Lithium ion battery electrolyte and application thereof

Abstract

The application provides a lithium ion battery electrolyte and application thereof, and the electrolyte comprises a non-aqueous solvent, a lithium salt, and an additive; the lithium salt comprises lithium bisfluorosulfonylimide; and the additive comprises a first additive, and the first additive comprises cyanomethyl diethyl phosphate. The lithium ion battery electrolyte and application thereof can effectively prevent corrosion of an aluminum foil current collector, improve gas production performance of a lithium ion battery, and improve cycle performance and fast charging 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] With the increasing demand of new energy automobile industry on the energy density of new energy batteries, the development trend of high nickelization of positive electrode materials, etc., the selection of lithium hexafluorophosphate (LiPF6) as the lithium salt in the electrolyte has been difficult to completely meet the performance requirements of lithium ion batteries. Lithium bisfluorosulfonylimide (LiFSI) is a new type of lithium salt with excellent performance. As the main salt of the electrolyte, it has the advantages of high conductivity, high chemical stability and high thermal stability, and is more suitable for the development direction of future high energy density, high power density and high safety lithium batteries. It is also one of the best choices to replace LiPF6. At the same time, LiFSI also shows great advantages as an additive.

[0003] However, in the high-voltage battery system, the FSI - ion in LiFSI may have a certain corrosion effect on aluminum foil, which may affect the performance and service life of lithium ion batteries, and also limits the commercial application of LiFSI to some extent. SUMMARY

[0004] The present application provides a lithium ion battery electrolyte and application thereof. The lithium ion battery electrolyte and application thereof can effectively prevent the corrosion of aluminum foil current collector, improve the cycle performance of lithium ion batteries, and improve the fast charging performance of the battery.

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

[0006] a non-aqueous solvent;

[0007] a lithium salt, wherein the lithium salt comprises lithium bisfluorosulfonylimide; and

[0008] an additive, wherein the additive comprises a first additive, and the first additive comprises cyanomethyl diethyl phosphate.

[0009] In an embodiment of the present application, the content of the first additive in the electrolyte is 0.1wt%-3wt%.

[0010] In an embodiment of the present application, the content of the first additive in the electrolyte is 0.5wt%-1wt%.

[0011] In an embodiment of the present application, the additive comprises a second additive, the second additive comprises lithium tetrafluoroborate, and the content of the second additive in the electrolyte is 0.2wt%-3wt%.

[0012] In one embodiment of the present invention, the mass ratio of the second additive to the first additive is 1.2:1 to 2.5:1. In one embodiment of the present invention, the mass ratio of the second additive to the first additive is 2:1 to 2.5:1.

[0013] In one embodiment of the present invention, the lithium salt further comprises lithium hexafluorophosphate, the content of the lithium bis(fluorosulfonyl)imide in the electrolyte is 3wt% to 6wt%, and the total content of the lithium bis(fluorosulfonyl)imide and the lithium hexafluorophosphate in the electrolyte is 13wt% to 16wt%.

[0014] In one embodiment of the present invention, the non-aqueous solvent includes carbonate, and the carbonate is selected from at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate.

[0015] In one embodiment of the present invention, the non-aqueous solvent further comprises a carboxylate ester, the carboxylate ester is selected from at least one of methyl acetate and ethyl acetate, and the content of the carboxylate ester in the electrolyte is 10 wt % to 20 wt %.

[0016] The present invention also provides a lithium ion battery, comprising at least:

[0017] A positive electrode sheet, comprising a positive electrode current collector and a positive electrode active layer disposed at least on one side of the positive electrode current collector, wherein the positive electrode active layer comprises a positive electrode active material, and the positive electrode active material comprises a nickel-cobalt-manganese ternary positive electrode active material;

[0018] negative electrode; and

[0019] The electrolyte is selected from the lithium-ion battery electrolyte described above.

[0020] The present invention also provides an electronic device comprising the lithium-ion battery described above.

[0021] In summary, the present invention proposes a lithium-ion battery electrolyte and its application, which can prevent the dissolution of transition metal ions in the positive electrode active material under high temperature and high pressure conditions, and improve the high-temperature cycle performance of the battery. It can effectively prevent LiFSI from corroding the aluminum foil current collector, and further improve the long cycle life of the lithium-ion battery. By using the first additive in combination with the second additive, the DC impedance of the lithium-ion battery is effectively reduced, and the fast charging performance is improved. By using lithium bis(fluorosulfonyl)imide and lithium hexafluorophosphate together, the chemical stability and thermal stability of the lithium-ion battery can be improved, the cycle performance of the lithium-ion battery can be improved, the conductivity of the electrolyte is improved, and the fast charging performance of the battery is further improved. DETAILED DESCRIPTION

[0022] Following, the advantages and effects of the present application will be apparent to those skilled in the art from the description of the embodiments of the present application. The present application can also be implemented or applied in other different embodiments, and the details in the description can be modified or changed based on different views and applications without departing from the spirit of the present application.

[0023] 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 presented in order to make the disclosure complete and full and to fully convey the scope of the present application to those skilled in the art.

[0024] The technical solutions of the present application will be further described in detail below in conjunction with the embodiments. Obviously, the described embodiments are only a part of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0025] The present application proposes a lithium ion battery, such as a primary battery or a secondary battery, and the secondary battery is, for example, a soft pack battery, a square case battery or a cylindrical battery, etc. The type of the lithium ion battery is not specifically limited in the present application. In an embodiment of the present application, the lithium ion battery comprises a shell and a bare cell arranged in the shell, the bare cell comprises a positive electrode sheet, a separator and a negative electrode sheet, the positive electrode sheet, the separator and the negative electrode sheet are sequentially laminated to ensure that the separator is arranged between any positive electrode sheet and negative electrode sheet, and a multi-layered sheet body is obtained in the form of winding or folding, which is loaded into the battery shell as the bare cell. Finally, the electrolyte is injected into the shell once or in multiple times, so that the bare cell is completely immersed in the electrolyte.

[0026] In an embodiment of the present 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 material formed after surface treatment of nickel, titanium, aluminum, silver, stainless steel or carbon, and the positive electrode current collector can also be used in the form of a film, a net, a porous material, a foam or a non-woven fabric, etc. in any one or a combination of multiple forms. The thickness of the positive electrode current collector is, for example, 8 μm to 15 μm. In the embodiment, the positive electrode current collector is, for example, an aluminum foil, and the thickness of the aluminum foil is, for example, 13 μm.

[0027] In an embodiment of the present application, the positive electrode active layer comprises a positive electrode active material, a binder and a conductive agent, etc. The positive electrode active material comprises, for example, a nickel-cobalt-manganese ternary positive electrode active material (NCM). The chemical formula of the nickel-cobalt-manganese ternary positive electrode active material is, for example, LiNi a Co b Mn 1-a-bO2, wherein 0 < a < 1.0, 0 < b < 0.5, 0 < a + b < 1.0. In another embodiment of the present application, the chemical formula of the ternary nickel-cobalt-manganese positive electrode active material is, for example, Li x [Ni y Co z Mn t M (1-y-z-t) ]O 2-δ , wherein M is selected from one or more of Cr, Zr, Ca, Mg, Cu, Ti, Al, Mo, W or Zn, etc., 0.9 < x < 1.1, 0 < x < 1.0, 0 < y < 0.5, 0 < y + z + t < 1.0, 0 ≤ δ ≤ 0.1. The binder is, for example, selected from any one or more of Polyvinylidene Fluoride (PVDF), Poly(ethylene oxide) (PEO), Polyamide (PA), Polyacrylonitrile (PAN), Polyacrylate, Polyvinylether, Polymethyl Methacrylate (PMMA), Ethylene-Propylene-Diene Terpolymer (EPDM), Polyhexafluoropropylene (PHFP), or Polymerized Styrene Butadiene Rubber (SBR), etc. The conductive agent is, for example, selected from any one or more of conductive carbon black (Super P), acetylene black, carbon nanotube, and graphene, etc. In the positive electrode active layer, the mass ratio of the positive electrode active material, the conductive agent, and the binder is, for example, (90-98):(1-5):(1-5).

[0028] In an embodiment of the present application, the positive electrode active material is, for example, LiNi 0.6 Mn 0.2 Co 0.2 O2, the binder is, for example, selected from Polyvinylidene Fluoride, and the conductive agent is, for example, selected from conductive carbon black. The positive electrode active material, the conductive agent, and the binder are mixed in a ratio of, for example, 98:1:1 by mass, an organic solvent is added, and the system is stirred in a vacuum stirrer until it is uniform to obtain a positive electrode slurry. The organic solvent is, for example, selected from N-Methylpyrrolidone (NMP). The positive electrode slurry is uniformly coated on an aluminum foil current collector, then dried at room temperature, transferred to an oven for drying, and subjected to cold pressing and slitting to obtain a positive electrode sheet. In other embodiments, the positive electrode sheet can also be obtained by any other method for forming a positive electrode sheet.

[0029] In an embodiment of the present application, the negative electrode sheet comprises, for example, a negative electrode current collector and a negative electrode active layer coated on at least one side surface of the negative electrode current collector. The negative electrode current collector is selected, for example, from one of a copper foil current collector, a composite copper foil current collector, a carbon current collector, a foamed copper current collector, a stainless steel current collector, and the like, and has a thickness of, for example, 8 μm to 15 μm. In this embodiment, the negative electrode current collector is selected, for example, as a copper foil, and the copper foil has a thickness of, for example, 13 μm.

[0030] In an embodiment of the present application, the negative electrode active layer comprises, for example, a negative electrode active material, a conductive agent, a binder, a thickening agent, and the like. The negative electrode active material is a compound capable of intercalating and deintercalating lithium ions. In an embodiment of the present application, the negative electrode active material comprises, for example, at least one of graphite, a silicon-oxygen material (SiO x x < 2) or a silicon-carbon material, and the like. When the negative electrode active material comprises the silicon-oxygen material or the silicon-carbon material, the mass ratio of the silicon-oxygen material or the silicon-carbon material to the graphite is, for example, 2:98 to 10:90. The binder is selected, for example, from any one or more of polyvinylidene fluoride, polyethylene oxide, polyamide, polypropylene, polyacrylate, polyvinyl ether, polymethyl methacrylate, polyhexafluoropropylene, or styrene butadiene rubber, and the like. The thickening agent is selected, for example, from sodium carboxymethyl cellulose (CMC-Na) and the like, and the conductive agent is selected, for example, from any one or more of conductive carbon black, acetylene black, ketjen black, carbon nanotubes, and graphene, and the like. The mass ratio of the negative electrode active material, the conductive agent, the binder, and the thickening agent in the negative electrode active layer is, for example, (90 to 96):(1 to 2):(1 to 3):(2 to 5).

[0031] In an embodiment of the present application, the negative electrode active material is selected, for example, from graphite and a silicon-oxygen material, and the mass ratio of the silicon-oxygen material to the graphite is, for example, 5:95, the conductive agent is selected, for example, from conductive carbon black, the thickening agent is selected, for example, from sodium carboxymethyl cellulose, and the binder is selected, for example, from styrene butadiene rubber. In an embodiment of the present application, the negative electrode active material, the conductive agent, the binder, and the thickening agent are mixed, for example, in a mass ratio of 96:1:1:2, deionized water is added, and the mixture is uniformly mixed under the action of 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 being dried at room temperature. The negative electrode sheet is obtained through processes such as cold pressing and slitting. In other embodiments, the negative electrode sheet can also be obtained in any other manner of forming a negative electrode sheet.

[0032] In an embodiment of the present application, the diaphragm is, for example, a polyethylene film (PE), a polypropylene film (PP), a glass fiber film, or a composite film, and the thickness of the diaphragm is, for example, 9-15 μm. In an embodiment of the present application, a polyethylene film with a thickness of 8-10 μm is selected as a base film, and a nanometer alumina coating with a thickness of 2-4 μm is coated on the base film to obtain the diaphragm.

[0033] In an embodiment of the present application, the lithium ion battery further comprises an electrolyte injected and filled in the entire internal space of the battery, and the positive electrode sheet, the diaphragm, and the negative electrode sheet are completely immersed in the electrolyte, which plays a role in conducting ions, providing ion channels, and maintaining chemical stability. The various components in the electrolyte can be divided into non-aqueous solvents, lithium salts, and additives according to their functions and additive amounts, the non-aqueous solvents are used to dissolve the lithium salts and the additives therein; the lithium salts are mainly used to provide lithium ions to form ion channels; in the entire electrochemical system of the battery, the directional movement of lithium ions and electrons generates electric power, and the lithium salts have a great influence on the energy density, power density, wide electrochemical window, cycle life, and safety performance of the lithium battery. The additives, as a small amount of substances added in the electrolyte, have various types and different effects, for example, they can improve the high and low temperature performance, cycle performance, film forming performance, and the like of the battery.

[0034] The present application provides a kind of lithium ion battery electrolyte, at least including non-aqueous solvent, lithium salt and additive etc., wherein, additive includes first additive and second additive, first additive includes diethyl cyanomethyl phosphonate (C6H 12 NO3P) and the like, and the second additive includes lithium tetrafluoroborate (LiBF4) and the like. Diethyl cyanomethyl phosphonate forms a uniform cathode-electrolyte interphase (CEI) at the interface between the positive electrode and the electrolyte to protect the positive electrode active material, prevents the dissolution of transition metal ions in the positive electrode active material under high temperature and high pressure conditions, and improves the high temperature cycle performance of the lithium ion battery. In addition, the first additive can also effectively prevent the corrosion of LiFSI on the aluminum foil current collector, and further improve the long cycle life of the lithium ion battery. When the first additive is used in combination with the second additive LiBF4, the direct current resistance (DCR) of the lithium ion battery can be effectively reduced, and the fast charging performance can be improved.

[0035] In an embodiment of the present application, the content of the first additive in the electrolyte is, for example, 0.1 wt% to 3 wt%, and for example, 0.5 wt% to 1 wt%. The content of the second additive in the electrolyte is, for example, 0.2 wt% to 3 wt%, and the mass ratio of the second additive to the first additive is, for example, 1.2:1 to 2.5:1. Further, the mass ratio of the second additive to the first additive is, for example, 2:1 to 2.5:1. If the content of the first additive is too low, the stability of the formed CEI film is poor, and the gas production performance is poor. If the content of the first additive is too high, the thickness of the CEI film is too thick, the direct current impedance of the lithium ion battery is large, and the capacity of the battery is not fully utilized. Controlling the content of the second additive can simultaneously optimize multiple performances of the lithium ion battery. Therefore, controlling the content and ratio of the first additive and the second additive can achieve the purposes of protecting the positive current collector, improving the fast charging performance, and improving the cycle performance.

[0036] In an embodiment of the present application, the lithium salt includes, for example, at least lithium bisfluorosulfonylimide. The fluorine ion in the structure of lithium bisfluorosulfonylimide has strong electron-withdrawing properties, which weakens the coordination effect between the anion and the cation in the lithium salt, so that the activity of lithium ions is stronger, thereby improving the conductivity of the electrolyte and further improving the fast charging performance of the battery. In this embodiment, the lithium salt also includes lithium hexafluorophosphate, and the content of lithium bisfluorosulfonylimide in the electrolyte is 3 wt% to 6 wt%, and the total content of lithium bisfluorosulfonylimide and lithium hexafluorophosphate in the electrolyte is 13 wt% to 16 wt%. By using lithium bisfluorosulfonylimide and lithium hexafluorophosphate together, the problem of corrosion of aluminum foil current collector caused by using single lithium bisfluorosulfonylimide can be avoided. At the same time, by controlling the total content of the lithium salt, if the total content of the lithium salt is too small, the fast charging performance of the lithium ion battery is not good, and lithium is easily precipitated. If the total content of the lithium salt is too large, the number of solvated lithium ions will decrease, the ionic conductivity of the electrolyte will decrease, and the fast charging performance will be affected. Therefore, by using lithium bisfluorosulfonylimide and lithium hexafluorophosphate together, the chemical stability and thermal stability of the lithium ion battery can be improved, the cycle performance of the lithium ion battery can be improved, and the corrosion of the positive current collector can be reduced while improving the fast charging performance of the lithium ion battery.

[0037] In an embodiment of the present application, the non-aqueous solvent comprises, for example, a carbonate selected from at least one of ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), and the like. The non-aqueous solvent also comprises, for example, a carboxylic acid ester selected from at least one of methyl acetate (MA), ethyl acetate (EA), and the like. The content of the carboxylic acid ester in the electrolyte is 10wt% to 20wt%. By adding the appropriate carboxylic acid ester to the electrolyte, a synergistic effect can be formed with the electrolyte additive, further improving the fast-charging performance of the lithium ion battery.

[0038] In an embodiment of the present application, when preparing the electrolyte, the non-aqueous solvent is mixed uniformly in a glove box under an inert gas atmosphere (such as argon) with a moisture content of less than or equal to 0.1 ppm, and then the lithium salt is added to the non-aqueous solvent after being sufficiently dried, and the additive is added to prepare the lithium ion battery electrolyte. The content described in the present application is the weight percentage based on the total weight of the electrolyte.

[0039] In an embodiment of the present application, the above positive electrode sheet, separator, and negative electrode sheet are sequentially placed with the separator in the middle of the positive electrode sheet and the negative electrode sheet to play a role of isolation, and a bare cell is obtained by winding or stacking. The bare cell is placed in a housing, dried in a vacuum oven, sealed after injecting the electrolyte prepared in the present application, and at least undergoes processes such as standing, formation, and capacity distribution to obtain a lithium ion battery.

[0040] The present application will be explained in more detail below by referring to the examples, which should not be understood as limiting. Appropriate modifications can be made within the scope consistent with the main idea of the present application, and all fall within the technical scope of the present application.

[0041] Example 1

[0042] Preparation of electrolyte: In an argon glove box with water content less than 0.1 ppm, ethylene carbonate, dimethyl carbonate and methyl ethyl carbonate were mixed uniformly in a mass ratio of 3:5:2 to obtain a mixed solvent, and then methyl acetate, lithium hexafluorophosphate, lithium bisfluorosulfonylimide and the first additive diethyl cyanomethyl phosphate were added to the mixed solvent to obtain the electrolyte. In the obtained electrolyte, the content of methyl acetate was 10 wt%, the content of lithium hexafluorophosphate was 12 wt%, the content of lithium bisfluorosulfonylimide was 4 wt%, and the content of diethyl cyanomethyl phosphate was 0.5 wt%.

[0043] Preparation of positive electrode sheet: LiNi 0.6 Mn 0.2 Co 0.2 After polyvinylidene fluoride and conductive carbon black were mixed in a mass ratio of 98:1:1, N-methyl pyrrolidone was added, and the system was stirred to be uniform under the action of a vacuum stirrer to obtain a positive electrode slurry. The positive electrode slurry was uniformly coated on an aluminum foil current collector, and then transferred to an oven for drying after being dried at room temperature, and then subjected to cold pressing and slitting processes to obtain a positive electrode sheet.

[0044] Preparation of negative electrode sheet: The negative active material was a graphite-silicon-oxygen material, and the mass ratio of the silicon-oxygen material to graphite was 5:95. The negative active material, conductive carbon black, sodium carboxymethyl cellulose and styrene-butadiene rubber were mixed in a mass ratio of 96:1:1:2, deionized water was added, and the mixture was uniformly mixed under the action of a vacuum stirrer to obtain a negative electrode slurry. The negative electrode slurry was coated on a copper foil, and then transferred to an oven for drying after being dried at room temperature, and then subjected to cold pressing and slitting processes to obtain a negative electrode sheet.

[0045] Selection of separator: a 12 μm thick polypropylene separator was selected.

[0046] Preparation of battery: the positive electrode sheet, the separator and the negative electrode sheet were sequentially wound, so that the separator was between the positive electrode sheet and the negative electrode sheet to play a role of isolation, to obtain a bare cell. Then the bare cell was placed in a shell, dried in a vacuum oven, and then injected with the electrolyte prepared above, sealed, subjected to formation process and obtained a lithium ion battery.

[0047] Example 2

[0048] In the electrolyte, the carboxylic acid ester includes methyl acetate and ethyl acetate, the content of methyl acetate is 10 wt%, and the content of ethyl acetate is 5 wt%, and the other steps remain the same as in Example 1.

[0049] Example 3

[0050] In the electrolyte, the carboxylic acid ester includes methyl acetate and ethyl acetate, the content of methyl acetate is 10 wt%, and the content of ethyl acetate is 10 wt%, and the other steps remain the same as in Example 1.

[0051] Example 4

[0052] In the electrolyte, the carboxylic acid ester includes methyl acetate and ethyl acetate, the content of methyl acetate is 10wt%, the content of ethyl acetate is 5wt%, the content of lithium hexafluorophosphate is 10wt%, the content of lithium bisfluorosulfonylimide is 6wt%, and the other steps remain unchanged with example 1.

[0053] Example 5

[0054] In the electrolyte, the carboxylic acid ester includes methyl acetate and ethyl acetate, the content of methyl acetate is 10wt%, the content of ethyl acetate is 5wt%, the content of diethyl cyanomethylphosphate is 0.1wt%, and the other steps remain unchanged with example 1.

[0055] Example 6

[0056] In the electrolyte, the carboxylic acid ester includes methyl acetate and ethyl acetate, the content of methyl acetate is 10wt%, the content of ethyl acetate is 5wt%, the content of diethyl cyanomethylphosphate is 1wt%, and the other steps remain unchanged with example 1.

[0057] Example 7

[0058] In the electrolyte, the carboxylic acid ester includes methyl acetate and ethyl acetate, the content of methyl acetate is 10wt%, the content of ethyl acetate is 5wt%, the content of diethyl cyanomethylphosphate is 3wt%, and the other steps remain unchanged with example 1.

[0059] Example 8

[0060] In the electrolyte, no carboxylic acid ester is included, and the other steps remain unchanged with example 1.

[0061] Example 9

[0062] In the electrolyte, the carboxylic acid ester includes methyl acetate and ethyl acetate, the content of methyl acetate is 15wt%, the content of ethyl acetate is 15wt%, and the other steps remain unchanged with example 1.

[0063] Example 10

[0064] In the electrolyte, the carboxylic acid ester includes methyl acetate and ethyl acetate, the content of methyl acetate is 10wt%, the content of ethyl acetate is 5wt%, the content of lithium hexafluorophosphate is 13wt%, the content of lithium bisfluorosulfonylimide is 3wt%, and the other steps remain unchanged with example 1.

[0065] Example 11

[0066] In the electrolyte, the carboxylic acid ester includes methyl acetate and ethyl acetate, the content of methyl acetate is 10wt%, the content of ethyl acetate is 5wt%, the content of lithium hexafluorophosphate is 13.5wt%, the content of lithium bisfluorosulfonylimide is 2.5wt%, and other steps remain unchanged with example 1.

[0067] Example 12

[0068] In the electrolyte, the carboxylic acid ester includes methyl acetate and ethyl acetate, the content of methyl acetate is 10wt%, the content of ethyl acetate is 5wt%, the positive active material is changed to LiCoO2(LCO), and other steps remain unchanged with example 1.

[0069] Example 13

[0070] In the electrolyte, the carboxylic acid ester includes methyl acetate and ethyl acetate, the content of methyl acetate is 10wt%, the content of ethyl acetate is 5wt%, and the second additive LiBF4 is added at the same time, the content of LiBF4 is 0.6wt%, and other steps remain unchanged with example 1.

[0071] Example 14

[0072] In the electrolyte, the content of LiBF4 is 1wt%, and other steps remain unchanged with example 13.

[0073] Example 15

[0074] In the electrolyte, the content of LiBF4 is 1.25wt%, and other steps remain unchanged with example 13.

[0075] Example 16

[0076] In the electrolyte, the content of LiBF4 is 1.5wt%, and other steps remain unchanged with example 13.

[0077] Comparative example 1

[0078] The electrolyte does not include cyanomethyl diethyl phosphate, and other steps remain unchanged with example 2.

[0079] Comparative example 2

[0080] In the electrolyte, the first additive cyanomethyl diethyl phosphate is replaced by 3-cyanophenyl diethyl phosphate, the content of 3-cyanophenyl diethyl phosphate is 0.5wt%, and other steps remain unchanged with example 2.

[0081] Comparative example 3

[0082] In the electrolyte, the first additive cyanomethyl diethyl phosphate is replaced by 4-cyanobenzyl diethyl phosphite, the content of 4-cyanobenzyl diethyl phosphite is 0.5wt%, and other steps remain the same as those in Example 2.

[0083] Comparative Example 4

[0084] In the electrolyte, the first additive cyanomethyl diethyl phosphate is replaced by 4-cyanobenzyl diethyl phosphite, the content of 4-cyanobenzyl diethyl phosphite is 0.5wt%, and other steps remain the same as those in Example 2.

[0085] In the present application, the components and systems of the electrolyte in lithium ion batteries in Examples 1-16 and Comparative Examples 1-4 are shown in Table 1, and different electrolytes or positive active materials are used to prepare lithium ion batteries, and the performance of the lithium ion batteries is tested, and the test results are shown in Tables 2 and 3.

[0086] In an embodiment of the present application, the fast charging cycle lithium precipitation test (ALP) is used to measure the fast charging capacity of the battery, and different rates are used for charging and discharging at different states of charge (SOC), such as 3% to 10% SOC-1C, 10% to 30% SOC-4C, 30% to 50% SOC-3C, 50% to 70% SOC-2.5C, 70% to 80% SOC-2C, and 80% to 97% SOC-1C. The fast charging cycle test is performed on the lithium ion battery, and the cycle is 20 times (cls). The negative electrode is observed for lithium precipitation.

[0087] In an embodiment of the present application, the DCR test at 25°C is to place the lithium ion battery in a constant temperature oven, adjust the temperature of the constant temperature oven to 25°C, and stand for 10 min. Then, charge at 0.33C constant current to 4.4V, and then charge at 4.4V constant voltage to 0.05C cutoff. After standing for 30 min, discharge at 0.33C constant current to 2.8V. Repeat the cycle 2 times, and record the last discharge capacity as C0. After standing for 30 min, discharge at 0.33C to 50% C0, adjust the SOC of the cell to 50%, stand for 30 min, record the end voltage V1, and then discharge at 4C0 constant current for 30s, record the end voltage V2 and the current I, and calculate DCR=(V1-V2) / I.

[0088] In an embodiment of the present application, the 45°C cycle 500 times gas generation growth rate test is to place the lithium ion battery in a constant temperature oven, adjust the temperature of the constant temperature oven to 45°C, and perform cycle charging and discharging at 1C current in the potential range of 2.8V-4.4V. Record the gas generation growth rate after 500 cycles.

[0089] In an embodiment of the present application, the 60℃ high-temperature storage 30-day corrosion test is as follows: at 25℃, the lithium ion battery is charged at a constant current of 0.33C to 4.4V, and then charged at a constant voltage until the current is 0.05C, and then left for 30 min. The fully charged battery is then placed in a 60℃ oven for 30 days. After the battery is cooled, the battery is disassembled, and the corrosion of the aluminum foil current collector is observed and recorded using a laser microscope.

[0090] In an embodiment of the present application, the fast-charging cycle capacity retention rate test is as follows: at 25℃, the charging and discharging voltage is set to 2.8V-4.4V, the charging current density is 3C, the discharging current density is 1C, and the cutoff current is 0.05C. The battery is cycled 200 times according to the above process, and the fast-charging cycle capacity retention rate is obtained by the discharging capacity at the 200th cycle / the discharging capacity at the 1st cycle.

[0091] Table 1, electrolytes and battery systems in Examples 1-16 and Comparative Examples 1-4

[0092]

[0093] Table 2, performance test results of lithium ion batteries in Examples 1-16 and Comparative Examples 1-4

[0094]

[0095] Table 3, fast-charging performance test results of lithium ion batteries in Examples 1, 2, 4, 10, and 11

[0096] Group Fast-charging cycle capacity retention rate (200 cycles) Example 1 94.1％ Example 2 94.1％ Example 4 94.8％ Example 10 92.7％ Example 11 87.4％

[0097] As shown in Tables 1 and 2, it can be seen from Comparative Examples 1, 5-7 and Comparative Example 1 that when the first additive is added to the electrolyte, and the content of the first additive is in the range of 0.1wt%-3wt%, the fast-charging performance and high-temperature cycle gas production performance of the lithium ion battery can be well balanced, and the corrosion of the aluminum foil current collector can be effectively prevented. Further, when the content of the first additive is in the range of 0.5wt%-1wt%, the comprehensive performance of the lithium ion battery is better.

[0098] As shown in Tables 1 and 2, it can be seen from Comparative Examples 1-3 and Examples 8-9 that when no carboxylate is added to the electrolyte, the DC impedance, fast-charging, and cycle performance of the lithium ion battery will deviate. When the carboxylate is added to the electrolyte, and the total content is controlled in the range of 10wt%-20wt%, the introduction of the carboxylate will reduce the DC impedance of the lithium ion battery, improve the fast-charging performance of the lithium ion battery, and improve the gas production. However, when the amount of the carboxylate exceeds the range, it will cause serious gas production during high-temperature cycle of the battery, so the amount of the carboxylate needs to be controlled.

[0099] As shown in Tables 1, 2 and 3, it can be seen from Comparative Examples 1, 4, 10-11 that when the total content of lithium salt in the electrolyte is 16wt%, the content of LiFSI is changed, as the content of LiFSI increases, the fast-charging cycle capacity retention rate increases, and the fast-charging cycle performance is improved, but too much will cause more gas production, therefore, the content of LiFSI is controlled to ensure that the comprehensive performance of the lithium ion battery is better. It can be seen from Comparative Example 2 and Examples 13-16 that when the first additive and the second additive are used at a specific content at the same time, the DC impedance of the lithium ion battery is reduced, lithium precipitation does not occur, and the cycle gas production performance is improved, and at the same time, the aluminum foil current collector is not corroded, further making the performance of the lithium ion battery achieve the best effect. It can be seen from Comparative Examples 2, 12 and Comparative Example 4 that when the positive active material is lithium cobaltate, adding the first additive diethyl cyanomethyl phosphonate in the electrolyte can also effectively inhibit the corrosion of the aluminum foil current collector, improve the fast-charging lithium precipitation, and reduce the DC impedance and gas production of the positive active material system, but compared with the nickel-cobalt-manganese ternary positive active material system, the DC impedance of the lithium ion battery is higher, and the gas production is serious. Therefore, diethyl cyanomethyl phosphonate has a better improvement effect on the nickel-cobalt-manganese ternary positive active material system.

[0100] As shown in Tables 1 and 2, it can be seen from Comparative Example 6 and Comparative Examples 7-8 that diethyl 3-cyanophenyl phosphate and diethyl 4-cyanobenzyl phosphite also have cyano and phosphate groups, but cannot inhibit the corrosion of the aluminum foil current collector, therefore, the first additive with a specific structure is selected to inhibit the corrosion of the aluminum foil current collector.

[0101] 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, 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 a range extended 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 car toy, an electric ship toy and an electric plane 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 therefore has the advantages of the lithium ion battery as described above, which will not be described here.

[0102] In summary, the application provides a lithium ion battery electrolyte and its application, by adding the first additive, the transition metal ion dissolution in the positive active material under high temperature and high pressure conditions can be prevented, the high temperature cycle performance of the battery is improved. It can effectively prevent the corrosion of LiFSI to aluminum foil current collector, further improve the long cycle life of lithium ion battery. Through the use of the first additive and the second additive, the direct current impedance of the lithium ion battery is effectively reduced, and the fast charging performance is improved. By using lithium bisfluorosulfonylimide and lithium hexafluorophosphate, the chemical stability and thermal stability of the lithium ion battery can be improved, the cycle performance of the lithium ion battery is improved, the conductivity of the electrolyte is improved, and the fast charging performance of the battery is further improved.

[0103] 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 scope of the application 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 their 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.

[0104] 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 the following components: Non-aqueous solvent; the non-aqueous solvent includes a carbonate and a carboxylate, the carboxylate is selected from at least one of methyl acetate or ethyl acetate, and the content of the carboxylate in the electrolyte is 10wt%~20wt%; A lithium salt, wherein the lithium salt includes lithium bis(fluorosulfonyl)imide and lithium hexafluorophosphate, wherein the content of the lithium bis(fluorosulfonyl)imide in the electrolyte is 3 wt% to 6 wt%, and the total content of the lithium bis(fluorosulfonyl)imide and the lithium hexafluorophosphate in the electrolyte is 13 wt% to 16 wt%; and The additive comprises a first additive comprising diethyl cyanomethyl phosphate.

2. The lithium-ion battery electrolyte according to claim 1, characterized in that The content of the first additive in the electrolyte is 0.1 wt % to 3 wt %.

3. The lithium-ion battery electrolyte according to claim 1, characterized in that The content of the first additive in the electrolyte is 0.5 wt % to 1 wt %.

4. The lithium-ion battery electrolyte according to claim 1, characterized in that The additive includes a second additive, the second additive includes lithium tetrafluoroborate, and the content of the second additive in the electrolyte is 0.2 wt % to 3 wt %.

5. The lithium-ion battery electrolyte according to claim 4, characterized in that The mass ratio of the second additive to the first additive is 1.2:1 to 2.5:

1.

6. The lithium-ion battery electrolyte according to claim 1, characterized in that The carbonate is selected from at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, ethyl methyl carbonate and diethyl carbonate.

7. The lithium-ion battery electrolyte according to claim 6, characterized in that The carbonate is selected from ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate.

8. A lithium ion battery, characterized in that: At least: A positive electrode sheet, comprising a positive electrode current collector and a positive electrode active layer disposed at least on one side of the positive electrode current collector, wherein the positive electrode active layer comprises a positive electrode active material, and the positive electrode active material comprises a nickel-cobalt-manganese ternary positive electrode active material; negative electrode; and The electrolyte is selected from the lithium ion battery electrolyte according to any one of claims 1 to 7.

9. An electronic device, characterized in that: Including the lithium ion battery according to claim 8.

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