Electrolyte additive and preparation method thereof, electrolyte and lithium ion battery

Abstract

The invention provides an electrolyte additive and a preparation method thereof, an electrolyte and a lithium ion battery. The electronegativity of S atoms on the electrolyte additive structure is small, the binding energy with lithium ions is small, the desolvation energy of the lithium ions can be reduced, the rate capability of the battery at low temperature is obviously improved, and the cycle life of the battery at low temperature is obviously prolonged. The solubility of the additive can be obviously improved by O atoms on the structure, so that the defect of poor solubility caused by S atoms is overcome. Besides, the additive contains unsaturated bonds, an S-containing compact SEI film can be formed, migration of lithium ions on an electrode / electrolyte interface at low temperature is facilitated, the S-containing SEI film can effectively inhibit generation of lithium dendrites at low temperature, the rate performance of the battery at low temperature is further improved, and the cycle life of the battery at low temperature is further prolonged.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion batteries, and particularly relates to an electrolyte additive, a preparation method thereof, an electrolyte and a lithium-ion battery. Background Art

[0002] Since entering the 21st century, lithium-ion batteries have developed rapidly, and lithium batteries with higher energy density have become the future trend. While pursuing higher energy density lithium-ion batteries, the requirements for safety performance have also become increasingly high.

[0003] A lithium-ion battery consists of a positive electrode, a negative electrode, a separator and an electrolyte. The electrolyte, as the "blood" of the battery and an important carrier for transporting lithium ions inside the battery, realizes the reversible shuttling between the positive electrode and the negative electrode as a medium during the charge and discharge process of the battery. However, the close contact between the electrode (especially the positive electrode) and the electrolyte will trigger a series of side reactions, which is one of the important reasons for the attenuation of battery capacity and the degradation of the structure, thereby affecting the actual use performance of the lithium-ion battery. In particular, the commonly used electrolyte at high voltage / high temperature is prone to oxidation and decomposition, making the formed solid electrolyte interface (SEI) film unstable. By adding a functional film-forming additive to the electrolyte, a stable cathode-electrolyte interface (CEI) film and SEI film can be constructed between the positive electrode / negative electrode and the electrolyte, effectively improving the electrochemical performance of the lithium-ion battery.

[0004] Currently, the mainstream cathode film-forming additives applied to lithium-ion electrolytes can be mainly divided into four types, including inorganic solid additives, electro-oxidative polymerization additives, phosphate additives and fluorinated organic additives. Inorganic solid additives have poor solubility in the electrolyte, which will have a negative impact on the conductivity of the electrolyte and cause problems of uneven dispersion in actual applications; electro-oxidative polymerization additives are prone to self-discharge phenomena. If the addition amount is too small, the electrolyte and the positive electrode cannot be well isolated, and if the addition amount is too large, the impedance will be too high; phosphate additives and fluorinated organic additives have good application prospects because they can form a relatively stable CEI film to isolate the positive electrode material and the electrolyte. However, the existing phosphate additives and fluorinated organic additives have single functions and cannot well take into account the improvement of the cycle performance of lithium-ion batteries. Therefore, there is an urgent need to develop a general-purpose multifunctional film-forming additive. Summary of the Invention

[0005] In view of this, the purpose of the present invention is to provide an electrolyte additive, a preparation method thereof, an electrolyte, and a lithium-ion battery. The S atom in the structure of the electrolyte additive of the present invention has a relatively small electronegativity and a relatively small binding energy with lithium ions, which can reduce the desolvation energy of lithium ions and significantly improve the rate performance and cycle life of the battery at low temperatures. Moreover, the O atom in its structure can significantly improve the solubility of the additive to make up for the defect of poor solubility brought by the S atom. In addition, the additive contains unsaturated bonds, which can form a dense SEI film containing S, facilitating the migration of lithium ions at the electrode / electrolyte interface at low temperatures, and the SEI film containing S can effectively inhibit the generation of lithium dendrites at low temperatures, further improving the rate performance and cycle life of the battery at low temperatures.

[0006] To achieve this purpose, the present invention adopts the following technical solutions: In the first aspect, the present invention provides an electrolyte additive, and its structural formula is as shown in formula (B); Formula (B) wherein, R 1~ R 2 independently selected from H, halogen atoms, nitro (-NO 2 ), trihalomethyl (-CX 3 , X = F, Cl), cyano (-CN), sulfonic acid group (-SO 3 H), formyl group (-CHO).

[0007] Among them, the halogen atom can be F, Cl, Br; preferably F, Cl; Trihalomethyl, -CX 3 , X is selected from F, Cl.

[0008] Preferably, the compound shown in the structural formula (B) is selected from at least one of formulas (1) to (6): .

[0009] In the second aspect, the present invention provides a preparation method of the electrolyte additive, including the following steps: Perform a dehydration condensation reaction on the compound shown in formula (C-1) and the compound shown in formula (C-2) in the presence of a catalyst sodium hydroxide solution to obtain the electrolyte additive; Formula C-1; Formula C-2; wherein, R 1~ R 2 independently selected from H, halogen atoms (-X = F, Cl), nitro (-NO 2 ), trihalomethyl (-CX 3, X = F, Cl), cyano (-CN), sulfonic acid group (-SO 3 H), formyl (-CHO).

[0010] Preferably, the molar ratio of the compound of formula (C-1), the compound of formula (C-2) and sodium hydroxide is 1: (2-4): (2-4); The temperature of the dehydration condensation reaction is 40-80 °C and the time is 3-6 h.

[0011] In a third aspect, the present invention provides an electrolyte, comprising a lithium salt, a solvent, a first electrolyte additive, and a second electrolyte additive; The solvent is a mixed solvent of two or more carbonate solvents or ether solvents, The solvent is selected from any one or more of dimethyl carbonate, ethylene carbonate, propylene carbonate, diethyl carbonate, propyl propionate, and ethylene glycol dimethyl ether.

[0012] Preferably, the solvent includes tetrahydrofuran, tetrahydropyran, and tetrahydrothiophene; The mass ratio of the tetrahydrofuran, tetrahydropyran, and tetrahydrothiophene is (20-60): (10-40): (10-40).

[0013] The first electrolyte additive is independently selected from the electrolyte additives described in any of the above items or the electrolyte additives prepared according to the preparation method described in any of the above items.

[0014] Preferably, the lithium salt is selected from any one or more of lithium hexafluorophosphate, lithium perchlorate, lithium nitrate, lithium tetrafluoroborate, lithium bis(trifluoromethylsulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium bis(oxalato)borate, lithium difluoro(oxalato)borate, or lithium difluorodioxalato phosphate.

[0015] Preferably, the electrolyte further includes a second electrolyte additive; The second electrolyte additive is selected from any one or more of vinylene carbonate, ethylene vinylene carbonate, propylene carbonate, fluoroethylene carbonate, ethylene sulfate, bis(ethylene sulfate), propylene sulfate, 1,3-propane sultone, 1,3-propene sultone, 1,4-butane sultone, 2,4-butane sultone, phenyl methanesulfonate, methylene methanedisulfonate, N-phenylbis(trifluoromethanesulfonyl)imide, triallyl phosphate, triprop-2-ynyl phosphate, tris(trimethylsilyl) phosphate, trimethyl phosphite, ethyl diprop-2-ynyl phosphate, tetramethyl methylenediphosphate, (2-allylphenoxy)trimethylsilane, 1,2-bis(cyanoethoxy)ethane, tris(trimethylsilyl) borate, 1,3,5-triallyl isocyanurate, isocyanatoethyl methacrylate, hexamethylene diisocyanate, p-phenylene diisocyanate or 2,4-toluene diisocyanate.

[0016] Preferably, the mass content of the solvent in the electrolyte is 72-91%, the sum of the first electrolyte additive and the second electrolyte additive accounts for 0.1-2% of the mass of the electrolyte, and the mass content of the lithium salt in the electrolyte is 8-25%.

[0017] In a fourth aspect, the present invention provides a lithium-ion battery, comprising a positive electrode, a negative electrode, a separator and an electrolyte; the electrolyte is the electrolyte according to any one of the above technical solutions.

[0018] Preferably, the active material of the positive electrode is selected from any one of lithium cobaltate, ternary nickel cobalt manganese lithium, lithium nickel manganate, lithium iron phosphate or lithium manganese iron phosphate; The active material of the negative electrode is selected from any one of artificial graphite, natural graphite, lithium titanate, metallic lithium, silicon-carbon composite or silicon monoxide; The separator is selected from a polypropylene separator or a polyethylene separator.

[0019] Preferably, the charge and discharge voltage of the lithium-ion battery is 2.5-3.65 V.

[0020] In the electrolyte additive of the present invention, the S atom in the structure has a relatively small electronegativity and a relatively small binding energy with lithium ions, which can reduce the desolvation energy of lithium ions and significantly improve the rate performance and cycle life of the battery at low temperatures. Moreover, the O atom in its structure can significantly improve the solubility of the additive to make up for the defect of poor solubility brought by the S atom. In addition, the additive contains unsaturated bonds, which can form a dense S-containing SEI film, which is beneficial to the migration of lithium ions at the electrode / electrolyte interface at low temperatures, and the S-containing SEI film can effectively inhibit the generation of lithium dendrites at low temperatures, further improving the rate performance and cycle life of the battery at low temperatures. Detailed Embodiments

[0021] Next, the technical solutions of the present invention will be clearly and completely described in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0022] In this application, "at least one" means one or more, and "a plurality" means two or more. "At least one of the following" or similar expressions refer to any combination of these items, including any combination of single items or plural items.

[0023] It should be understood that in various embodiments of the present application, the magnitudes of the serial numbers of the above processes do not mean the order of execution. Some or all of the steps can be executed in parallel or sequentially. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation to the implementation process of the embodiments of the present application.

[0024] In addition, terms such as "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance.

[0025] The present invention provides an electrolyte additive, and its structural formula is shown as formula (B);

[0026] Formula (B) Wherein, R 1~ R 2 independently selected from H, halogen atoms, nitro (-NO 2 ), trihalomethyl (-CX 3 , X = F, Cl), cyano (-CN), sulfonic acid group (-SO 3 H), formyl (-CHO).

[0027] Among them, the halogen atom can be F, Cl, Br; preferably F, Cl; Trihalomethyl, -CX 3 , X = F, Cl.

[0028] In a specific embodiment, the compound shown in the structural formula (B) is selected from at least one of formulas (1) to (6): .

[0029] The structural formula of the electrolyte additive is shown in Formula (B). The S atom in its structure has a relatively small electronegativity and a relatively small binding energy with lithium ions, which can reduce the desolvation energy of lithium ions and significantly improve the rate performance and cycle life of the battery at low temperatures. Moreover, the O atom in its structure can significantly increase the solubility of the additive to make up for the defect of poor solubility brought by the S atom. In addition, the additive contains unsaturated bonds, which can form a dense S-containing SEI film, facilitating the migration of lithium ions at the electrode / electrolyte interface at low temperatures, and the S-containing SEI film can effectively inhibit the generation of lithium dendrites at low temperatures, further improving the rate performance and cycle life of the battery at low temperatures.

[0030] The present invention provides a preparation method of the electrolyte additive, including the following steps: The compound shown in Formula (C-1) and the compound shown in Formula (C-2) are subjected to a dehydration condensation reaction in the presence of a catalyst sodium hydroxide solution to obtain the electrolyte additive; Formula C-1; Formula C-2; Among them, R 1~ R 2 independently selected from H, halogen atoms (-X = F, Cl), nitro (-NO 2 ), trihalomethyl (-CX 3 , X = F, Cl), cyano (-CN), sulfonic acid group (-SO 3 H), formyl group (-CHO).

[0031] The reaction formula is as follows:

[0032] According to the present invention, the molar ratio of the compound shown in Formula (C-1), the compound shown in Formula (C-2) and sodium hydroxide is 1:(2-4):(2-4).

[0033] In some embodiments, the molar ratio of the compound shown in Formula (C-1), the compound shown in Formula (C-2) and sodium hydroxide is 1:(1-4):(2-4).

[0034] The present invention preferably uses NaOH to adjust the pH to 9.

[0035] The dehydration condensation reaction is a two-step heating reaction. The temperature of the first step is 60-80 °C and the time is 5-8 h; the temperature of the second step is 80 °C and the time is 6-8 h.

[0036] In some embodiments, the temperature of the dehydration condensation reaction is 50-80 °C and the time is 4-6 h.

[0037] In some embodiments, the temperature of the dehydration condensation reaction is 60~80°C, and the time is 5~6h.

[0038] The preparation method of the above electrolyte additive provided by the present invention is simple, does not require expensive instruments and equipment, and is easy to implement.

[0039] The present invention also provides an electrolyte, which includes a lithium salt, a solvent, a first electrolyte additive, and a second electrolyte additive.

[0040] The first electrolyte additive is independently selected from the electrolyte additives described in any one of the above technical solutions or the electrolyte additives prepared according to the preparation method described in any one of the above technical solutions.

[0041] Among them, the lithium salt is selected from any one or more of lithium hexafluorophosphate, lithium perchlorate, lithium nitrate, lithium tetrafluoroborate, lithium bis(trifluoromethylsulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium bis(oxalato)borate, lithium difluoro(oxalato)borate, or lithium difluoro(dioxalato)phosphate.

[0042] Preferably, the lithium salt is selected from any two or more of lithium hexafluorophosphate, lithium perchlorate, lithium nitrate, lithium tetrafluoroborate, lithium bis(trifluoromethylsulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium bis(oxalato)borate, lithium difluoro(oxalato)borate, or lithium difluoro(dioxalato)phosphate; more preferably, it is lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide.

[0043] In the embodiments of the present invention, it can be a mixed lithium salt of lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide mixed in a mass percentage of 3.0% and 8.0%; it can be a mixed lithium salt of lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide mixed in a mass percentage of 5.0% and 5.0%; it can be lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide mixed in a mass percentage of 3.0% and 15.0%.

[0044] The electrolyte further includes a second electrolyte additive; the second electrolyte additive is selected from any one or more of vinylene carbonate, ethylene vinylene carbonate, fluoroethylene carbonate, ethylene sulfate, bis(ethylene sulfate), propylene sulfate, 1,3-propane sultone, 1,3-propene sultone, 1,4-butane sultone, 2,4-butane sultone, phenyl methanesulfonate, methylene methanedisulfonate, N-phenylbis(trifluoromethanesulfonyl)imide, triallyl phosphate, tripropargyl phosphate, tris(trimethylsilyl) phosphate, trimethyl phosphite, ethyl diprop-2-ynyl phosphate, tetramethyl methylenediphosphate, (2-allylphenoxy)trimethylsilane, 1,2-bis(cyanoethoxy)ethane, tris(trimethylsilyl) borate, 1,3,5-triallyl isocyanurate, isocyanatoethyl methacrylate, hexamethylene diisocyanate, p-phenylene diisocyanate, or 2,4-toluene diisocyanate.

[0045] In some embodiments of the present invention, the mass percentage of the lithium salt in the electrolyte is 8% to 25%; preferably 9% to 23%; more preferably 10% to 20%.

[0046] The mass content of the solvent in the electrolyte is 72 to 91%, preferably 75% to 90%; more preferably 77% to 89%.

[0047] In some embodiments of the present invention, the sum of the first electrolyte additive and the second electrolyte additive accounts for 0.1% to 2% of the mass of the electrolyte; preferably 0.5% to 2%.

[0048] In some embodiments of the present invention, during the preparation of the electrolyte, it is preferably carried out in an argon glove box. It is only necessary to mix the organic solvent, lithium salt and electrolyte additive evenly. More preferably, it is carried out in an argon glove box with a water and oxygen content of ≤0.1 ppm. The specific steps are as follows: In a glove box filled with argon (moisture content <0.1 ppm), stir the solvent and then put it into a refrigerator at -20°C for 30 minutes. Add the formulated amount of the first electrolyte additive, then add the electrolyte salt. After stirring until completely dissolved, add the second additive and stir for 10 to 15 minutes to obtain the low-temperature electrolyte.

[0049] The solvent of the present invention is a mixed solvent of two or more carbonate solvents or ether solvents, and the solvent is selected from any one or more of dimethyl carbonate, ethylene carbonate, propylene carbonate, diethyl carbonate, propyl propionate, and ethylene glycol dimethyl ether.

[0050] The solvent of the present invention may further include tetrahydrofuran, tetrahydropyran, and tetrahydrothiophene; The mass ratio of the tetrahydrofuran, tetrahydropyran, and tetrahydrothiophene is (20 to 60):(10 to 40):(10 to 40).

[0051] Through quantum chemical calculations, when the mixture of tetrahydrofuran + tetrahydropyran + tetrahydrothiophene of the present invention is used as a solvent, its desolvation energy is low, and there is no relevant report and exploration of this mixed solvent in the prior art. Further, after adding an ester group structure to the above mixed solvent, the desolvation energy can be reduced again and the solubility of the lithium salt can be increased.

[0052] The present invention also provides a lithium-ion battery, which includes a positive electrode, a negative electrode, a separator, and the electrolyte involved in the above technical solution. Among them, the material of the positive electrode is selected from any one of lithium cobaltate, ternary nickel cobalt manganese lithium, lithium nickel manganate, lithium iron phosphate, or lithium manganese iron phosphate. The present invention preferably selects lithium iron phosphate; the active material of the negative electrode is preferably selected from any one of artificial graphite, natural graphite, lithium titanate, metallic lithium, silicon-carbon composite material, or silicon monoxide. The present invention preferably selects artificial graphite. The separator is selected from one of polypropylene separator or polyethylene separator. The present invention preferably selects polyethylene separator.

[0053] The lithium-ion battery made of the electrolyte of the present invention has a charge-discharge voltage of 2.5~3.65 V; significantly improves the rate performance and cycle life of the battery at low temperature.

[0054] In some embodiments, the preparation of the positive electrode: Add the positive electrode active material LiFePO 4 , conductive agent carbon black, and binder polyvinylidene fluoride (PVDF) to the solvent N-methylpyrrolidone. The mass ratio of the positive electrode active material LiFePO 4 , conductive agent carbon black, and binder polyvinylidene fluoride (PVDF) is 90:5:5. Mix evenly to obtain the positive electrode slurry; uniformly coat the positive electrode slurry on the positive electrode current collector Al foil with a thickness of 13 μm, dry and roll it to obtain the positive electrode; The preparation of the negative electrode: Add the negative electrode active material artificial graphite, conductive agent carbon black, thickening agent sodium carboxymethyl cellulose (CMC), and binder SBR (styrene-butadiene rubber) to the solvent deionized water. The mass ratio of the negative electrode active material artificial graphite, conductive agent carbon black, thickening agent CMC, and binder SBR is 90:4:3:3. Mix evenly to obtain the negative electrode slurry; uniformly coat the negative electrode slurry on the negative electrode current collector Cu foil with a thickness of 8 μm, dry and roll it to obtain the negative electrode; Cell assembly: Stack the positive electrode, separator, and negative electrode to form a cell assembly, and install it in the shell; Injection of the electrolyte: Inject the above low-temperature electrolyte into the battery shell to obtain the low-temperature lithium-ion battery.

[0055] In order to further illustrate the present invention, the following detailed description is provided through the following examples. For those conditions not specified in the following examples of the present invention, they can be carried out according to conventional conditions or conditions recommended by the manufacturer. For reagents or instruments whose manufacturers are not specified, they are all conventional products that can be obtained through commercial channels.

[0056] Example 1 Synthesis of additives Take 5 g of Formula C-1.1 and add it to a flask equipped with a condenser. Then add Formula C-2.1 and sodium hydroxide (the molar ratio of C-1.1, C-2.1 and sodium hydroxide is 1:1.2:2), heat at 80 °C for 5 h, continuously discharge water vapor during this period. After the reaction is completed, pour the product into a separatory funnel for liquid separation, take out the product layer, and then use column chromatography for purification. The eluent is dichloromethane. After purification, rotary evaporate to remove the solvent to obtain the pure product of Formula (1) with a yield of 92.8%.

[0057] Formula C-1.1 Formula C-2.1 Analyze the product obtained in Example 1 by mass spectrometry, and the result is HRMS (ESI): calcd. for C 11 H 14 O 3 S, 226.07, found 226.65。

[0058] The low-temperature electrolyte for lithium-ion batteries in this example is composed of an organic solvent, an electrolyte salt, and an additive. The mass percentages of the mixed lithium salts of lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide in the low-temperature electrolyte are 3.0% and 8.0% respectively, and the mass percentage of the additive in the low-temperature electrolyte is 0.8%. The balance is a mixed solvent; the mixed solvent is a mixture of dimethyl carbonate and ethylene carbonate with a volume ratio of 2:1; The additive is a mixture of Formula (1) and fluoroethylene carbonate with a mass ratio of 3:5.

[0059] Formula (1) The preparation method of the low-temperature electrolyte for lithium-ion batteries in this example is as follows: In a glove box filled with argon (moisture content < 0.1 ppm), take the mixed solvent, stir for 15 min, then put it in a refrigerator at -20 °C to cool for 30 minutes. Add the formulated amounts of lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide electrolyte salts. After the electrolyte salts are completely dissolved, add the formulated amounts of Formula (1) and fluoroethylene carbonate to the system, and stir for another 15 min to obtain the low-temperature electrolyte.

[0060] The low-temperature lithium-ion battery in this example includes a positive electrode, a negative electrode, a separator, and an electrolyte. The electrolyte is the above-mentioned low-temperature electrolyte; the positive electrode active material used for the positive electrode is LiFePO 4 ; the negative electrode active material used for the negative electrode is artificial graphite.

[0061] The preparation method of the low-temperature lithium-ion battery in this example is as follows: Preparation of the positive electrode: Add the positive electrode active material LiFePO to the solvent N-methylpyrrolidone4 , the conductive agent carbon black and the binder polyvinylidene fluoride (PVDF), the positive electrode active material LiFePO 4 , the mass ratio of the conductive agent carbon black to the binder polyvinylidene fluoride (PVDF) is 90:5:5, and they are mixed evenly to obtain the positive electrode slurry; the positive electrode slurry is evenly coated on the positive electrode current collector Al foil with a thickness of 13 μm, dried and then roll-pressed to obtain the positive electrode; Preparation of the negative electrode: Add the negative electrode active material artificial graphite, the conductive agent carbon black, the thickener sodium carboxymethyl cellulose (CMC) and the binder SBR (styrene-butadiene rubber) to the solvent deionized water. The mass ratio of the negative electrode active material artificial graphite, the conductive agent carbon black, the thickener CMC and the binder SBR is 90:4:3:3, and they are mixed evenly to obtain the negative electrode slurry; the negative electrode slurry is evenly coated on the negative electrode current collector Cu foil with a thickness of 8 μm, dried and then roll-pressed to obtain the negative electrode; Cell assembly: Stack the positive electrode, separator and negative electrode to form a cell assembly, and install it in the shell; Injection of the electrolyte: Inject the above-mentioned low-temperature electrolyte into the battery shell to obtain the low-temperature lithium-ion battery.

[0062] Example 2 Synthesis of the additive Take 5 g of formula C-1.1 and add it to a flask equipped with a condenser, then add formula C-2.2 and sodium hydroxide (the molar ratio of C-1.1, C-2.2 and sodium hydroxide is 1:1.3:2), heat at 70 °C for 6 h, continuously discharge water vapor during this period, after the reaction is completed, pour the product into a separating funnel for liquid separation, take out the product layer, and then use column chromatography for purification. The eluent is dichloromethane. After purification, rotary evaporate to remove the solvent to obtain the pure product of formula (2) with a yield of 90.6%.

[0063] Formula C-1.1; Formula C-2.2; Use mass spectrometry to analyze the product of formula (2) obtained in Example 1, and the result is HRMS (ESI): calcd.for C 10 H 11 ClO 3 S, 246.71, found 246.87。

[0064] Formula (2).

[0065] Except that formula (1) is replaced by formula (2), the low-temperature electrolyte for the lithium-ion battery in this example is the same as that in Example 1.

[0066] The low-temperature lithium-ion battery of this embodiment includes a positive electrode, a negative electrode, a separator, and an electrolyte. The electrolyte is the above-mentioned low-temperature electrolyte; the rest is the same as in Embodiment 1.

[0067] Embodiment 3 Take 5 g of Formula C-1.1 and add it to a flask equipped with a condenser. Then add Formula C-2.3 and sodium hydroxide (the molar ratio of C-1.1, C-2.3, and sodium hydroxide is 1:1.4:2), and heat at 60 °C for 7 h. During this period, water vapor is continuously discharged. After the reaction is completed, pour the product into a separatory funnel for liquid separation, take out the product layer, and then use column chromatography for purification. The eluent is dichloromethane. After purification, rotary evaporate to remove the solvent to obtain the pure product Formula (3) with a yield of 93.2%.

[0068] Formula C-1.1 Formula C-2.3 Use mass spectrometry to analyze the product Formula (3) obtained in Embodiment 1, and the result is HRMS (ESI): calcd.for C 10 H 11 FO 3 S, 230.26, found 230.41.

[0069] Formula (3).

[0070] The low-temperature electrolyte for the lithium-ion battery of this embodiment is the same as that of Embodiment 1 except that Formula (1) is replaced by Formula (3).

[0071] The low-temperature lithium-ion battery of this embodiment includes a positive electrode, a negative electrode, a separator, and an electrolyte. The electrolyte is the above-mentioned low-temperature electrolyte; the rest is the same as in Embodiment 1.

[0072] Embodiment 4 Take 5 g of Formula C-1.2 and add it to a flask equipped with a condenser. Then add Formula C-2.4 and sodium hydroxide (the molar ratio of C-1.2, C-2.4, and sodium hydroxide is 1:1.5:2), and heat at 80 °C for 8 h. During this period, water vapor is continuously discharged. After the reaction is completed, pour the product into a separatory funnel for liquid separation, take out the product layer, and then use column chromatography for purification. The eluent is dichloromethane. After purification, rotary evaporate to remove the solvent to obtain the pure product Formula (4) with a yield of 91.0%.

[0073] Formula C-1.2 Formula C-2.4 Use mass spectrometry to analyze the product Formula (3) obtained in Embodiment 1, and the result is HRMS (ESI): calcd.for C 10 H 8 F3 NO 5 S, 311.23, found 311.56。

[0074] Formula (4).

[0075] Except for replacing Formula (1) with Formula (4), the low-temperature electrolyte for lithium-ion batteries in this embodiment is the same as that in Embodiment 1 for the rest.

[0076] The low-temperature lithium-ion battery in this embodiment includes a positive electrode, a negative electrode, a separator, and an electrolyte, and the electrolyte is the above-mentioned low-temperature electrolyte; the rest is the same as that in Embodiment 1.

[0077] Embodiment 5 Take 5 g of Formula C-1.3 and add it to a flask equipped with a condenser tube. Then add Formula C-2.3 and sodium hydroxide (the molar ratio of C-1.3, C-2.3, and sodium hydroxide is 1:1.2:2), heat at 70 °C for 5 h, continuously discharge water vapor during this period. After the reaction is completed, pour the product into a separating funnel for liquid separation, take out the product layer, and then use column chromatography for purification. The eluent is dichloromethane. After purification, rotary evaporate to remove the solvent to obtain the pure product Formula (5) with a yield of 93.4%.

[0078] Formula C-1.3 Formula C-2.3 Use mass spectrometry to analyze the product Formula (5) obtained in Embodiment 1, and the result is HRMS (ESI): calcd.for C 10 H 8 FNO 3 S, 241.24, found 241.29。

[0079] Formula (5).

[0080] Except for replacing Formula (1) with Formula (5), the low-temperature electrolyte for lithium-ion batteries in this embodiment is the same as that in Embodiment 1 for the rest.

[0081] The low-temperature lithium-ion battery in this embodiment includes a positive electrode, a negative electrode, a separator, and an electrolyte, and the electrolyte is the above-mentioned low-temperature electrolyte; the rest is the same as that in Embodiment 1.

[0082] Embodiment 6 Take 5 g of Formula C-1.3 and add it to a flask equipped with a condenser. Then add Formula C-2.1 and sodium hydroxide (the molar ratio of C-1.3, C-2.1 and sodium hydroxide is 1:1.2:2.4), heat at 60 °C for 6 h, continuously discharge water vapor during this period. After the reaction is completed, pour the product into a separatory funnel for liquid separation, take out the product layer, and then purify it by column chromatography. The eluent is dichloromethane. After purification, rotary evaporate to remove the solvent to obtain the pure product of Formula (6) with a yield of 90.9%.

[0083] Formula C-1.3 Formula C-2.1 Analyze the product of Formula (6) obtained in Example 1 by mass spectrometry, and the result is HRMS (ESI): calcd.for C 10 H 9 NO 3 S, 223.25, found 223.49。

[0084] Formula (6).

[0085] Except for replacing Formula (1) with Formula (6), the low-temperature electrolyte for lithium-ion batteries in this example is the same as that in Example 1.

[0086] The low-temperature lithium-ion battery in this example includes a positive electrode, a negative electrode, a separator and an electrolyte. The electrolyte is the above-mentioned low-temperature electrolyte; the rest is the same as that in Example 1.

[0087] Example 7 Take 5 g of Formula C-1.1 and add it to a flask equipped with a condenser. Then add Formula C-2.1 and sodium hydroxide (the molar ratio of C-1.1, C-2.1 and sodium hydroxide is 1:1.2:2.6), heat at 70 °C for 7 h, continuously discharge water vapor during this period. After the reaction is completed, pour the product into a separatory funnel for liquid separation, take out the product layer, and then purify it by column chromatography. The eluent is dichloromethane. After purification, rotary evaporate to remove the solvent to obtain the pure product of Formula (1) with a yield of 91.5%.

[0088] Formula C-1.1 Formula C-2.1 Analyze the product obtained in Example 1 by mass spectrometry, and the result is HRMS (ESI): calcd. forC 11 H 14 O 3 S, 226.07, found 226.65。

[0089] The low-temperature electrolyte for lithium-ion batteries in this example is the same as that in Example 1.

[0090] The low-temperature lithium-ion battery of this embodiment includes a positive electrode, a negative electrode, a separator, and an electrolyte. The electrolyte is the above-mentioned low-temperature electrolyte; the rest is the same as in Embodiment 1.

[0091] Embodiment 8 Take 5 g of Formula C-1.1 and add it to a flask equipped with a condenser. Then add Formula C-2.1 and sodium hydroxide (the molar ratio of C-1.1, C-2.1, and sodium hydroxide is 1:1.2:2.8), and heat at 60 °C for 8 h. During this period, water vapor is continuously discharged. After the reaction is completed, pour the product into a separatory funnel for liquid separation, take out the product layer, and then use column chromatography for purification. The eluent is dichloromethane. After purification, rotary evaporate to remove the solvent, and a pure product of Formula (1) is obtained after purification, with a yield of 90.3%.

[0092] Formula C-1.1 Formula C-2.1 The product obtained in Embodiment 1 was analyzed by mass spectrometry, and the results were HRMS (ESI): calcd. for C 11 H 14 O 3 S, 226.07, found 226.65.

[0093] The low-temperature electrolyte for the lithium-ion battery of this embodiment is the same as that in Embodiment 1.

[0094] The low-temperature lithium-ion battery of this embodiment includes a positive electrode, a negative electrode, a separator, and an electrolyte. The electrolyte is the above-mentioned low-temperature electrolyte; the rest is the same as in Embodiment 1.

[0095] Table 1 is a statistical table of the process parameters of Embodiments 1 to 8 of the present invention.

[0096] Table 1

[0097] Comparative Example 1 An additive of Formula D-1 was added to the electrolyte of this comparative example, and its mass ratio accounted for 0.5% of the total amount of the electrolyte. The structural formula of D-1 is as follows:

[0098] Formula D-1 The usage amounts of LiPF 6 , ethylene carbonate, propylene carbonate, diethyl carbonate, and propyl propionate in the electrolyte are 15.42%, 21.79%, 9.89%, 22.40%, and 30.50% of the total mass of the electrolyte, respectively. The experimenters found through orthogonal experiments that the electrochemical performance of the electrolyte under this ratio is optimal in the following battery systems.

[0099] In a glove box filled with argon (moisture content < 0.1 ppm), take the formulated amounts of ethylene carbonate, propylene carbonate, diethyl carbonate, and propyl propionate, stir for 15 min, then place them in a refrigerator at -20 °C to cool for 30 minutes, and add the formulated amount of LiPF 6 After complete dissolution, add the formulated amount of D-1 to the system and stir for another 15 min to obtain the low-temperature electrolyte.

[0100] The preparation method of the low-temperature lithium-ion battery in this comparative example is as follows: Preparation of the positive electrode: Add the positive electrode active material LiFePO to the solvent N-methylpyrrolidone 4 , conductive agent carbon black, and binder polyvinylidene fluoride (PVDF). The mass ratio of the positive electrode active material LiFePO 4 , conductive agent carbon black, and binder polyvinylidene fluoride (PVDF) is 90:5:5. Mix them evenly to obtain the positive electrode slurry; uniformly coat the positive electrode slurry on the positive electrode current collector Al foil with a thickness of 13 μm, dry it, and roll it to obtain the positive electrode; Preparation of the negative electrode: Add the negative electrode active material artificial graphite, conductive agent carbon black, thickening agent sodium carboxymethyl cellulose (CMC), and binder SBR (styrene-butadiene rubber) to the solvent deionized water. The mass ratio of the negative electrode active material artificial graphite, conductive agent carbon black, thickening agent CMC, and binder SBR is 90:4:3:3. Mix them evenly to obtain the negative electrode slurry; uniformly coat the negative electrode slurry on the negative electrode current collector Cu foil with a thickness of 8 μm, dry it, and roll it to obtain the negative electrode; Cell assembly: Stack the positive electrode, separator, and negative electrode to form a cell assembly, and place it in the shell; Injection of the electrolyte: Inject the above-mentioned low-temperature electrolyte into the battery shell to obtain the low-temperature lithium-ion battery.

[0101] Prepare the experimental comparative example 1 battery according to the method of reference example 1.

[0102] Comparative example 2 Add additive D-2 to the electrolyte in this comparative example, and its mass ratio accounts for 0.5% of the total amount of the electrolyte. The structural formula of D-2 is as follows:

[0103] Formula D-2 In the electrolyte, the volume ratio of the solvent ethylene glycol dimethyl ether to additive D-2 is 4.5:1, and 0.75 mol of lithium bis(fluorosulfonyl)imide (LiFSI) and 5% mass ratio of lithium nitrate are dissolved. The experimenters found through orthogonal experiments that the electrolyte under this ratio shows the best electrochemical performance in the following battery systems.

[0104] In a glove box filled with argon (moisture content < 0.1 ppm), take the formulated amount of ethylene glycol dimethyl ether, stir for 15 min, then place it in a refrigerator at -20 °C to cool for 30 minutes. After adding the formulated amount of lithium nitrate and dissolving it completely, add the formulated amount of D-2 to the system and stir for another 15 min to obtain the low-temperature electrolyte.

[0105] The preparation method of the low-temperature lithium-ion battery in this comparative example is as follows: Preparation of the positive electrode: Add the positive electrode active material LiFePO to the solvent N-methylpyrrolidone 4 , conductive agent carbon black, and binder polyvinylidene fluoride (PVDF). The mass ratio of the positive electrode active material LiFePO 4 , conductive agent carbon black, and binder polyvinylidene fluoride (PVDF) is 90:5:5. Mix them evenly to obtain the positive electrode slurry; uniformly coat the positive electrode slurry on the positive electrode current collector Al foil with a thickness of 13 μm, dry it, and roll it to obtain the positive electrode; Preparation of the negative electrode: Add the negative electrode active material artificial graphite, conductive agent carbon black, thickening agent sodium carboxymethyl cellulose (CMC), and binder SBR (styrene-butadiene rubber) to the solvent deionized water. The mass ratio of the negative electrode active material artificial graphite, conductive agent carbon black, thickening agent CMC, and binder SBR is 90:4:3:3. Mix them evenly to obtain the negative electrode slurry; uniformly coat the negative electrode slurry on the negative electrode current collector Cu foil with a thickness of 8 μm, dry it, and roll it to obtain the negative electrode; Cell assembly: Stack the positive electrode, separator, and negative electrode to form a cell assembly, and place it in the shell; Injection of the electrolyte: Inject the above-mentioned low-temperature electrolyte into the battery shell to obtain the low-temperature lithium-ion battery.

[0106] The electrochemical performances of the low-temperature lithium-ion batteries prepared in Examples 1 to 8 and the comparative example at -20 °C are shown in Table 2. Table 2 is the electrochemical performance table of the low-temperature lithium-ion batteries prepared in Examples 1 to 8 and the comparative example at -20 °C: Table 2

[0107] As can be seen from the above table, the low-temperature electrochemical performances of Examples 1 to 8 are all better than those of Comparative Examples 1 and 2. Since the additives in the examples all have an ester group structure, the solubility of the additives can be effectively improved, thereby increasing the upper limit of the addition amount. The S atom in its structure has a relatively small electronegativity and a relatively small binding energy with lithium ions, which can reduce the desolvation energy of lithium ions and significantly improve the rate performance and cycle life of the battery at low temperature; and the examples use cyclic ether solvents with low desolvation energy, while Comparative Example 1 uses ester solvents that are difficult to desolvate, which is not conducive to the low-temperature cycle performance. The additives in the examples have an S atom in their structure with a relatively small electronegativity and a relatively small binding energy with lithium ions, which can reduce the desolvation energy of lithium ions and significantly improve the rate performance and cycle life of the battery at low temperature; and a mixed cyclic ether solvent with low desolvation energy is used in the examples, including tetrahydrothiophene, and the S-containing solvent is more easily desolvated. However, Comparative Example 2 uses a single ethylene glycol dimethyl ether that is difficult to desolvate as the solvent, and its reducibility resistance is poor, which is not conducive to the low-temperature cycle performance. Therefore, the low-temperature electrochemical performances of Examples 1 to 8 are all better than those of Comparative Examples 1 and 2.

[0108] Through quantum chemical calculations, we found that when tetrahydrofuran + tetrahydropyran + tetrahydrothiophene are mixed as solvents, their desolvation energy is low, and there is no relevant report in the prior art to explore this mixed solvent. Further, after adding an ester group structure to the above mixed solvent, the desolvation energy can be reduced again and the solubility of lithium salts can be increased. Compared with most current low-temperature electrolytes that improve low-temperature performance by forming a SEI film through additives, reducing the desolvation energy is a more effective method. The following are related examples.

[0109] Example 9 The low-temperature electrolyte for lithium-ion batteries in this example is composed of a weakly solvating solvent, an electrolyte salt, and an additive. The mass percentages of the mixed lithium salts of lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide in the low-temperature electrolyte are 3.0% and 8.0% respectively, and the mass percentage of the additive in the low-temperature electrolyte is 0.8%, and the balance is an organic solvent; The weakly solvating solvent is composed of the following components in volume percentages: 58.2% of tetrahydrofuran, 20% of tetrahydropyran, and 10% of tetrahydrothiophene; The additive is a mixture of the compound of formula (1) and fluoroethylene carbonate with a mass ratio of 3:5.

[0110] Formula (1) The preparation method of the low-temperature electrolyte for lithium-ion batteries in this example is as follows: In a glove box filled with argon (moisture content < 0.1 ppm), take the formulated amount of tetrahydrofuran + tetrahydropyran + tetrahydrothiophene and mix them. After stirring for 15 minutes, place the mixture in a refrigerator at -20°C to cool for 30 minutes. Then add the formulated amount of electrolyte salts lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide. After the electrolyte salts are completely dissolved, add the formulated amount of formula (1) and fluoroethylene carbonate to the system, and stir for another 15 minutes to obtain the low-temperature electrolyte.

[0111] The lithium-ion battery of this example includes a positive electrode, a negative electrode, a separator, and an electrolyte. The electrolyte is the above-mentioned low-temperature electrolyte; the positive electrode active material used for the positive electrode is LiFePO 4 ; the negative electrode active material used for the negative electrode is artificial graphite.

[0112] The preparation method of the low-temperature lithium-ion battery of this example is as follows: Preparation of the positive electrode: Add the positive electrode active material LiFePO to the solvent N-methylpyrrolidone 4 , conductive agent carbon black, and binder polyvinylidene fluoride (PVDF). The mass ratio of the positive electrode active material LiFePO 4 , conductive agent carbon black to binder polyvinylidene fluoride (PVDF) is 90:5:5. Mix them evenly to obtain the positive electrode slurry; evenly coat the positive electrode slurry on a positive electrode current collector Al foil with a thickness of 13 μm, dry it, and roll it to obtain the positive electrode; Preparation of the negative electrode: Add the negative electrode active material artificial graphite, conductive agent carbon black, thickening agent sodium carboxymethyl cellulose (CMC), and binder SBR (styrene-butadiene rubber) to the solvent deionized water. The mass ratio of the negative electrode active material artificial graphite, conductive agent carbon black, thickening agent CMC, and binder SBR is 90:4:3:3. Mix them evenly to obtain the negative electrode slurry; evenly coat the negative electrode slurry on a negative electrode current collector Cu foil with a thickness of 8 μm, dry it, and roll it to obtain the negative electrode; Cell assembly: Stack the positive electrode, separator, and negative electrode to form a cell assembly, and place it in a shell; Injection of the electrolyte: Inject the above-mentioned low-temperature electrolyte into the battery shell to obtain the low-temperature lithium-ion battery.

[0113] Example 10 Synthesis of additives The low-temperature electrolyte for the lithium-ion battery of this example is composed of an organic solvent, an electrolyte salt, and an additive. The mass percentages of the mixed lithium salts of electrolyte salts lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide in the low-temperature electrolyte are 5.0% and 5.0% respectively, and the mass percentage of the additive in the low-temperature electrolyte is 3.0%. The balance is an organic solvent; The organic solvent consists of the following components in volume percentages: tetrahydrofuran 50%, tetrahydropyran ester 10%, tetrahydrothiophene 27%; The additive is a mixture with a mass ratio of the compound of formula (2) to fluoroethylene carbonate of 2:1.

[0114] Formula (2); The preparation method of the low-temperature electrolyte for the lithium-ion battery in this example is the same as that in Example 9.

[0115] The low-temperature lithium-ion battery in this example includes a positive electrode, a negative electrode, a separator, and an electrolyte. The electrolyte is the above-mentioned low-temperature electrolyte; the rest is the same as in Example 9.

[0116] Example 11 The low-temperature electrolyte for the lithium-ion battery in this example is composed of an organic solvent, an electrolyte salt, and an additive. The concentrations of the mixed lithium salts of lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide in the low-temperature electrolyte are 3.0% and 15.0% respectively, and the mass percentage of the additive in the low-temperature electrolyte is 1%. The balance is the organic solvent; The organic solvent consists of the following components in volume percentages: 40% of tetrahydrofuran, 10% of tetrahydropyran, and 31% of tetrahydrothiophene; The additive is a mixture with a mass ratio of the compound of formula (3) to fluoroethylene carbonate of 1:1.

[0117] Formula (3); The preparation method of the electrolyte for the lithium-ion battery in this example is the same as that in Example 9.

[0118] The low-temperature lithium-ion battery in this example includes a positive electrode, a negative electrode, a separator, and an electrolyte. The electrolyte is the above-mentioned low-temperature electrolyte; the rest is the same as in Example 9.

[0119] Example 12 The low-temperature electrolyte for the lithium-ion battery in this example is composed of an organic solvent, an electrolyte salt, and an additive. The concentrations of the mixed lithium salts of lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide in the low-temperature electrolyte are 7.0% and 7.0% respectively, and the mass percentage of the additive in the low-temperature electrolyte is 2%. The balance is the organic solvent; The organic solvent consists of the following components in volume percentages: 55% of tetrahydrofuran, 13% of tetrahydropyran, and 16% of tetrahydrothiophene; The additive is a mixture with a mass ratio of the compound of formula (4) to 1,4-butanesultone of 1:1.

[0120] Formula (4); The preparation method of the electrolyte for the lithium-ion battery in this example is the same as that in Example 9.

[0121] The low-temperature lithium-ion battery of this embodiment includes a positive electrode, a negative electrode, a separator, and an electrolyte. The electrolyte is the above-mentioned low-temperature electrolyte; the rest is the same as in Embodiment 9.

[0122] Embodiment 13 The low-temperature electrolyte for a lithium-ion battery of this embodiment is composed of an organic solvent, an electrolyte salt, and an additive. The concentrations of the mixed lithium salts of lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide as the electrolyte salt in the low-temperature electrolyte are 5.0% and 11.0% respectively, and the mass percentage of the additive in the low-temperature electrolyte is 3%. The balance is the organic solvent; The organic solvent is composed of the following components by volume percentage: 30% tetrahydrofuran, 30% tetrahydropyran, and 21% tetrahydrothiophene; The additive is a mixture of the compound of formula (5) and 1,4-butanesultone with a mass ratio of 2:1.

[0123] Formula (5) The preparation method of the electrolyte for a lithium-ion battery of this embodiment is the same as that of Embodiment 9.

[0124] The low-temperature lithium-ion battery of this embodiment includes a positive electrode, a negative electrode, a separator, and an electrolyte. The electrolyte is the above-mentioned low-temperature electrolyte; the rest is the same as in Embodiment 9.

[0125] Embodiment 14 The low-temperature electrolyte for a lithium-ion battery of this embodiment is composed of an organic solvent, an electrolyte salt, and an additive. The concentrations of the mixed lithium salts of lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide as the electrolyte salt in the low-temperature electrolyte are 10.0% and 2.0% respectively, and the mass percentage of the additive in the low-temperature electrolyte is 1.5%. The balance is the organic solvent; The organic solvent is composed of the following components by volume percentage: 60% tetrahydrofuran, 10.5% tetrahydropyran, and 16% tetrahydrothiophene; The additive is a mixture of the compound of formula (6) and 1,4-butanesultone with a mass ratio of 2:1.

[0126] Formula (6) The preparation method of the electrolyte for a lithium-ion battery of this embodiment is the same as that of Embodiment 9.

[0127] The low-temperature lithium-ion battery of this embodiment includes a positive electrode, a negative electrode, a separator, and an electrolyte. The electrolyte is the above-mentioned low-temperature electrolyte; the rest is the same as in Embodiment 9.

[0128] Table 3 is a comparison table of the electrochemical performance of the low-temperature lithium-ion batteries prepared in Embodiments 9 to 14 and the comparative example at -20 °C: Table 3

[0129] The additives in Examples 9 to 14 have an ester group structure, which can effectively improve the solubility of the additives, thereby increasing the upper limit of the addition amount. The S atom in its structure has a relatively small electronegativity and a relatively small binding energy with lithium ions, which can reduce the desolvation energy of lithium ions and significantly improve the rate performance and cycle life of the battery at low temperatures. Moreover, a mixed solvent with a lower desolvation energy is used in Example 9, while a difficult-to-desolvate ester solvent is used in Comparative Example 1, which is not conducive to the low-temperature cycle performance.

[0130] The additives in Examples 9 to 14 have an S atom in their structure with a relatively small electronegativity and a relatively small binding energy with lithium ions, which can reduce the desolvation energy of lithium ions and significantly improve the rate performance and cycle life of the battery at low temperatures. Moreover, a mixed cyclic ether solvent with a lower desolvation energy, including tetrahydrothiophene, is used in Examples 9 to 14. The S-containing solvent is more easily desolvated. However, a single difficult-to-desolvate ethylene glycol dimethyl ether is used in Comparative Example 2, and its reducibility resistance is poor, which is not conducive to the low-temperature cycle performance.

[0131] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be obvious to those skilled in the art. The general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to these embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. An electrolyte additive, characterized in that: Its structural formula is shown in formula (B); Formula (B); Among them, R 1~ R2 is independently selected from H, a halogen atom, a nitro group, a trifluoromethyl group, a trichloromethyl group, a cyano group, a sulfonic acid group, and a formyl group; The halogen atom is selected from F, Cl, and Br.

2. The electrolyte additive according to claim 1, characterized in that: The compound represented by the structural formula (B) is selected from at least one of the formulas (1) to (6): 。 3. The method for preparing an electrolyte additive according to any one of claims 1 to 2, characterized in that: The steps include: The compound described in formula (C-1) and the compound described in formula (C-2) are subjected to a dehydration condensation reaction in the presence of a sodium hydroxide solution as a catalyst to obtain the electrolyte additive; Formula (C-1); Formula (C-2); Among them, R 1~ R2 is independently selected from H, a halogen atom, a nitro group, a trifluoromethyl group, a trichloromethyl group, a cyano group, a sulfonic acid group, and a formyl group.

4. The preparation method according to claim 3, characterized in that: The molar ratio of the compound of formula (C-1), the compound of formula (C-2) and sodium hydroxide is 1:(1-4):(2-4); The dehydration condensation reaction is a two-step heating reaction, wherein the first step is at a temperature of 60-80° C. for 5-8 hours, and the second step is at a temperature of 80° C. for 6-8 hours.

5. An electrolyte, characterized in that: including lithium salt, solvent, and first electrolyte additive; The first electrolyte additive is selected from the electrolyte additive according to any one of claims 1 to 2 or the electrolyte additive prepared by the preparation method according to claim 3.

6. The electrolyte according to claim 5, characterized in that The lithium salt is selected from any one or more of lithium hexafluorophosphate, lithium perchlorate, lithium nitrate, lithium tetrafluoroborate, lithium bis(trifluoromethylsulfonyl imide), lithium bis(fluorosulfonyl imide), lithium bis(oxalatoborate), lithium difluorooxalatoborate or lithium difluorobis(oxalatophosphate).

7. The electrolyte according to claim 5, characterized in that The solvent is selected from any one or more of dimethyl carbonate, ethylene carbonate, propylene carbonate, diethyl carbonate, propyl propionate, and ethylene glycol dimethyl ether.

8. The electrolyte according to claim 5, characterized in that The electrolyte further includes a second electrolyte additive; The second electrolyte additive is selected from vinylene carbonate, ethylene carbonate, propylene carbonate, fluoroethylene carbonate, vinyl sulfate, vinyl bissulfate, propylene sulfate, 1,3-propane sultone, 1,3-propylene sultone, 1,4-butane sultone, 2,4-butane sultone, phenyl methanesulfonate, methylene methanedisulfonate, N-phenylbis(trifluoromethanesulfonyl)imide, triallyl phosphate, tripropargyl phosphate, tris(trifluoromethanesulfonyl)imide ... Any one or more of (trimethylsilyl) phosphate, trimethyl phosphite, ethyl diprop-2-ynyl phosphate, tetramethyl methylene diphosphate, (2-allylphenoxy) trimethylsilane, 1,2-bis(cyanoethoxy)ethane, tris(trimethylsilyl) borate, 1,3,5-triallyl isocyanurate, isocyanoethyl methacrylate, hexamethylene diisocyanate, p-phenylene diisocyanate or 2,4-toluene diisocyanate.

9. The electrolyte according to claim 5, characterized in that The mass percentage of the solvent in the electrolyte is 72-91%, the mass percentage of the sum of the first electrolyte additive and the second electrolyte additive in the electrolyte is 0.1-3%, and the mass percentage of the lithium salt in the electrolyte is 8-25%.

10. The electrolyte according to claim 5, characterized in that The solvent includes tetrahydrofuran, tetrahydropyran and tetrahydrothiophene; The mass ratio of tetrahydrofuran, tetrahydropyran and tetrahydrothiophene is (20-60):(10-40):(10-40).

11. A lithium ion battery, characterized in that: Including positive electrode, negative electrode, separator and electrolyte; The electrolyte is the electrolyte according to claim 5; The active material of the positive electrode is selected from any one of lithium cobalt oxide, ternary nickel cobalt manganese lithium, lithium nickel manganese oxide, lithium iron phosphate or lithium iron manganese phosphate; The active material of the negative electrode is selected from any one of artificial graphite, natural graphite, lithium titanate, metallic lithium, silicon-carbon composite material or silicon oxide; The diaphragm is selected from a polypropylene diaphragm or a polyethylene diaphragm.

12. The lithium ion battery according to claim 11, characterized in that: The charging and discharging voltage of the lithium-ion battery is 2.5-3.65V.

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