High-temperature sodium ion electrolyte and high-safety sodium ion battery

Abstract

A high-temperature sodium ion electrolyte and a high-safety sodium ion battery. The electrolyte comprises a sodium salt, a non-aqueous organic solvent, and an additive a; the non-aqueous organic solvent is only propylene carbonate. The electrolyte only uses propylene carbonate as the non-aqueous organic solvent, and the propylene carbonate can form a stable primary solvation structure for Na+-PC-DTD-FEC-HMDI-FSI - anions together with sodium ions and three additives, i.e., FEC, HMDI and DTD, such that the sodium ion battery has high thermal stability, and a robust and stable cathode electrolyte interphase and solid electrolyte interphase can be formed on the surface of an electrode. Thus, the problems of short high-temperature cycle life, poor high-temperature storage stability, and gas evolution of existing sodium ion batteries are solved, and a high-safety sodium ion battery is provided.

Description

A high-temperature sodium-ion electrolyte and a high-safety sodium-ion battery Technical Field

[0001] This invention relates to the field of sodium-ion battery technology, and more specifically, to a high-temperature sodium-ion electrolyte and a high-safety sodium-ion battery. Background Technology

[0002] Sodium-ion batteries possess similar physical and chemical properties to lithium-ion batteries. Given the abundance and low cost of sodium resources, they are considered the most promising candidate for large-scale energy storage, with high-temperature performance, high safety, and long cycle life attracting widespread attention. In sodium-ion battery systems, the electrolyte plays a crucial role as the intermediary bridge between the positive and negative electrode materials. Ethylene carbonate (EC) is a high-performance organic solvent. As a non-protic polar organic solvent, it has a high dielectric constant and can dissolve various organic and inorganic salts, making it a widely used electrolyte solvent. However, its high melting point (35–38°C), relatively narrow liquid range, and crystalline solid state at room temperature (25°C) necessitate heating and melting before use. More importantly, ethylene carbonate is easily reduced, resulting in low electrochemical stability. In harsh environments, it can easily generate gas, leading to battery failure, fire, or even explosion. Propylene carbonate (PC), as a solvent similar to ethylene carbonate, not only has a high dielectric constant and strong dissolving ability, but also has the characteristics of low melting point, high boiling point, wide liquid temperature range, wide electrochemical window, and good chemical stability. Using it as a solvent can improve the operating temperature range and safety of batteries, and has great application advantages in sodium-ion batteries.

[0003] However, most existing technologies borrow from lithium-ion battery systems and use compounded organic solvents as electrolytes for high-temperature sodium-ion batteries, with very few technologies using propylene carbonate as a single solvent. Furthermore, existing technologies often require the addition of specially prepared additives to the electrolyte to achieve good high-temperature cycle performance. Summary of the Invention

[0004] To address the aforementioned deficiencies of the prior art, the primary objective of this invention is to provide a high-temperature sodium ion electrolyte that uses only propylene carbonate as a non-aqueous organic solvent. This electrolyte forms a stable Na+ electrolyte through the reaction of propylene carbonate with sodium ions and three commonly used additives in the art: FEC, HMDI, and DTD. + -PC-DTD-FEC-HMDI-FSI - The anion-based solvation structure forms a robust and stable cathode electrolyte membrane (CEI) and solid electrolyte membrane (SEI) on the electrode surface. The highly conductive ion-interface membrane components formed by the main solvation structure significantly improve the thermodynamic and electrochemical stability of sodium-ion batteries.

[0005] Another object of the present invention is to provide the application of the above-mentioned high-temperature sodium ion electrolyte in the preparation of high-safety sodium ion batteries.

[0006] Another object of the present invention is to provide a high-safety sodium-ion battery.

[0007] The above-mentioned objective of the present invention is achieved through the following technical solution:

[0008] This invention protects a high-temperature sodium ion electrolyte, characterized in that it comprises a sodium salt, a non-aqueous organic solvent, and additive a;

[0009] The non-aqueous organic solvent is propylene carbonate;

[0010] The additive a is fluoroethylene carbonate (FEC), hexamethylene diisocyanate (HMDI), and ethylene sulfate (DTD).

[0011] This invention uses only propylene carbonate as a non-aqueous organic solvent, through which propylene carbonate reacts with sodium ions and three additives, FEC, HMDI, and DTD, to form a stable Na+. + -PC-DTD-FEC-HMDI - The anion-dominant solvation structure contributes to the high thermal stability of sodium-ion batteries, forming a robust and stable cathode electrolyte membrane (CEI) and solid electrolyte membrane (SEI) on the electrode surface. Adjusting the structure and composition of the interfacial membranes significantly improves the overall performance of sodium-ion batteries in terms of thermodynamic and electrochemical stability. Moreover, the pure propylene carbonate-based electrolyte does not undergo solvent co-intercalation decomposition with soft carbon or hard carbon anodes, thus preventing anode layer stripping and ensuring cycle performance.

[0012] Preferably, the amount of additive a is >0.1 wt% and ≤30 wt%. More preferably, the amount of additive a is ≥2.0 wt% and ≤10 wt%. Even more preferably, the amount of additive a is ≥2.0 wt% and ≤7 wt%.

[0013] Preferably, the mass ratio of fluoroethylene carbonate, hexamethylene diisocyanate and ethylene sulfate in additive a is 1-15:0.2-3:0.3-5, more preferably 2-5:0.3-1:0.6-2.

[0014] Preferably, the total amount of the non-aqueous organic solvent and additive a is ≥40wt% and ≤97wt%. More preferably, the total amount of the non-aqueous organic solvent and additive a is ≥50wt% and ≤90wt%.

[0015] Preferably, the amount of sodium salt added is 8-42 wt%.

[0016] Preferably, the sodium salt is selected from one or two of inorganic sodium salts or organic sodium salts. More preferably, the sodium salt is selected from one or more of sodium hexafluorophosphate (NaPF6), sodium perchlorate (NaClO4), sodium tetrafluoroborate (NaBF4), sodium hexafluoroarsenate (NaAsF6), sodium bis(fluorosulfonyl)imide (NaFSI), sodium fluoromalonate borate (NaBFMB), sodium bis(trifluoromethylsulfonyl)imide (NaTFSI), sodium bis(oxalate borate) (NaBOB), sodium difluorooxalate borate (NaODFB), sodium difluorophosphate (NaPO2F2), or halogenated derivatives of the above sodium salts.

[0017] More preferably, the sodium salt is selected from one or two of sodium hexafluorophosphate, sodium difluorosulfonyl imide, sodium difluorophosphate, and sodium bis(trifluoromethylsulfonyl)imide.

[0018] More preferably, the sodium salt is sodium hexafluorophosphate and sodium difluorosulfonamide. Specifically, the mass ratio of sodium hexafluorophosphate to sodium difluorosulfonamide is 4–9:3–7.

[0019] Preferably, the concentration of the sodium salt is 1M to 4M. More preferably, the concentration of the sodium salt is 1.2M to 3M.

[0020] Preferably, the high-temperature sodium ion electrolyte further includes additive b.

[0021] Preferably, the additive b is selected from one or more of the following: vinylene carbonate, ethylene ethylene carbonate, tris(trimethylsilane) phosphate, tris(trimethylsilane) borate, 1,3-propane sulpholactone, propenyl-1,3-propane sulpholactone, pentafluoro(phenoxy)cyclotriphosphazene, tetrafluoroethyltetrafluoropropyl ether, pyridine, ethylene glycol dibutyl ether, propylene sulfite, 4-methyl ethylene sulfate, succinate, and adiponitrile.

[0022] More preferably, the additive b is selected from one of the following: 1,3-propanesulfonyl lactone, pentafluoro(phenoxy)cyclotriphosphazene, tris(trimethylsilane)borate, adiponitrile, or a combination of vinylene carbonate and 1,3-propanesulfonyl lactone.

[0023] In the electrolyte system of this invention, additive b can work synergistically with additive a to improve the cycle performance and residual recovery value of sodium-ion batteries after high-temperature storage.

[0024] Preferably, the total amount of additive a and co-additive b is >0.1 wt% and ≤40 wt%. More preferably, the total amount of additive a and co-additive b is ≥2.0 wt% and ≤10 wt%.

[0025] Preferably, the total amount of the non-aqueous organic solvent, additive a, and co-additive b is ≥40 wt% and ≤97 wt%. More preferably, the total amount of the non-aqueous organic solvent, additive a, and co-additive b is ≥50 wt% and ≤90 wt%.

[0026] This invention also protects the application of the above-mentioned high-temperature sodium-ion battery in the preparation of high-safety sodium-ion batteries.

[0027] This invention also protects a high-safety sodium-ion battery, comprising a positive electrode, a negative electrode, a separator, and the aforementioned high-temperature sodium-ion electrolyte.

[0028] Furthermore, the positive electrode sheet includes a positive active material, a conductive agent, and a binder.

[0029] Preferably, the positive electrode active material of the positive electrode sheet is selected from one or more of layered oxide type, polyanionic type, Prussian blue type, and Prussian white type.

[0030] Preferably, the conductive agent of the positive electrode sheet is selected from one or more of conductive graphite, carbon black, carbon fiber, carbon nanotubes, and graphene.

[0031] Preferably, the binder of the positive electrode sheet is selected from one or more of polyvinylidene fluoride, polyacrylic acid, polyacrylonitrile, polyimide, and polytetrafluoroethylene.

[0032] Furthermore, the negative electrode sheet includes a negative electrode material, a conductive agent, and a binder.

[0033] Preferably, the negative electrode active material of the negative electrode sheet is hard carbon or soft carbon.

[0034] Preferably, the conductive agent of the negative electrode sheet is selected from one or more of conductive graphite, carbon black, carbon fiber, carbon nanotubes and graphene.

[0035] Preferably, the binder of the negative electrode sheet is selected from one or more of polyacrylic acid, polyacrylonitrile, sodium carboxymethyl cellulose, styrene-butadiene rubber, polyvinylidene fluoride, and polytetrafluoroethylene.

[0036] Preferably, the separator is selected from one of PP, PE, PP and PE multilayer composite separator, ceramic layer modified separator, PMMA coated separator, aramid modified separator, and oxide solid electrolyte coated separator.

[0037] Compared with the prior art, the beneficial effects of the present invention are:

[0038] 1. The high-temperature sodium ion electrolyte provided by this invention uses only propylene carbonate as a non-aqueous organic solvent. The electrolyte has the characteristics of high boiling point, wide liquid range and good stability. By compounding propylene carbonate with three additives, FEC, HMDI and DTD, the overall performance of sodium ion batteries in terms of thermodynamic and electrochemical stability is improved.

[0039] 2. The high-temperature sodium ion electrolyte provided by this invention will not cause solvent co-intercalation and decomposition with commonly used sodium ion battery negative electrodes (soft carbon, hard carbon), thus preventing the negative electrode layer from peeling off, and the cycle performance is also guaranteed.

[0040] 3. The high-safety sodium-ion battery prepared using the high-temperature sodium-ion electrolyte of this invention has excellent high-temperature cycling and storage performance, and can withstand ultra-high temperature hot plate tests and thermal shock safety tests. Detailed Implementation

[0041] To more clearly and completely describe the technical solution of the present invention, the present invention will be further described in detail below through specific embodiments. It should be understood that the specific embodiments described herein are only for explaining the present invention and are not intended to limit the present invention. Various changes can be made within the scope of the claims of the present invention.

[0042] Example 1

[0043] A high-temperature sodium ion electrolyte comprises: sodium salt NaPF6 with a concentration of 1.2M; non-aqueous organic solvent propylene carbonate; additive a consisting of FEC, HMDI, and DTD; and co-additive b consisting of 1,3-propanesulfonyl lactone. The amounts of sodium salt, non-aqueous organic solvent, additive a, and co-additive b are 16.8 wt%, 74.88 wt%, 6.656 wt%, and 1.664 wt% of the total mass of the high-temperature sodium ion electrolyte, respectively. The mass ratio of fluoroethylene carbonate, hexamethylene diisocyanate, and ethylene sulfate in additive a is 4.1:0.556:2.

[0044] Example 2

[0045] A high-temperature sodium ion electrolyte comprises: sodium salt NaFSI with a concentration of 3M; non-aqueous organic solvent propylene carbonate; additive a consisting of FEC, HMDI, and DTD; and co-additive b consisting of pentafluoro(phenoxy)cyclotriphosphazene. The amounts of sodium salt, non-aqueous organic solvent, additive a, and co-additive b are 42 wt%, 54.23 wt%, 2.9 wt%, and 0.87 wt% of the total mass of the high-temperature sodium ion electrolyte, respectively. The mass ratio of fluoroethylene carbonate, hexamethylene diisocyanate, and ethylene sulfate in additive a is 2:0.3:0.6.

[0046] Example 3

[0047] A high-temperature sodium ion electrolyte comprises: sodium salts NaPF6 and NaFSI, with a sodium salt concentration of 1.4M and a mass ratio of NaPF6 to NaFSI of 7:4; a non-aqueous organic solvent propylene carbonate; additive a comprising FEC, HMDI, and DTD; and co-additive b comprising tris(trimethylsilane) phosphate. The amounts of sodium salt, non-aqueous organic solvent, additive a, and co-additive b are 19.6 wt%, 73.968 wt%, 5.628 wt%, and 0.804 wt% of the total mass of the high-temperature sodium ion electrolyte, respectively. The mass ratio of fluoroethylene carbonate, hexamethylene diisocyanate, and ethylene sulfate in additive a is 3:0.628:2.

[0048] Example 4

[0049] A high-temperature sodium ion electrolyte comprises: sodium salts NaPO2F2 and NaFSI, with a sodium salt concentration of 1.4M and a mass ratio of NaPO2F2 to NaFSI of 1:13; a non-aqueous organic solvent propylene carbonate; additive a comprising FEC, HMDI, and DTD; and co-additive b comprising vinylene carbonate and 1,3-propane sulpholactone. The amounts of sodium salt, non-aqueous organic solvent, additive a, and co-additive b are 19.6 wt%, 74.37 wt%, 4.824 wt%, and 1.206 wt% of the total mass of the high-temperature sodium ion electrolyte, respectively. The mass ratio of fluoroethylene carbonate, hexamethylene diisocyanate, and vinyl sulfate in additive a is 2:0.824:2, and the mass ratio of vinylene carbonate and 1,3-propane sulpholactone in co-additive b is 0.206:1.

[0050] Example 5

[0051] A high-temperature sodium ion electrolyte comprises: sodium salts NaFSI and NaTFSI, with a sodium salt concentration of 1.2M and a mass ratio of NaFSI to NaTFSI of 2:1; a non-aqueous organic solvent propylene carbonate; additive a comprising FEC, HMDI, and DTD; and co-additive b comprising adiponitrile. The amounts of sodium salt, non-aqueous organic solvent, additive a, and co-additive b are 16.8 wt%, 78.208 wt%, 4.576 wt%, and 0.416 wt% of the total mass of the high-temperature sodium ion electrolyte, respectively. The mass ratio of fluoroethylene carbonate, hexamethylene diisocyanate, and ethylene sulfate in additive a is 2.5:0.576:1.5.

[0052] Example 6

[0053] A high-temperature sodium ion electrolyte comprises: a sodium salt of NaPF6 with a concentration of 1.2M; a non-aqueous organic solvent of propylene carbonate; and additive a of FEC, HMDI, and DTD. The sodium salt, non-aqueous organic solvent, and additive a constitute 16.8 wt%, 76.544 wt%, and 6.656 wt% of the total mass of the high-temperature sodium ion electrolyte, respectively. The mass ratio of fluoroethylene carbonate, hexamethylene diisocyanate, and ethylene sulfate in additive a is 4.1:0.556:2.

[0054] Comparative Example 1

[0055] A sodium ion electrolyte comprises: a sodium salt of NaPF6 with a concentration of 1M; a non-aqueous organic solvent of propylene carbonate / dimethyl carbonate / propyl acetate with a mass ratio of propylene carbonate / dimethyl carbonate / propyl acetate of 20:30:50; additive a of FEC, HMDI, and DTD; and co-additive b of 1,3-propanesulfonyl lactone. The amounts of sodium salt, non-aqueous organic solvent, additive a, and co-additive b are 14 wt%, 80.41 wt%, 4.73 wt%, and 0.86 wt% of the total mass of the high-temperature sodium ion electrolyte, respectively. The mass ratio of fluoroethylene carbonate, hexamethylene diisocyanate, and vinyl sulfate in additive a is 3:0.53:1.2.

[0056] Comparative Example 2

[0057] A high-temperature sodium ion electrolyte comprises: sodium salt NaPF6 with a concentration of 1.2M, non-aqueous organic solvent propylene carbonate, additive a is FEC, and co-additive b is 1,3-propanesulfonyl lactone. The amounts of sodium salt, non-aqueous organic solvent, additive a, and co-additive b are 16.8 wt%, 77.436 wt%, 4.1 wt%, and 1.664 wt% of the total mass of the high-temperature sodium ion electrolyte, respectively.

[0058] Comparative Example 3

[0059] A high-temperature sodium ion electrolyte comprises: sodium salt NaPF6 with a concentration of 1.2M, non-aqueous organic solvent propylene carbonate, additive a is DTD, and co-additive b is 1,3-propanesulfonyl lactone. The amounts of sodium salt, non-aqueous organic solvent, additive a, and co-additive b are 16.8 wt%, 79.536 wt%, 2 wt%, and 1.664 wt% of the total mass of the high-temperature sodium ion electrolyte, respectively.

[0060] Comparative Example 4

[0061] A high-temperature sodium ion electrolyte comprises: sodium salt NaPF6 with a concentration of 1.2M; non-aqueous organic solvent propylene carbonate; additive a is HMDI; and auxiliary additive b is 1,3-propanesulfonyl lactone. The amounts of sodium salt, non-aqueous organic solvent, additive a, and auxiliary additive b are 16.8 wt%, 80.98 wt%, 0.556 wt%, and 1.664 wt% of the total mass of the high-temperature sodium ion electrolyte, respectively.

[0062] Comparative Example 5

[0063] A high-temperature sodium ion electrolyte comprises: sodium salt NaPF6 with a concentration of 1.2M; non-aqueous organic solvent propylene carbonate; additive a consisting of FEC and HMDI; and co-additive b consisting of 1,3-propanesulfonyl lactone. The amounts of sodium salt, non-aqueous organic solvent, additive a, and co-additive b are 16.8 wt%, 74.88 wt%, 6.656 wt%, and 1.664 wt% of the total mass of the high-temperature sodium ion electrolyte, respectively. The mass ratio of fluoroethylene carbonate to hexamethylene diisocyanate in additive a is 4.1:0.556.

[0064] Comparative Example 6

[0065] A high-temperature sodium ion electrolyte comprises: sodium salt NaPF6 with a concentration of 1.2M; non-aqueous organic solvent propylene carbonate; additive a consisting of HMDI and DTD; and co-additive b consisting of 1,3-propanesulfonyl lactone. The amounts of sodium salt, non-aqueous organic solvent, additive a, and co-additive b are 16.8 wt%, 74.88 wt%, 6.656 wt%, and 1.664 wt% of the total mass of the high-temperature sodium ion electrolyte, respectively. The mass ratio of hexamethylene diisocyanate to vinyl sulfate in additive a is 0.556:2.

[0066] Comparative Example 7

[0067] A high-temperature sodium ion electrolyte comprises: sodium salt NaPF6 with a concentration of 1.2M; non-aqueous organic solvent propylene carbonate; additive a consisting of FEC and DTD; and co-additive b consisting of 1,3-propanesulfonyl lactone. The amounts of sodium salt, non-aqueous organic solvent, additive a, and co-additive b are 16.8 wt%, 74.88 wt%, 6.656 wt%, and 1.664 wt% of the total mass of the high-temperature sodium ion electrolyte, respectively. The mass ratio of fluoroethylene carbonate to ethylene sulfate in additive a is 4.1:2.

[0068] Performance testing

[0069] 1. Preparation of high-temperature sodium ion electrolyte, including the following steps:

[0070] In an argon-filled glove box, with H2O < 0.1 ppm and O2 < 0.1 ppm, add sodium salt to a solution containing only propylene carbonate as the non-aqueous organic solvent, and stir until homogeneous (if two sodium salts are added, add one first, stir until homogeneous, then add the other, and stir until homogeneous again). After the sodium salts are completely dissolved, add additive a and auxiliary additive b, stir until homogeneous, and then use... The molecular sieve is dried and filtered to obtain a high-temperature electrolyte.

[0071] 2. Preparation of high-safety sodium-ion batteries

[0072] (1) Preparation of positive electrode sheet: The positive active material (sodium iron pyrophosphate), conductive agent (SP and CNT in a mass ratio of 1:1), binder (PVDF) and sodium ion conduction agent are weighed and mixed in a mass ratio of 93:2:3:2 and then added to N-methylpyrrolidone (NMP). The mixture is stirred evenly with a planetary mixer to obtain a positive electrode slurry. The positive electrode slurry is evenly coated on both sides of aluminum foil with a coating machine. After baking, rolling and cutting, the positive electrode sheet is obtained. Finally, it is vacuum dried for later use.

[0073] (2) Preparation of negative electrode sheet: The negative electrode active material (hard carbon), conductive agent (SP), binder (CMC and SBR in a mass ratio of 1:1) and sodium ion-conducting agent are weighed and mixed in a mass ratio of 92:3:3:2 and added to deionized water. The mixture is stirred evenly with a planetary mixer to obtain a negative electrode slurry. The negative electrode slurry is evenly coated on both sides of aluminum foil with a coating machine. After baking, rolling and cutting, the negative electrode sheet is obtained. Finally, it is vacuum dried for later use.

[0074] (3) Assembly of high safety sodium-ion batteries: The positive electrode, separator and negative electrode are wound to obtain bare cells, and then packaged to obtain dry cells; high-temperature sodium-ion electrolyte is injected into the dry cells, and high safety sodium-ion batteries are obtained through formation and capacity testing.

[0075] 3. High-temperature cycling test:

[0076] After placing the battery in a constant temperature oven at 45℃ / 60℃ for 3 hours, charge it at a constant current of 1C to 3.45V, then charge it at a constant voltage to 0.05C, and then discharge it at a constant current of 1C to 1.5V. Repeat this cycle, recording the initial capacity and the discharge capacity on the last cycle (800th cycle). Capacity retention rate = (Discharge capacity on the last cycle (800th cycle) / Initial capacity) × 100%.

[0077] 4.85℃ High Temperature Storage Test:

[0078] Standard charging: Charge the battery at a constant current of 0.5C to 3.45V in an environment of 25℃, cut off at 0.02C, and then discharge it at a constant current of 0.2C to 1.5V. Record the initial thickness, initial capacity and internal resistance R1 of the cell.

[0079] Charge the battery to 3.45V using standard charging, place it in an oven at a constant temperature of 85℃ for 28 days, and after the battery cools to room temperature, measure the cell thickness, internal resistance R2, and capacity after discharging to 1.5V at a current of 0.2C. Record this as the remaining capacity. Charge the stored cell to 3.45V with a constant current of 0.5C, cut off at 0.02C, and then discharge it to 1.5V with a constant current of 0.2C. Record this as the recovered capacity.

[0080] Residual value = Remaining capacity / Initial capacity × 100%

[0081] Recovery value = Recovery capacity / Initial capacity × 100%

[0082] Thickness expansion rate = (Thickness after storage - Thickness before storage) / Thickness before storage × 100%

[0083] Internal resistance growth rate = (internal resistance after storage - internal resistance before storage) / internal resistance before storage × 100%.

[0084] 5. Hot plate safety test:

[0085] Charge the battery cell at 25℃ to 3.45V with 1C and cut off at 0.02C. Then place the battery cell on a graphene heating plate and heat it until the bottom temperature of the battery cell is about 300℃. Keep it above 300℃ for 30 to 40 minutes and observe the voltage change and whether the battery cell expands or fails.

[0086] 6. Thermal shock safety test:

[0087] At 25℃, charge the battery cell to 3.45V with 1C and cut off at 0.02C. Then place the fully charged cell in an air-circulating heating furnace with an initial temperature of 25±3℃ and heat it to 180±2℃ at a heating rate of 5±2℃ / min and hold it for 30 minutes. If it does not catch fire or explode, it is considered to pass.

[0088] Table 1 High-Temperature Cycling and Storage Performance

[0089] Table 2 Hot Plate and Thermal Shock Safety Tests

[0090] As shown in Table 1, the examples all exhibited better high-temperature cycling and high-temperature storage performance, while the comparative example showed greater thickness expansion and gas generation. Table 2 shows that after high-temperature hot plate and thermal shock tests, the voltage of the examples remained stable at 3.39V or higher, indicating no cell failure. In contrast, the voltage of the comparative example dropped to 0V, and the cell expanded and emitted smoke, indicating complete failure due to an internal short circuit. This demonstrates that the pure PC-based electrolyte possesses excellent thermal stability, and the Na formed in the electrolyte... + -PC-DTD-FEC-HMDI - The anion-dominant solvation structure gives sodium-ion batteries high thermal stability and good cycle performance.

[0091] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art can make other variations or modifications based on the above description. It is neither necessary nor possible to exhaustively describe all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A high-temperature sodium-ion electrolyte, comprising a sodium salt, a nonaqueous organic solvent, and an additive a, characterized in that the nonaqueous organic solvent is propylene carbonate; the additive a is fluoroethylene carbonate, hexamethylene diisocyanate, and vinyl sulfate.

2. The high-temperature sodium-ion electrolyte of claim 1, wherein The additive a is added in an amount of > 0.1 wt% and ≤ 30 wt%.

3. The high temperature sodium-ion electrolyte of claim 1, wherein, The mass ratio of the fluoroethylene carbonate, hexamethylene diisocyanate, and vinyl sulfate in the additive a is 0.1-29: 0.1-5: 0.1-8.

4. The high temperature sodium-ion electrolyte of claim 1, wherein, The sodium salt is added in an amount of 8-42 wt%.

5. The high temperature sodium-ion electrolyte of claim 1, wherein, The high-temperature sodium-ion electrolyte further comprises an auxiliary additive b.

6. The high temperature sodium-ion electrolyte of claim 5, wherein, The auxiliary additive b is selected from one or more of vinylene carbonate, vinyl ethylene carbonate, tris(trimethylsilyl)phosphate, tris(trimethylsilyl)borate, 1,3-propane sultone, propenyl-1,3-propane sultone, pentafluoro(phenoxy)cyclotriphosphazene, tetrafluoroethyl tetrafluoropropyl ether, pyridine, ethylene glycol dibutyl ether, propylene sulfite, 4-methyl ethylene sulfite, butanedinitrile, and hexanedinitrile.

7. The high temperature sodium-ion electrolyte of claim 5, wherein, The total amount of the additive a and the auxiliary additive b is > 0.1 wt% and ≤ 40 wt%.

8. The high temperature sodium-ion electrolyte of claim 5, wherein, The total amount of the nonaqueous organic solvent, the additive a, and the auxiliary additive b is ≥ 40% and ≤ 97%. 9.Use of the high-temperature sodium-ion electrolyte according to any one of claims 1-8 in the preparation of a high-safety sodium-ion battery.

10. A high safety sodium-ion battery, characterized in that, The high-safety sodium-ion battery comprises a positive electrode sheet, a negative electrode sheet, a separator, and the high-temperature sodium-ion electrolyte according to any one of claims 1-8.

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