Non-aqueous electrolyte and lithium ion secondary battery

Abstract

The present invention relates to a non-aqueous electrolyte and a lithium ion secondary battery. In order to solve the problem that the existing non-aqueous electrolyte cannot take into account both the high temperature stability and high temperature cycle performance of the lithium battery, the present invention proposes a non-aqueous electrolyte, which includes a lithium salt, a non-aqueous organic solvent and an additive, wherein the additive includes an additive A, an additive B and an additive C, wherein the additive A is thiazole isocyanate and its derivatives. By compounding the additive A, the additive B and the additive C, the increase of the water content, acidity and color number of the electrolyte under a high temperature environment is effectively suppressed, and further using an appropriate amount of other additives, the cycle performance of the lithium battery, especially the high temperature cycle performance and high temperature shelf performance, is effectively improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium batteries, and in particular relates to a non-aqueous electrolyte and a lithium ion secondary battery. Background Art

[0002] At present, the market has higher and higher requirements for the application of lithium-ion batteries. The electrical performance of lithium-ion batteries is closely related to the electrolyte. If a stable and dense passivation film cannot be formed at the electrolyte-electrode material interface, the positive / negative electrode materials will be exposed to the electrolyte. Affected by the moisture and acidity in the electrolyte, adverse factors such as changes in the surface structure of the positive electrode material, metal ion precipitation, gas escape, and metal ion diffusion to the negative electrode to destroy the SEI film will occur, causing the battery cycle life to deteriorate continuously. This degradation is more serious in a high temperature environment.

[0003] In the digital field where high volume energy density is required, the design concept of lithium batteries is high-voltage lithium cobalt oxide & silicon-carbon negative electrode. The voltage of commercial lithium cobalt oxide has gradually increased from the initial 4.2V to 4.48V, which also brings certain negative effects. For example, due to the presence of dangling bonds and unsaturated coordination relationships on the surface of the material, its reaction activity is significantly higher than that of the bulk phase. When charging a lithium cobalt oxide battery, the following reaction processes will occur: (1) The positive electrode material begins to delithiate from the surface; (2) After delithiation occurs, the oxygen atoms in the Li layer lose their barrier and repel each other, resulting in unstable surface structure; (3) Continuous delithiation promotes gas overflow due to surface lattice activity; (4) The overflowing gas causes the surface Co atoms to become less stable and dissolve; (5) The dissolved high-valent Co element will also oxidize the electrolyte and participate in the electrolyte chemical reaction. Side reactions at the solid-liquid interface are an inevitable problem in the development of lithium batteries. The chemical window of the currently used non-aqueous organic electrolyte is usually lower than 4.4V. When the charging cut-off voltage is higher than 4.4V, the electrolyte will undergo oxidation and decomposition on the battery surface. This process causes the battery capacity to "dive" sharply. At the same time, the products of oxidation decomposition also cover the surface of the electrode material, increasing the internal resistance of the battery. The separation of the products of the side reactions on the surface catalyzed by the free transition metal elements causes the electrode material to maintain a high active state, which brings hidden dangers.

[0004] The most common way to solve the above problems is to seek suitable additives, including developing new additives or combining different types of additives to form a passivation film through oxidation and reduction at the interface of the positive and negative electrode materials. The formed passivation film must be dense, elastic, and able to expand and shrink with the expansion and contraction of the positive and negative electrode materials during the charging and discharging process, rather than cracking. At the same time, it needs to be able to effectively inhibit the reduction and decomposition of the electrolyte at the negative electrode interface, thereby improving the electrochemical properties of high-voltage lithium-ion batteries, especially high-temperature cycle performance and high-temperature safety performance. Summary of the invention

[0005] The object of the present invention is to provide a non-aqueous electrolyte which is suitable for high voltage conditions and has good stability and cycle performance under high temperature conditions.

[0006] Another object of the present invention is to provide a lithium ion secondary battery containing the above nonaqueous electrolyte.

[0007] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0008] A non-aqueous electrolyte comprising a lithium salt, a non-aqueous organic solvent and an additive, wherein the additive comprises an additive A, an additive B and an additive C.

[0009] The additive A is one or more of the substances represented by structural formula (1),

[0010] R1 and R2 are independently H, a halogen atom, an alkyl group, a haloalkyl group, a cyano group, a siloxane group, an alkoxy group or a haloalkoxy group, or R1 and R2 are linked to form a cyclic hydrocarbon;

[0011] The additive B is one or more of the substances represented by the structural formulas (2), (3) and (4).

[0012] m and n are independently 0, 1 or 2, and A, B, and D are independently a group consisting of one or more of O, S, N, and P, or an alkyl group;

[0013] a, b, c are independently 0, 1 or 2; E, G, L, J are independently a group consisting of one or more of O, S, N, P, or an alkyl group;

[0014] R 6 , R 7 are independently hydrogen, alkyl, halogen or alkoxy;

[0015] The additive C is one or more fluorine-containing lithium borate salts.

[0016] Preferably, in the structural formula (1), R1 and R2 are independently H, F, a straight-chain alkyl group having 1 to 4 carbon atoms or a tert-butyl group, R1 and R2 are connected to form a hexacyclic aromatic hydrocarbon, or R1 and R2 are connected to form a hexacyclic alkane having 3 to 10 carbon atoms.

[0017] Preferably, in the structural formula (2), n is 0, m is 1, and at least one of A, B, and D is O.

[0018] Preferably, in the structural formula (3), E, ​​G, L and J are all O.

[0019] Preferably, the additive A is and / or

[0020] Preferably, the additive B is one or more of methylene methanedisulfonate, 1,3-propanedisulfonic anhydride, vinyl sulfate, and 4-methylethylene sulfate.

[0021] Preferably, the additive C is one or more of lithium difluorooxalatoborate, lithium tetrafluoroborate or lithium monooxalatodifluoroborate.

[0022] Preferably, the mass ratio of the additive A, the additive B and the additive C is (0.1-3):(0.1-3):1.

[0023] More preferably, the mass ratio of the additive A, the additive B and the additive C is (1-3):(0.5-3):1.

[0024] Preferably, the mass percentage of the additive A in the non-aqueous electrolyte is 0.1% to 2%.

[0025] Further preferably, the mass percentage of the additive A in the non-aqueous electrolyte is 0.5% to 2%, for example, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.2%, 1.4%, 1.6%, 1.8%, 2.0%.

[0026] Preferably, the mass percentage of the additive B in the non-aqueous electrolyte is 0.1% to 2%.

[0027] Further preferably, the mass percentage of the additive B in the non-aqueous electrolyte is 0.3% to 1.5%, for example, 0.3%, 0.5%, 0.7%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%.

[0028] Preferably, the mass percentage of the additive C in the non-aqueous electrolyte is 0.2% to 1%.

[0029] Further preferably, the mass percentage of the additive C in the non-aqueous electrolyte is 0.2% to 0.8%, for example, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%.

[0030] Preferably, the additives also include other additives, and the other additives include one or more of vinyl ethylene carbonate (VC), tris(trimethylsilyl) borate, 1,3,6-hexanetrinitrile (HTCN), 1-3 propane sultone, tris(trimethylsilyl) phosphate, succinonitrile (SN), fluoroethylene carbonate (FEC), lithium bis(fluorosulfonyl)imide, 1,2-bis(2-cyanoethoxy)ethane, 1,4-dicyano-2-butene, 1,2,3-tris(2-cyanoethoxy)propane, sebacate, adiponitrile, tris(2,2,2-trifluoroethyl) borate, vinylene carbonate, biphenyl, cyclohexylbenzene (CHB), trioctyl phosphate (TOP), and vinyl sulfite (ES).

[0031] Preferably, the mass percentage of the other additives in the electrolyte is 0.1% to 15%, for example, 0.1%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%.

[0032] Preferably, the non-aqueous organic solvent is a mixture of cyclic esters and chain esters, wherein the cyclic ester is one or more of γ-butyrolactone (GBL), ethylene carbonate (EC), propylene carbonate (PC), and fluoroethylene carbonate (FEC); the chain ester is one or more of dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), methylpropyl carbonate (MPC), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl butyrate (MB), ethyl butyrate (EB), propyl butyrate (PB), methyl fluoropropionate (FMP), propyl fluoropropionate, ethyl fluoropropionate, and ethyl fluoroacetate.

[0033] More preferably, the non-aqueous organic solvent is a mixture of one or more of ethylene carbonate, propylene carbonate, propyl propionate, ethyl propionate and diethyl carbonate.

[0034] Still more preferably, the non-aqueous organic solvent is composed of dimethyl carbonate, ethylene carbonate and propyl propionate, and the volume ratio of dimethyl carbonate, ethylene carbonate and propyl propionate is (1-3):1:(4-6).

[0035] Still further preferably, the non-aqueous organic solvent is composed of diethyl carbonate, ethylene carbonate, propylene carbonate, ethyl propionate and propyl propionate, and the volume ratio of diethyl carbonate, ethylene carbonate, propylene carbonate, ethyl propionate and propyl propionate is (0.5-1.5):(1-3):1:(1-5):(1-5).

[0036] Preferably, the lithium salt is one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium hexafluoroarsenate (LiAsF6), anhydrous lithium perchlorate (LiClO4), lithium bis(trifluoromethylsulfonyl)imide (LiN(SO2CF3)2), lithium difluorobis(oxalyl)phosphate (LiPF2(C2O4)2), lithium difluorophosphate (LiPO2F2), lithium trifluoromethylsulfonate (LiSO3CF3), and lithium bis(fluorosulfonyl)imide (LiN(SO2F)2).

[0037] Further preferably, the concentration of the lithium salt is 0.8-3 mol / L, for example 0.8 mol / L, 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L, 3 mol / L.

[0038] The present invention also provides a lithium ion secondary battery, comprising a positive electrode, a negative electrode and a non-aqueous electrolyte, wherein the non-aqueous electrolyte is the non-aqueous electrolyte described above.

[0039] Preferably, the positive electrode of the lithium-ion secondary battery is lithium iron phosphate or lithium cobalt oxide, and the negative electrode of the lithium battery is graphite.

[0040] Due to the application of the above technical solution, the present invention has the following advantages compared with the prior art: the present invention effectively suppresses the increase of water content, acidity and color number of the electrolyte under high temperature environment by compounding additive A, additive B and additive C, thereby improving the high temperature performance of lithium ion secondary batteries. Furthermore, by using appropriate amounts of other additives, the cycle performance of high-voltage lithium batteries is effectively improved, especially the high temperature cycle performance and high temperature shelf performance. DETAILED DESCRIPTION

[0041] The present invention is further described below in conjunction with the examples. However, the present invention is not limited to the following examples. The implementation conditions used in the examples can be further adjusted according to the different requirements of specific use, and the implementation conditions not specified are conventional conditions in the industry. The technical features involved in each embodiment of the present invention can be combined with each other as long as they do not conflict with each other.

[0042] In the following examples and comparative examples, the materials used are all commercially available products.

[0043] 2-Thiazolyl isocyanate: Benzothiazol-2-yl isocyanate:

[0044] Embodiment 1:

[0045] In an argon-filled glove box (H2O content <10ppm), EC, PC and PP were mixed uniformly in a volume ratio of 2:1:5, LiPF6 with a final concentration of 1.2 mol / L was added to the mixed solution, and then 0.5wt% of lithium difluorooxalatoborate, 1wt% of methylene disulfonate and 0.1wt% of 2-thiazole isocyanate were added respectively to prepare an electrolyte.

[0046] Embodiment 2:

[0047] In an argon-filled glove box (H2O content <10ppm), EC, PC and PP were mixed uniformly in a volume ratio of 2:1:5, LiPF6 with a final concentration of 1.2 mol / L was added to the mixed solution, and then 0.5wt% of lithium difluorooxalatoborate, 1wt% of methylene disulfonate and 0.5wt% of 2-thiazole isocyanate were added respectively to prepare an electrolyte.

[0048] Embodiment 3:

[0049] In an argon-filled glove box (H2O content <10ppm), EC, PC and PP were mixed uniformly in a volume ratio of 2:1:5, LiPF6 with a final concentration of 1.2 mol / L was added to the mixed solution, and then 0.5wt% of lithium difluorooxalatoborate, 1wt% of methylene disulfonate and 1wt% of 2-thiazole isocyanate were added respectively to prepare an electrolyte.

[0050] Embodiment 4:

[0051] In an argon-filled glove box (H2O content <10ppm), EC, PC and PP were mixed uniformly in a volume ratio of 2:1:5, LiPF6 with a final concentration of 1.2 mol / L was added to the mixed solution, and then 0.5wt% of lithium difluorooxalatoborate, 1wt% of vinyl sulfate and 0.1wt% of 2-thiazole isocyanate were added respectively to prepare an electrolyte.

[0052] Embodiment 5:

[0053] In an argon-filled glove box (H2O content <10ppm), EC, PC and PP were mixed uniformly in a volume ratio of 2:1:5, LiPF6 with a final concentration of 1.2 mol / L was added to the mixed solution, and then 0.5wt% of lithium difluorooxalatoborate, 1wt% of vinyl sulfate and 0.5wt% of 2-thiazole isocyanate were added respectively to prepare an electrolyte.

[0054] Embodiment 6:

[0055] In an argon-filled glove box (H2O content <10ppm), EC, PC and PP were mixed uniformly in a volume ratio of 2:1:5, LiPF6 with a final concentration of 1.2 mol / L was added to the mixed solution, and then 0.5wt% of lithium difluorooxalatoborate, 1wt% of vinyl sulfate and 1wt% of 2-thiazole isocyanate were added respectively to prepare an electrolyte.

[0056] Embodiment 7:

[0057] In an argon-filled glove box (H2O content <10ppm), EC, PC and PP were mixed uniformly in a volume ratio of 2:1:5, LiPF6 with a final concentration of 1.2 mol / L was added to the mixed solution, and then 0.5wt% of lithium difluorooxalatoborate, 1wt% of methylene disulfonate and 0.1wt% of benzothiazol-2-yl isocyanate were added respectively to prepare an electrolyte.

[0058] Embodiment 8:

[0059] In an argon-filled glove box (H2O content <10ppm), EC, PC and PP were mixed uniformly in a volume ratio of 2:1:5, LiPF6 with a final concentration of 1.2 mol / L was added to the mixed solution, and then 0.5wt% of lithium difluorooxalatoborate, 1wt% of methylene disulfonate and 0.5wt% of benzothiazol-2-yl isocyanate were added respectively to prepare an electrolyte.

[0060] Embodiment 9:

[0061] In an argon-filled glove box (H2O content <10ppm), EC, PC and PP were mixed uniformly in a volume ratio of 2:1:5, LiPF6 with a final concentration of 1.2 mol / L was added to the mixed solution, and then 0.5wt% of lithium difluorooxalatoborate, 1wt% of methylene disulfonate and 1wt% of benzothiazol-2-yl isocyanate were added respectively to prepare an electrolyte.

[0062] Embodiment 10:

[0063] In an argon-filled glove box (H2O content <10ppm), EC, PC and PP were mixed uniformly in a volume ratio of 2:1:5, LiPF6 with a final concentration of 1.2 mol / L was added to the mixed solution, and then 0.5wt% of lithium difluorooxalatoborate, 1wt% of vinyl sulfate and 0.1wt% of benzothiazol-2-yl isocyanate were added respectively to prepare an electrolyte.

[0064] Embodiment 11:

[0065] In an argon-filled glove box (H2O content <10ppm), EC, PC and PP were mixed uniformly in a volume ratio of 2:1:5, LiPF6 with a final concentration of 1.2 mol / L was added to the mixed solution, and then 0.5wt% of lithium difluorooxalatoborate, 1wt% of vinyl sulfate and 0.5wt% of benzothiazol-2-yl isocyanate were added respectively to prepare an electrolyte.

[0066] Embodiment 12:

[0067] In an argon-filled glove box (H2O content <10ppm), EC, PC and PP were mixed uniformly in a volume ratio of 2:1:5, LiPF6 with a final concentration of 1.2 mol / L was added to the mixed solution, and then 0.5wt% of lithium difluorooxalatoborate, 1wt% of vinyl sulfate and 1wt% of benzothiazol-2-yl isocyanate were added respectively to prepare an electrolyte.

[0068] Comparative Example 1:

[0069] In an argon-filled glove box (H2O content <10ppm), EC, PC and PP were mixed evenly in a volume ratio of 2:1:5, LiPF6 with a final concentration of 1.2 mol / L was added to the mixed solution, and then 0.5wt% of lithium difluorooxalatoborate and 1wt% of methylene disulfonate were added respectively to prepare an electrolyte.

[0070] Comparative Example 2:

[0071] In an argon-filled glove box (H2O content <10ppm), EC, PC and PP were mixed uniformly in a volume ratio of 2:1:5, LiPF6 with a final concentration of 1.2 mol / L was added to the mixed solution, and then 0.5wt% of lithium difluorooxalatoborate and 1wt% of vinyl sulfate were added respectively to prepare an electrolyte.

[0072] The electrolytes of Examples 1 to 12 and Comparative Examples 1 and 2 were sealed and packaged in 250 ml plastic bottles, respectively, and placed at 45° C. for 1 week. The water content of the electrolytes before and after placement was tested by the Karl Fischer method, the HF content was tested by the acid-base titration method, and the color number was tested by the Pt-Co colorimetry method. The relevant experimental data are shown in Table 1.

[0073] Table 1

[0074]

[0075] Embodiment 13:

[0076] In an argon-filled glove box (H2O content <10ppm), DEC, EC, PC, EP and PP were uniformly mixed in a volume ratio of 1:2:1:3:3, LiPF6 was added to the mixed solution with a final concentration of 1.15 mol / L, and then 2wt% of succinonitrile, 4wt% of fluoroethylene carbonate, 0.5wt% of lithium difluorooxalatoborate, 0.3wt% of methylene disulfonate and 0.1wt% of 2-thiazole isocyanate were added respectively to prepare an electrolyte.

[0077] Embodiment 14:

[0078] In an argon-filled glove box (H2O content <10ppm), DEC, EC, PC, EP and PP were uniformly mixed in a volume ratio of 1:2:1:3:3, LiPF6 was added to the mixed solution with a final concentration of 1.15 mol / L, and then 2wt% of succinonitrile, 4wt% of fluoroethylene carbonate, 0.5wt% of lithium difluorooxalatoborate, 0.3wt% of methylene disulfonate and 0.5wt% of 2-thiazole isocyanate were added respectively to prepare an electrolyte.

[0079] Embodiment 15:

[0080] In an argon-filled glove box (H2O content <10ppm), DEC, EC, PC, EP and PP were uniformly mixed in a volume ratio of 1:2:1:3:3, LiPF6 was added to the mixed solution with a final concentration of 1.15 mol / L, and then 2wt% of succinonitrile, 4wt% of fluoroethylene carbonate, 0.5wt% of lithium difluorooxalatoborate, 0.3wt% of methylene disulfonate and 1wt% of 2-thiazole isocyanate were added respectively to prepare an electrolyte.

[0081] Embodiment 16:

[0082] In an argon-filled glove box (H2O content <10ppm), DEC, EC, PC, EP and PP were uniformly mixed in a volume ratio of 1:2:1:3:3, LiPF6 was added to the mixed solution with a final concentration of 1.15 mol / L, and then 2wt% of succinonitrile, 4wt% of fluoroethylene carbonate, 0.5wt% of lithium difluorooxalatoborate, 0.3wt% of methylene disulfonate and 0.1wt% of benzothiazol-2-yl isocyanate were added respectively to prepare an electrolyte.

[0083] Embodiment 17:

[0084] In an argon-filled glove box (H2O content <10ppm), DEC, EC, PC, EP and PP were uniformly mixed in a volume ratio of 1:2:1:3:3, LiPF6 was added to the mixed solution with a final concentration of 1.15 mol / L, and then 2wt% of succinonitrile, 4wt% of fluoroethylene carbonate, 0.5wt% of lithium difluorooxalatoborate, 0.3wt% of methylene disulfonate and 0.5wt% of benzothiazol-2-yl isocyanate were added respectively to prepare an electrolyte.

[0085] Embodiment 18:

[0086] In an argon-filled glove box (H2O content <10ppm), DEC, EC, PC, EP and PP were uniformly mixed in a volume ratio of 1:2:1:3:3, LiPF6 was added to the mixed solution with a final concentration of 1.15 mol / L, and then 2wt% of succinonitrile, 4wt% of fluoroethylene carbonate, 0.5wt% of lithium difluorooxalatoborate, 0.3wt% of methylene disulfonate and 1wt% of benzothiazol-2-yl isocyanate were added respectively to prepare an electrolyte.

[0087] Embodiment 19:

[0088] In an argon-filled glove box (H2O content <10ppm), DEC, EC, PC, EP and PP were uniformly mixed in a volume ratio of 1:2:1:3:3, LiPF6 with a final concentration of 1.15 mol / L was added to the mixed solution, and then 2wt% of succinonitrile, 4wt% of fluoroethylene carbonate, 0.5wt% of lithium difluorooxalatoborate, 0.5wt% of vinyl sulfate and 0.1wt% of 2-thiazole isocyanate were added respectively to prepare an electrolyte.

[0089] Embodiment 20:

[0090] In an argon-filled glove box (H2O content <10ppm), DEC, EC, PC, EP and PP were uniformly mixed in a volume ratio of 1:2:1:3:3, LiPF6 with a final concentration of 1.15 mol / L was added to the mixed solution, and then 2wt% of succinonitrile, 4wt% of fluoroethylene carbonate, 0.5wt% of lithium difluorooxalatoborate, 0.5wt% of vinyl sulfate and 0.5wt% of 2-thiazole isocyanate were added respectively to prepare an electrolyte.

[0091] Embodiment 21:

[0092] In an argon-filled glove box (H2O content <10ppm), DEC, EC, PC, EP and PP were uniformly mixed in a volume ratio of 1:2:1:3:3, LiPF6 with a final concentration of 1.15 mol / L was added to the mixed solution, and then 2wt% of succinonitrile, 4wt% of fluoroethylene carbonate, 0.5wt% of lithium difluorooxalatoborate, 0.5wt% of vinyl sulfate and 1wt% of 2-thiazole isocyanate were added respectively to prepare an electrolyte.

[0093] Embodiment 22:

[0094] In an argon-filled glove box (H2O content <10ppm), DEC, EC, PC, EP and PP were uniformly mixed in a volume ratio of 1:2:1:3:3, LiPF6 was added to the mixed solution with a final concentration of 1.15 mol / L, and then 2wt% of succinonitrile, 4wt% of fluoroethylene carbonate, 0.5wt% of lithium difluorooxalatoborate, 0.5wt% of vinyl sulfate and 0.1wt% of benzothiazol-2-yl isocyanate were added respectively to prepare an electrolyte.

[0095] Embodiment 23:

[0096] In an argon-filled glove box (H2O content <10ppm), DEC, EC, PC, EP and PP were uniformly mixed in a volume ratio of 1:2:1:3:3, LiPF6 was added to the mixed solution with a final concentration of 1.15 mol / L, and then 2wt% of succinonitrile, 4wt% of fluoroethylene carbonate, 0.5wt% of lithium difluorooxalatoborate, 0.5wt% of vinyl sulfate and 0.5wt% of benzothiazol-2-yl isocyanate were added respectively to prepare an electrolyte.

[0097] Embodiment 24:

[0098] In an argon-filled glove box (H2O content <10ppm), DEC, EC, PC, EP and PP were uniformly mixed in a volume ratio of 1:2:1:3:3, LiPF6 with a final concentration of 1.15 mol / L was added to the mixed solution, and then 2wt% of succinonitrile, 4wt% of fluoroethylene carbonate, 0.5wt% of lithium difluorooxalatoborate, 0.5wt% of vinyl sulfate and 1wt% of benzothiazol-2-yl isocyanate were added respectively to prepare an electrolyte.

[0099] Embodiment 25:

[0100] In an argon-filled glove box (H2O content <10ppm), DEC, EC, PC, EP and PP were uniformly mixed in a volume ratio of 1:2:1:3:3, LiPF6 was added to the mixed solution with a final concentration of 1.15 mol / L, and then 2wt% of succinonitrile, 4wt% of fluoroethylene carbonate, 0.5wt% of lithium difluorooxalatoborate, 0.1wt% of methylene disulfonate and 0.5wt% of 2-thiazole isocyanate were added respectively to prepare an electrolyte.

[0101] Embodiment 26:

[0102] In an argon-filled glove box (H2O content <10ppm), DEC, EC, PC, EP and PP were uniformly mixed in a volume ratio of 1:2:1:3:3, LiPF6 was added to the mixed solution with a final concentration of 1.15 mol / L, and then 2wt% of succinonitrile, 4wt% of fluoroethylene carbonate, 0.5wt% of lithium difluorooxalatoborate, 0.5wt% of methylene disulfonate and 0.5wt% of 2-thiazole isocyanate were added respectively to prepare an electrolyte.

[0103] Embodiment 27:

[0104] In an argon-filled glove box (H2O content <10ppm), DEC, EC, PC, EP and PP were uniformly mixed in a volume ratio of 1:2:1:3:3, LiPF6 with a final concentration of 1.15 mol / L was added to the mixed solution, and then 2wt% of succinonitrile, 4wt% of fluoroethylene carbonate, 0.5wt% of lithium difluorooxalatoborate, 1wt% of methylene disulfonate and 0.5wt% of 2-thiazole isocyanate were added respectively to prepare an electrolyte.

[0105] Embodiment 28:

[0106] In an argon-filled glove box (H2O content <10ppm), DEC, EC, PC, EP and PP were uniformly mixed in a volume ratio of 1:2:1:3:3, LiPF6 with a final concentration of 1.15 mol / L was added to the mixed solution, and then 2wt% of succinonitrile, 4wt% of fluoroethylene carbonate, 0.5wt% of lithium difluorooxalatoborate, 1wt% of lithium bis(fluorosulfonyl)imide, 0.5wt% of methylene disulfonate and 0.5wt% of 2-thiazole isocyanate were added respectively to prepare an electrolyte.

[0107] Embodiment 29:

[0108] In an argon-filled glove box (H2O content <10ppm), DEC, EC, PC, EP and PP were uniformly mixed in a volume ratio of 1:2:1:3:3, LiPF6 was added to the mixed solution with a final concentration of 1.15 mol / L, and then 2wt% of succinonitrile, 4wt% of fluoroethylene carbonate, 0.5wt% of lithium difluorooxalatoborate, 1wt% of tris(trimethylsilyl)phosphate, 1wt% of methylene disulfonate and 0.5wt% of 2-thiazole isocyanate were added respectively to prepare an electrolyte.

[0109] Embodiment 30:

[0110] In an argon-filled glove box (H2O content <10ppm), DEC, EC, PC, EP and PP were uniformly mixed in a volume ratio of 1:2:1:3:3, LiPF6 was added to the mixed solution with a final concentration of 1.15 mol / L, and then 2wt% of succinonitrile, 4wt% of fluoroethylene carbonate, 0.5wt% of lithium difluorooxalatoborate, 1wt% of tris(trimethylsilyl)borate, 1wt% of methylene disulfonate and 0.5wt% of 2-thiazole isocyanate were added respectively to prepare an electrolyte.

[0111] Embodiment 31:

[0112] In an argon-filled glove box (H2O content <10ppm), DEC, EC, PC, EP and PP were uniformly mixed in a volume ratio of 1:2:1:3:3, LiPF6 with a final concentration of 1.15 mol / L was added to the mixed solution, and then 2wt% of succinonitrile, 4wt% of fluoroethylene carbonate, 0.5wt% of lithium difluorooxalatoborate, 3wt% of 1,3,6-hexanetrinitrile, 1wt% of methanedisulfonic acid methylene ester and 0.5wt% of 2-thiazole isocyanate were added respectively to prepare an electrolyte.

[0113] Embodiment 32:

[0114] In an argon-filled glove box (H2O content <10ppm), DEC, EC, PC, EP and PP were uniformly mixed in a volume ratio of 1:2:1:3:3, LiPF6 was added to the mixed solution with a final concentration of 1.15 mol / L, and then 2wt% of succinonitrile, 4wt% of fluoroethylene carbonate, 0.5wt% of lithium difluorooxalatoborate, 3wt% of 1-3-propane sultone, 1wt% of methanedisulfonic acid methylene ester and 0.5wt% of 2-thiazole isocyanate were added respectively to prepare an electrolyte.

[0115] Comparative Example 3:

[0116] In an argon-filled glove box (H2O content <10ppm), DEC, EC, PC, EP and PP were uniformly mixed in a volume ratio of 1:2:1:3:3, LiPF6 was added to the mixed solution with a final concentration of 1.15 mol / L, and then 2wt% of succinonitrile, 4wt% of fluoroethylene carbonate and 0.5wt% of lithium difluorooxalatoborate were added respectively to prepare an electrolyte.

[0117] Comparative Example 4:

[0118] In an argon-filled glove box (H2O content <10ppm), DEC, EC, PC, EP and PP were uniformly mixed in a volume ratio of 1:2:1:3:3, LiPF6 was added to the mixed solution with a final concentration of 1.15 mol / L, and then 2wt% of succinonitrile, 4wt% of fluoroethylene carbonate, 0.5wt% of lithium difluorooxalatoborate and 0.3wt% of methylene methanedisulfonate were added respectively to prepare an electrolyte.

[0119] Comparative Example 5:

[0120] In an argon-filled glove box (H2O content <10ppm), DEC, EC, PC, EP and PP were uniformly mixed in a volume ratio of 1:2:1:3:3, LiPF6 was added to the mixed solution with a final concentration of 1.15 mol / L, and then 2wt% of succinonitrile, 4wt% of fluoroethylene carbonate, 0.5wt% of lithium difluorooxalatoborate and 0.5wt% of 2-thiazole isocyanate were added respectively to prepare an electrolyte.

[0121] Comparative Example 6:

[0122] In an argon-filled glove box (H2O content <10ppm), DEC, EC, PC, EP and PP were uniformly mixed in a volume ratio of 1:2:1:3:3, LiPF6 was added to the mixed solution with a final concentration of 1.15 mol / L, and then 2wt% of succinonitrile, 4wt% of fluoroethylene carbonate, 0.5wt% of lithium difluorooxalatoborate and 0.5wt% of vinyl sulfate were added respectively to prepare an electrolyte.

[0123] Comparative Example 7:

[0124] In an argon-filled glove box (H2O content <10ppm), DEC, EC, PC, EP and PP were uniformly mixed in a volume ratio of 1:2:1:3:3, LiPF6 was added to the mixed solution with a final concentration of 1.15 mol / L, and then 2wt% of succinonitrile, 4wt% of fluoroethylene carbonate, 0.5wt% of lithium difluorooxalatoborate and 0.5wt% of benzothiazol-2-yl isocyanate were added respectively to prepare an electrolyte.

[0125] The electrolytes prepared in Examples 13 to 32 and Comparative Examples 3 to 7 were tested in 4.55V lithium cobalt oxide graphite batteries for capacity retention after being placed at 85°C for 4 hours, i.e., the batteries were charged to 4.55V at 1C under constant current / constant voltage (CC / CV) conditions at 25°C, and then placed in an oven at 85°C for 4 hours; the capacity of the batteries discharged at 1C to 3.0V after placing them was divided by the capacity of the batteries charged under the same conditions before placing them and then discharged at 1C to 3.0V; the battery swelling rate after placing them at 85°C for 4 hours, i.e., the battery swelling rate after placing them at 85°C for 4 hours was The difference between the battery thickness and the battery thickness before shelving is divided by the battery thickness before shelving; the capacity retention rate at 45°C for 300 cycles, that is, the capacity after 300 cycles at 45°C constant current / constant voltage (CC / CV) conditions when charged to 4.55V at 1C and then discharged to 3.0V at 1C divided by the capacity before the cycle when charged to 4.55V and then discharged to 3.0V at 1C under the same conditions; the battery swelling rate at 45°C for 300 cycles, that is, the difference between the battery thickness after the cycle and the battery thickness before the cycle divided by the battery thickness before the cycle. The relevant experimental data are shown in Table 2.

[0126] Table 2

[0127]

[0128] The above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable people familiar with this technology to understand the contents of the present invention and implement them accordingly. They cannot be used to limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention should be included in the protection scope of the present invention.

Claims

1. A non-aqueous electrolyte comprising a lithium salt, a non-aqueous organic solvent and an additive, characterized in that: The additives include additive A, additive B and additive C, The additive A is one or more of the substances represented by structural formula (1), R1 and R2 are independently H, a halogen atom, an alkyl group, a haloalkyl group, a cyano group, a siloxane group, an alkoxy group or a haloalkoxy group, or R1 and R2 are linked to form a cyclic hydrocarbon; The additive B is one or more of the substances represented by the structural formulas (2), (3) and (4). m and n are independently 0, 1 or 2, and A, B, and D are independently a group consisting of one or more of O, S, N, and P, or an alkyl group; a, b, c are independently 0, 1 or 2; E, G, L, J are independently a group consisting of one or more of O, S, N, P, or an alkyl group; R 6 , R 7 are independently hydrogen, alkyl, halogen or alkoxy; The additive C is one or more fluorine-containing lithium borate salts.

2. The non-aqueous electrolyte according to claim 1, characterized in that: In the structural formula (1), R1 and R2 are independently H, F, a straight-chain alkyl group having 1 to 4 carbon atoms or a tert-butyl group, R1 and R2 are connected to form a six-membered aromatic hydrocarbon, or R1 and R2 are connected to form a six-membered cycloalkane having 3 to 10 carbon atoms; And / or, in the structural formula (2), n is 0, m is 1, and at least one of A, B, and D is O; And / or, in the structural formula (3), E, ​​G, L, and J are all O.

3. The non-aqueous electrolyte according to claim 1, characterized in that: The additive A is and / or And / or, the additive B is one or more of methylene methanedisulfonate, 1,3-propanedisulfonic anhydride, vinyl sulfate, and 4-methylethylene sulfate; And / or, the additive C is one or more of lithium difluorooxalatoborate, lithium tetrafluoroborate or lithium monooxalatodifluoroborate.

4. The non-aqueous electrolyte according to claim 1, characterized in that: The mass ratio of the additive A, the additive B and the additive C is (0.1-3):(0.1-3):

1.

5. The non-aqueous electrolyte according to claim 1, characterized in that: The mass percentage of the additive A in the non-aqueous electrolyte is 0.1% to 2%; And / or, the mass percentage of the additive B in the non-aqueous electrolyte is 0.1% to 2%; And / or, the mass percentage of the additive C in the non-aqueous electrolyte is 0.2% to 1%.

6. The non-aqueous electrolyte according to claim 1, characterized in that: The additives also include other additives, and the other additives include one or more of vinyl ethylene carbonate, tris(trimethylsilyl)borate, 1,3,6-hexanetrinitrile, 1-3 propane sultone, tris(trimethylsilyl)phosphate, succinonitrile, fluoroethylene carbonate, lithium bis(fluorosulfonyl)imide, 1,2-bis(2-cyanoethoxy)ethane, 1,4-dicyano-2-butene, 1,2,3-tris(2-cyanoethoxy)propane, sebacate, adiponitrile, tris(2,2,2-trifluoroethyl)borate, vinylene carbonate, biphenyl, cyclohexylbenzene, trioctyl phosphate, and vinyl sulfite; And / or, the mass percentage of the other additives in the electrolyte is 0.1% to 15%.

7. The non-aqueous electrolyte according to claim 1, characterized in that: The non-aqueous organic solvent is a mixture of cyclic esters and chain esters, the cyclic ester is one or more of γ-butyrolactone, ethylene carbonate, propylene carbonate, and fluoroethylene carbonate; the chain ester is one or more of dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, methylpropyl carbonate, methyl propionate, ethyl propionate, propyl propionate, methyl acetate, ethyl acetate, propyl acetate, methyl butyrate, ethyl butyrate, propyl butyrate, methyl fluoropropionate, ethyl fluoropropionate, and ethyl fluoroacetate.

8. The non-aqueous electrolyte according to claim 1, characterized in that: The lithium salt is one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenate, anhydrous lithium perchlorate, lithium bis(trifluoromethylsulfonyl)imide, lithium difluorophosphate, lithium trifluoromethylsulfonate, and lithium bis(trifluorosulfonyl)imide.

9. The non-aqueous electrolyte according to claim 1, characterized in that: The concentration of the lithium salt is 0.8-1.5 mol / L.

10. A lithium ion secondary battery comprising a positive electrode, a negative electrode and a non-aqueous electrolyte, characterized in that: The non-aqueous electrolyte is the non-aqueous electrolyte according to any one of claims 1 to 9.

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