxy)ethane were dehydrated using McLean 4A sodium molecular sieve with a pore size of 2mm-3mm. Then, 0.5mL of each solution was taken from a syringe cleaned and dried with ethanol and injected into a titration cup of a Karl Fischer moisture tester for water content testing. When the water content of ethylene glycol dimethyl ether was 28ppm and the water content of 1,2-bis(1,1,2,2-tetrafluoroethoxy)ethane was 25ppm, ethylene glycol dimethyl ether and 1,2-bis(1,1,2,2-tetrafluoroethoxy)ethane were mixed and stirred to obtain a mixture.

[0070] The third step is to place the mixture in an auxiliary refrigerator configured in the glove box, freeze it at -10°C for 6 hours, take it out and add sodium tetrafluoroborate to the mixture, mix it and let it stand for acidity test, the actual measured acidity result is 46.3ppm, and a negative electrode-free sodium ion battery electrolyte is obtained, wherein the mass ratio of ethylene glycol dimethyl ether, 1,2-bis(1,1,2,2-tetrafluoroethoxy)ethane and sodium tetrafluoroborate in the negative electrode-free sodium ion battery electrolyte is 55%:35%:10%.

[0071] The testing process is the same as in Example 1.

[0072] Example 5

[0073] In the first step, the water and oxygen levels in the glove box filled with argon were adjusted to ≤ 0.01 ppm.

[0074] In the second step, non-fluorinated conventional ether substances: ethylene glycol dimethyl ether and fluoroether substances: 1,2-bis(1,1,2,2-tetrafluoroethoxy)ethane were dehydrated using McLean 4A sodium molecular sieve with a pore size of 2mm-3mm. Then, 0.5mL of each solution was taken from a syringe cleaned and dried with ethanol and injected into a titration cup of a Karl Fischer moisture tester for water content testing. When the water content of ethylene glycol dimethyl ether was 28ppm and the water content of 1,2-bis(1,1,2,2-tetrafluoroethoxy)ethane was 25ppm, ethylene glycol dimethyl ether and 1,2-bis(1,1,2,2-tetrafluoroethoxy)ethane were mixed and stirred to obtain a mixture.

[0075] The third step is to place the mixture in an auxiliary refrigerator equipped in the glove box, freeze it at -10°C for 6 hours, take it out and add sodium tetrafluoroborate to the mixture, mix it and let it stand for acidity test, the actual measured acidity result is 33.5ppm, and a negative electrode-free sodium ion battery electrolyte is obtained, wherein the mass ratio of ethylene glycol dimethyl ether, 1,2-bis(1,1,2,2-tetrafluoroethoxy)ethane and sodium tetrafluoroborate in the negative electrode-free sodium ion battery electrolyte is 35%:55%:10%.

[0076] The testing process is the same as in Example 1.

[0077] Example 6

[0078] In the first step, the water and oxygen levels in the glove box filled with argon were adjusted to ≤ 0.01 ppm.

[0079] In the second step, non-fluorinated conventional ether substances: ethylene glycol dimethyl ether and fluoroether substances: 1,2-bis(1,1,2,2-tetrafluoroethoxy)ethane were dehydrated using McLean 4A sodium molecular sieve with a pore size of 2mm-3mm. Then, 0.5mL of each solution was taken from a syringe cleaned and dried with ethanol and injected into a titration cup of a Karl Fischer moisture tester for water content testing. When the water content of ethylene glycol dimethyl ether was 28ppm and the water content of 1,2-bis(1,1,2,2-tetrafluoroethoxy)ethane was 25ppm, ethylene glycol dimethyl ether and 1,2-bis(1,1,2,2-tetrafluoroethoxy)ethane were mixed and stirred to obtain a mixture.

[0080] The third step is to place the mixture in an auxiliary refrigerator configured in the glove box, freeze it at -10°C for 6 hours, take it out and add sodium tetrafluoroborate to the mixture, mix it and let it stand for acidity test, the actual measured acidity result is 39.8ppm, and a negative electrode-free sodium ion battery electrolyte is obtained, wherein the mass ratio of ethylene glycol dimethyl ether, 1,2-bis(1,1,2,2-tetrafluoroethoxy)ethane and sodium tetrafluoroborate in the negative electrode-free sodium ion battery electrolyte is 20%:70%:10%.

[0081] The testing process is the same as in Example 1.

[0082] Example 7

[0083] In the first step, the water and oxygen levels in the glove box filled with argon were adjusted to ≤ 0.01 ppm.

[0084] In the second step, non-fluorinated conventional ether substances: ethylene glycol dimethyl ether and fluoroether substances: 1,2-bis(1,1,2,2-tetrafluoroethoxy)ethane were dehydrated using McLean 4A sodium molecular sieve with a pore size of 2mm-3mm. Then, 0.5mL of each solution was taken from a syringe cleaned and dried with ethanol and injected into a titration cup of a Karl Fischer moisture tester for water content testing. When the water content of ethylene glycol dimethyl ether was 28ppm and the water content of 1,2-bis(1,1,2,2-tetrafluoroethoxy)ethane was 25ppm, ethylene glycol dimethyl ether and 1,2-bis(1,1,2,2-tetrafluoroethoxy)ethane were mixed and stirred to obtain a mixture.

[0085] The third step is to place the mixture in an auxiliary refrigerator configured in the glove box, freeze it at -10°C for 6 hours, take it out and add sodium tetrafluoroborate to the mixture, mix it and let it stand for acidity test, the actual measured acidity result is 45.5ppm, and a negative electrode-free sodium ion battery electrolyte is obtained, wherein the mass ratio of ethylene glycol dimethyl ether, 1,2-bis(1,1,2,2-tetrafluoroethoxy)ethane and sodium tetrafluoroborate in the negative electrode-free sodium ion battery electrolyte is 10%:80%:10%.

[0086] The testing process is the same as in Example 1.

[0087] Example 8

[0088] In the first step, the water and oxygen levels in the glove box filled with argon were adjusted to ≤ 0.01 ppm.

[0089] In the second step, non-fluorinated conventional ether substances: ethylene glycol dimethyl ether and fluorinated ether substances: 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether are respectively dehydrated using McLean 4A sodium molecular sieve with a pore size of 2mm-3mm. Then, 0.5mL of each substance is taken out of a syringe cleaned and dried with ethanol and injected into a titration cup of a Karl Fischer moisture tester for water content testing. When the water content of ethylene glycol dimethyl ether is 28ppm and the water content of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether is 25ppm, ethylene glycol dimethyl ether and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether are mixed and stirred to obtain a mixture.

[0090] The third step is to place the mixture in an auxiliary refrigerator configured in the glove box, freeze it at -10°C for 6 hours, take it out and add sodium tetrafluoroborate to the mixture, mix it and let it stand for acidity test, the actual measured acidity result is 42.3ppm, and a negative electrode-free sodium ion battery electrolyte is obtained, wherein the mass ratio of ethylene glycol dimethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether and sodium tetrafluoroborate in the negative electrode-free sodium ion battery electrolyte is 10%:80%:10%.

[0091] The testing process is the same as in Example 1.

[0092] Example 9

[0093] In the first step, the water and oxygen levels in the glove box filled with argon were adjusted to ≤ 0.01 ppm.

[0094] In the second step, non-fluorinated conventional ether substances: ethylene glycol dimethyl ether and fluorinated ether substances: 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether are respectively dehydrated using McLean 4A sodium molecular sieves with a pore size of 2mm-3mm. Then, 0.5mL of the solution is taken from a syringe cleaned and dried with ethanol and injected into a titration cup of a Karl Fischer moisture tester for water content testing. When the water content of ethylene glycol dimethyl ether is 28ppm and the water content of 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether is 25ppm, ethylene glycol dimethyl ether and 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether are mixed and stirred to obtain a mixture.

[0095] The third step is to place the mixture in an auxiliary refrigerator configured in the glove box, freeze it at -10°C for 6 hours, take it out and add sodium tetrafluoroborate to the mixture, mix it and let it stand for acidity test, the actual measured acidity result is 38.5ppm, and a negative electrode-free sodium ion battery electrolyte is obtained, wherein the mass ratio of ethylene glycol dimethyl ether, 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether and sodium tetrafluoroborate in the negative electrode-free sodium ion battery electrolyte is 10%:80%:10%.

[0096] The testing process is the same as in Example 1.

[0097] Example 10

[0098] In the first step, the water and oxygen levels in the glove box filled with argon were adjusted to ≤ 0.01 ppm.

[0099] In the second step, non-fluorinated conventional ether substances: ethylene glycol dimethyl ether and fluoroether substances: 1,2-bis(1,1,2,2-tetrafluoroethoxy)ethane were dehydrated using McLean 4A sodium molecular sieve with a pore size of 2mm-3mm. Then, 0.5mL of each solution was taken from a syringe cleaned and dried with ethanol and injected into a titration cup of a Karl Fischer moisture tester for water content testing. When the water content of ethylene glycol dimethyl ether was 28ppm and the water content of 1,2-bis(1,1,2,2-tetrafluoroethoxy)ethane was 25ppm, ethylene glycol dimethyl ether and 1,2-bis(1,1,2,2-tetrafluoroethoxy)ethane were mixed and stirred to obtain a mixture.

[0100] The third step is to place the mixture in an auxiliary refrigerator equipped in the glove box, freeze it at -10°C for 6 hours, take it out and add sodium tetrafluoroborate to the mixture, mix it and let it stand for acidity test, the actual measured acidity result is 38.2ppm, and a negative electrode-free sodium ion battery electrolyte is obtained, wherein the mass ratio of ethylene glycol dimethyl ether, 1,2-bis(1,1,2,2-tetrafluoroethoxy)ethane and sodium tetrafluoroborate in the negative electrode-free sodium ion battery electrolyte is 5%:85%:10%.

[0101] The testing process is the same as in Example 1.

[0102] Embodiment 11

[0103] In the first step, the water and oxygen levels in the glove box filled with argon were adjusted to ≤ 0.01 ppm.

[0104] In the second step, non-fluorinated conventional ether substances: ethylene glycol dimethyl ether and fluoroether substances: 1,2-bis(1,1,2,2-tetrafluoroethoxy)ethane were dehydrated using McLean 4A sodium molecular sieve with a pore size of 2mm-3mm. Then, 0.5mL of each solution was taken from a syringe cleaned and dried with ethanol and injected into a titration cup of a Karl Fischer moisture tester for water content testing. When the water content of ethylene glycol dimethyl ether was 28ppm and the water content of 1,2-bis(1,1,2,2-tetrafluoroethoxy)ethane was 25ppm, ethylene glycol dimethyl ether and 1,2-bis(1,1,2,2-tetrafluoroethoxy)ethane were mixed and stirred to obtain a mixture.

[0105] The third step is to place the mixture in an auxiliary refrigerator configured in the glove box, freeze it at -10°C for 6 hours, take it out and add sodium hexafluorophosphate to the mixture, mix it and let it stand for acidity test, the actual measured acidity result is 48.1ppm, and a negative electrode-free sodium ion battery electrolyte is obtained, wherein the mass ratio of ethylene glycol dimethyl ether, 1,2-bis(1,1,2,2-tetrafluoroethoxy)ethane and sodium hexafluorophosphate in the negative electrode-free sodium ion battery electrolyte is 20%:70%:10%.

[0106] The testing process is the same as in Example 1.

[0107] Example 12

[0108] In the first step, the water and oxygen levels in the glove box filled with argon were adjusted to ≤ 0.01 ppm.

[0109] In the second step, non-fluorinated conventional ether substances: ethylene glycol dimethyl ether and fluoroether substances: 1,2-bis(1,1,2,2-tetrafluoroethoxy)ethane were dehydrated using McLean 4A sodium molecular sieve with a pore size of 2mm-3mm. Then, 0.5mL of each solution was taken from a syringe cleaned and dried with ethanol and injected into a titration cup of a Karl Fischer moisture tester for water content testing. When the water content of ethylene glycol dimethyl ether was 28ppm and the water content of 1,2-bis(1,1,2,2-tetrafluoroethoxy)ethane was 25ppm, ethylene glycol dimethyl ether and 1,2-bis(1,1,2,2-tetrafluoroethoxy)ethane were mixed and stirred to obtain a mixture.

[0110] The third step is to place the mixture in an auxiliary refrigerator equipped in the glove box, freeze it at -10°C for 6 hours, take it out and add sodium bis(fluorosulfonyl)imide to the mixture, mix it and let it stand for acidity test, the actual measured acidity result is 42.3ppm, and a negative electrode-free sodium ion battery electrolyte is obtained, wherein the mass ratio of ethylene glycol dimethyl ether, 1,2-bis(1,1,2,2-tetrafluoroethoxy)ethane and sodium bis(fluorosulfonyl)imide in the negative electrode-free sodium ion battery electrolyte is 10%:80%:10%.

[0111] The testing process is the same as in Example 1.

[0112] Embodiment 13

[0113] In the first step, the water and oxygen levels in the glove box filled with argon were adjusted to ≤ 0.01 ppm.

[0114] In the second step, McLean 4A sodium molecular sieve with a pore size of 2mm-3mm is used to dewater the non-fluorinated conventional ether substances: tetrahydrofuran and the fluorinated ether substances: 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether. Then, 0.5mL is taken from the syringe cleaned and dried with ethanol and injected into the titration cup of the Karl Fischer moisture tester for water content testing. When the water content of tetrahydrofuran is 25ppm and the water content of 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether is 26ppm, tetrahydrofuran and 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether are mixed and stirred to obtain a mixture.

[0115] The third step is to place the mixture in an auxiliary refrigerator configured in the glove box, freeze it at -10°C for 6 hours, take it out and add sodium perchlorate to the mixture, mix it and let it stand for acidity test, the actual measured acidity result is 48.0ppm, and a negative electrode-free sodium ion battery electrolyte is obtained, wherein the mass ratio of ethylene glycol dimethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether and sodium perchlorate in the negative electrode-free sodium ion battery electrolyte is 15%:65%:20%.

[0116] The testing process is the same as in Example 1.

[0117] Embodiment 14

[0118] In the first step, the water and oxygen levels in the glove box filled with argon were adjusted to ≤ 0.01 ppm.

[0119] In the second step, McLean 4A sodium molecular sieve with a pore size of 2mm-3mm is used to dewater the non-fluorinated conventional ether substances: dimethoxypropane and the fluorinated ether substances: 1,1,2,3,3,3-hexafluoropropyl methyl ether, and then 0.5mL is taken from the syringe cleaned and dried with ethanol and injected into the titration cup of the Karl Fischer moisture tester for water content testing. When the water content of dimethoxypropane is 28ppm and the water content of 1,1,2,3,3,3-hexafluoropropyl methyl ether is 25ppm, dimethoxypropane and 1,1,2,3,3,3-hexafluoropropyl methyl ether are mixed and stirred to obtain a mixture.

[0120] The third step is to place the mixture in an auxiliary refrigerator configured in the glove box, freeze it at -10°C for 6 hours, take it out and add sodium bis(trifluoromethylsulfonyl)imide to the mixture, mix it and let it stand for acidity test, the actual measured acidity result is 43.9ppm, and a negative electrode-free sodium ion battery electrolyte is obtained, wherein the mass ratio of dimethoxypropane, 1,1,2,3,3,3-hexafluoropropyl methyl ether and sodium bis(trifluoromethylsulfonyl)imide in the negative electrode-free sodium ion battery electrolyte is 10%:85%:5%.

[0121] The testing process is the same as in Example 1.

[0122] Embodiment 15

[0123] In the first step, the water and oxygen levels in the glove box filled with argon were adjusted to ≤ 0.01 ppm.

[0124] In the second step, McLean 4A sodium molecular sieve with a pore size of 2mm-3mm is used to dewater the non-fluorinated conventional ether substances: 1,3-dioxolane and the fluorinated ether substances: 1,1,2,3,3,3-hexafluoropropyldifluoromethyl ether, and then 0.5mL is taken from the syringe cleaned and dried with ethanol and injected into the titration cup of the Karl Fischer moisture tester for water content testing. When the water content of 1,3-dioxolane is 28ppm and the water content of 1,1,2,3,3,3-hexafluoropropyldifluoromethyl ether is 25ppm, 1,3-dioxolane and 1,1,2,3,3,3-hexafluoropropyldifluoromethyl ether are mixed and stirred to obtain a mixture.

[0125] The third step is to place the mixture in an auxiliary refrigerator equipped in the glove box, freeze it at -10°C for 6 hours, take it out and add sodium hexafluorophosphate to the mixture, mix it and let it stand for acidity test, the actual measured acidity result is 43.3ppm, and a negative electrode-free sodium ion battery electrolyte is obtained, wherein the mass ratio of 1,3-dioxolane, 1,1,2,3,3,3-hexafluoropropyldifluoromethyl ether and sodium hexafluorophosphate in the negative electrode-free sodium ion battery electrolyte is 36%:34%:30%.

[0126] The testing process is the same as in Example 1.

[0127] Comparative Example 1

[0128] In the first step, the water and oxygen levels in the glove box filled with argon were adjusted to ≤ 0.01 ppm.

[0129] In the second step, the non-fluorinated conventional ether substance, ethylene glycol dimethyl ether, was dehydrated using a McLean 4A sodium molecular sieve with a pore size of 2mm-3mm. Then, 0.5mL was taken from a syringe cleaned and dried with ethanol and injected into the titration cup of a Karl Fischer moisture tester for water content testing until the water content of ethylene glycol dimethyl ether reached 28ppm.

[0130] The third step is to place ethylene glycol dimethyl ether in an auxiliary refrigerator equipped in the glove box, freeze it at -10°C for 6 hours, take it out and add sodium tetrafluoroborate to ethylene glycol dimethyl ether, mix it and let it stand for acidity test, the actual measured acidity result is 38.1ppm, and a negative electrode-free sodium ion battery electrolyte is obtained, wherein the mass ratio of ethylene glycol dimethyl ether and sodium tetrafluoroborate in the negative electrode-free sodium ion battery electrolyte is 90%:10%.

[0131] The testing process is the same as in Example 1.

[0132] Comparative Example 2

[0133] In the first step, the water and oxygen levels in the glove box filled with argon were adjusted to ≤ 0.01 ppm.

[0134] In the second step, the non-fluorinated conventional ether substances: ethylene glycol dimethyl ether and 1,3-dioxolane were dehydrated using a McLean 4A sodium molecular sieve with a pore size of 2mm-3mm. Then, 0.5mL was taken from a syringe cleaned and dried with ethanol and injected into the titration cup of a Karl Fischer moisture tester for water content testing. When the water content of ethylene glycol dimethyl ether was 28ppm and the water content of 1,3-dioxolane was 25ppm, ethylene glycol dimethyl ether and 1,3-dioxolane were mixed and stirred to obtain a mixture.

[0135] The third step is to place the mixture in an auxiliary refrigerator equipped in the glove box, freeze it at -10°C for 6 hours, take it out and add sodium tetrafluoroborate to the mixture, mix it and let it stand for acidity test, the actual measured acidity result is 29.9ppm, and a negative electrode-free sodium ion battery electrolyte is obtained, wherein the mass ratio of ethylene glycol dimethyl ether, 1,3-dioxolane and sodium tetrafluoroborate in the negative electrode-free sodium ion battery electrolyte is 55%:35%:10%.

[0136] The testing process is the same as in Example 1.

[0137] Table 1 is a summary of the test results of Examples 1-15 of the present invention and Comparative Examples 1-2.

[0138]

[0139]

[0140] Table 1

[0141] As can be seen from Table 1, the first coulombic efficiency, capacity retention rate after 50 cycles and ES I impedance of the button cell of Example 1-15 are better than those of Comparative Example 1-2. This is because the introduction of fluoroether substances can enhance the overall antioxidant capacity of the electrolyte, making up for the disadvantage of low oxidation stability of non-fluorinated conventional ethers, so that the electrolyte can be adapted to high-voltage positive electrode materials. In addition, the content and density of the inorganic component NaF in the SE I membrane component formed by the participation of fluoroether substances are significantly improved, and the SE I formed by the participation of NaF-rich components is more conducive to the uniform deposition and stripping of sodium ions, further inhibiting the growth of sodium dendrites, effectively reducing the interface impedance, improving the first coulombic efficiency and cycle capacity retention rate, and being able to operate stably at a high operating voltage (3.8V).

[0142] However, there is no fluorinated ether in the electrolytes of Comparative Examples 1-2. Although two non-fluorinated conventional ethers are added to Comparative Example 2, the antioxidant performance of the electrolyte is still not improved. In addition, due to the high content of organic components in its solid electrolyte membrane, the formed SE I membrane has fewer ion transmission channels and lower density, and cannot induce uniform deposition and stripping of sodium ions, and cannot effectively inhibit the formation of sodium dendrites, so that the electrochemical performance of the battery prepared therefrom is average.

[0143] In addition, it can be seen from Examples 1-7 that as the amount of fluoroether substances added increases, the electrochemical performance is better. However, when comparing Example 7 with Example 10, the electrochemical performance of the battery in Example 10 has decreased, indicating that the higher the amount of fluoroether substances added, the better. This is because the fluorinated 1,2-bis(1,1,2,2-tetrafluoroethoxy)ethane is an inert solvent, and the inert solvent molecules have the characteristics of low dielectric constant and low electron donor, and the ability to dissolve sodium salts and dissociate solvents is weak, while the active solvent molecules with relatively strong electron donors achieve high dissociation of sodium salts and high Na+ in electrolytes. + The use of ethylene glycol dimethyl ether with high conductivity is too low, resulting in a certain degree of reduction in electrochemical performance.

[0144] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A negative electrode-free sodium ion battery electrolyte, characterized in that: The negative electrode-free sodium ion battery electrolyte includes non-fluorinated conventional ether substances, fluorinated ether substances and sodium salts; the mass percentages of the non-fluorinated conventional ether substances, fluorinated ether substances and sodium salts are: 5%-85%: 5%-85%: 5%-30%; wherein the non-fluorinated conventional ether substances include linear ethers and / or cyclic ethers.

2. The negative electrode-free sodium ion battery electrolyte according to claim 1, characterized in that: The cyclic ether includes at least one of 1,3-dioxolane, tetrahydrofuran, and 2-methyltetrahydrofuran.

3. The negative electrode-free sodium ion battery electrolyte according to claim 1, characterized in that: The linear ether includes at least one of dimethoxypropane, dimethoxymethane, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether and tetraethylene glycol dimethyl ether.

4. The negative electrode-free sodium ion battery electrolyte according to claim 1, characterized in that: The fluoroether substances include: 1,1,2,2-tetrafluoroethyl methyl ether, 1,1,2,2-tetrafluoroethyl ethyl ether, bis(2,2,2-trifluoroethyl) ether, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, perfluoropropyl vinyl ether, 1,1,2,3,3,3-hexafluoropropyl methyl ether, methyl 2,2,3,3,3-pentafluoropropyl ether, difluoromethyl 2, At least one of 2,3,3-tetrafluoropropyl ether, allyl 1,1,2,3,3,3-hexafluoropropyl ether, 1,1,2,3,3,3-hexafluoropropyl difluoromethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 2-(heptafluoropropoxy)hexafluoropropyl trifluorovinyl ether, 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether, and 1,2-bis(1,1,2,2-tetrafluoroethoxy)ethane.

5. The negative electrode-free sodium ion battery electrolyte according to claim 1, characterized in that: The sodium salt includes any one or more of sodium tetrafluoroborate, sodium hexafluorophosphate, sodium perchlorate, sodium bis(trifluoromethylsulfonyl)imide, and sodium bis(trifluoromethylsulfonyl)imide.

6. A method for preparing a negative electrode-free sodium ion battery electrolyte according to any one of claims 1 to 5, characterized in that: The preparation method comprises: The water value and oxygen value of the glove box filled with argon are adjusted to within the preset value range; After dehydrating the non-fluorinated conventional ether substance and the fluorinated ether substance, respectively, a water content test is performed, and when the water content of the non-fluorinated conventional ether substance and the fluorinated ether substance is not greater than a preset water content, the non-fluorinated conventional ether substance and the fluorinated ether substance are mixed and stirred to obtain a mixture; Sodium salt is added to the mixture, mixed and allowed to stand, and an acidity test is performed. When the acidity value is not greater than a preset acidity value, the negative electrode-free sodium ion battery electrolyte is obtained; the mass percentages of non-fluorinated conventional ether substances, fluoroether substances and sodium salt in the negative electrode-free sodium ion battery electrolyte are: 5%-85%: 5%-85%: 5%-30%; wherein the non-fluorinated conventional ether substances include linear ethers and / or cyclic ethers.

7. The preparation method according to claim 6, characterized in that: The preset value range is less than or equal to 0.01 ppm.

8. The preparation method according to claim 6, characterized in that: The preset water content is 30 ppm.

9. The preparation method according to claim 6, characterized in that: The preset acidity value is 50 ppm.

10. A negative electrode-free sodium ion battery, characterized in that: The negative electrode-free sodium ion battery comprises a positive electrode plate, a negative electrode plate, a separator, and the negative electrode-free sodium ion battery electrolyte described in any one of claims 1 to 5 above or the negative electrode-free sodium ion battery electrolyte prepared by the preparation method described in any one of claims 6 to 9 above.

Images