Non-aqueous electrolyte and lithium-ion battery

Abstract

A non-aqueous electrolyte and a lithium-ion battery. The non-aqueous electrolyte comprises a lithium salt, an organic solvent, an additive A and an additive B, wherein the structural formula of the additive A is as shown in (I), where R1 is selected from an alkylene group, a fluoroalkylene group, an alkenylene group or a fluoroalkenylene group, and R2 is selected from a fluoroalkyl group or a fluoroalkenyl group; and the additive B is a boron-containing lithium salt. By compounding the additive A and the boron-containing lithium salt additive, the cycle performance, high-temperature performance and rate capability of a lithium-ion battery are improved; and by means of further combination with other components in the non-aqueous electrolyte, the high-temperature performance and cycle performance of the lithium-ion battery at a conventional voltage are ensured, and moreover when the voltage is increased to 4.5 V or even higher, the lithium-ion battery still has better high-temperature performance and cycle performance, and also has better safety performance and electrochemical performance.

Description

Non-aqueous electrolyte and lithium-ion battery Technical Field

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

[0002] With the emergence of emerging consumer sectors such as mobile phones, tablets, smart wearables, and ETC (Electronic Toy Cars), lithium-ion batteries (Li-ion Batteries) have demonstrated significant advantages due to their high energy density and long cycle life. Sulfonyl compounds, typically in the form of small organic molecules, are used in electrolytes as solvent additives for non-aqueous electrolytes in Li-ion batteries. Utilizing the film-forming properties of the sulfonyl group, they form a stable SEI film / protective film on the electrode surface, thereby inhibiting gas evolution and improving the battery's high-temperature storage performance, cycle performance, and lifespan. Lithium salts containing sulfonyl groups are also widely used in electrolytes, particularly sulfonylimide salts. The EU REACH regulation requires manufacturers or importers of SVHCs to notify the European Chemicals Agency (ECHA) of any substance present in an article if the substance accounts for more than 0.1% by weight of the total article and the total production or import volume reaches 1 ton per year or more. Within six months of a substance being included on the REACH Candidate List for Authorization (also known as the SVHC List), companies must submit this notification document to ECHA. PS was added to the SVHC (Substances of Very High Concern) list on December 17, 2015. As a hazardous substance, while not on the Restriction and Authorization List, it is on the Candidate List for Authorization (meaning it may be formally included on the Authorization List in the future). If it is formally included on the Authorization List, importers will need to obtain authorization for its use. If authorization is denied, the substance will be banned. As the SVHC list expands, many sulfur-containing compounds may be restricted in the future. Therefore, it is necessary to develop a sulfur-free electrolyte with good high-temperature and cycle performance.

[0003] In previous studies, a non-aqueous electrolyte and lithium battery that does not contain sulfur and has excellent cycle performance and high-temperature storage performance were developed, as detailed in patent CN112510259B. However, as the research continued to deepen, it was found that when the voltage of the lithium battery in the patent gradually increased to 4.5V and above, the high-temperature performance and cycle performance of the battery decreased, and the safety performance decreased accordingly. In response to the problem of battery performance under high voltage, based on the research of this patent, an electrolyte and lithium battery that does not contain sulfur additives and can improve the high-temperature performance and discharge performance of the battery under high voltage were developed, as detailed in patent CN116154281A. However, as the research continued to deepen, it was found that the high-temperature performance and high-temperature cycle performance of the lithium battery involved in patent CN116154281A still need to be further improved.

[0004] Summary of the Invention

[0005] The object of the present invention is to provide a non-aqueous electrolyte and a lithium ion battery with better high temperature performance, cycle performance and rate performance.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0007] A non-aqueous electrolyte comprising a lithium salt, an organic solvent and an additive, wherein the additive comprises an additive A and an additive B, and the structural formula of the additive A is wherein R1 is selected from alkylene, fluoroalkylene, alkenylene or fluoroalkenylene, and R2 is selected from fluoroalkyl or fluoroalkenyl;

[0008] The additive B is a boron-containing lithium salt.

[0009] Preferably, R1 is selected from an alkylene group having 1 to 3 carbon atoms or a fluoroalkylene group having 1 to 3 carbon atoms.

[0010] Further preferably, the R1 is selected from methylene (-CH2-), ethylene (-CH2CH2-) or propylene (-CH2CH2CH2- or -C(CH3)2-).

[0011] Preferably, R2 is selected from a fluoroalkyl group having 1 to 3 carbon atoms.

[0012] Further preferably, R2 is selected from fluoroethyl (-CH2CH2F, -CHFCH3), difluoroethyl (-CH2CHF2, -CHFCH2F, -CF2CH3) or trifluoroethyl (-CH2CF3, -CF3CH3, -CF2CH2F, -CHFCHF2).

[0013] In some embodiments, the additive A is one or more of trifluoroethyl propargyl carbonate, difluoroethyl propargyl carbonate, and fluoroethyl propargyl carbonate.

[0014] Preferably, the additive A accounts for 0.01 to 1% of the total mass of the non-aqueous electrolyte.

[0015] Further preferably, the additive A accounts for 0.1-1% of the total mass of the non-aqueous electrolyte, for example, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9% or 1%.

[0016] Preferably, the boron-containing lithium salt of the additive B includes one or more of lithium difluorooxalatoborate, lithium tetrafluoroborate, lithium dioxalatoborate, lithium tetraborate, lithium triphenyl-n-butylborate, and lithium trimethylimidazolium tetrafluoroborate.

[0017] Preferably, the additive B accounts for 0.01-2% of the total mass of the non-aqueous electrolyte.

[0018] Further preferably, the additive B accounts for 0.1-1% of the total mass of the non-aqueous electrolyte.

[0019] Still further preferably, the additive B accounts for 0.3-1% of the total mass of the non-aqueous electrolyte, for example, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9% or 1%.

[0020] Preferably, the additives further include other additives, and the other additives are one or more of vinylene carbonate, vinyl ethylene carbonate, tris(trimethylsilyl)borate, tris(trimethylsilyl)phosphate, methyl maleic anhydride, succinic anhydride, biphenyl, cyclohexylbenzene, trioctyl phosphate, fluoroethylene carbonate, succinonitrile, adiponitrile, 1,3,6-hexanetrionitrile, 1,2-bis(2-cyanoethoxy)ethane, 1,4-dicyano-2-butene, 1,2,3-tris(2-cyanoethoxy)propane, and sebaconitrile.

[0021] Preferably, the other additives account for 2-15% of the total mass of the non-aqueous electrolyte.

[0022] Further preferably, the other additives account for 2-10% of the total mass of the non-aqueous electrolyte, for example, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9% or 10%.

[0023] In certain embodiments, the other additives include 1-3% of the total mass of the non-aqueous electrolyte, 4-8% of the total mass of the non-aqueous electrolyte, and 2-4% of the total mass of the non-aqueous electrolyte.

[0024] Preferably, the organic solvent is a mixture of cyclic esters and chain esters.

[0025] More preferably, the cyclic ester is one or more of γ-butyrolactone, ethylene carbonate, propylene carbonate, and fluoroethylene carbonate.

[0026] Further preferably, 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.

[0027] In some embodiments, the organic solvent is a mixture of dimethyl carbonate, ethylene carbonate, and ethyl methyl carbonate.

[0028] In some embodiments, the organic solvent is a mixture of ethylene carbonate, propylene carbonate, ethyl propionate, and propyl propionate.

[0029] In some embodiments, the organic solvent is a mixture of diethyl carbonate, ethylene carbonate, propylene carbonate, ethyl propionate, and propyl propionate.

[0030] Preferably, the lithium salt is one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenate, anhydrous lithium perchlorate, lithium bis(trifluoromethylsulfonyl)imide, lithium difluorobisoxalatephosphate, lithium difluorophosphate, lithium trifluoromethylsulfonate, lithium difluorobisoxalatephosphate, lithium difluorobis(oxalato)phosphate, lithium fluorosulfonate, lithium monooxalatobisfluoroborate, and lithium bisfluorosulfonylimide.

[0031] Preferably, the concentration of the lithium salt is 0.8 to 1.5 mol / L.

[0032] Further preferably, the concentration of the lithium salt is 1 to 1.3 mol / L, for example, 1 mol / L, 1.1 mol / L, 1.2 mol / L or 1.3 mol / L.

[0033] The present invention also provides a lithium ion battery comprising the non-aqueous electrolyte as described above.

[0034] Furthermore, the lithium-ion battery is a lithium cobalt oxide graphite battery or a lithium cobalt oxide silicon oxygen carbon battery.

[0035] Preferably, the lithium-ion battery is a lithium cobalt oxide graphite battery of 4.2V and above or a lithium cobalt oxide silicon oxygen carbon battery of 4.5V and above.

[0036] Due to the application of the above technical solution, the present invention has the following advantages compared with the prior art:

[0037] The present invention improves the cycle performance, high-temperature performance and rate performance of the lithium-ion battery by compounding the additive A and the boron-containing lithium salt additive B. By combining other components in the non-aqueous electrolyte, while ensuring the high-temperature performance and cycle performance of the lithium-ion battery at conventional voltage, the lithium-ion battery still has more excellent high-temperature performance, cycle performance, safety performance and electrochemical performance when the voltage is increased to 4.5V or even higher. DETAILED DESCRIPTION

[0038] The present invention is further described below with reference to the following examples. However, the present invention is not limited to the following examples. The implementation conditions used in the examples may be further adjusted according to the specific requirements of the application. Unspecified implementation conditions are conventional conditions in the industry. The technical features involved in the various embodiments of the present invention may be combined with each other as long as they do not conflict with each other.

[0039] Unless otherwise specified, the raw materials involved in the following examples and comparative examples are all commercially available products.

[0040] Unless otherwise specified, "wt%" in the present invention refers to mass percentage.

[0041] The raw materials involved in the following examples and comparative examples include: dimethyl carbonate (DMC), ethylene carbonate (EC), ethyl methyl carbonate (EMC), lithium hexafluorophosphate (LiPF6), propylene carbonate (PC), ethyl propionate (EP), propyl propionate (PP), diethyl carbonate (DEC), trifluoroethyl propargyl carbonate (CAS No.: 2361539-53-7), difluoroethyl propargyl carbonate (CAS No.: 2244079-46-5), fluoroethyl propargyl carbonate (CAS No.: 929294-69-9), propargyl acetate (CAS No.: 627-09-8), and dipropargyl carbonate (CAS No.: 79493-91-7).

[0042] Example 1

[0043] In an argon-filled glove box (H2O content <10ppm), DMC, EC and EMC were mixed in a volume ratio of 2:1:6, 1.0mol / L LiPF6 was added to the mixed solution, and then 0.1wt% of trifluoroethyl propargyl carbonate and 0.3wt% of lithium difluorooxalatoborate were added to the electrolyte respectively.

[0044] Example 2

[0045] In an argon-filled glove box (H2O content <10ppm), DMC, EC and EMC were mixed in a volume ratio of 2:1:6, 1.0mol / L LiPF6 was added to the mixed solution, and then 0.3wt% of trifluoroethyl propargyl carbonate and 0.3wt% of lithium difluorooxalatoborate were added to the electrolyte respectively.

[0046] Example 3

[0047] In an argon-filled glove box (H2O content <10ppm), DMC, EC and EMC were mixed in a volume ratio of 2:1:6, 1.0mol / L LiPF6 was added to the mixed solution, and then 0.5wt% of trifluoroethyl propargyl carbonate and 0.3wt% of lithium difluorooxalatoborate were added to the electrolyte respectively.

[0048] Example 4

[0049] In an argon-filled glove box (H2O content <10ppm), DMC, EC and EMC were mixed in a volume ratio of 2:1:6, 1.0mol / L LiPF6 was added to the mixed solution, and then 1wt% of trifluoroethyl propargyl carbonate and 0.3wt% of lithium difluorooxalatoborate were added to the electrolyte respectively.

[0050] Example 5

[0051] In an argon-filled glove box (H2O content <10ppm), DMC, EC and EMC were mixed in a volume ratio of 2:1:6, 1.0mol / L LiPF6 was added to the mixed solution, and then 0.5wt% of difluoroethyl propargyl carbonate and 0.3wt% of lithium difluorooxalatoborate were added to the electrolyte respectively.

[0052] Example 6

[0053] In an argon-filled glove box (H2O content <10ppm), DMC, EC and EMC were mixed in a volume ratio of 2:1:6, 1.0mol / L LiPF6 was added to the mixed solution, and then 0.5wt% of fluoroethyl propargyl carbonate and 0.3wt% of lithium difluorooxalatoborate were added to the electrolyte respectively.

[0054] Example 7

[0055] In an argon-filled glove box (H2O content <10ppm), DMC, EC and EMC were mixed in a volume ratio of 2:1:6, 1.0 mol / L LiPF6 was added to the mixed solution, and then 0.5 wt% of fluoroethyl propargyl carbonate and 0.1 wt% of lithium difluorooxalatoborate were added to the electrolyte respectively.

[0056] Example 8

[0057] In an argon-filled glove box (H2O content <10ppm), DMC, EC and EMC were mixed in a volume ratio of 2:1:6, 1.0 mol / L LiPF6 was added to the mixed solution, and then 0.5 wt% of fluoroethyl propargyl carbonate and 0.5 wt% of lithium difluorooxalatoborate were added to the electrolyte respectively.

[0058] Example 9

[0059] In an argon-filled glove box (H2O content <10ppm), DMC, EC and EMC were mixed in a volume ratio of 2:1:6, 1.0 mol / L LiPF6 was added to the mixed solution, and then 0.5 wt% of fluoroethyl propargyl carbonate and 1 wt% of lithium difluorooxalatoborate were added to the electrolyte respectively.

[0060] Example 10

[0061] In an argon-filled glove box (H2O content <10ppm), EC, PC, EP and PP were mixed in a volume ratio of 2:1:3:4, 1.2mol / L LiPF6 was added to the mixed solution, and then 2wt% of succinonitrile, 4wt% of fluoroethylene carbonate, 3wt% of 1,3,6-hexanetrinitrile, 0.5wt% of trifluoroethyl propargyl carbonate and 0.5wt% of lithium difluorooxalatoborate were added to the electrolyte to prepare the electrolyte.

[0062] Example 11

[0063] In an argon-filled glove box (H2O content <10ppm), EC, PC, EP and PP were mixed in a volume ratio of 2:1:3:4, 1.2mol / L LiPF6 was added to the mixed solution, and then 2wt% of succinonitrile, 4wt% of fluoroethylene carbonate, 3wt% of 1,3,6-hexanetrinitrile, 0.5wt% of difluoroethyl propargyl carbonate and 0.5wt% of lithium difluorooxalatoborate were added to the electrolyte to prepare the electrolyte.

[0064] Example 12

[0065] In an argon-filled glove box (H2O content <10ppm), EC, PC, EP and PP were mixed in a volume ratio of 2:1:3:4, 1.2mol / L LiPF6 was added to the mixed solution, and then 2wt% of succinonitrile, 4wt% of fluoroethylene carbonate, 3wt% of 1,3,6-hexanetrinitrile, 0.5wt% of fluoroethyl propargyl carbonate and 0.5wt% of lithium difluorooxalatoborate were added to the electrolyte to prepare the electrolyte.

[0066] Example 13

[0067] In an argon-filled glove box (H2O content <10ppm), DEC, EC, PC, EP and PP were mixed in a volume ratio of 1:2:1:3:3, 1.2mol / L LiPF6 was added to the mixed solution, and then 2wt% of succinonitrile, 8wt% of fluoroethylene carbonate, 3wt% of 1,3,6-hexanetrinitrile, 0.5wt% of trifluoroethyl propargyl carbonate and 0.5wt% of lithium difluorooxalatoborate were added to the electrolyte to prepare an electrolyte.

[0068] Example 14

[0069] In an argon-filled glove box (H2O content <10ppm), DEC, EC, PC, EP and PP were mixed in a volume ratio of 1:2:1:3:3, 1.2mol / L LiPF6 was added to the mixed solution, and then 2wt% of succinonitrile, 8wt% of fluoroethylene carbonate, 3wt% of 1,3,6-hexanetrinitrile, 0.5wt% of difluoroethyl propargyl carbonate and 0.5wt% of lithium difluorooxalatoborate were added to the electrolyte to prepare an electrolyte.

[0070] Example 15

[0071] In an argon-filled glove box (H2O content <10ppm), DEC, EC, PC, EP and PP were mixed in a volume ratio of 1:2:1:3:3, 1.2mol / L LiPF6 was added to the mixed solution, and then 2wt% of succinonitrile, 8wt% of fluoroethylene carbonate, 3wt% of 1,3,6-hexanetrinitrile, 0.5wt% of fluoroethyl propargyl carbonate and 0.5wt% of lithium difluorooxalatoborate were added to the electrolyte to prepare an electrolyte.

[0072] Example 16

[0073] In an argon-filled glove box (H2O content <10ppm), DEC, EC, PC, EP and PP were mixed in a volume ratio of 1:2:1:3:3, 1.2mol / L LiPF6 was added to the mixed solution, and then 2wt% of succinonitrile, 8wt% of fluoroethylene carbonate, 3wt% of 1,3,6-hexanetricarbonitrile, 0.5wt% of fluoroethyl propargyl carbonate and 0.5wt% of lithium tetrafluoroborate were added to the electrolyte to prepare an electrolyte.

[0074] Example 17

[0075] In an argon-filled glove box (H2O content <10ppm), DEC, EC, PC, EP and PP were mixed in a volume ratio of 1:2:1:3:3, 1.2mol / L LiPF6 was added to the mixed solution, and then 2wt% of succinonitrile, 8wt% of fluoroethylene carbonate, 3wt% of 1,3,6-hexanetrinitrile, 0.5wt% of fluoroethyl propargyl carbonate and 0.5wt% of lithium dioxalatoborate were added to the electrolyte to prepare an electrolyte.

[0076] Example 18

[0077] In an argon-filled glove box (H2O content <10ppm), DEC, EC, PC, EP and PP were mixed in a volume ratio of 1:2:1:3:3, 1.2mol / L LiPF6 was added to the mixed solution, and then 2wt% of succinonitrile, 8wt% of fluoroethylene carbonate, 3wt% of 1,3,6-hexanetrinitrile, 0.5wt% of fluoroethyl propargyl carbonate and 0.5wt% of lithium triphenyl-n-butylborate were added to the electrolyte to prepare an electrolyte.

[0078] Comparative Example 1

[0079] In an argon-filled glove box (H2O content <10 ppm), DMC, EC, and EMC were mixed uniformly in a volume ratio of 2:1:6, and 1.0 mol / L LiPF6 was added to the mixed solution to prepare an electrolyte.

[0080] Comparative Example 2

[0081] In an argon-filled glove box (H2O content <10ppm), DMC, EC and EMC were mixed in a volume ratio of 2:1:6, 1.0mol / L LiPF6 was added to the mixed solution, and then 0.5wt% trifluoroethyl propargyl carbonate was added to the electrolyte.

[0082] Comparative Example 3

[0083] In an argon-filled glove box (H2O content <10ppm), DMC, EC and EMC were mixed in a volume ratio of 2:1:6, 1.0mol / L LiPF6 was added to the mixed solution, and then 0.3wt% lithium difluorooxalatoborate was added to the electrolyte.

[0084] Comparative Example 4

[0085] In an argon-filled glove box (H2O content <10ppm), DMC, EC and EMC were mixed in a volume ratio of 2:1:6, 1.0mol / L LiPF6 was added to the mixed solution, and then 0.5wt% propargyl acetate was added to the electrolyte.

[0086] Comparative Example 5

[0087] In an argon-filled glove box (H2O content <10ppm), DMC, EC and EMC were mixed in a volume ratio of 2:1:6, 1.0mol / L LiPF6 was added to the mixed solution, and then 0.5wt% of dipropargyl carbonate was added to the electrolyte.

[0088] Comparative Example 6

[0089] In an argon-filled glove box (H2O content <10ppm), EC, PC, EP and PP were mixed in a volume ratio of 2:1:3:4, 1.2mol / L LiPF6 was added to the mixed solution, and then 2wt% of succinonitrile, 4wt% of fluoroethylene carbonate, 3wt% of 1,3,6-hexanetricarbonitrile and 0.5wt% of lithium difluorooxalatoborate were added to the electrolyte to prepare the electrolyte.

[0090] Comparative Example 7

[0091] In an argon-filled glove box (H2O content <10ppm), EC, PC, EP and PP were mixed in a volume ratio of 2:1:3:4, 1.2mol / L LiPF6 was added to the mixed solution, and then 2wt% of succinonitrile, 4wt% of fluoroethylene carbonate, 3wt% of 1,3,6-hexanetrinitrile and 0.5wt% of trifluoroethyl propargyl carbonate were added to the electrolyte to prepare the electrolyte.

[0092] Comparative Example 8

[0093] In an argon-filled glove box (H2O content <10ppm), EC, PC, EP and PP were mixed in a volume ratio of 2:1:3:4, 1.2mol / L LiPF6 was added to the mixed solution, and then 2wt% of succinonitrile, 4wt% of fluoroethylene carbonate, 3wt% of 1,3,6-hexanetrinitrile, 0.5wt% of propynyl acetate and 0.5wt% of lithium difluorooxalatoborate were added to the electrolyte to prepare the electrolyte.

[0094] Comparative Example 9

[0095] In an argon-filled glove box (H2O content <10ppm), EC, PC, EP and PP were mixed in a volume ratio of 2:1:3:4, 1.2mol / L LiPF6 was added to the mixed solution, and then 2wt% of succinonitrile, 4wt% of fluoroethylene carbonate, 3wt% of 1,3,6-hexanetrinitrile, 0.5wt% of dipropargyl carbonate and 0.5wt% of lithium difluorooxalatoborate were added to the electrolyte to prepare the electrolyte.

[0096] Comparative Example 10

[0097] In an argon-filled glove box (H2O content <10ppm), DEC, EC, PC, EP and PP were mixed in a volume ratio of 1:2:1:3:3, 1.2mol / L LiPF6 was added to the mixed solution, and then 2wt% of succinonitrile, 8wt% of fluoroethylene carbonate, 3wt% of 1,3,6-hexanetricarbonitrile and 0.5wt% of lithium difluorooxalatoborate were added to the electrolyte to prepare an electrolyte.

[0098] Comparative Example 11

[0099] In an argon-filled glove box (H2O content <10ppm), DEC, EC, PC, EP and PP were mixed in a volume ratio of 1:2:1:3:3, 1.2mol / L LiPF6 was added to the mixed solution, and then 2wt% of succinonitrile, 8wt% of fluoroethylene carbonate, 3wt% of 1,3,6-hexanetrinitrile and 0.5% of trifluoroethyl propargyl carbonate were added to the electrolyte to prepare the electrolyte.

[0100] Comparative Example 12

[0101] In an argon-filled glove box (H2O content <10ppm), DEC, EC, PC, EP and PP were mixed in a volume ratio of 1:2:1:3:3, 1.2mol / L LiPF6 was added to the mixed solution, and then 2wt% of succinonitrile, 8wt% of fluoroethylene carbonate, 3wt% of 1,3,6-hexanetrinitrile, 0.5wt% of propargyl acetate and 0.5wt% of lithium difluorooxalatoborate were added to the electrolyte to prepare an electrolyte.

[0102] Comparative Example 13

[0103] In an argon-filled glove box (H2O content <10ppm), DEC, EC, PC, EP and PP were mixed in a volume ratio of 1:2:1:3:3, 1.2mol / L LiPF6 was added to the mixed solution, and then 2wt% of succinonitrile, 8wt% of fluoroethylene carbonate, 3wt% of 1,3,6-hexanetrinitrile, 0.5wt% of dipropargyl carbonate and 0.5wt% of lithium difluorooxalatoborate were added to the electrolyte to prepare an electrolyte.

[0104] Performance Testing

[0105] 1. The electrolytes prepared in Examples 1 to 9 and Comparative Examples 1 to 5 were injected into 4.2V lithium cobalt oxide graphite batteries. The 4.2V lithium cobalt oxide graphite batteries were prepared as follows:

[0106] Positive electrode: Lithium cobalt oxide (LCO) / conductive graphite / binder PVDF are mixed and coated in a ratio of 93.5% / 3.5% / 3% to form a positive electrode sheet for use;

[0107] Negative electrode: artificial graphite / conductive graphite / binder SBR (styrene-butadiene rubber) / thickener CMC (carboxymethyl cellulose) are mixed in a ratio of 95.5% / 1% / 2% / 1.5% and coated to make a negative electrode sheet for later use;

[0108] The positive electrode sheet is rolled to a compaction density of 2.50g / cm3 The negative electrode sheet is rolled to a compaction density of 1.65g / cm 3 After the tabs are welded in strips, they are wound into bare cells on a semi-automatic winding machine, and then encapsulated with aluminum-plastic film to make AHB083048 model cells for use.

[0109] The above-mentioned batteries were tested for capacity retention and swelling after being stored at 85°C for 4 hours. The testing method included charging to 4.2V at 1C under constant current / constant voltage (CC / CV) conditions at 25°C, then storing in an 85°C oven for 4 hours. After storage, the batteries were discharged at 1C to 3.0V. The capacity and thickness of the batteries after being stored at 85°C for 4 hours were then measured. The capacity retention of the above-mentioned batteries after being stored at 85°C for 4 hours was equal to the capacity after being stored at 85°C for 4 hours divided by the capacity charged and discharged under the same conditions without being stored at 85°C. The swelling of the above-mentioned batteries after being stored at 85°C for 4 hours was equal to the difference between the battery thickness after storage and the battery thickness before storage divided by the battery thickness before storage. The batteries were tested for 1000-cycle capacity retention at 45°C and DCR at 50% SCO and 2C for 10s. The 1000-cycle capacity retention at 45°C was measured by charging at 1C to 4.2V and then discharging at 1C to 3.0V at 45°C under constant current / constant voltage (CC / CV) conditions. The battery capacities after the initial charge / discharge cycle and after 1000 cycles were measured. The 1000-cycle capacity retention at 45°C was calculated as the battery capacity after 1000 cycles divided by the battery capacity after the initial charge / discharge cycle. The 50% SCO and 2C for 10s DCR was measured as the ratio of the voltage difference to the current during 10s of 2C constant current discharge at 50% SCO. The relevant experimental data are shown in Table 1.

[0110] Table 1

[0111] As shown in Table 1, while the use of Additive A or Additive B alone improves the battery's high-temperature capacity retention and high-temperature cycling performance, it also increases the battery's high-temperature swelling and DCR. Unexpectedly, the inventors discovered that by combining Additive A and Additive B, they were able to improve the battery's high-temperature capacity retention and high-temperature cycling performance while also reducing high-temperature swelling and lowering the battery's internal resistance.

[0112] Further comparison of Examples 1 to 4 reveals that as the content of additive A in the electrolyte increases, the improvement effect on battery performance increases, but as the content of additive A further increases, the improvement effect on battery performance decreases. Therefore, the additive A preferably accounts for 0.1 to 1% of the total mass of the electrolyte.

[0113] Further comparison of Examples 6 to 9 shows that as the content of additive B in the electrolyte increases, the improvement effect on battery performance increases, but as the content of additive B further increases, the improvement effect on battery performance decreases, especially the battery internal resistance. Therefore, the content of additive B in the total mass of the electrolyte is preferably 0.1 to 1%.

[0114] 2. The electrolytes prepared in Examples 10 to 12 and Comparative Examples 6 to 9 were respectively injected into 4.52V lithium cobalt oxide graphite batteries. The preparation method of the 4.52V lithium cobalt oxide graphite batteries is as follows:

[0115] Positive electrode: Lithium cobalt oxide (LCO) / conductive graphite / binder PVDF are mixed and coated in a ratio of 93.5% / 3.5% / 3% to form a positive electrode sheet for use;

[0116] Negative electrode: artificial graphite / conductive graphite / binder SBR (styrene-butadiene rubber) / thickener CMC (carboxymethyl cellulose) are mixed in a ratio of 95.5% / 1% / 2% / 1.5% and coated to make a negative electrode sheet for later use;

[0117] The positive electrode sheet is rolled to a compaction density of 2.50g / cm 3 The negative electrode sheet is rolled to a compaction density of 1.65g / cm 3 After the tabs are welded in strips, they are wound into bare cells on a semi-automatic winding machine, and then encapsulated with aluminum-plastic film to make AHB083048 model cells for use.

[0118] The above-mentioned batteries were tested for capacity retention and swelling after being stored at 85°C for 4 hours. The testing method included charging to 4.52V at 1C under constant current / constant voltage (CC / CV) conditions at 25°C, then storing in an 85°C oven for 4 hours. After storage, the batteries were discharged at 1C to 3.0V. The capacity and thickness of the batteries after being stored at 85°C for 4 hours were then measured. The capacity retention of the above-mentioned batteries after being stored at 85°C for 4 hours was equal to the capacity after being stored at 85°C for 4 hours divided by the capacity charged and discharged under the same conditions without being stored at 85°C. The swelling of the above-mentioned batteries after being stored at 85°C for 4 hours was equal to the difference between the battery thickness after storage and the battery thickness before storage divided by the battery thickness before storage. The batteries were tested for 200-cycle capacity retention at 45°C and DCR at 50% SCO and 2C for 10s. The 200-cycle capacity retention at 45°C was measured by charging at 1C to 4.52V and then discharging at 1C to 3.0V at 45°C under constant current / constant voltage (CC / CV) conditions. The battery capacity after the initial charge / discharge cycle and after 200 cycles were measured. The 200-cycle capacity retention at 45°C was calculated as the battery capacity after 200 cycles divided by the battery capacity after the initial charge / discharge cycle. The 50% SCO and 2C for 10s DCR was measured by measuring the ratio of the voltage difference to the current during 10s of 2C constant current discharge at 50% SCO. The relevant experimental data are shown in Table 2.

[0119] Table 2

[0120] As can be seen from Table 2, even at a higher voltage (4.52 V), the battery containing additives A and B still has higher high-temperature performance, high-temperature cycle performance and lower DCR.

[0121] Compared with adding one of additive A and additive B to the electrolyte, adding both additives simultaneously has a better effect on improving the battery's high-temperature capacity retention rate, high-temperature swelling rate, high-temperature cycle retention rate and DCR.

[0122] Compared with the combination of propargyl acetate and additive B or the combination of dipropargyl carbonate and additive B, the combination of additives A and B has better effect.

[0123] 3. The electrolytes prepared in Examples 13 to 18 and Comparative Example 10 and Comparative Example 13 were injected into 4.5V lithium cobalt oxide silicon oxygen carbon batteries, respectively. The preparation method of the 4.5V lithium cobalt oxide silicon oxygen carbon battery is as follows:

[0124] Positive electrode: Lithium cobalt oxide (LCO) / conductive graphite / binder PVDF are mixed and coated in a ratio of 93.5% / 3.5% / 3% to form a positive electrode sheet for use;

[0125] Negative electrode: Silicon oxygen carbon / conductive graphite / binder SBR (styrene butadiene rubber) / thickener CMC (carboxymethyl cellulose) are mixed in a ratio of 95.5% / 1% / 2% / 1.5% and coated to make a negative electrode sheet for later use;

[0126] The positive electrode sheet is rolled to a compaction density of 2.50g / cm 3 The negative electrode sheet is rolled to a compaction density of 1.65g / cm 3 After welding the tabs in strips, they are wound into bare cells on a semi-automatic winding machine, and then encapsulated with aluminum-plastic film to make AHB083048 model cells for use.

[0127] The above-mentioned batteries were tested for capacity retention and swelling after being stored at 85°C for 4 hours. The testing method included charging to 4.5V at 1C under constant current / constant voltage (CC / CV) conditions at 25°C, then storing in an 85°C oven for 4 hours. After storage, the batteries were discharged at 1C to 3.0V. The capacity and thickness of the batteries after being stored at 85°C for 4 hours were then measured. The capacity retention of the above-mentioned batteries after being stored at 85°C for 4 hours was equal to the capacity after being stored at 85°C for 4 hours divided by the capacity charged and discharged under the same conditions without being stored at 85°C. The swelling of the above-mentioned batteries after being stored at 85°C for 4 hours was equal to the difference between the battery thickness after storage and the battery thickness before storage divided by the battery thickness before storage. The batteries were tested for 200-cycle capacity retention at 45°C and DCR at 50% SCO and 2C for 10s. The 200-cycle capacity retention at 45°C was measured by charging the battery to 4.5V at 1C and then discharging it to 3.0V at 1C under constant current / constant voltage (CC / CV) conditions at 45°C. The battery capacity after the initial charge / discharge cycle and after 200 cycles were measured. The 200-cycle capacity retention at 45°C was calculated as the battery capacity after 200 cycles divided by the battery capacity after the initial charge / discharge cycle. The 50% SCO and 2C for 10s DCR was measured by measuring the ratio of the voltage difference to the current during 10s of 2C constant current discharge at 50% SCO. The relevant experimental data are shown in Table 3.

[0128] Table 3

[0129] As can be seen from Table 3, even at a higher voltage (4.5V), the batteries containing additives A and B still have higher high-temperature shelf performance, high-temperature cycle performance and lower DCR.

[0130] Compared to adding either Additive A or Additive B alone to the electrolyte, adding both additives simultaneously improved the battery's high-temperature capacity retention, high-temperature swelling rate, high-temperature cycle retention, and DCR. Furthermore, the combination of Additives A and B was more effective than either propargyl acetate and Additive B alone or dipropargyl carbonate and Additive B alone.

[0131] Boron-containing lithium salts can improve the rate performance and cycle performance of lithium batteries. They can form a passivated solid cathode electrolyte interface (CEI) containing borate on the cathode surface. This CEI film not only prevents the electrolyte from leaching to the boundary, but also eliminates adverse reactions at the cathode electrolyte interface, while promoting lithium ion diffusion kinetics and improving its rate performance. In addition, by compounding additive A and boron-containing lithium salt additive B, the cycle performance, high temperature performance and rate performance of lithium-ion batteries are further improved. By combining other components in the non-aqueous electrolyte, while ensuring the high temperature performance and cycle performance of lithium-ion batteries at conventional voltages, when the voltage is increased to 4.5V or even higher, the lithium-ion battery still has more excellent high temperature performance, cycle performance, and more excellent safety performance and electrochemical performance.

[0132] The above detailed description of the present invention is intended to enable persons familiar with the art to understand the contents of the present invention and implement them. It does not limit the scope of protection of the present invention. Any equivalent changes or modifications made based on the spirit of the present invention should be included in the scope of protection of the present invention.

Claims

1. A non-aqueous electrolyte comprising a lithium salt, an organic solvent and an additive, characterized in that: The additives include additive A and additive B, and the structural formula of additive A is wherein R1 is selected from alkylene, fluoroalkylene, alkenylene or fluoroalkenylene, and R2 is selected from fluoroalkyl or fluoroalkenyl; The additive B is a boron-containing lithium salt.

2. The non-aqueous electrolyte according to claim 1, characterized in that: The R1 is selected from an alkylene group having 1 to 3 carbon atoms or a fluoroalkylene group having 1 to 3 carbon atoms; and / or, The R2 is selected from a fluorinated alkyl group having 1 to 3 carbon atoms.

3. The non-aqueous electrolyte according to claim 2, characterized in that: The R1 is selected from methylene, ethylene or propylene; and / or, The R2 is selected from fluoroethyl, difluoroethyl or trifluoroethyl.

4. The non-aqueous electrolyte according to claim 3, characterized in that: The additive A is one or more of trifluoroethyl propargyl carbonate, difluoroethyl propargyl carbonate, and fluoroethyl propargyl carbonate.

5. The non-aqueous electrolyte according to any one of claims 1 to 4, characterized in that: The additive A accounts for 0.01-1% of the total mass of the non-aqueous electrolyte.

6. The non-aqueous electrolyte according to claim 5, characterized in that: The additive A accounts for 0.1-1% of the total mass of the non-aqueous electrolyte.

7. The non-aqueous electrolyte according to claim 1, characterized in that: The boron-containing lithium salt includes one or more of lithium difluorooxalatoborate, lithium tetrafluoroborate, lithium dioxalatoborate, lithium tetraborate, lithium triphenyl-n-butylborate, and trimethylimidazolium lithium tetrafluoroborate.

8. The non-aqueous electrolyte according to claim 1 or 7, characterized in that: The additive B accounts for 0.01-2% of the total mass of the non-aqueous electrolyte.

9. The non-aqueous electrolyte according to claim 8, characterized in that: The additive B accounts for 0.1-1% of the total mass of the non-aqueous electrolyte.

10. The non-aqueous electrolyte according to claim 1, characterized in that: The additives also include other additives, which are one or more of vinylene carbonate, vinyl ethylene carbonate, tris(trimethylsilyl)borate, tris(trimethylsilyl)phosphate, methyl maleic anhydride, succinic anhydride, biphenyl, cyclohexylbenzene, trioctyl phosphate, fluoroethylene carbonate, succinonitrile, adiponitrile, 1,3,6-hexanetrinitrile, 1,2-bis(2-cyanoethoxy)ethane, 1,4-dicyano-2-butene, 1,2,3-tris(2-cyanoethoxy)propane, and sebaconitrile.

11. The non-aqueous electrolyte according to claim 10, characterized in that: The other additives account for 2-15% of the total mass of the non-aqueous electrolyte.

12. The non-aqueous electrolyte according to claim 11, characterized in that: The other additives account for 2-13% of the total mass of the non-aqueous electrolyte.

13. The non-aqueous electrolyte according to claim 1, characterized in that: The 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.

14. 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 difluorobisoxalate phosphate, lithium difluorophosphate, lithium trifluoromethylsulfonate, lithium difluorobisoxalate phosphate, lithium difluorobis(oxalate) phosphate, lithium fluorosulfonate, lithium monooxalate bisfluoroborate, and lithium bis(fluorosulfonyl)imide; and / or, The concentration of the lithium salt is 0.8-1.5 mol / L.

15. A lithium ion battery, characterized in that: The lithium ion battery comprises the nonaqueous electrolyte according to any one of claims 1 to 14.

16. The lithium ion battery according to claim 15, characterized in that: The lithium-ion battery is a lithium cobalt oxide graphite battery or a lithium cobalt oxide silicon oxygen carbon battery.

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