Fluorosulfonylimide salt, method for preparing the same, electrolyte, and secondary battery

Abstract

This invention provides a fluorosulfonyl imide salt, its preparation method, an electrolyte, and a secondary battery. The structural formula of the fluorosulfonyl imide salt is shown in Formula I, where R is selected from O or S, M is selected from Li, Na, K, Cs, and Mg, and m×n=4. This fluorosulfonyl imide salt can form a dense CEI film rich in organic sulfur compounds, which can suppress CEI rupture caused by volume changes during cycling and reduce metal ions in the electrolyte, thereby reducing continuous electrolyte decomposition and lithium loss. The CEI film maintains good stability under high temperature conditions, reducing interfacial impedance at high temperatures. This fluorosulfonyl imide salt can be used as a high-performance electrolyte additive, especially suitable for secondary batteries using lithium manganese iron phosphate materials. Formula I

Description

Technical Field

[0001] This invention relates to the field of energy storage device technology, and more particularly to the synthesis of a secondary battery electrolyte material, and even more particularly to a fluorosulfonyl imide salt and its preparation method, electrolyte and secondary battery. Background Technology

[0002] With the rapid development of the electric vehicle and large-scale energy storage markets, higher demands are being placed on the energy density, safety, cycle life, and cost of rechargeable batteries. As the core component of a battery, the performance of the cathode material is crucial. Currently, the most widely used commercial cathode materials mainly include lithium iron phosphate (LFP) and layered ternary materials. LFP dominates in fields with high safety requirements due to its excellent thermal stability, safety, and long cycle life; however, its relatively low operating voltage platform (approximately 3.2V) and limited theoretical energy density restrict further improvements in battery range. While ternary materials possess high energy density, their poor thermal stability, high cost, and dependence on strategic resources such as cobalt and nickel limit their large-scale application, especially in energy storage and fields with extremely stringent safety requirements.

[0003] To balance high safety and high energy density, lithium manganese iron phosphate (LiFePO4) has attracted widespread attention in the industry as an ideal upgrade solution. The general chemical formula of LiFePO4 is LiMn2. x Fe 1-x-y M y PO4 (0 < x < 1, 0 ≤ y ≤ 0.1, M selected from at least one of Al, Mg, Zr, and Ti) is a solid solution of lithium iron phosphate and lithium manganese phosphate. It combines the advantages of both: on the one hand, it inherits the stable olivine crystal structure and excellent thermal safety of lithium iron phosphate; on the other hand, it introduces the high voltage plateau (approximately 4.1V) of lithium manganese phosphate, thereby increasing the average operating voltage of the material to 3.8~4.1V, resulting in a theoretical energy density that is approximately 15%-20% higher than that of lithium iron phosphate. Simultaneously, it uses abundant and lower-cost manganese as a raw material, reducing material costs.

[0004] Despite LiMn x Fe 1-x-y M y PO4 cathode materials possess advantages such as high energy density, good thermal stability, safety, reliability, and low cost. However, manganese readily dissolves in the electrolyte during cycling, and the inherent Jahn-Teller effect of manganese in manganese-based cathode materials affects their cycle performance. Furthermore, its near-insulator low conductivity and poor thermal stability also lead to unsatisfactory electrochemical performance. Therefore, providing a non-aqueous electrolyte that inhibits manganese ion dissolution and protects the cathode material, along with its secondary battery, remains a key technical challenge. Summary of the Invention

[0005] Based on the above problems, the purpose of this invention is to provide a fluorosulfonyl imide salt, its preparation method, electrolyte, and secondary battery. The fluorosulfonyl imide salt can form a dense CEI film rich in organic sulfur compounds, which can suppress CEI rupture caused by volume changes during cycling and reduce metal ions in the electrolyte, thereby reducing continuous electrolyte decomposition and lithium loss. The CEI film can still maintain good stability under high temperature conditions and reduce interfacial impedance at high temperatures. It can be used as a high-performance electrolyte additive, especially suitable for secondary batteries made of lithium manganese iron phosphate. To achieve the above objectives, the first aspect of the present invention provides a fluorosulfonyl imide salt. Its structural formula is shown in Formula I, wherein R is selected from O or S, M is selected from Li, Na, K, Cs, Mg, and m×n=4.

[0006] Formula I This fluorosulfonylimide salt possesses a unique structure with fluorosulfonylimide and polycarbonyl groups. During charge and discharge, it preferentially undergoes oxidation on the positive electrode surface, forming a dense CEI film rich in organic sulfur compounds. The presence of sulfur in this film enhances its flexibility and ionic conductivity, suppresses CEI film rupture due to volume changes during cycling, and reduces continuous electrolyte decomposition and lithium loss. Under high voltage conditions, the CEI film with polycarbonyl structures effectively complexes dissolved metal ions, reducing the metal ion content in the electrolyte. This reduces side reactions catalyzed by metal ions and decreases battery gas production, thereby improving cycle performance. Furthermore, the superior performance of the CEI film effectively prevents direct contact between the electrolyte solvent and the highly active positive electrode material, maintaining good stability at high temperatures and reducing interfacial impedance. Fluorosulfonylimide salt can be used as a high-performance electrolyte additive, particularly suitable for secondary batteries using lithium manganese iron phosphate materials. As a technical solution of the present invention, at least one of compounds one to six is ​​selected.

[0007]

[0008] Compound 1 Compound 2

[0009] Compound 3 Compound 4

[0010] Compound Five Compound Six A second aspect of this invention provides a method for preparing fluorosulfonyl imide salts, comprising the steps of: (a) Preparation of fluorosulfonic acid isocyanate; (ii) Add urea or thiourea to the solvent, add the fluorosulfonic acid isocyanate dropwise to react, and then add hydroxide to neutralize.

[0011] The preparation method of this invention involves reacting urea or thiourea with fluorosulfonate isocyanate, followed by a neutralization reaction with hydroxide to obtain the fluorosulfonamide salt shown in Formula I. This preparation method utilizes readily available raw materials, is simple in process, has high yield, high purity, and good atom economy, making it easy for industrial production. The obtained fluorosulfonamide salt can effectively improve the cycle life, high-temperature performance, and safety performance of secondary batteries.

[0012] As one technical solution of the present invention, the solvent is selected from at least one of acetonitrile, butyronitrile, n-hexane, cyclohexane, dichloromethane, 1,2-dichloroethane, tetrachloroethane, methyl tert-butyl ether, ethylene glycol dimethyl ether, tetrahydrofuran, dioxane, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, methyl acetate, ethyl acetate, propyl acetate, acetone, cyclohexanone, and 4-methyl-2-pentanone.

[0013] As a technical solution of the present invention, the fluorosulfonic acid isocyanate is produced by reacting chlorosulfonic acid isocyanate and fluorine. It is obtained by a displacement reaction of potassium chloride.

[0014] As one technical solution of the present invention, the hydroxide is selected from lithium hydroxide, sodium hydroxide, cesium hydroxide or magnesium hydroxide.

[0015] As a technical solution of the present invention, the reaction temperature is -5~5℃, and after the addition of the isofluorosulfonic acid... After cyanate ester, react for another 0.5~1.0 h.

[0016] A third aspect of this invention provides an electrolyte comprising a non-aqueous organic solvent, an electrolyte salt, and an additive, wherein the additive includes the aforementioned fluorosulfonylimide salt. This fluorosulfonylimide salt, when used in a secondary battery, can effectively improve the battery's cycle life, high-temperature performance, and safety.

[0017] As one technical solution of the present invention, the fluorosulfonamide salt accounts for 0.1 to 5.0% of the mass of the electrolyte. A fourth aspect of the present invention provides a secondary battery comprising a positive electrode material, a negative electrode material and an electrolyte, characterized in that the electrolyte is the aforementioned non-aqueous electrolyte, and the positive electrode material comprises a lithium manganese iron phosphate-based positive electrode material. Attached Figure Description

[0018] Figure 1 The NMR spectrum of compound one in Example 1 is a fluorine spectrum. Detailed Implementation

[0019] The fluorosulfonamide salt of the present invention can be used as an electrolyte additive to improve the electrochemical performance of secondary batteries, such as cycle life, high temperature resistance, and safety.

[0020] Secondary batteries consist of positive electrode active materials, negative electrode active materials, and non-aqueous electrolytes.

[0021] The positive electrode active material can be a layered transition metal lithium oxide or an olivine-type lithium compound. The layered transition metal lithium oxide can be, but is not limited to, lithium cobalt oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, and lithium nickel cobalt manganese oxide (chemical formula LiNi). x Co y Mn (1-x-y) M z O2, where 0.6≤x<0.9, x+y<1, 0≤z<0.08, and M is at least one of Al, Mg, Zr, and Ti, and coatings and dopants of the above materials. In particular, the fluorosulfonylimide salt of the present invention is applicable to secondary batteries using lithium manganese iron phosphate cathode materials. The general chemical formula of lithium manganese iron phosphate is LiMn. x Fe 1-x-y M y PO4, 0 < x < 1, 0 ≤ y ≤ 0.1, M is selected from at least one of Al, Mg, Zr and Ti.

[0022] The negative electrode active material includes at least one of carbon-based materials, silicon-based materials, and tin-based materials. The carbon-based material may include, but is not limited to, at least one of artificial graphite, natural graphite, hard carbon, soft carbon, graphene, and mesophase carbon microspheres. The silicon-based material may include, but is not limited to, at least one of elemental silicon, silicon-oxygen composite materials, silicon-carbon composite materials, and silicon alloy materials. The tin-based material may include elemental tin, tin-carbon composite materials, tin-oxygen composite materials, and tin alloy compounds.

[0023] Non-aqueous electrolytes include electrolyte salts, non-aqueous organic solvents, and additives.

[0024] The electrolyte salt may be, but is not limited to, at least one of lithium hexafluorophosphate (LiPF6), lithium perchlorate (LiClO4), lithium tetrafluoroborate (LiBF4), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium methanesulfonate (LiCH3SO3), lithium trifluoromethanesulfonate (LiCF3SO3), lithium dioxalatoborate (C4BLiO8), lithium difluorooxalatoborate (C2BF2LiO4), lithium difluorophosphate (LiPO2F2), and lithium difluorobis(oxalato)imide (LiDFBP). The lithium salt accounts for 5.0% to 37.5% of the total mass of the non-aqueous electrolyte. Further, the lithium salt accounts for 6.0% to 20.0% of the total mass of the non-aqueous electrolyte, preferably 8.0% to 18.0% of the total mass of the non-aqueous electrolyte. As an example, the mass of lithium salt accounts for 5.0%, 8.0%, 9.0%, 10.0%, 11.0%, 12.0%, 13.0%, 14.0%, 15.0%, 16.0%, 17.0%, 18.0%, 20.0%, 25.0%, 30.0%, 35.0%, and 37.5% of the total mass of the non-aqueous electrolyte, but is not limited to the listed values; other unlisted values ​​within this range also apply.

[0025] The non-aqueous organic solvent is at least one of chain carbonates, cyclic carbonates, carboxylic acid esters, and ether compounds. Specifically, the non-aqueous organic solvent is selected from at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (EMC), propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate (BC), methyl acetate (MA), ethyl acetate (EA), propyl acetate (EP), propyl propionate (PP), γ-butyrolactone (GBL), γ-valerolactone (GVL), 1,3-dioxolane (DOL), 1,4-dioxane (DX), tetrahydrofuran (THF), ethylene glycol di-n-butyl ether (EDB), and diethylene glycol dimethyl ether (DEGME), but the present invention is not limited thereto.

[0026] The additive may include at least a fluorosulfonamide salt. Further, the fluorosulfonamide salt has the structural formula shown in Formula I, wherein R is selected from alkylsilyl groups, C2-C6 aldehyde groups, or halogen boron groups. Even further, R is selected from O or S, M is selected from Li, Na, K, Cs, or Mg, and m × n = 4.

[0027]

[0028] Formula I Furthermore, the fluorosulfonamide salt is at least one of compounds one through six.

[0029]

[0030] Compound 1 Compound 2

[0031] Compound 3 Compound 4

[0032] Compound Five Compound Six The fluorosulfonamide salt accounts for 0.1% to 5.0% of the electrolyte mass. For example, the percentage of fluorosulfonamide salt may be, but is not limited to, 0.1%, 0.3%, 0.5%, 0.7%, 1.0%, 1.3%, 1.5%, 1.7%, 2.0%, 2.3%, 2.5%, 3.0%, 3.5%, 4.0%, 4.5%, and 5.0%.

[0033] The method for preparing the fluorosulfonyl imide salt of the present invention may include the following steps.

[0034] (a) Preparation of fluorosulfonic acid isocyanate; (ii) Add urea or thiourea to the solvent, add the fluorosulfonic acid isocyanate dropwise to react, and then add hydroxide to neutralize.

[0035] The solvent is selected from at least one of acetonitrile, butyronitrile, n-hexane, cyclohexane, dichloromethane, 1,2-dichloroethane, tetrachloroethane, methyl tert-butyl ether, ethylene glycol dimethyl ether, tetrahydrofuran, dioxane, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, methyl acetate, ethyl acetate, propyl acetate, acetone, cyclohexanone, and 4-methyl-2-pentanone. The fluorosulfonate isocyanate is obtained by a displacement reaction between chlorosulfonate isocyanate and potassium fluoride. The hydroxide is selected from lithium hydroxide, sodium hydroxide, cesium hydroxide, or magnesium hydroxide. The reaction temperature is -5 to 5°C; for example, the reaction temperature may be, but is not limited to, -5°C, -4°C, -3°C, -2°C, -1°C, 0°C, 1°C, 2°C, 3°C, 4°C, and 5°C. After adding the fluorosulfonate isocyanate dropwise, react for 0.5–1.0 h. For example, the reaction time can be, but is not limited to, 0.5 h, 0.6 h, 0.7 h, 0.8 h, 0.9 h, or 1.0 h. After neutralization, adjust the pH to 6–7, then filter, wash, and vacuum dry to obtain purified fluorosulfonamide salt. Filtration can be performed by centrifugation, vacuum filtration, or ordinary filtration. Washing can be done multiple times with hydrochloric acid solution, saturated saline solution, or water. The drying temperature is 35–120 °C. For example, the temperature can be, but is not limited to, 35 °C, 45 °C, 55 °C, 65 °C, 75 °C, 85 °C, 95 °C, 105 °C, 110 °C, 115 °C, or 120 °C. The drying time is 1–24 h. Not limited to 1h, 3h, 5h, 7h, 9h, 10h, 12h, 14h, 16h, 18h, 20h, 22h, 24h.

[0036] To better illustrate the purpose, technical solution, and beneficial effects of this invention, the invention will be further described below with reference to specific embodiments. It should be noted that the methods described below are further explanations of this invention and should not be construed as limiting it.

[0037] Part 1: Preparation of Fluorosulfonylimide Salts Preparation of fluorosulfonic acid isocyanate: The reaction temperature was set at 35°C. 68g of anhydrous potassium fluoride was added to a dry three-necked flask and stirred with a mechanical stirrer. A condenser was installed, and the condensate temperature was set to -20°C. 141.5g of chlorosulfonic acid isocyanate was added dropwise to the three-necked flask to initiate the reaction. The temperature was first raised to 100°C. After the chlorosulfonic acid isocyanate was added, the temperature was raised to 130°C and refluxed for 6 hours. After the reaction was complete, the temperature was lowered to room temperature, and then distilled at atmospheric pressure using a simple distillation apparatus. The temperature was raised to 100°C, and the fraction collected between 65°C and 100°C yielded 106g of fluorosulfonic acid isocyanate, with a yield of 85% and a purity of 99%. The fluorosulfonic acid isocyanate prepared in this manner is used as an example to synthesize compounds one through six, as detailed in Examples 1-6.

[0038] Example 1 This embodiment describes the preparation of compound one, and the preparation method includes the following steps.

[0039] The reaction temperature was set to -5°C. 6g of urea and 134g of anhydrous acetonitrile were added to a dry three-necked flask and stirred for 10 minutes. Then, 25g of fluorosulfonate isocyanate was added to a dropping funnel. When the solution temperature dropped to -5°C, fluorosulfonate isocyanate was slowly added dropwise, maintaining the reaction temperature within the range of -5°C to 5°C. After the addition of fluorosulfonate isocyanate was complete, the reaction was allowed to proceed for another 45 minutes. Then, 9.6g of anhydrous lithium hydroxide was added in batches for neutralization, and the pH was adjusted to between 6 and 7. After the reaction was complete, the mixture was filtered, washed, and vacuum dried to obtain 31.7g of compound one, with a yield of 95%.

[0040] The NMR spectrum of compound 1 - fluorine spectrum is shown below. Figure 1 As shown, this indicates that compound one was synthesized.

[0041] Example 2 This embodiment describes the preparation of compound two, and the preparation method includes the following steps.

[0042] The reaction temperature was set to -5°C. 7.6 g of thiourea and 140 g of anhydrous acetonitrile were added to a dry three-necked flask and stirred for 15 min. Then, 25 g of fluorosulfonate isocyanate was added to a dropping funnel. When the solution temperature dropped to -5°C, fluorosulfonate isocyanate was slowly added dropwise, maintaining the reaction temperature within the range of -5°C to 5°C. After the addition of fluorosulfonate isocyanate was complete, the reaction was allowed to proceed for another 1 h. Then, 9.6 g of anhydrous lithium hydroxide was added in batches for neutralization, and the pH was adjusted to between 6 and 7. After the reaction was complete, the mixture was filtered, washed, and vacuum dried to obtain 32.5 g of compound II, with a yield of 93%.

[0043] Example 3 This embodiment describes the preparation of compound three, and the preparation method includes the following steps.

[0044] The reaction temperature was set to -5°C. 6g of urea and 160g of n-hexane were added to a dry three-necked flask and stirred for 20 minutes. Then, 25g of fluorosulfonate isocyanate was added to a dropping funnel. When the solution temperature dropped to -5°C, fluorosulfonate isocyanate was slowly added dropwise, maintaining the reaction temperature within the range of -5°C to 5°C. After the addition of fluorosulfonate isocyanate was complete, the reaction was allowed to continue for another 30 minutes. Then, 16g of sodium hydroxide was added in batches for neutralization, and the pH was adjusted to between 6 and 7. After the reaction was complete, the mixture was filtered, washed, and vacuum dried to obtain 37.6g of compound III, with a yield of 94%.

[0045] Example 4 This embodiment describes the preparation of compound four, and the preparation method includes the following steps.

[0046] The reaction temperature was set to -5°C. 6g of urea and 335g of anhydrous acetonitrile were added to a dry three-necked flask and stirred for 10 minutes. Then, 25g of fluorosulfonate isocyanate was added to a dropping funnel. When the solution temperature dropped to -5°C, fluorosulfonate isocyanate was slowly added dropwise, maintaining the reaction temperature within the range of -5°C to 5°C. After the addition of fluorosulfonate isocyanate was complete, the reaction was allowed to proceed for another 40 minutes. Then, 67.2g of cesium hydroxide monohydrate was added in batches for neutralization, and the pH was adjusted to between 6 and 7. After the reaction was complete, the mixture was filtered, washed, and vacuum dried to obtain 80.4g of compound IV, with a yield of 96%.

[0047] Example 5 This embodiment describes the preparation of compound five, and the preparation method includes the following steps.

[0048] The reaction temperature was set to -5°C. 7.6 g of thiourea and 341 g of anhydrous acetonitrile were added to a dry three-necked flask and stirred for 10 min. Then, 25 g of fluorosulfonic acid isocyanate was added to a dropping funnel. When the solution temperature dropped to -5°C, fluorosulfonic acid isocyanate was slowly added dropwise, maintaining the reaction temperature within the range of -5°C to 5°C. After the addition of fluorosulfonic acid isocyanate was complete, the reaction was allowed to proceed for another 45 min. Then, 67.2 g of cesium hydroxide monohydrate was added in batches for neutralization, and the pH was adjusted to between 6 and 7. After the reaction was complete, the mixture was filtered, washed, and vacuum dried to obtain 78.5 g of compound five, with a yield of 92%.

[0049] Example 6 This embodiment describes the preparation of compound six, and the preparation method includes the following steps.

[0050] The reaction temperature was set to -5℃. 6g of urea and 142g of anhydrous acetonitrile were added to a dry three-necked flask and stirred for 10 minutes. Then, 25g of fluorosulfonate isocyanate was added to a dropping funnel. When the solution temperature dropped to -5℃, fluorosulfonate isocyanate was slowly added dropwise, maintaining the reaction temperature within the range of -5℃ to 5℃. After the addition of fluorosulfonate isocyanate was complete, the reaction was allowed to proceed for another 45 minutes. Then, 23.2g of magnesium hydroxide was added in batches for neutralization, and the pH was adjusted to between 6 and 7. After the reaction was complete, the mixture was filtered, washed, and vacuum dried to obtain 33g of compound six, with a yield of 93%.

[0051] Part Two: Application of Fluorosulfonylimide Salts in Secondary Batteries 1.1 Preparation of non-aqueous electrolyte In a nitrogen-filled glove box (O2 < 1 ppm, H2O < 1 ppm), dimethyl carbonate (DMC), ethyl acetate (EA), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed thoroughly in a mass ratio of 3:1:2:2. The resulting mixed solvent was used as the organic solvent to add compounds one through six prepared in Examples 1-6, respectively, to obtain mixed solutions. The mixed solutions were sealed and packaged, then frozen in a freezer (-4°C) for 2 hours. After removal, lithium hexafluorophosphate (LiPF6) was slowly added to the mixed solutions in a nitrogen-filled glove box (O2 < 1 ppm, H2O < 1 ppm). After thorough mixing, non-aqueous electrolytes 1-6# were prepared.

[0052] In a nitrogen-filled glove box (O2 < 1 ppm, H2O < 1 ppm), dimethyl carbonate (DMC), ethyl acetate (EA), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed thoroughly in a mass ratio of 3:1:2:2 to obtain a mixed solvent, which was then used as the organic solvent. The organic solvent was sealed and packaged, then frozen in a freezer (-4℃) for 2 hours. After removal, lithium hexafluorophosphate (LiPF6) was slowly added to the mixed solution in a nitrogen-filled glove box (O2 < 1 ppm, H2O < 1 ppm), and mixed thoroughly to prepare non-aqueous electrolyte #7.

[0053] 1.2 Preparation of the positive electrode sheet LiMn manganese iron phosphate material 0.5 Fe 0.5 PO4, PVDF binder, and Super P conductive agent are mixed evenly at a mass ratio of 95:1:4 to prepare a lithium secondary battery positive electrode slurry with a certain viscosity. The mixed slurry is coated on both sides of aluminum foil, dried, and rolled to obtain the positive electrode sheet.

[0054] 1.3 Preparation of negative electrode sheet Artificial graphite, conductive agent SuperP, thickener CMC, and binder SBR (styrene-butadiene rubber latex) are mixed in a mass ratio of 95:1.5:1.0:2.5 to form a slurry. The mixture is then coated on both sides of a copper foil, dried, and rolled to obtain a negative electrode sheet, thus producing a secondary battery negative electrode sheet that meets the requirements.

[0055] 1.4 Preparation of Secondary Batteries The positive electrode, negative electrode, and separator prepared according to the above process are stacked in sequence, and then layered as needed. After the tabs are welded, they are placed in the aluminum-plastic film of the battery outer packaging. The prepared electrolyte is injected into the dried bare cell, and vacuum sealing, standing, formation (0.05C constant current charging to 3.0V, then 0.1C constant current charging to 4.3V), capacity testing, and other processes are carried out in sequence to finally obtain 1Ah soft-pack lithium secondary batteries 1~7#.

[0056] Performance tests were conducted on secondary batteries #1 to #7. The test results are shown in Table 1. The test conditions are as follows.

[0057] (1) Room temperature cycling performance test Under normal temperature (25℃) conditions, the secondary battery is subjected to one 1.0C / 1.0C charge and discharge cycle (battery discharge capacity is recorded as C0), with an upper limit voltage of 4.1V; then subjected to 500 cycles of 1.0C / 1.0C charge and discharge (battery discharge capacity is C1), and the capacity retention rate is calculated.

[0058] Capacity retention rate = (C1 / C0) × 100% (2) Room temperature cycling performance test Under high temperature (45℃) conditions, a lithium-ion battery is subjected to one 1.0C / 1.0C charge and discharge cycle (battery discharge capacity is C0), with an upper limit voltage of 4.1V. Then, it is subjected to 400 cycles of 1.0C / 1.0C charge and discharge at room temperature (battery discharge capacity is C1). The capacity retention rate is calculated.

[0059] Capacity retention rate = (C1 / C0) × 100% (3) Safety performance test At room temperature (25℃), the battery is charged at a constant current of 1C until the charging termination voltage (7V) is reached. Then, it is switched to constant voltage charging until the charging current rate drops to 0.05C. Charging is then stopped, and the battery is allowed to stand for 2.5 hours. The battery is then placed in a test chamber, which is heated at a rate of 5℃ / min. Once the temperature inside the chamber reaches 130±2℃, it is held at this temperature for 1 hour. The battery passes if it does not smoke, catch fire, or explode; otherwise, it fails.

[0060] Table 1 Electrochemical performance test results of secondary batteries #1-#7

[0061] The results in Table 1 show that adding fluorosulfonyl imide salt with the structural formula shown in Formula I to the electrolyte can improve the battery's cycle life, high-temperature performance, and safety. Comparing secondary batteries #1 to #6, it is evident that Compound I exhibits superior performance. This is because Compound I is a multi-carbonyl lithium salt. On one hand, the oxygen atoms on the carbonyl groups can effectively complex transition metal ions in the positive electrode material, preventing the dissolution of these ions from damaging the SEI of the negative electrode, thereby improving the battery's cycle performance. On the other hand, the anions of Compound I can be oxidized at the positive electrode to form a CEI film containing Li3N and LiSO3F components. This CEI film is more structurally stable and has stronger oxidation resistance than ordinary CEI films, preventing continuous side reactions at the electrolyte-electrode interface and improving the stability of the electrolyte-electrode interface, thus enhancing the battery's cycle performance and safety. Compound 2 exhibits inferior cycle performance compared to Compound 1, possibly because its anion contains a sulfur atom with a covalent radius of 94 pm, which is 42% larger than the covalent radius of oxygen (66 pm). This significantly reduces the ability of the polycarbonyl group to complex transition metal ions. The main reason why Compounds 3, 4, 5, and 6 show inferior cycle performance compared to Compound 1 is likely that their cations do not contain lithium ions. Since the electrolyte system in the examples is a lithium salt system, the cations in Compounds 3 to 6 do not have a positive effect on battery performance. However, it can be predicted that Compound 3 will perform better in sodium-ion batteries.

[0062] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, it is not limited to those listed in the embodiments. Those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A fluorosulfonylimide salt characterized in that, The structural formula is shown in Formula I, where R is selected from O or S, M is selected from Li, Na, K, Cs, Mg, and m×n=4. Formula I.

2. The fluorosulfonimine salt of claim 1, wherein Selected from at least one of compounds one through six, Compound 1 Compound 2 Compound 3 Compound 4 Compound 5 and Compound 6.

3. The method for preparing fluorosulfonyl imide salt according to any one of claims 1 to 2, characterized in that, Including the following steps: (a) Preparation of fluorosulfonic acid isocyanate; (ii) Add urea or thiourea to the solvent, add the fluorosulfonic acid isocyanate dropwise to react, and then add hydroxide to neutralize.

4. The method for preparing fluorosulfonyl imide salt according to claim 3, characterized in that, The solvent is selected from at least one of acetonitrile, butyronitrile, n-hexane, cyclohexane, dichloromethane, 1,2-dichloroethane, tetrachloroethane, methyl tert-butyl ether, ethylene glycol dimethyl ether, tetrahydrofuran, dioxane, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, methyl acetate, ethyl acetate, propyl acetate, acetone, cyclohexanone, and 4-methyl-2-pentanone.

5. The method for preparing fluorosulfonyl imide salt according to claim 3, characterized in that, The fluorine The acid isocyanate is obtained by a displacement reaction between chlorosulfonic acid isocyanate and potassium fluoride.

6. The method for preparing fluorosulfonyl imide salt according to claim 3, characterized in that, The hydroxide is selected from lithium hydroxide, sodium hydroxide, cesium hydroxide, or magnesium hydroxide.

7. The method for preparing fluorosulfonyl imide salt according to claim 3, characterized in that, The reaction The temperature is -5~5℃, and the reaction continues for 0.5~1.0h after the fluorosulfonic acid isocyanate is added dropwise.

8. A non-aqueous electrolyte, comprising a non-aqueous organic solvent, an electrolyte salt, and additives, characterized in that, The additive includes the fluorosulfonyl imide salt according to any one of claims 1 to 2.

9. The non-aqueous electrolyte according to claim 8, characterized in that, The fluorosulfonamide salt accounts for 0.1 to 5.0% of the mass of the electrolyte.

10. A secondary battery, comprising a positive electrode material, a negative electrode material, and an electrolyte, characterized in that, The electrolyte is the non-aqueous electrolyte according to any one of claims 8 to 9, and the cathode material comprises lithium manganese iron phosphate cathode material.

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