An ultralow-temperature sodium-ion battery electrolyte, an ultralow-temperature sodium-ion battery and application

Abstract

This invention belongs to the field of sodium-ion battery technology, specifically disclosing an ultra-low temperature sodium-ion battery electrolyte, an ultra-low temperature sodium-ion battery, and its applications. The ultra-low temperature sodium-ion battery electrolyte is composed of an organic solvent and a sodium salt; the organic solvent is a monodentate ring ether-based solvent. This invention can improve the bulk ionic conductivity of the electrolyte, reduce the desolvation energy of the electrolyte at low temperatures, and improve the electrochemical performance of the sodium-ion battery in ultra-low temperature environments.

Description

Technical Field

[0001] This invention belongs to the field of sodium-ion battery technology, specifically relating to an ultra-low temperature sodium-ion battery electrolyte, an ultra-low temperature sodium-ion battery, and its applications. Background Technology

[0002] Sodium-ion batteries, with their advantages of abundant sodium resources, low cost, and environmental friendliness, have shown significant potential in the field of energy storage and have become an important supplement and alternative to lithium-ion batteries. Especially against the backdrop of the global carbon neutrality strategy, the rapid development of large-scale energy storage technologies has placed higher demands on the sustainability and economic viability of battery materials.

[0003] Compared to lithium-ion batteries, sodium-ion batteries exhibit unique advantages in low-temperature environments. Sodium ions have a smaller Stokes radius, meaning they have faster migration capabilities and higher potential ionic conductivity in the electrolyte. This characteristic makes sodium-ion batteries stand out in low-temperature and fast-charging applications, opening up possibilities for energy applications in extremely cold regions and special environments. However, traditional sodium-ion batteries still face significant challenges in ultra-low temperature environments (≤-40℃), including decreased ionic conductivity and difficulties in desolvation at the electrode-electrolyte interface, severely limiting their application performance in extreme environments.

[0004] The development of ultra-low temperature sodium-ion battery technology will greatly expand its application range in special environments, mainly including the following fields: polar scientific research and exploration equipment, aerospace, cold-region transportation, power grid energy storage and communication base stations, and deep-sea and deep-earth exploration. All of these require sodium-ion batteries to achieve stable charging and discharging at extremely low temperatures.

[0005] Currently, solvents used in sodium-ion battery electrolytes mainly include carbonates, ethers, sulfates, and carboxylic acids. Carbonate electrolytes are ideal for room-temperature and high-temperature batteries due to their good chemical stability; however, under low-temperature conditions (≤-20℃), Na... + The desolvation process becomes extremely difficult, leading to a sharp decline in battery capacity. Carboxylic acid esters and sulfate esters, with their low melting points, show some application potential at low temperatures, but their poor electrochemical stability and safety limit their further application. Existing ether-based electrolytes solidify below -40°C and still face difficulties in desolvation. Therefore, achieving optimal performance of sodium-ion batteries in ultra-low temperature environments (-40 to -80°C) remains a challenge.

[0006] To address the shortcomings of existing technologies, it is essential to develop a novel ultra-low temperature sodium-ion battery electrolyte system and an ultra-low temperature sodium-ion battery to expand the application of ion batteries in extreme environments. Summary of the Invention

[0007] The purpose of this invention is to provide an ultra-low temperature sodium-ion battery electrolyte, an ultra-low temperature sodium-ion battery, and its application, which can improve the bulk ionic conductivity of the electrolyte, reduce the desolvation energy of the electrolyte at low temperatures, and improve the electrochemical performance of the sodium-ion battery in an ultra-low temperature environment.

[0008] To achieve the above objectives, the present invention employs the following technical solution: According to a first aspect of the present invention, an ultra-low temperature sodium-ion battery electrolyte is provided, which is composed of an organic solvent and a sodium salt; wherein the organic solvent is a monodentate cyclic ether solvent.

[0009] Monodentate ring ether solvents possess low melting points and low viscosity, along with moderate dielectric constants and electron donor numbers, exhibiting excellent ion transport performance at low temperatures. Furthermore, their oxidative stability deficiencies can be compensated for by using sodium salt-derived inorganic-rich interfacial phases. Therefore, using monodentate ring ether solvents in combination with sodium salts to prepare electrolytes helps lower the freezing point of the electrolyte at low temperatures, increases the bulk ionic conductivity of the electrolyte, and thus improves the electrochemical performance of sodium-ion batteries at low temperatures.

[0010] It should be noted that ultra-low temperature sodium-ion electrolyte refers to a sodium-ion battery electrolyte system that can maintain ionic conductivity and electrochemical stability at temperatures below -40°C. This electrolyte is a component that enables sodium-ion batteries to achieve low-temperature charge and discharge.

[0011] In the aforementioned ultra-low temperature sodium-ion battery electrolyte, the organic solvent is a monodentate ring ether solvent with a high lowest unoccupied molecular orbital (LUMO) energy level, exhibiting excellent reduction stability on the negative electrode surface. Furthermore, the solvation structure formed at low temperature has moderate strength, preventing it from agglomerating into aggregates or forming an ordered hydrogen bond network that would cause the electrolyte to solidify.

[0012] Furthermore, the organic solvent is at least one selected from tetrahydrofuran (THF), 2-methyltetrahydrofuran (2-MTHF), 3-methyltetrahydrofuran (3-MTHF), tetrahydropyran (THP), 2-methyltetrahydropyran (2-MTHP), 3-methyltetrahydropyran (3-MTHP), 2-cyanotetrahydrofuran (2-NTHF), 3-cyanotetrahydrofuran (3-NTHF), 2-aminotetrahydrofuran (2-ATHF), and 3-aminotetrahydrofuran (3-ATHF).

[0013] Organic solvents used to prepare ultra-low temperature sodium-ion battery electrolytes contain methyl, cyano, or amino groups. Their substitution effect helps to control the solvation configuration of the electrolyte at low temperatures, making it insensitive to temperature changes. This has led to the successful construction of a separation-contact ion pair configuration with rapid kinetics at low temperatures in ultra-low temperature sodium-ion battery electrolytes, enabling the production of Na+ at low temperatures. + The difficulty of the desolvation process is greatly reduced.

[0014] Furthermore, the organic solvent is 3-methyltetrahydrofuran; the sodium-ion battery prepared using the ultra-low temperature sodium-ion battery electrolyte can be charged at temperatures below -40°C, and the soft-pack battery prepared using the ultra-low temperature sodium-ion battery electrolyte has a discharge capacity at -60°C that exceeds 70% of that at 25°C.

[0015] Furthermore, the concentration of the sodium salt is 0.2 mol / L to 1.0 mol / L.

[0016] By controlling the sodium salt concentration within the range of 0.2 mol / L to 1.0 mol / L, the problems of limited ion transport and poor stability of sodium-ion battery electrolytes under ultra-low temperature conditions can be effectively solved. This ensures that there are a sufficient number of sodium ions in the electrolyte as charge carriers, thereby guaranteeing good ionic conductivity, reducing the internal resistance of the battery, and avoiding the sharp increase in electrolyte viscosity and sodium salt precipitation caused by excessive sodium salt concentration. This maintains the rapid migration ability of sodium ions and the long-term stability of the electrolyte.

[0017] Furthermore, the sodium salt is at least one of sodium hexafluorophosphate (NaPF6), sodium difluorosulfonyl imide (NaFSI), sodium difluorooxalate borate (NaDFOB), and sodium bis(trifluoromethylsulfonyl)imide (NaTFSI).

[0018] Choosing sodium salts such as NaPF6, NaFSI, NaDFOB, or NaTFSI provides excellent solubility and dissociation in monodentate ring ether solvents, ensuring that the electrolyte still provides sufficient sodium ions with high migration rates even at ultra-low temperatures. Furthermore, these sodium salts help form a stable and dense solid electrolyte interphase (SEI) film on the electrode surface, effectively suppressing the continuous decomposition of the electrolyte and side reactions of the electrode, thereby significantly improving the electrochemical stability and cycle life of the battery.

[0019] Based on the good fluidity and solvation ability of monodentate ring ether solvents at low temperatures, their combination with the aforementioned sodium salts can synergistically optimize the ion conduction path and interfacial stability of the electrolyte, ultimately enabling ultra-low temperature sodium-ion batteries to still exhibit excellent charge-discharge performance and long-term stability under harsh low-temperature conditions.

[0020] According to a second aspect of the present invention, an ultra-low temperature sodium-ion battery is provided, comprising any of the above-described ultra-low temperature sodium-ion battery electrolytes.

[0021] The ultra-low temperature sodium-ion battery electrolyte, formulated with a low-melting-point, low-viscosity monodentate ring ether solvent, is suitable for sodium-ion batteries operating under extreme low-temperature conditions. The resulting ultra-low temperature sodium-ion battery can operate normally in low-temperature environments below -40℃, ensuring application performance under extreme conditions.

[0022] Furthermore, the negative electrode of the ultra-low temperature sodium-ion battery is hard carbon or metallic sodium, and the positive electrode is a layered oxide, Prussian blue compound, or polyanionic compound.

[0023] According to a third aspect of the present invention, the application of the above-described ultra-low temperature sodium-ion battery in a transport vehicle is provided.

[0024] According to a fourth aspect of the present invention, the above-described ultra-low temperature sodium-ion battery is provided for energy storage in cold regions. The "cold region" referred to in this invention is a region where the average temperature of the coldest month is -10°C to 0°C, and the number of days with an average daily temperature ≤5°C is 90 to 145 days.

[0025] According to a fifth aspect of the present invention, the application of the above-described ultra-low temperature sodium-ion battery in polar scientific research and exploration equipment is provided.

[0026] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention uses low-melting-point / low-viscosity monodentate cyclic ethers and their derivatives as solvents for ultra-low temperature sodium-ion battery electrolytes, thereby reducing the freezing point of the electrolyte at low temperatures and improving the bulk ionic conductivity of the electrolyte.

[0027] 2. In the ultra-low temperature sodium-ion battery electrolyte provided by the present invention, the organic solvent used can regulate the solvation configuration of the electrolyte at low temperature through the substitution effect of methyl / cyano / amino groups, making it insensitive to temperature changes. This successfully constructs a separation-contact ion pair configuration with rapid kinetic properties at low temperature, and reduces the desolvation energy at low temperature.

[0028] 3. The method for preparing ultra-low temperature sodium-ion battery electrolyte provided by the present invention is simple in process, highly operable, and easy to promote and apply on a large scale.

[0029] 4. The sodium-ion battery prepared using the ultra-low temperature sodium-ion battery electrolyte of the present invention has achieved a breakthrough in the performance of ultra-low temperature sodium-ion batteries, with a discharge capacity exceeding 70% of that at room temperature in an ultra-low temperature environment of -60℃. Attached Figure Description

[0030] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings: Figure 1The charge-discharge curves of the hard carbon PB pouch cell in Example 3 are shown. Detailed Implementation

[0031] The present invention will now be described in detail with reference to the accompanying drawings and embodiments. It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other.

[0032] The following detailed descriptions are exemplary and intended to provide further detailed explanation of the present invention. Unless otherwise specified, all technical terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains. The terminology used in this invention is for the purpose of describing specific embodiments only and is not intended to limit the scope of exemplary embodiments according to the present invention. Where specific techniques or conditions are not specified in the embodiments, they are performed in accordance with the techniques or conditions described in the literature in the art, or in accordance with the product instructions. Where the manufacturers of reagents or instruments are not specified, they are all conventional products that can be purchased through legitimate channels.

[0033] This application proposes an ultra-low temperature sodium-ion battery electrolyte, comprising: an organic solvent and a sodium salt; the organic solvent is a monodentate ring ether-based solvent. By employing an organic solvent, this electrolyte addresses the problems of electrolyte solidification and impaired ion transport in existing technologies at low temperatures, thereby improving the performance of sodium-ion batteries under low-temperature conditions.

[0034] Example 1 S1. Preparation of ultra-low temperature sodium-ion battery electrolyte An ultra-low temperature sodium-ion battery electrolyte was prepared using 3-MTHF as the organic solvent and NaPF6 as the sodium salt. The concentration of the sodium salt was 0.5 mol / L.

[0035] S2. Assemble an ultra-low temperature sodium-ion battery Coin cells are assembled using the ultra-low temperature sodium-ion battery electrolyte obtained in step S1 as the electrolyte.

[0036] Specifically, the positive electrode active material is NaNi. 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 (NFM), conductive agent is conductive carbon black (Super P, Timcal Ltd.), binder is polyvinylidene fluoride (PVDF, HSV 900, Arkema), and dispersant is N-methyl-2-pyrrolidone (NMP). These are mixed and ground at a mass ratio of NFM:Super P:PVDF = 8:1:1, coated onto aluminum foil, and then dried, rolled, and stamped to form electrode sheets. The active material concentration on the electrode surface is controlled at 3 mg / cm³. 2The negative electrode is a sodium sheet, the separator is a polypropylene microporous membrane, and the electrolyte for the ultra-low temperature sodium-ion battery in step S1 is used as the electrolyte. A button cell is fabricated in a glove box filled with argon gas to obtain a Na||NFM battery.

[0037] Example 2 The difference between this embodiment and Embodiment 1 is that: In step S2, during the assembly of the ultra-low temperature sodium-ion battery, the ultra-low temperature sodium-ion battery electrolyte from step S1 is used as the electrolyte to assemble the pouch battery.

[0038] Specifically, the positive electrode active material is NaNi. 1 / 3 Fe 1 / 3 Mn 1 / 3 The cathode material was prepared by mixing and grinding O2 (NFM), conductive carbon black (Super P, Timcal Ltd.) as the conductive agent, polyvinylidene fluoride (PVDF, HSV 900, Arkema) as the binder, and N-methyl-2-pyrrolidone (NMP) as the dispersant, according to a mass ratio of NFM:Super P:PVDF = 96:2:2. The cathode material had a single-sided areal density of 13.8 mg / cm³. 2 The active material of the negative electrode is hard carbon, which accounts for 94.5% of the total mass, and the areal density of the negative electrode on one side is 7.4 mg / cm³. 2 The electrolyte used was the ultra-low temperature sodium-ion battery electrolyte from step S1; a pouch cell was fabricated in a dry room to obtain a hard carbon ||NFM pouch cell. The theoretical discharge capacity of the obtained hard carbon ||NFM pouch cell is 1 Ah.

[0039] The remaining steps and conditions are the same.

[0040] Example 3 The difference between this embodiment and Embodiment 1 is that: In step S1, during the preparation of the ultra-low temperature sodium-ion battery electrolyte, the concentration of sodium salt is 0.6 mol / L.

[0041] In step S2, during the assembly of the ultra-low temperature sodium-ion battery, the ultra-low temperature sodium-ion battery electrolyte from step S1 is used as the electrolyte to assemble the pouch battery.

[0042] Specifically, the positive electrode active material is a Prussian blue compound, the conductive agent is conductive carbon black (Super P, Timcal Ltd.), the binder is polyvinylidene fluoride (PVDF, HSV 900, Arkema), and the dispersant is N-methyl-2-pyrrolidone (NMP). The positive electrode material is prepared by mixing and grinding Prussian blue compound:Super P:PVDF at a mass ratio of 94:3:3. The areal density of the positive electrode material on one side is 15.9 mg / cm³. 2The active material of the negative electrode is hard carbon, which accounts for 94.5% of the total mass, and the areal density of the negative electrode on one side is 9 mg / cm³. 2 The ultra-low temperature sodium-ion battery electrolyte used in step S1 is used to fabricate a soft-pack battery in a dry room, resulting in a hard carbon ||PB soft-pack battery. The theoretical discharge capacity of the obtained hard carbon ||PB soft-pack battery is 1.5 Ah.

[0043] The remaining steps and conditions are the same.

[0044] Example 4 The difference between this embodiment and Embodiment 1 is that: In step S1, during the preparation of the ultra-low temperature sodium-ion battery electrolyte, 2-ATHF was used as the organic solvent and NaFSI as the sodium salt. The concentration of the sodium salt was 0.2 mol / L.

[0045] The remaining steps and conditions are the same.

[0046] Example 5 The difference between this embodiment and Embodiment 1 is that: In step S1, during the preparation of the ultra-low temperature sodium-ion battery electrolyte, 3-MTHP was used as the organic solvent, and NaPF6 and NaDFOB were used as sodium salts. The mass ratio of NaPF6 to NaDFOB was 1:1, and the total concentration of sodium salts was 1 mol / L.

[0047] The remaining steps and conditions are the same.

[0048] Example 6 The difference between this embodiment and Embodiment 1 is that: In step S1, during the preparation of the ultra-low temperature sodium-ion battery electrolyte, 2-NTHF is used as the organic solvent.

[0049] The remaining steps and conditions are the same.

[0050] Example 7 The difference between this embodiment and Embodiment 1 is that: In step S1, during the preparation of the ultra-low temperature sodium-ion battery electrolyte, 3-NTHF is used as the organic solvent.

[0051] The remaining steps and conditions are the same.

[0052] Example 8 The difference between this embodiment and Embodiment 1 is that: In step S1, during the preparation of the ultra-low temperature sodium-ion battery electrolyte, 2-ATHF is used as the organic solvent.

[0053] The remaining steps and conditions are the same.

[0054] Example 9 The difference between this embodiment and Embodiment 1 is that: In step S1, during the preparation of the ultra-low temperature sodium-ion battery electrolyte, 3-ATHF is used as the organic solvent.

[0055] The remaining steps and conditions are the same.

[0056] Example 10 The difference between this embodiment and Embodiment 1 is that: In step S1, during the preparation of the ultra-low temperature sodium-ion battery electrolyte, a mixed solution of 3-MTHP and 2-ATHF was used as the organic solvent, and NaPF6 was used as the sodium salt. The concentration of the sodium salt was 1 mol / L; the volume ratio of 3-MTHP to 2-ATHF was 2:1.

[0057] The remaining steps and conditions are the same.

[0058] Example 11 The difference between this embodiment and Embodiment 1 is that: In step S1, during the preparation of the ultra-low temperature sodium-ion battery electrolyte, a mixed solution of 3-MTHP and THF was used as the organic solvent, and NaPF6 was used as the sodium salt. The concentration of the sodium salt was 1 mol / L; the volume ratio of 3-MTHP to THF was 2:1.

[0059] The remaining steps and conditions are the same.

[0060] Example 12 The difference between this embodiment and Embodiment 1 is that: In step S1, during the preparation of the ultra-low temperature sodium-ion battery electrolyte, a mixed solution of 3-NTHF, 3-MTHF, and 2-ATHF is used as the organic solvent. The volume ratio of 3-NTHF, 3-MTHF, and 2-ATHF is 1:1:1.

[0061] The remaining steps and conditions are the same.

[0062] Example 13 The difference between this embodiment and Embodiment 1 is that: In step S1, during the preparation of the ultra-low temperature sodium-ion battery electrolyte, a mixture of NaPF6, NaFSI, and NaDFOB is used as the sodium salt, with a mass ratio of NaPF6, NaFSI, and NaDFOB of 1:1:1.

[0063] The remaining steps and conditions are the same.

[0064] Example 14 The difference between this embodiment and Embodiment 1 is that: In step S1, during the preparation of the ultra-low temperature sodium-ion battery electrolyte, a mixture of NaDFOB and NaTFSI is used as the sodium salt, with a mass ratio of NaDFOB to NaTFSI of 1:2.

[0065] The remaining steps and conditions are the same.

[0066] Comparative Example S1. Preparation of sodium-ion battery electrolyte An ultra-low temperature sodium-ion battery electrolyte was prepared using a mixed solution of EC (ethylene carbonate) and DEC (diethyl carbonate) as the organic solvent and NaPF6 as the sodium salt. The concentration of the sodium salt was 0.5 mol / L; the volume ratio of EC to DEC was 1:1.

[0067] S2. Assemble an ultra-low temperature sodium-ion battery Coin cells are assembled using the ultra-low temperature sodium-ion battery electrolyte obtained in step S1 as the electrolyte.

[0068] Specifically, the positive electrode active material is NaNi. 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 (NFM), conductive agent is conductive carbon black (Super P, Timcal Ltd.), binder is polyvinylidene fluoride (PVDF, HSV 900, Arkema), and dispersant is N-methyl-2-pyrrolidone (NMP). These are mixed and ground at a mass ratio of NFM:Super P:PVDF = 8:1:1, coated onto aluminum foil, and then dried, rolled, and stamped to form electrode sheets. The active material concentration on the electrode surface is controlled at 3 mg / cm³. 2 The negative electrode is a sodium sheet, the separator is a polypropylene microporous membrane, and the electrolyte for the sodium-ion battery in step S1 is used as the electrolyte. A coin cell is fabricated in a glove box filled with argon gas, and it is denoted as NaPF6-EC / DEC cell.

[0069] Test case Using the Xinwei Battery Testing System (CT-4008Tn, MHW-100-2-160CH), the sodium-ion batteries prepared in Examples 1-3 and the comparative example were tested at low temperatures of -40℃, -50℃, and -60℃ using a 0.1C charge-discharge cycle (current 0.1A). The test results were as follows: the Na||NFM battery of Example 1 had a discharge specific capacity of 128mAh / g at -40℃; the hard carbon||NFM pouch battery of Example 2 had a discharge capacity of 0.78Ah (theoretical 1Ah) at -50℃; the hard carbon||PB pouch battery of Example 3 had a discharge capacity of 1.04Ah (theoretical 1.5Ah) at -60℃; while the NaPF6-EC / DEC battery of the comparative example could not be charged at -40℃.

[0070] The charge-discharge curves of the 1.5Ah-class hard carbon || PB pouch cell in Example 3 were measured using the Newway battery testing system at charge-discharge voltages of 1.5V-3.6V, 25℃, and -60℃. (See attached text.) Figure 1 It can be seen that the ultra-low temperature sodium-ion battery electrolyte prepared by the present invention with monodentate ring ether solvent and sodium salt can ensure that the obtained sodium-ion battery can be charged and discharged at a low temperature of -60°C, and the discharge capacity exceeds 70% of that at room temperature (25°C).

[0071] Therefore, the ultra-low temperature sodium-ion battery electrolyte of this invention, by using a monodentate ring ether solvent with a low melting point and low viscosity, can not only ensure normal charging and discharging of the ultra-low temperature sodium-ion battery under ultra-low temperature conditions of ≤-40℃, or even -50℃ or lower, but also ensure a high battery capacity. This is likely because a low-melting-point, low-viscosity monodentate ring ether and its derivatives are used as solvents, and the organic solvent is used as a component of the electrolyte, responsible for dissolving sodium salts and providing a medium for sodium ion transport. The use of a monodentate ring ether solvent in this invention lowers the freezing point of the ultra-low temperature sodium-ion battery electrolyte at low temperatures, thereby maintaining the fluidity of the electrolyte in low-temperature environments and improving the bulk ionic conductivity of the ultra-low temperature sodium-ion battery electrolyte. The organic solvent contains methyl, cyano, or amino groups, whose substitution effect helps to regulate the solvation configuration of the electrolyte at low temperatures, making it insensitive to temperature changes. This successfully constructs a separation-contact ion pair configuration with rapid kinetic properties at low temperatures, allowing the monodentate ring ether solvent to react with Na+. + The coordination strength of Na + Matching the desolvation process, Na at low temperature + The desolvation process is significantly reduced in difficulty, thereby improving the transport efficiency of sodium ions.

[0072] The applicant declares that the detailed method of the present invention is illustrated by the above embodiments, but the present invention is not limited to the above detailed method, that is, it does not mean that the present invention must rely on the above detailed method to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions of the raw materials of the product of the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. An ultra-low temperature sodium-ion battery electrolyte, characterized in that, It is composed of an organic solvent and a sodium salt; the organic solvent is a monodentate cyclic ether solvent.

2. The ultra-low temperature sodium-ion battery electrolyte according to claim 1, characterized in that, The organic solvent is at least one selected from tetrahydrofuran, 2-methyltetrahydrofuran, 3-methyltetrahydrofuran, tetrahydropyran, 2-methyltetrahydropyran, 3-methyltetrahydropyran, 2-cyanotetrahydrofuran, 3-cyanotetrahydrofuran, 2-aminotetrahydrofuran, and 3-aminotetrahydrofuran.

3. The ultra-low temperature sodium-ion battery electrolyte according to claim 1, characterized in that, The organic solvent is 3-methyltetrahydrofuran; the sodium-ion battery prepared using the ultra-low temperature sodium-ion battery electrolyte can be charged at temperatures below -40°C, and the soft-pack battery prepared using the ultra-low temperature sodium-ion battery electrolyte has a discharge capacity at -60°C that exceeds 70% of that at 25°C.

4. The ultra-low temperature sodium-ion battery electrolyte according to claim 1, characterized in that, The concentration of the sodium salt is 0.2 mol / L to 1.0 mol / L.

5. The ultra-low temperature sodium-ion battery electrolyte according to claim 1, characterized in that, The sodium salt is at least one of sodium hexafluorophosphate, sodium difluorosulfonyl imide, sodium difluorooxalate borate, and sodium bis(trifluoromethylsulfonyl)imide.

6. An ultra-low temperature sodium-ion battery, characterized in that, Includes the ultra-low temperature sodium-ion battery electrolyte according to any one of claims 1-5.

7. The ultra-low temperature sodium-ion battery according to claim 6, characterized in that, The negative electrode of the ultra-low temperature sodium-ion battery is hard carbon or metallic sodium, and the positive electrode is a layered oxide, Prussian blue compound, or polyanionic compound.

8. The application of the ultra-low temperature sodium-ion battery of claim 6 in a transport vehicle.

9. The application of the ultra-low temperature sodium-ion battery of claim 6 in energy storage in cold regions.

10. The application of the ultra-low temperature sodium-ion battery as described in claim 6 in polar scientific research and exploration equipment.

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