High-rate ultralow-temperature sodium-ion battery electrolyte as well as preparation method and application thereof

Abstract

The invention provides a high-rate ultralow-temperature sodium-ion battery electrolyte as well as a preparation method and application thereof, and belongs to the technical field of sodium-ion batteries. The super-low-temperature sodium-ion battery electrolyte capable of operating at-60 DEG C is obtained by taking a strong-solvation carbonic ester solvent as a main solvent and matching with a weak-solvation ether diluent, a film-forming additive and sodium salt. Besides, the solvent-solvent strong interaction between the ether diluent and the carbonic ester solvent in the system weakens the interaction between Na < + > and the strong solvent, thereby realizing the improvement of sodium ion kinetics, realizing high rate and high cycle stability at room temperature, and showing higher capacity and cycle stability at low temperature of-60 DEG C.

Description

Technical Field

[0001] The present invention relates to the technical field of sodium ion batteries, and in particular to a high-rate ultra-low-temperature sodium ion battery electrolyte and a preparation method and application thereof. Background Art

[0002] Currently, the research background of low-temperature sodium-ion batteries is becoming increasingly important, mainly due to the increasing global demand for renewable energy and electric vehicles. Sodium-ion batteries have become a powerful alternative to lithium-ion batteries due to the wide availability and low cost of sodium resources, especially in large-scale energy storage systems. However, the performance of traditional sodium-ion batteries decreases significantly in low-temperature environments, which limits their application in cold climates.

[0003] The impact of low temperature on sodium-ion batteries is mainly reflected in several aspects: First, low temperature environment will cause the viscosity of the electrolyte to increase, thereby reducing ionic conductivity and affecting the battery's charge and discharge efficiency. Secondly, the electrode reaction kinetics slow down at low temperatures, resulting in a decrease in reaction rate, further affecting the battery's power performance and cycle life. In addition, low temperature may also make the intercalation and deintercalation process of sodium ions in electrode materials difficult, thereby affecting the overall performance of the battery.

[0004] In order to solve these problems, researchers are actively exploring the formulation of new electrolytes. Current research directions include the development of organic electrolytes, ionic liquids, and aqueous electrolytes with high ionic conductivity and good low-temperature performance. These new electrolytes not only need to maintain good ionic conductivity at low temperatures, but also have chemical stability to ensure the safety and long-term service life of the battery. In addition, optimizing the compatibility of the electrolyte with the electrode material is also key to ensure that the battery can be effectively charged and discharged under low temperature conditions. At the same time, researchers are also exploring the modification of electrode materials to improve their performance at low temperatures. For example, the conductivity and electrochemical activity of the electrode material are enhanced by doping or surface modification technology, thereby improving the charging and discharging capabilities at low temperatures.

[0005] However, in recent years, despite the progress made in electrode materials for sodium-ion batteries, it is still difficult to meet the large-scale energy storage needs in terms of electrolyte exploration. Conventional electrolytes are usually difficult to work effectively in a lower temperature range (below -20°C), which limits the application of sodium-ion batteries in extreme environmental conditions. Summary of the invention

[0006] The purpose of the present invention is to provide a high-rate ultra-low temperature sodium ion battery electrolyte and a preparation method and application thereof, so as to solve the problem that the existing sodium ion battery electrolyte cannot operate at ultra-low temperatures (below -40°C) and has poor rate performance at low temperatures.

[0007] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0008] The present invention provides a high-rate ultra-low-temperature sodium ion battery electrolyte, the preparation raw materials comprising: sodium salt electrolyte, carbonate solvent, film-forming additive and ether diluent; wherein the volume ratio of the carbonate solvent, the film-forming additive and the ether diluent is 10-40:5-20:30-80;

[0009] The carbonate solvent includes one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate and butylene carbonate;

[0010] The ether diluent includes one or more of 1,3-dioxolane, cyclopentyl methyl ether, tetrahydrofuran, 2-methyltetrahydrofuran and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether.

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

[0012] Preferably, the concentration of the sodium salt electrolyte in the high-rate ultra-low temperature sodium ion battery electrolyte is 0.5 to 2 mol / L.

[0013] Preferably, the film-forming additive includes one or more of fluoroethylene carbonate, vinylene carbonate and tris(trimethylsilyl)borate.

[0014] The present invention provides a method for preparing a high-rate ultra-low temperature sodium ion battery electrolyte as described in the above technical solution, comprising the following steps:

[0015] A sodium salt electrolyte, a carbonate solvent, a film-forming additive and an ether diluent are mixed to obtain a high-rate ultra-low-temperature sodium ion battery electrolyte.

[0016] The present invention provides the use of the high-rate ultra-low temperature sodium ion battery electrolyte described in the above technical scheme or the high-rate ultra-low temperature sodium ion battery electrolyte prepared by the preparation method described in the above technical scheme in a sodium ion battery, wherein the use temperature of the high-rate ultra-low temperature sodium ion battery electrolyte is 35 to -60°C.

[0017] Preferably, the sodium ion battery comprises a positive electrode, a negative electrode, a high-rate ultra-low temperature sodium ion battery electrolyte and a diaphragm.

[0018] Preferably, the positive electrode includes a positive electrode current collector and a positive electrode membrane; the positive electrode membrane includes a positive electrode active material, a conductive agent and a binder; the positive electrode active material includes one or more of sodium vanadium phosphate, sodium iron phosphate, sodium nickel iron manganate and sodium vanadium fluorophosphate.

[0019] The present invention provides a high-rate ultra-low-temperature sodium ion battery electrolyte. The present invention selects a strong solvating carbonate solvent as the main solvent, matches a weak solvating ether diluent with a film-forming additive and a sodium salt to form a high-rate ultra-low-temperature sodium ion battery electrolyte. + With strong solvation interaction, ether diluents and Na + The strong solvent-solvent interaction between ether diluents and carbonates weakens the Na + The interaction between the battery and the strong solvent improves the sodium ion dynamics, achieving high rate and high cycle stability at room temperature, and exhibiting high capacity and cycle stability at low temperature of -60°C.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] (1) The present invention uses a strong solvating carbonate solvent as the main solvent, which can ensure that the electrolyte has high ionic conductivity and high solubility.

[0022] (2) The present invention uses an ether diluent with a freezing point below -40°C to regulate the strong solvating carbonate solvent and Na + The interaction between strong and weak solvents leads to an increase in the mixing entropy of the electrolyte, which greatly improves the ion dynamics of the electrolyte. Taking tetrahydrofuran as an example, its melting point is -136°C, and it is miscible with strong solvating carbonate solvents and film-forming additives (such as propylene carbonate and fluoroethylene carbonate), but basically does not dissolve in Na + Combine, consume solvent and increase Na + With anions (such as PF6 + ) effect, thereby further weakening the Na + The interaction with the solvent promotes the Na + The desolvation of the battery ultimately improves the low temperature and fast charging performance of the battery. The present invention uses film-forming additives to improve the interface stability of the electrode. The film-forming additives are conducive to the formation of a surface rich in phosphate (Na x PO y F z / Na x PF y ), the internal NaF-rich inorganic membrane can also increase the organic components in the solid electrolyte interface membrane (SEI membrane) and the electrochemical interface membrane (CEI membrane); the formed organic and inorganic composite SEI membrane and CEI membrane have high toughness and high ionic conductivity.

[0023] (3) The high-rate ultra-low-temperature sodium ion battery electrolyte provided by the present invention can operate in a wide temperature range from room temperature to -60°C, has a low freezing point and high electrochemical performance, and not only achieves rate performance and cycle stability far superior to commercial electrolytes (such as 1MNaClO4-EC / DMC+5%FEC) at room temperature, but also exhibits excellent electrochemical performance even at -60°C.

[0024] (4) The high-rate ultra-low-temperature sodium ion battery electrolyte of the present invention realizes the high-rate, long-cycle, and ultra-low-temperature operation of the sodium vanadium phosphate electrode material, and is expected to provide new ideas for the application of sodium ion batteries under extreme climatic conditions, and is expected to play a greater role in electric vehicles, renewable energy storage, and other fields that require efficient energy management. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 The appearance of the electrolytes obtained in Example 1 and Comparative Example 1 at room temperature;

[0026] Figure 2 The first three cycles of charge and discharge curves of Application Example 1 at room temperature;

[0027] Figure 3 This is the charge and discharge curve of the first three cycles at room temperature for comparative application example 1;

[0028] Figure 4 This is a comparison chart of the rate performance of Application Example 1 and Comparative Application Example 1 at room temperature;

[0029] Figure 5 This is a comparison chart of the cycle performance of Application Example 1 and Comparative Application Example 1 at room temperature;

[0030] Figure 6 The charge and discharge performance diagram of Application Example 1 at -40°C, where a is the charge and discharge performance of the first two cycles at a current density of 0.1C at -40°C, and b is the rate performance at -40°C;

[0031] Figure 7 For comparison, the first three charge and discharge curves of Application Example 1 at -40°C and 0.1C current density are shown;

[0032] Figure 8 The appearance of the electrolyte in Comparative Example 1 at room temperature and low temperature -40°C;

[0033] Fig. 9 This is the appearance of the electrolyte in Example 1 at a low temperature of -70°C;

[0034] Fig.10 The first three charge and discharge curves of Application Example 1 at -50°C and 0.1C current density;

[0035] Fig.11The first three charge and discharge curves of Application Example 1 at -60°C and 0.1C current density;

[0036] Fig.12 This is the cycling performance diagram of Application Example 1 at -60°C and 0.1C current density. DETAILED DESCRIPTION

[0037] In the present invention, unless otherwise specified, the required raw materials or reagents are commercially available products well known to those skilled in the art.

[0038] The present invention provides a high-rate ultra-low-temperature sodium ion battery electrolyte, the preparation raw materials comprising: sodium salt electrolyte, carbonate solvent, film-forming additive and ether diluent; wherein the volume ratio of the carbonate solvent, the film-forming additive and the ether diluent is 10-40:5-20:30-80;

[0039] The carbonate solvent includes one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate and butylene carbonate;

[0040] The ether diluent includes one or more of 1,3-dioxolane, cyclopentyl methyl ether, tetrahydrofuran, 2-methyltetrahydrofuran and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether.

[0041] In the present invention, the sodium salt electrolyte preferably includes one or more of sodium hexafluorophosphate, sodium bis(trifluoromethylsulfonyl)imide, sodium bis(fluorosulfonyl)imide, sodium perchlorate, sodium difluorooxalate borate and sodium tetrafluoroborate; further preferably includes one of sodium hexafluorophosphate, sodium bis(trifluoromethylsulfonyl)imide, sodium bis(fluorosulfonyl)imide and sodium difluorooxalate borate, more preferably sodium bis(fluorosulfonyl)imide (NaFSI). When the sodium salt electrolyte is two or more of the above, the present invention has no special limitation on the ratio of different types of sodium salt electrolytes, and any ratio is acceptable.

[0042] In the present invention, the concentration of the sodium salt electrolyte in the high-rate ultra-low-temperature sodium ion battery electrolyte is preferably 0.5 to 2 mol / L, more preferably 0.8 to 1.5 mol / L, and further preferably 1 mol / L.

[0043] In the present invention, the carbonate solvent includes one or more of ethylene carbonate, propylene carbonate (PC), dimethyl carbonate and butylene carbonate, more preferably ethylene carbonate or propylene carbonate, and further preferably propylene carbonate; when the carbonate solvent is two or more of the above, the present invention has no special limitation on the ratio of different types of carbonate solvents, and any ratio is acceptable.

[0044] In the present invention, the film-forming additive preferably includes one or more of fluoroethylene carbonate (FEC), vinylene carbonate and tris(trimethylsilyl)borate, more preferably fluoroethylene carbonate or vinylene carbonate, further preferably fluoroethylene carbonate (FEC); when the film-forming additive is two or more of the above, the present invention has no special limitation on the ratio of different types of film-forming additives, and any ratio is acceptable.

[0045] In the present invention, the ether diluent includes one or more of 1,3-dioxolane (DOL), cyclopentyl methyl ether, tetrahydrofuran (THF), 2-methyltetrahydrofuran and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, and is further preferably tetrahydrofuran (THF); when the ether diluent is two or more of the above, the present invention has no special limitation on the ratio of different types of ether diluents, and any ratio is acceptable.

[0046] In the present invention, the volume ratio of the carbonate solvent, the film-forming additive and the ether diluent is 10-40:5-20:30-80, preferably 10-15:5-15:30-60, and more preferably 10:5:30.

[0047] The present invention provides a method for preparing a high-rate ultra-low temperature sodium ion battery electrolyte as described in the above technical solution, comprising the following steps:

[0048] A sodium salt electrolyte, a carbonate solvent, a film-forming additive and an ether diluent are mixed to obtain a high-rate ultra-low-temperature sodium-ion battery electrolyte.

[0049] In the present invention, the sodium salt electrolyte, carbonate solvent, film-forming additive and ether diluent are preferably mixed in the following manner: the carbonate solvent and the ether diluent are stirred and mixed for 10 minutes, then mixed with the film-forming additive, and then the sodium salt electrolyte is added and stirred and mixed for 10 hours.

[0050] The present invention has no particular limitation on the mixing conditions, and the materials can be mixed uniformly according to a mixing process well known in the art.

[0051] The present invention provides the use of the high-rate ultra-low temperature sodium ion battery electrolyte described in the above technical scheme or the high-rate ultra-low temperature sodium ion battery electrolyte prepared by the preparation method described in the above technical scheme in a sodium ion battery, wherein the use temperature of the high-rate ultra-low temperature sodium ion battery electrolyte is 35 to -60°C.

[0052] In the present invention, the sodium ion battery preferably includes a positive electrode, a negative electrode, a high-rate ultra-low temperature sodium ion battery electrolyte and a diaphragm.

[0053] The present invention does not limit the materials and preparation methods of the negative electrode and the separator, and any method familiar to those skilled in the art may be used.

[0054] In the present invention, the positive electrode preferably includes a positive electrode current collector and a positive electrode membrane; the present invention does not limit the positive electrode current collector, and materials well known to those skilled in the art may be used.

[0055] In the present invention, the positive electrode membrane preferably includes a positive electrode active material, a conductive agent and a binder; the positive electrode active material preferably includes one or more of sodium vanadium phosphate, sodium iron phosphate, sodium nickel iron manganate and sodium vanadium fluorophosphate, more preferably one of sodium vanadium phosphate, sodium iron phosphate and sodium vanadium fluorophosphate, and further preferably sodium vanadium phosphate.

[0056] The present invention has no special restrictions on the types and sources of the conductive agent and the binder, and the preparation method of the positive electrode active material, and corresponding materials well known to those skilled in the art can be used.

[0057] The technical solutions provided by the present invention are described in detail below in conjunction with the embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0058] Unless otherwise specified, the reagents and materials used in the implementation cases can be purchased commercially or prepared by conventional methods, and the instruments used can be purchased commercially.

[0059] Example 1

[0060] The high-rate ultra-low-temperature sodium ion battery electrolyte provided in this embodiment comprises the following raw materials: sodium bis(fluorosulfonyl)imide (NaFSI), propylene carbonate (PC), fluoroethylene carbonate (FEC) and tetrahydrofuran (THF); the concentration of NaFSI is 1 mol / L; and the volume ratio of PC:FEC:THF is 10:5:30.

[0061] The preparation method of the above electrolyte comprises the following steps:

[0062] PC solvent was added to THF, mixed, stirred for 10 minutes, and then FEC was added to obtain a mixed solvent; NaFSI was then dissolved in the mixed solvent, stirred for 10 hours to mix evenly, and a high-rate ultra-low temperature sodium ion battery electrolyte was obtained, which was recorded as N-SW.

[0063] Example 2

[0064] The high-rate ultra-low-temperature sodium ion battery electrolyte provided in this embodiment comprises the following raw materials: sodium bis(fluorosulfonyl)imide (NaFSI), propylene carbonate (PC), fluoroethylene carbonate (FEC) and tetrahydrofuran (THF); the concentration of NaFSI is 1 mol / L; and the volume ratio of PC:FEC:THF is 20:5:20.

[0065] Example 3

[0066] The high-rate ultra-low-temperature sodium ion battery electrolyte provided in this embodiment comprises the following raw materials: sodium bis(fluorosulfonyl)imide (NaFSI), propylene carbonate (PC), fluoroethylene carbonate (FEC) and tetrahydrofuran (THF); the concentration of NaFSI is 1 mol / L; and the volume ratio of PC:FEC:THF is 15:5:25.

[0067] Comparative Example 1

[0068] The carbonate sodium ion battery electrolyte provided in this comparative example has the following raw materials: sodium perchlorate (NaClO4), ethylene carbonate (EC), dimethyl carbonate (DMC), and FEC; the concentration of NaClO4 is 1 mol / L; the volume ratio of EC to DMC is 1:1; the volume fraction of FEC is 5% of the total volume of EC+DMC solvent; the electrolyte is recorded as a commercial ester electrolyte (i.e., 1MNaClO4-EC / DMC+5%FEC).

[0069] The appearance of the sodium ion battery electrolyte obtained in Example 1 and Comparative Example 1 at room temperature is as follows: Figure 1 As shown, both are transparent liquids.

[0070] Application Example 1

[0071] This application example provides a method for preparing a 2032 sodium ion battery, comprising the following steps:

[0072] (1) Preparation of positive electrode sheet: Sodium vanadium phosphate, binder polyvinylidene fluoride, and conductive agent acetylene black are mixed in a mass ratio of 8:1:1, and then N-methylpyrrolidone (NMP) solvent (the mass volume ratio of binder polyvinylidene fluoride and NMP is 40 mg:1 mL) is added and mixed evenly to obtain positive electrode slurry. The positive electrode slurry is coated on the aluminum foil current collector using a coating apparatus with a coating thickness of 100 μm. The heating plate of the coating apparatus is heated to 80°C to preliminarily dry the positive electrode. The preliminarily dried electrode is placed in a vacuum drying oven and dried at 120°C for 10 hours. Finally, the dried electrode is cut into a 10 mm diameter positive electrode sheet using a wafer slicer.

[0073] Preparation of negative electrode sheet: Mix hard carbon, binder polyvinylidene fluoride, and conductive agent acetylene black in a mass ratio of 8:1:1, then add NMP (the mass volume ratio of binder polyvinylidene fluoride and NMP is 40mg:1mL) and mix evenly to obtain negative electrode slurry. The negative electrode slurry is coated on the current collector copper foil with a coating apparatus, and the coating thickness is 100μm. The heating plate of the coating apparatus is heated to 80℃ to preliminarily dry the negative electrode. Place the preliminarily dried electrode in a vacuum drying oven and dry it at 120℃ for 10h. Finally, the dried electrode is cut into a 12mm diameter negative electrode sheet with a wafer slicer.

[0074] Isolation membrane: Adopt CROOD commercial glass fiber membrane (GF / D), model: MA-EN-SE-02.

[0075] (2) In a glove box, a battery was assembled in the order of a negative electrode shell, a negative electrode sheet, a separator, the electrolyte of Example 1, a gasket, a positive electrode sheet, and a positive electrode shell. The amount of electrolyte added was 200 μL. The battery was left to stand for 10 h before an electrochemical test.

[0076] Comparative application example 1

[0077] The carbonate sodium ion battery electrolyte of Comparative Example 1 was used.

[0078] Test the electrochemical performance of different electrolytes.

[0079] Figure 2 The first three cycles of charge and discharge curves of Application Example 1 at room temperature are shown. It can be found that Application Example 1 can be stabilized after one cycle at 0.1C, forming an efficient CEI, thereby showing high reversibility.

[0080] Figure 3 For comparison, the first three cycles of charge and discharge curves of Application Example 1 at room temperature show obvious capacity decay in the first three cycles, with low coulombic efficiency, indicating that it has low reversibility and it is difficult to form a stable CEI film to effectively inhibit the decomposition of the electrolyte.

[0081] Figure 4 The figure is a comparison of the rate performance of Application Example 1 and Comparative Application Example 1 at room temperature. Sodium vanadium phosphate exhibits a high rate in the electrolyte of Application Example 1 (N-SW), and still has a high current density of 90.6 mAh g at a high current density of 50C. -1 The discharge specific capacity is far superior to the rate performance of sodium vanadium phosphate in commercial ester electrolytes.

[0082] Figure 5 The figure is a comparison of the cycle performance at room temperature of Application Example 1 and Comparative Application Example 1. Sodium vanadium phosphate exhibits high capacity and high cycle stability at 10C current density in the electrolyte of Application Example 1 (N-SW), which is better than the cycle performance of sodium vanadium phosphate in commercial ester electrolytes.

[0083] Figure 6 The charge and discharge performance of Application Example 1 at -40°C, where a is the charge and discharge performance of the first two cycles at 0.1C current density at -40°C, and b is the rate performance at -40°C. It can be seen from a that even at low temperatures, sodium vanadium phosphate still has a high capacity (discharge capacity of 90 mAh g) in the electrolyte of Application Example 1. -1 ), extremely high first-cycle coulomb efficiency (99%), and discharge capacity can reach Figure 2 Medium room temperature capacity (108 mAh g -1 As can be seen from b, sodium vanadium phosphate exhibits high rate characteristics in the electrolyte of Application Example 1 at -40°C, and still has 41 mAh g at 1C current density. -1 The discharge capacity.

[0084] Figure 7 The first three charge and discharge curves of Comparative Application Example 1 at -40°C and 0.1C current density are shown. It can be seen that at low temperatures, the capacity of sodium vanadium phosphate in the electrolyte of Comparative Application Example 1 decays severely.

[0085] Figure 8 The appearance of the electrolyte in Comparative Example 1 at room temperature and low temperature -40°C is shown. It can be seen that the commercial ester electrolyte freezes at -40°C, resulting in poor electrochemical performance and severe capacity decay.

[0086] Fig. 9 This is the appearance of the electrolyte in Example 1 at a low temperature of -70°C. It can be seen that even at -70°C, the electrolyte in Application Example 1 does not freeze, remains transparent, and achieves a wide liquid range.

[0087] Fig.10 The first three cycles of charge and discharge curves of Application Example 1 at -50°C and 0.1C current density are shown in Figure 1. It can be seen that even at a low temperature of -50°C, sodium vanadium phosphate still has a high capacity in the electrolyte of Application Example 1, which can reach Figure 2 Medium room temperature capacity (108 mAh g -1 )’s 63%.

[0088] Fig.11 The first three cycles of charge and discharge curves of Application Example 1 at -60°C and 0.1C current density are shown in Figure 1. It can be seen that at ultra-low temperature -60°C, sodium vanadium phosphate still has high capacity in the electrolyte of Application Example 1, which can reach Figure 2 Medium room temperature capacity (108 mAhg -1 )’s 47%.

[0089] Fig.12This is a cycle performance diagram of Application Example 1 at -60°C and 0.1C current density. It can be seen that at ultra-low temperature -60°C, sodium vanadium phosphate has excellent cycle stability in the electrolyte of Application Example 1.

[0090] In summary, the present invention uses strongly solvated carbonate solvents as the main solvent, matches weakly solvated ethers as diluents, and matches suitable film-forming additives to form a high-rate ultra-low temperature sodium ion battery electrolyte, which achieves high-rate, long-cycle, and ultra-low temperature operation of sodium vanadium phosphate electrode materials, provides design ideas for sodium ion batteries used in extreme climates, and provides new ideas for other ultra-low temperature battery fields.

[0091] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A high-rate ultra-low-temperature sodium-ion battery electrolyte, It is characterized in that The preparation raw materials include: sodium salt electrolyte, carbonate solvent, film-forming additive and ether diluent; wherein the volume ratio of the carbonate solvent, the film-forming additive and the ether diluent is 10-40:5-20:30-80; The carbonate solvent includes one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate and butylene carbonate; The ether diluent includes one or more of 1,3-dioxolane, cyclopentyl methyl ether, tetrahydrofuran, 2-methyltetrahydrofuran and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether.

2. The high-rate ultra-low temperature sodium ion battery electrolyte according to claim 1, It is characterized in that The sodium salt electrolyte includes one or more of sodium hexafluorophosphate, sodium bis(trifluoromethylsulfonyl)imide, sodium bis(fluorosulfonyl)imide, sodium perchlorate, sodium difluorooxalatoborate and sodium tetrafluoroborate.

3. The high-rate ultra-low-temperature sodium ion battery electrolyte according to claim 1, It is characterized in that The concentration of the sodium salt electrolyte in the high-rate ultra-low-temperature sodium ion battery electrolyte is 0.5 to 2 mol / L.

4. The high-rate ultra-low temperature sodium ion battery electrolyte according to claim 1, It is characterized in that The film-forming additive includes one or more of fluoroethylene carbonate, vinylene carbonate and tris(trimethylsilyl)borate.

5. The method for preparing the high-rate ultra-low-temperature sodium ion battery electrolyte according to any one of claims 1 to 4, It is characterized in that The following steps are involved: A sodium salt electrolyte, a carbonate solvent, a film-forming additive and an ether diluent are mixed to obtain a high-rate ultra-low-temperature sodium ion battery electrolyte.

6. Use of the high-rate ultra-low temperature sodium ion battery electrolyte according to any one of claims 1 to 4 or the high-rate ultra-low temperature sodium ion battery electrolyte prepared by the preparation method according to claim 5 in a sodium ion battery, It is characterized in that The operating temperature of the high-rate ultra-low temperature sodium ion battery electrolyte is 35 to -60°C.

7. The use according to claim 6, It is characterized in that The sodium ion battery comprises a positive electrode, a negative electrode, a high-rate ultra-low-temperature sodium ion battery electrolyte and a diaphragm.

8. The use according to claim 7, It is characterized in that The positive electrode includes a positive electrode current collector and a positive electrode membrane; the positive electrode membrane includes a positive electrode active material, a conductive agent and a binder; the positive electrode active material includes one or more of sodium vanadium phosphate, sodium iron phosphate, sodium nickel iron manganese oxide and sodium vanadium fluorophosphate.

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