Sodium ion battery electrolyte, sodium ion battery and electrical device

Abstract

A sodium ion battery electrolyte, a sodium ion battery and an electrical device. The sodium ion battery electrolyte comprises a sodium salt and a sulfonate compound, and the sulfonate compound comprises one or more of compounds represented by formula (I), formula (II) and formula (III), wherein R1, R5, R6, R9 and R10 are each selected from C1-C3 alkylene groups, and R2, R3, R4, R7, R8 and R11 are each selected from C1-C3 alkyl groups or C1-C3 fluoroalkyl groups. The sulfonate compound contains both a sulfonate group and a carbonate group in the molecules, and thus can be used as a film-forming additive to promote generation of a uniform and stable SEI film rich in sulfates and sulfites on the surface of an electrode, thereby improving the cycle performance and the rate capability of the sodium ion battery.

Description

Sodium ion battery electrolyte, sodium ion battery and electrical equipment

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on December 27, 2023, with application number 202311834197.4 and application name “Sodium Ion Battery Electrolyte, Sodium Ion Battery and Electrical Equipment”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present disclosure relates to the technical field of sodium ion batteries, and in particular to a sodium ion battery electrolyte, a sodium ion battery, and an electrical device. Background Art

[0003] As a supplement or alternative to lithium-ion batteries, sodium-ion batteries have application prospects and value in a variety of scenarios, such as large-scale energy storage, small-scale home storage, and powered forklifts. In the sodium-ion battery system, the electrolyte plays a vital role as an intermediate bridge connecting the positive and negative electrode material systems, and the addition of functional molecules can improve the overall performance of the battery. At present, organic sulfur-containing compound additives are often added to the electrolyte to promote the formation of a stable solid electrolyte membrane (SEI) between the positive and negative electrodes, thereby improving the cycle performance of the battery. However, the improvement of battery cycle performance by existing organic sulfur-containing compound additives is limited, and because the commonly used carbonate electrolyte solvents have a high solubility in the SEI membrane of sodium-ion batteries, it is easy to cause the battery capacity to gradually decrease during continuous charge and discharge, resulting in deterioration of the battery cycle performance. Therefore, it is necessary to improve the electrolyte of sodium-ion batteries to improve the battery cycle performance.

[0004] Summary of the Invention

[0005] Based on this, the embodiments of the present disclosure provide a sodium ion battery electrolyte, which includes a sulfonate compound. The molecular structure of the compound contains both sulfonate groups and carbonate groups. The compound can act as a film-forming additive to promote the formation of a uniform and stable SEI film rich in sulfate and sulfite on the electrode surface. It can also be used as a solvent to dissolve sodium salts and transport sodium ions well. Moreover, due to its low dielectric constant and low solubility in the SEI film, it can inhibit the corrosion of the electrolyte on the SEI film, thereby improving the cycle performance and rate performance of the sodium ion battery.

[0006] In a first aspect, an embodiment of the present disclosure provides a sodium ion battery electrolyte, wherein the sodium ion battery electrolyte comprises a sodium salt and a sulfonate compound, wherein the sulfonate compound comprises one or more compounds represented by formula (I), formula (II) and formula (III),

[0007] Among them, R1, R5, R6, R9 and R 10are independently selected from C1-C3 alkylene, R2, R3, R4, R7, R8 and R 11 are independently selected from C1-C3 alkyl or C1-C3 fluoroalkyl.

[0008] In the embodiment of the present disclosure, the C1-C3 alkylene group is -CH2-, -CH2CH2- or -C(CH3)2-; the C1-C3 alkyl group is -CH3, -CH2CH3, -CH2CH2CH3 or -CH(CH3)2; the C1-C3 fluoroalkyl group is -CF3, -CHF2 or -CH2F.

[0009] In the embodiment of the present disclosure, the volume proportion of the sulfonate compound in the sodium ion battery electrolyte is 0.1%-20%.

[0010] In the embodiment of the present disclosure, in the sodium ion battery electrolyte, the volume proportion of the compound represented by formula (I) is 0%-20%; the volume proportion of the compound represented by formula (II) is 0%-10%; and the volume proportion of the compound represented by formula (III) is 0%-10%.

[0011] In an embodiment of the present disclosure, the sodium salt includes one or more of sodium hexafluorophosphate, sodium perchlorate, sodium bis(trifluoromethylsulfonyl)imide, sodium bis(fluorosulfonyl)imide, sodium trifluoromethanesulfonate, sodium difluorooxalatoborate, sodium bisoxalatoborate, sodium hexafluoroarsenate, sodium tetrafluoroborate, sodium nitrate and sodium chloride.

[0012] In an embodiment of the present disclosure, the concentration of the sodium salt in the sodium ion battery electrolyte is 0.1 mol / L-10 mol / L.

[0013] In an embodiment of the present disclosure, the sodium ion battery electrolyte further comprises one or more of a solvent, an additive, and a diluent;

[0014] The solvent comprises one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, 1,3-dioxolane, methyl acetate, ethyl acetate, ethyl propionate, propyl propionate, dimethyl sulfoxide, tetrahydrofuran, acetonitrile and N,N-dimethylformamide;

[0015] The additives include one or more of fluoroethylene carbonate, vinylene carbonate, 1,3-propane sultone, propylene sulfate, propenyl-1,3-sultone, vinyl sulfate, methylene methanedisulfonate, succinonitrile, adiponitrile, tris(trimethylsilyl)phosphite, trimethyl phosphate and ethoxy(pentafluoro)cyclotriphosphazene;

[0016] The diluent includes one or more of 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether and bis(2,2,2-trifluoroethyl) ether.

[0017] In the embodiment of the present disclosure, in the sodium ion battery electrolyte, the volume proportion of the solvent is 40%-99%; the volume proportion of the additive is 1%-20%; and the volume proportion of the diluent is 0-45%.

[0018] The sodium ion battery electrolyte provided by the embodiments of the present disclosure contains a sulfonate compound, which has both a sulfonate group and a carbonate group in its molecule. It can act as a film-forming additive for the sodium ion battery electrolyte, promoting the formation of a uniform and stable SEI film rich in sulfate and sulfite on the electrode surface. It can also be used as a solvent for the sodium ion battery electrolyte, effectively dissolving sodium salts and transporting sodium ions. Moreover, due to its low dielectric constant and low solubility in the SEI film, it can inhibit the corrosion of the electrolyte on the SEI film, thereby improving the cycle performance and rate performance of the sodium ion battery.

[0019] In a second aspect, an embodiment of the present disclosure provides a sodium ion battery comprising a positive electrode, a negative electrode, a separator located between the positive electrode and the negative electrode, and an electrolyte, wherein the electrolyte comprises the sodium ion battery electrolyte described in the first aspect.

[0020] The electrolyte of the sodium ion battery provided by the embodiments of the present disclosure contains a sulfonate compound, which can promote the formation of a uniform and stable SEI film on the surface of the battery electrode. The SEI film has good corrosion resistance, helps to inhibit the occurrence of side reactions and the loss of active lithium, thereby improving the cycle life and rate performance of the battery.

[0021] In a third aspect, an embodiment of the present disclosure further provides an electrical device, which includes the sodium ion battery described in the second aspect.

[0022] The electric device provided by the embodiment of the present disclosure includes the sodium ion battery described in the second aspect. The sodium ion battery has a long cycle life and good rate performance, so that the electric device can be used stably for a long time, which is conducive to improving the performance of the electric device. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] FIG1 is a cycle performance diagram of the sodium ion battery provided in Example 4 of the present disclosure at a current density of 1C.

[0024] FIG2 is a cycle performance diagram of the sodium ion battery provided in Example 6 of the present disclosure at a current density of 1C.

[0025] FIG3 is a cycle performance diagram of the sodium ion battery provided in Comparative Example 3 of the present disclosure at a current density of 1C.

[0026] FIG4 is an XPS S2p spectrum of sulfur element on the positive electrode surface of the sodium ion battery provided in Example 6 of the present disclosure.

[0027] FIG5 is an XPS S2p spectrum of sulfur element on the negative electrode surface of the sodium ion battery provided in Example 6 of the present disclosure.

[0028] FIG6 is an XPS C1s spectrum of carbon elements on the positive electrode surface of the sodium ion battery provided in Example 6 of the present disclosure.

[0029] FIG7 is an XPS C1s spectrum of carbon elements on the negative electrode surface of the sodium ion battery provided in Example 6 of the present disclosure.

[0030] FIG8 is an XPS S2p spectrum of sulfur element on the positive electrode surface of the sodium ion battery provided in Comparative Example 3 of the present disclosure.

[0031] FIG9 is an XPS S2p spectrum of sulfur element on the negative electrode surface of the sodium ion battery provided in Comparative Example 3 of the present disclosure.

[0032] FIG10 is a three-dimensional distribution diagram of Na2SO4 in the negative electrode SEI film of the sodium ion battery provided in Example 6 and Comparative Example 3 of the present disclosure.

[0033] FIG. 11 is a schematic diagram of a battery according to an embodiment of the present disclosure.

[0034] FIG12 is a schematic diagram of an electric device according to an embodiment of the present disclosure.

[0035] Reference numerals: battery 60, positive electrode 61, negative electrode 63, separator 65, electrolyte 67, power-consuming device 70 DETAILED DESCRIPTION

[0036] The embodiments of the present disclosure are described below with reference to the accompanying drawings.

[0037] In recent years, with the large-scale commercial application of lithium-ion batteries, the shortage of lithium resources and rising prices have attracted attention. Sodium-ion batteries, due to their abundant sodium reserves, considerable energy density, and low cost, hold great promise for future large-scale energy storage applications. Sodium-ion batteries share similar principles and processes with lithium-ion batteries, and most sodium-ion battery development draws on experience gained from lithium-ion battery development. However, despite this, sodium-ion batteries still differ significantly from lithium-ion batteries in many aspects, particularly regarding the electrolyte. Currently, organic sulfur compounds are often added to the electrolyte to promote the formation of a stable solid electrolyte interface (SEI) between the positive and negative electrodes, thereby improving the battery's cycling performance. However, the improvement in battery cycling performance achieved with existing organic sulfur compound additives is limited. Furthermore, the high solubility of commonly used carbonate electrolyte solvents in the SEI of sodium-ion batteries can lead to a gradual decrease in battery capacity during continuous charge and discharge, resulting in deterioration in battery cycling performance. Therefore, improvements to sodium-ion battery electrolytes are necessary to enhance cycling performance.

[0038] Based on this, the present disclosure provides an electrolyte for a sodium ion battery. The electrolyte for a sodium ion battery includes a sodium salt and a sulfonate compound, wherein the sulfonate compound includes one or more compounds represented by formula (I), formula (II) and formula (III).

[0039] Among them, R1, R5, R6, R9 and R 10 are independently selected from C1-C3 alkylene, R2, R3, R4, R7, R8 and R 11 are independently selected from C1-C3 alkyl or C1-C3 fluoroalkyl.

[0040] The sulfonate compounds provided in the embodiments of the present disclosure have the functions of both film-forming additives and solvents, and can promote the formation of a uniform and stable SEI film on the electrode surface, thereby improving the cycle stability and rate performance of the battery. Specifically, the sulfonate compound contains both sulfonate groups and carbonate groups, which can act as sulfonate and carbonate film-forming additives, decompose to form sulfates, sulfites and carbonates, and the formed sulfates, sulfites and carbonates can stabilize the SEI film. The uniform stability of the SEI film contributes to the rapid transmission of charges and ions, which can prevent excessive consumption and loss of electrolytes, reduce the concentration gradient in the electrolyte, and prevent damage and dissolution of electrode materials, thereby obtaining a sodium ion battery with high rate performance and long life; the sulfonate compound can also act as a carbonate solvent, dissolving sodium salts and transporting sodium ions well, and compared with traditional carbonate solvents, the sulfonate compound has a linear structure, a lower dielectric constant, and low solubility in the SEI film, which can inhibit the corrosion of the electrolyte on the SEI film, and is beneficial to improving the structural stability of the electrode. At the same time, the linear structure of the sulfonate compound has a low impedance, which can improve battery efficiency, reduce energy loss, improve discharge performance, and extend the cycle life of the battery.

[0041] In the embodiments of the present disclosure, a C1-C3 alkylene group refers to an alkylene group having 1 to 3 carbon atoms. Specifically, the C1-C3 alkylene group may be -CH2-, -CH2CH2-, -CH(CH3)-, -CH2CH2CH2-, -CH(CH3)CH2-, -CH2CH(CH3)-, or -C(CH3)2-. In some embodiments, the C1-C3 alkylene group is -CH2-, -CH2CH2-, or -C(CH3)2-, which facilitates the preparation of sulfonate compounds and facilitates the decomposition of sulfonate compounds to form a stable SEI film.

[0042] In the embodiments of the present disclosure, a C1-C3 alkyl group refers to an alkyl group having 1 to 3 carbon atoms. Specifically, the C1-C3 alkyl group may be -CH3, -CH2CH3, -CH2CH2CH3, or -CH(CH3)2. In some embodiments, the C1-C3 alkyl group is -CH3, -CH2CH3, -CH2CH2CH3, or -CH(CH3)2, which facilitates the preparation of sulfonate compounds and facilitates the decomposition of sulfonate compounds to form a stable SEI film.

[0043] In the embodiments of the present disclosure, the C1-C3 fluoroalkyl group refers to a fluoroalkyl group having 1 to 3 carbon atoms, wherein the number of fluorine atoms may be 1 to 7. In some embodiments, the C1-C3 fluoroalkyl group may be a monofluoromethyl group, a difluoromethyl group, a trifluoromethyl group, a difluoroethyl group, a trifluoroethyl group, a tetrafluoroethyl group, a pentafluoroethyl group, a trifluoropropyl group, a tetrafluoropropyl group, a pentafluoropropyl group, a hexafluoropropyl group, or a perfluoropropyl group. Specifically, the C1-C3 fluoroalkyl group may be -CF3, -CHF2, -CH2F, -CH2CHF2, -CH2CF3, -CF2CHF2, -CF2CF3, -CH2CH2CF3, -CH2CF2CHF2, -CH2CF2CF3, -CF2CHFCF3, or -CF2CF2CF3. In some embodiments, the C1-C3 fluoroalkyl group is -CF3, -CHF2, or -CH2F, which facilitates the preparation of sulfonate compounds and facilitates the decomposition of sulfonate compounds to form a stable SEI film.

[0044] In the embodiment of the present disclosure, in formula (I), R2 and R3 can be the same or different groups, for example, R2 and R3 are both methyl -CH3; in formula (II), R4 and R7 can be the same or different groups, and R5 and R6 can also be the same or different groups; in formula (III), R9 and R 10 Can be the same or different groups, R8 and R 11 They may be the same or different groups.

[0045] In the embodiment of the present disclosure, in formula (I), R1 is -CH2-, -CH2CH2- or -C(CH3)2-, and R2 and R3 are -CH3, -CH2CH3, -CH2CH2CH3, -CH(CH3)2, -CF3, -CHF2 or -CH2F.

[0046] In the embodiment of the present disclosure, in formula (II), R4 and R7 are independently -CH3, -CH2CH3, -CH2CH2CH3, -CH(CH3)2, -CF3, -CHF2 or -CH2F, and R5 and R6 are independently -CH2-, -CH2CH2- or -C(CH3)2-.

[0047] In the embodiment of the present disclosure, in formula (III), R8 and R 11 are independently -CH3, -CH2CH3, -CH2CH2CH3, -CH(CH3)2, -CF3, -CHF2 or -CH2F, R9 and R 10 are independently -CH2-, -CH2CH2- or -C(CH3)2-.

[0048] In some specific embodiments, the sulfonate compound includes one of the compounds represented by formula (I-1), formula (II-1) and formula (III-1),

[0049] In the disclosed embodiments, the volume proportion of the sulfonate compound in the sodium ion battery electrolyte can be 0.1%-20%, which can not only improve the structural stability of the SEI film on the electrode surface, but also avoid the occurrence of side reactions, and also help control costs. In some embodiments, the volume proportion of the sulfonate compound in the sodium ion battery electrolyte can be 0.1%, 0.5%, 0.8%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 12%, 14, 16, 18 or 20%.

[0050] In an embodiment of the present disclosure, the sodium ion battery electrolyte includes one or more compounds represented by formula (I), formula (II) and formula (III); in the sodium ion battery electrolyte, the volume proportion of the compound represented by formula (I) can be 0%-20%, specifically, the volume proportion of the compound represented by formula (I) can be, for example, 0.1%, 0.5%, 0.8%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 12, 14, 16, 18 or 20%; the volume proportion of the compound represented by formula (II) can be 0%-10%, specifically, the volume proportion of the compound represented by formula (II) can be, for example, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%; the volume proportion of the compound represented by formula (III) can be 0%-10%, Specifically, the volume proportion of the compound represented by formula (III) can be, for example, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or 10%.

[0051] The compounds represented by formula (I), formula (II) and formula (III) can be used alone or in combination. In one embodiment of the present disclosure, the sodium ion battery electrolyte includes the compound represented by formula (I), but does not include the compounds represented by formula (II) and formula (III), and the volume proportion of the compound represented by formula (I) in the sodium ion battery electrolyte can be 0.1%-20%. In another embodiment of the present disclosure, the sodium ion battery electrolyte includes the compound represented by formula (II), but does not include the compounds represented by formula (I) and formula (III), and the volume proportion of the compound represented by formula (II) in the sodium ion battery electrolyte can be 0.1%-10%. In another embodiment of the present disclosure, the sodium ion battery electrolyte includes the compound represented by formula (III), but does not include the compounds represented by formula (I) and formula (II), and the volume proportion of the compound represented by formula (III) in the sodium ion battery electrolyte can be 0.1%-10%. In another embodiment of the present disclosure, the sodium ion battery electrolyte includes compounds represented by formula (I) and formula (II), but does not include the compound represented by formula (III). In the sodium ion battery electrolyte, the volume ratio of the compound represented by formula (I) may be 0.1%-19.9%, and the volume ratio of the compound represented by formula (II) may be 0.1%-10%. In another embodiment of the present disclosure, the sodium ion battery electrolyte includes compounds represented by formula (I) and formula (III), but does not include the compound represented by formula (II). In the sodium ion battery electrolyte, the volume ratio of the compound represented by formula (I) may be 0.1%-19.9%, and the volume ratio of the compound represented by formula (III) may be 0.1%-10%. In another embodiment of the present disclosure, the sodium ion battery electrolyte includes compounds represented by formula (II) and formula (III), but does not include the compound represented by formula (I). In the sodium ion battery electrolyte, the volume ratio of the compound represented by formula (II) may be 0.1%-10%, and the volume ratio of the compound represented by formula (III) may be 0.1%-10%. In another embodiment of the present disclosure, the sodium ion battery electrolyte includes compounds represented by formula (I), formula (II) and formula (III) at the same time. In the sodium ion battery electrolyte, the volume proportion of the compound represented by formula (I) can be 0.1%-19.8%, the volume proportion of the compound represented by formula (II) can be 0.1%-10%, and the volume proportion of the compound represented by formula (III) can be 0.1%-10%.

[0052] It should be noted that the volume ratio of each component of the sodium ion battery electrolyte in this application is the ratio of the volume of each component to the volume of the electrolyte excluding the sodium salt.

[0053] In the embodiments of the present disclosure, the main function of the sodium salt is to provide sodium ions to ensure that the battery has sufficient sodium ions during the charge and discharge process. These sodium ions are transferred between the positive and negative electrodes and are embedded and deintercalated in the negative electrode material during the charge and discharge process. In some embodiments, the sodium salt includes one or more of sodium hexafluorophosphate, sodium perchlorate, sodium bis(trifluoromethylsulfonyl)imide, sodium bis(fluorosulfonyl)imide, sodium trifluoromethanesulfonate, sodium difluorooxalatoborate, sodium bisoxalatoborate, sodium hexafluoroarsenate, sodium tetrafluoroborate, sodium nitrate and sodium chloride.

[0054] In the embodiments of the present disclosure, the concentration of the sodium salt in the sodium ion battery electrolyte can be 0.1 mol / L-10 mol / L, which can not only ensure the electrochemical performance of the electrolyte, but also avoid the waste of sodium salt, which is beneficial to control costs. In some embodiments, the concentration of the sodium salt in the sodium ion battery electrolyte can be 0.1 mol / L, 0.5 mol / L, 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L, 3 mol / L, 3.5 mol / L, 4 mol / L, 5 mol / L, 6 mol / L, 7 mol / L, 8 mol / L, 9 mol / L or 10 mol / L.

[0055] In the embodiment of the present disclosure, the sodium ion battery electrolyte further includes one or more of a solvent, an additive, and a diluent, which is beneficial to further improve the electrochemical performance of the sodium ion battery electrolyte.

[0056] In the embodiments of the present disclosure, the solvent may be one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, 1,3-dioxolane, methyl acetate, ethyl acetate, ethyl propionate, propyl propionate, dimethyl sulfoxide, tetrahydrofuran, acetonitrile, and N,N-dimethylformamide. The above solvents can help transfer cations and anions in the battery, thereby making the electrolyte more conductive.

[0057] In embodiments of the present disclosure, the volume proportion of the solvent in the sodium ion battery electrolyte can be 40%-99%, which can improve the conductivity of the electrolyte without affecting the stability of the electrolyte / electrode interface. In some embodiments, the volume proportion of the solvent can be 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 98% or 99%.

[0058] In the embodiment of the present disclosure, the additives include one or more of film-forming additives, flame retardants, dehumidifiers and anti-overcharge additives. Film-forming additives can further improve the stability of the electrolyte / electrode interface; dehumidifiers can reduce the moisture content and help inhibit the generation of harmful components; flame retardants and anti-overcharge additives can effectively reduce battery side reactions and ensure safe and stable operation of the battery. In some embodiments, the additive can be one or more of fluoroethylene carbonate, vinylene carbonate, 1,3-propane sultone, propylene sulfate, propylene-1,3-sultone, vinyl sulfate, methylene disulfonate, succinonitrile, adiponitrile, tris(trimethylsilyl)phosphite, trimethyl phosphate and ethoxy(pentafluoro)cyclotriphosphazene.

[0059] In the disclosed embodiments, the volume percentage of the additive in the sodium ion battery electrolyte can be 1%-20%, which can further improve the electrode stability and safety of the battery without affecting the energy density of the battery. In some embodiments, the volume percentage of the additive in the sodium ion battery electrolyte can be 1%, 1.5%, 2%, 3%, 4%, 5%, 8%, 10%, 12%, 15%, 18% or 20%.

[0060] In the disclosed embodiments, the diluent includes one or more of 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, and bis(2,2,2-trifluoroethyl) ether. Adding the diluent to the sodium ion electrolyte can form a locally high-concentration electrolyte system, reducing the system viscosity while further improving film formation stability.

[0061] In embodiments of the present disclosure, the volume percentage of the diluent in the sodium ion battery electrolyte can be 0-45%, which can reduce the viscosity of the electrolyte and enhance the stability at the electrolyte / electrode interface without affecting the energy density of the battery. In some embodiments, the volume percentage of the diluent in the sodium ion battery electrolyte can be 0%, 10%, 20%, 30%, 40% or 45%.

[0062] In the embodiments of the present disclosure, solvents, additives, and diluents may be added to the sodium ion battery electrolyte simultaneously to synergistically improve the safety, stability, and electrochemical performance of the electrolyte.

[0063] An embodiment of the present disclosure also provides a sodium ion battery, comprising a positive electrode, a negative electrode, a separator located between the positive electrode and the negative electrode, and an electrolyte, wherein the electrolyte comprises the sodium ion battery electrolyte in any of the above embodiments.

[0064] The electrolyte of the sodium ion battery provided by the embodiments of the present disclosure contains a sulfonate compound, which can promote the formation of a uniform and stable SEI film on the surface of the battery electrode. The SEI film has good corrosion resistance, helps to inhibit the occurrence of side reactions and the loss of active lithium, thereby improving the cycle life and rate performance of the battery.

[0065] The present disclosure also provides an electric device. FIG12 shows a block diagram of the electric device. As shown in FIG12 , the electric device 70 includes a sodium-ion battery 60 according to any of the aforementioned embodiments. Specifically, the electric device can be an electric vehicle, an electric motorcycle, an electric bicycle, a power bank, an unmanned aerial vehicle, a mobile phone, a computer, a camera, a power tool, a smart home appliance, or a wearable device.

[0066] The electrical equipment provided in the embodiments of the present disclosure includes a sodium ion battery, which has a long cycle life and good rate performance, so that the electrical equipment can be used stably for a long time, which is beneficial to improving the performance of the electrical equipment.

[0067] The technical solution of the present disclosure is further illustrated below through specific embodiments and comparative examples.

[0068] Example 1

[0069] Methyl carbonate methanesulfonate represented by formula (I-1) and dimethyl carbonate are mixed in a volume ratio of 1:4 to prepare an electrolyte mother liquor, and the moisture in the mother liquor is removed by using a molecular sieve. Then, sodium hexafluorophosphate is added in batches to the dry and anhydrous electrolyte mother liquor while stirring, and finally a clear, colorless and transparent sodium ion battery electrolyte with a sodium hexafluorophosphate concentration of 1 mol / L is obtained.

[0070] Example 2

[0071] Methyl carbonate methanesulfonate, ethylene glycol dimethyl ether and 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether represented by formula (I-1) are mixed in a volume ratio of 1:4:4 to prepare an electrolyte mother liquor. The water in the mother liquor is removed by using a molecular sieve. Then, sodium bis(fluorosulfonyl)imide is added in batches to the dry and anhydrous electrolyte mother liquor while stirring, and finally a clear, colorless and transparent sodium ion battery electrolyte with a sodium bis(fluorosulfonyl)imide concentration of 1 mol / L is obtained.

[0072] Example 3

[0073] Methyl carbonate methanesulfonate, ethylene carbonate and dimethyl carbonate represented by formula (I-1) are mixed in a volume ratio of 1:2:7 to prepare an electrolyte mother liquor. The water in the mother liquor is removed by using a molecular sieve. Then, sodium hexafluorophosphate is added in batches to the dry and anhydrous electrolyte mother liquor while stirring, and finally a clear, colorless and transparent sodium ion battery electrolyte with a sodium hexafluorophosphate concentration of 1 mol / L is obtained.

[0074] Example 4

[0075] Methyl carbonate methanesulfonate, ethylene carbonate and dimethyl carbonate shown in formula (I-1) are mixed in a volume ratio of 1:2:7 to prepare an electrolyte mother liquor, and the moisture in the mother liquor is removed by using a molecular sieve. Then, sodium hexafluorophosphate is added in batches to the dry and anhydrous electrolyte mother liquor while stirring to obtain an electrolyte with a sodium hexafluorophosphate concentration of 1 mol / L. After cooling, an additive fluoroethylene carbonate (FEC) with a volume fraction of 1% is added to the electrolyte to obtain a clear, colorless and transparent sodium ion battery electrolyte.

[0076] Example 5

[0077] Ethylene carbonate and dimethyl carbonate are mixed in a volume ratio of 1:4 to prepare an electrolyte mother liquor, and the water in the mother liquor is removed by using a molecular sieve. Then, sodium hexafluorophosphate is added in batches to the dry and anhydrous electrolyte mother liquor while stirring to obtain an electrolyte with a sodium hexafluorophosphate concentration of 1 mol / L. After cooling, methyl (methyl carbonate) methanesulfonate represented by formula (I-1) is added to the electrolyte with a volume fraction of 1%, and finally a clear, colorless and transparent sodium ion battery electrolyte is obtained.

[0078] Example 6

[0079] Ethylene carbonate and dimethyl carbonate are mixed in a volume ratio of 1:4 to prepare an electrolyte mother liquor, and the water in the mother liquor is removed by using a molecular sieve. Then, sodium hexafluorophosphate is added in batches to the dry and anhydrous electrolyte mother liquor while stirring to obtain an electrolyte with a sodium hexafluorophosphate concentration of 1 mol / L. After cooling, 1% by volume of FEC and 1% by volume of methyl (methyl carbonate) methanesulfonate represented by formula (I-1) are added to the electrolyte to finally obtain a clear, colorless and transparent sodium ion battery electrolyte.

[0080] Example 7

[0081] Ethylene carbonate and dimethyl carbonate are mixed in a volume ratio of 1:4 to prepare an electrolyte mother liquor, and the water in the mother liquor is removed with a molecular sieve. Then, sodium hexafluorophosphate is added in batches to the dry and anhydrous electrolyte mother liquor while stirring to obtain an electrolyte with a sodium hexafluorophosphate concentration of 1 mol / L. After cooling, 1% FEC and 1% of the compound represented by formula (II-1) are added to the electrolyte respectively with a volume fraction of 1%, and finally a clear, colorless and transparent sodium ion battery electrolyte is obtained.

[0082] Example 8

[0083] Ethylene carbonate and dimethyl carbonate are mixed in a volume ratio of 1:4 to prepare an electrolyte mother liquor, and the water in the mother liquor is removed with a molecular sieve. Then, sodium hexafluorophosphate is added in batches to the dry and anhydrous electrolyte mother liquor while stirring to obtain an electrolyte with a sodium hexafluorophosphate concentration of 1 mol / L. After cooling, 1% FEC and 1% of the compound represented by formula (III-1) are added to the electrolyte respectively with a volume fraction of 1%, and finally a clear, colorless and transparent sodium ion battery electrolyte is obtained.

[0084] Comparative Example 1

[0085] Ethylene carbonate and dimethyl carbonate are mixed in a volume ratio of 1:4 to prepare an electrolyte mother liquor, and the water in the mother liquor is removed by using a molecular sieve. Then, sodium hexafluorophosphate is added in batches to the dry and anhydrous electrolyte mother liquor while stirring, and finally a clear, colorless and transparent sodium ion battery electrolyte with a sodium hexafluorophosphate concentration of 1 mol / L is obtained.

[0086] Comparative Example 2

[0087] Ethylene carbonate and dimethyl carbonate are mixed in a volume ratio of 1:4 to prepare an electrolyte mother liquor. The water in the mother liquor is removed with a molecular sieve. Sodium hexafluorophosphate is then added in batches to the dry and anhydrous electrolyte mother liquor while stirring to obtain an electrolyte with a sodium hexafluorophosphate concentration of 1 mol / L. After cooling, 1,3-propane sultone (PS) with a volume fraction of 1% is added to the electrolyte to finally obtain a clear, colorless and transparent sodium ion battery electrolyte.

[0088] Comparative Example 3

[0089] Ethylene carbonate and dimethyl carbonate were mixed in a volume ratio of 1:4 to prepare an electrolyte mother liquor. Molecular sieves were used to remove moisture from the mother liquor. Sodium hexafluorophosphate was then added in batches to the dry and anhydrous electrolyte mother liquor while stirring to obtain an electrolyte with a sodium hexafluorophosphate concentration of 1 mol / L. After cooling, 1% FEC and 1% 1,3-propane sultone (PS) were added to the electrolyte respectively with a volume fraction of 1%, and finally a clear, colorless and transparent sodium ion battery electrolyte was obtained.

[0090] The sodium ion battery electrolytes provided in Examples 1-8 and Comparative Examples 1-3 were assembled into soft-pack sodium ion batteries according to the following methods.

[0091] Preparation of positive electrode sheet: Sodium iron pyrophosphate positive electrode material (NFPP), polyvinylidene fluoride (PVDF) binder, and acetylene black (SuperP) conductive agent are mixed in a mass ratio of 8:1:1, and a certain amount of N-methylpyrrolidone (NMP) is added to prepare a positive electrode slurry. The solid content of the slurry is adjusted to about 50%. After degassing and sieving, the slurry is evenly coated on the surface of aluminum foil. After drying, rolling, and cutting, the positive electrode sheet is obtained.

[0092] Preparation of negative electrode sheet: Hard carbon negative electrode material (HC), styrene-butadiene rubber (SBR) / carboxymethyl cellulose (CMC) composite binder and acetylene black (SuperP) conductive agent are mixed in a mass ratio of 8:1:1, and deionized water is added to prepare negative electrode slurry. The solid content is adjusted to about 45%. After degassing and sieving, it is evenly coated on the surface of aluminum foil. After drying, rolling and cutting, the negative electrode sheet is obtained.

[0093] Preparation of soft-pack batteries: The negative electrode sheet, the separator, and the positive electrode sheet are stacked in sequence to form a battery cell, which is encapsulated in an aluminum-plastic shell. After the battery cell is baked to remove moisture, the sodium ion battery electrolyte of Examples 1-8 and Comparative Examples 1-3 is respectively injected into the soft-pack batteries. After aging, formation, aging, and capacity separation, the soft-pack sodium ion batteries of Examples 1-8 and Comparative Examples 1-3 are obtained.

[0094] FIG11 is a schematic block diagram of a sodium ion battery according to an embodiment of the present disclosure. As shown in FIG11 , the sodium ion battery 60 (referred to as battery 60 ) includes a positive electrode 61, a negative electrode 63, a separator 65 located between the positive electrode and the negative electrode, and an electrolyte 67. The electrolyte injected is the sodium ion battery electrolyte of Examples 1-8 and Comparative Examples 1-3.

[0095] 1. Electrochemical performance test

[0096] At 25°C, the soft-pack sodium ion battery was charged to 3.6V at a current density of 1C and a constant current and voltage, and then discharged to 1.5V at a current density of 1C. The initial discharge capacity, first efficiency, and capacity retention rate after 500 cycles of each soft-pack sodium ion battery were tested. The test results are shown in Table 1, and the cycle performance diagrams of Example 4, Example 6, and Comparative Example 3 are shown in Figures 1 to 3.

[0097] Table 1 Electrochemical performance test results

[0098] As can be seen from Table 1, compared with Comparative Examples 1-3, the sodium ion batteries prepared with the sodium ion battery electrolyte provided by the embodiments of the present disclosure have higher initial discharge capacity, first effect and 1C cycle 500 cycle capacity retention rate, indicating that these sodium ion batteries have less irreversible active sodium loss and good cycle stability, which is conducive to the long-term stable use of sodium ion batteries; as can be seen from Examples 6-8, the initial discharge capacity, first effect and capacity retention rate of Example 6 are the best, indicating that the compound represented by formula (I-1) has better ability to improve the electrochemical performance of the battery than the compounds represented by formula (II-1) and formula (III-1); as can be seen from Examples 3 and 4, the sulfonate compounds provided in the embodiments of the present disclosure are used in combination with other film-forming additives to further improve the electrochemical performance of sodium ion batteries.

[0099] As can be seen from Figures 1 to 3, before the capacity retention rate drops to 80%, the sodium ion battery of Example 4 can be cycled more than 1250 times, the sodium ion battery of Example 6 can be cycled more than 700 times, and the sodium ion battery of Comparative Example 3 can only be cycled 200 times, indicating that the sodium ion battery provided by the embodiments of the present disclosure has a better capacity retention rate and a longer cycle service life, which is conducive to the long-term and stable use of the sodium ion battery.

[0100] 2. SEI film characterization

[0101] (1) X-ray photoelectron spectroscopy (XPS) characterization

[0102] XPS characterization was performed on the SEI films on the positive and negative electrode surfaces of the sodium ion batteries of Example 6 and Comparative Example 3, and the results are shown in Figures 4 to 9. As can be seen from Figures 4, 5, 8 and 9, the SEI films of Example 6 and Comparative Example 3 all contain products such as ROSO3Na / Na2SO4, ROSO2Na / Na2SO3 and Na2S, but the content of ROSO3Na / Na2SO4 in Example 6 is higher, indicating that the sodium ion battery electrolyte provided by the disclosed embodiment can promote the formation of a stable SEI film rich in sulfate and sulfite on the electrode surface, which is beneficial to improving electrode stability. In addition, as can be seen from Figures 6 and 7, the SEI film of Example 6 also contains more Na2CO3 inorganic products, which is mainly due to the fact that methyl (methyl carbonate) methanesulfonate combines carbonate groups and sulfonate groups to jointly regulate the SEI film components, producing more inorganic products, which is beneficial to reducing the solubility of the SEI film and improving the structural stability of the positive and negative electrodes.

[0103] (2) Characterization of Na2SO4 longitudinal distribution

[0104] Time-of-flight secondary ion mass spectrometry (TOF-SIMS) was used to characterize the longitudinal (i.e., thickness direction) distribution of Na2SO4 in the SEI film of the negative electrode of the sodium ion battery of Example 6 and Comparative Example 3. The results are shown in Figure 10. The Na2SO4 in the negative electrode of Example 6 can penetrate deep into the SEI film and is evenly distributed throughout the SEI film, while the Na2SO4 in the negative electrode of Comparative Example 3 is unevenly distributed throughout the SEI film and has a low content, indicating that the sodium ion battery electrolyte provided by the embodiments of the present disclosure can increase the content and uniformity of sulfate in the SEI film, which is beneficial to improving the structural stability of the battery negative electrode, thereby extending the cycle life of the battery.

[0105] The above-described embodiments merely represent several implementation methods of the present application. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person of ordinary skill in the art may make various modifications and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be determined by the appended claims.

Claims

1. A sodium-ion battery electrolyte, characterized in that, The sodium-ion battery electrolyte includes a sodium salt and a sulfonate compound, and the sulfonate compound includes one or more of the compounds represented by formula (I), formula (II), and formula (III). Among them, R1, R5, R6, R9 and R 10 are respectively selected from C1-C3 alkylene groups, and R2, R3, R4, R7, R8 and R 11 are respectively selected from C1-C3 alkyl groups or C1-C3 fluoroalkyl groups.

2. The sodium-ion battery electrolyte according to claim 1, characterized in that, The C1-C3 alkylene group is -CH2-, -CH2CH2- or -C(CH3)2-; the C1-C3 alkyl group is -CH3, -CH2CH3, -CH2CH2CH3 or -CH(CH3)2; the C1-C3 fluoroalkyl group is -CF3, -CHF2 or -CH2F.

3. The sodium ion battery electrolyte according to claim 1, characterized in that, The volume ratio of the sulfonate compound in the sodium ion battery electrolyte is 0.1%-20%.

4. The sodium ion battery electrolyte according to claim 3, wherein In the sodium ion battery electrolyte, the volume ratio of the compound shown in formula (I) is 0%-20%; the volume ratio of the compound shown in formula (II) is 0%-10%; the volume ratio of the compound shown in formula (III) is 0%-10%.

5. The sodium ion battery electrolyte according to claim 1, characterized in that, The sodium salt includes one or more of sodium hexafluorophosphate, sodium perchlorate, sodium bis(trifluoromethylsulfonyl)imide, sodium bis(fluorosulfonyl)imide, sodium trifluoromethanesulfonate, sodium difluorooxalate borate, sodium bis(oxalate) borate, sodium hexafluoroarsenate, sodium tetrafluoroborate, sodium nitrate and sodium chloride.

6. The sodium ion battery electrolyte according to claim 1 or 5, characterized in that, The concentration of the sodium salt in the sodium ion battery electrolyte is 0.1 mol / L - 10 mol / L.

7. The sodium ion battery electrolyte according to any one of claims 1-6, characterized in that, The sodium ion battery electrolyte further includes one or more of a solvent, an additive and a diluent.

8. The sodium-ion battery electrolyte according to any one of claims 1-7, characterized in that, The solvent includes one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, 1,3-dioxolane, methyl acetate, ethyl acetate, ethyl propionate, propyl propionate, dimethyl sulfoxide, tetrahydrofuran, acetonitrile and N,N-dimethylformamide.

9. The sodium ion battery electrolyte according to any one of claims 1-8, characterized in that, The additive includes one or more of fluoroethylene carbonate, vinylene carbonate, 1,3-propane sultone, propylene sulfate, allyl-1,3-sultone, ethylene sulfate, methylene methanedisulfonate, succinonitrile, adiponitrile, tris(trimethylsilyl) phosphite, trimethyl phosphate and ethoxy(pentafluoro)cyclotriphosphazene.

10. The sodium ion battery electrolyte according to any one of claims 1-9, characterized in that, The diluent includes one or more of 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether and bis(2,2,2-trifluoroethyl) ether.

11. The sodium ion battery electrolyte according to any one of claims 7-10, characterized in that, In the sodium ion battery electrolyte, the volume ratio of the solvent is 40%-99%; the volume ratio of the additive is 1%-20%; the volume ratio of the diluent is 0-45%.

12. A sodium-ion battery (60), characterized in that, It includes a positive electrode (61), a negative electrode (63), a separator (65) located between the positive electrode (61) and the negative electrode (63), and an electrolyte (67), and the electrolyte (67) includes the sodium ion battery electrolyte according to any one of claims 1-11.

13. An electrical device (70), characterized in that, The electrical device includes the sodium ion battery (60) according to claim 12.

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