Ether electrolyte and sodium ion battery thereof

Abstract

The invention provides an ether electrolyte and a sodium ion battery thereof, the ether electrolyte comprises methyl 2, 2-difluoro-2-(fluorosulfonyl) acetate, an ether solvent and a sodium salt, and the ether solvent is ethylene glycol dimethyl ether, diethylene glycol dimethyl ether or triethylene glycol dimethyl ether. The sodium ion battery comprises a positive electrode, a negative electrode and the electrolyte, the electrolyte is the electrolyte, the positive electrode comprises a current collector and sodium vanadyl fluorophosphate (NVOPF) loaded on the current collector, and / or the negative electrode comprises a current collector and a hard carbon (HC) material loaded on the current collector. The ether electrolyte can improve the cycling stability of a hard carbon negative electrode and a sodium vanadyl fluorophosphate positive electrode.

Description

Technical Field

[0001] The present invention belongs to the technical field of sodium ion batteries, and in particular relates to an ether electrolyte and a sodium ion battery thereof. Background Art

[0002] Sodium-ion batteries are rechargeable, secondary batteries that store and release electrical energy through the intercalation and deintercalation of sodium ions between the positive and negative electrodes. Due to the global availability and low cost of sodium resources, sodium-ion batteries are considered a potential alternative to lithium-ion batteries, particularly for large-scale energy storage systems such as grid storage.

[0003] Hard carbon (HC) is an amorphous carbon material characterized by an irregular graphite layer structure and numerous micropores and defects. These properties make hard carbon an ideal anode material for sodium-ion batteries. Compared to other carbon materials, hard carbon offers higher sodium storage capacity and exhibits superior structural stability during cycling. Hard carbon is typically prepared by pyrolysis of biomass, polymers, or other carbon-containing precursors. Ether electrolytes are electrolytes whose solvents primarily consist of ether compounds. These electrolytes have a low dielectric constant and high chemical stability, maintaining stability over a wide voltage window. For sodium-ion batteries, ether electrolytes can effectively reduce side reactions and facilitate the formation of a stable solid electrolyte interface (SEI) film, thereby improving battery safety and cycle life. Ether electrolytes also reduce the risk of reductive decomposition of the sodium metal or hard carbon anode surface, contributing to improved overall battery performance. Although ether electrolytes facilitate the formation of a stable SEI film, the stability of this film on the hard carbon surface may not be as expected. During long-term cycling, the SEI film may rupture or dissolve, leading to continuous decomposition of the electrolyte, affecting the battery's cycle life and capacity retention. In particular, the formation of an unstable SEI film significantly affects the sodium storage performance of the hard carbon anode material, further affecting the cycling stability of the electrode itself and the operating life of the battery device.

[0004] In addition, sodium vanadyl fluorophosphate (Na3V2(OPO4)2F, NVOPF), as a high-voltage cathode material for sodium-ion batteries, is considered an ideal candidate for large-scale energy storage due to its high theoretical specific energy (~507 Wh / kg) and safety. Ethylene glycol dimethyl ether solvents, typical solvents for ether electrolytes, have become key media for improving NVOPF battery performance due to their low melting point, high ionic conductivity, and excellent sodium ion solvation ability. However, in actual use, the high voltage operating conditions (>4.2 V) of NVOPF-based sodium-ion batteries cause the continuous decomposition of ethylene glycol dimethyl ether solvents, resulting in decreased cycling stability, which needs to be further addressed. Summary of the Invention

[0005] In order to solve the problems existing in the prior art, the present invention proposes an ether electrolyte and a sodium ion battery thereof, wherein the ether electrolyte can improve the cycle stability of the hard carbon negative electrode and the NVOPF positive electrode.

[0006] The present invention is achieved through the following technical solutions: In a first aspect, the present invention provides an ether electrolyte comprising methyl 2,2-difluoro-2-(fluorosulfonyl)acetate, an ether solvent and a sodium salt, wherein the ether solvent is ethylene glycol dimethyl ether, diethylene glycol dimethyl ether or triethylene glycol dimethyl ether.

[0007] Preferably, the ether solvent is ethylene glycol dimethyl ether.

[0008] Preferably, the sodium salt is sodium bis(fluorosulfonyl)imide, sodium bis(trifluorosulfonyl)imide, sodium perchlorate or sodium hexafluorophosphate.

[0009] Furthermore, the sodium salt is sodium bis(fluorosulfonyl)imide or sodium hexafluorophosphate.

[0010] Preferably, the content of methyl 2,2-difluoro-2-(fluorosulfonyl)acetate is 0.1 wt% to 5 wt% of the total mass of the ether solvent and the sodium salt.

[0011] Preferably, the concentration of the sodium salt is 0.5-2 mol / L.

[0012] Furthermore, the concentration of the sodium salt is 0.5~1.2 mol / L.

[0013] In a second aspect, the present invention provides a sodium ion battery comprising a positive electrode, a negative electrode and an electrolyte, wherein the electrolyte is the ether electrolyte as described above, and the positive electrode comprises a current collector and sodium vanadium fluorophosphate loaded on the current collector.

[0014] Furthermore, the negative electrode includes a current collector and a hard carbon material supported on the current collector.

[0015] In a second aspect, the present invention provides a sodium ion battery comprising a positive electrode, a negative electrode and an electrolyte, wherein the electrolyte is the ether electrolyte as described above, and the negative electrode comprises a current collector and a hard carbon material loaded on the current collector.

[0016] Compared with the prior art, the present invention has the following beneficial effects: The present invention introduces methyl 2,2-difluoro-2-(fluorosulfonyl) acetate (MDFSA) into an ether electrolyte system based on ethylene glycol dimethyl ether. The sulfonyl oxygen (-S=O) and carbonyl oxygen (-C=O) groups on the methyl 2,2-difluoro-2-(fluorosulfonyl) acetate molecule possess lone pairs of electrons, serving as potential coordination sites. Due to the high polarity and specific oxygen atom type (especially the sulfonyl oxygen) of the methyl 2,2-difluoro-2-(fluorosulfonyl) acetate molecule, it retains a strong affinity for Na⁺ (a strong Lewis acid). Consequently, the methyl 2,2-difluoro-2-(fluorosulfonyl) acetate molecules compete with and partially replace the ethylene glycol dimethyl ether solvent molecules originally coordinated around Na⁺, forming [Na⁺(solvent) x (additive) y ] mixed solvation sheath structure. Therefore, the introduction of 2,2-difluoro-2-(fluorosulfonyl)acetic acid methyl ester can change the solvation structure of sodium ions in the electrolyte. When the oxidation reaction occurs under high voltage conditions on the positive electrode surface, the reaction occurs in advance at the interface. The constructed electrode electrolyte interface passivates the degree of reaction at the interface, thereby inhibiting the decomposition reaction of ethylene glycol dimethyl ether solvents, thereby improving the stability of sodium ion batteries based on NVOPF. At the same time, after the introduction of 2,2-difluoro-2-(fluorosulfonyl)acetic acid methyl ester, the interaction with sodium ions and solvents is enhanced, which broadens the electrochemical window of the electrolyte and improves the antioxidant capacity and stability of the electrolyte under high voltage conditions. In addition, during the first cycle, 2,2-difluoro-2-(fluorosulfonyl)acetic acid methyl ester decomposes to generate sodium fluoride and sodium sulfide and deposits on the surface of the hard carbon negative electrode, forming a relatively stable SEI film on the surface of the hard carbon negative electrode, thereby improving the reversible sodium storage stability of the hard carbon negative electrode. The generated SEI film acts as a fast ion conductor for sodium ions, improving the Na + The migration kinetics of Na + The uniform deposition of 2,2-difluoro-2-(fluorosulfonyl)acetate improves the cycling stability of the hard carbon anode. Furthermore, the introduction of methyl 2,2-difluoro-2-(fluorosulfonyl)acetate increases the decomposition voltage of the electrolyte, improves the decomposition pathway of substances on the electrode surface, inhibits the side reactions of ethylene glycol dimethyl ether solvents on the anode surface, reduces unnecessary solvent loss during cycling, and extends battery life.

[0017] The sodium ion battery of the present invention uses NVOPF as the positive electrode material and an ether electrolyte of 2,2-difluoro-2-(fluorosulfonyl) methyl acetate and ethylene glycol dimethyl ether as the electrolyte. The 2,2-difluoro-2-(fluorosulfonyl) methyl acetate molecules will compete with and partially replace the ethylene glycol dimethyl ether solvent molecules originally coordinated around Na⁺, forming [Na⁺(solvent) x (additive) y]'s mixed solvation sheath structure reacts in advance at the interface when an oxidation reaction occurs under high voltage conditions on the positive electrode surface. The constructed electrode-electrolyte interface passivates the degree of reaction at the interface, thereby inhibiting the decomposition reaction of ethylene glycol dimethyl ether solvents, thereby improving the stability of sodium-ion batteries based on NVOPF.

[0018] Furthermore, using hard carbon as the negative electrode material, during the first cycle, 2,2-difluoro-2-(fluorosulfonyl)acetic acid methyl ester decomposes to produce sodium fluoride and sodium sulfide and deposits on the surface of the hard carbon negative electrode, forming a relatively stable SEI film on the surface of the hard carbon negative electrode, thereby improving the cycle stability of the hard carbon negative electrode. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0020] Figure 1 This is a graph showing the long cycle performance test of hard carbon in Example 1.

[0021] Figure 2 This is a graph showing the voltage-capacity of the hard carbon of Example 1 at 30 cycles.

[0022] Figure 3 This is a graph showing the voltage capacity of the hard carbon of Comparative Example 1 at 30 cycles.

[0023] Figure 4 This is a voltage-capacity diagram of the NVOPF of Example 7 during the first cycle.

[0024] Figure 5 This is the voltage-capacity diagram of the NVOPF of comparative example 1 during the first cycle. DETAILED DESCRIPTION

[0025] The following describes the embodiments of the present invention through specific examples. Those skilled in the art will readily understand the other advantages and benefits of the present invention from the disclosure herein. The present invention may also be implemented or applied through various other specific embodiments, and the details in this specification may be modified or altered based on different viewpoints and applications without departing from the spirit of the present invention.

[0026] It should be noted that the process equipment or devices not specifically specified in the following embodiments are all conventional equipment or devices in the art.

[0027] It should be noted that the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions. For example, a process, method, system, product, or apparatus comprising a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to these processes, methods, products, or apparatuses. Furthermore, unless otherwise specified, the numbering of each method step is merely a convenient tool for identifying each method step, and is not intended to limit the order of arrangement of each method step or to define the scope of the invention. Changes or adjustments to their relative relationships, without substantially changing the technical content, should also be considered within the scope of the invention.

[0028] The ether electrolyte of the present invention comprises methyl 2,2-difluoro-2-(fluorosulfonyl)acetate, an ether solvent and a sodium salt, wherein the ether solvent is ethylene glycol dimethyl ether (DME), diethylene glycol dimethyl ether (DEGDME) or triethylene glycol dimethyl ether (TEGDME).

[0029] In the ether electrolyte, the 2,2-difluoro-2-(fluorosulfonyl)acetic acid methyl ester is used as an additive, and its structural formula is:

[0030] The sodium salt includes but is not limited to sodium bis(fluorosulfonyl)imide (NaFSI), sodium bis(trifluorosulfonyl)imide (NaTFSI), sodium perchlorate (NaClO4) and sodium hexafluorophosphate (NaPF6). The concentration of the sodium salt in the ether electrolyte is 0.5-2 mol / L, preferably 0.5-1.2 mol / L.

[0031] In the ether electrolyte, the content of methyl 2,2-difluoro-2-(fluorosulfonyl)acetate is 0.1 wt% to 5 wt% of the total mass of the ether solvent and the sodium salt, and more preferably 1 wt% to 5 wt%.

[0032] The preparation method of the ether electrolyte of the present invention is: 2,2-difluoro-2-(fluorosulfonyl)acetic acid methyl ester, an ether solvent and a sodium salt are mixed. The preparation process is simple and controllable, the cost is reduced, and scalable production is possible.

[0033] As an embodiment of the present invention, the sodium ion battery described in the present invention includes a positive electrode, a negative electrode and the above-mentioned ether electrolyte, the positive electrode includes a current collector and sodium vanadium fluorophosphate loaded on the current collector; preferably, the negative electrode includes a current collector and a hard carbon material loaded on the current collector.

[0034] As another embodiment of the present invention, the sodium ion battery of the present invention includes a positive electrode, a negative electrode and the above-mentioned ether electrolyte, and the negative electrode includes a current collector and a hard carbon material supported on the current collector.

[0035] The specific mechanism of the improvement of the cycle stability of sodium ion batteries by introducing 2,2-difluoro-2-(fluorosulfonyl)acetic acid methyl ester into the ether electrolyte of the present invention is as follows: (1) The 2,2-difluoro-2-(fluorosulfonyl)acetic acid methyl ester molecule has high polarity and a specific oxygen atom type (especially sulfonyl oxygen), which makes it still have a strong affinity for Na⁺ (strong Lewis acid), competing with and partially replacing the glycol dimethyl ether solvent molecules originally coordinated around Na⁺, forming [Na⁺(solvent) x (additive) y ] mixed solvation sheath structure, that is, changing the solvation structure of sodium ions in the electrolyte, when the oxidation reaction occurs under high voltage conditions on the positive electrode surface, the reaction occurs in advance at the interface, and the constructed electrode electrolyte interface passivates the reaction degree at the interface, thereby inhibiting the decomposition reaction of ethylene glycol dimethyl ether solvents, thereby improving the cycle stability of the NVOPF positive electrode; (2) Sodium fluoride and sodium sulfide produced by the decomposition of the fluorosulfonyl group of 2,2-difluoro-2-(fluorosulfonyl)acetic acid methyl ester have high electrical conductivity. At the same time, the two fluorine atoms on the inside are also conducive to the formation of sodium fluoride. Inorganic substances such as sodium fluoride and sodium sulfide cover the hard A stable SEI film is formed on the surface of the carbon negative electrode. The formed SEI film has a certain mechanical strength and is also conducive to the rapid migration and uniform deposition of sodium ions, improving the cycle stability of the hard carbon negative electrode, and thus improving the cycle stability of the sodium ion battery; (3) 2,2-difluoro-2-(fluorosulfonyl)acetic acid methyl ester gives the electrolyte a highly stable redox property, increases the decomposition voltage of the electrolyte, improves the material decomposition path on the electrode surface, and inhibits the side reaction of ethylene glycol dimethyl ether solvents on the negative electrode surface; (4) The SEI film formed by the decomposition of 2,2-difluoro-2-(fluorosulfonyl)acetic acid methyl ester before the cycle is conducive to the Na + Rapidly cross the SEI film to inhibit Na + uneven deposition.

[0036] The present invention achieves synergistic effects between the solvent and the additive by optimizing the reasonable ratio of 2,2-difluoro-2-(fluorosulfonyl)acetic acid methyl ester, while maximizing the high specific energy and high capacity characteristics of the hard carbon material.

[0037] The present invention will be further described below with reference to the accompanying drawings and embodiments, but the protection scope of the present invention is not limited to these embodiments.

[0038] Example 1 The ether electrolyte of this embodiment is prepared by compounding sodium salt NaFSI, solvent DME and methyl 2,2-difluoro-2-(fluorosulfonyl)acetate.

[0039] The preparation method is as follows: DME and NaFSI are prepared into a solution according to the molar concentration of NaFSI of 1 mol / L in a glove box with water and oxygen content less than 0.1 ppm, and then 2,2-difluoro-2-(fluorosulfonyl)acetic acid methyl ester is added at a concentration of 2 wt%, and the mixture is thoroughly stirred and mixed to obtain a sodium ion battery ether electrolyte.

[0040] The ether electrolyte system was used in the HC||Na half-cell to conduct physical and electrochemical cycle tests. The test results are as follows Figure 1 As shown, it can be seen that the battery is able to -1 ) The capacity retention rate is 99.2% after 150 stable cycles at a high rate. Figure 2 This is a graph showing the voltage capacity of the hard carbon of this embodiment at 30 cycles.

[0041] Example 2 The ether electrolyte of this embodiment is prepared by compounding sodium salt NaPF6, solvent DME and methyl 2,2-difluoro-2-(fluorosulfonyl)acetate.

[0042] The preparation method is as follows: DME and NaPF6 are prepared into a solution according to the NaPF6 molar concentration of 1 mol / L in a glove box with water and oxygen content less than 0.1 ppm, and then 2,2-difluoro-2-(fluorosulfonyl)acetic acid methyl ester is added at a concentration of 2wt%, and the mixture is thoroughly stirred and mixed to obtain a sodium ion battery ether electrolyte.

[0043] The ether electrolyte system was used in the electrochemical cycle test of HC||Na half-cell. The test results showed that the battery could -1 ) The capacity retention rate is 98.5% after 150 stable cycles at a high rate.

[0044] Example 3 The ether electrolyte of this embodiment is prepared by compounding sodium salt NaPF6, solvent DME and methyl 2,2-difluoro-2-(fluorosulfonyl)acetate.

[0045] The preparation method is as follows: DME and NaPF6 are prepared into a solution according to the NaPF6 molar concentration of 1 mol / L in a glove box with water and oxygen content less than 0.1 ppm, and then 2,2-difluoro-2-(fluorosulfonyl)acetic acid methyl ester is added at a concentration of 1wt%, and the mixture is thoroughly stirred and mixed to obtain a sodium ion battery ether electrolyte.

[0046] The ether electrolyte system was used in the electrochemical cycle test of HC||Na half-cell. The test results showed that the battery could -1) The capacity retention rate after 200 stable cycles is 85.77%.

[0047] Example 4 The ether electrolyte of this embodiment is prepared by compounding sodium salt NaPF6, solvent DME and methyl 2,2-difluoro-2-(fluorosulfonyl)acetate.

[0048] The preparation method is as follows: DME and NaPF6 are prepared into a solution according to the NaPF6 molar concentration of 1 mol / L in a glove box with water and oxygen content less than 0.1 ppm, and then 2,2-difluoro-2-(fluorosulfonyl)acetic acid methyl ester is added at a concentration of 5wt%, and the mixture is thoroughly stirred and mixed to obtain a sodium ion battery ether electrolyte.

[0049] The ether electrolyte system was used in the electrochemical cycle test of HC||Na half-cell. The test results showed that the battery could -1 ) The capacity retention rate after 200 stable cycles is 88.8%.

[0050] Example 5 The ether electrolyte of this embodiment is prepared by compounding sodium salt NaPF6, solvent DME and methyl 2,2-difluoro-2-(fluorosulfonyl)acetate.

[0051] The preparation method is as follows: DME and NaPF6 are prepared into a solution according to the NaPF6 molar concentration of 1 mol / L in a glove box with water and oxygen content less than 0.1 ppm, and then 2,2-difluoro-2-(fluorosulfonyl)acetic acid methyl ester is added at a concentration of 1wt%, and the mixture is thoroughly stirred and mixed to obtain a sodium ion battery ether electrolyte.

[0052] The ether electrolyte system was used in the NVOPF||Na half-cell for electrochemical cycling test. The test results showed that the battery could -1 ) The capacity retention rate after 200 stable cycles at a rate of 94.40%.

[0053] Example 6 The ether electrolyte of this embodiment is prepared by compounding sodium salt NaPF6, solvent DME and methyl 2,2-difluoro-2-(fluorosulfonyl)acetate.

[0054] The preparation method is as follows: DME and NaPF6 are prepared into a solution according to the NaPF6 molar concentration of 1 mol / L in a glove box with water and oxygen content less than 0.1 ppm, and then 2,2-difluoro-2-(fluorosulfonyl)acetic acid methyl ester is added at a concentration of 5wt%, and the mixture is thoroughly stirred and mixed to obtain a sodium ion battery ether electrolyte.

[0055] The ether electrolyte system was used in the NVOPF||Na half-cell for electrochemical cycling test. The test results showed that the battery could -1 ) The capacity retention rate after 200 stable cycles at a rate of 91.27%.

[0056] Example 7 The ether electrolyte of this embodiment is prepared by compounding sodium salt NaFSI, solvent DME and methyl 2,2-difluoro-2-(fluorosulfonyl)acetate.

[0057] The preparation method is as follows: DME and NaFSI are prepared into a solution according to the molar concentration of NaFSI of 1 mol / L in a glove box with water and oxygen content less than 0.1 ppm, and then 2,2-difluoro-2-(fluorosulfonyl)acetic acid methyl ester is added at a concentration of 3wt%, and the mixture is thoroughly stirred and mixed to obtain a sodium ion battery ether electrolyte.

[0058] The ether electrolyte system was used in the NVOPF||Na half-cell for electrochemical cycling test. The test results showed that the battery could -1 ) The capacity retention rate after 200 stable cycles is 88.71%. Figure 4 The voltage-capacity diagram of NVOPF in the first cycle shows that the specific capacity exceeds 120 mAh g at a high voltage of 4.2 V. -1 .

[0059] Comparative Example 1 The ether electrolyte in this comparative example is prepared by compounding sodium salt NaFSI and solvent DME.

[0060] The preparation method is as follows: DME and NaFSI are prepared into a solution at a molar concentration of 1 mol / L in a glove box where the water and oxygen content are both less than 0.1 ppm, and the solution is fully stirred and mixed to obtain a sodium ion battery electrolyte.

[0061] The ether electrolyte system was used in HC||Na and NVOPF||Na half-cells for electrochemical cycling tests.

[0062] Figure 3 The voltage-capacity diagram of the hard carbon (HC||Na half-cell) in comparative example 1 at 30 cycles shows that the battery has a capacity of 1C (1C=300mA g -1 ) After 30 cycles at a rate of + The uneven deposition leads to abnormal charging capacity.

[0063] Figure 5This is the voltage-capacity diagram of comparative example 1 NVOPF (NVOPF||Na half-cell) in the first cycle. It can be seen that the voltage of the NVOPF material cannot fully reach 4.2 V.

[0064] contrast Figure 2 and Figure 3 It can be seen that in Comparative Example 1, the SEI film formed by the solvent DME is not stable on the hard carbon surface, which makes Na + Uneven deposition leads to abnormal charging capacity, which will greatly affect the sodium storage performance of the hard carbon negative electrode material and further affect the cycle stability of the electrode itself. The introduction of 2,2-difluoro-2-(fluorosulfonyl)acetic acid methyl ester into the electrolyte of Example 1 of the present invention can stabilize the SEI film and improve the Na + The migration kinetics of Na + The uniform deposition of hard carbon anode greatly improves the reversible sodium storage stability.

[0065] contrast Figure 4 and Figure 5 As can be seen, in Comparative Example 1, the solvent DME easily decomposes under high voltage conditions, resulting in the NVOPF material voltage being unable to fully reach 4.2 V. Consequently, the NVOPF cannot properly charge and discharge, leading to a significant decrease in specific capacity. However, the introduction of methyl 2,2-difluoro-2-(fluorosulfonyl)acetate into the electrolyte of Example 1 of the present invention effectively inhibits the decomposition of the solvent DME under high voltage conditions, thereby significantly improving the charge and discharge performance of the NVOPF.

[0066] The test data of the sodium ion batteries of Examples 3 to 7 are shown in Table 1.

[0067] Table 1

[0068] As can be seen from Table 1, the cycle stability of the hard carbon negative electrode and the NVOPF positive electrode of the present invention are both high.

[0069] In summary, by comparing the examples and comparative examples, it can be seen that the introduction of methyl 2,2-difluoro-2-(fluorosulfonyl)acetate can greatly improve the cycle stability of the hard carbon negative electrode and the NVOPF positive electrode, thereby improving the cycle stability and capacity retention rate of the sodium ion battery.

[0070] The above content is only for explaining the technical idea of ​​the present invention and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution in accordance with the technical idea proposed by the present invention shall fall within the protection scope of the claims of the present invention.

Claims

1. An ether electrolyte, characterized in that The invention comprises methyl 2,2-difluoro-2-(fluorosulfonyl)acetate, an ether solvent and a sodium salt, wherein the ether solvent is ethylene glycol dimethyl ether, diethylene glycol dimethyl ether or triethylene glycol dimethyl ether.

2. The ether electrolyte according to claim 1, characterized in that The ether solvent is ethylene glycol dimethyl ether.

3. The ether electrolyte according to claim 1, characterized in that The sodium salt is sodium bis(fluorosulfonyl)imide, sodium bis(trifluorosulfonyl)imide, sodium perchlorate or sodium hexafluorophosphate.

4. The ether electrolyte according to claim 3, characterized in that The sodium salt is sodium bis(fluorosulfonyl)imide or sodium hexafluorophosphate.

5. The ether electrolyte according to claim 1, characterized in that The content of the methyl 2,2-difluoro-2-(fluorosulfonyl)acetate is 0.1 wt% to 5 wt% of the total mass of the ether solvent and the sodium salt.

6. The ether electrolyte according to claim 1, characterized in that The concentration of sodium salt is 0.5~2 mol / L.

7. The ether electrolyte according to claim 6, characterized in that The concentration of sodium salt is 0.5~1.2 mol / L.

8. A sodium ion battery, characterized in that: The invention comprises a positive electrode, a negative electrode and an electrolyte, wherein the electrolyte is the ether electrolyte according to any one of claims 1 to 7, and the positive electrode comprises a current collector and sodium vanadium fluorophosphate loaded on the current collector.

9. The sodium ion battery according to claim 8, characterized in that The negative electrode includes a current collector and a hard carbon material supported on the current collector.

10. A sodium ion battery comprising a positive electrode, a negative electrode and an electrolyte, wherein the electrolyte is the ether electrolyte according to any one of claims 1 to 7, and the negative electrode comprises a current collector and a hard carbon material supported on the current collector.

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