Electrolyte for sodium-ion battery, sodium-ion battery, and electric device

Abstract

An electrolyte for a sodium-ion battery, a sodium-ion battery, and an electric device. The electrolyte comprises a sodium salt, an organic solvent, and a first additive represented by formula (I), (I), wherein X is selected from one or more of -(CH2)n, -O-, -COO-, -C＝C-, and -C≡C-, n is an integer greater than or equal to 1, and R1 and R2 are independently selected from one or more of F, Cl, Br, and I. The electrolyte has a good flame retardant effect, thereby improving the use safety of a battery and an electric device; moreover, the electrolyte enables the battery to maintain good storage performance, which is favorable for long-term use of the battery.

Description

Electrolyte for sodium ion battery, sodium ion battery and electric device

[0001] The present application claims priority to the Chinese patent application No. 202410816772.6, filed on June 21, 2024, and entitled "Electrolyte for sodium ion battery, sodium ion battery and electric device", the whole content of which is incorporated herein by reference. TECHNICAL FIELD

[0002] The present application relates to the technical field of sodium ion battery, in particular to an electrolyte for sodium ion battery, a sodium ion battery and an electric device. BACKGROUND

[0003] Lithium ion battery is the most widely commercialized electrochemical energy storage device at present, which realizes the conversion between chemical energy and electrical energy through the reversible intercalation / deintercalation of lithium ions between the positive and negative electrodes. Sodium and lithium belong to the same main group, but the reserves of sodium on earth are much higher than those of lithium, and China has abundant sodium resources and sodium extraction technology, so the cost of sodium ion battery will be greatly reduced compared with lithium ion battery.

[0004] With the continuous expansion of the application scenarios of sodium ion battery, its safety performance and storage performance have attracted widespread attention from the society. In order to improve the storage performance and safety of sodium ion battery, selecting appropriate electrolyte additives has become a research hotspot. In the related technology, phosphorus-based flame retardants are added to the electrolyte to reduce its flammability, but it cannot effectively improve the cycle performance and storage performance of sodium ion battery. SUMMARY

[0005] In view of this, the present application provides an electrolyte for sodium ion battery, a sodium ion battery and an electric device. The electrolyte for sodium ion battery has excellent flame retardant effect, improves the use safety of the battery and the electric device, and can make the battery maintain good cycle performance and storage performance, which is conducive to the long-term use of the battery.

[0006] In a first aspect, the present application provides an electrolyte for sodium ion battery, comprising a sodium salt, an organic solvent and a first additive represented by formula (I),

[0007] wherein X is selected from one or more of -(CH2) n , -O-, -COO-, -C=C-, -C≡C-, n is an integer greater than or equal to 1, R1, R2 are independently selected from one or more of F, Cl, Br, I.

[0008] In an embodiment, the first additive comprises a compound represented by formula (II),

[0009] wherein R1, R2 are independently selected from one or more of F, Cl, Br, I.

[0010] In one embodiment, the first additive comprises one or more of the compounds shown in formula (III) or formula (IV)

[0011]

[0012] In one embodiment, the content of the first additive is 1-30 wt%, preferably 0.5%-5%, based on the total weight of the electrolyte.

[0013] In one embodiment, the sodium salt is selected from one or more of sodium hexafluorophosphate, sodium perchlorate, sodium tetrafluoroborate, sodium difluoro(oxalato)borate, sodium bis(oxalato)borate, sodium bis(trifluoromethylsulfonyl)imide, and sodium bisfluorosulfonylimide.

[0014] In one embodiment, the concentration of the sodium salt in the electrolyte is 0.5-2 mol / L.

[0015] In one embodiment, the electrolyte comprises a second additive, and the second additive comprises a fluorinated carbonate.

[0016] In one embodiment, the second additive is selected from one or more of fluoroethylene carbonate, bisfluoroethylene carbonate, and 3,3,3-trifluoropropylene carbonate.

[0017] In one embodiment, the content of the second additive is 0.01-10 wt%, based on the total weight of the electrolyte.

[0018] In one embodiment, the ratio of the first additive to the second additive is (1-3):1.

[0019] In one embodiment, the organic solvent is selected from one or more of dimethyl carbonate, ethylene carbonate, methyl ethyl carbonate, diethyl carbonate, propylene carbonate, and diethyl carbonate.

[0020] The electrolyte for sodium ion batteries provided in the present application has excellent flame retardant effect, and can improve the cycle performance and storage performance of the battery.

[0021] In a second aspect, the present application provides a sodium ion battery, the sodium ion battery comprising a positive electrode, a negative electrode, and an electrolyte, the positive electrode and the negative electrode being disposed in the electrolyte, and the electrolyte being the electrolyte for sodium ion batteries provided in the first aspect of the present application.

[0022] In one embodiment, the negative electrode comprises a negative electrode current collector and a negative electrode active material, the negative electrode active material being coated on the negative electrode current collector, and the negative electrode active material comprising one or more of graphite, hard carbon, and sodium alloy powder. ​

[0023] In one implementation, the positive electrode includes a negative electrode current collector and a positive electrode active material, the positive electrode active material is coated on the positive electrode current collector, and the positive electrode active material includes one or more of sodium ferric pyrophosphate, sodium ferrous sulfate, sodium nickel ferrite, and Prussian blue.

[0024] In a third aspect, the present application provides a battery, comprising the battery provided in the third aspect of the present application.

[0025] The electrolyte for sodium ion batteries provided by the present application has excellent flame retardant performance and storage performance, improves the use safety and durability of the battery and the electric device, and improves the cycle performance of the battery, which is conducive to the use of the battery in the electric device. Specific embodiments

[0026] The technical solutions in the embodiments of the present application are described below in a clear and complete manner. Obviously, the described embodiments are only some of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0027] Unless otherwise defined, all technical and scientific terms used in the present application have the same meanings as commonly understood by those skilled in the art to which the present application belongs. The terms used in the specification of the present application are only for the purpose of describing specific embodiments and are not intended to limit the present application. The term "and / or" used in the present application includes any and all combinations of one or more related listed items.

[0028] Some embodiments of the present application are described in detail below. In the case of no conflict, the embodiments described below and the features in the embodiments can be combined with each other.

[0029] Lithium ion batteries are the most widely used commercial electrochemical energy storage devices at present, which realize the conversion between chemical energy and electrical energy through the reversible intercalation / deintercalation of lithium ions between the positive and negative electrodes. Sodium and lithium belong to the same main group, but the reserves of sodium on earth are much higher than those of lithium, and China has abundant sodium resources and sodium extraction technology, so the cost of sodium ion batteries will be greatly reduced compared with lithium ion batteries.

[0030] The prior art often adds phosphorus-based flame retardants into the electrolyte to reduce its flammability. After adding the flame retardant, the viscosity of the electrolyte rises, leading to a decrease in the ionic mobility of the electrolyte, which will cause greater concentration polarization during the battery cycle process, and have a serious impact on the performance of the battery, especially the cycle performance. During the charging process of the battery, the phosphate molecules in the phosphate ester flame retardant will be co-intercalated into the negative active material along with the active ions, causing the expansion and peeling of the negative active material, further affecting the cycle performance of the battery, and unable to improve the storage performance of the sodium ion battery.

[0031] Based on this, the present application provides an electrolyte for a sodium ion battery, comprising a sodium salt, an organic solvent and a first additive represented by formula (I),

[0032] wherein X is selected from one or more of -(CH2) n , -O-, -COO-, -C=C-, -C≡C-, n is an integer greater than or equal to 1, R1, R2 are independently selected from one or more of F, Cl, Br, I. Halogen elements such as fluorine, chlorine, bromine, iodine, etc. can combine with hydrogen atoms in hydrocarbons to form stable halogenated hydrocarbons, thereby blocking the chain reaction of combustion and improving the flame retardancy of the substance. Small molecules substituted with halogen participate in the formation of a more stable and denser SEI layer, which can prevent direct contact between the electrolyte and the electrode material, reduce the occurrence of side reactions, while maintaining the rapid transmission of ions in the SEI layer, which helps to improve the cycle stability and storage performance of the battery.

[0033] In one embodiment, the first additive comprises a compound represented by formula (II),

[0034] R1, R2 are independently selected from one or more of F, Cl, Br, I. In this embodiment, the first additive can be a halogen-substituted pentane end group. Optionally, the first additive can be one or more of 1-bromopentane, 1-fluoropentane, 1-iodopentane, 1-chloropentane. In this embodiment, different carbon chain lengths have different steric hindrance effects. In the electrolyte, this steric hindrance effect helps to reduce direct contact between electrolyte molecules and electrode materials, thereby reducing the occurrence of side reactions and improving the cycle performance and storage performance of the battery.

[0035] In one embodiment, the first additive comprises a compound represented by formula (III) or formula (IV)

[0036] One or more of the C-Br bonds. Compared to common P-based flame retardant additives (TMP, PFPN), etc., the C-Br bond has a weaker bond energy, is easy to break, and is more efficient in capturing free radicals generated during battery cycling and storage. It can more efficiently cut off the chain reaction to achieve the purpose of flame retardation and improve the safety of the battery. Moreover, NaBr has a lower energy barrier than NaF, Na2CO3, and other sodium SEI inorganic components, which facilitates ion dissociation and has a higher ionic conductivity, which is beneficial to improving the cycle performance of the battery. NaBr has a lower solubility in electrolyte than NaF, Na2CO3, and other sodium SEI inorganic components. The SEI will not decompose and reconfigure during long-term storage, which slows down the self-discharge of the battery and is beneficial to improving the storage performance of the battery.

[0037] In one embodiment, the content of the first additive is 1-30 wt%, preferably 0.5%-5%, based on the total weight of the electrolyte. When the amount of the first additive is within the above range, the cycle performance, storage performance, and flame retardancy of the battery can be improved, and the electrolyte has good flowability and wettability. Alternatively, the content of the first additive can be 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 9 wt%, 10 wt%, 15 wt%, 20 wt%, 30 wt%, and further, when the content of the first additive is 0.5%-5%, the battery performance is further improved.

[0038] In one embodiment, the sodium salt is selected from one or more of sodium hexafluorophosphate, sodium perchlorate, sodium tetrafluoroborate, sodium difluoro oxalate borate, bisoxalate sodium borate, sodium bis(trifluoromethylsulfonyl)imide, and sodium bisfluorosulfonylimide. Such sodium salts have good ionic conductivity and chemical stability, and can maintain stable performance during battery operation. Moreover, the concentration of the sodium salt in the electrolyte is 0.5-2 mol / L, and the concentration of the sodium salt directly affects the ionic conductivity of the electrolyte. Within this concentration range, the electrolyte can maintain a high ionic mobility, thereby ensuring a low internal resistance of the sodium-ion battery. Alternatively, the concentration of the sodium salt in the electrolyte can be 0.5 mol / L, 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L.

[0039] In one embodiment, the electrolyte includes a second additive, and the second additive includes a fluorinated carbonate. The fluorinated carbonate can form a layer of SEI (solid electrolyte interface) film with a compact structure and better performance on the negative electrode surface during battery cycling, which helps to reduce the battery impedance and improve the specific capacity, cycle stability, and cycle life of the lithium battery. Illustratively, the second additive is selected from one or more of fluorinated ethylene carbonate, bis-fluorinated ethylene carbonate, and 3,3,3-trifluoropropylene carbonate.

[0040] In an embodiment, the content of the second additive is 0.01-10wt% based on the total weight of the electrolyte.

[0041] The second additive can significantly improve the electrochemical performance of the electrolyte when the content of the second additive is in the range of 0.01-10wt%, which helps to form a stable SEI (solid electrolyte interface) film on the surface of the negative electrode, reduces the impedance of the battery, and improves the cycle stability and cycle life of the battery. Alternatively, the content of the second additive can be 0.01wt%, 0.1wt%, 1wt%, 2wt%, 3wt%, 4wt%, 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, or 10wt%.

[0042] In an embodiment, the ratio of the first additive to the second additive is (1-3):1. The first additive can improve the flame retardancy and storage performance of the electrolyte, while the second additive can form a stable SEI film on the surface of the negative electrode and inhibit the growth of lithium dendrites. When the ratio of the first additive to the second additive is (1-3):1, the two additives can synergistically act in the electrolyte, fully exert the advantages of the two additives, and improve the overall performance of the battery. Alternatively, the mass ratio of the first additive to the second additive can be 1:1, 1.5:1, 2:1, or 3:1.

[0043] In an embodiment, the organic solvent is selected from one or more of dimethyl carbonate, ethylene carbonate, methyl ethyl carbonate, diethyl carbonate, propylene carbonate, and diethyl carbonate. These carbonate solvents have good chemical, electrochemical, and thermal stability, can maintain stable performance during battery operation, have high electrical conductivity and low viscosity, can provide excellent ion transport capability, and help efficient transport of sodium ions in the battery, thereby improving the charge-discharge efficiency and energy density of the battery.

[0044] The present application provides a sodium-ion battery, which comprises a positive electrode, a negative electrode, and an electrolyte according to any one of the embodiments described above. The battery has excellent use safety and cycle performance, and is beneficial for use in electrical equipment. At least part of the positive electrode and at least part of the negative electrode are soaked in the electrolyte.

[0045] In the present application, the positive electrode comprises a positive electrode current collector and a positive electrode active material layer, and the positive electrode active material layer contains a positive electrode active material, a positive electrode conductive agent, a positive electrode binder, and a dispersant. The weight ratio of the positive electrode active material, the positive electrode conductive agent, the positive electrode binder, and the dispersant is (60-100):1:(1-3):(1-3). Specifically, the weight ratio of the positive electrode active material, the positive electrode conductive agent, the positive electrode binder, and the dispersant can be 60:1:1:1, 80:1:2:2, or 100:1:3:3.

[0046] In the present application, the positive electrode current collector is selected from one or more of aluminum foil, carbon-coated aluminum foil, or aluminum foam.

[0047] In one specific embodiment of the present application, the positive electrode current collector is aluminum foil.

[0048] In the present application, the positive electrode active material is selected from one or more of sodium ferric pyrophosphate, sodium ferrous sulfate, sodium nickel iron manganese acid, and Prussian blue.

[0049] In the present application, the positive electrode conductive agent is selected from one or more of conductive carbon black, single-walled carbon nanotubes, multi-walled carbon nanotubes, graphene, and graphene oxide.

[0050] In the present application, the positive electrode binder is selected from one or more of polyvinylidene fluoride, sodium hydroxymethyl cellulose, sodium alginate, chitosan, guar gum, lignin, sericin, and polyacrylic acid.

[0051] In the present application, the dispersant is selected from one or more of polyvinylpyrrolidone, styrene maleic anhydride, and polyacrylic acid.

[0052] In one specific embodiment of the present application, the dispersant is polyvinylpyrrolidone (PVP).

[0053] In one specific embodiment of the present application, the positive electrode film is a combination of sodium nickel iron manganese acid, conductive carbon black, polyvinylidene fluoride, and PVP, and the weight ratio of sodium nickel iron manganese acid, conductive carbon black, polyvinylidene fluoride, and PVP is 80:1:1:1.

[0054] In the present application, the negative electrode includes a negative electrode current collector and a negative electrode active material layer containing negative electrode active material, negative electrode conductive agent, negative electrode binder, and dispersant. The weight ratio of negative electrode active material, negative electrode conductive agent, negative electrode binder, and dispersant is (60-100):1:(1-3):(1-3). Specifically, the weight ratio of negative electrode active material, negative electrode conductive agent, negative electrode binder, and dispersant can be 60:1:1:1, 80:1:2:2, or 100:1:3:3.

[0055] In the present application, the negative electrode current collector is selected from one or more of copper foil, aluminum foil, and nickel foam.

[0056] In one specific embodiment of the present application, the negative electrode current collector is aluminum foil.

[0057] In the present application, the negative electrode active material is selected from one or more of graphite, hard carbon, and sodium alloy powder.

[0058] In the present application, the negative electrode conductive agent is selected from one or more of conductive carbon black, graphene, and nanocarbon fiber.

[0059] In the present application, the negative electrode binder is selected from one or more of sodium polyacrylate, carboxymethyl cellulose, butadiene rubber and polyacrylonitrile.

[0060] In one specific embodiment of the present application, the negative electrode active material layer is a combination of graphite, conductive carbon black, sodium polyacrylate and PVP, and the weight ratio of graphite, conductive carbon black, sodium polyacrylate and PVP is 100:1:3:3.

[0061] In the present application, the sodium-ion battery further comprises a separator, the separator has electrical insulation and liquid retention properties, and the separator can be selected as needed. The separator is selected from one or more of single-layer polypropylene, double-layer polypropylene and three-layer polypropylene-polyethylene-polypropylene.

[0062] In one specific embodiment of the present application, the separator is single-layer polypropylene.

[0063] In the present application, the sodium-ion battery further comprises a battery shell, the battery shell is used to assemble the positive electrode, the separator, the electrolyte and the negative electrode.

[0064] The present application provides an electric device comprising the sodium-ion battery of any of the above embodiments. The electric device provided by the present application has excellent performance, high safety and strong product competitiveness. The electric device of the present application can refer to a vehicle, an electronic device, an energy storage system, etc., and the above-mentioned battery can be arranged in the electric device in the form of a single battery, a battery module, a battery pack, a capacitor, etc.

[0065] The present application will be described in detail below through examples, comparative examples and test examples. The examples, comparative examples and test examples are implemented on the premise of the technical solutions of the present application, and the specific operation processes are given, but the protection scope of the present application is not limited to the following examples.

[0066] The experimental methods in the following examples, comparative examples and test examples are all conventional methods in the art unless otherwise specified. The experimental materials used in the following examples, comparative examples and test examples are all commercially available unless otherwise specified.

[0067] Example 1

[0068] (1) Preparation of the positive electrode: Take the positive electrode material (aluminum foil, sodium nickel manganese acid, conductive carbon black, polyvinylidene fluoride and PVP), mix 80 g of sodium nickel manganese acid, 10 g of conductive carbon black, 10 g of polyvinylidene fluoride into 10 g of PVP to prepare a positive electrode slurry, uniformly coat the positive electrode slurry on an aluminum foil with a thickness of 18 μm, and then dry, roll, cut to prepare the positive electrode;

[0069] (2) Preparation of the negative electrode: Take the negative electrode material (copper foil, graphite, conductive carbon black, sodium polyacrylate and PVP), mix 100 g of graphite, 1 g of conductive carbon black, 3 g of sodium polyacrylate into 3 g of PVP to prepare a negative electrode slurry, uniformly coat the negative electrode slurry on an aluminum foil with a thickness of 18 μm, and then dry, roll, and cut to prepare the negative electrode;

[0070] (3) Preparation of the electrolyte: In a glove box with water content and oxygen content less than 0.1 ppm, 168 g of NaPF6 was dissolved in 1000 mL (1200 g) of solvent at room temperature (25°C) to obtain a NaPF6 solution, the solvent being a combination of ethylene carbonate, propylene carbonate and diethyl carbonate (volume ratio of ethylene carbonate, propylene carbonate and diethyl carbonate being 1:1:2), the concentration of the NaPF6 solution being 1 mol / L, then 13.7 g of the first additive (1-bromopentane) and 6.9 g of the second additive (fluoroethylene carbonate) were sequentially added into the NaPF6 solution, and the electrolyte was prepared after mixing uniformly;

[0071] (4) Assembly of the sodium ion battery: the positive electrode, single-layer polypropylene and negative electrode were sequentially stacked and wound into a bare cell, which was then loaded into a battery shell and injected with the electrolyte to seal and prepare the sodium ion battery.

[0072] Example 2

[0073] According to the method of Example 1, except that the first additive used in Example 2 is 1,5-dibromopentane, the electrolyte is prepared, and finally the sodium ion battery is prepared.

[0074] Example 3

[0075] According to the method of Example 1, except that the first additive used in Example 3 is 1-fluoropentane, the electrolyte is prepared, and finally the sodium ion battery is prepared.

[0076] Example 4

[0077] According to the method of Example 1, except that the first additive used in Example 4 is 1-chloropentane, the electrolyte is prepared, and finally the sodium ion battery is prepared.

[0078] Example 5

[0079] According to the method of Example 1, except that the first additive used in Example 5 is 1-iodopentane, the electrolyte is prepared, and finally the sodium ion battery is prepared.

[0080] Example 6

[0081] According to the method of Example 1, except that the amount of the first additive used in Example 6 is 41.1 g, the electrolyte is prepared, and finally the sodium ion battery is prepared.

[0082] Example 7

[0083] The method of Example 1 was followed, except that the first additive was added in an amount of 68.5 g in Example 7 to prepare the electrolyte and finally to prepare the sodium-ion battery.

[0084] Comparative Example 1

[0085] The method of Example 1 was followed, except that no first additive was used in Comparative Example 1 to prepare the electrolyte and finally to prepare the sodium-ion battery.

[0086] Comparative Example 2

[0087] The method of Example 1 was followed, except that 13.7 g of phosphorus-based flame retardant (triethyl phosphate TEP, CAS: 78-40-0) was used instead of the first additive in Comparative Example 2 to prepare the electrolyte and finally to prepare the sodium-ion battery.

[0088] Performance test

[0089] Flame retardant test: self extinguish time (SET) test, test procedure: ignite 3 ml of the tested electrolyte under the condition of 25±1.5℃ and no wind flow, and monitor the time from ignition to extinguishment.

[0090] Cycle performance test: use the Blue Electric battery test system, under the condition of 25±1.5℃, charge at 0.2C to 3.5V, then discharge at 0.2C to 2V, after 3 cycles, charge at 1C to 3.5V, then discharge at 1C to 2V, calculate the capacity retention rate of the 300th cycle after 300 cycles of charge / discharge, the calculation formula is: capacity retention rate = discharge capacity of the 300th cycle / discharge capacity of the 1st cycle x 100%;

[0091] Storage performance test:

[0092] ①Discharge to 2V in 0.2C constant current discharge mode, and then charge to 3.4V in constant current charge mode, record as initial capacity C1;

[0093] ②Storage: store the battery in a constant temperature oven at 60℃ for 28 days;

[0094] ③Residual capacity / recovery capacity: discharge to 2V in 0.2C constant current discharge mode, and record the residual capacity C2, then perform 3 cycles of charge / discharge according to the standard charge / discharge mode, and take the maximum discharge capacity as the recovery capacity C3. Capacity residual rate = C2(residual capacity) / C1(initial capacity)*100% Capacity recovery rate = C3(recovery capacity) / C1(initial capacity)*100%

[0095] Table 1: Results of the detection of the flame retardant performance of electrolyte

[0096] Table 2: Results of the detection of the cycle performance of the battery

[0097] Table 3: Results of the detection of the storage performance of the battery

[0098] From Table 1, it can be concluded that the first additive added in the electrolyte has played a role in flame retardation to varying degrees, preferably, the electrolyte with the first additive substituted by Br is almost non-flammable (Examples 1-2, 6-7), the increase of the content of the first additive substituted by Br plays a role in complete non-flammability (Examples 6-7), the electrolyte without any first additive (Comparative Example 1) has no flame retardant effect and is flammable. Therefore, the use of the electrolyte of the present application can improve the flame retardant performance of the electrolyte.

[0099] From Table 2 and Table 3, it can be concluded that the battery assembled with the electrolyte without the first additive (Comparative Example 1) has poorer cycle performance than the battery containing the first additive, and the addition of the phosphoric acid additive (Comparative Example 2) also degrades the cycle performance of the battery to a certain extent. Further screening of the type and content of the first additive can find that when further meeting the preferred range of the present application, the cycle performance and storage performance of the battery are further improved.

[0100] The above is the preferred embodiment of the present application, but it cannot be understood as a limitation on the scope of the present application. It should be noted that for ordinary skilled persons in the technical field, several improvements and refinements can be made without departing from the principles of the present application, and these improvements and refinements are also considered to be within the protection scope of the present application.

Claims

1. An electrolyte for sodium-ion batteries, characterized in that, Includes sodium salt, organic solvent and first additive as shown in formula (I), Wherein, X is selected from -(CH2). n R1 and R2 are selected from one or more of F, Cl, Br, and I, where n is an integer greater than or equal to 1.

2. The electrolyte according to claim 1, characterized in that, The first additive comprises a compound as shown in formula (II), R1 and R2 are independently selected from one or more of F, Cl, Br, and I.

3. The electrolyte according to claim 2, characterized in that, The first additive includes formula (III) or formula (IV). One or more of the compounds shown.

4. The electrolyte according to any one of claims 1-3, characterized in that, Based on the total weight of the electrolyte, the content of the first additive is 1-30 wt%, preferably 0.5%-5%.

5. The electrolyte according to any one of claims 1-3, characterized in that, The sodium salt is selected from one or more of sodium hexafluorophosphate, sodium perchlorate, sodium tetrafluoroborate, sodium difluorooxalate borate, sodium dioxalate borate, sodium di(trifluoromethylsulfonyl)imide, and sodium difluorosulfonylimide.

6. The electrolyte according to any one of claims 1-3, characterized in that, The concentration of the sodium salt in the electrolyte is 0.5-2 mol / L.

7. The electrolyte according to any one of claims 1-3, characterized in that, The electrolyte includes a second additive, which includes fluorocarbonate.

8. The electrolyte according to claim 7, characterized in that, The second additive is selected from one or more of fluoroethylene carbonate, difluoroethylene carbonate, and 3,3,3-trifluoropropylene carbonate.

9. The electrolyte according to claim 8, characterized in that, Based on the total weight of the electrolyte, the content of the second additive is 0.01wt%-10wt%.

10. The electrolyte according to any one of claims 7-9, characterized in that, The mass ratio of the first additive to the second additive is (1-3):

1.

11. The electrolyte according to any one of claims 1-3, characterized in that, The organic solvent is selected from one or more of dimethyl carbonate, ethylene carbonate, ethyl methyl carbonate, diethyl carbonate, propylene carbonate, and diethyl carbonate.

12. A sodium-ion battery, characterized in that, The sodium-ion battery includes a positive electrode, a negative electrode, and an electrolyte, wherein the positive electrode and the negative electrode are placed in the electrolyte, and the electrolyte is the electrolyte according to any one of claims 1-11.

13. The sodium-ion battery according to claim 12, characterized in that, The negative electrode includes a negative electrode current collector and a negative electrode active material. The negative electrode active material is coated on the negative electrode current collector and includes one or more of graphite, hard carbon, and sodium alloy powder.

14. The sodium-ion battery according to claim 12, characterized in that, The positive electrode includes a positive electrode current collector and a positive electrode active material. The positive electrode active material is coated on the positive electrode current collector. The positive electrode active material includes one or more of sodium ferric pyrophosphate, sodium ferrous sulfate, sodium nickel iron manganate, and Prussian blue.

15. An electrical appliance, characterized in that, Including the sodium-ion battery according to any one of claims 12-14.

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