Fluorinated thiophene compounds, their preparation methods, and electrolytes

Abstract

The present invention provides a fluorinated thiophene compound, a preparation method thereof, and an electrolyte. The structural formula of the fluorinated thiophene compound is shown in Formula I, wherein R1 is fluorine or fluorosulfonyl, R2 is hydrogen, halogen, cyano, nitro, a C1-C6 hydrocarbon group or a C1-C6 halogenated hydrocarbon group, and R3 is hydrogen, a C1-C6 hydrocarbon group or a C1-C6 halogenated hydrocarbon group. The fluorinated thiophene compound is improved on the basis of a conventional thiophene compound by introducing fluorine or fluorosulfonyl, which can overcome the drawbacks of the conventional thiophene compound. When used as an additive, it can reduce the decomposition and oxidation reactions of the electrolyte in a high-pressure and high-temperature system, thereby improving the electrochemical performance of the lithium-ion battery under high temperature and high pressure.

Description

Technical Field

[0001] The present invention relates to the technical field of material synthesis, and more particularly to a compound applied to a battery, and even more particularly to a fluorinated thiophene compound, a preparation method thereof, and an electrolyte solution. Background Art

[0002] With the increasing demand for lithium-ion batteries, the deficiencies in their high energy density and long cycle life have attracted much attention. To achieve a high energy density for lithium-ion batteries, battery materials with high specific capacity and working voltage are required. The cathode materials of lithium-ion batteries have shifted from lithium iron phosphate and lithium manganate systems to ternary nickel cobalt manganese oxide materials systems.

[0003] Ternary nickel cobalt manganese oxide materials have higher capacity, but in a traditional electrolyte solution system, obvious interfacial catalytic reactions will occur under high voltage and high temperature conditions, resulting in the decomposition of the electrolyte solution and gas generation, ultimately affecting the life and safety performance of the battery.

[0004] Currently in the industry, additives that can form a film at the interface of ternary nickel cobalt manganese oxide materials are added to the electrolyte solution, such as VC, PS, DTD, TMSP, LiPO2F2, LiFSI, LiTFSI, LiPF2(C2O4)2, LiBOB, etc. The interface film formation is used to protect the positive electrode, increase the voltage resistance window of the electrolyte solution, and increase the cycle life of the battery.

[0005] Thiophene is a five-membered aromatic heterocycle containing one sulfur atom and two conjugated double bonds in the ring, and has a 6-π electron large conjugated system similar to that of a benzene ring. The thiophene functional group has good chemical stability, can stably exist under high voltage, reduce the oxidative decomposition of the electrolyte solution, and thus extend the cycle life of the battery. However, the protective film formed by the thiophene group under high voltage is not stable enough and is easy to decompose during the cycling process, resulting in poor cycle stability of the battery, and the self-discharge of the thiophene group increases. Using an additive containing a thiophene group may cause an increase in the self-discharge of the battery, affecting the energy efficiency and life of the battery, and an additive containing a thiophene group may also increase the internal resistance of the battery, affecting the high-frequency discharge performance and overall performance of the battery. Due to the above problems, additives containing a thiophene group are not widely used in practical applications and have not reached the practical level.

[0006] Therefore, if a thiophene compound is to be used as an additive and applied to a lithium-ion battery system, such drawbacks need to be overcome first. Summary of the Invention

[0007] Based on the above problems, the object of the present invention is to provide a fluorinated thiophene compound, a preparation method thereof, and an electrolyte. The fluorinated thiophene compound is improved on the basis of conventional thiophene compounds by introducing fluorine or fluorosulfonyl groups, which can overcome the disadvantages of conventional thiophene compounds. When used as an additive, it can reduce the decomposition and oxidation reactions of the electrolyte in high-pressure and high-temperature systems, thereby improving the electrochemical performance of lithium-ion batteries under high temperature and high pressure.

[0008] To achieve the above object, in the first aspect of the present invention, a fluorinated thiophene compound is provided, and its structural formula is shown as Formula I, wherein, R1 is fluorine or fluorosulfonyl, R2 is hydrogen, halogen, cyano, nitro, a C1-C6 hydrocarbon group or a C1-C6 halogenated hydrocarbon group, and R3 is hydrogen, a C1-C6 hydrocarbon group or a C1-C6 halogenated hydrocarbon group.

[0009]

[0010] The fluorinated thiophene compound of the present invention is the compound shown in Formula I, and the five-membered aromatic heterocyclic thiophene structure containing one sulfur atom and two conjugated double bonds in the ring has good chemical stability and electron transport characteristics. By introducing fluorine or fluorosulfonyl groups in the present invention, the sulfonyl fluoride functional group can reduce the polarity of the sulfonyl group, thereby reducing the decomposition of the electrolyte under high-pressure conditions and prolonging the cycle life of the battery. By reducing the conductivity, the sulfonyl fluoride functional group helps to reduce the side reactions of the electrolyte in the battery and improve the high-voltage performance and cycle life of the battery. At the same time, the F-group has a high electron-withdrawing tendency, and substances rich in F can resist oxidation. This fluorinated compound can form a stronger SEI / CEI film. Therefore, the fluorinated thiophene compound shown in Formula I is an excellent additive for lithium-ion battery electrolytes and can expand the application field of thiophene compounds.

[0011] As a technical solution of the present invention, R2 is hydrogen, fluorine, cyano, nitro, a C1-C3 alkyl group or a C1-C3 fluorinated alkyl group, and R3 is hydrogen, a C1-C3 alkyl group or a C1-C3 fluorinated alkyl group.

[0012] As a technical solution of the present invention, the fluorinated thiophene compound is at least one of the following compounds 1 to compound 9.

[0013]

[0014]

[0015] In the second aspect of the present invention, a preparation method of a fluorinated thiophene compound is provided, including the steps:

[0016] (1) Dissolve the fluorination reagent in an organic solvent, and add the thiophene compound thereto under stirring to carry out a fluorination reaction to obtain a product. The reaction formula of the fluorination reaction is shown in Formula 1 or Formula 2, wherein R2 is hydrogen, halogen, cyano, nitro, a C1-C6 hydrocarbon group or a C1-C6 halogenated hydrocarbon group, and R3 is hydrogen, a C1-C6 hydrocarbon group or a C1-C6 halogenated hydrocarbon group;

[0017] (2) Purify and refine the product.

[0018]

[0019] The preparation method of the present invention is simple, the reaction process is mild, the process is simple, and the product yield is high. The thiophene compound can be prepared by fluorinating the thiophene compound with a fluorination reagent. The thiophene compound not only has a thiophene structure, but also has a fluorine or fluorosulfonyl group structure, which can improve the high-voltage and high-temperature performance of the lithium-ion battery.

[0020] As a technical solution of the present invention, the fluorination reagent includes one or more of KF, AgF, CsF, NaF, CaF, bis(2-methoxyethyl)aminosulfur trifluoride, triethylamine trihydrofluoride, and tetrabutylammonium fluoride.

[0021] As a technical solution of the present invention, the molar ratio of the fluorination reagent to the thiophene compound is 1-10:1.

[0022] As a technical solution of the present invention, the temperature of the fluorination reaction is 20-100 °C, and the time is 0.5-10.0 h.

[0023] As a technical solution of the present invention, the organic solvent includes one or more of dichloromethane, dichloroethane, acetonitrile, ethyl acetate, tetrahydrofuran, chloroform, toluene, xylene, n-hexane, and petroleum ether.

[0024] As a technical solution of the present invention, the steps of purification and refinement include: filtering the product to remove impurities and concentrating to obtain a crude product, and then subjecting the crude product to low-temperature distillation and then high-temperature distillation.

[0025] The third aspect of the present invention provides an electrolyte, which includes a non-aqueous organic solvent, an electrolyte salt, and an additive. The additive includes the aforementioned fluorinated thiophene compound or the fluorinated thiophene compound prepared by the preparation method of the aforementioned fluorinated thiophene compound, and the fluorinated thiophene compound accounts for 1.0-10.0% of the mass of the electrolyte. Specific Embodiments

[0026] The fluorinated thiophene compounds of the present invention can be used in pharmaceutical synthesis, dye and plastic production, pesticide production, spice production, and batteries. In particular, the fluorinated thiophene compounds can be used in lithium-ion batteries, and the fluorinated thiophene compounds as electrolyte additives can improve the electrochemical performance of lithium-ion batteries under high temperature and high pressure.

[0027] A lithium-ion battery includes a positive electrode active material, a negative electrode active material, and an electrolyte. 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 not limited to lithium cobalt oxide (according to LiCoO2), lithium nickel oxide (according to LiNiO2), lithium manganese oxide (according to LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (chemical formula is 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. It is particularly suitable for ternary materials of lithium nickel cobalt manganese oxide. These positive electrode active materials can be used alone or in combination of two or more.

[0028] The negative electrode active material includes at least one of a carbon-based material, a silicon-based material, and a tin-based material. Among them, the carbon-based material can be but not limited to at least one of artificial graphite, natural graphite, hard carbon, soft carbon, graphene, and mesophase carbon microspheres. The silicon-based material can be but not limited to at least one of silicon, silicon-oxygen composite material, silicon-carbon composite material, and silicon alloy material. The tin-based material can include tin, tin-carbon composite material, tin-oxygen composite material, and tin alloy compound.

[0029] The electrolyte includes an electrolyte salt, a non-aqueous organic solvent, and an additive.

[0030] The electrolyte salt can 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(trifluoromethylsulfonyl)imide (LiTFSI), lithium methylsulfonate (LiCH3SO3), lithium trifluoromethanesulfonate (LiCF3SO3), lithium bis(oxalato)borate (C4BLiO8), lithium difluoro(oxalato)borate (C2BF2LiO4), lithium difluorophosphate (LiPO2F2), and lithium difluoro(bis(oxalato))phosphate (LiDFBP). The non-aqueous organic solvent is selected from carbonates and / or carboxylates. Further, the non-aqueous organic solvent is selected from at least one of ethylene carbonate (PC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), γ-butyrolactone, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, ethyl propionate, propyl propionate, and butyl propionate.

[0031] The additive is a fluorinated thiophene compound. Further, the additive is a compound represented by Formula I. The fluorinated thiophene compound accounts for 1.0 to 10.0% of the mass of the electrolyte. As an example, the proportion of the fluorinated thiophene compound can be, but is not limited to, 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, 4.0%, 4.5%, 5.0%, 5.5%, 6.0%, 6.5%, 7.0%, 7.5%, 8.0%, 8.5%, 9.0%, 9.5%, 10.0%.

[0032]

[0033] Wherein, R1 is fluorine or fluorine sulfonyl, R2 is hydrogen, halogen, nitrile, nitro, C1~C6 hydrocarbon group or C1~C6 halogenated hydrocarbon group, R3 is hydrogen, C1~C6 hydrocarbon group or C1~C6 halogenated hydrocarbon group. Further, R2 is hydrogen, fluorine, nitrile, nitro, C1~C3 alkyl or C1~C3 fluoroalkyl, R3 is hydrogen, C1~C3 alkyl or C1~C3 fluoroalkyl. By way of example, R2 can be, but is not limited to, hydrogen, fluorine, chlorine, nitrile, nitro, methyl, ethyl, propyl, isopropyl, butyl, pentyl, hexyl, vinyl, propenyl, isopropenyl, butenyl, pentenyl, hexenyl, ethynyl, propynyl, isopropynyl, butynyl, pentynyl, hexynyl, fluoromethyl, fluoroethyl, fluoropropyl, fluoroisopropyl, fluorobutyl, fluoropentyl, fluorohexyl, fluorovinyl, fluoropropenyl, fluoroisopropenyl, fluorobutenyl, Fluoropentenyl, fluorohexenyl, fluoroethynyl, fluoropropynyl, fluoroisopropynyl, fluorobutynyl, fluoropentynyl, fluorohexynyl, chloromethyl, chloroethyl, chloropropyl, chloroisopropyl, chlorobutyl, chloropentyl, chlorohexyl, chlorovinyl, chloropropenyl, chloroisopropenyl, chlorobutenyl, chloropentenyl, chlorohexenyl, chloroethynyl, chloropropynyl, chloroisopropynyl, chlorobutynyl, chloropentynyl, chlorohexynyl.

[0034] More specifically, the fluorine-containing thiophene compound is at least one of the following compounds 1 to 9.

[0035]

[0036]

[0037] The preparation method of the fluorine-containing thiophene compound of the present invention may include the following steps.

[0038] (1) A fluorination agent is dissolved in an organic solvent, and a thiophene compound is added under stirring to carry out a fluorination reaction to obtain a product.

[0039] (2) Purify and refine the product.

[0040] The reaction formula of the fluorination reaction is shown in Formula 1 or Formula 2, and the chlorine on the thiophene compound is replaced by fluorine through the fluorination reaction, thereby preparing a thiophene compound containing fluorine or fluorine sulfonyl. Wherein, R2 is hydrogen, halogen, nitrile, nitro, C1~C6 hydrocarbon group or C1~C6 halogenated hydrocarbon group, and R3 is hydrogen, C1~C6 hydrocarbon group or C1~C6 halogenated hydrocarbon group.

[0041]

[0042] The organic solvents include one or more of dichloromethane, dichloroethane, acetonitrile, ethyl acetate, tetrahydrofuran, chloroform, toluene, xylene, n-hexane and petroleum ether. The fluorination reagents include one or more of KF, AgF, CsF, NaF, CaF, bis(2-methoxyethyl)aminosulfur trifluoride, triethylamine trihydrofluoride and tetrabutylammonium fluoride. If inorganic fluorinated salts such as KF, AgF, CsF, NaF, CaF are used, they need to be activated in advance. The molar ratio of the fluorination reagent to the thiophene compound is 1-10:1. As an example, the molar ratio can be but is not limited to 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1. The temperature of the fluorination reaction is 20-100 °C. As an example, the temperature can be but is not limited to 20 °C, 30 °C, 40 °C, 50 °C, 60 °C, 70 °C, 80 °C, 90 °C, 100 °C. The time is 0.5-10.0 h. As an example, the time can be but is not limited to 0.5 h, 1.0 h, 1.5 h, 2.0 h, 2.5 h, 3.0 h, 3.5 h, 4.0 h, 4.5 h, 5.0 h, 5.5 h, 6.0 h, 6.5 h, 7.0 h, 7.5 h, 8.0 h, 8.5 h, 9.0 h, 9.5 h, 10.0 h.

[0043] In step (2), the steps of purification and refinement may include: subjecting the product to suction filtration to remove impurities, concentrating to obtain a crude product, and then subjecting the crude product to low-temperature distillation and then high-temperature distillation. The product is suction filtered to remove the solid fluorination reagent and other solid impurities, concentrated under reduced pressure to remove the organic solvent, and a part of the fluorination reagent slightly soluble in the organic solvent is precipitated, and then suction filtered again to obtain a crude product. The crude product is subjected to low-temperature distillation at 0-50 °C under vacuum to further remove the organic solvent, and then subjected to high-temperature distillation at 50-120 °C under vacuum to distill out the high-purity product.

[0044] To better illustrate the purpose, technical solution and beneficial effects of the present invention, the present invention will be further described below in conjunction with specific embodiments. It should be noted that the methods described in the following embodiments are further explanatory descriptions of the present invention and should not be regarded as limitations of the present invention.

[0045] The reagents used in the examples are reagent grade and can be obtained commercially. The hydrogen spectrum data can be derived from the test results of the nuclear magnetic resonance spectrometer BRUKER AVANCE 400. 5-Cyano-2-thiophenesulfonyl chloride can be purchased from Changzhou Hejing Chemical Co., Ltd.

[0046] Part 1: Preparation of fluorinated thiophene compounds

[0047] Example 1

[0048] This example is for the preparation of fluorinated thiophene compounds, and its preparation method includes the following steps.

[0049] (1) 5-Methylthiophene-2-sulfonyl chloride (CAS: 55854-45-0, 33.5 g, 0.17 mol) was dissolved in dichloromethane, and tetrabutylammonium fluoride (177 g, 0.68 mol) was added dropwise within 1 h under stirring. The reaction was carried out at 20 °C for 5 h, and the reaction was stopped by gas-phase monitoring to obtain the product.

[0050] (2) The product was subjected to the first suction filtration, concentration under reduced pressure, and the second suction filtration to obtain the crude product. Then the crude product was distilled at low temperature at 20 °C and then distilled under reduced pressure at 60 °C to obtain 27.6 g of 5-methylthiophene-2-sulfonyl fluoride (Compound 1), with a yield of 90%.

[0051] The 1H NMR data of the prepared Compound 1 are as follows: 1H NMR (400 MHz, DMSO-d6): δ 2.49 (3H), 7.03 (1H), 7.15 (1H).

[0052] Example 2

[0053] This example is for the preparation of fluorinated thiophene compounds, and its preparation method includes the following steps.

[0054] (1) 2,3-Dimethylthiophene-5-sulfonyl chloride (CAS: 74616-28-7, 56.9 g, 0.27 mol) was dissolved in dichloromethane, and AgF (34.4 g, 0.273 mol) was added dropwise within 1 h under stirring. The reaction was carried out at 70 °C for 3 h, and the reaction was stopped by gas-phase monitoring to obtain the product.

[0055] (2) The product was subjected to the first suction filtration, concentration under reduced pressure, and the second suction filtration to obtain the crude product. Then the crude product was distilled at low temperature at 20 °C and then distilled under reduced pressure at 50 °C to obtain 44.58 g of 2,3-dimethylthiophene-5-sulfonyl fluoride (Compound 2), with a yield of 85%.

[0056] The 1H NMR data of the prepared Compound 2 are as follows: 1H NMR (400 MHz, DMSO-d6): δ 2.45 (3H), 2.64 (3H), 6.58 (1H).

[0057] Example 3

[0058] This example is for the preparation of fluorinated thiophene compounds, and its preparation method includes the following steps.

[0059] (1) 2-Chlorothiophene (CAS: 96-43-5, 11.8 g, 0.1 mol) was dissolved in dichloromethane, and triethylamine hydrofluoride (33.0 g, 0.2 mol) was added dropwise within 0.5 h under stirring. The reaction was carried out at 50 °C for 5 h, and the reaction was stopped by gas-phase monitoring to obtain the product.

[0060] (2) The product was subjected to the first suction filtration, concentration under reduced pressure, and the second suction filtration to obtain the crude product. The crude product was then subjected to low-temperature distillation at 20 °C and then vacuum distillation at 60 °C to obtain 9.5 g of 2-fluorothiophene ((Compound 3)), with a yield of 93%.

[0061] The 1H NMR data of the prepared Compound 3 were as follows: 1H NMR (400 MHz, DMSO-d6): δ 6.58 (1H), 7.13 (1H), 7.41 (1H).

[0062] Example 4

[0063] This example is for the preparation of fluorothiophene compounds, and its preparation method includes the following steps.

[0064] (1) 5-Chlorothiophene-2-carbonitrile (CAS: 50478-16-5, 39.0, 0.272 mol) was dissolved in dichloromethane, and KF (47.4 g, 0.816 mol) was added dropwise within 1 h under stirring. The reaction was carried out at 50 °C for 0.5 h, and the reaction was stopped by gas-phase monitoring to obtain the product.

[0065] (2) The product was subjected to the first suction filtration, concentration under reduced pressure, and the second suction filtration to obtain the crude product. The crude product was then subjected to low-temperature distillation at 20 °C and then vacuum distillation at 55 °C to obtain 30.7 g of 5-fluorothiophene-2-carbonitrile (Compound 4), with a yield of 89%.

[0066] The 1H NMR data of the prepared Compound 4 were as follows: 1H NMR (400 MHz, DMSO-d6): δ 6.05 (1H), 7.15 (1H).

[0067] Example 5

[0068] This example is for the preparation of fluorothiophene compounds, and its preparation method includes the following steps.

[0069] (1) 5-Chloro-2-thiophenesulfonyl chloride (CAS: 2766-74-7, 59.05 g, 0.272 mol) was dissolved in dichloromethane, and CsF (82.4 g, 0.546 mol) was added dropwise within 0.5 h under stirring. The reaction was carried out at 20 °C for 4 h, and the reaction was stopped by gas-phase monitoring to obtain the product.

[0070] (2) The product was subjected to the first suction filtration, concentration under reduced pressure, and the second suction filtration to obtain the crude product. The crude product was then subjected to low-temperature distillation at 20 °C and then vacuum distillation at 70 °C to obtain 49.0 g of 5-fluoro-2-thiophenesulfonyl fluoride (Compound 5), with a yield of 98%.

[0071] The 1H NMR data of the prepared Compound 5 were as follows: 1H NMR (400 MHz, DMSO-d6): δ 7.03 (1H), 6.19 (1H).

[0072] Example 6

[0073] This example is for the preparation of fluorinated thiophene compounds, and its preparation method includes the following steps.

[0074] (1) Dissolve 4,5-difluorothiophene-2-sulfonyl chloride (CAS: 2657625-63-12, 21.9 g, 0.1 mol) in dichloromethane, and dropwise add ethylamine hydrofluoride (33 g, 0.2 mol) within 0.5 h under stirring. React at 60 °C for 3 h, and stop the reaction by gas-phase monitoring to obtain the product.

[0075] (2) Filter the product for the first time, concentrate it under reduced pressure, filter it for the second time to obtain the crude product, and then distill the crude product at a low temperature of 20 °C and then under reduced pressure at 60 °C to obtain 17.8 g of 4,5-difluorothiophene-2-sulfonyl fluoride (Compound 6), with a yield of 88%.

[0076] The 1H NMR data of the prepared Compound 6 is: 1HNMR(400MHz,DMSO-d6):δ6.58(1H).

[0077] Example 7

[0078] This example is for the preparation of fluorinated thiophene compounds, and its preparation method includes the following steps.

[0079] (1) Dissolve 5-trifluoromethyl-2-thiophene sulfonyl chloride (CAS: 954377-22-1, 39.8 g, 0.16 mol) in dichloromethane, and dropwise add tetrabutylammonium fluoride (177 g, 0.68 mol) within 1 h under stirring. React at 30 °C for 4.5 h, and stop the reaction by gas-phase monitoring to obtain the product.

[0080] (2) Filter the product for the first time, concentrate it under reduced pressure, filter it for the second time to obtain the crude product, and then distill the crude product at a low temperature of 20 °C and then under reduced pressure at 50 °C to obtain 34.85 g of 5-trifluoromethyl-2-thiophene sulfonyl fluoride (Compound 7), with a yield of 93%.

[0081] The 1H NMR data of the prepared Compound 7 is: 1HNMR(400MHz,DMSO-d6):δ7.03(1H),7.15(1H).

[0082] Example 8

[0083] This example is for the preparation of fluorinated thiophene compounds, and its preparation method includes the following steps.

[0084] (1) Dissolve 5-cyano-2-thiophenesulfonyl chloride (41.4 g, 0.20 mol) in dichloromethane, and dropwise add KF (23.2 g, 0.4 mol) within 1 h under stirring. React at 50 °C for 0.5 h, and stop the reaction monitored by gas phase to obtain the product.

[0085] (2) Filter the product by suction for the first time, concentrate under reduced pressure, and filter by suction for the second time to obtain the crude product. Then, distill the crude product at a low temperature of 20 °C and then distill under reduced pressure at 55 °C to obtain 34.0 g of 5-cyano-2-thiophenesulfonyl fluoride (Compound 8), with a yield of 89%.

[0086] The 1H NMR data of the prepared Compound 8 are as follows: 1H NMR (400 MHz, DMSO-d6): δ 7.03 (1H), 7.15 (1H).

[0087] Example 9

[0088] This example is for the preparation of fluorinated thiophene compounds, and its preparation method includes the following steps.

[0089] (1) Dissolve 5-nitro-2-thiophenesulfonyl chloride (CAS: 36035-01-5, 45.4 g, 0.20 mol) in dichloromethane, and dropwise add AgF (37.8 g, 0.3 mol) within 0.5 h under stirring. React at 70 °C for 1 h, and stop the reaction monitored by gas phase to obtain the product.

[0090] (2) Filter the product by suction for the first time, concentrate under reduced pressure, and filter by suction for the second time to obtain the crude product. Then, distill the crude product at a low temperature of 20 °C and then distill under reduced pressure at 50 °C to obtain 35.87 g of 5-nitro-2-thiophenesulfonyl fluoride (Compound 9), with a yield of 85%.

[0091] The 1H NMR data of the prepared Compound 9 are as follows: 1H NMR (400 MHz, DMSO-d6): δ 7.03 (1H), 6.58 (1H).

[0092] Second part: Application of fluorinated thiophene compounds in batteries

[0093] 1.1 Preparation of non-aqueous electrolyte:

[0094] In a glove box filled with nitrogen (O2 < 1 ppm, H2O < 1 ppm), 88 g of a mixed solvent obtained by uniformly mixing diethyl carbonate (DEC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) in a mass ratio of 3:2:1 was used as an organic solvent. Then, 0.5 g of the fluorinated thiophene compounds prepared in Examples 1 to 9 was added to obtain a mixed solution. The mixed solution was sealed and packed, placed in a freezer (-4°C) for 2 h, and then taken out. In a glove box filled with nitrogen (O2 < 1 ppm, H2O < 1 ppm), 11.5 g of lithium hexafluorophosphate (LiPF6) was slowly added to the mixed solution. After mixing evenly, non-aqueous electrolytes 1 to 9 were prepared.

[0095] In a glove box filled with nitrogen (O2 < 1 ppm, H2O < 1 ppm), 88 g of a mixed solvent obtained by uniformly mixing diethyl carbonate (DEC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) in a mass ratio of 3:2:1 was used as an organic solvent. Then, 0.5 g of 2-methylthiophene (CAS: 554-14-3) was added to obtain a mixed solution. The mixed solution was sealed and packed, placed in a freezer (-4°C) for 2 h, and then taken out. In a glove box filled with nitrogen (O2 < 1 ppm, H2O < 1 ppm), 11.5 g of lithium hexafluorophosphate (LiPF6) was slowly added to the mixed solution. After mixing evenly, non-aqueous electrolyte 10 was prepared.

[0096] 1.2 Preparation of the positive electrode sheet:

[0097] The ternary material LiNi 0.8 Co 0.1 Mn 0.1 O2, conductive agent SuperP, binder PVDF, and carbon nanotubes (CNT) were mixed evenly in a mass ratio of 96.5:1.5:1:1 to prepare a lithium-ion battery positive electrode paste with a certain viscosity. After coating both sides of the aluminum foil and drying and rolling, a positive electrode sheet was obtained, and a lithium-ion battery positive electrode sheet meeting the requirements was prepared.

[0098] 1.3 Preparation of the negative electrode sheet:

[0099] Artificial graphite, conductive agent SuperP, thickener CMC, and binder SBR (styrene-butadiene rubber latex) were made into a paste in a mass ratio of 95:1.5:1.0:2.5, mixed evenly, and the prepared paste was coated on both sides of the copper foil. After drying and rolling, a negative electrode sheet was obtained, and a lithium-ion battery negative electrode sheet meeting the requirements was prepared.

[0100] 1.4 Preparation of the lithium-ion battery:

[0101] The positive electrode sheet, negative electrode sheet and separator prepared according to the above process are made into lithium-ion batteries through a winding process, vacuum baked at 75 °C for 10 h, and respectively injected with 1-10# non-aqueous electrolyte. After standing for 24 h, it is charged at a constant current of 0.1C (200 mA) to 3.65 V, and then charged at a constant voltage of 3.65 V until the current drops to 0.05C (100 mA); then discharged at 0.2C (400 mA) to 2.5 V, and the charge and discharge are repeated 2 times. Finally, the battery is charged to 3.65 V at 0.1C (200 mA), and lithium-ion batteries 1-10# are manufactured.

[0102] Perform performance tests on lithium-ion batteries 1-10#, and the test results are shown in Table 1. The test conditions are as follows.

[0103] (1) High-temperature cycle test

[0104] Place lithium-ion batteries 1-10# in an environment of 45 °C, charge at a constant current of 0.5C to 4.5 V, then charge at a constant voltage until the current drops to 0.05C, and then discharge at a constant current of 0.5C to 2.0 V. Cycle in this way, record the discharge capacity of the first cycle and the discharge capacity of the last cycle, and calculate the capacity retention rate according to the following formula.

[0105] Capacity retention rate = discharge capacity of the last cycle / discharge capacity of the first cycle × 100%

[0106] (2) High-temperature storage test

[0107] Place lithium-ion batteries 1-10# in an environment of 25 °C, charge at a constant current of 0.5C to 4.5 V, then charge at a constant voltage until the current drops to 0.05C, and then discharge at a constant current of 0.5C to 2.0 V. Record the discharge capacity at this time as C0. Then charge the battery at a constant current of 0.5C to 4.5 V, then charge at a constant voltage until the current drops to 0.05C, and record the thickness of the battery at this time as V0. Then place the battery in a 60 °C constant-temperature oven for 30 d, take out the battery, and the thickness of the battery at this time is V1. Then place the battery in an environment of 25 °C for 2 h, and discharge at a constant current of 0.5C to 2.0 V in an environment of 25 °C. Record the discharge capacity at this time as C1, and then charge at a constant current of 0.5C to 4.5 V, then charge at a constant voltage until the current drops to 0.05C,

[0108] Discharge at a constant current of 0.5C to 2.0 V. Record the discharge capacity at this time as C2.

[0109] Capacity retention rate = C1 / C0 × 100%

[0110] Capacity recovery rate = C2 / C0 × 100%

[0111] Thickness expansion rate = V1 / V0 × 100%

[0112] Table 1 Electrochemical performance test results of each example

[0113]

[0114]

[0115] As can be seen from the results in Table 1, the high-temperature cycle and high-temperature storage performance of lithium-ion batteries 1-9# at high voltages are superior to those of lithium-ion battery 10#. This is because in lithium-ion batteries 1-9#, fluorinated thiophene compounds are used as additives, which are improved on the basis of conventional thiophene compounds by introducing fluorine or fluorosulfonyl groups. The drawbacks of conventional thiophene compounds can be overcome to improve the high-voltage and high-temperature performance of the battery.

[0116] Furthermore, by comparing lithium-ion batteries 1-9#, it can be seen that when the fluorinated thiophene compound is Compound 8, the performance is better. This is because Compound 8 itself contains a thiophene functional group, a fluorosulfonyl group, and a cyano functional group. The fluorosulfonyl group can reduce the polarity of the sulfonyl group, thereby reducing the decomposition of the electrolyte under high-voltage conditions, improving the stability of the electrolyte, and prolonging the cycle life of the battery. At the same time, it can help reduce the side reactions of the electrolyte in the battery by reducing the conductivity, improving the high-voltage performance of the battery. In addition, the cyano functional group participates in the formation of the positive electrode film, can capture the transition metal ions dissolved in the electrode material, and avoid its damage to the battery, thereby improving the high-temperature performance and safety of the battery. In addition, the cyano functional group can also protect the SEI film of the battery negative electrode and prolong the service life of the battery.

[0117] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit the protection scope of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, it is not limited to only those listed in the embodiments. Those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. An electrolyte solution, comprising a non-aqueous organic solvent, an electrolyte salt, and an additive, characterized in that, The additive includes fluorinated thiophene compounds, and the fluorinated thiophene compounds account for 1.0 to 10.0% of the mass of the electrolyte. The structural formula of the fluorinated thiophene compounds is as shown in Formula I. Formula I.

2. The electrolyte according to claim 1, characterized in that, The preparation method of the fluorinated thiophene compounds includes the steps of: (1) Dissolving a fluorination reagent in an organic solvent, and adding a thiophene compound thereto under stirring for a fluorination reaction to obtain a product. The reaction formula of the fluorination reaction is as shown in Formula One; (2) Purifying and refining the product. Formula One.

3. The electrolyte according to claim 2, wherein The fluorination reagent is selected from one or more of KF, AgF, CsF, NaF, bis(2-methoxyethyl)aminosulfur trifluoride, triethylamine trihydrofluoride, and tetrabutylammonium fluoride.

4. The electrolyte according to claim 2, characterized in that, The molar ratio of the fluorination reagent to the thiophene compound is 1 to 10:

1.

5. The electrolyte according to claim 2, wherein The temperature of the fluorination reaction is 20 to 100 °C, and the time is 0.5 to 10.0 h.

6. The electrolyte according to claim 2, characterized in that, The organic solvent is selected from one or more of dichloromethane, dichloroethane, acetonitrile, ethyl acetate, tetrahydrofuran, chloroform, toluene, xylene, n-hexane, and petroleum ether.

7. The electrolyte according to claim 2, characterized in that, The steps of purification and refining include: subjecting the product to suction filtration to remove impurities and concentration to obtain a crude product, and then distilling the crude product at 0 to 50 °C and then distilling at 50 to 120 °C.

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