Multifunctional electrolyte additive containing thiophene group, nonaqueous electrolyte containing the same, and lithium secondary battery

Abstract

The present application is named as multifunctional electrolyte additive containing thiophene group, non-aqueous electrolyte containing the additive and lithium secondary battery, belongs to lithium secondary battery technical field. The technical problem to be solved is to provide a multifunctional electrolyte additive containing thiophene group, the formed solid electrolyte interface film (SEI film) has the characteristics of low impedance and high stability, which can significantly reduce the capacity decay rate of the battery in a wide temperature range, and prolong the service life of the battery. The technical scheme points are as follows: the structure general formula of the multifunctional electrolyte additive containing thiophene group is: wherein, R1, R2, R3, R4, R5 and R6 are defined as shown in the text.

Description

Technical Field

[0001] This application relates to the field of lithium secondary battery technology, and in particular to a multifunctional electrolyte additive containing a thiophene group, a non-aqueous electrolyte containing the additive, and a lithium secondary battery. Background Technology

[0002] Lithium-ion batteries are widely used in new energy vehicles, energy storage power stations, and consumer electronics due to their high energy density and long cycle life. Improving the electrochemical performance of lithium-ion batteries under extreme environments is crucial for their global development and large-scale application in specialized fields such as aerospace. However, wide-temperature-range lithium-ion batteries face many challenges. At low temperatures, ion transport in the electrolyte phase and at the electrode-electrolyte interface deteriorates; at high temperatures, lithium salt thermal decomposition and hydrolysis produce HF, causing the dissolution of transition metal ions at the positive electrode and triggering severe side reactions at the electrode / electrolyte interface. The chemical properties and stability of the electrode-electrolyte interface play a key role in achieving continuous and stable operation of lithium-ion batteries over a wide temperature range, dominating the electrochemical properties of lithium-ion batteries. + Electrode-electrolyte interfaces influence transport kinetics and affect the electrochemical performance and safety of batteries. Therefore, designing and constructing ideal electrode-electrolyte interfaces with high ionic conductivity and thermal stability is crucial for achieving stable operation in harsh environments. Compared to interfacial modulation of electrode materials through complex synthetic processes, designing suitable electrolyte additive molecular structures is the most efficient means of optimizing electrode-electrolyte interface properties. Summary of the Invention

[0003] The purpose of this invention is to provide: Multifunctional electrolyte additives containing thiophene groups, non-aqueous electrolytes containing these additives, and lithium secondary batteries are developed to address the technical problems of rapid capacity decay and poor lifespan faced by lithium secondary batteries under wide temperature range conditions.

[0004] The first aspect of this invention relates to a multifunctional electrolyte additive containing a thiophene group, the multifunctional electrolyte additive having the following general structural formula: ; R1, R2, R3, R4, R5 and R6 are each independently selected from H, halogens, unsubstituted C1-C5 alkyl groups, or optionally substituted with one or more substituents.

[0005] Preferably, the substituent is selected from halogen, CN group, alkyl, alkoxy, olefinic and alkyne groups.

[0006] Preferably, the multifunctional electrolyte additive is selected from at least one of the following compounds: .

[0007] A second aspect of the present invention relates to a non-aqueous electrolyte containing the above-mentioned electrolyte additives, wherein the non-aqueous electrolyte further comprises a non-aqueous organic solvent and a conductive lithium salt electrolyte.

[0008] Preferably, the non-aqueous organic solvent is selected from at least one of carbonate compounds, carboxylic acid ester compounds, ether compounds, and corresponding fluorinated carbonate compounds, fluorinated carboxylic acid ester compounds, and fluorinated ether compounds.

[0009] Preferably, the non-aqueous organic solvent includes, but is not limited to, ethylene carbonate, propylene carbonate, γ-butyrolactone, γ-valerolactone, δ-valerolactone, ε-caprolactone, 1,3-dioxolane, 1,4-dioxane, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, dimethyl 2,5-dioxaadipic acid, methyl formate, ethyl formate, propyl formate, methyl acetate, ethyl acetate, n-propyl acetate, n-butyl acetate, etc. Isobutyl acetate, n-amyl acetate, isoamyl acetate, methyl propionate, ethyl propionate, n-propyl propionate, methyl n-butyrate, ethyl n-butyrate, n-propyl n-butyrate, methyl pvalerate, ethyl pvalerate, n-propyl pvalerate, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, tetraethylene glycol dimethyl ether, tetraethylene glycol diethyl ether, and one or more of their respective fluorides in which some or all of their hydrogen atoms are replaced by fluorine atoms.

[0010] Preferably, the conductive lithium salt electrolyte is selected from lithium hexafluorophosphate (LiPF6), lithium hexafluoroarsenate (LiAsF6), lithium hexafluoroantimonyate (LiSbF6), lithium bis(oxalato)borate (LiBOB), lithium difluorooxalato)borate (LiODFB), lithium tetrafluoroborate (LiBF4), lithium difluorobis(oxalato)borate (LiODFP), lithium tetrafluorooxalato)borate (LiOTFP), lithium difluorophosphate (LiDFP or LiPO2F2), and 4,5-dicyano-2-trifluoromethyl One or more of the following: lithium imidazole (LiTDI), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethyl)sulfonyl)imide (LiTFSI), lithium bis(pentafluoroethyl)sulfonyl)imide (LiBETI), lithium tri(trifluoromethyl)sulfonyl (LiC(SO2CF3)3), lithium tri(pentafluoroethyl)sulfonyl (LiC(SO2C2F5)3), lithium trifluoromethanesulfonate (LiCF3SO3), or lithium nonafluoro-1-butanesulfonate (LiC4F9SO3).

[0011] Preferably, based on the total mass percentage of the non-aqueous electrolyte being 100%, the mass percentage of the non-aqueous organic solvent is 45%-96.99%, the mass percentage of the conductive lithium salt electrolyte is 3%-30%, the mass percentage of the thiophene-containing multifunctional electrolyte additive is 0.01%-5%, and the mass percentage of other commercial electrolyte additives is 0%-20%.

[0012] Preferably, the other commercial electrolyte additives include, but are not limited to, one or more of the following: ethylene carbonate, fluoroethylene carbonate, ethylene ethylene carbonate, 1,3-propanesulfonate lactone, propylene sulfonate lactone, ethylene sulfate, methyl vinyl sulfate, trifluoromethyl vinyl sulfate, propylene sulfate, vinyl sulfite, butane sulfonate lactone, methane disulfonate methylene, erythrose bicyclic sulfate, pentaerythritol bicyclic sulfate, succinic acid, adiponitrile, glutaronitrile, 1,2-bis(2-cyanoethoxy)ethane, 1,3,6-hexanetrionitrile, tris(trimethylsilane) phosphate, tris(trimethylsilane) borate, tris(trimethylsilane) phosphite, triallyl phosphate, and triargyl phosphate.

[0013] A third aspect of the present invention relates to a lithium secondary battery, the lithium secondary battery comprising a positive electrode, a negative electrode, a separator and the above-mentioned non-aqueous electrolyte.

[0014] Preferably, the positive electrode comprises a positive electrode current collector, a positive electrode active material, a conductive agent, and a binder; the positive electrode active material is selected from lithium transition metal oxides, specifically olivine-type LiM... z N 1-z PO4, spinel-type Li 1+x Ni y Mn 2-x-y O4 and layered oxide cathode Li 1+a Ni b Co c M' 1-a-b-c One or more of O2; Wherein, M and N are one of Fe, Mn, Co or Ni respectively, and M' is one or more of Mg, Al, Ca, Sc, Ti, V, Cr, Mn, Fe, Zn, Ga, Y, Zr, Nb, Mo, Sn, Ba or rare earth elements; 0≤z≤1, 0≤x, y≤0.5, 0≤a≤0.5, 0≤b, c≤1 and 0≤a+b+c≤1.

[0015] More preferably, the positive electrode current collector is made of a substance with high conductivity that will not cause adverse chemical changes in the battery, including but not limited to aluminum.

[0016] Preferably, the negative electrode comprises a negative electrode current collector, a negative electrode active material, a conductive agent, and a binder, or the negative electrode active material is used directly as the negative electrode sheet; the negative electrode active material is selected from natural graphite, artificial graphite, mesophase carbon microspheres, elemental Si, and silicon oxide SiO. X One or more of the following: silicon-carbon composite materials, lithium titanate, lithium metal, and lithium alloys, wherein 0 <X≤2。

[0017] More preferably, the negative electrode current collector material is a substance with high conductivity that will not cause adverse chemical changes in the battery, including but not limited to one or a combination of two or more of copper, stainless steel, aluminum, nickel, titanium, and carbon cloth.

[0018] Preferably, the diaphragm comprises a porous polymer membrane, a nonwoven fabric, or one or more of the following high-molecular organic materials coated on the surface of the porous polymer membrane or nonwoven fabric: boehmite, silica, titanium dioxide, zirconium dioxide, alumina, magnesium oxide, zinc oxide, or PVDF, aramid fiber, etc.

[0019] More preferably, the diaphragm comprises a porous polymer membrane made of polyolefin polymers such as polyethylene (PE), polypropylene (PP), ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or a nonwoven fabric made of polyester fiber, aramid fiber, glass fiber, etc., and the porous polymer membrane and nonwoven fabric are coated with ceramics such as boehmite, silica, titanium dioxide, zirconium dioxide, alumina, magnesium oxide, zinc oxide, etc., or coated with PVDF, aramid, etc.

[0020] The multifunctional electrolyte additive containing thiophene groups provided in this application allows the thiophene groups to electropolymerize in situ on the electrode surface to form a polythiophene interfacial film. While retaining the core passivation protection function of the SEI film, this enables the polythiophene-based SEI film to achieve electron-Li... + Dual conduction allows electrons and Li to... +Synchronous transport at the interface reduces concentration polarization, resulting in more uniform electrochemical reactions at the electrode / electrolyte interface. This significantly reduces interfacial impedance and improves the battery's electrochemical performance at low temperatures and high rates. Simultaneously, the polythiophene-based SEI film exhibits high electrochemical and chemical stability, inhibiting the dissolution of transition metal ions and preventing SEI / CEI film rupture, thus enhancing battery stability at high temperatures and during long-term cycling. Furthermore, the introduction of a benzene ring structure into the molecular structure allows the planar rigid structure of the benzene ring to construct a three-dimensional cross-linked network during SEI film formation, improving the mechanical strength and toughness of the SEI film and alleviating interfacial stress caused by electrode volume expansion. Moreover, the π-π interaction between the benzene ring and the carbon-based anode enhances interfacial adhesion, preventing SEI film detachment and rupture during charge-discharge cycles, reducing active material exposure and side reactions. Thanks to the thiophene and benzene ring groups in the molecular structure, the SEI film formed by this additive molecule possesses both low impedance and high stability, significantly improving the battery's electrochemical performance over a wide temperature range.

[0021] The present invention has at least the following beneficial effects: The solid electrolyte interphase (SEI) film formed by the multifunctional electrolyte additive containing thiophene groups provided in this application has both low impedance and high stability characteristics, which can significantly reduce the capacity decay rate of the battery over a wide temperature range and extend the battery life. Detailed Implementation

[0022] To make the objectives, technical solutions, and beneficial effects of this invention clearer, detailed explanations are provided below through specific embodiments. It should be noted that these embodiments are for illustrative purposes only and do not constitute any limitation on the scope of the invention. Unless otherwise stated, the experimental methods described in the embodiments are conventional techniques in the art, and the materials and reagents used are commercially available.

[0023] The labeling of the additives used in the following examples or comparative examples is as follows:

[0024] Example 1 This application provides a lithium-ion battery, the specific composition and manufacturing process of which are as follows: (1) Composition and preparation of positive electrode: Lithium iron phosphate (LiFePO4) positive electrode active material, polyvinylidene fluoride binder (PVDF), acetylene black conductive agent (SP) and carbon nanotube conductive agent (CNTs) are mixed in a weight ratio of 96:2:1.5:0.5, and an appropriate amount of N-methylpyrrolidone (NMP) is added. The mixture is stirred in a vacuum mixer to form a uniformly flowing positive electrode slurry. The positive electrode slurry is then uniformly coated on the two surfaces of double-sided carbon-coated aluminum foil using a coating machine. The coated electrode is dried and then rolled and slit to obtain the required positive electrode.

[0025] (2) Composition and preparation of negative electrode sheet: Artificial graphite: sodium carboxymethyl cellulose (CMC-Na): styrene-butadiene rubber (SBR): acetylene black = 95.5:1.2:1.8:1.5 by mass ratio, deionized water is added, and negative electrode slurry is obtained under the action of vacuum stirrer; then the negative electrode slurry is evenly coated on both surfaces of copper foil by coating machine, the coated electrode sheet is dried, and then the required negative electrode sheet is obtained by rolling and slitting.

[0026] (3) Battery assembly: The prepared positive and negative electrode sheets and PP separator were assembled into a soft-pack battery cell, and the cell was baked in a vacuum drying oven at 85°C for 48 hours to ensure that the moisture content of the positive and negative electrodes and the separator was below 200 ppm before being transferred to a glove box for electrolyte injection. After electrolyte injection, the lithium-ion battery underwent standing, formation, aging, shaping, and capacity testing, and then underwent corresponding electrochemical tests. The charge and discharge voltage range of the prepared LiFePO4 / graphite lithium-ion battery was 2.5-3.65 V.

[0027] Electrolyte preparation: In a circulating glove box filled with argon (H2O and O2 content <1ppm), ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) were mixed evenly in a mass ratio of 3:5:2 to obtain a non-aqueous organic solvent. 82.7 wt.% of the non-aqueous organic solvent was taken, and 10 wt.% of lithium hexafluorophosphate (LiPF6) and 3 wt.% of lithium difluorosulfonyl imide (LiFSI) conductive lithium salt electrolyte were slowly added to it. Finally, 3 wt.% of vinylene carbonate (VC), 0.5 wt.% of fluoroethylene carbonate (FEC), 0.5 wt.% of methanedisulfonate (MMDS), and 0.3 wt.% of the compound shown in Formula A were added, and the mixture was stirred evenly to obtain the electrolyte.

[0028] Example 2 Electrolyte preparation: In an argon-filled glove box (H2O, O2 content <1ppm), ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) were mixed evenly in a mass ratio of 3:5:2 to obtain a non-aqueous organic solvent. 82.5 wt.% of the non-aqueous organic solvent was taken, and then 10 wt.% of lithium hexafluorophosphate (LiPF6) and 3 wt.% of lithium difluorosulfonyl imide (LiFSI) conductive lithium salt electrolyte were slowly added to it. Finally, 3 wt.% of vinylene carbonate (VC), 0.5 wt.% of fluoroethylene carbonate (FEC), 0.5 wt.% of methanedisulfonate (MMDS), and 0.5 wt.% of the compound shown in formula C were added and mixed evenly to obtain the electrolyte.

[0029] The manufacturing process of the lithium-ion battery is the same as that in Example 1.

[0030] Example 3 Electrolyte preparation: In an argon-filled glove box (H2O, O2 content <1ppm), ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) were mixed evenly in a mass ratio of 3:5:2 to obtain a non-aqueous organic solvent. 82.5 wt.% of the non-aqueous organic solvent was taken, and then 10 wt.% of lithium hexafluorophosphate (LiPF6) and 3 wt.% of lithium difluorosulfonyl imide (LiFSI) conductive lithium salt electrolyte were slowly added to it. Finally, 3 wt.% of vinylene carbonate (VC), 0.5 wt.% of fluoroethylene carbonate (FEC), 0.5 wt.% of methanedisulfonate (MMDS), and 0.5 wt.% of the compound shown in formula D were added and mixed evenly to obtain the electrolyte.

[0031] The manufacturing process of the lithium-ion battery is the same as that in Example 1.

[0032] Example 4 Electrolyte preparation: In an argon-filled glove box (H2O, O2 content <1ppm), ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) were mixed evenly in a mass ratio of 3:5:2 to obtain a non-aqueous organic solvent. 82.5 wt.% of the non-aqueous organic solvent was taken, and then 10 wt.% of lithium hexafluorophosphate (LiPF6) and 3 wt.% of lithium difluorosulfonyl imide (LiFSI) conductive lithium salt electrolyte were slowly added to it. Finally, 3 wt.% of vinylene carbonate (VC), 0.5 wt.% of fluoroethylene carbonate (FEC), 0.5 wt.% of methanedisulfonate (MMDS), and 0.5 wt.% of the compound shown in Formula E were added and mixed evenly to obtain the electrolyte.

[0033] The manufacturing process of the lithium-ion battery is the same as that in Example 1.

[0034] Example 5 Electrolyte preparation: In an argon-filled glove box (H2O, O2 content <1ppm), ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed evenly at a mass ratio of 3:7 to obtain a non-aqueous organic solvent. 81.7 wt.% of the non-aqueous organic solvent was taken, and then 12.5 wt.% of a conductive lithium salt electrolyte of lithium hexafluorophosphate (LiPF6) was slowly added to it. Finally, 2.5 wt.% of vinylene carbonate (VC), 1 wt.% of fluoroethylene carbonate (FEC), 1 wt.% of erythrosine bicyclic sulfate (BiDTD), 0.5 wt.% of methanedisulfonate (MMDS), and 0.8 wt.% of the compound shown in formula F were added and mixed evenly to obtain the electrolyte.

[0035] The manufacturing process of the lithium-ion battery is the same as that in Example 1.

[0036] Example 6 Electrolyte preparation: In an argon-filled glove box (H2O, O2 content <1ppm), ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed evenly at a mass ratio of 3:7 to obtain a non-aqueous organic solvent. 82.0 wt.% of the non-aqueous organic solvent was taken, and then 12.5 wt.% of a conductive lithium salt electrolyte of lithium hexafluorophosphate (LiPF6) was slowly added to it. Finally, 2.5 wt.% of vinylene carbonate (VC), 1 wt.% of fluoroethylene carbonate (FEC), 1 wt.% of erythrosine bicyclic sulfate (BiDTD), 0.5 wt.% of methanedisulfonate (MMDS), and 0.5 wt.% of the compound shown in formula G were added and mixed evenly to obtain the electrolyte.

[0037] The manufacturing process of the lithium-ion battery is the same as that in Example 1.

[0038] Example 7 Electrolyte preparation: In an argon-filled glove box (H2O, O2 content <1ppm), ethylene carbonate (EC), diethyl carbonate (DEC), and methyl ethyl carbonate (EMC) were mixed evenly in a mass ratio of 3:5:2 to obtain a non-aqueous organic solvent. 80.9 wt.% of the non-aqueous organic solvent was taken, and then 13 wt.% of a conductive lithium salt electrolyte, lithium hexafluorophosphate (LiPF6), was slowly added. Finally, 0.5 wt.% vinylene carbonate (VC), 1 wt.% fluoroethylene carbonate (FEC), 1 wt.% 1,3-propanesulfonyl lactone (PS), 0.3 wt.% propylene sulfonyl lactone (PST), 1 wt.% vinyl sulfate (DTD), 0.5 wt.% tris(trimethylsilane) phosphate (TMSP), 0.5 wt.% lithium difluorooxalate borate (LiODFB), and 0.8 wt.% lithium difluorooxalate borate (LiODFB) were added. The electrolyte was obtained by mixing wt.% lithium difluorophosphate (LiPO2F2) and 0.5 wt.% of the compound shown in formula K.

[0039] Preparation of lithium-ion batteries Composition and preparation of the positive electrode: LiNi 0.8 Co 0.1 Mn 0.1 O2 (NCM811) positive electrode active material, polyvinylidene fluoride binder (PVDF), acetylene black conductive agent (SP), and carbon nanotube conductive agent (CNTs) are mixed in a weight ratio of 96.5:2:1:0.5, and N-methylpyrrolidone (NMP) is added. The mixture is stirred in a vacuum mixer to form a uniformly flowing positive electrode slurry. The positive electrode slurry is then uniformly coated onto the two surfaces of double-sided carbon-coated aluminum foil using a coating machine. The coated electrode is dried and then rolled and slit to obtain the positive electrode sheet.

[0040] The preparation of the negative electrode and the assembly of the battery were the same as in Example 1. The charge / discharge voltage range of the prepared NCM811 / graphite lithium-ion battery was 3.0-4.3 V.

[0041] Example 8 Electrolyte preparation: In an argon-filled glove box (H2O, O2 content <1ppm), ethylene carbonate (EC), diethyl carbonate (DEC), and methyl ethyl carbonate (EMC) were mixed evenly in a mass ratio of 3:5:2 to obtain a non-aqueous organic solvent. 80.9 wt.% of the non-aqueous organic solvent was taken, and then 13 wt.% of a conductive lithium salt electrolyte, lithium hexafluorophosphate (LiPF6), was slowly added. Finally, 0.5 wt.% vinylene carbonate (VC), 1 wt.% fluoroethylene carbonate (FEC), 1 wt.% 1,3-propanesulfonyl lactone (PS), 0.3 wt.% propylene sulfonyl lactone (PST), 1 wt.% vinyl sulfate (DTD), 0.5 wt.% tris(trimethylsilane) phosphate (TMSP), 0.5 wt.% lithium difluorooxalate borate (LiODFB), and 0.8 wt.% lithium difluorooxalate borate (LiODFB) were added. The electrolyte is obtained by mixing wt.% lithium difluorophosphate (LiPO2F2) and 0.5 wt.% of the compound shown in formula L.

[0042] The manufacturing process of the lithium-ion battery is the same as that in Example 7.

[0043] Example 9 Electrolyte preparation: In an argon-filled glove box (H2O, O2 content <1ppm), ethylene carbonate (EC), diethyl carbonate (DEC), and methyl ethyl carbonate (EMC) were mixed evenly in a mass ratio of 3:5:2 to obtain a non-aqueous organic solvent. 80.9 wt.% of the non-aqueous organic solvent was taken, and then 13 wt.% of a conductive lithium salt electrolyte, lithium hexafluorophosphate (LiPF6), was slowly added. Finally, 0.5 wt.% vinylene carbonate (VC), 1 wt.% fluoroethylene carbonate (FEC), 1 wt.% 1,3-propanesulfonyl lactone (PS), 0.3 wt.% propylene sulfonyl lactone (PST), 1 wt.% vinyl sulfate (DTD), 0.5 wt.% tris(trimethylsilane) phosphate (TMSP), 0.5 wt.% lithium difluorooxalate borate (LiODFB), and 0.8 wt.% lithium difluorooxalate borate (LiODFB) were added. The electrolyte was obtained by mixing wt.% lithium difluorophosphate (LiPO2F2) and 0.5 wt.% of the compound shown in formula M.

[0044] The manufacturing process of the lithium-ion battery is the same as that in Example 7.

[0045] Example 10 Electrolyte preparation: In an argon-filled glove box (H2O, O2 content <1ppm), ethylene carbonate (EC), diethyl carbonate (DEC), and methyl ethyl carbonate (EMC) were mixed evenly in a mass ratio of 3:5:2 to obtain a non-aqueous organic solvent. 81.1 wt.% of the non-aqueous organic solvent was taken, and then 13 wt.% of a conductive lithium salt electrolyte, lithium hexafluorophosphate (LiPF6), was slowly added. Finally, 0.5 wt.% vinylene carbonate (VC), 1 wt.% fluoroethylene carbonate (FEC), 1 wt.% 1,3-propanesulfonyl lactone (PS), 0.3 wt.% propylene sulfonyl lactone (PST), 1 wt.% vinyl sulfate (DTD), 0.5 wt.% tris(trimethylsilane) phosphate (TMSP), 0.5 wt.% lithium difluorooxalate borate (LiODFB), and 0.8 wt.% lithium difluorooxalate borate (LiODFB) were added. The electrolyte was obtained by mixing wt.% lithium difluorophosphate (LiPO2F2) and 0.3 wt.% of the compound shown in formula N.

[0046] The manufacturing process of the lithium-ion battery is the same as that in Example 7.

[0047] Example 11 Electrolyte preparation: In an argon-filled glove box (H2O, O2 content <1ppm), ethylene carbonate (EC), ethyl propionate (EP), propyl propionate (PP), and ethyl methyl carbonate (EMC) were mixed evenly in a mass ratio of 3:2:3:2 to obtain a non-aqueous organic solvent. 70.2 wt.% of the non-aqueous organic solvent was then slowly added to a 15 wt.% lithium hexafluorophosphate (LiPF6) conductive lithium salt electrolyte. Finally, 5 wt.% fluoroethylene carbonate (FEC), 2 wt.% 1,3-propanesulfonyl lactone (PS), 0.3 wt.% propylene sulfonyl lactone (PST), 1 wt.% vinyl sulfate (DTD), 0.5 wt.% tris(trimethylsilane)borate (TMSB), 0.5 wt.% lithium difluorooxalate borate (LiODFB), 1 wt.% succinic anhydride (SN), and 1.5 wt.%... An electrolyte was obtained by mixing adiponitrile (ADN), 2 wt.% 1,3,6-hexanetrionitrile (HTCN) and 1 wt.% of the compound shown in formula P.

[0048] Composition and preparation of the positive electrode: Lithium cobalt oxide (LCO) positive electrode active material, polyvinylidene fluoride binder (PVDF), acetylene black conductive agent (SP), and carbon nanotube conductive agent (CNTs) are mixed in a weight ratio of 96.5:2:1:0.5, and N-methylpyrrolidone (NMP) is added. The mixture is stirred in a vacuum mixer to form a uniformly flowing positive electrode slurry. The positive electrode slurry is then uniformly coated onto the two surfaces of double-sided carbon-coated aluminum foil using a coating machine. The coated electrode is dried and then rolled and slit to obtain the positive electrode sheet.

[0049] The preparation of the negative electrode and the assembly of the battery were the same as in Example 1. The charge / discharge voltage range of the prepared LCO / graphite lithium-ion battery was 3.0-4.45 V.

[0050] Preparation of lithium-ion batteries The manufacturing process of the lithium-ion battery is the same as that in Example 1.

[0051] Example 12 Electrolyte preparation: In an argon-filled glove box (H2O, O2 content <1ppm), ethylene carbonate (EC), ethyl propionate (EP), propyl propionate (PP), and ethyl methyl carbonate (EMC) were mixed evenly in a mass ratio of 3:2:3:2 to obtain a non-aqueous organic solvent. 70.4 wt.% of the non-aqueous organic solvent was then slowly added to a 15 wt.% lithium hexafluorophosphate (LiPF6) conductive lithium salt electrolyte. Finally, 5 wt.% fluoroethylene carbonate (FEC), 2 wt.% 1,3-propanesulfonyl lactone (PS), 0.3 wt.% propylene sulfonyl lactone (PST), 1 wt.% vinyl sulfate (DTD), 0.5 wt.% tris(trimethylsilane)borate (TMSB), 0.5 wt.% lithium difluorooxalate borate (LiODFB), 1 wt.% succinic anionyl nitrile (SN), and 1.5 wt.%... An electrolyte was obtained by mixing adiponitrile (ADN), 2 wt.% 1,3,6-hexanetrionitrile (HTCN) and 0.8 wt.% of the compound shown in formula S.

[0052] Preparation of lithium-ion batteries The manufacturing process of the lithium-ion battery is the same as that in Example 11.

[0053] Example 13 Electrolyte preparation: In an argon-filled glove box (H2O, O2 content <1ppm), ethylene carbonate (EC), ethyl propionate (EP), propyl propionate (PP), and ethyl methyl carbonate (EMC) were mixed evenly in a mass ratio of 3:2:3:2 to obtain a non-aqueous organic solvent. 70.7 wt.% of the non-aqueous organic solvent was then slowly added to a 15 wt.% lithium hexafluorophosphate (LiPF6) conductive lithium salt electrolyte. Finally, 5 wt.% fluoroethylene carbonate (FEC), 2 wt.% 1,3-propanesulfonyl lactone (PS), 0.3 wt.% propylene sulfonyl lactone (PST), 1 wt.% vinyl sulfate (DTD), 0.5 wt.% tris(trimethylsilane)borate (TMSB), 0.5 wt.% lithium difluorooxalate borate (LiODFB), 1 wt.% succinic anionyl nitrile (SN), and 1.5 wt.%... An electrolyte was obtained by mixing adiponitrile (ADN), 2 wt.% 1,3,6-hexanetrionitrile (HTCN) and 0.5 wt.% of the compound shown in formula U.

[0054] Preparation of lithium-ion batteries The manufacturing process of the lithium-ion battery is the same as that in Example 11.

[0055] Comparative Example 1 Referring to Examples 1-4 of the present invention, the difference is that the electrolyte containing the thiophene group is not added to the comparative electrolyte.

[0056] The manufacturing process of the lithium-ion battery is the same as that in Example 1.

[0057] Comparative Example 2 Referring to Examples 5 and 6 of the present invention, the difference is that the electrolyte of the comparative example does not contain the electrolyte additive containing the thiophene group.

[0058] The manufacturing process of the lithium-ion battery is the same as that in Example 1.

[0059] Comparative Example 3 Referring to Examples 7-10 of the present invention, the difference is that the electrolyte of the comparative examples does not contain the electrolyte additive containing thiophene groups.

[0060] The manufacturing process of the lithium-ion battery is the same as that in Example 7.

[0061] Comparative Example 4 Referring to Examples 11-13 of the present invention, the difference is that the electrolyte of the comparative examples does not contain the electrolyte additive containing thiophene groups.

[0062] The manufacturing process of the lithium-ion battery is the same as that in Example 11.

[0063] The following experiments were conducted on the batteries obtained in Examples 1-13 and Comparative Examples 1-4: Cyclic performance test: The lithium-ion batteries of Examples 1-13 and Comparative Examples 1-4 were subjected to charge-discharge cycle tests at 25°C room temperature and 45°C high temperature at 1C / 1C rate. The capacity retention rate at the end of the cycle was calculated, i.e., capacity retention rate = discharge capacity of the battery in the last cycle / discharge capacity of the battery in the first cycle × 100%.

[0064] Low-temperature discharge performance test: The batteries of Examples 1-13 and Comparative Examples 1-4 were cycled 3 times at room temperature at a rate of 1C / 1C, and then fully charged at a current of 1C. The discharge capacity of the battery in the last cycle was recorded as C0. After being placed at -20 ℃ for 24 hours, the batteries were discharged at 0.1C and the low-temperature discharge capacity was recorded as C1. The low-temperature capacity retention rate was = C1 / C0 × 100%.

[0065] High-temperature storage performance test: The batteries of Examples 1-13 and Comparative Examples 1-4 were cycled 3 times at 1C / 1C rate at room temperature, and then fully charged at 1C current. The discharge capacity of the battery in the last cycle was recorded as C0. The batteries were then placed in a 60℃ oven for 7 days. After the batteries were taken out and cooled to room temperature, a 1C discharge test was performed first, and the discharge capacity of the battery was recorded as C2. Then, the batteries were cycled 3 times at 1C / 1C rate, and the discharge capacity of the third cycle was recorded as C3. The capacity retention rate of the battery is C2 / C0×100%, and the capacity recovery rate of the battery is C3 / C0×100%.

[0066] Examples 1-4 were compared with Comparative Example 1; Examples 5-6 were compared with Comparative Example 2; Examples 7-10 were compared with Comparative Example 3; Examples 11-13 were compared with Comparative Example 4; and the recorded results are shown in Table 1.

[0067] Table 1: Battery test results of Examples 1-13 and Comparative Examples 1-4

[0068] The data above demonstrates that adding the thiophene-containing electrolyte additive to the electrolyte significantly improves the cycle stability of lithium-ion batteries at room temperature and high temperature, as well as their chemical performance at high and low temperatures. Therefore, lithium-ion batteries prepared using the electrolyte of this invention exhibit superior electrochemical performance over a wide temperature range, showing great promise for application in lithium-ion battery systems.

[0069] The above detailed description is a specific illustration of one feasible embodiment of the present invention, and this embodiment is not intended to limit the patent scope of the present invention. It should be noted that all equivalent implementations or modifications made without departing from the present invention should be included within the scope of the technical solution of the present invention. Therefore, the protection scope of the present invention should be determined by the appended claims.

Claims

1. A multifunctional electrolyte additive containing a thiophene group, characterized in that, The general structural formula of the multifunctional electrolyte additive is: ； R1, R2, R3, R4, R5 and R6 are each independently selected from H, halogens, unsubstituted C1-C5 alkyl groups, or optionally substituted with one or more substituents.

2. The multifunctional electrolyte additive containing thiophene groups according to claim 1, characterized in that, The substituents are selected from halogen, CN group, alkyl, alkoxy, olefin group and alkyne group.

3. The multifunctional electrolyte additive containing a thiophene group according to claim 1, characterized in that, The multifunctional electrolyte additive is selected from at least one of the following compounds: 。 4. A non-aqueous electrolyte containing the electrolyte additive according to any one of claims 1-3, characterized in that, The non-aqueous electrolyte also includes a non-aqueous organic solvent and a conductive lithium salt electrolyte.

5. The non-aqueous electrolyte according to claim 4, characterized in that, The non-aqueous organic solvent is selected from at least one of carbonate compounds, carboxylic acid ester compounds, ether compounds, and corresponding fluorinated carbonate compounds, fluorinated carboxylic acid ester compounds, and fluorinated ether compounds.

6. The non-aqueous electrolyte according to claim 4, characterized in that, The non-aqueous organic solvent is selected from ethylene carbonate, propylene carbonate, γ-butyrolactone, γ-valerolactone, δ-valerolactone, ε-caprolactone, 1,3-dioxolane, 1,4-dioxane, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, dimethyl 2,5-dioxaadipic acid, methyl formate, ethyl formate, propyl formate, methyl acetate, ethyl acetate, n-propyl acetate, n-butyl acetate, and isobutyl acetate. One or more of the following: n-amyl acetate, isoamyl acetate, methyl propionate, ethyl propionate, n-propyl propionate, methyl n-butyrate, ethyl n-butyrate, n-propyl n-butyrate, methyl pvalerate, ethyl pvalerate, n-propyl pvalerate, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, tetraethylene glycol dimethyl ether, tetraethylene glycol diethyl ether, and their respective fluorides in which some or all of their hydrogen atoms are replaced by fluorine atoms.

7. The non-aqueous electrolyte according to claim 4, characterized in that, The conductive lithium salt electrolyte is selected from one or more of lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium hexafluoroantimonyate, lithium bis(oxalato)borate, lithium difluorooxalato)borate, lithium tetrafluoroborate, lithium difluorobis(oxalato)phosphate, lithium tetrafluorooxalato)phosphate, lithium difluorophosphate, lithium 4,5-dicyano-2-trifluoromethylimidazolium, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethyl)sulfonyl)imide, lithium bis(pentafluoroethyl)sulfonyl)imide, lithium tri(trifluoromethyl)methyl lithium, lithium tri(pentafluoroethyl)sulfonyl)methyl lithium, lithium trifluoromethanesulfonate, and lithium nonafluoro-1-butanesulfonate.

8. The non-aqueous electrolyte according to any one of claims 4-7, characterized in that, Based on the total mass percentage of the non-aqueous electrolyte being 100%, the mass percentage of the non-aqueous organic solvent is 45%-96.99%, the mass percentage of the conductive lithium salt electrolyte is 3%-30%, the mass percentage of the thiophene-containing multifunctional electrolyte additive is 0.01%-5%, and the mass percentage of other commercial electrolyte additives is 0%-20%.

9. A lithium secondary battery, characterized in that, The lithium secondary battery includes a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the electrolyte is the non-aqueous electrolyte as described in any one of claims 4-7.

10. The lithium secondary battery according to claim 9, characterized in that, The positive electrode comprises a positive electrode current collector, a positive electrode active material, a conductive agent, and a binder; the positive electrode active material is selected from lithium transition metal oxides, specifically olivine-type LiMnO4. z N 1-z PO4, spinel-type Li 1+x Ni y Mn 2-x-y O4 and layered oxide cathode Li 1+a Ni b Co c M' 1-a-b-c One or more of O2; Wherein, M and N are one of Fe, Mn, Co or Ni respectively, and M' is one or more of Mg, Al, Ca, Sc, Ti, V, Cr, Mn, Fe, Zn, Ga, Y, Zr, Nb, Mo, Sn, Ba or rare earth elements; 0≤z≤1, 0≤x, y≤0.5, 0≤a≤0.5, 0≤b, c≤1 and 0≤a+b+c≤1.

11. The lithium secondary battery according to claim 9, characterized in that, The negative electrode includes a negative electrode current collector, a negative electrode active material, a conductive agent, and a binder, or the negative electrode active material can be used directly as the negative electrode sheet; the negative electrode active material is selected from natural graphite, artificial graphite, mesophase carbon microspheres, elemental Si, and silicon oxide SiO. X One or more of the following: silicon-carbon composite materials, lithium titanate, lithium metal, and lithium alloys, wherein 0 <X≤2。 12. The lithium secondary battery according to claim 9, characterized in that, The diaphragm comprises a porous polymer membrane, a nonwoven fabric, or one or more organic or inorganic substances coated on the surface of the porous polymer membrane or nonwoven fabric. The inorganic material is selected from one or more of boehmite, silicon dioxide, titanium dioxide, zirconium dioxide, aluminum oxide, magnesium oxide, and zinc oxide; The organic compound is selected from one or more of PVDF and aramid fibers.

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