A fluorosulfonate compound, application thereof, sodium ion battery electrolyte and sodium ion battery

Abstract

The present application relates to a kind of fluorosulfonate compounds and its application, sodium-ion battery electrolyte and sodium-ion battery, belong to sodium-ion battery electrolyte technical field.The fluorosulfonate compound of the present application is used as electrolyte additive, can improve the stability of existing sodium-ion battery electrolyte, avoid the decomposition of effective ingredient in electrolyte under high pressure, and then improve the electrochemical performance of battery under high pressure, improve discharge voltage platform, so that the energy density of battery cell increases.Fluorosulfonate compound has excellent antioxidant property, can prevent electrolyte from a large amount of oxidative decomposition on the surface of positive electrode, and then improve the high-pressure stability of electrolyte.

Description

TECHNICAL FIELD

[0001] The application relates to a fluorosulfonate compound and application thereof, a sodium ion battery electrolyte and a sodium ion battery, and belongs to the technical field of sodium ion battery electrolytes. BACKGROUND

[0002] In recent years, the public demand for cheap, safe and environmentally friendly rechargeable batteries has been increasing. The current shortage of lithium resources and the rising price of lithium have greatly limited the widespread use of lithium ion batteries. Therefore, developing and finding new energy storage systems to replace lithium is currently a hot topic.

[0003] Sodium ion batteries have the advantages of abundant raw material resources, low cost and wide distribution of raw materials. They have similar working principles to lithium ion batteries. Therefore, sodium ion batteries provide a new choice for electrochemical energy storage. More importantly, sodium and lithium are elements in the same main group, so they have similar chemical properties. Compared with existing lithium ion battery systems, sodium ion batteries have more potential in large-scale energy storage, so their application prospects are very broad. As a positive electrode material for sodium ion batteries, polyanion-type compound positive electrode materials have the advantages of high working voltage, abundant sodium ion insertion sites, high structural stability and safety, etc. Therefore, they have become a hot research topic. These characteristics also make polyanion-type materials more suitable for rechargeable secondary batteries. Among them, sulfate polyanion-type compound positive electrode materials have high electronegativity and strong induction effect, and also have a high working voltage.

[0004] High voltage helps to improve the energy density of sodium ion batteries, but high voltage can cause decomposition of electrolyte components. The main component of the electrolyte is carbonate, which has weak oxidation resistance. When the battery has a high working voltage, the carbonate will undergo severe oxidative decomposition and generate products such as CO2 and H2O, which will increase the internal resistance of the battery and ultimately cause the battery capacity to decrease rapidly and the cycle life to decay. Therefore, the development of electrolytes that can match high-voltage positive electrode materials is particularly important for the development of sodium ion batteries. For example, Chinese patent document CN116742129A discloses a sodium ion battery electrolyte. The electrolyte disclosed in the patent document comprises a sodium salt, a non-aqueous solvent, and an additive; the additive comprises a sulfonate. Chinese patent document CN116154270A discloses a sodium ion battery non-aqueous electrolyte. The electrolyte disclosed in the patent document comprises: (a) a non-aqueous organic solvent composed of a long-chain ether solvent with a carbon atom number of 8 or more; (b) a surfactant; (c) a mixed sodium salt composed of sodium hexafluorophosphate and sodium bisfluorosulfonylimide; (d) an additive composed of a cyclic sulfonate compound. The stability of the sodium ion battery electrolyte disclosed in the above prior art is still poor and is prone to decomposition under high voltage, resulting in rapid decrease in battery capacity and decay of cycle life. SUMMARY

[0005] The present application aims to provide a fluorosulfonate compound, which can solve the problem that the current sodium-ion battery electrolyte is easily decomposed under high pressure, thereby rapidly reducing the capacity of the battery.

[0006] The second object of the present application is to provide an application of the fluorosulfonate compound as an electrolyte additive, which can solve the problem that the current sodium-ion battery electrolyte is easily decomposed under high pressure, thereby rapidly reducing the capacity of the battery.

[0007] The third object of the present application is to provide a sodium-ion battery electrolyte, which can solve the problem that the current sodium-ion battery electrolyte is easily decomposed under high pressure, thereby rapidly reducing the capacity of the battery.

[0008] The fourth object of the present application is to provide a sodium-ion battery, which can solve the problem that the current sodium-ion battery has a low capacity retention rate.

[0009] To achieve the above objects, the technical scheme adopted by the fluorosulfonate compound of the present application is as follows:

[0010] A fluorosulfonate compound, which has the structure shown in Formula I:

[0011]

[0012] In Formula I, R is a C1-C5 fluorinated alkyl group.

[0013] When the fluorosulfonate compound of the present application is used as an electrolyte additive, the stability of the existing sodium-ion battery electrolyte can be improved, the decomposition of the effective components in the electrolyte under high pressure can be avoided, thereby improving the electrochemical performance of the battery under high pressure, increasing the discharge voltage platform, and increasing the energy density of the battery cell. The fluorosulfonate compound has excellent oxidation resistance, which can prevent the electrolyte from being oxidized and decomposed on the surface of the positive electrode, thereby improving the high-pressure stability of the electrolyte.

[0014] Preferably, R is selected from one of R1, R2, R3, R4, R5, R6, R7, and R8:

[0015]

[0016] It can be understood that when R is R1, the fluorosulfonate compound is 1,1,2,2-tetrafluoroethyl fluorosulfonate; when R is R2, the fluorosulfonate compound is 2-(difluoromethyl)-1,1,3,3-tetrafluoro-2-propyl fluorosulfonate; when R is R3, the fluorosulfonate compound is 2-(difluoromethyl)-1,1,3,3-tetrafluoro-propyl fluorosulfonate; when R is R4, the fluorosulfonate compound is perfluoroethyl fluorosulfonate; when R is R5, the fluorosulfonate compound is perfluoropropyl fluorosulfonate; when R is R6, the fluorosulfonate compound is 2-trifluoromethyl-1,1,2,3,3,3-hexafluoropropyl fluorosulfonate; when R is R7, the fluorosulfonate compound is perfluorobutyl fluorosulfonate; and when R is R8, the fluorosulfonate compound is perfluoropentyl fluorosulfonate.

[0017] Preferably, the fluorosulfonate compound is prepared by a method comprising the following steps: mixing and reacting chlorosulfonyl fluoride and a halogenated hydrocarbon compound at -45-120°C, and then purifying the system after the mixing and reacting to obtain the fluorosulfonate compound; the halogenated hydrocarbon compound has a structure shown in Formula II:

[0018] R0-X

[0019] II

[0020] In Formula II, X is -Cl, -Br or -I, and R0 is selected from one of R 01 , R 02 , R 03 , R 04 , R 05 , R 06 , R 07 , and R 08 .

[0021]

[0022] The chlorosulfonyl fluoride has a structure shown in Formula III:

[0023]

[0024] In order to better control the mixing and reacting of the chlorosulfonyl fluoride and the halogenated hydrocarbon compound, it is further preferred that the temperature of the mixing and reacting of the chlorosulfonyl fluoride and the halogenated hydrocarbon compound is -45-40°C.

[0025] In order to avoid excessive impurities and facilitate the purification of the product, it is preferred that the molar ratio of the chlorosulfonyl fluoride to the halogenated hydrocarbon compound is 5:(6.5-7).

[0026] Preferably, the mixing reaction time is 10-24 hours. The above reaction time can ensure that the raw materials are fully reacted and avoid the generation of too many impurities.

[0027] Preferably, the purification is chromatographic separation of the system after the mixing reaction. The eluent used in the chromatographic separation is composed of an ester eluent and an ether eluent. For example, the ester eluent is ethyl acetate, and the ether eluent is diethyl ether. The volume ratio of the ester eluent to the ether eluent is (8-8.5):(2-2.5). The above purification method can remove a large amount of impurities in the product and improve the purity of the product.

[0028] The application of the fluorosulfonate compound as an electrolyte additive employs the technical scheme of:

[0029] The application of a fluorosulfonate compound as an electrolyte additive, the fluorosulfonate compound has a structure shown in formula I:

[0030]

[0031] In formula I, R is a C1-C5 fluorinated alkyl group.

[0032] The use of the fluorosulfonate compound as an electrolyte additive can improve the stability of the existing sodium-ion battery electrolyte, avoid the decomposition of the effective components in the electrolyte under high pressure, and further improve the electrochemical performance of the battery under high pressure, increase the discharge voltage platform, and increase the energy density of the battery. The fluorosulfonate compound has excellent oxidation resistance and can prevent the electrolyte from undergoing a large amount of oxidative decomposition on the surface of the positive electrode, thereby improving the high-pressure stability of the electrolyte.

[0033] Preferably, R is selected from one of R1, R2, R3, R4, R5, R6, R7, and R8:

[0034]

[0035] The technical scheme employed by the sodium-ion battery electrolyte of the application is:

[0036] A sodium-ion battery electrolyte includes an organic solvent, a sodium salt, and a fluorosulfonate compound; the fluorosulfonate compound has a structure shown in formula I:

[0037]

[0038] In formula I, R is a C1-C5 fluorinated alkyl group.

[0039] The fluorosulfonate compound in the sodium-ion battery electrolyte of the present application can improve the stability of the electrolyte, avoid the decomposition of the effective components in the electrolyte under high pressure, and thus improve the electrochemical performance of the battery under high pressure, increase the discharge voltage platform, and increase the energy density of the battery.

[0040] Preferably, R is selected from one of R1, R2, R3, R4, R5, R6, R7, and R8:

[0041]

[0042] To improve the stability of the electrolyte, preferably, the organic solvent is selected from one or any combination of ester solvents, ether solvents, nitrile solvents, furan solvents, and sulfone solvents. For example, the ester solvent is selected from one or any combination of vinyl carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl ethyl carbonate, methyl formate, ethyl formate, propyl formate, butyl formate, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl difluoroacetate, and ethyl difluoroacetate; the ether solvent is selected from one or any combination of dimethyl ether of ethylene glycol, dimethyl ether of triethylene glycol, dimethyl ether of tetraethylene glycol, 1,3-dioxolane, and 1,4-dioxane; the nitrile solvent is malononitrile and / or glutaronitrile; the furan solvent is tetrahydrofuran and / or 2-methyltetrahydrofuran; and the sulfone solvent is sulfolane and / or dimethyl sulfoxide.

[0043] The sodium salt for the sodium-ion battery electrolyte is suitable for the present application, and preferably, the sodium salt is selected from one or any combination of sodium hexafluorophosphate, sodium bisfluorosulfonylimide, sodium bis(trifluoromethanesulfonyl)imide, sodium trifluoromethylsulfonate, sodium perchlorate, sodium tetrafluoroborate, and sodium nitrate. Preferably, the concentration of the sodium salt is 0.5-3 mol / L.

[0044] Preferably, the sodium-ion battery electrolyte further comprises a functional additive; the functional additive is selected from one or any combination of fluorinated vinyl carbonate, bis-fluorinated vinyl carbonate, vinylene carbonate, 1,3-propane sulfonic acid lactone, acetonitrile, butanedinitrile, and succinic anhydride. Preferably, the mass fraction of the functional additive is 0.5-5%. The functional additive can promote the formation of a more stable interface layer and improve the cycle stability of the battery, and excessive amount will increase the viscosity and cost of the electrolyte.

[0045] Preferably, the mass fraction of the fluorosulfonate compound is 0.3-3%. A mass fraction of the fluorosulfonate compound that is too small cannot effectively improve the high-pressure resistance and cycle stability of the sodium-ion battery, and a mass fraction of the fluorosulfonate compound that is too large will increase the thickness of the formed CEI / SEI film, resulting in reduced initial efficiency, reduced capacity, and poor cycle performance of the battery.

[0046] The technical scheme of the sodium ion battery of the present application is as follows:

[0047] The sodium ion battery comprises a negative electrode, a positive electrode and a sodium ion battery electrolyte; the sodium ion battery electrolyte comprises an organic solvent, a sodium salt and a fluorosulfonate compound; the fluorosulfonate compound has a structure shown in Formula I:

[0048]

[0049] In Formula I, R is a C1-C5 fluorinated alkyl group.

[0050] The sodium ion battery of the present application comprises an electrolyte containing a fluorosulfonate compound, and has good high-voltage resistance, high capacity retention rate and discharge voltage platform.

[0051] Preferably, R is selected from one of R1, R2, R3, R4, R5, R6, R7 and R8:

[0052]

[0053] In order to improve the stability of the electrolyte, preferably, the organic solvent is selected from one or any combination of ester solvents, ether solvents, nitrile solvents, furan solvents and sulfone solvents. For example, the ester solvent is selected from one or any combination of vinyl carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl ethyl carbonate, methyl formate, ethyl formate, propyl formate, butyl formate, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl difluoroacetate and ethyl difluoroacetate; the ether solvent is selected from one or any combination of ethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, 1,3-dioxolane and 1,4-dioxane; the nitrile solvent is malononitrile and / or glutaronitrile; the furan solvent is tetrahydrofuran and / or 2-methyltetrahydrofuran; and the sulfone solvent is sulfolane and / or dimethyl sulfoxide.

[0054] The sodium salt used in the sodium ion battery electrolyte is suitable for the present application, and preferably, the sodium salt is selected from one or any combination of sodium hexafluorophosphate, sodium bisfluorosulfonylimide, sodium bis(trifluoromethanesulfonyl)imide, sodium trifluoromethylsulfonate, sodium perchlorate, sodium tetrafluoroborate and sodium nitrate. Preferably, the concentration of the sodium salt is 0.5-3 mol / L.

[0055] Preferably, the sodium-ion battery electrolyte further comprises a functional additive; the functional additive is selected from one or any combination of fluorinated ethylene carbonate, difluoroethylene carbonate, vinylene carbonate, 1,3-propane sultone, acetonitrile, succinonitrile, succinic anhydride. Preferably, the mass fraction of the functional additive is 0.5-5%. The functional additive can promote the formation of a more stable interface layer, improve the cycle stability of the battery, and excessive amount will increase the viscosity and cost of the electrolyte.

[0056] Preferably, the mass fraction of the fluorosulfonate compound is 0.3-3%. The mass fraction of the fluorosulfonate compound is too small to effectively improve the high-pressure resistance and cycle stability of the sodium-ion battery, and the mass fraction of the fluorosulfonate compound is too large to cause the thickness of the formed CEI / SEI film to increase, resulting in reduced initial efficiency, reduced capacity, and poor cycle performance of the battery.

[0057] The negative electrode comprises a negative electrode current collector and a negative electrode active material coated on the surface of the negative electrode current collector, and the negative electrode active material is a metal sodium and / or a sodium-embedded compound material. For example, the negative electrode active material is soft carbon, hard carbon, sodium titanate, metal sodium, and sodium alloy.

[0058] The positive electrode comprises a positive electrode current collector and a positive electrode active material coated on the surface of the positive electrode current collector, and the chemical formula of the positive electrode active material is Na x Fe y (SO4)3, wherein 1.5≤x<2.5, 1.6≤y<1.8. DETAILED DESCRIPTION

[0059] The technical solutions of the present application will be further described below in combination with specific embodiments.

[0060] First, the specific embodiments of the fluorosulfonate compound of the present application are as follows:

[0061] The structural formula of the fluorosulfonate compound of embodiments 1-8 is shown in formula I:

[0062]

[0063] When R in Formula I is R1, the compound shown in Formula I is the fluorosulfonate compound of Example 1; when R in Formula I is R2, the compound shown in Formula I is the fluorosulfonate compound of Example 2; when R in Formula I is R3, the compound shown in Formula I is the fluorosulfonate compound of Example 3; when R in Formula I is R4, the compound shown in Formula I is the fluorosulfonate compound of Example 4; when R in Formula I is R5, the compound shown in Formula I is the fluorosulfonate compound of Example 5; when R in Formula I is R6, the compound shown in Formula I is the fluorosulfonate compound of Example 6; when R in Formula I is R7, the compound shown in Formula I is the fluorosulfonate compound of Example 7; when R in Formula I is R8, the compound shown in Formula I is the fluorosulfonate compound of Example 8.

[0064] The structures of R1, R2, R3, R4, R5, R6, R7, and R8 are as follows:

[0065]

[0066] The preparation methods of the fluorosulfonate compounds in Examples 1-8 are as follows: 5 mmol of chlorosulfonyl fluoride and 6.5 mmol of haloalkanes are added to a round-bottom flask. The material in the flask is then controlled at a certain temperature T and stirred for a certain time t. The material in the flask is then purified by column chromatography. The eluent used in the column chromatography consists of ethyl acetate and diethyl ether in a volume ratio of 8:2. Finally, the purified product is dried to obtain the fluorosulfonate compounds.

[0067] The haloalkanes in the preparation methods of the fluorosulfonate compounds in Examples 1-8 have the structure shown in Formula II:

[0068] R0-X

[0069] II

[0070] When X in equation II is -Cl, R0 is R 01 When the compound represented by Formula II is the halogenated hydrocarbon compound used in the preparation method of the fluorosulfonate compound in Example 1; when X in Formula II is -Br and R0 is R 02 When the compound represented by Formula II is the halogenated hydrocarbon compound used in the preparation method of the fluorosulfonate compound in Example 2; when X in Formula II is -I and R0 is R 03 When the compound represented by Formula II is the halogenated hydrocarbon compound used in the preparation method of the fluorosulfonate compound in Example 3; when X in Formula II is -Br and R0 is R 04 When the compound represented by Formula II is the halogenated hydrocarbon compound used in the preparation method of the fluorosulfonate compound in Example 4; when X in Formula II is -Cl and R0 is R05 When the compound represented by Formula II is the halogenated hydrocarbon compound in the preparation method of the fluorosulfonate compound of Example 5; when X in Formula II is -I and R0 is R 06 When the compound represented by Formula II is the halogenated hydrocarbon compound used in the preparation method of the fluorosulfonate compound in Example 6; when X in Formula II is -Cl and R0 is R 07 When the compound represented by Formula II is the halogenated hydrocarbon compound used in the preparation method of the fluorosulfonate compound in Example 7; when X in Formula II is -Br and R0 is R 08 When the compound shown in Formula II is the halogenated hydrocarbon compound in the preparation method of the fluorosulfonate compound in Example 8;

[0071] R 01 R 02 R 03 R 04 R 05 R 06 R 07 R 08 The structure is as follows:

[0072]

[0073] The chlorosulfonyl fluoride in the preparation methods of the fluorosulfonate compounds in Examples 1-8 has the structure shown in Formula III:

[0074]

[0075] In the preparation methods of the fluorosulfonate compounds in Examples 1-8, the reaction temperatures T were -45℃, -10℃, 0℃, 10℃, 20℃, 30℃, 25℃, and 40℃, respectively, and the reaction times t were 24h, 22h, 20h, 18h, 16h, 14h, 12h, and 10h, respectively. The purity of the prepared fluorosulfonate compounds was not less than 99%, and the yields (based on chlorosulfonyl fluoride) were 70%, 71%, 70%, 75%, 80%, 78%, 76%, and 80%, respectively.

[0076] II. Specific embodiments of the application of the fluorosulfonate compound of the present invention as an electrolyte additive are as follows:

[0077] The fluorosulfonate compounds of Examples 1-8 can be used as electrolyte additives in sodium-ion battery electrolytes.

[0078] III. Specific embodiments of the sodium-ion battery electrolyte of the present invention are as follows:

[0079] Example 9

[0080] The sodium ion battery electrolyte of the embodiment is composed of an organic solvent, a sodium salt, a functional additive and a fluorosulfonate compound. The organic solvent is composed of ethylene carbonate, methyl ethyl carbonate and propylene carbonate. The mass ratio of ethylene carbonate, methyl ethyl carbonate and propylene carbonate is 0.8:6:3.2. The sodium salt is sodium perchlorate. The concentration of the sodium salt is 1.12 mol / L. The functional additive is fluorinated ethylene carbonate. The mass fraction of the functional additive is 1%. The fluorosulfonate compound is perfluoropentyl fluorosulfonate (i.e., the fluorosulfonate compound of Example 8). The mass fraction of the fluorosulfonate compound is 0.5%. The structural formula of perfluoropentyl fluorosulfonate is as shown in the following formula:

[0081]

[0082] In the formula, R is R8. The structure of R8 is as shown below:

[0083]

[0084] Example 10

[0085] The sodium ion battery electrolyte of the embodiment is composed of an organic solvent, a sodium salt, a functional additive and a fluorosulfonate compound. The organic solvent is composed of ethylene carbonate, methyl ethyl carbonate and propylene carbonate. The mass ratio of ethylene carbonate, methyl ethyl carbonate and propylene carbonate is 0.8:6:3.2. The sodium salt is sodium perchlorate. The concentration of the sodium salt is 1.12 mol / L. The functional additive is composed of fluorinated ethylene carbonate and vinylene carbonate. The mass ratio of fluorinated ethylene carbonate and vinylene carbonate is 1:1. The mass fraction of the functional additive is 2%. The fluorosulfonate compound is perfluoropentyl fluorosulfonate (i.e., the fluorosulfonate compound of Example 8). The mass fraction of the fluorosulfonate compound is 0.5%. The structural formula of perfluoropentyl fluorosulfonate is as shown in the following formula:

[0086]

[0087] In the formula, R is R8. The structure of R8 is as shown below:

[0088]

[0089] Example 11

[0090] The sodium ion battery electrolyte of the embodiment is composed of an organic solvent, a sodium salt, a functional additive and a fluorosulfonate compound. The organic solvent is composed of ethylene carbonate, methyl ethyl carbonate and propylene carbonate. The mass ratio of ethylene carbonate, methyl ethyl carbonate and propylene carbonate is 0.8:6:3.2. The sodium salt is sodium perchlorate. The concentration of the sodium salt is 1.12 mol / L. The functional additive is composed of fluorinated ethylene carbonate, vinylene carbonate and 1,3-propane sultone. The mass ratio of fluorinated ethylene carbonate, vinylene carbonate and 1,3-propane sultone is 1:0.5:1. The mass fraction of the functional additive is 2.5%. The fluorosulfonate compound is perfluoropentyl fluorosulfonate (i.e. the fluorosulfonate compound of Example 8). The mass fraction of the fluorosulfonate compound is 0.5%. The structural formula of perfluoropentyl fluorosulfonate is as shown in the following formula:

[0091]

[0092] In the formula, R is R8. The structure of R8 is as follows:

[0093]

[0094] Example 12

[0095] The sodium ion battery electrolyte of the embodiment is composed of an organic solvent, a sodium salt, a functional additive and a fluorosulfonate compound. The organic solvent is composed of ethylene carbonate, methyl ethyl carbonate and propylene carbonate. The mass ratio of ethylene carbonate, methyl ethyl carbonate and propylene carbonate is 0.8:6:3.2. The sodium salt is sodium perchlorate. The concentration of the sodium salt is 1.12 mol / L. The functional additive is composed of fluorinated ethylene carbonate and 1,3-propane sultone. The mass ratio of fluorinated ethylene carbonate and 1,3-propane sultone is 1:1. The mass fraction of the functional additive is 2%. The fluorosulfonate compound is perfluoropentyl fluorosulfonate (i.e. the fluorosulfonate compound of Example 8). The mass fraction of the fluorosulfonate compound is 0.5%. The structural formula of perfluoropentyl fluorosulfonate is as shown in the following formula:

[0096]

[0097] In the formula, R is R8. The structure of R8 is as follows:

[0098]

[0099] Example 13

[0100] The sodium ion battery electrolyte of the embodiment is composed of an organic solvent, a sodium salt, a functional additive and a fluorosulfonate compound. The organic solvent is composed of ethylene carbonate, methyl ethyl carbonate and propylene carbonate. The mass ratio of ethylene carbonate, methyl ethyl carbonate and propylene carbonate is 0.8:6:3.2. The sodium salt is sodium bisfluorosulfonylimide. The concentration of the sodium salt is 1.12 mol / L. The functional additive is composed of vinylene carbonate and 1,3-propane sultone. The mass ratio of vinylene carbonate and 1,3-propane sultone is 1:1. The mass fraction of the functional additive is 2%. The fluorosulfonate compound is 2-trifluoromethyl-1,1,2,3,3,3-hexafluoropropylfluorosulfonate (i.e., the fluorosulfonate compound of Example 6). The mass fraction of the fluorosulfonate compound is 0.3%. The structural formula of 2-trifluoromethyl-1,1,2,3,3,3-hexafluoropropylfluorosulfonate is shown in the following formula:

[0101]

[0102] In the formula, R is R6. The structure of R6 is as follows:

[0103]

[0104] Example 14

[0105] The sodium ion battery electrolyte of the embodiment is composed of an organic solvent, a sodium salt, a functional additive and a fluorosulfonate compound. The organic solvent is composed of ethylene carbonate, methyl ethyl carbonate and propylene carbonate. The mass ratio of ethylene carbonate, methyl ethyl carbonate and propylene carbonate is 0.8:6:3.2. The sodium salt is sodium bisfluorosulfonylimide. The concentration of the sodium salt is 1.12 mol / L. The functional additive is composed of fluorinated vinylene carbonate and acetonitrile. The mass ratio of fluorinated vinylene carbonate and acetonitrile is 1:1. The mass fraction of the functional additive is 2%. The fluorosulfonate compound is 2-trifluoromethyl-1,1,2,3,3,3-hexafluoropropylfluorosulfonate (i.e., the fluorosulfonate compound of Example 6). The mass fraction of the fluorosulfonate compound is 0.3%. The structural formula of 2-trifluoromethyl-1,1,2,3,3,3-hexafluoropropylfluorosulfonate is shown in the following formula:

[0106]

[0107] In the formula, R is R6. The structure of R6 is as follows:

[0108]

[0109] Example 15

[0110] The sodium ion battery electrolyte of the embodiment is composed of an organic solvent, a sodium salt, a functional additive and a fluorosulfonate compound. The organic solvent is composed of ethylene carbonate, methyl ethyl carbonate and propylene carbonate. The mass ratio of ethylene carbonate, methyl ethyl carbonate and propylene carbonate is 0.8:6:3.2. The sodium salt is sodium hexafluorophosphate. The concentration of the sodium salt is 1.12 mol / L. The functional additive is composed of fluorinated ethylene carbonate and succinic anhydride. The mass ratio of fluorinated ethylene carbonate and succinic anhydride is 1:1. The mass fraction of the functional additive is 2%. The fluorosulfonate compound is 2-(difluoromethyl)-1,1,3,3-tetrafluoro-propyl fluorosulfonate (i.e., the fluorosulfonate compound of Example 3). The mass fraction of the fluorosulfonate compound is 0.3%. The structural formula of 2-(difluoromethyl)-1,1,3,3-tetrafluoro-propyl fluorosulfonate is as shown in the following formula:

[0111]

[0112] In the formula, R is R3, and the structure of R3 is as follows:

[0113]

[0114] Example 16

[0115] The sodium ion battery electrolyte of the embodiment is composed of an organic solvent, a sodium salt, a functional additive and a fluorosulfonate compound. The organic solvent is composed of ethylene carbonate, methyl ethyl carbonate and propylene carbonate. The mass ratio of ethylene carbonate, methyl ethyl carbonate and propylene carbonate is 0.8:6:3.2. The sodium salt is sodium hexafluorophosphate. The concentration of the sodium salt is 1.12 mol / L. The functional additive is composed of fluorinated ethylene carbonate and succinic anhydride. The mass ratio of fluorinated ethylene carbonate and succinic anhydride is 1:1. The mass fraction of the functional additive is 2%. The fluorosulfonate compound is 2-(difluoromethyl)-1,1,3,3-tetrafluoro-propyl fluorosulfonate (i.e., the fluorosulfonate compound of Example 3). The mass fraction of the fluorosulfonate compound is 0.3%. The structural formula of 2-(difluoromethyl)-1,1,3,3-tetrafluoro-propyl fluorosulfonate is as shown in the following formula:

[0116]

[0117] In the formula, R is R3, and the structure of R3 is as follows:

[0118]

[0119] Comparative Example 1

[0120] The sodium ion battery electrolyte of the embodiment is composed of an organic solvent, a sodium salt, a functional additive and a fluorosulfonate compound. The organic solvent is composed of ethylene carbonate, methyl ethyl carbonate and propylene carbonate. The mass ratio of ethylene carbonate, methyl ethyl carbonate and propylene carbonate is 0.8:6:3.2. The sodium salt is sodium hexafluorophosphate. The concentration of the sodium salt is 1.12 mol / L. The functional additive is composed of fluorinated ethylene carbonate and succinic anhydride. The mass ratio of fluorinated ethylene carbonate and succinic anhydride is 1:1. The mass fraction of the functional additive is 2%. The fluorosulfonate compound is 2-(difluoromethyl)-1,1,3,3-tetrafluoro-propyl fluorosulfonate (i.e., the fluorosulfonate compound of Example 3). The mass fraction of the fluorosulfonate compound is 0.3%. The structural formula of 2-(difluoromethyl)-1,1,3,3-tetrafluoro-propyl fluorosulfonate is as shown in the following formula:

[0121] Comparative Example 2

[0122] The sodium-ion battery electrolyte of the present comparative example differs from the sodium-ion battery electrolyte of Example 5 only in that the mass fraction of the fluorosulfonate compound in the sodium-ion battery electrolyte of the present comparative example is 0, and the sum of the mass fractions of the sodium salt and the functional additive is equal to the sum of the mass fractions of the sodium salt and the functional additive in the electrolyte of Example 5, and the mass ratio of the sodium salt and the functional additive is equal to the mass ratio of the sodium salt and the functional additive in the electrolyte of Example 5.

[0123] Comparative Example 3

[0124] The sodium-ion battery electrolyte of the present comparative example differs from the sodium-ion battery electrolyte of Example 5 only in that the mass fraction of the functional additive in the sodium-ion battery electrolyte of the present comparative example is 0, and the sum of the mass fractions of the sodium salt and the fluorosulfonate compound is equal to the sum of the mass fractions of the sodium salt and the fluorosulfonate compound in the electrolyte of Example 5, and the mass ratio of the sodium salt and the fluorosulfonate compound is equal to the mass ratio of the sodium salt and the fluorosulfonate compound in the electrolyte of Example 5.

[0125] Comparative Example 4

[0126] The sodium-ion battery electrolyte of the present comparative example differs from the sodium-ion battery electrolyte of Example 5 only in that the mass fraction of the sodium salt in the sodium-ion battery electrolyte of the present comparative example is 0, and the sum of the mass fractions of the functional additive and the fluorosulfonate compound is equal to the sum of the mass fractions of the functional additive and the fluorosulfonate compound in the electrolyte of Example 5, and the mass ratio of the functional additive and the fluorosulfonate compound is equal to the mass ratio of the functional additive and the fluorosulfonate compound in the electrolyte of Example 5.

[0127] Fourth, the specific implementation of the sodium-ion battery of the present application is as follows:

[0128] The sodium-ion battery of the present embodiment comprises a negative electrode, a positive electrode and an electrolyte, and the electrolyte is the sodium-ion battery electrolyte described in any one of Examples 9-16; the preparation method of the sodium-ion battery is as follows: assembling the positive electrode sheet, the negative electrode sheet and the separator film to obtain an electric core, placing the electric core into an aluminum plastic film shell, injecting the electrolyte and then sealing, and then performing the processes of standing, formation, exhaust, second sealing, and capacity distribution to obtain the sodium-ion battery.

[0129] The preparation method of the positive electrode sheet in the sodium-ion battery is as follows: adding the positive electrode active material, the binder and the conductive agent into a vacuum stirrer in a mass ratio of 90:5:5, then adding N-methyl pyrrolidone, stirring uniformly to obtain a positive electrode slurry, uniformly coating the positive electrode slurry on an aluminum foil, drying in a blast oven at 120°C, and then cold pressing and die cutting to obtain the positive electrode sheet; the positive electrode active material is sodium ferrous sulfate, and the chemical formula is Na 2.5Fe 1.7 The preparation method of the positive electrode sheet in the sodium-ion battery is as follows: the positive electrode active material, the binder and the conductive agent are added into a vacuum stirrer in a mass ratio of 90:5:5, then N-methyl pyrrolidone is added, and stirring is uniformly performed to obtain a positive electrode slurry, the positive electrode slurry is uniformly coated on an aluminum foil, and drying is performed in a blast oven at 120 DEG C, and then cold pressing, die cutting are performed to obtain the positive electrode sheet; the positive electrode active material is sodium ferrous sulfate, the chemical formula is Na

[0130] Experimental example

[0131] In order to evaluate the application effect of the fluorosulfonate compound of the present application as an electrolyte additive and the performance of the sodium-ion battery electrolyte of each example and comparative example, the sodium-ion battery electrolyte of examples 9-16 and comparative examples 1-4 is used in a sodium-ion battery, and then the performance of the sodium-ion battery is tested. Among them, the sodium-ion battery includes a positive electrode sheet, a negative electrode sheet and an electrolyte.

[0132] The preparation method of the positive electrode sheet in the sodium-ion battery is as follows: the positive electrode active material, the binder and the conductive agent are added into a vacuum stirrer in a mass ratio of 90:5:5, then N-methyl pyrrolidone is added, and stirring is uniformly performed to obtain a positive electrode slurry, the positive electrode slurry is uniformly coated on an aluminum foil, and drying is performed in a blast oven at 120 DEG C, and then cold pressing, die cutting are performed to obtain the positive electrode sheet; the positive electrode active material is sodium ferrous sulfate, the chemical formula is Na 2.5 Fe 1.7 The preparation method of the positive electrode sheet in the sodium-ion battery is as follows: the positive electrode active material, the binder and the conductive agent are added into a vacuum stirrer in a mass ratio of 90:5:5, then N-methyl pyrrolidone is added, and stirring is uniformly performed to obtain a positive electrode slurry, the positive electrode slurry is uniformly coated on an aluminum foil, and drying is performed in a blast oven at 120 DEG C, and then cold pressing, die cutting are performed to obtain the positive electrode sheet; the positive electrode active material is sodium ferrous sulfate, the chemical formula is Na

[0133] The preparation method of the sodium-ion battery is as follows: the positive electrode sheet, the negative electrode sheet and the separator are assembled to obtain an electric core, the electric core is placed in an aluminum plastic film shell, the electrolyte is injected, and then the mouth is sealed, and then the processes of standing, formation, exhaust, second sealing, and capacity distribution are performed to obtain the sodium-ion battery.

[0134] The performance test method of the sodium ion battery is as follows: the sodium ion battery is charged at 1C constant current to 4.5V at 25℃, then charged at constant voltage until the current is less than or equal to 0.05C, and then rested for 10min, and then discharged at 1C constant current to 2V, which is one charge-discharge cycle. Then, 200 cycles are carried out according to the above method. The capacity retention rate (%) of the sodium ion battery after n cycles is (discharge capacity in the nth charge-discharge cycle experiment / discharge capacity in the first charge-discharge cycle experiment) x 100%, wherein n is the number of charge-discharge cycles. The test results of the first coulomb efficiency, the capacity retention rate after 200 cycles of charge-discharge, and the discharge voltage platform of the sodium ion battery prepared by the sodium ion battery electrolyte of each example and the comparative example are shown in Table 1.

[0135] Table 1 Test results of the first coulomb efficiency, the capacity retention rate after 200 cycles of charge-discharge, and the discharge voltage platform of the sodium ion battery prepared by the sodium ion battery electrolyte of each example and the comparative example

[0136] Electrolyte Initial coulombic efficiency (%) Capacity retention after 200 cycles (%) Discharge voltage plateau (V) Example 9 84.59 95.33 3.73 Example 10 88.17 97.72 3.75 Example 11 90.15 98.77 3.78 Example 12 89.85 98.21 3.79 Example 13 86.78 96.11 3.76 Example 14 85.35 97.42 3.74 Example 15 86.78 96.36 3.73 Example 16 87.14 97.21 3.73 Comparative Example 1 68.76 80.46 3.36 Comparative Example 2 77.39 89.47 3.53 Comparative Example 3 80.18 92.29 3.65 Comparative Example 4 67.31 77.65 3.32

[0137] As can be seen from Table 1, compared with the electrolyte of Comparative Example 1, the sodium ion battery prepared by using the electrolyte of the present application has more excellent capacity retention rate at high voltage, and has higher discharge voltage platform and cell energy density. Therefore, the experiment proves that when the fluorosulfonate compound of the present application is used as an electrolyte additive, it can effectively improve the capacity retention rate and discharge voltage platform of the sodium ion battery.

[0138] In addition, in order to evaluate the influence of fluorosulfonate compounds with different structures on the performance of the prepared sodium ion battery, the sodium ion battery is prepared and tested for performance by the above method, wherein the electrolyte used is composed of an organic solvent, a sodium salt, a functional additive and a fluorosulfonate compound, the organic solvent is composed of ethylene carbonate, methyl ethyl carbonate and propylene carbonate, the mass ratio of ethylene carbonate, methyl ethyl carbonate and propylene carbonate is 0.8:6:3.2, the sodium salt is sodium perchlorate, the concentration of the sodium salt is 1.12mol / L, the functional additive is fluorinated ethylene carbonate, the mass fraction of the functional additive is 1%, the mass fraction of the fluorosulfonate compound is 0.5%, and the fluorosulfonate compound has the structure shown in Formula I:

[0139]

[0140] In Formula I, R is selected from one of R1, R2, R3, R4, R5, R6, R7 and R8:

[0141]

[0142] The performance test results of the sodium ion battery prepared by using fluorosulfonate compounds with different structures are shown in Table 2.

[0143] Table 2 Performance test results of sodium ion batteries prepared by using fluorosulfonate compounds with different structures

[0144] Type of R substituent Initial coulombic efficiency (%) Capacity retention after 200 cycles (%) Discharge voltage plateau (V) R1 82.53 93.37 3.52 R2 83.45 94.33 3.70 R3 84.14 94.21 3.73 R4 82.62 93.43 3.66 R5 83.69 94.23 3.73 R6 84.78 95.11 3.76 R7 83.98 94.36 3.74 R8 84.59 95.33 3.73

[0145] As shown in Table 2, among the eight fluorosulfonate compounds, the sodium ion batteries prepared by using the fluorosulfonate compounds with R6or R8as the substituent R have the best performance, followed by the fluorosulfonate compounds with R7, R3or R5as the substituent R. The fluorosulfonate compounds can provide sufficient fluorine atoms in the film forming process, form SEI and CEI rich in NaF, inhibit the interface side reactions, and thus improve the cycle life of the battery.

[0146] In addition, in order to investigate the influence of the concentration of sodium salt, the mass fraction of functional additives and the mass fraction of fluorosulfonate compound in the electrolyte on the experimental results, sodium ion batteries were prepared according to the method of the experimental example, and the electrolyte in the sodium ion batteries was only different from the electrolyte of the sodium ion battery of Example 1 in that the concentration of sodium salt was 0.5 or 3 mol / L, or the mass fraction of functional additives was 0.5 or 5%, or the mass fraction of fluorosulfonate compound was 3%. The experimental results showed that after changing the concentration of sodium salt, the mass fraction of functional additives and the mass fraction of fluorosulfonate compound in the electrolyte of the sodium ion battery of Example 1, the performance (the first coulombic efficiency, the capacity retention rate after 200 charge-discharge cycles or the discharge voltage platform) of the prepared sodium ion battery was close to the corresponding performance of the sodium ion battery prepared by using the electrolyte of the sodium ion battery of Example 1, and the difference was not more than 5%.

Claims

1. A fluorosulfonate compound, characterized by, The fluorosulfonate compound has a structure shown in Formula I: ； In Formula I, R is 。 2. The fluorosulfonate compound according to claim 1, wherein The fluorosulfonate compound is prepared by a method comprising the following steps: mixing and reacting chlorosulfonyl fluoride and halogenated hydrocarbon compound at-45~120℃, and then purifying the system after the mixing and reaction to obtain the fluorosulfonate compound; the halogenated hydrocarbon compound has a structure shown in Formula II: ； In formula II, X is -CI, -Br or -I, and R0is selected from one of R 06 or R 08 . ； The chlorosulfonyl fluoride has a structure shown in Formula III: 。 3. The fluorosulfonate compound according to claim 2, wherein The molar ratio of the chlorosulfonyl fluoride and the halogenated hydrocarbon compound is 5:(6.5~7); the mixing and reaction time is 10~24h; the purification is chromatographic separation of the system after the mixing and reaction, and the eluent used in the chromatographic separation is composed of ester eluent and ether eluent.

4. Use of the fluorosulfonate compound as claimed in any one of claims 1-3 as an electrolyte additive.

5. A sodium-ion battery electrolyte, characterized in that, The sodium ion battery electrolyte comprises organic solvent, sodium salt and the fluorosulfonate compound as claimed in any one of claims 1-3.

6. The sodium-ion battery electrolyte of claim 5, wherein, The mass fraction of the fluorosulfonate compound is 0.3~3%; the organic solvent is selected from one or any combination of ester solvent, ether solvent, nitrile solvent, furan solvent and sulfone solvent; the sodium salt is selected from one or any combination of sodium hexafluorophosphate, sodium bisfluorosulfonimide, sodium bis(trifluoromethanesulfonimide), sodium trifluoromethylsulfonate, sodium perchlorate, sodium tetrafluoroborate and sodium nitrate; the concentration of the sodium salt is 0.5~3mol / L.

7. The sodium-ion battery electrolyte of claim 6, wherein, The ester solvent is selected from one or any combination of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl ethyl carbonate, methyl formate, ethyl formate, propyl formate, butyl formate, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl difluoroacetate and ethyl difluoroacetate; the ether solvent is selected from one or any combination of dimethyl ether of ethylene glycol, dimethyl ether of triethylene glycol, dimethyl ether of tetraethylene glycol, 1,3-dioxolane and 1,4-dioxane; the nitrile solvent is malononitrile and / or glutaronitrile; the furan solvent is tetrahydrofuran and / or 2-methyltetrahydrofuran; and the sulfone solvent is sulfolane and / or dimethyl sulfoxide.

8. The sodium-ion battery electrolyte of any one of claims 6-7, wherein, The sodium ion battery electrolyte further comprises functional additive; the functional additive is selected from one or any combination of fluorinated ethylene carbonate, bisfluorinated ethylene carbonate, vinylene carbonate, 1,3-propane sultone, acetonitrile, succinonitrile and succinic anhydride; and the mass fraction of the functional additive is 0.5~5%.

9. A sodium-ion battery, characterized in that, The sodium ion battery electrolyte comprises negative electrode, positive electrode and the sodium ion battery electrolyte as claimed in any one of claims 5-8.

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