Electrolyte and lithium ion battery

Abstract

The invention relates to an electrolyte and a lithium ion battery, and mainly solves the problems of poor cycle performance, poor rate capability and gas production of the existing lithium ion battery. One or more of oxa-bicyclohexane derivatives are added into the electrolyte, the structural formula of the oxa-bicyclohexane derivatives is # imgabs0, at least one group of R1, R2, R3, R4, R5, R6 and R7 is selected from cyano, alkyl, alkenyl, sulfonyl, carboxylic ester group, halogen, halogenated alkyl, halogenated cyano, halogenated alkenyl, halogenated sulfonyl, acyl or halogenated acyl, and the structural formula of the oxa-bicyclohexane derivatives is # imgabs0, and at least one group of R1, R2, R3, R4, R5, R6 and R7 is selected from cyano, alkyl, alkenyl, sulfonyl, carboxylic ester group, halogen, halogenated alkyl, halogenated cyano, halogenated alkenyl, halogenated sulfonyl, acyl or halogenated acyl. When one of R1 to R7 is a cyano group, at least one of the residual groups is selected from alkyl, alkenyl, sulfonyl, carboxylic ester group, halogen group, halogenated alkyl, halogenated cyano group, halogenated alkenyl, halogenated sulfonyl, acyl or halogenated acyl. By adding the oxa-bicyclohexane derivative into the electrolyte, the cycle life and the rate capability of the lithium ion battery can be improved, and high-temperature gas production of the battery can be inhibited.

Description

Technical Field

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

[0002] Lithium-ion batteries have the advantages of high energy density, good cycle performance, long storage time and low self-discharge, and have been widely used. However, with the increasing demand for energy storage and power, higher requirements are placed on the discharge capacity, cycle life and safety performance of lithium-ion batteries.

[0003] The negative electrode of lithium-ion batteries is considered to be the limiting factor for battery discharge capacity, cycle life, and safety performance due to its slow electrochemical reaction kinetics. In practical applications, the formation of a SEI film (solid electrolyte interface film) at the negative electrode is particularly important to improve thermodynamic stability, mechanical properties, structural density, and ionic conductivity. Summary of the invention

[0004] With the expansion of lithium-ion battery application scenarios, it is necessary to further improve the cycle performance and rate performance of lithium-ion batteries and inhibit battery gas production. The present invention forms an optimized SEI film at the negative electrode by adding oxabicyclohexane derivatives to the electrolyte, thereby improving battery performance. The scheme of the present invention is further discussed below.

[0005] The object of the present invention is to provide an electrolyte which can improve the cycle life and rate performance of a lithium ion battery and inhibit the high temperature gas generation of the battery.

[0006] Another object of the present invention is to provide a lithium ion battery.

[0007] In order to achieve the above object, the present invention adopts the following technical scheme:

[0008] An electrolyte comprises an organic solvent, a lithium salt and an additive, wherein the additive comprises one or more oxabicyclohexane derivatives, wherein the structural formula of the oxabicyclohexane derivative is Among them, R 1 , R 2 , R 3 , R 4 , R 5 , R 6 , R 7 At least one group is selected from cyano, alkyl, alkenyl, sulfonyl, carboxylate, halo, haloalkyl, halocyano, haloalkenyl, halosulfonyl, acyl or haloacyl, and the remaining groups are hydrogen,

[0009] When the R 1 , R 2 , R 3 , R4 , R 5 , R 6 , R 7 When one group is a cyano group, at least one of the remaining groups is selected from an alkyl group, an alkenyl group, a sulfonyl group, a carboxylate group, a halo group, a haloalkyl group, a halocyano group, a haloalkenyl group, a halosulfonyl group, an acyl group or a haloacyl group, and the remaining other groups are hydrogen.

[0010] Preferably, the carbon number of the cyano group, alkyl group, alkenyl group, carboxylate group, halogenated alkyl group, halogenated alkenyl group, halogenated cyano group, acyl group or halogenated acyl group is independently 1 to 5, and further 1 to 3.

[0011] Preferably, the halogen element in the halogen group or the halogenated alkyl group, the halogenated cyano group, the halogenated alkenyl group, the halogenated sulfonyl group and the halogenated acyl group is fluorine.

[0012] In some embodiments, the cyano group is acetonitrile (-CN) or propionitrile (-CH 2 CN).

[0013] In some embodiments, the alkyl group is methyl, ethyl or propyl.

[0014] In some embodiments, the alkenyl group is vinyl or propenyl.

[0015] In some embodiments, the acyl group is acetyl (-COCH 3 ) or propionyl (-COCH 2 CH 3 ).

[0016] In some embodiments, the carboxylate group is ethyl formate (-COOC 2 H 5 ).

[0017] In some embodiments, the haloalkyl group is a methyl group, an ethyl group, or a propyl group in which hydrogen atoms are completely or partially substituted by fluorine.

[0018] In some embodiments, the halogenocyano group is a propionocyano group in which the hydrogen atom is completely or partially substituted by fluorine.

[0019] In some embodiments, the haloalkenyl group is a vinyl or propenyl group in which hydrogen atoms are completely or partially substituted by fluorine.

[0020] In some embodiments, the halosulfonyl group is a fluorosulfonyl group.

[0021] In some embodiments, the halogenated acyl group is an acetyl or propionyl group in which the hydrogen atoms are completely or partially replaced by fluorine, such as -COCF 3 .

[0022] Preferably, the R 1 , R 2 , R 3 , R 4 , R 5 , R 6 , R 7 One of the groups is selected from halosulfonyl or haloacyl, and the remaining groups are hydrogen;

[0023] or the R 1 , R 2 , R 3 , R 4 , R 5 , R 6 , R 7 One of the groups is selected from cyano, one or two of the remaining groups are selected from carboxylate or alkyl, and the remaining other groups are hydrogen;

[0024] or the R 1 , R 2 , R 3 , R 4 , R 5 , R 6 , R 7 At least three of the groups are selected from alkyl groups and the remaining groups are hydrogen.

[0025] More preferably, the R 1 , R 2 , R 3 , R 4 , R 5 , R 6 , R 7 One of the groups is a fluorosulfonyl group or a fluorinated acetyl group, and the remaining groups are hydrogen;

[0026] or the R 1 , R 2 , R 3 , R 4 , R 5 , R 6 , R 7 One of the groups is acetyl cyano, one or two of the remaining groups are selected from ethyl formate or methyl, and the remaining other groups are hydrogen;

[0027] or the R 1 , R 2 , R 3 , R 4 , R 5 , R 6 , R 7 At least three groups are selected from methyl groups, and the remaining groups are hydrogen.

[0028] In some specific and preferred embodiments, the oxabicyclohexane derivatives include

[0029] Preferably, the oxabicyclohexane derivative accounts for 0.05% to 5% of the total mass of the electrolyte.

[0030] Further preferably, the oxabicyclohexane derivative accounts for 0.5% to 2% of the total mass of the electrolyte, for example, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8% or 2%.

[0031] Preferably, the additive further comprises one or more of cyclic carbonates and sulfonates containing halogen.

[0032] Further preferably, the halogen-containing cyclic carbonate includes fluoroethylene carbonate, and the sulfonate includes one or more of methylene methanedisulfonate and 1,3-propane sultone.

[0033] Preferably, when the additive includes a halogen-containing cyclic carbonate, the halogen-containing cyclic carbonate accounts for 0.3% to 20% of the total mass of the electrolyte, more preferably 2% to 10%, and even more preferably 4% to 6%.

[0034] Preferably, when the additive includes sulfonate, the sulfonate accounts for 0.1% to 5% of the total mass of the electrolyte, more preferably 0.5% to 3%, and even more preferably 0.5% to 2%.

[0035] Preferably, the additive further comprises one or more of cyclic carbonates, sulfates, sulfites, acid anhydrides, benzene compounds, fluorobenzene compounds, nitrile compounds, phosphates, phosphites, boron compounds, amine compounds, silicon-containing compounds, and heterocyclic compounds containing double bonds.

[0036] Further preferably, the additives include vinyl carbonate, ethylene carbonate, vinyl sulfate, propylene sulfate, vinyl sulfite, biphenyl, succinic anhydride, glutaric anhydride, cyclohexylbenzene, tert-butylbenzene, tert-amylbenzene, m-fluorotoluene, 3,4-difluorotoluene, p-fluorotoluene, p-xylene, 1,2-dimethoxy-4-nitrobenzene, N-phenylmaleimide, pentafluoroanisole, 2,5-di-tert-butyl, 1,4-dimethoxybenzene, hexanediol, One or more of nitrile, hexanetrinitrile, succinonitrile, 1,2,3-tris(2-cyanoethoxy)propane, N,N-dicyclohexylcarbodiimide, N,N-diethylaminotrimethylsilane, hexamethyldisilazane, tris(trimethylsilane)phosphate, tris(trimethylsilane)borate, triallyl isocyanurate, triphenyl phosphate, pimelonitrile, 2-ethoxy-2,4,4,6,6-pentafluorotriphosphazene, 2-fluoropyridine, and 1,3-dioxane.

[0037] Preferably, the lithium salt includes one or more of lithium hexafluorophosphate, lithium bistrifluoromethylsulfonyl imide, lithium bisfluorosulfonyl imide, lithium tetrafluoroborate, lithium dioxalatoborate, lithium oxalatodifluoroborate, lithium difluorooxalatophosphate, lithium tetrafluorooxalatophosphate, lithium fluorosulfonate and lithium 4,5-dicyano-2-trifluoromethylimidazole.

[0038] Further preferably, the lithium salt includes three or more of lithium hexafluorophosphate, lithium bis(trifluoromethylsulfonyl imide), lithium bis(fluorosulfonyl imide), lithium tetrafluoroborate, lithium dioxalatoborate, lithium oxalatodifluoroborate, lithium difluorooxalatophosphate, lithium tetrafluorooxalatophosphate, lithium fluorosulfonate and lithium 4,5-dicyano-2-trifluoromethylimidazole.

[0039] In some embodiments, the lithium salt is lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide and lithium oxalate difluoroborate.

[0040] Furthermore, the mass ratio of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide and lithium difluoroborate oxalate is (10-20):(1-3):1, and further (12-17):(1-3):1.

[0041] Preferably, the lithium salt accounts for 8% to 30% of the total mass of the electrolyte, more preferably 10% to 25%, and further preferably 15% to 20%.

[0042] Preferably, the organic solvent comprises one or more of substituted or unsubstituted carbonate, substituted or unsubstituted carboxylate, substituted or unsubstituted ether, substituted or unsubstituted sulfone, substituted or unsubstituted sulfoxide, substituted or unsubstituted benzene, and the substituting group is fluorine.

[0043] Further preferably, the substituted or unsubstituted carbonate includes one or more of fluoroethylene carbonate, difluoroethylene carbonate, trifluoroethyl carbonate, dimethyl carbonate, diethyl carbonate, ethylene carbonate, propylene carbonate, and ethyl methyl carbonate.

[0044] Further preferably, the substituted or unsubstituted carboxylic acid ester includes one or more of methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methyl propionate, propyl propionate, butyl propionate, methyl butyrate, and ethyl butyrate.

[0045] Further preferably, the substituted or unsubstituted ether includes one or more of tetrafluoroethyl tetrafluoropropyl ether and trifluoroethyl hexafluoropropyl ether.

[0046] Further preferably, the substituted or unsubstituted sulfone includes one or more of fluoroethyl sulfone, cyclopentane, and methyl ethyl sulfone.

[0047] Further preferably, the substituted or unsubstituted sulfoxide comprises dimethyl sulfoxide.

[0048] Further preferably, the substituted or unsubstituted benzene includes fluorobenzene.

[0049] Preferably, the organic solvent accounts for 60% to 90% of the total mass of the electrolyte, more preferably 70% to 85%, for example 70%, 73%, 75%, 78%, 80%, 83% or 85%.

[0050] In some embodiments, the organic solvent includes ethylene carbonate, diethyl carbonate, ethyl methyl carbonate, and propylene carbonate.

[0051] Furthermore, the ratio of ethylene carbonate, diethyl carbonate, ethyl methyl carbonate and propylene carbonate is (3-5):(2-3):(7-10):1, and more preferably (3.5-4.5):(2-3):(7.5-9):1.

[0052] The present invention also provides a lithium ion battery, comprising a positive electrode, a negative electrode, a separator and an electrolyte, wherein the electrolyte is the electrolyte described above.

[0053] Preferably, the positive electrode comprises a positive electrode active material, and the positive electrode active material is LiNi x Co y M z O 2 , wherein M is Mn or Al, x+y+z=1, the value of x is 0.2 to 1, the value of y is 0 to 0.0.4, and the value of z is 0 to 0.4.

[0054] Preferably, the negative electrode comprises a negative electrode active material, and the negative electrode active material is selected from metallic lithium, metal oxides, lithium aluminum alloys, graphite, modified carbon materials, silicon, silicon oxygen or silicon oxygen carbon.

[0055] Compared with the prior art, the present invention has the following advantages:

[0056] The invention can improve the cycle life and rate performance of lithium ion batteries and inhibit high-temperature gas generation of batteries by adding oxabicyclohexane derivatives into the electrolyte. DETAILED DESCRIPTION

[0057] The present invention is further described below in conjunction with the examples, but 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.

[0058] The raw materials used in the specific embodiments or comparative examples of the present invention can all be commercially available products.

[0059] Unless otherwise specified in the present invention, "wt %" refers to mass percentage.

[0060] Electrolyte preparation:

[0061] The specific embodiments and comparative examples of the present invention are prepared in a glove box according to the formulas described in Tables 1 and 2 below. The configuration method refers to the prior art and is not limited by the present invention. Among them, the substances involved in the table are ethylene carbonate (EC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), propylene carbonate (PC), fluoroethylene carbonate (FEC), lithium bis(fluorosulfonyl)imide (LiFSI), lithium difluoroborate oxalate (LiDFOB), 1,3-propane sultone (PS), vinylene carbonate (VC), lithium hexafluorophosphate (LiPF 6 ), dithiothreitol (DTD);

[0062] The structural formula of additive 1 is: CAS No.: 1820718-58-8;

[0063] Additive 2 is: CAS No.: 1194799-52-4;

[0064] Additive 3 is: CAS No.: 1315366-09-6;

[0065] Additive 4 is: CAS No.: 1690-54-6;

[0066] Additive 5 is: CAS No.: 91328-70-0;

[0067] Additive 6 is: CAS No.: 2704530-37-8;

[0068] Additive 7 is: CAS number: 2167978-69-8.

[0069] Table 1

[0070]

[0071]

[0072] Table 2

[0073]

[0074] Experimental test content:

[0075] The electrolytes obtained in Examples 1 to 21 and Comparative Examples 1 to 7 were injected into 1Ah LiNi 0.6 Co 0.2 Mn 0.2 O 2 (NCM622)||Artificial graphite polymer soft pack battery, the preparation method is as follows.

[0076] Positive electrode: LiNi 0.6 Co 0.2 Mn 0.2 O 2 (NCM622) / conductive graphite / binder PVDF are mixed and coated in a ratio of 93.5% / 3.5% / 3% to form a positive electrode sheet for standby use;

[0077] Negative electrode: artificial graphite / conductive graphite / binder SBR (styrene-butadiene rubber) / thickener CMC (carboxymethyl cellulose) are mixed and coated in a ratio of 95.5% / 1% / 2% / 1.5% to form a negative electrode sheet for standby use;

[0078] 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 pole ears are welded in strips, they are wound into bare cells on a semi-automatic winding machine, and then packaged with aluminum-plastic film to make AHB083048 model cells for standby use.

[0079] Perform the following tests respectively:

[0080] 1) When the battery is tested at 25°C, voltage between 2.75-4.3V, and current of 1C, the capacity retention rate L1% (discharge capacity after 1000 cycles / average discharge capacity in the first 5 weeks × 100%) and the internal resistance growth rate R1% (internal resistance after 1000 cycles - internal resistance before cycle) / internal resistance before cycle × 100%) after 1000 cycles of charge and discharge cycles.

[0081] 2) When the test battery is charged and discharged for 500 cycles at 25°C, voltage between 2.75-4.3V, and current of 3C, the capacity retention rate is L2% (discharge capacity after 500 cycles / average discharge capacity before 5 weeks × 100%), and the internal resistance growth rate is R2% (internal resistance after 500 cycles - internal resistance before cycle) / internal resistance before cycle × 100%).

[0082] 3) The test battery was fully charged to 4.3V and stored at 60°C for 70 days. The battery swelling rate was H1% (thickness before storage - thickness after storage) / thickness before storage × 100%).

[0083] The above experimental results are shown in Table 3.

[0084] Table 3

[0085]

[0086]

[0087] By comparing Comparative Example 1 and Examples 1 to 21, it is found that the addition of oxabicyclohexane derivatives can improve the cycle performance, impedance and rate performance of the battery, and inhibit the high temperature gas production of the battery. As its content increases, the improvement of the battery cycle performance, impedance and rate performance and the inhibition of high temperature gas production of the battery is more obvious, but as its content further increases, the improvement of the battery performance is weakened. Preferably, the addition amount of oxabicyclohexane derivatives accounts for 0.5 to 2% of the total mass of the electrolyte.

[0088] By comparing Comparative Examples 2 to 7 and Examples 1 to 21, it is found that, compared with VC or FEC, adding the same amount of oxabicyclohexane derivatives into the electrolyte can more significantly improve battery performance, especially impedance, rate performance and high temperature performance.

[0089] Experimental test content:

[0090] The electrolytes obtained in Examples 22 to 42 and Comparative Examples 8 to 14 were injected into 1Ah LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM811) || Silicon oxygen carbon (420mAh) polymer soft pack battery, the soft pack battery is prepared as follows:

[0091] Positive electrode: LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM811) / conductive graphite / binder PVDF are mixed and coated in a ratio of 93.5% / 3.5% / 3% to form a positive electrode sheet for standby use;

[0092] Negative electrode: Silicon oxygen carbon (420mAh) / conductive graphite / binder SBR (styrene butadiene rubber) / thickener CMC (carboxymethyl cellulose) are mixed and coated in a ratio of 95.5% / 1% / 2% / 1.5% to make a negative electrode sheet for standby use;

[0093] 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 pole ears are welded in strips, they are wound into bare cells on a semi-automatic winding machine, and then packaged with aluminum-plastic film to make AHB083048 model cells for standby use.

[0094] Perform the following tests respectively:

[0095] 1) When the battery is tested at 25°C, voltage between 2.75-4.2V, and current of 1C, the capacity retention rate after 1000 charge and discharge cycles is L3% (discharge capacity after 1000 cycles / average discharge capacity in the first 5 weeks × 100%), and the internal resistance growth rate is R3% (internal resistance after 1000 cycles - internal resistance before cycle) / internal resistance before cycle × 100%).

[0096] 2) When the test battery is charged and discharged for 500 cycles at 25°C, voltage between 2.75-4.2V, and current of 3C, the capacity retention rate is L4% (discharge capacity after 500 cycles / average discharge capacity before 5 weeks × 100%), and the internal resistance growth rate is R4% (internal resistance after 500 cycles - internal resistance before cycle) / internal resistance before cycle × 100%).

[0097] 3) The test battery was fully charged to 4.2V and stored at 60°C for 70 days. The battery swelling rate was H2% (thickness before storage - thickness after storage) / thickness before storage × 100%).

[0098] The above experimental results are shown in Table 4.

[0099] Table 4

[0100]

[0101]

[0102] By comparing Comparative Example 8 and Examples 22 to 42, it is found that the addition of oxabicyclohexane derivatives can improve the cycle performance, impedance and rate performance of the battery, and inhibit the high temperature gas production of the battery. As its content increases, the improvement of the battery cycle performance, impedance and rate performance and the inhibition of high temperature gas production of the battery is more obvious, but as its content further increases, the improvement of the battery performance is weakened. Preferably, the addition amount of oxabicyclohexane derivatives accounts for 0.5 to 2% of the total mass of the electrolyte.

[0103] By comparing Comparative Examples 9 to 14 and Examples 22 to 42, it is found that, compared with VC or DTD, adding the same amount of oxabicyclohexane derivatives into the electrolyte improves the battery performance more significantly.

[0104] 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 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. An electrolyte comprising an organic solvent, a lithium salt and an additive, Features: The additive includes one or more oxabicyclohexane derivatives, and the structural formula of the oxabicyclohexane derivative is Among them, R 1 , R 2 , R 3 , R 4 , R 5 , R 6 , R 7 At least one group is selected from cyano, alkyl, alkenyl, sulfonyl, carboxylate, halo, haloalkyl, halocyano, haloalkenyl, halosulfonyl, acyl or haloacyl, and the remaining groups are hydrogen, When the R 1 , R 2 , R 3 , R 4 , R 5 , R 6 , R 7 When one group is a cyano group, at least one of the remaining groups is selected from an alkyl group, an alkenyl group, a sulfonyl group, a carboxylate group, a halo group, a haloalkyl group, a halocyano group, a haloalkenyl group, a halosulfonyl group, an acyl group or a haloacyl group, and the remaining other groups are hydrogen.

2. The electrolyte according to claim 1, Features: The carbon number of the cyano group, alkyl group, alkenyl group, carboxylate group, haloalkyl group, haloalkenyl group, halogenated cyano group, acyl group or halogenated acyl group is independently 1 to 5, and the halogen element in the halo group or haloalkyl group, halocyano group, haloalkenyl group, halogenated sulfonyl group or halogenated acyl group is fluorine.

3. The electrolyte according to claim 1 or 2, Features: The R 1 , R 2 , R 3 , R 4 , R 5 , R 6 , R 7 One of the groups is selected from halosulfonyl or haloacyl, and the remaining groups are hydrogen; or the R 1 , R 2 , R 3 , R 4 , R 5 , R 6 , R 7 One of the groups is selected from cyano, one or two of the remaining groups are selected from carboxylate or alkyl, and the remaining other groups are hydrogen; or the R 1 , R 2 , R 3 , R 4 , R 5 , R 6 , R 7 At least three of the groups are selected from alkyl groups and the remaining groups are hydrogen.

4. The electrolyte according to claim 3, Features: The R 1 , R 2 , R 3 , R 4 , R 5 , R 6 , R 7 One of the groups is a fluorosulfonyl group or a fluorinated acetyl group, and the remaining groups are hydrogen; or the R 1 , R 2 , R 3 , R 4 , R 5 , R 6 , R 7 One of the groups is acetyl cyano, and one or two of the remaining groups are selected from ethyl formate or methyl; or the R 1 , R 2 , R 3 , R 4 , R 5 , R 6 , R 7 At least three groups are selected from methyl groups, and the remaining groups are hydrogen.

5. The electrolyte according to claim 4, Features: The oxabicyclohexane derivatives include 6. The electrolyte according to claim 1, Features: The oxabicyclohexane derivative accounts for 0.05% to 5% of the total mass of the electrolyte.

7. The electrolyte according to claim 1, Features: The additive further comprises one or more of cyclic carbonates and sulfonates containing halogen.

8. The electrolyte according to claim 7, Features: The halogen-containing cyclic carbonate includes fluoroethylene carbonate, and the sulfonate includes one or more of methylene methanedisulfonate and 1,3-propane sultone; and / or, When the additive comprises a cyclic carbonate containing halogen, the cyclic carbonate containing halogen accounts for 0.3% to 20% of the total mass of the electrolyte; and / or, When the additive includes sulfonate, the sulfonate accounts for 0.1% to 5% of the total mass of the electrolyte.

9. The electrolyte according to claim 1, Features: The lithium salt includes one or more of lithium hexafluorophosphate, lithium bis(trifluoromethylsulfonyl imide), lithium bis(fluorosulfonyl imide), lithium tetrafluoroborate, lithium dioxalatoborate, lithium oxalatodifluoroborate, lithium difluorooxalatophosphate, lithium tetrafluorooxalatophosphate, lithium fluorosulfonate and lithium 4,5-dicyano-2-trifluoromethylimidazole; and / or, The lithium salt accounts for 8% to 30% of the total mass of the electrolyte.

10. The electrolyte according to claim 1, Features: The organic solvent comprises one or more of substituted or unsubstituted carbonate, substituted or unsubstituted carboxylate, substituted or unsubstituted ether, substituted or unsubstituted sulfone, substituted or unsubstituted sulfoxide, substituted or unsubstituted benzene, and the substituting group is fluorine; and / or, The organic solvent accounts for 60% to 90% of the total mass of the electrolyte.

11. A lithium ion battery comprising a positive electrode, a negative electrode, a separator and an electrolyte, Features: The electrolyte is the electrolyte according to any one of claims 1 to 10.

12. The lithium ion battery according to claim 11, Features: The positive electrode includes a positive electrode active material, and the positive electrode active material is LiNi x Co y M z O 2 , wherein M is Mn or Al, x+y+z=1, and the value of x is 0.2 to 1.0, the value of y is 0 to 0.4, and the value of z is 0 to 0.4; The negative electrode comprises a negative electrode active material, and the negative electrode active material is selected from metallic lithium, metal oxides, lithium aluminum alloys, graphite, modified carbon materials, silicon, silicon oxygen or silicon oxygen carbon.

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