Electrolyte and lithium ion battery

Abstract

The present invention relates to the field of battery manufacturing, and provides an electrolyte and a lithium ion battery. The electrolyte includes an electrolyte salt, an organic solvent and an additive; the electrolyte salt includes a compound S1, the compound S1 includes at least one of a fluorine element and a lithium element, and the organic solvent includes ethylene carbonate; the additive includes an additive S2, and the additive S2 has a structure as shown in formula (1): #imgabs0# wherein R1, R2, R3, R4, R5, and R6 each independently include halogen-substituted or unsubstituted Any one of a substituted C1-C20 alkyl group, a C3-C20 cycloalkyl group substituted or unsubstituted by halogen, a phenyl group substituted or unsubstituted by halogen, a C1-C20 olefin group substituted or unsubstituted by halogen, a biphenyl group substituted or unsubstituted by halogen, a C6-C26 phenylalkyl group substituted or unsubstituted by halogen, and a C6-C26 condensed ring aromatic group substituted or unsubstituted by halogen, wherein X is O or S; the mass percentage of the additive S2 in the electrolyte is 0.3% to 10%.

Description

Technical Field

[0001] The present invention relates to the field of battery manufacturing, in particular to an electrolyte and a lithium ion battery. Background Art

[0002] Lithium-ion batteries are widely used in 3C digital, power tools, aerospace, energy storage, power vehicles and other fields. With the rapid development of science and technology and consumer products, lithium-ion batteries need to have higher operating voltage and energy density.

[0003] As the operating voltage of lithium-ion batteries continues to increase, the existing lithium-ion batteries will suffer from the problem of deterioration of electrochemical performance when undergoing long-term cycle charge and discharge processes at high voltage (>4.5V). Summary of the Invention

[0004] The purpose of the present invention is to overcome the deficiencies of the prior art and to provide an electrolyte and a lithium-ion battery that cleverly solve the above-mentioned technical problems.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] The present invention provides an electrolyte solution comprising an electrolyte salt, an organic solvent and an additive;

[0007] The electrolyte salt includes compound S1, the compound S1 includes at least one of fluorine and lithium, and the organic solvent includes ethylene carbonate;

[0008] The additive includes additive S2, and the additive S2 has a structure as shown in formula (1):

[0009]

[0010] wherein R1, R2, R3, R4, R5, and R6 independently represent any one of a C1-C20 alkyl group substituted or unsubstituted by halogen, a C3-C20 cycloalkyl group substituted or unsubstituted by halogen, a phenyl group substituted or unsubstituted by halogen, a C1-C20 olefin group substituted or unsubstituted by halogen, a biphenyl group substituted or unsubstituted by halogen, a C6-C26 phenylalkyl group substituted or unsubstituted by halogen, and a C6-C26 condensed ring aromatic group substituted or unsubstituted by halogen, and X represents O or S;

[0011] The mass percentage of the additive S2 in the electrolyte is 0.3% to 10%.

[0012] Optionally, the additive S2 has a structure as shown in formula (2) or formula (3):

[0013]

[0014] Optionally, the mass percentage of the additive S2 in the electrolyte is 1%.

[0015] Optionally, compound S1 includes at least one of hexafluorophosphate, hexafluoroarsenate, lithium perchlorate, trifluorosulfonyl lithium, difluoro(trifluoromethylsulfonyl)imide lithium, tris(trifluoromethylsulfonyl)methyl lithium, and bisfluoroimide sulfonate lithium.

[0016] Optionally, the concentration of compound S1 is 0.8 to 1.3 mol / L.

[0017] Optionally, the organic solvent further comprises at least one of propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl formate, ethyl formate, ethyl propionate, propyl propionate, methyl butyrate, and tetrahydrofuran.

[0018] Optionally, the additives further include fluorinated carbonates and nitrile compounds.

[0019] The present invention also provides a lithium-ion battery comprising a positive electrode sheet, a negative electrode sheet, a lithium battery separator and the electrolyte as described above.

[0020] Optionally, the positive electrode sheet includes a positive electrode current collector and a positive electrode slurry layer disposed on the positive electrode current collector, wherein the positive electrode slurry layer includes a positive electrode material;

[0021] The negative electrode sheet includes a negative electrode current collector and a negative electrode slurry layer disposed on the negative electrode current collector, wherein the negative electrode slurry layer includes a negative electrode material.

[0022] Optionally, the positive electrode material includes at least one of lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium ferrous phosphate, and lithium manganese oxide;

[0023] And / or, the negative electrode material includes natural graphite, artificial graphite, mesophase carbon microspheres, hard carbon, soft carbon, silicon, silicon-carbon composite material, lithium tin alloy, lithium tin alloy oxide, metallic tin, stannous oxide, tin oxide, spinel structure lithiated Li4Ti5O 12 -At least one of TiO2 composite electrode material and lithium aluminum alloy.

[0024] The beneficial effect of the present invention is that, compared with the prior art, the present invention protects the positive and negative electrodes of the lithium-ion battery through the additive S2, and the additive S2 will undergo an oxidogen reaction under a high-voltage working state and participate in the formation of SEI film and CEI film on the positive and negative electrodes; wherein, when the additive S2 is located near the positive electrode, it will be oxidized under a high-voltage working state, and the oxidation product of the additive S2 can undergo a polymerization reaction with the ethylene carbonate in the electrolyte, and its polymerization product will be coated on the surface of the positive electrode to play a protective role; when the additive S2 is located near the negative electrode, after being continuously reduced for a long time, the reduction product of the additive S2 will form a compound protective layer containing RSOF sulfonate on the surface of the negative electrode; in addition, the fluoride ions of the fluoride in the electrolyte will be captured by the silicon group in the additive S2, thereby avoiding the generation of excessive hydrofluoric acid in the electrolyte, thereby reducing the negative effect of hydrofluoric acid on the lithium-ion battery. Therefore, the electrolyte in the present invention can protect the lithium-ion battery under high-voltage working conditions and effectively improve the problem of deterioration of the electrochemical performance of the lithium-ion battery. DETAILED DESCRIPTION

[0025] Lithium-ion batteries are widely used in various portable electronic products, such as mobile phones, laptops, tablets, and digital cameras. Lithium cobalt oxide, due to its high volume-to-density ratio, is often used as an electrode material in lithium-ion batteries.

[0026] Lithium cobalt oxide has the advantages of low production process difficulty, high operating voltage, stable release current and long cycle life. However, under high voltage, the internal stress of LiCoO2 lattice will increase, causing structural collapse and violent interface side reactions, which will lead to irreversible deterioration of battery performance.

[0027] The technical solutions and embodiments of the present invention are now described in detail.

[0028] The technical solutions adopted in the present invention are as follows:

[0029] The present invention provides an electrolyte solution comprising an electrolyte salt, an organic solvent and an additive;

[0030] The electrolyte salt includes compound S1, the compound S1 includes at least one of fluorine and lithium, and the organic solvent includes ethylene carbonate;

[0031] The additive includes additive S2, and the additive S2 has a structure as shown in formula (1):

[0032]

[0033] Among them, R1, R2, R3, R4, R5, and R6 independently include any one of a C1-C20 alkyl group substituted or unsubstituted by halogen, a C3-C20 cycloalkyl group substituted or unsubstituted by halogen, a phenyl group substituted or unsubstituted by halogen, a C1-C20 olefin group substituted or unsubstituted by halogen, a biphenyl group substituted or unsubstituted by halogen, a C6-C26 phenylalkyl group substituted or unsubstituted by halogen, and a C6-C26 condensed ring aromatic group substituted or unsubstituted by halogen, and X is O or S; the mass percentage of the additive S2 in the electrolyte is 0.3% to 10%.

[0034] In an optional embodiment, the mass percentage of additive S2 in the electrolyte can be 0.3%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, etc.

[0035] Additive S2 undergoes an oxidative reaction under high voltage conditions and participates in the formation of SEI and CEI films on the positive and negative electrodes, thereby protecting the positive and negative electrodes of the lithium-ion battery. In addition, the fluoride ions in the electrolyte are captured by the silicon groups in additive S2, preventing the formation of excessive hydrofluoric acid in the electrolyte and reducing the negative effects of hydrofluoric acid on the lithium-ion battery.

[0036] When X in additive S2 is O, additive S2 is a compound having both sulfate and sulfonate functional groups. The sulfate functional group can reduce the interfacial impedance of the positive and negative electrode surfaces, thereby optimizing and improving the electrochemical performance of the lithium-ion battery.

[0037] Furthermore, the additive S2 has a structure as shown in formula (2) or formula (3):

[0038]

[0039] When the additive S2 has a structure as shown in formula (2), the additive S2 is a compound having both sulfate and sulfonate functional groups; when the additive S2 has a structure as shown in formula (3), the additive S2 is a compound having both sulfonate functional groups.

[0040] The sulfate functional group can reduce the interfacial resistance on the surface of the positive and negative electrodes of the lithium-ion battery. The additive S2 will undergo an oxidogen reaction under high voltage working conditions and participate in the formation of SEI film and CEI film on the positive and negative electrodes, thereby effectively improving the problem of deterioration of the electrochemical performance of the lithium-ion battery.

[0041] Among them, when additive S2 is located near the positive electrode, it will be oxidized under high-voltage working conditions. The oxidation product of additive S2 can react with ethylene carbonate in the electrolyte, and its polymerization product will be coated on the surface of the positive electrode to play a protective role; when additive S2 is located near the negative electrode, after being continuously reduced for a long time, the reduction product of additive S2 will form a protective layer of a compound containing RSOF sulfonate on the surface of the negative electrode.

[0042] In addition, the fluoride ions in the fluoride in the electrolyte will be captured by the silicon groups in the additive S2, thereby avoiding the generation of excessive hydrofluoric acid in the electrolyte, thereby reducing the negative effects of hydrofluoric acid on lithium-ion batteries.

[0043] Specifically, the mass percentage of the additive S2 in the electrolyte is 1%.

[0044] Furthermore, compound S1 includes at least one of hexafluorophosphate, hexafluoroarsenate, lithium perchlorate, trifluorosulfonyl lithium, difluoro(trifluoromethylsulfonyl)imide lithium, tris(trifluoromethylsulfonyl)methyl lithium, and bis(trifluoromethylsulfonyl)imide lithium.

[0045] Specifically, the concentration of compound S1 is 0.8 to 1.3 mol / L. In an optional embodiment, the concentration of compound S1 can be 0.8 mol / L, 0.9 mol / L, 1 mol / L, 1.1 mol / L, 1.2 mol / L, 1.3 mol / L, etc.

[0046] Furthermore, the organic solvent further comprises at least one of propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl formate, ethyl formate, ethyl propionate, propyl propionate, methyl butyrate, and tetrahydrofuran.

[0047] Furthermore, the additives also include fluorinated carbonates and nitrile compounds.

[0048] Fluorinated molecules have a high oxidation potential and a high reduction potential, which makes the compounds containing fluorinated molecules have significant antioxidant and low reduction stability, enabling them to improve the oxidation stability of the electrolyte, thereby improving the electrochemical performance of lithium-ion batteries; nitrile compounds have excellent thermal stability and high antioxidant ability, and nitrile compounds can improve the stability of the positive electrode / electrolyte surface.

[0049] The present invention also provides a lithium-ion battery comprising a positive electrode sheet, a negative electrode sheet, a lithium battery separator and the electrolyte as described above.

[0050] Furthermore, the positive electrode sheet includes a positive electrode current collector and a positive electrode slurry layer disposed on the positive electrode current collector, the positive electrode slurry layer including a positive electrode material. The negative electrode sheet includes a negative electrode current collector and a negative electrode slurry layer disposed on the negative electrode current collector, the negative electrode slurry layer including a negative electrode material.

[0051] Furthermore, the positive electrode material includes at least one of lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium ferrous phosphate, and lithium manganese oxide.

[0052] Furthermore, the negative electrode materials include natural graphite, artificial graphite, mesophase carbon microspheres, hard carbon, soft carbon, silicon, silicon-carbon composite materials, lithium-tin alloy, lithium-tin alloy oxide, metallic tin, stannous oxide, tin oxide, spinel structured lithiated Li4Ti5O 12 -At least one of TiO2 composite electrode material and lithium aluminum alloy.

[0053] The present invention is described in detail below through specific examples. The examples are exemplary and intended to be used to explain the present invention, but should not be understood as limiting the present invention.

[0054] Example 1

[0055] 1. Preparation of Electrolyte

[0056] 1.1 Ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), and propyl propionate (PP) were mixed in a mass ratio of 10:10:20:60, and after mixing evenly, an organic solvent was prepared;

[0057] 1.2 Add 1,3-propane sultone (PS), fluoroethylene carbonate (FEC), and compound S1 to the organic solvent prepared in step 1.1 to prepare a mixed solution; wherein the concentration of compound S1 in the mixed solution is 1.1 mol / L, and compound S1 is lithium hexafluorophosphate (LiPF6).

[0058] 1.3 Add adiponitrile (ADN), 1,3,6-hexanetricarbonitrile (HTCN) and additive S2 to the mixed solution prepared in step 1.2 above, mix well, and prepare an electrolyte; wherein the mass percentage of 1,3-propane sultone (PS) in the electrolyte is 3%, the mass percentage of fluoroethylene carbonate (FEC) in the electrolyte is 8%, the mass percentage of adiponitrile (ADN) in the electrolyte is 1%, and the mass percentage of 1,3,6-hexanetricarbonitrile (HTCN) in the electrolyte is 2%; the mass percentage of additive S2 in the electrolyte is 0.3%, and the additive S2 is selected from

[0059]

[0060] 2. Preparation of positive electrode

[0061] 2.1 The positive electrode material lithium cobalt oxide (LCO), the conductive agent carbon nanotubes (CNT), and the binder polyvinylidene fluoride (PVDF) were added to N-methylpyrrolidone solvent (NMP) in a mass ratio of 97:1.5:1.5, and the mixture was thoroughly stirred to prepare a positive electrode slurry;

[0062] 2.2 The positive electrode slurry prepared in step 2.1 is coated on the positive electrode current collector aluminum foil, and after drying, cold pressing and cutting, a positive electrode sheet is obtained.

[0063] 3. Preparation of negative electrode sheet

[0064] 3.1 Add the negative electrode material graphite, conductive agent acetylene black (ACET), binder styrene butadiene rubber (SBR), and thickener sodium carboxymethyl cellulose (CMC-Na) in a mass ratio of 95:2:2:1 to deionized water solvent, stir and mix thoroughly to prepare the negative electrode slurry;

[0065] 3.2 The negative electrode slurry prepared in step 2.1 is coated on the negative electrode current collector copper foil, and after drying, cold pressing and cutting, a negative electrode sheet is obtained.

[0066] 4. Preparation of lithium-ion batteries

[0067] The positive electrode sheet prepared in the above step 2.2, the negative electrode sheet prepared in the above step 2.2 and the isolation film are assembled and wound into a bare battery cell, wherein the isolation film needs to be located between the positive electrode sheet and the negative electrode sheet; the bare battery cell is placed in an outer packaging bag, injected with electrolyte, and subjected to vacuum packaging, standing, forming, shaping and other processes to obtain a lithium-ion battery; wherein the battery cell model is 515974.

[0068] Example 2

[0069] 1. Preparation of Electrolyte

[0070] 1.1 Ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), and propyl propionate (PP) were mixed in a mass ratio of 10:10:20:60, and after mixing evenly, an organic solvent was prepared;

[0071] 1.2 Add 1,3-propane sultone (PS), fluoroethylene carbonate (FEC), and compound S1 to the organic solvent prepared in step 1.1 to prepare a mixed solution; wherein the concentration of compound S1 in the mixed solution is 1.1 mol / L, and compound S1 is lithium hexafluorophosphate (LiPF6).

[0072] 1.3 Add adiponitrile (ADN), 1,3,6-hexanetricarbonitrile (HTCN) and additive S2 to the mixed solution prepared in step 1.2 above, mix well, and prepare an electrolyte; wherein the mass percentage of 1,3-propane sultone (PS) in the electrolyte is 3%, the mass percentage of fluoroethylene carbonate (FEC) in the electrolyte is 8%, the mass percentage of adiponitrile (ADN) in the electrolyte is 1%, and the mass percentage of 1,3,6-hexanetricarbonitrile (HTCN) in the electrolyte is 2%; the mass percentage of additive S2 in the electrolyte is 0.5%, and the additive S2 is selected from

[0073]

[0074] 2. Preparation of positive electrode

[0075] 2.1 The positive electrode material lithium cobalt oxide (LCO), the conductive agent carbon nanotubes (CNT), and the binder polyvinylidene fluoride (PVDF) were added to N-methylpyrrolidone solvent (NMP) in a mass ratio of 97:1.5:1.5, and the mixture was thoroughly stirred to prepare a positive electrode slurry;

[0076] 2.2 The positive electrode slurry prepared in step 2.1 is coated on the positive electrode current collector aluminum foil, and after drying, cold pressing and cutting, a positive electrode sheet is obtained.

[0077] 3. Preparation of negative electrode sheet

[0078] 3.1 Add the negative electrode material graphite, conductive agent acetylene black (ACET), binder styrene butadiene rubber (SBR), and thickener sodium carboxymethyl cellulose (CMC-Na) in a mass ratio of 95:2:2:1 to deionized water solvent, stir and mix thoroughly to prepare the negative electrode slurry;

[0079] 3.2 The negative electrode slurry prepared in step 2.1 is coated on the negative electrode current collector copper foil, and after drying, cold pressing and cutting, a negative electrode sheet is obtained.

[0080] 4. Preparation of lithium-ion batteries

[0081] The positive electrode sheet prepared in the above step 2.2, the negative electrode sheet prepared in the above step 2.2 and the isolation film are assembled and wound into a bare battery cell, wherein the isolation film needs to be located between the positive electrode sheet and the negative electrode sheet; the bare battery cell is placed in an outer packaging bag, injected with electrolyte, and subjected to vacuum packaging, standing, forming, shaping and other processes to obtain a lithium-ion battery; wherein the battery cell model is 515974.

[0082] Example 3

[0083] 1. Preparation of Electrolyte

[0084] 1.1 Ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), and propyl propionate (PP) were mixed in a mass ratio of 10:10:20:60, and after mixing evenly, an organic solvent was prepared;

[0085] 1.2 Add 1,3-propane sultone (PS), fluoroethylene carbonate (FEC), and compound S1 to the organic solvent prepared in step 1.1 to prepare a mixed solution; wherein the concentration of compound S1 in the mixed solution is 1.1 mol / L, and compound S1 is lithium hexafluorophosphate (LiPF6).

[0086] 1.3 Add adiponitrile (ADN), 1,3,6-hexanetricarbonitrile (HTCN) and additive S2 to the mixed solution prepared in step 1.2 above, mix well, and prepare an electrolyte; wherein the mass percentage of 1,3-propane sultone (PS) in the electrolyte is 3%, the mass percentage of fluoroethylene carbonate (FEC) in the electrolyte is 8%, the mass percentage of adiponitrile (ADN) in the electrolyte is 1%, and the mass percentage of 1,3,6-hexanetricarbonitrile (HTCN) in the electrolyte is 2%; the mass percentage of additive S2 in the electrolyte is 1%, and the additive S2 is selected from

[0087]

[0088] 2. Preparation of positive electrode

[0089] 2.1 The positive electrode material lithium cobalt oxide (LCO), the conductive agent carbon nanotubes (CNT), and the binder polyvinylidene fluoride (PVDF) were added to N-methylpyrrolidone solvent (NMP) in a mass ratio of 97:1.5:1.5, and the mixture was thoroughly stirred to prepare a positive electrode slurry;

[0090] 2.2 The positive electrode slurry prepared in step 2.1 is coated on the positive electrode current collector aluminum foil, and after drying, cold pressing and cutting, a positive electrode sheet is obtained.

[0091] 3. Preparation of negative electrode sheet

[0092] 3.1 Add the negative electrode material graphite, conductive agent acetylene black (ACET), binder styrene butadiene rubber (SBR), and thickener sodium carboxymethyl cellulose (CMC-Na) in a mass ratio of 95:2:2:1 to deionized water solvent, stir and mix thoroughly to prepare the negative electrode slurry;

[0093] 3.2 The negative electrode slurry prepared in step 2.1 is coated on the negative electrode current collector copper foil, and after drying, cold pressing and cutting, a negative electrode sheet is obtained.

[0094] 4. Preparation of lithium-ion batteries

[0095] The positive electrode sheet prepared in the above step 2.2, the negative electrode sheet prepared in the above step 2.2 and the isolation film are assembled and wound into a bare battery cell, wherein the isolation film needs to be located between the positive electrode sheet and the negative electrode sheet; the bare battery cell is placed in an outer packaging bag, injected with electrolyte, and subjected to vacuum packaging, standing, forming, shaping and other processes to obtain a lithium-ion battery; wherein the battery cell model is 515974.

[0096] Example 4

[0097] 1. Preparation of Electrolyte

[0098] 1.1 Ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), and propyl propionate (PP) were mixed in a mass ratio of 10:10:20:60, and after mixing evenly, an organic solvent was prepared;

[0099] 1.2 Add 1,3-propane sultone (PS), fluoroethylene carbonate (FEC), and compound S1 to the organic solvent prepared in step 1.1 to prepare a mixed solution; wherein the concentration of compound S1 in the mixed solution is 1.1 mol / L, and compound S1 is lithium hexafluorophosphate (LiPF6).

[0100] 1.3 Add adiponitrile (ADN), 1,3,6-hexanetricarbonitrile (HTCN) and additive S2 to the mixed solution prepared in step 1.2 above, mix well, and prepare an electrolyte; wherein the mass percentage of 1,3-propane sultone (PS) in the electrolyte is 3%, the mass percentage of fluoroethylene carbonate (FEC) in the electrolyte is 8%, the mass percentage of adiponitrile (ADN) in the electrolyte is 1%, and the mass percentage of 1,3,6-hexanetricarbonitrile (HTCN) in the electrolyte is 2%; the mass percentage of additive S2 in the electrolyte is 2%, and the additive S2 is selected from

[0101]

[0102] 2. Preparation of positive electrode

[0103] 2.1 The positive electrode material lithium cobalt oxide (LCO), the conductive agent carbon nanotubes (CNT), and the binder polyvinylidene fluoride (PVDF) were added to N-methylpyrrolidone solvent (NMP) in a mass ratio of 97:1.5:1.5, and the mixture was thoroughly stirred to prepare a positive electrode slurry;

[0104] 2.2 The positive electrode slurry prepared in step 2.1 is coated on the positive electrode current collector aluminum foil, and after drying, cold pressing and cutting, a positive electrode sheet is obtained.

[0105] 3. Preparation of negative electrode sheet

[0106] 3.1 Add the negative electrode material graphite, conductive agent acetylene black (ACET), binder styrene butadiene rubber (SBR), and thickener sodium carboxymethyl cellulose (CMC-Na) in a mass ratio of 95:2:2:1 to deionized water solvent, stir and mix thoroughly to prepare the negative electrode slurry;

[0107] 3.2 The negative electrode slurry prepared in step 2.1 is coated on the negative electrode current collector copper foil, and after drying, cold pressing and cutting, a negative electrode sheet is obtained.

[0108] 4. Preparation of lithium-ion batteries

[0109] The positive electrode sheet prepared in the above step 2.2, the negative electrode sheet prepared in the above step 2.2 and the isolation film are assembled and wound into a bare battery cell, wherein the isolation film needs to be located between the positive electrode sheet and the negative electrode sheet; the bare battery cell is placed in an outer packaging bag, injected with electrolyte, and subjected to vacuum packaging, standing, forming, shaping and other processes to obtain a lithium-ion battery; wherein the battery cell model is 515974.

[0110] Example 5

[0111] 1. Preparation of Electrolyte

[0112] 1.1 Ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), and propyl propionate (PP) were mixed in a mass ratio of 10:10:20:60, and after mixing evenly, an organic solvent was prepared;

[0113] 1.2 Add 1,3-propane sultone (PS), fluoroethylene carbonate (FEC), and compound S1 to the organic solvent prepared in step 1.1 to prepare a mixed solution; wherein the concentration of compound S1 in the mixed solution is 1.1 mol / L, and compound S1 is lithium hexafluorophosphate (LiPF6).

[0114] 1.3 Add adiponitrile (ADN), 1,3,6-hexanetricarbonitrile (HTCN) and additive S2 to the mixed solution prepared in step 1.2 above, mix well, and prepare an electrolyte; wherein the mass percentage of 1,3-propane sultone (PS) in the electrolyte is 3%, the mass percentage of fluoroethylene carbonate (FEC) in the electrolyte is 8%, the mass percentage of adiponitrile (ADN) in the electrolyte is 1%, and the mass percentage of 1,3,6-hexanetricarbonitrile (HTCN) in the electrolyte is 2%; the mass percentage of additive S2 in the electrolyte is 5%, and the additive S2 is selected from

[0115]

[0116] 2. Preparation of positive electrode

[0117] 2.1 The positive electrode material lithium cobalt oxide (LCO), the conductive agent carbon nanotubes (CNT), and the binder polyvinylidene fluoride (PVDF) were added to N-methylpyrrolidone solvent (NMP) in a mass ratio of 97:1.5:1.5, and the mixture was thoroughly stirred to prepare a positive electrode slurry;

[0118] 2.2 The positive electrode slurry prepared in step 2.1 is coated on the positive electrode current collector aluminum foil, and after drying, cold pressing and cutting, a positive electrode sheet is obtained.

[0119] 3. Preparation of negative electrode sheet

[0120] 3.1 Add the negative electrode material graphite, conductive agent acetylene black (ACET), binder styrene butadiene rubber (SBR), and thickener sodium carboxymethyl cellulose (CMC-Na) in a mass ratio of 95:2:2:1 to deionized water solvent, stir and mix thoroughly to prepare the negative electrode slurry;

[0121] 3.2 The negative electrode slurry prepared in step 2.1 is coated on the negative electrode current collector copper foil, and after drying, cold pressing and cutting, a negative electrode sheet is obtained.

[0122] 4. Preparation of lithium-ion batteries

[0123] The positive electrode sheet prepared in the above step 2.2, the negative electrode sheet prepared in the above step 2.2 and the isolation film are assembled and wound into a bare battery cell, wherein the isolation film needs to be located between the positive electrode sheet and the negative electrode sheet; the bare battery cell is placed in an outer packaging bag, injected with electrolyte, and subjected to vacuum packaging, standing, forming, shaping and other processes to obtain a lithium-ion battery; wherein the battery cell model is 515974.

[0124] Example 6

[0125] 1. Preparation of Electrolyte

[0126] 1.1 Ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), and propyl propionate (PP) were mixed in a mass ratio of 10:10:20:60, and after mixing evenly, an organic solvent was prepared;

[0127] 1.2 Add 1,3-propane sultone (PS), fluoroethylene carbonate (FEC), and compound S1 to the organic solvent prepared in step 1.1 to prepare a mixed solution; wherein the concentration of compound S1 in the mixed solution is 1.1 mol / L, and compound S1 is lithium hexafluorophosphate (LiPF6).

[0128] 1.3 Add adiponitrile (ADN), 1,3,6-hexanetricarbonitrile (HTCN) and additive S2 to the mixed solution prepared in step 1.2 above, mix well, and prepare an electrolyte; wherein the mass percentage of 1,3-propane sultone (PS) in the electrolyte is 3%, the mass percentage of fluoroethylene carbonate (FEC) in the electrolyte is 8%, the mass percentage of adiponitrile (ADN) in the electrolyte is 1%, and the mass percentage of 1,3,6-hexanetricarbonitrile (HTCN) in the electrolyte is 2%; the mass percentage of additive S2 in the electrolyte is 10%, and the additive S2 is selected from

[0129]

[0130] 2. Preparation of positive electrode

[0131] 2.1 The positive electrode material lithium cobalt oxide (LCO), the conductive agent carbon nanotubes (CNT), and the binder polyvinylidene fluoride (PVDF) were added to N-methylpyrrolidone solvent (NMP) in a mass ratio of 97:1.5:1.5, and the mixture was thoroughly stirred to prepare a positive electrode slurry;

[0132] 2.2 The positive electrode slurry prepared in step 2.1 is coated on the positive electrode current collector aluminum foil, and after drying, cold pressing and cutting, a positive electrode sheet is obtained.

[0133] 3. Preparation of negative electrode sheet

[0134] 3.1 Add the negative electrode material graphite, conductive agent acetylene black (ACET), binder styrene butadiene rubber (SBR), and thickener sodium carboxymethyl cellulose (CMC-Na) in a mass ratio of 95:2:2:1 to deionized water solvent, stir and mix thoroughly to prepare the negative electrode slurry;

[0135] 3.2 The negative electrode slurry prepared in step 2.1 is coated on the negative electrode current collector copper foil, and after drying, cold pressing and cutting, a negative electrode sheet is obtained.

[0136] 4. Preparation of lithium-ion batteries

[0137] The positive electrode sheet prepared in the above step 2.2, the negative electrode sheet prepared in the above step 2.2 and the isolation film are assembled and wound into a bare battery cell, wherein the isolation film needs to be located between the positive electrode sheet and the negative electrode sheet; the bare battery cell is placed in an outer packaging bag, injected with electrolyte, and subjected to vacuum packaging, standing, forming, shaping and other processes to obtain a lithium-ion battery; wherein the battery cell model is 515974.

[0138] Comparative Example 1

[0139] 1. Preparation of Electrolyte

[0140] 1.1 Ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), and propyl propionate (PP) were mixed in a mass ratio of 10:10:20:60, and after mixing evenly, an organic solvent was prepared;

[0141] 1.2 Add 1,3-propane sultone (PS), fluoroethylene carbonate (FEC), and compound S1 to the organic solvent prepared in step 1.1 to prepare a mixed solution with a concentration of 1.1 mol / L; wherein compound S1 is lithium hexafluorophosphate (LiPF6).

[0142] 1.3 Add adiponitrile (ADN) and 1,3,6-hexanetricarbonitrile (HTCN) to the mixed solution prepared in the above step 1.2, mix well, and prepare an electrolyte; wherein the mass percentage of 1,3-propane sultone (PS) in the electrolyte is 3%, the mass percentage of fluoroethylene carbonate (FEC) in the electrolyte is 8%, the mass percentage of adiponitrile (ADN) in the electrolyte is 1%, and the mass percentage of 1,3,6-hexanetricarbonitrile (HTCN) in the electrolyte is 2%.

[0143] 2. Preparation of positive electrode

[0144] 2.1 The positive electrode material lithium cobalt oxide (LCO), the conductive agent carbon nanotubes (CNT), and the binder polyvinylidene fluoride (PVDF) were added to N-methylpyrrolidone solvent (NMP) in a mass ratio of 97:1.5:1.5, and the mixture was thoroughly stirred to prepare a positive electrode slurry;

[0145] 2.2 The positive electrode slurry prepared in step 2.1 is coated on the positive electrode current collector aluminum foil, and after drying, cold pressing and cutting, a positive electrode sheet is obtained.

[0146] 3. Preparation of negative electrode sheet

[0147] 3.1 Add the negative electrode material graphite, conductive agent acetylene black (ACET), binder styrene butadiene rubber (SBR), and thickener sodium carboxymethyl cellulose (CMC-Na) in a mass ratio of 95:2:2:1 to deionized water solvent, stir and mix thoroughly to prepare the negative electrode slurry;

[0148] 3.2 The negative electrode slurry prepared in step 2.1 is coated on the negative electrode current collector copper foil, and after drying, cold pressing and cutting, a negative electrode sheet is obtained.

[0149] 4. Preparation of lithium-ion batteries

[0150] The positive electrode sheet prepared in the above step 2.2, the negative electrode sheet prepared in the above step 2.2 and the isolation film are assembled and wound into a bare battery cell, wherein the isolation film needs to be located between the positive electrode sheet and the negative electrode sheet; the bare battery cell is placed in an outer packaging bag, injected with electrolyte, and subjected to vacuum packaging, standing, forming, shaping and other processes to obtain a lithium-ion battery; wherein the battery cell model is 515974.

[0151] The electrochemical performance was tested using the following methods:

[0152] (1) High temperature cycle test: Place the battery in an environment of 45±2 degrees, follow the standard charge and discharge cycle, cycle rate 1C, charging voltage 3.0-4.5V, and calculate the capacity retention rate of the battery after the cycle. The calculation formula is as follows:

[0153] nth cycle capacity retention rate (%) = (nth cycle discharge capacity) / (first cycle discharge capacity) * 100%

[0154] (2) High temperature storage test:

[0155] Test method: Charge the battery to 4.5V at 0.5C at 25±2°C. Place the fully charged battery in an 85°C environment for 6 hours and measure the thickness expansion rate. After returning to room temperature, discharge the battery to 3.0V at 0.5C and record the discharge capacity.

[0156] The electrochemical performance test results of the lithium ion batteries prepared in Examples 1 to 6 and Comparative Example 1 are summarized in Table 1:

[0157] Table 1

[0158]

[0159] The test results of the high-temperature cycle test show that compared with the lithium-ion battery in Comparative Example 1, the capacity retention rate and thickness expansion rate of the lithium-ion batteries in Examples 1 to 5 at different cycle numbers are significantly improved; among them, the capacity retention rate and high-temperature storage thickness expansion rate of the lithium-ion battery in Example 3 at different cycle numbers are significantly better.

[0160] The test results of the high-temperature storage test show that compared with the lithium-ion battery in Comparative Example 1, the capacity retention rate and thickness expansion rate of the lithium-ion batteries in Examples 1 to 5 are significantly improved; among them, the capacity retention rate and thickness expansion rate of the lithium-ion battery in Example 3 are significantly better.

[0161] In summary, compared with the lithium ion battery in Comparative Example 1, the lithium ion batteries in Examples 1 to 5 have most of the relevant parameters in the electrochemical performance test significantly improved, indicating that they have better electrochemical performance, and further indicating that the addition of additive S2 improves the electrochemical performance of the lithium ion battery under high voltage working conditions; among them, the lithium ion battery in Example 3 has significantly better relevant parameters in the electrochemical performance test, and further indicating that when the mass percentage of additive S2 in the electrolyte is 1%, it has a better effect on improving the electrochemical performance of the lithium ion battery under high voltage working conditions.

[0162] The above description is merely a preferred embodiment of the present invention, and the above specific embodiment is not intended to limit the present invention. Various variations and modifications are possible within the technical scope of the present invention. Any modifications, alterations, or equivalent substitutions made by a person skilled in the art based on the above description are within the scope of protection of the present invention.

Claims

1. An electrolyte, characterized in that including electrolyte salts, organic solvents and additives; The electrolyte salt includes compound S1, the compound S1 includes at least one of fluorine and lithium, and the organic solvent includes ethylene carbonate; The additive includes an additive S2, and the additive S2 has a structure as shown in formula (1): wherein R1, R2, R3, R4, R5, and R6 independently represent any one of a C1-C20 alkyl group substituted or unsubstituted by halogen, a C3-C20 cycloalkyl group substituted or unsubstituted by halogen, a phenyl group substituted or unsubstituted by halogen, a C1-C20 olefin group substituted or unsubstituted by halogen, a biphenyl group substituted or unsubstituted by halogen, a C6-C26 phenylalkyl group substituted or unsubstituted by halogen, and a C6-C26 condensed ring aromatic group substituted or unsubstituted by halogen, and X represents O or S; The mass percentage of the additive S2 in the electrolyte is 0.3% to 10%.

2. The electrolyte according to claim 1, characterized in that The additive S2 has a structure as shown in formula (2) or formula (3):

3. The electrolyte according to claim 2, characterized in that The mass percentage of the additive S2 in the electrolyte is 1%.

4. The electrolyte according to claim 1, characterized in that The compound S1 includes at least one of hexafluorophosphate, hexafluoroarsenate, lithium perchlorate, trifluorosulfonyl lithium, difluoro(trifluoromethylsulfonyl)imide lithium, tris(trifluoromethylsulfonyl)methyl lithium, and bisfluoroimide sulfonate lithium.

5. The electrolyte according to claim 4, characterized in that The concentration of the compound S1 is 0.8-1.3 mol / L.

6. The electrolyte according to claim 1, characterized in that The organic solvent further comprises at least one of propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl formate, ethyl formate, ethyl propionate, propyl propionate, methyl butyrate, and tetrahydrofuran.

7. The electrolyte according to claim 1, characterized in that The additives also include fluorinated carbonates and nitrile compounds.

8. A lithium ion battery, characterized in that: The invention comprises a positive electrode sheet, a negative electrode sheet, a lithium battery separator and the electrolyte according to any one of claims 1 to 7.

9. The lithium-ion battery according to claim 8, characterized in that The positive electrode sheet includes a positive electrode current collector and a positive electrode slurry layer disposed on the positive electrode current collector, wherein the positive electrode slurry layer includes a positive electrode material; The negative electrode sheet includes a negative electrode current collector and a negative electrode slurry layer disposed on the negative electrode current collector, wherein the negative electrode slurry layer includes a negative electrode material.

10. The lithium-ion battery according to claim 9, characterized in that The positive electrode material includes at least one of lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium ferrous phosphate, and lithium manganese oxide; And / or, the negative electrode material includes natural graphite, artificial graphite, mesophase carbon microspheres, hard carbon, soft carbon, silicon, silicon-carbon composite material, lithium tin alloy, lithium tin alloy oxide, metallic tin, stannous oxide, tin oxide, spinel structure lithiated Li4Ti5O 12 -At least one of TiO2 composite electrode material and lithium aluminum alloy.

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