Lithium ion battery electrolyte and application thereof

Abstract

The application provides a lithium ion battery electrolyte and application thereof, and the electrolyte comprises at least the following components: a solvent, a lithium salt and an additive, wherein the solvent comprises a first solvent and a second solvent, the first solvent is at least one selected from trifluorotoluene, difluorobenzene, trifluorobenzene, toluene, ethylbenzene, decafluoropentane, perfluorohexanone, perfluorobutyl ether or perfluorobutyl methyl ether, and the second solvent is at least one selected from methyl ethyl carbonate, dimethyl carbonate, diethyl carbonate, propylene carbonate or ethylene carbonate; and the additive comprises a first additive, and the general structure of the first additive is: wherein R1, R2 and R3 are each independently selected from one of substituted groups with 1-6 carbon atoms, 0-4 unsaturations and 0-3 heteroatoms, and the heteroatoms are at least one selected from oxygen, nitrogen or sulfur. The lithium ion battery electrolyte and application thereof can improve the fast charging performance and kinetic performance of the battery.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of power batteries, in particular to a lithium ion battery electrolyte and application thereof. BACKGROUND

[0002] At present, lithium ion batteries are rapidly developing in the fields of electric vehicles and large-scale energy storage, and have occupied a large market share. With the wide application of lithium ion batteries, consumers have higher demands for the energy density and cycle life of lithium ion batteries. High-nickel positive electrode materials or silicon negative electrode materials and other positive and negative electrode materials with high specific capacity can improve the energy density of lithium ion batteries, but will increase the impedance of the battery, affect the kinetic performance and cycle life of the battery, and also cause the decomposition of lithium salt to produce acidic substances, which will destroy the interface phase and worsen the performance of the battery.

[0003] Moreover, with the rapid development of lithium ion batteries in the fields of electric vehicles and large-scale energy storage, more stringent requirements are put forward for the fast charging performance of the battery to shorten the charging time of the battery. However, the current lithium ion battery has a limitation in the migration rate of lithium ions in the electrolyte system and the lithium intercalation capacity of the negative electrode, and lithium is easily deposited on the negative electrode side at a large rate. Therefore, the electrochemical stability of the existing electrolyte system is poor, and the fast charging performance of the battery cannot be improved. SUMMARY

[0004] The present application provides a lithium ion battery electrolyte and application thereof, which can improve the electrochemical stability and kinetic performance of the electrolyte, and can also capture acidic substances generated by the decomposition of lithium salt in time to avoid the destruction of the interface phase, thereby improving the fast charging performance and kinetic performance of the battery.

[0005] To solve the above technical problems, the present application provides a lithium ion battery electrolyte, which comprises at least the following components:

[0006] a solvent comprising a first solvent and a second solvent, the first solvent being selected from at least one of trifluorotoluene, difluorobenzene, trifluorobenzene, toluene, ethylbenzene, decafluoropentane, perfluorohexanone, perfluorobutyl ether or perfluorobutyl methyl ether, and the second solvent being selected from at least one of methyl ethyl carbonate, dimethyl carbonate, diethyl carbonate, propylene carbonate or ethylene carbonate;

[0007] a lithium salt; and

[0008] an additive comprising a first additive, the structure of the first additive being as follows:

[0009] wherein R1, R2 and R3 are each independently selected from one of the substituents having 1-6 carbon atoms, 0-4 unsaturations and 0-3 heteroatoms, the heteroatoms being selected from at least one of oxygen, nitrogen or sulfur.

[0010] In an embodiment of the present application, the content of the first solvent in the electrolyte is 25wt%-55wt%.

[0011] In an embodiment of the present application, the content of the second solvent in the electrolyte is 25wt%-55wt%, and the mass ratio of the second solvent to the first solvent is 1:1.83-1.25:1.

[0012] In an embodiment of the present application, the substituents are selected from at least one of alkyl, alkenyl, alkynyl, carbonyl, ester, amino or heterocycle.

[0013] In an embodiment of the present application, the first additive is selected from at least one of Compound 1, Compound 2 or Compound 3.

[0014] In an embodiment of the present application, the content of the first additive in the electrolyte is 0.01wt%-2wt%.

[0015] In an embodiment of the present application, the additive further comprises a second additive, the second additive being selected from at least one of lithium difluorophosphate, lithium difluorodioxophosphate or lithium difluorophosphate borate, the content of the second additive in the electrolyte being 0.01wt%-1.2wt%, and the mass ratio of the first additive to the second additive being (0.3-0.6):1.

[0016] In an embodiment of the present application, the additive further comprises a third additive, the third additive being selected from at least one of tripropargyl phosphate, tris(trimethylsilyl)phosphate or methanedisulfonate methylene, and the content of the third additive in the electrolyte being 0.01wt%-1wt%.

[0017] In an embodiment of the present application, the lithium salt is selected from at least one of lithium hexafluorophosphate, lithium bisfluorosulfonimide or lithium bis(trifluoromethyl)sulfonimide, and the content of the lithium salt in the electrolyte is 10wt%-20wt%.

[0018] The present application further provides a lithium ion battery, comprising at least:

[0019] a positive electrode sheet;

[0020] a negative electrode sheet;

[0021] a separator disposed between the positive electrode tab and the negative electrode tab; and

[0022] an electrolyte selected from the lithium ion battery electrolytes described above.

[0023] In summary, the present application provides a lithium ion battery electrolyte and its application. The first solvent can regulate the solvation structure of the electrolyte, improve the electrochemical stability of the electrolyte, and further improve the fast charging performance of the battery. The synergistic effect of the first additive and the first solvent can timely capture the acidic substances generated by the decomposition of lithium salt, avoid the destruction of the acidic substances to the solid electrolyte interface (SEI) film and the chemical-electrochemical interface (CEI) film, improve the stability of the interface phase, and further significantly improve the fast charging performance of the battery. The first solvent and the second solvent can make the electrolyte have good electrochemical stability and good kinetic performance at the same time, thereby improving the fast charging performance and kinetic performance of the battery. The second additive and the third additive can further improve the fast charging performance and kinetic performance of the battery. DETAILED DESCRIPTION

[0024] The embodiments of the present application will be described in detail below with specific reference to the drawings. Those skilled in the art can easily understand other advantages and effects of the present application from the content disclosed in the specification. The present application can also be implemented or applied in other different specific embodiments, and the details in the specification can be modified or changed based on different views and applications without departing from the spirit of the present application.

[0025] It should be understood that the present application can be implemented in different forms, and should not be interpreted as being limited to the embodiments presented herein. On the contrary, these embodiments are provided to make the disclosure complete and complete, and to fully convey the scope of the present application to those skilled in the art.

[0026] The technical solutions of the present application will be further described in detail below in combination with the embodiments. Obviously, the described embodiments are only a part of the embodiments of the present application, not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0027] The application provides a lithium ion battery electrolyte, which at least comprises a solvent, a lithium salt and an additive, wherein the solvent comprises a first solvent and a second solvent, the first solvent is at least one selected from trifluorotoluene, difluorobenzene, trifluorobenzene, toluene, ethylbenzene, decafluoropentane, perfluorohexanone, perfluorobutyl ether or perfluorobutyl methyl ether, etc., the second solvent is at least one selected from methyl ethyl carbonate, dimethyl carbonate, diethyl carbonate, propylene carbonate or ethylene carbonate, etc., and the additive comprises a first additive, and the structural general formula of the first additive is: wherein R1, R2 and R3 are each independently selected from one of the substituents with 1-6 carbon atoms, 0-4 unsaturation and 0-3 heteroatoms, and the heteroatoms are at least one selected from oxygen, nitrogen or sulfur, etc. In the lithium ion battery electrolyte provided by the application, the first solvent and the first additive synergistically act to improve the electrochemical stability and kinetic performance of the electrolyte, and at the same time, the acidic substances generated by the rapid reaction of the salt anion can be captured in time, the stability of the interface phase is improved, and the fast charging performance of the lithium ion battery is improved.

[0028] In an embodiment of the application, the first solvent is, for example, a non-polar diluent, which can regulate the solvation structure of the electrolyte, improve the electrochemical stability of the electrolyte, and further improve the fast charging performance of the battery. Specifically, since the non-polar diluent has low solubility for the lithium salt and does not have direct coordination with lithium ions, by introducing the non-polar diluent, the free solvent molecules in the electrolyte can be reduced, the coordination of lithium ions and anions is promoted, and a solvation structure dominated by anions is formed, which effectively improves the lithium ion transference number. In the electrolyte with such a solvation structure, the salt anions at the electrode / electrolyte interface will preferentially and more decompose into inorganic compounds including lithium fluoride, the decomposition of the solvent at the interface is reduced, and thus the ionic conductivity of the interface phase is enhanced.

[0029] In an embodiment of the present application, for the solvent, the content of the first solvent in the electrolyte is, for example, 25wt%-55wt%, and further, for example, 30wt%-45wt%, the content of the second solvent in the electrolyte is, for example, 25wt%-55wt%, and the mass ratio of the second solvent to the first solvent is, for example, 1:2.4-1.183:1, and further, for example, 1:1.83-1.25:1. When the mass ratio of the second solvent to the first solvent is less than 1:2.4, the content of the first solvent is too much, and there is not enough second solvent in the electrolyte to dissolve and dissociate the lithium salt, which affects the kinetic performance of the electrolyte and cannot make the battery have good capacity. When the mass ratio of the second solvent to the first solvent is greater than 1.183:1, the content of the first solvent is too little, which cannot effectively regulate the solvation structure of the electrolyte, and the electrochemical stability of the electrolyte cannot be improved, thereby affecting the fast-charging performance of the battery. Therefore, by controlling the mass ratio of the second solvent to the first solvent, the electrolyte has good electrochemical stability and good kinetic performance at the same time, thereby improving the fast-charging performance and kinetic performance of the battery.

[0030] In an embodiment of the present application, in the first additive, the substituents of R1, R2and R3are each independently selected from alkyl, alkenyl, alkynyl, carbonyl, ester, amino or heterocycle, etc. Specifically, in the present embodiment, the first additive is, for example, selected from at least one of Compound 1, Compound 1, Compound 2 or Compound 3, etc. Although the first solvent can improve the fast-charging performance of the battery, when the battery is subjected to large-rate charging, the decomposition rate of the lithium salt is accelerated, and more acidic substances are generated, which accelerates the acid increase rate of the electrolyte system. By introducing the first additive as an acid-suppressing additive, the acidic substances generated by the decomposition of the lithium salt can be captured in time, avoiding the destruction of the SEI film and the CEI film by the acidic substances, and improving the stability of the interface phase, thereby further improving the fast-charging performance of the battery.

[0031] In an embodiment of the present application, the content of the first additive in the electrolyte is, for example, 0.01wt%-2wt%, and further, for example, 0.1wt%-0.5wt%. By controlling the content of the first additive, the acidic substances generated during the cycling of the battery can be removed, and the problems of increased viscosity and reduced conductivity of the electrolyte caused by excessive content of the first additive can be avoided, thereby improving the kinetic performance of the battery and avoiding the increase of the impedance and the decrease of the capacity of the battery.

[0032] In an embodiment of the present application, the additive further comprises a second additive, for example a lithium salt type additive, for example at least one selected from lithium difluorophosphate (LiPO2F2), lithium difluorodioxalate phosphate (LiODFP), or lithium difluoroxalate borate (LiODFB), etc. In this embodiment, the content of the second additive in the electrolyte is for example 0.01wt%-1.2wt%, and the mass ratio of the first additive to the second additive is for example (0.3-0.6):1. By introducing the second additive and controlling the mass ratio of the first additive to the second additive, the fast charging performance and kinetic performance of the battery can be further improved.

[0033] In an embodiment of the present application, the additive further comprises a third additive, for example at least one selected from tripropargyl phosphate, tris(trimethylsilyl)phosphate, or methanedi sulfonate methylene, etc., and the content of the third additive in the electrolyte is for example 0.01wt%-1wt%. By introducing the third additive and controlling the content of the third additive, the fast charging performance and kinetic performance of the battery can be further improved.

[0034] In an embodiment of the present application, the lithium salt is at least one selected from lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium bisfluorosulfonylimide (LiFSI), lithium bis(trifluoromethyl)sulfonylimide (LiTFSI), lithium bisoxalate borate (LiBOB), LiODFP, lithium difluoroxalate borate (LiODFB), LiPO2F2, or lithium trifluoromethanesulfonate (CF3SO3Li), etc. Further, in this embodiment, the lithium salt is at least one selected from LiPF6, LiFSI, or LiTFSI, etc., the content of the lithium salt in the electrolyte is for example 10wt%-20wt%, and the concentration of the lithium salt in the electrolyte is for example 0.1mol / L-2mol / L, for example 0.5mol / L-1.5mol / L.

[0035] In an embodiment of the present application, when preparing the electrolyte, in a glove box in a stable gas atmosphere such as argon, the battery grade first solvent and the second solvent are mixed uniformly according to the mass ratio to obtain a mixed solvent, and the lithium salt and the additive are added to the mixed solvent and mixed uniformly to prepare a lithium ion battery electrolyte. In this embodiment, the content of argon in the glove box is for example greater than or equal to 99.999%, the oxygen content is for example less than 0.1ppm, and the water content is for example less than 0.1ppm.

[0036] The application also provides a lithium ion battery, which comprises a positive electrode sheet, a separator, a negative electrode sheet and an electrolyte. The separator is arranged between the positive electrode sheet and the negative electrode sheet to prevent short circuit between the positive electrode sheet and the negative electrode sheet, and the lithium ion can pass through. The electrolyte is filled between the positive electrode sheet, the separator and the negative electrode sheet, and the electrolyte is the lithium ion battery electrolyte described above, which can conduct ions. The lithium ion battery is, for example, a primary battery or a secondary battery, and the secondary battery is, for example, a soft package battery, a hard shell battery or a cylindrical battery. The application does not specifically limit the type and category of the lithium ion battery.

[0037] In an embodiment of the application, the positive electrode sheet comprises a positive electrode current collector and a positive electrode active layer coated on one side surface of the positive electrode current collector. The positive electrode current collector is, for example, a foil formed by surface treatment of nickel, titanium, aluminum, silver, stainless steel or carbon. In addition to the foil, the positive electrode current collector can also adopt any one or a combination of multiple forms such as a film, a mesh, a porous material, a foam or a non-woven fabric.

[0038] In an embodiment of the application, the positive electrode active layer comprises a positive electrode active material, a conductive agent and a binder. The ratio of the positive electrode active material, the conductive agent and the binder can be selected according to actual needs. In this embodiment, the positive electrode active material is, for example, a high-nickel positive electrode material selected from at least one of lithium manganese oxide, lithium iron phosphate, lithium manganese iron phosphate, lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide or lithium nickel cobalt aluminum oxide. By selecting the high-nickel positive electrode material as the positive electrode active material, the energy density of the battery can be improved due to the high specific capacity of the high-nickel positive electrode material.

[0039] In an embodiment of the application, the conductive agent is, for example, selected from at least one of conductive carbon black, acetylene black, carbon nanotubes or graphene, and the binder is, for example, selected from at least one of polyvinylidene fluoride (PVDF), poly(ethylene oxide) (PEO), polyamide (PA), polyacrylonitrile (PAN), polyacrylate, polyvinyl ether, polymethyl methacrylate (PMMA), ethylene-propylene-diene terpolymer (EPDM), polyhexafluoropropylene or polymerized styrene butadiene rubber (SBR).

[0040] In an embodiment of the present application, the positive current collector is, for example, an aluminum foil, and the positive active material is, for example, LiNi 0.9 Mn 0.05 Co 0.05 O2, the conductive agent is, for example, acetylene black, and the binder is, for example, PVDF. The positive active material, acetylene black and PVDF are mixed, for example, in a mass ratio of 95:3:2, dissolved in an organic solvent, and stirred in a vacuum stirrer until the system is homogeneous to obtain a positive slurry, which is then uniformly coated on the aluminum foil, and then transferred to an oven for drying after being dried at room temperature, and subjected to cold pressing and slitting to obtain a positive electrode sheet. The organic solvent is, for example, N-methylpyrrolidone (NMP).

[0041] In an embodiment of the present application, the negative electrode sheet includes, for example, a negative current collector and a negative active layer coated on at least one side surface of the negative current collector. The negative current collector is, for example, selected from one of a copper foil current collector, a composite copper foil current collector, a carbon current collector, a foamed copper current collector, or a stainless steel current collector.

[0042] In an embodiment of the present application, the negative active layer includes, for example, a negative active material, a conductive agent, a thickening agent, and a binder. The mass ratio of the negative active material, the conductive agent, the thickening agent, and the binder can be selected according to actual needs. In this embodiment, the negative active material is selected from at least one of soft carbon, hard carbon, artificial graphite, natural graphite, silicon, silicon oxide compounds, silicon carbon compounds, or lithium titanate.

[0043] In an embodiment of the present application, the conductive agent is, for example, selected from at least one of conductive carbon black, acetylene black, ketjen black, carbon nanotubes, or graphene. The thickening agent includes, for example, carboxymethyl cellulose sodium (CMC-Na). The binder is, for example, selected from at least one of PVDF, PEO, PA, polypropylene, polyacrylate, polyvinyl ether, PMMA, polyhexafluoropropylene, or SBR.

[0044] In an embodiment of the present application, the negative current collector is, for example, a copper foil, the negative active material includes, for example, artificial graphite and silicon oxide compounds, the content of the artificial graphite in the negative active material is 90wt%, the content of the silicon oxide compounds in the negative active material is 10wt%, the conductive agent is, for example, acetylene black, the thickening agent is, for example, CMC-Na, and the binder is, for example, SBR. Specifically, the negative active material, the conductive agent, the thickening agent, and the binder are mixed in a mass ratio of 96:2:1:1, and deionized water is added as a solvent, and then fully stirred and mixed uniformly in a vacuum stirrer to obtain a negative slurry, which is coated on the copper foil, and then transferred to an oven for drying after being dried at room temperature, and subjected to cold pressing and slitting to obtain a negative electrode sheet.

[0045] In an embodiment of the present application, the separator comprises a base film and a coating layer, for example, the base film is a single-layer polypropylene (PP) film, a single-layer polyethylene (PE) film, a double-layer PP / PE film, a double-layer PP / PP film, or a triple-layer PP / PE / PP film, and the thickness of the base film is, for example, 9-15 μm, and the coating layer is arranged on the base film, and the material of the coating layer comprises nano-aluminum oxide, and the thickness of the coating layer is, for example, 1-5 μm. In this embodiment, a single-layer PE film with a thickness of 9 μm is selected as the base film, and a nano-aluminum oxide coating layer with a thickness of 3 μm is arranged on the base film.

[0046] In an embodiment of the present application, the above positive electrode sheet, the separator, and the negative electrode sheet are sequentially placed, and the separator is arranged between the positive electrode sheet and the negative electrode sheet to play a role of isolation. Then, the aluminum plastic film is wrapped, and is transferred to an oven at 80°C for drying. After the lithium ion battery electrolyte prepared above is injected at 3.0 g / Ah, the opening is sealed. After the processes of standing, hot and cold pressing, formation, clamping, and capacity distribution, a soft-pack lithium ion secondary battery with a capacity of 1 Ah is obtained.

[0047] The present application will be explained in more detail by reference to the following examples, which should not be construed as limiting. Suitable modifications can be made within the scope of the main idea of the present application, and all of them fall within the technical scope of the present application.

[0048] Example 1

[0049] Preparation of the positive electrode sheet: LiNi 0.9 Mn 0.05 Co 0.05 O2, acetylene black, and PVDF are mixed in a mass ratio of 95:3:2, dissolved in an organic solvent NMP, and stirred in a vacuum stirrer until the system is uniform, to obtain a positive electrode slurry. The positive electrode slurry is uniformly coated on an aluminum foil, and then transferred to an oven for drying after air-drying at room temperature. After the processes of cold pressing and slitting, a positive electrode sheet is obtained.

[0050] Preparation of the negative electrode sheet: artificial graphite and silicon oxide compound are mixed in a mass ratio of 9:1 to obtain a negative electrode active material. The negative electrode active material, acetylene black, CMC-Na, and SBR are mixed in a mass ratio of 96:2:1:1, and deionized water is added as a solvent. Then, the mixture is fully stirred and mixed uniformly in a vacuum stirrer to obtain a negative electrode slurry. The negative electrode slurry is coated on a copper foil, and then transferred to an oven for drying after air-drying at room temperature. After the processes of cold pressing and slitting, a negative electrode sheet is obtained.

[0051] Preparation of electrolyte: In a glove box with argon content of 99.999%, oxygen content less than 0.1 ppm and water content less than 0.1 ppm, the first solvent trifluorotoluene and the second solvent methyl ethyl carbonate of battery grade were mixed uniformly according to the mass ratio of 1:1 to obtain a mixed solvent according to the composition of the electrolyte described in Table 1, and then LiPF6 and compound 1 were added to the mixed solvent and mixed uniformly to prepare a lithium ion battery electrolyte. Among them, the content of LiPF6 and compound 1 in the electrolyte is 15wt% and 0.3wt% respectively.

[0052] Selection of separator: a single-layer PE film with a thickness of 9 μm was used as a base film, and a nano-aluminum oxide coating with a thickness of 3 μm was coated on the base film to obtain a separator.

[0053] Preparation of battery: the positive electrode sheet, the separator and the negative electrode sheet were placed in turn, and the aluminum plastic film was wrapped outside, and then transferred to 80°C for dehydration baking. After injecting 3.0 g / Ah of the above prepared lithium ion battery electrolyte, it was sealed, and after standing, hot and cold pressing, formation, clamp and capacity, a soft pack lithium ion battery with a capacity of 1 Ah was obtained.

[0054] Example 2

[0055] The mass ratio of the second solvent methyl ethyl carbonate and the first solvent trifluorotoluene in the mixed solvent was 1:3.25, and the other steps were the same as example 1.

[0056] Example 3

[0057] The mass ratio of the second solvent methyl ethyl carbonate and the first solvent trifluorotoluene in the mixed solvent was 1:2.4, and the other steps were the same as example 1.

[0058] Example 4

[0059] The mass ratio of the second solvent methyl ethyl carbonate and the first solvent trifluorotoluene in the mixed solvent was 1:1.83, and the other steps were the same as example 1.

[0060] Example 5

[0061] The mass ratio of the second solvent methyl ethyl carbonate and the first solvent trifluorotoluene in the mixed solvent was 1:1.25, and the other steps were the same as example 1.

[0062] Example 6

[0063] The mass ratio of the second solvent methyl ethyl carbonate and the first solvent trifluorotoluene in the mixed solvent was 1.25:1, and the other steps were the same as example 1.

[0064] Example 7

[0065] The mass ratio of the second solvent methyl ethyl carbonate and the first solvent trifluoromethylbenzene in the mixed solvent is 1.183:1, and other steps are the same as example 1.

[0066] Example 8

[0067] The mass ratio of the second solvent methyl ethyl carbonate and the first solvent trifluoromethylbenzene in the mixed solvent is 2.4:1, and other steps are the same as example 1.

[0068] Example 9

[0069] The second solvent is diethyl carbonate, and other steps are the same as example 1.

[0070] Example 10

[0071] The first solvent is toluene, and other steps are the same as example 1.

[0072] Example 11

[0073] The first solvent is ethylbenzene, and other steps are the same as example 1.

[0074] Example 12

[0075] The first solvent is decafluoropentane, and other steps are the same as example 1.

[0076] Example 13

[0077] The first solvent is perfluorobutyl ether, and other steps are the same as example 1.

[0078] Example 14

[0079] The first solvent is perfluorobutyl methyl ether, and other steps are the same as example 1.

[0080] Example 15

[0081] The content of compound 1 in the electrolyte is 0.1wt%, and other steps are the same as example 1.

[0082] Example 16

[0083] The content of compound 1 in the electrolyte is 2wt%, and other steps are the same as example 1.

[0084] Example 17

[0085] The electrolyte contains compound 2, and the contents of compound 2 and compound 1 in the electrolyte are 0.3wt% and 0, respectively, and other steps are the same as example 1.

[0086] Example 18

[0087] The electrolyte contains compound 3, and the content of compound 3 and compound 1 in the electrolyte is 0.3wt% and 0 respectively, and other steps are the same as example 1.

[0088] Example 19

[0089] The electrolyte contains second additive LiPO2F2, and the content of LiPO2F2 in the electrolyte is 1.2wt%, and other steps are the same as example 1.

[0090] Example 20

[0091] The electrolyte contains second additive LiPO2F2, and the content of LiPO2F2 in the electrolyte is 1wt%, and other steps are the same as example 1.

[0092] Example 21

[0093] The electrolyte contains second additive LiPO2F2, and the content of LiPO2F2 in the electrolyte is 0.5wt%, and other steps are the same as example 1.

[0094] Example 22

[0095] The electrolyte contains third additive tripropargyl phosphate, and the content of tripropargyl phosphate in the electrolyte is 0.01wt%, and other steps are the same as example 1.

[0096] Example 23

[0097] The electrolyte contains third additive tripropargyl phosphate, and the content of tripropargyl phosphate in the electrolyte is 0.5wt%, and other steps are the same as example 1.

[0098] Example 24

[0099] The electrolyte contains third additive tripropargyl phosphate, and the content of tripropargyl phosphate in the electrolyte is 1wt%, and other steps are the same as example 1.

[0100] Example 25

[0101] The electrolyte contains second additive LiPO2F2 and third additive tripropargyl phosphate, and the content of LiPO2F2 and tripropargyl phosphate in the electrolyte is 1wt% and 0.5wt% respectively, and other steps are the same as example 1.

[0102] Comparative example 1

[0103] The electrolyte does not contain first solvent, and other steps are the same as example 1.

[0104] Comparative example 2

[0105] The electrolyte does not contain compound 1, and other steps are the same as example 1.

[0106] Comparative example 3

[0107] The electrolyte does not contain compound 1, and other steps are the same as comparative example 1.

[0108] Comparative example 4

[0109] The electrolyte does not contain compound 1, and other steps are the same as example 20.

[0110] Comparative example 5

[0111] The electrolyte does not contain compound 1, and other steps are the same as example 23.

[0112] The content of the required raw material components and the mass ratio of the raw materials for the electrolyte prepared in each example and comparative example are shown in Table 1.

[0113] Table 1, composition table of electrolyte in examples 1-25 and comparative examples 1-5

[0114]

[0115]

[0116] In the present application, the lithium ion batteries prepared by using different electrolyte formulations in examples 1-25 and comparative examples 1-5 are tested for performance, and the test results are shown in Table 2.

[0117] In an embodiment of the present application, for example, the lithium ion battery is tested for Directive Current Resistance (DCR). Specifically, at 25℃, after the battery is left standing for 10 min, the battery is charged at a rate of 0.33C to 4.3V, then constant voltage to 0.05C, left standing for 10 min, discharged at a rate of 0.33C to 50% State Of Charge (SOC), then charged at a rate of 0.33C to 4.3V, constant voltage to 0.05C, left standing for 10 min, discharged at a rate of 0.33C to 50% SOC. After standing for 1 hour, record the initial voltage V1 of the battery, then discharge the battery at a current I0 of 4C for 30s, record the voltage V2 of the battery after discharging. The DCR at 50% SOC is calculated according to the following formula:

[0118] DCR = (V1-V2) / I0.

[0119] In an embodiment of the present application, a fast-charging capacity retention test is performed on a lithium ion battery. Specifically, the lithium ion battery is charged at different rates (0.33C, 1C, 2C, 3C and 4C) to 4.3V at 25°C, then charged at 4.3V constant voltage to a current less than 0.05C, and after 10 minutes of rest, discharged at 0.33C constant current to 2.5V. After two cycles at each charging rate, the charging rate is adjusted to the next rate in turn, and the charging capacity at the second cycle at 0.33C and the second cycle at 4C are recorded as the charging capacity of the lithium ion battery at 0.33C and 4C, respectively. The fast-charging capacity retention at 4C is calculated according to the following formula:

[0120] Fast-charging capacity retention (%) = (charging capacity at 4C / charging capacity at 0.33C) x 100%.

[0121] Table 2, performance test results of lithium ion batteries in Examples 1-25 and Comparative Examples 1-5

[0122] Group DCR (mOhm) Fast charging capacity retention rate (%) Example 1 120.3 83.9 Example 2 128.1 78.3 Example 3 125.4 80.6 Example 4 123.6 84.2 Example 5 120.5 82.6 Example 6 118.3 82.8 Example 7 114.6 80.4 Example 8 111.9 77.9 Example 9 128.7 82.9 Example 10 110.2 82.7 Example 11 118.4 82.9 Example 12 125.6 82.1 Example 13 128.5 84.4 Example 14 128.1 83.5 Example 15 114.6 82.1 Example 16 118.7 82.8 Example 17 118.4 81.2 Example 18 125.8 82.0 Example 19 123.0 83.5 Example 20 118.0 84.3 Example 21 118.4 84.1 Example 22 120.6 84.0 Example 23 121.2 84.4 Example 24 125.3 83.8 Example 25 120.4 84.6 Comparative Example 1 110.7 71.2 Comparative Example 2 117.3 75.3 Comparative Example 3 108.6 68.0 Comparative Example 4 117.9 78.5 Comparative Example 5 120.1 78.7

[0123] As shown in Tables 1 and 2, when the first additive compound 1 is contained in the electrolyte, the fast-charging capacity retention of the battery increases slightly, indicating that the electrolyte cannot provide sufficient intrinsic electrochemical stability and cannot significantly improve the fast-charging performance of the battery when the first additive is used alone.

[0124] As shown in Tables 1 and 2, when the first solvent trifluorotoluene is contained in the electrolyte, the fast-charging capacity retention of the battery increases significantly, but the impedance also increases significantly, indicating that the use of the first solvent alone can improve the electrochemical stability of the electrolyte and thus improve the fast-charging performance of the battery, but can accelerate the acid rise rate of the electrolyte system, leading to the destruction of the interface phase and affecting the impedance performance.

[0125] As shown in Tables 1 and 2, when the first solvent trifluorotoluene and the first additive compound 1 are both contained in the electrolyte, the fast-charging capacity retention of the battery increases significantly, and the impedance does not increase significantly, indicating that the first solvent and the first additive have a synergistic effect, the first solvent can improve the electrochemical stability of the electrolyte and thus improve the fast-charging performance of the battery, and the first additive can inhibit the acid rise rate of the electrolyte, avoid the destruction of the interface phase, improve the kinetic performance of the electrolyte, improve the impedance of the battery, and further improve the fast-charging performance of the battery.

[0126] As shown in Table 1 and Table 2, it can be seen from Comparative Examples 1-8 that when the mass ratio of the second solvent to the first solvent increases from 1:3.25 to 2.4:1, the impedance of the battery gradually decreases as a whole, but when the mass ratio of the second solvent to the first solvent is greater than 1.183:1, the fast-charging capacity retention rate of the battery is significantly reduced to below 80%, and when the mass ratio of the second solvent to the first solvent is less than 1:2.4, the impedance of the battery is maintained at a relatively high value of about 128 mOhm, indicating that when the mass ratio of the second solvent to the first solvent is too small, the content of the first solvent is too much, and there is not enough second solvent in the electrolyte to dissolve and dissociate the lithium salt, which affects the kinetic performance of the electrolyte and cannot make the battery exhibit good capacity, and when the mass ratio of the second solvent to the first solvent is too large, the content of the first solvent is too small, which cannot effectively regulate the solvation structure of the electrolyte, resulting in that the electrochemical stability of the electrolyte cannot be improved, thereby affecting the fast-charging performance of the battery. Therefore, by controlling the mass ratio of the second solvent to the first solvent, the fast-charging performance and kinetic performance of the battery can be considered.

[0127] As shown in Table 1 and Table 2, it can be seen from Comparative Example 1 and Example 9 that compared with carbonic acid dimethyl ester and carbonic acid diethyl ester, when carbonic acid methyl ethyl ester is used as the second solvent, the fast-charging capacity retention rate of the battery is greater, and the impedance of the battery is smaller, indicating that by controlling the type of the second solvent, the fast-charging performance and kinetic performance of the battery can be improved.

[0128] As shown in Table 1 and Table 2, it can be seen from Comparative Example 1 and Examples 10-14 that compared with trifluorotoluene, toluene, ethylbenzene, decafluoropentane, perfluorobutyl ether and perfluorobutyl methyl ether, when trifluorotoluene is used as the first solvent, the fast-charging capacity retention rate of the battery is relatively large, and the impedance of the battery is not greatly affected, indicating that trifluorotoluene as the first solvent can comprehensively improve the fast-charging performance and kinetic performance of the battery. Therefore, by controlling the type of the first solvent, the fast-charging performance and kinetic performance of the battery can be further improved.

[0129] As shown in Table 1 and Table 2, it can be seen from Comparative Example 1 and Examples 15-16 that as the content of the first additive compound 1 in the electrolyte increases from 0.1wt% to 0.3wt% and 2wt%, the impedance and fast-charging capacity retention rate of the battery increase, indicating that the increase of the content of the first additive can remove more acidic substances generated during the cycling of the battery, inhibit the acid rising rate of the electrolyte, protect the stability of the interface phase, and improve the fast-charging performance of the battery, but when the content of the first additive is too large, the viscosity of the electrolyte increases and the conductivity decreases, resulting in an increase in impedance and affecting the kinetic performance of the battery. Therefore, by controlling the content of the first additive, the fast-charging performance and kinetic performance of the battery can be considered.

[0130] As shown in Table 1 and Table 2, it can be seen from Comparative Example 1 and Examples 17-18 that, for the three first additives of Comparative Compound 1, Compound 2 and Compound 3, when Compound 1 is selected as the first additive, the battery has a greater fast-charging capacity retention rate, i.e., the battery has better fast-charging performance, and when Compound 2 is selected as the first additive, the battery has a smaller impedance, i.e., the battery has better kinetic performance. Therefore, by controlling the type of the first additive, the kinetic performance and fast-charging performance of the battery can be further improved.

[0131] As shown in Table 1 and Table 2, it can be seen from Comparative Example 1, Example 20, Comparative Example 2 and Comparative Example 4 that, for the first additive and the second additive, when the electrolyte contains only the second additive LiPO2F2, the fast-charging capacity retention rate of the battery increases, but the increase is very small, indicating that the second additive alone cannot significantly improve the fast-charging performance of the battery. When the electrolyte contains only the first additive Compound 1, the fast-charging capacity retention rate of the battery increases, but the impedance also increases, indicating that the first additive can improve the fast-charging performance of the battery, but affects the kinetic performance of the battery. When the electrolyte contains both the first additive Compound 1 and the second additive LiPO2F2, the battery has a greater fast-charging capacity retention rate and a smaller impedance, indicating that by adding the second additive to the electrolyte containing the first additive, the kinetic performance and fast-charging performance of the battery can be further significantly improved.

[0132] As shown in Table 1 and Table 2, it can be seen from Comparative Examples 19-21 that, as the mass ratio of the first additive to the second additive increases from 0.3:1.2 to 0.3:1, the impedance of the battery decreases and the fast-charging capacity retention rate increases, i.e., the kinetic performance and fast-charging performance of the battery are improved. However, when the mass ratio continues to increase from 0.3:1 to 0.3:0.5, the impedance of the battery increases and the fast-charging capacity retention rate decreases, i.e., the kinetic performance and fast-charging performance of the battery are affected, indicating that too much second additive is difficult to dissolve, resulting in an increase in the viscosity and a decrease in the conductivity of the electrolyte, thereby affecting the kinetic performance and fast-charging performance of the battery. Therefore, by controlling the mass ratio of the first additive to the second additive, the kinetic performance and fast-charging performance of the battery can be improved.

[0133] As shown in Table 1 and Table 2, it can be seen from Comparative Example 1, Example 23, Comparative Example 2 and Comparative Example 5 that, for the first additive and the third additive, when the electrolyte contains only the third additive tripropargyl phosphate, the fast-charging capacity retention of the battery increases relatively insignificantly, indicating that the third additive alone is difficult to effectively improve the fast-charging performance of the battery. When the electrolyte contains only the first additive Compound 1, the fast-charging capacity retention of the battery increases, indicating that the first additive can improve the fast-charging performance of the battery. When the electrolyte contains both the first additive Compound 1 and the third additive tripropargyl phosphate, the fast-charging capacity retention of the battery is greater, indicating that by adding the third additive to the electrolyte containing the first additive, the fast-charging performance of the battery can be further improved.

[0134] As shown in Table 1 and Table 2, it can be seen from Comparative Examples 22-24 that, as the content of the third additive tripropargyl phosphate in the electrolyte increases from 0.01wt% to 1wt%, the impedance of the battery increases, and the fast-charging capacity retention first increases and then decreases, indicating that, as the content of the third additive increases, although the kinetic performance of the battery is affected, the fast-charging performance shows a trend of first improving and then decreasing. Therefore, by controlling the content of the third additive, the fast-charging performance of the battery can be improved while the kinetic performance of the battery is not significantly affected.

[0135] As shown in Table 1 and Table 2, it can be seen from Comparative Example 1, Example 20, Example 23 and Example 25 that, when the electrolyte contains the first additive, the second additive and the third additive at the same time, the fast-charging capacity retention of the battery is the largest, and the impedance value is not high, indicating that the first additive, the second additive and the third additive synergistically act, which can significantly improve the fast-charging performance while the kinetic performance of the battery is not significantly affected.

[0136] The application also provides an electronic device comprising at least one lithium ion battery as described above for providing electric energy. The electronic device can be a vehicle, a mobile phone, a portable device, a notebook computer, a ship, a spacecraft, an electric toy and an electric tool, etc. In an embodiment of the application, the vehicle is a new energy vehicle, which can be a pure electric vehicle, a hybrid vehicle or an extended-range vehicle, etc. The spacecraft includes an airplane, a rocket, a space shuttle and a spacecraft, etc. The electric toy includes a fixed or mobile electric toy, such as a game console, an electric vehicle toy, an electric ship toy and an electric airplane toy, etc. The electric tool includes a metal cutting electric tool, a grinding electric tool, an assembly electric tool and a railway electric tool, such as an electric drill, an electric grinder, an electric wrench, an electric screwdriver, an electric hammer, an impact drill, a concrete vibrator and an electric planer, etc. The electronic device comprises the lithium ion battery as described above, and thus has the advantages of the lithium ion battery as described above, which will not be described here.

[0137] To sum up, the application provides a lithium ion battery electrolyte and application thereof, by introducing a first solvent into the electrolyte, the electrochemical stability of the electrolyte can be improved, thereby improving the fast charging performance of the battery. By introducing a first additive into the electrolyte, the first additive can timely capture acidic substances generated by lithium salt decomposition, avoid the destruction of the acidic substances to the SEI film and the CEI film, improve the stability of the interface phase, thereby further improving the fast charging performance of the battery, and can also reduce the viscosity of the electrolyte, improve the conductivity of the electrolyte, avoid the impedance of the battery from increasing, and improve the kinetic performance of the battery.

[0138] The above description is only the preferred embodiment of the application and the explanation of the applied technical principles, and those skilled in the art should understand that the application range involved in the application is not limited to the technical solutions formed by the specific combination of the above technical features, and also covers other technical solutions formed by any combination of the above technical features or equivalent features without departing from the inventive concept, for example, the technical solutions formed by replacing the above features with the technical features disclosed in the application (but not limited to) having similar functions.

[0139] In addition to the technical features described in the specification, the remaining technical features are known to those skilled in the art, and in order to highlight the innovative features of the application, the remaining technical features will not be described here.

Claims

1. A lithium-ion battery electrolyte, characterized in that, at least comprising: a solvent, comprising a first solvent selected from at least one of trifluorotoluene, difluorobenzene, trifluorobenzene, toluene, ethylbenzene, decafluoropentane, perfluorohexanone, perfluorobutyl ethyl ether or perfluorobutyl methyl ether, and a content of the first solvent in the electrolyte being 25wt%-55wt%, and a second solvent selected from at least one of methyl ethyl carbonate, dimethyl carbonate, diethyl carbonate, propylene carbonate or ethylene carbonate, and a content of the second solvent in the electrolyte being 25wt%-55wt%, and a mass ratio of the second solvent to the first solvent being 1:1.83-1.25:1; a lithium salt; and an additive, comprising a first additive and a second additive, the first additive having a general structure of: wherein R1, R2, and R3 are each independently selected from one of substituents having a carbon atom number of 1-6, an unsaturation degree of 0-4, and a heteroatom number of 0-3, the heteroatom being selected from at least one of oxygen, nitrogen, or sulfur, the first additive having a content of 0.01wt%-2wt% in the electrolyte, the second additive being selected from at least one of lithium difluorophosphate, lithium difluorodioxaphosphinate, or lithium difluorooxalato borate, the second additive having a content of 0.01wt%-1.2wt% in the electrolyte.

2. The electrolyte for lithium ion batteries according to claim 1, characterized in that, the substituent being selected from at least one of an alkyl group, an alkenyl group, an alkynyl group, a carbonyl group, an ester group, an amino group or a heterocyclic ring.

3. The electrolyte for lithium ion batteries according to claim 1, characterized in that, The first additive is selected from Compound 1, Compound 2 or Compound 3.

4. The electrolyte for lithium ion batteries according to claim 1, characterized in that, a mass ratio of the first additive to the second additive being (0.3-0.6):

1.

5. The electrolyte for lithium ion batteries according to claim 1, characterized in that, the additive further comprising a third additive selected from at least one of tripropargyl phosphate, tris(trimethylsilyl)phosphate or methanedi sulfonic acid methylene ester, and a content of the third additive in the electrolyte being 0.01wt%-1wt%.

6. The electrolyte for lithium-ion batteries according to claim 1, characterized in that, the lithium salt being selected from at least one of lithium hexafluorophosphate, lithium bisfluorosulfonylimide or lithium bis(trifluoromethyl)sulfonylimide, and a content of the lithium salt in the electrolyte being 10wt%-20wt%.

7. A lithium-ion battery, characterized by comprising: a positive electrode tab; a negative electrode tab; a separator disposed between the positive electrode tab and the negative electrode tab; and an electrolyte, the electrolyte being selected from the lithium ion battery electrolyte according to any one of claims 1-6.

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