Sodium-ion battery electrolyte and sodium-ion battery prepared therefrom

Abstract

A sodium-ion battery electrolyte and a sodium-ion battery prepared therefrom. The electrolyte has the characteristics of high boiling point, wide liquidus range temperature, and good stability. The electrolyte combines a sodium salt having a trifluoro-substituted group with a conventional sodium salt in an appropriate ratio, thereby overcoming the problems of low ion mobility and difficult desolvation of a sodium-ion battery caused by using only propylene carbonate as a solvent. The sodium-ion battery prepared from the electrolyte has excellent high-temperature and low-temperature cycle performance and high-temperature storage performance, and the safety of the battery is greatly improved.

Description

A sodium-ion battery electrolyte and the sodium-ion battery prepared therefrom Technical Field

[0001] This invention belongs to the field of sodium-ion battery technology, specifically relating to a sodium-ion battery electrolyte and the sodium-ion battery prepared therefrom. Background Technology

[0002] Cyclic carbonates are organic solvents with high dielectric constant, wide temperature range, and excellent performance. As a non-protic polar organic solvent, they can dissolve a variety of organic substances and inorganic salts due to their high dielectric constant, making them a widely used electrolyte solvent. Ethylene carbonate is a crystalline solid at room temperature (25°C), which means it needs to be melted before use. It is usually mixed with linear carbonates or carboxylic acid esters. More importantly, ethylene carbonate is easily reduced and has low electrochemical stability. When used in harsh environments, it is prone to gas generation, leading to battery failure, fire, or even explosion. Propylene carbonate (PC, C4H6O3) possesses advantages such as low melting point, high boiling point, wide liquid temperature range (-48.8℃~242℃), wide electrochemical window, and good chemical stability, along with strong solubility, making it a significant advantage in sodium-ion batteries. However, using propylene carbonate alone as an electrolyte solvent still faces challenges such as high viscosity at low temperatures, low ion mobility, and difficulty in desolvation, leading to increased cell polarization and inability to charge and discharge normally at low temperatures. Therefore, existing sodium-ion battery electrolytes primarily consist of a combination of at least two cyclic carbonates. However, such compounded electrolytes typically only function within a narrow temperature range; otherwise, cell failure due to excessively low temperatures renders them unusable. Furthermore, their safety is insufficient at higher temperatures. Due to the inability to simultaneously achieve high and low temperature performance, the development of wide-temperature batteries with high safety and excellent cycle performance has been a major focus, necessitating a technical solution to address these issues. Summary of the Invention

[0003] The purpose of this invention is to overcome the shortcomings of the prior art and provide a sodium-ion battery electrolyte that has a wide operating temperature range and good conductivity, and uses only propylene carbonate as the electrolyte solvent.

[0004] Another object of the present invention is to provide a method for preparing the sodium-ion battery electrolyte.

[0005] Another object of the present invention is to provide a sodium-ion battery.

[0006] To achieve the above objectives, the present invention employs the following technical solution:

[0007] A sodium-ion battery electrolyte includes a sodium salt, an organic solvent, and additives; the sodium salt includes a first sodium salt and a second sodium salt.

[0008] The first sodium salt is a sodium salt other than a trifluoro substituent, and the second sodium salt is a sodium salt with a trifluoro substituent;

[0009] The mass ratio of the first sodium salt to the second sodium salt is 8-10:0.1-1;

[0010] The organic solvent is propylene carbonate.

[0011] The inventors discovered that sodium salts with appropriate amounts of trifluorine substituents can be used as diluents for sodium salts. This not only enhances the antioxidant properties of the ion-solvated structure but also facilitates its entry into and modification of the metal ion-solvated structure. Furthermore, the introduction of trifluorine substituents is more effective than monofluorine and difluorine substituents in reducing the electronegativity of the carbonyl oxygen on the electrolyte solvent molecule. The interaction between sodium ions and carbonyl groups weakens, ensuring that sodium ion desolvation is promoted even at low temperatures, reducing the desolvation energy during sodium ion migration, and significantly improving the low-temperature electrical performance of the battery cell. Trifluorine substituents, compared to fluorine substituents, exhibit a relatively moderate interaction strength with sodium ions, allowing for effective entry into the sodium ion-solvated structure without excessively reducing the electrolyte conductivity, and also offering a lower cost advantage. Therefore, with the addition of trifluorine-substituent sodium salts, the high-temperature range of propylene carbonate can be better utilized, improving the operating temperature range of the electrolyte and resulting in sodium-ion batteries with excellent high- and low-temperature cycle performance and high-temperature storage performance, while significantly enhancing battery safety.

[0012] Preferably, the first sodium salt is any one or more of sodium hexafluorophosphate, sodium perchlorate, sodium tetrafluoroborate, sodium hexafluoroarsenate, sodium difluorosulfonamide, sodium fluoromalonate borate, sodium bis(oxalate)borate, sodium difluorooxalate borate, or sodium difluorophosphate.

[0013] Preferably, the second sodium salt is any one or more of sodium trifluoromethanesulfinate, sodium trifluoroalkylcarboxylate, sodium 3,3,3-trifluoropropane-1-trifluoroborate, sodium tridecylfluoroheptanoate, sodium trifluorobenzoate, sodium triflusulfonate, sodium flusulfanilamide, or sodium tetra(3,5-bis(trifluoromethyl)phenyl)borate or their alkyl-substituted derivatives.

[0014] The alkyl carboxylic acid in the sodium trifluoroalkyl carboxylate can be selected from C1 to C8 alkyl carboxylic acids, namely formic acid, acetic acid, propionic acid, butyric acid, valeric acid, hexanoic acid, heptanoic acid, or octanoic acid.

[0015] Preferably, the concentration of sodium salt in the sodium-ion battery electrolyte is 5 wt% to 35 wt%.

[0016] Preferably, the organic solvent in the sodium-ion battery electrolyte has a mass percentage of 50 wt% to 90 wt%.

[0017] More preferably, the organic solvent in the sodium-ion battery electrolyte has a mass percentage of 60 wt% to 85 wt%.

[0018] Preferably, the additive in the sodium-ion battery electrolyte has a mass percentage of no more than 15 wt%.

[0019] More preferably, the additive is present in the sodium-ion battery electrolyte at a mass percentage of 3 wt% to 10 wt%.

[0020] Preferably, the additive comprises any one or more of the following: vinylene carbonate, ethylene ethylene carbonate, fluoroethylene carbonate, hexamethylene diisocyanate, vinyl sulfate, tris(trimethylsilane) phosphate, tris(trimethylsilane) borate, 1,3-propane sulpholol, propenyl-1,3-propane sulpholol, pentafluoro(phenoxy)cyclotriphosphazene, tetrafluoroethyltetrafluoropropyl ether, pyridine, ethylene glycol dibutyl ether, propylene sulfite, 4-methylethylene sulfate, succinate, or adiponitrile.

[0021] The method for preparing the sodium-ion battery electrolyte includes the following steps:

[0022] S1. Dissolve the first sodium salt in an organic solvent to obtain the first mixture;

[0023] S2. Add the second sodium salt to the first mixture to obtain the second mixture;

[0024] S3. Add additives to the second mixture and stir until homogeneous to obtain the sodium-ion battery electrolyte.

[0025] More specifically, the organic solvent is dried before being added. The drying process can be carried out using... Molecular sieves are used.

[0026] A sodium-ion battery, using the sodium-ion battery electrolyte as its electrolyte.

[0027] More specifically, the sodium-ion battery includes a positive electrode, a negative electrode, a separator, and the electrolyte.

[0028] The positive electrode sheet described in this invention can be commercially available or self-made.

[0029] Specifically, the positive electrode sheet includes a positive active material, a conductive agent, a binder, etc.

[0030] The positive electrode active material can be selected from one or more mixed systems of layered oxide type, polyanionic type (such as sodium vanadium phosphate, sodium iron sulfate, sodium iron pyrophosphate), Prussian blue type or Prussian white type.

[0031] The conductive agent is a commonly used carbon conductive agent, which can be selected from one or more of conductive graphite, carbon black, carbon fiber, carbon nanotubes or graphene.

[0032] The adhesive is a commonly used adhesive, which can be selected from one or more of polyvinylidene fluoride, polyacrylic acid, polyacrylonitrile, polyimide or polytetrafluoroethylene.

[0033] The negative electrode sheet includes a negative electrode active material, a conductive agent, a binder, etc.

[0034] The negative electrode active material can be amorphous carbon such as hard carbon or soft carbon.

[0035] The conductive agent is a commonly used carbon conductive agent, which can be selected from one or more of conductive graphite, carbon black, carbon fiber, carbon nanotubes or graphene.

[0036] The adhesive is a commonly used adhesive, which can be selected from one or more of polyacrylic acid, polyacrylonitrile, sodium carboxymethyl cellulose, styrene-butadiene rubber, polyvinylidene fluoride and polytetrafluoroethylene.

[0037] The diaphragm can be selected from one of PP, PE, PP and PE multilayer composite diaphragm, ceramic layer modified diaphragm, PMMA coated diaphragm, aramid modified diaphragm or oxide solid electrolyte coated diaphragm.

[0038] The method for preparing the sodium-ion battery specifically includes the following steps: S1, obtaining a bare cell by winding the positive electrode, separator and negative electrode, and then encapsulating it to obtain a dry cell; S2, injecting the sodium-ion battery electrolyte into the dry cell, and obtaining the sodium-ion battery through formation and capacity testing.

[0039] In some specific embodiments, the positive electrode sheet can be prepared by the following method:

[0040] The positive electrode material (e.g., Na4Fe(PO4)2P2O7), conductive agent (e.g., a mixture of SP and CNT in a mass ratio of 1:1), and binder (e.g., polytetrafluoroethylene) are dispersed in N-methylpyrrolidone (NMP) solvent at a mass ratio of 94:3:3. The mixture is stirred evenly using a planetary mixer to obtain a positive electrode slurry. The positive electrode slurry is then evenly coated on both sides of an aluminum foil using a coating machine. After baking, rolling, and slitting, the positive electrode sheet is obtained and finally vacuum dried for later use.

[0041] In some specific embodiments, the negative electrode sheet can be prepared by the following method:

[0042] The negative electrode material (e.g., hard carbon), conductive agent (SP), and binder (CMC to SBR mass ratio 1:1) are mixed together at a mass ratio of 94:3:3 and dispersed in deionized water. The mixture is stirred evenly using a planetary mixer to obtain a negative electrode slurry. The negative electrode slurry is then evenly coated on both sides of an aluminum foil using a coating machine. After baking, rolling, and slitting, the negative electrode sheet is obtained and finally vacuum dried for later use.

[0043] Compared with the prior art, the present invention has the following beneficial effects:

[0044] This invention provides an electrolyte containing only a single organic solvent, which features a high boiling point, a wide liquid temperature range, and good stability. It overcomes the problems of low ion mobility and difficult desolvation in sodium-ion batteries caused by using only propylene carbonate as a solvent by combining a sodium salt with a sodium salt containing a trifluorine substituent in an appropriate ratio. Sodium-ion batteries prepared with this electrolyte exhibit excellent high- and low-temperature cycling performance and high-temperature storage performance, while significantly improving battery safety. Detailed Implementation

[0045] The present invention will be further described in detail below with reference to specific embodiments. These embodiments are only used to explain the present invention and are not intended to limit the scope of the present invention. Unless otherwise specified, the experimental methods used in the following embodiments are conventional methods; the materials and reagents used are commercially available unless otherwise specified.

[0046] The positive electrode sheets used in the examples and comparative examples were prepared by the following method:

[0047] The positive electrode material Na4Fe(PO4)2P2O7, the conductive agent (a mixture of SP and CNT in a mass ratio of 1:1), and the binder (PVDF) were dispersed in N-methylpyrrolidone (NMP) solvent at a mass ratio of 94:3:3. The mixture was stirred evenly using a planetary mixer to obtain a positive electrode slurry. The positive electrode slurry was then evenly coated on both sides of an aluminum foil using a coating machine. After baking, rolling, and slitting, the positive electrode sheet was obtained and finally vacuum dried for later use.

[0048] The negative electrode sheets used in the examples and comparative examples were prepared by the following method:

[0049] The negative electrode material (e.g., hard carbon), conductive agent (SP), and binder (carboxymethyl cellulose CMC and styrene-butadiene rubber SBR in a mass ratio of 1:1) are mixed together in a mass ratio of 94:3:3 and dispersed in deionized water. The mixture is stirred evenly using a planetary mixer to obtain a negative electrode slurry. The negative electrode slurry is then evenly coated on both sides of an aluminum foil using a coating machine. After baking, rolling, and slitting, the negative electrode sheet is obtained and finally vacuum dried for later use.

[0050] In the examples and comparative examples, the preparation method of the sodium-ion battery electrolyte includes the following steps:

[0051] S1. Dissolve the first sodium salt in an organic solvent to obtain the first mixture;

[0052] S2. Add the second sodium salt to the first mixture to obtain the second mixture;

[0053] S3. Add additives to the second mixture and stir until homogeneous to obtain the sodium-ion battery electrolyte.

[0054] The method for preparing the sodium-ion battery specifically includes the following steps: S4, obtaining a bare cell by winding the positive electrode, separator and negative electrode, and then packaging it to obtain a dry cell; S5, injecting the sodium-ion battery electrolyte into the dry cell, and obtaining the sodium-ion battery through formation and capacity testing.

[0055] Example 1

[0056] A sodium-ion battery electrolyte includes a sodium salt, an organic solvent, and additives; the sodium salt includes a first sodium salt and a second sodium salt.

[0057] The organic solvent is propylene carbonate;

[0058] The first sodium salt is NaPF6 and NaFSI; the mass ratio of NaPF6 to NaFSI is 1:2.

[0059] The second sodium salt is sodium trifluoromethanesulfinate;

[0060] The mass ratio of the first sodium salt to the second sodium salt is 6:0.25;

[0061] The total mass of sodium salt is 14% of the mass of electrolyte;

[0062] The additives are fluoroethylene carbonate, ethylene sulfate, and 1,3-propane sulcolone, in a mass ratio of 2:1:1.

[0063] The total mass of the additives is 4% of the battery electrolyte;

[0064] The total mass of the solvent is 82% of the battery electrolyte.

[0065] Sodium-ion batteries were prepared using this electrolyte.

[0066] Example 2

[0067] A sodium-ion battery electrolyte includes a sodium salt, an organic solvent, and additives; the sodium salt includes a first sodium salt and a second sodium salt.

[0068] The organic solvent is propylene carbonate;

[0069] The first sodium salt is NaPF6 and NaPO2F2; the mass ratio of NaPF6 to NaPO2F2 is 13:1;

[0070] The second sodium salt is sodium trifluoromethanesulfinate;

[0071] The mass ratio of the first sodium salt to the second sodium salt is 6:0.25;

[0072] The total mass of sodium salt is 15% of the mass of electrolyte;

[0073] The additives are fluoroethylene carbonate, ethylene sulfate, and 1,3-propane sulcolone, in a mass ratio of 2:1:1.

[0074] The total mass of the additives is 5% of the battery electrolyte;

[0075] The total mass of the solvent is 80% of the battery electrolyte.

[0076] Sodium-ion batteries were prepared using this electrolyte.

[0077] Example 3

[0078] A sodium-ion battery electrolyte includes a sodium salt, an organic solvent, and additives; the sodium salt includes a first sodium salt and a second sodium salt.

[0079] The organic solvent is propylene carbonate;

[0080] The first sodium salt is NaPF6;

[0081] The second sodium salt is sodium trifluoromethanesulfinate;

[0082] The mass ratio of the first sodium salt to the second sodium salt is 10:0.5;

[0083] The total mass of sodium salt is 14% of the electrolyte mass; the additives are fluoroethylene carbonate, ethylene sulfate, and 1,3-propane sulpholol in a mass ratio of 2:1:1.

[0084] The total mass of the additives is 4% of the battery electrolyte;

[0085] The total mass of the solvent is 82% of the battery electrolyte.

[0086] Sodium-ion batteries were prepared using this electrolyte.

[0087] Example 4

[0088] A sodium-ion battery electrolyte includes a sodium salt, an organic solvent, and additives; the sodium salt includes a first sodium salt and a second sodium salt.

[0089] The organic solvent is propylene carbonate;

[0090] The first sodium salt is NaPF6;

[0091] The second sodium salt is sodium tetrakis(3,5-bis(trifluoromethyl)phenyl)borate;

[0092] The mass ratio of the first sodium salt to the second sodium salt is 6:0.5;

[0093] The total mass of sodium salt is 14% of the mass of electrolyte. The additives are fluoroethylene carbonate, ethylene sulfate, and 1,3-propane sulpholol in a mass ratio of 2:1:1.

[0094] The total mass of the additives is 4% of the battery electrolyte;

[0095] The total mass of the solvent is 82% of the battery electrolyte.

[0096] Sodium-ion batteries were prepared using this electrolyte.

[0097] Example 5

[0098] A sodium-ion battery electrolyte includes a sodium salt, an organic solvent, and additives; the sodium salt includes a first sodium salt and a second sodium salt.

[0099] The organic solvent is propylene carbonate;

[0100] The first sodium salt is NaPF6;

[0101] The second sodium salt is sodium trifluoroacetate;

[0102] The mass ratio of the first sodium salt to the second sodium salt is 6.5:0.5;

[0103] The total mass of sodium salt is 16.8% of the electrolyte mass. The additives are fluoroethylene carbonate, ethylene sulfate, and 1,3-propane sulpholol in a mass ratio of 2:1:1.

[0104] The total mass of the additives is 3.2% of the battery electrolyte;

[0105] The total mass of the solvent is 80% of the battery electrolyte.

[0106] Sodium-ion batteries were prepared using this electrolyte.

[0107] Example 6

[0108] A sodium-ion battery electrolyte includes a sodium salt, an organic solvent, and additives; the sodium salt includes a first sodium salt and a second sodium salt.

[0109] The organic solvent is propylene carbonate;

[0110] The first sodium salt is NaPF6;

[0111] The second sodium salt is triflusulfonamide sodium;

[0112] The mass ratio of the first sodium salt to the second sodium salt is 6.5:0.25;

[0113] The total mass of sodium salt is 14% of the electrolyte mass; the additives are fluoroethylene carbonate, ethylene sulfate, and 1,3-propane sulpholol in a mass ratio of 1:1:1.

[0114] The total mass of the additives is 4% of the battery electrolyte;

[0115] The total mass of the solvent is 82% of the battery electrolyte.

[0116] Sodium-ion batteries were prepared using this electrolyte.

[0117] Example 7

[0118] A sodium-ion battery electrolyte includes a sodium salt, an organic solvent, and additives; the sodium salt includes a first sodium salt and a second sodium salt.

[0119] The organic solvent is propylene carbonate;

[0120] The first sodium salt is NaPF6 and NaFSI; the mass ratio of NaPF6 to NaFSI is 1:2.

[0121] The second sodium salt is sodium 3,3,3-trifluoropropane-1-trifluoroborate;

[0122] The mass ratio of the first sodium salt to the second sodium salt is 6.5:0.25;

[0123] The total mass of sodium salt is 28% of the mass of electrolyte. The additives are fluoroethylene carbonate, ethylene sulfate, and 1,3-propane sulpholol in a mass ratio of 1:1:0.5.

[0124] The total mass of the additives is 4% of the battery electrolyte;

[0125] The total mass of the solvent is 68% of the battery electrolyte.

[0126] Sodium-ion batteries were prepared using this electrolyte.

[0127] Comparative Example 1

[0128] A sodium-ion battery electrolyte includes a sodium salt, an organic solvent, and additives;

[0129] The organic solvent is propylene carbonate;

[0130] The sodium salt is NaPF6;

[0131] The total mass of sodium salt is 14% of the mass of electrolyte. The additives are fluoroethylene carbonate, ethylene sulfate, and 1,3-propane sulpholol in a mass ratio of 2:1:1.

[0132] The total mass of the additives is 4% of the battery electrolyte;

[0133] The total mass of the solvent is 82% of the battery electrolyte.

[0134] Sodium-ion batteries were prepared using this electrolyte.

[0135] Comparative Example 2

[0136] A sodium-ion battery electrolyte includes a sodium salt, an organic solvent, and additives; the sodium salt includes a first sodium salt and a second sodium salt.

[0137] The organic solvent is ethylene carbonate to propylene carbonate in a mass ratio of 3:7.

[0138] The first sodium salt is NaPF6;

[0139] The second sodium salt is sodium trifluoromethanesulfinate;

[0140] The mass ratio of the first sodium salt to the second sodium salt is 10:0.5;

[0141] The total mass of sodium salt is 14% of the mass of electrolyte. The additives are fluoroethylene carbonate, ethylene sulfate, and 1,3-propane sulpholol in a mass ratio of 2:1:1.

[0142] The total mass of the additives is 4% of the battery electrolyte;

[0143] The total mass of the solvent is 82% of the battery electrolyte.

[0144] Sodium-ion batteries were prepared using this electrolyte.

[0145] Performance testing

[0146] 1. Testing Method

[0147] (1) Battery cycle performance test:

[0148] High-temperature cycling test:

[0149] After placing the battery in a 60°C oven for 3 hours, charge it at a constant current of 1C to 3.45V, then charge it at a constant voltage until the current drops 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 = Discharge capacity on the last cycle (800th cycle) / Initial capacity × 100%.

[0150] -10°C low-temperature cycling test:

[0151] After placing the battery in a cryogenic chamber at a constant temperature of -10℃ for 3 hours, it was charged at a constant current of 0.33C to 3.45V, then charged at a constant voltage until the current reached 0.05C, and then discharged at a constant current of 0.5C to 1.5V. This cycle was repeated, and the initial capacity and the discharge capacity of the battery in the last cycle (500th cycle) were recorded. Capacity retention rate = discharge capacity in the last cycle (500th cycle) / initial capacity × 100%.

[0152] (2) Battery storage performance test:

[0153] 85℃ high-temperature storage:

[0154] Standard charging: The battery is charged at a constant current of 0.5C to 3.45V in an environment of 25℃, cut off at 0.02C, and then discharged at a constant current of 0.2C to 1.5V. This is recorded as the initial cell thickness, initial capacity, and internal resistance R1. After standard charging to 3.45V, the battery is placed in an oven at a constant temperature of 85℃ for 28 days. After the battery cools to room temperature, the cell thickness, internal resistance R2, and capacity after discharging at 0.2C to 1.5V are measured and recorded as the remaining capacity. The stored cell is charged at a constant current of 0.5C to 3.45V, cut off at 0.02C, and then discharged at a constant current of 0.2C to 1.5V. This is recorded as the recovered capacity.

[0155] Residual value = Remaining capacity / Initial capacity × 100%

[0156] Recovery value = Recovery capacity / Initial capacity × 100%

[0157] Thickness expansion rate = (Thickness after storage - Thickness before storage) / Thickness before storage × 100%

[0158] Internal resistance growth rate = (internal resistance after storage - internal resistance before storage) / internal resistance before storage × 100%.

[0159] The results of the above cycle and high-temperature storage performance tests are shown in Table 1.

[0160] (3) Battery safety performance test:

[0161] Hot plate safety test:

[0162] Charge the battery cell to 3.45V at 1C at 25℃, 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 280℃. Keep it above 280℃ for 30-40 minutes and observe the voltage change and whether the battery cell expands or fails.

[0163] Thermal shock safety test:

[0164] A fully charged cell is placed in an air-circulating heating furnace with an initial temperature of 25±3℃, heated to 170±2℃ at a heating rate of 5±2℃ / min and held for 30 minutes. It passes if it does not catch fire or explode.

[0165] The results of the above hot plate and thermal shock safety tests are shown in Table 2.

[0166] 2. Test Results

[0167] Table 1 High-Temperature Cycling and Storage Performance

[0168] Table 2 Hot Plate and Thermal Shock Safety Tests

[0169] As can be seen from Tables 1 and 2, the sodium-ion battery prepared by the sodium-ion battery electrolyte provided by the present invention has excellent high-temperature and low-temperature cycle performance and high-temperature storage performance, and the safety of the battery is greatly improved.

[0170] As can be seen from Comparative Example 1, without the addition of sodium salt with trifluorine substituents, there are defects such as poor low-temperature cycling performance and reduced thermal shock safety performance. This indicates that the combination electrolyte with the addition of sodium salt with trifluorine substituents and pure propylene carbonate as the single solvent has excellent wide temperature range performance.

[0171] As can be seen from Comparative Example 2, using ethylene carbonate and propylene carbonate as a mixed solvent has drawbacks such as poor high-temperature performance, easy gas generation at high temperatures, and low safety performance at high temperatures, while also exhibiting insufficient low-temperature performance. Hot plate and thermal shock safety tests particularly demonstrate that the voltage in Examples 1 and Comparative Example 1 remained stable at around 3.40V or higher, indicating no cell failure. However, in Comparative Example 2, the voltage dropped to 0V, the cell expanded and emitted smoke, and an internal short circuit led to complete failure. This indicates that pure PC-based electrolyte has high thermal stability, resulting in good safety performance for sodium-ion batteries.

[0172] 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 sodium-ion battery electrolyte, characterized in that, Includes sodium salt, organic solvent, and additives; the sodium salt includes a first sodium salt and a second sodium salt; The first sodium salt is a sodium salt other than a trifluoro substituent, and the second sodium salt is a sodium salt with a trifluoro substituent; The mass ratio of the first sodium salt to the second sodium salt is 8-10:0.1-1; The organic solvent is propylene carbonate.

2. The sodium-ion battery electrolyte according to claim 1, characterized in that, The first sodium salt is any one or more of sodium hexafluorophosphate, sodium perchlorate, sodium tetrafluoroborate, sodium hexafluoroarsenate, sodium difluorosulfonamide, sodium fluoromalonate borate, sodium bis(oxalate)borate, sodium difluorooxalate borate, or sodium difluorophosphate.

3. The sodium-ion battery electrolyte according to claim 1, characterized in that, The second sodium salt is any one or more of sodium trifluoromethanesulfinate, sodium trifluoroalkylcarboxylate, sodium 3,3,3-trifluoropropane-1-trifluoroborate, sodium tridecylfluoroheptanoate, sodium trifluorobenzoate, sodium triflusulfonate, sodium flusulfanilamide, or sodium tetra(3,5-bis(trifluoromethyl)phenyl)borate or their alkyl-substituted derivatives.

4. The sodium-ion battery electrolyte according to claim 1, characterized in that, The sodium salt in the sodium-ion battery electrolyte has a mass percentage of 5 wt% to 35 wt%.

5. The sodium-ion battery electrolyte according to claim 1, characterized in that, The organic solvent in the sodium-ion battery electrolyte has a mass percentage of 50 wt% to 90 wt%.

6. The sodium-ion battery electrolyte according to claim 5, characterized in that, The organic solvent has a mass percentage of 60 wt% to 85 wt% in the sodium-ion battery electrolyte.

7. The sodium-ion battery electrolyte according to claim 1, characterized in that, The additive in the sodium-ion battery electrolyte has a mass percentage of no more than 15 wt%.

8. The sodium-ion battery electrolyte according to claim 1, characterized in that, The additives include any one or more of the following: vinylene carbonate, ethylene ethylene carbonate, fluoroethylene carbonate, hexamethylene diisocyanate, vinyl sulfate, tris(trimethylsilane) phosphate, tris(trimethylsilane) borate, 1,3-propane sulpholol, propenyl-1,3-propane sulpholol, pentafluoro(phenoxy)cyclotriphosphazene, tetrafluoroethyltetrafluoropropyl ether, pyridine, ethylene glycol dibutyl ether, propylene sulfite, 4-methylethylene sulfate, succinate, or adiponitrile.

9. The method for preparing the sodium-ion battery electrolyte according to any one of claims 1 to 8, characterized in that, Includes the following steps: S1. Dissolve the first sodium salt in an organic solvent to obtain the first mixture; S2. Add the second sodium salt to the first mixture to obtain the second mixture; S3. Add additives to the second mixture and stir until homogeneous to obtain the sodium-ion battery electrolyte.

10. A sodium-ion battery, characterized in that, The sodium-ion battery electrolyte according to any one of claims 1 to 8 is used as its electrolyte.

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