An electrolyte and a battery containing the same

Abstract

The application belongs to the technical field of batteries and relates to an electrolyte and a battery containing the electrolyte. The electrolyte comprises an organic solvent, an electrolyte salt, a first additive and a second additive; the first additive comprises a sulfuryl benzothi-oxazole compound, and the second additive comprises an oxazolone compound. The use of the electrolyte of the application can effectively improve the high-temperature storage performance, high-temperature cycle performance, high-temperature floating performance and low-temperature discharge performance of a lithium ion battery.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of batteries, and relates to an electrolyte and a battery containing the electrolyte. BACKGROUND

[0002] Lithium ion batteries have been widely used as power sources in life due to their irreplaceable advantages such as low self-discharge rate, long cycle life, high working voltage, and small pollution. They have broad application prospects in mobile communication, notebook computers, new energy vehicles, and other fields. At the same time, users also have requirements for high energy density and fast charging of lithium ion batteries. In the lithium ion battery system, the continuously increasing battery working voltage and working temperature will cause different degrees of electrolyte decomposition, thereby accelerating the deterioration and failure of battery performance. SUMMARY

[0003] In order to improve the deficiencies of the prior art, the present application provides an electrolyte and a battery containing the electrolyte. During the first charge and discharge process, the electrolyte will partially decompose to form a passivation film on the surface of the electrode material, which is called a solid electrolyte interface film (SEI film). The chemical composition and structure of the SEI film play a key role in improving the working voltage, working temperature, and cycle life of the battery. Adding a small amount of additives to optimize the composition of the SEI film is the most economical and convenient method to improve battery performance. The electrolyte provided by the present application utilizes the mutual cooperation of sulfonyl benzothiathiazole compounds and oxazolone compounds. Both of them can stabilize the quality of the electrolyte and have good film-forming properties. When used in batteries, they can significantly improve the high-temperature storage performance, high-temperature cycle performance, high-temperature floating charge performance, and low-temperature discharge performance of the batteries.

[0004] In order to achieve the above-mentioned purposes, the present application adopts the following technical solutions:

[0005] An electrolyte, comprising an organic solvent, an electrolyte salt, a first additive, and a second additive; the first additive comprises a sulfonyl benzothiathiazole compound, and the second additive comprises an oxazolone compound.

[0006] According to an embodiment of the present application, the sulfonyl benzothiathiazole compound is a benzothiathiazole compound containing a sulfonyl group.

[0007] According to an embodiment of the present application, the sulfonyl benzothiathiazole compound comprises at least one of the compounds shown in Formula I:

[0008]

[0009] Wherein, R1 is selected from hydrogen, halogen, substituted or unsubstituted alkyl, substituted or unsubstituted alkoxy; if substituted, the substituent is alkyl or halogen; R2 is selected from halogen, substituted or unsubstituted alkyl, substituted or unsubstituted alkenyl, substituted or unsubstituted alkoxy, substituted or unsubstituted aryl, substituted or unsubstituted heteroaryl; if substituted, the substituent is alkyl or halogen; Y is an element O or an element S.

[0010] According to an embodiment of the present invention, R1 is selected from halogens, substituted or unsubstituted C. 1-12 Alkyl, substituted or unsubstituted C 1-12 alkoxy group; if substituted, the substituent is C. 1-12 Alkyl or halogen; R2 is selected from halogen, substituted or unsubstituted C. 1-12 Alkyl, substituted or unsubstituted C 2-12 alkenyl, substituted or unsubstituted C 1-12 Alkoxy, substituted or unsubstituted C 6-12 Aryl, substituted, or unsubstituted 5-12 heteroaryl groups; if substituted, the substituent is C. 1-12 Alkyl or halogen; Y is an element O or an element S.

[0011] According to an embodiment of the present invention, R1 is selected from halogens, substituted or unsubstituted C. 1-6 Alkyl, substituted or unsubstituted C 1-6 alkoxy group; if substituted, the substituent is C. 1-6 Alkyl or halogen; R2 is selected from halogen, substituted or unsubstituted C. 1-6 Alkyl, substituted or unsubstituted C 2-6 alkenyl, substituted or unsubstituted C 1-6 Alkoxy, substituted or unsubstituted C 6-10 Aryl, substituted or unsubstituted 5-10 membered heteroaryl; if substituted, the substituent is C. 1-6 Alkyl or halogen; Y is an element O or an element S.

[0012] According to an embodiment of the present invention, R1 is selected from halogens, substituted or unsubstituted C. 1-3 Alkyl, substituted or unsubstituted C 1-3 alkoxy group; if substituted, the substituent is C. 1-3 Alkyl or halogen; R2 is selected from halogen, substituted or unsubstituted C. 1-3 Alkyl, substituted or unsubstituted C 2-3 alkenyl, substituted or unsubstituted C 1-3 Alkoxy, substituted or unsubstituted C 6-8 Aryl, substituted, or unsubstituted 5-6 membered heteroaryl; if substituted, the substituent is C. 1-3 Alkyl or halogen; Y is an element O or an element S.

[0013] According to embodiments of the present application, R1 is selected from methyl, ethyl, propyl, methoxy, trifluoromethyl or fluorine; and R2 is selected from methyl, ethyl, propyl, vinyl, trifluoromethyl, thienyl or furanyl.

[0014] According to embodiments of the present application, the first additive comprises at least one of the following compounds I-1 to I-11:

[0015]

[0016] According to embodiments of the present application, the first additive can be obtained by commercial purchase or prepared by methods known in the art.

[0017] According to embodiments of the present application, the first additive has a mass percentage of 0.02wt% to 5wt% of the total mass of the electrolyte, preferably 0.05wt% to 3wt%, for example, 0.02wt%, 0.03wt%, 0.05wt%, 0.08wt%, 0.1wt%, 0.2wt%, 0.3wt%, 0.4wt%, 0.5wt%, 0.6wt%, 0.7wt%, 0.8wt%, 0.9wt%, 1.0wt%, 1.2wt%, 1.3wt%, 1.4wt%, 1.5wt%, 1.8wt%, 2wt%, 2.2wt%, 2.5wt%, 2.6wt%, 2.8wt%, 3wt%, 3.2wt%, 3.5wt%, 3.6wt%, 3.8wt%, 4wt%, 4.2wt%, 4.5wt%, 4.8wt%, 5wt% or any value within the range of any two of the above values.

[0018] According to embodiments of the present application, the second additive comprises at least one of the compounds of formula II:

[0019]

[0020] wherein R3 is selected from substituted or unsubstituted alkyl, substituted or unsubstituted aryl, substituted or unsubstituted heteroaryl; and if substituted, the substituent is alkoxy, alkyl or halogen.

[0021] According to embodiments of the present application, R3 is selected from substituted or unsubstituted C 1-12 alkyl, substituted or unsubstituted C 6-12 aryl, substituted or unsubstituted 5-12 membered heteroaryl; and if substituted, the substituent is C 1-12 alkoxy, C 1-12 alkyl or halogen.

[0022] According to embodiments of the present application, R3 is selected from substituted or unsubstituted C 1-6alkyl, substituted or unsubstituted C 6-10 aryl, substituted or unsubstituted 5-10 membered heteroaryl; if substituted, the substituents are C 1-6 alkoxy, C 1-6 alkyl or halogen.

[0023] According to embodiments of the present application, R3is selected from substituted or unsubstituted C 1-3 alkyl, substituted or unsubstituted C 6-8 aryl, substituted or unsubstituted 5-6 membered heteroaryl; if substituted, the substituents are C 1-3 alkoxy, C 1-3 alkyl or halogen.

[0024] According to embodiments of the present application, R3is selected from methyl, substituted or unsubstituted phenyl, substituted or unsubstituted thienyl; if substituted, the substituents are fluoro, trifluoromethyl or methoxy.

[0025] According to embodiments of the present application, the term "halogen" includes fluorine, chlorine, bromine and iodine.

[0026] According to embodiments of the present application, the second additive comprises at least one of the following compounds II-1 to II-7:

[0027]

[0028]

[0029] According to embodiments of the present application, the second additive can be obtained by purchasing from commercial channels or by preparing using methods known in the art.

[0030] According to embodiments of the present application, the second additive has a mass percentage in the total mass of the electrolyte in the range of 0.1 wt% to 8 wt%, preferably in the range of 0.2 wt% to 5 wt%, for example 0.2 wt%, 0.3 wt%, 0.4 wt%, 0.5 wt%, 0.6 wt%, 0.7 wt%, 0.8 wt%, 0.9 wt%, 1.0 wt%, 1.2 wt%, 1.3 wt%, 1.4 wt%, 1.5 wt%, 1.6 wt%, 1.7 wt%, 1.8 wt%, 1.9 wt%, 2 wt%, 2.2 wt%, 2.5 wt%, 3 wt%, 3.2 wt%, 3.5 wt%, 3.8 wt%, 4 wt%, 4.2 wt%, 4.5 wt%, 4.8 wt%, 5 wt%, 5.2 wt%, 5.5 wt%, 6 wt%, 6.5 wt%, 7 wt%, 7.5 wt%, 8 wt% or any value in the range defined by any two of the above values.

[0031] According to embodiments of the present application, the electrolyte further comprises a third additive, the third additive comprising a sulfolane compound.

[0032] According to embodiments of the present application, the sulfolane compound comprises at least one of the compounds shown in Formula III:

[0033]

[0034] wherein R4, R5, R6are the same or different, and are independently selected from hydrogen, halogen, substituted or unsubstituted alkyl; if substituted, the substituent is alkyl or halogen.

[0035] According to embodiments of the present application, R4, R5, R6are the same or different, and are independently selected from hydrogen, halogen, substituted or unsubstituted C 1-12 alkyl; if substituted, the substituent is C 1-12 alkyl or halogen.

[0036] According to embodiments of the present application, R4, R5, R6are the same or different, and are independently selected from hydrogen, halogen, substituted or unsubstituted C 1-6 alkyl; if substituted, the substituent is C 1-6 alkyl or halogen.

[0037] According to embodiments of the present application, R4, R5, R6are the same or different, and are independently selected from hydrogen, halogen, substituted or unsubstituted C 1-3 alkyl; if substituted, the substituent is C 1-3 alkyl or halogen.

[0038] According to embodiments of the present application, the sulfolane compound is selected from at least one of the following compounds III-1 to III-10:

[0039]

[0040] According to embodiments of the present application, the third additive has a mass percentage in the total mass of the electrolyte in the range of 0.1 wt% to 10 wt%, preferably in the range of 1.0 wt% to 3.5 wt%, for example 1 wt%, 1.1 wt%, 1.2 wt%, 1.3 wt%, 1.4 wt%, 1.5 wt%, 2.0 wt%, 2.5 wt%, 3.0 wt%, 3.5 wt%, 3.8 wt%, 4 wt%, 4.2 wt%, 4.5 wt%, 4.8 wt%, 5 wt%, 5.2 wt%, 5.5 wt%, 6 wt%, 6.5 wt%, 7 wt%, 7.5 wt%, 8 wt%, 8.5 wt%, 9 wt%, 9.5 wt%, 10 wt%, or any value in the range defined by any two of the above values.

[0041] According to an embodiment of the present application, the organic solvent comprises a cyclic carbonate and / or a chain carbonate.

[0042] Preferably, the cyclic carbonate comprises at least one of ethylene carbonate and propylene carbonate.

[0043] Preferably, the chain carbonate comprises at least one of dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate or ethyl propyl carbonate.

[0044] According to an embodiment of the present application, the organic solvent is a cyclic carbonate and a chain carbonate.

[0045] Preferably, the mass ratio of the cyclic carbonate and the chain carbonate is 1:(2-3), for example 1:2, 1:2.2, 1:2.4, 1:2.6, 1:2.8 or 1:3. When the mass ratio of the cyclic carbonate and the chain carbonate is 1:(2-3), the electrolyte has reasonable viscosity and conductivity, which can ensure good electrochemical performance. When the content of the cyclic carbonate is too low (e.g. less than 1:2), although the viscosity of the electrolyte is low, the conductivity is also low, the battery polarization increases, and the cycle and rate performance is poor; when the content of the cyclic carbonate is too high (e.g. more than 1:3), the viscosity of the electrolyte increases, the battery polarization is also large, and the electrochemical performance is reduced.

[0046] According to an embodiment of the present application, the electrolyte salt is selected from at least one of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium hexafluoroarsenate (LiAsF6), lithium difluorophosphate (LiPF2O2), lithium difluorobisoxalate phosphate (LiPF2(C2O4)2), lithium tetrafluorooxalate phosphate (LiPF4C2O4), lithium oxalate phosphate (LiPO2C2O4), lithium bisoxalate borate (LiBOB), lithium difluoro oxalate borate (LiODFB), lithium bisfluorosulfonylimide (LiTFSI), lithium bis(trifluoromethylsulfonyl)imide (LiN(CF3SO2)2) and lithium bisfluorosulfonylimide (LiFSI).

[0047] According to an embodiment of the present application, the molar concentration of the electrolyte salt in the organic solvent is 1.0-1.5 mol / L, for example 1.0 mol / L, 1.1 mol / L, 1.2 mol / L, 1.3 mol / L, 1.4 mol / L or 1.5 mol / L.

[0048] According to an embodiment of the present application, the electrolyte is used for a lithium ion battery.

[0049] The present application also provides a preparation method of the above electrolyte, which comprises the following steps:

[0050] The organic solvent, the electrolyte salt, the first additive, the second additive, and optionally the third additive are mixed to prepare the electrolyte.

[0051] According to an embodiment of the present application, the mixing comprises stirring mixing or ultrasonic mixing.

[0052] Preferably, the temperature of the mixing is -10℃ to 25℃, for example -10℃, -5℃, 0℃, 5℃, 10℃ or 15℃.

[0053] The present application also provides a battery comprising the electrolyte described above.

[0054] According to an embodiment of the present application, the battery is a lithium ion battery.

[0055] According to an embodiment of the present application, the battery further comprises a positive electrode sheet, a negative electrode sheet and a separator.

[0056] According to an embodiment of the present application, the positive electrode sheet comprises a positive electrode current collector and a positive electrode active material layer coated on one side or both sides of the positive electrode current collector, the positive electrode active material layer comprising a positive electrode active material, a conductive agent and a binder.

[0057] According to an embodiment of the present application, the positive electrode active material comprises a high-nickel ternary material.

[0058] According to an embodiment of the present application, the high-nickel ternary material has a chemical formula of Li z Ni x Co y Mn 1-x-y O2, wherein 0.75≤x≤0.85, 0.075≤y≤0.125, 1.0≤z≤1.1; or a chemical formula of Li z Ni x Co y Al 1-x-y O2, wherein 0.75≤x≤0.85, 0.075≤y≤0.125, 1.0≤z≤1.1.

[0059] According to an embodiment of the present application, the negative electrode sheet comprises a negative electrode current collector and a negative electrode active material layer coated on one side or both sides of the negative electrode current collector, the negative electrode active material layer comprising a negative electrode active material, a conductive agent and a binder.

[0060] According to an embodiment of the present application, the negative electrode active material comprises at least one of artificial graphite, natural graphite, mesocarbon microbeads, hard carbon and soft carbon.

[0061] According to an embodiment of the present application, the negative electrode sheet has a compacted density of 1.5 to 1.8 g / cm 3 , for example 1.5 g / cm3 1.6 g / cm 3 1.7 g / cm 3 1.8 g / cm 3 .

[0062] According to an embodiment of the present application, the average particle size of the negative active material is 13-21 μm.

[0063] According to an embodiment of the present application, the tap density of the negative active material is 0.9-1.2 g / cm 3 , for example, 0.9 g / cm 3 1.0 g / cm 3 1.1 g / cm 3 or 1.2 g / cm 3 .

[0064] According to an embodiment of the present application, the hardness of the negative active material is 30-60 N / mm 2 , for example, 30 N / mm 2 35 N / mm 2 40 N / mm 2 45 N / mm 2 50 N / mm 2 55 N / mm 2 or 60 N / mm 2 .

[0065] According to an embodiment of the present application, the battery satisfies:

[0066] 5.0 x 10 -3 ≤ A / B ≤ 8.0 x 10 -2 ;

[0067] 1.5 ≤ α ≤ 1.8;

[0068] wherein A is the percentage of the mass of the first additive in the total mass of the electrolyte, in wt%; B is the hardness of the negative active material, in N / mm 2 ; and α is the compacted density of the negative plate, in g / cm 3 .

[0069] According to an embodiment of the present application, A / B is 7.5 x 10 -3 8 x 10 -3 1 x 10 -2 2 x 10 -2 2.5 x 10 -2 3 x 10 -2 3.5 x 10 -2 4 x 10 -2 4.5 x 10 -25 x 10 -2 6 x 10 -2 7 x 10 -2 or 8 x 10 -2 .

[0070] It is found that by adjusting the hardness of the negative active material, the migration path of lithium ions can be adjusted; when the hardness of the negative active material is increased within a proper range, the migration path of lithium ions can be greatly shortened, effectively improving the low-temperature performance of the battery while also taking into account the energy density of the battery.

[0071] In particular, when the battery satisfies the following relationship 5.0 x 10 -3 ≤ A / B ≤ 8.0 x 10 -2 and 1.5 ≤ α ≤ 1.8, the dynamics of the battery are significantly improved, the low-temperature performance of the battery is improved, and the high-energy density characteristics of the battery are also taken into account; when the battery does not satisfy the above relationship, due to the mismatch between the amount of the first additive and the negative active material, the low-temperature performance of the battery will deteriorate, making it impossible for the battery to simultaneously take into account the low-temperature performance and the high-energy density.

[0072] According to an embodiment of the present application, the mass percentage content of each component in the positive active material layer is: 80-99.8wt% of positive active material, 0.1-10wt% of conductive agent, and 0.1-10wt% of binder.

[0073] Preferably, the mass percentage content of each component in the positive active material layer is: 90-99.6wt% of positive active material, 0.2-5wt% of conductive agent, and 0.2-5wt% of binder.

[0074] According to an embodiment of the present application, the mass percentage content of each component in the negative active material layer is: 80-99.8wt% of negative active material, 0.1-10wt% of conductive agent, and 0.1-10wt% of binder.

[0075] Preferably, the mass percentage content of each component in the negative active material layer is: 90-99.6wt% of negative active material, 0.2-5wt% of conductive agent, and 0.2-5wt% of binder.

[0076] According to an embodiment of the present application, the conductive agent is selected from at least one of conductive carbon black, acetylene black, ketjen black, conductive graphite, conductive carbon fiber, carbon nanotube, and metal powder.

[0077] According to an embodiment of the present application, the binder is selected from at least one of sodium carboxymethyl cellulose, styrene butadiene latex, polytetrafluoroethylene, and polyethylene oxide.

[0078] According to an embodiment of the present application, the positive electrode of the battery is a high-nickel ternary positive electrode, and the negative electrode of the battery is an artificial graphite negative electrode.

[0079] According to an embodiment of the present application, when the electrolyte is used in combination with a high-nickel ternary positive electrode-artificial graphite negative electrode, the effect of the electrolyte can be highlighted. Specifically, the introduction of the additives can reduce the acidity of the electrolyte, which can effectively avoid the risk of gas production of the battery caused by the high residual alkali on the surface of the high-nickel ternary positive electrode material, and the additives can also form an effective protective dense interface film at the positive electrode interface and inhibit the destruction of the structure of the high-nickel ternary positive electrode material, the dense interface film on the surface of the positive electrode can effectively protect the high-nickel ternary positive electrode material from pulverization due to volume expansion / contraction, reduce the dissolution of transition metal nickel elements at high temperature, and reduce the oxidative decomposition of the electrolyte by transition metal nickel ions; in addition, a protective film rich in Li2SO3 is formed on the surface of the negative electrode; the interface film formed on the surface of the positive and negative electrodes has the characteristics of low impedance, good chemical stability, and high high-temperature resistance, and the stable and dense positive and negative electrode interface film can effectively reduce the reaction of the electrolyte penetrating into the cracks and alleviate the capacity decay, which makes the battery well balanced in terms of high and low temperature performance.

[0080] According to an embodiment of the present application, the charge cut-off voltage of the battery is 4.2 V or higher.

[0081] Beneficial effects:

[0082] By adding the first additive and the second additive to the electrolyte, the two additives jointly act on the surface of the positive and negative electrodes, which can significantly improve the performance of the battery. Specifically, the combined use of the sulfonated benzothiazole compound and the oxazolone compound can significantly reduce the acidity of the electrolyte, improve the stability of the electrolyte, and ensure the quality of the electrolyte; the sulfonated benzothiazole compound can act on the positive electrode interface to oxidize and form a lithium sulfonate interface film, which has good high-temperature resistance, avoids direct contact between the positive active material and the electrolyte, stabilizes the microstructure of the positive active material, reduces the dissolution of transition metal nickel elements at high temperature, and realizes the complexation of transition metal nickel ions, thereby reducing the oxidative decomposition of the electrolyte by transition metal nickel ions. The high-temperature performance of the battery can be significantly improved; the oxazolone compound can act on the negative electrode interface to open ring polymerization and form a polyoxazolone interface film, which has good stability, inhibits the reduction reaction of organic solvents at the negative electrode interface, and also reduces the interface impedance; at the same time, the solid electrolyte film formed by the two additives has low impedance, which is beneficial to improving the migration dynamics characteristics of lithium ions at the interface, thereby effectively improving the high-temperature storage performance, high-temperature cycle performance, high-temperature floating performance, and low-temperature discharge performance of the lithium ion battery.

[0083] The further introduced sulfolactone compound can participate in the film forming reaction on the positive and negative electrode surfaces, which can work together with the first additive and the second additive and make the stability of the formed solid electrolyte film better and the impedance lower, further improving the high-temperature storage performance, cycle performance, high-temperature floating performance and low-temperature discharge performance of the obtained battery. DETAILED DESCRIPTION

[0084] The technical solutions of the present application will be further described in detail below in combination with specific examples. It should be understood that the following examples are only illustratively described and explained, and should not be interpreted as limiting the scope of protection of the present application. Any technology realized based on the above description of the present application is covered within the scope intended to be protected by the present application.

[0085] Unless otherwise specified, the raw materials and reagents used in the following examples are commercially available or can be prepared by known methods.

[0086] Preparation method of lithium ion battery:

[0087] The positive active material high-nickel ternary material (NCM811), the binder polyvinylidene fluoride (PVDF) and the conductive carbon black are mixed in a weight ratio of 95:2:3, N-methyl pyrrolidone (NMP) is added, and stirring is performed under the action of a vacuum stirrer until the mixed system becomes a positive electrode slurry with uniform fluidity; the positive electrode slurry is uniformly coated on the current collector aluminum foil; the coated aluminum foil is baked in an oven with different temperature gradients in 5 stages, then dried in an oven at 120°C for 8h, and then subjected to rolling and cutting to obtain the desired positive electrode sheet.

[0088] The negative active material artificial graphite, the binder styrene-butadiene rubber and the conductive agent acetylene black are mixed in a weight ratio of 94:3:3, deionized water is added, and a negative electrode slurry is obtained under the action of a vacuum stirrer; the negative electrode slurry is uniformly coated on a high-strength carbon-coated copper foil to obtain an electrode sheet; the obtained electrode sheet is dried at room temperature and then transferred to a 80°C oven for drying for 10h, and then subjected to rolling and cutting to obtain a negative electrode sheet.

[0089] The positive electrode sheet, the negative electrode sheet and the separator film prepared above are stacked in the order of positive electrode sheet, separator film PP film and negative electrode sheet, and then wound to obtain a battery cell; the battery cell is placed in an outer packaging aluminum foil, and an electrolyte is injected into the outer packaging, and then subjected to vacuum packaging, standing, formation, shaping, sorting and other processes to obtain a lithium ion battery.

[0090] Example 1

[0091] The present embodiment provides an electrolyte, which comprises the following:

[0092] The additive consists of a first additive of formula I-1 and a second additive of formula II-1;

[0093] the solvent comprises a cyclic carbonate and a chain carbonate, wherein the cyclic carbonate is ethylene carbonate and the chain carbonate is methyl ethyl carbonate;

[0094] the electrolyte salt is LiPF6;

[0095] wherein the mass ratio of the cyclic carbonate and the chain carbonate is 1:2.5; the molar concentration of the electrolyte salt in the mixed solvent formed by the cyclic carbonate and the chain carbonate is 1.2 mol / L; the mass of the first additive is 0.3% of the total mass of the electrolyte; and the mass of the second additive is 1.2% of the total mass of the electrolyte.

[0096] Preparation method: the above-mentioned cyclic carbonate, chain carbonate, electrolyte salt, first additive and second additive are stirred and mixed at 25°C to obtain the electrolyte.

[0097] Examples 2-33 and Comparative Examples 1-6

[0098] The electrolytes of Examples 2-33 and Comparative Examples 1-6 are the same as those of Example 1, except that the types and contents of the additives in the electrolytes are different, as shown in Table 1.

[0099] Examples 34-35

[0100] The electrolytes of Examples 34-35 are the same as those of Example 17, except that the compaction densities of the negative electrode sheets are different, as shown in Table 1.

[0101] Example 36

[0102] The electrolyte of Example 36 is the same as that of Example 17, except that the hardnesses of the negative electrode active materials are different, as shown in Table 1.

[0103] Table 1 Composition of lithium ion batteries of examples and comparative examples

[0104]

[0105]

[0106] Electrochemical performance test: electrochemical performance tests were carried out by the following test method using a blue electric charge and discharge test cabinet:

[0107] (1) High temperature cycle performance test

[0108] High temperature cycle performance test: at 45°C, the battery after being divided into groups was charged to 4.2V at 1C constant current and constant voltage, the cutoff current was 0.05C, then discharged to 2.8V at 1C constant current, and the cycle was repeated, after 500 cycles of charge and discharge, the capacity retention rate at the 500th week was calculated, and the calculation formula was as follows:

[0109] 500th cycle capacity retention rate (%) = (500th cycle discharge capacity / first cycle discharge capacity) x 100%.

[0110] (2) Low-temperature discharge performance test

[0111] At 25°C ambient conditions, discharge the battery after the partition at 1C to 2.8V, and stand for 5 min; then charge it to 4.2V at 1C, and when the cell voltage reaches 4.2V, change it to 4.2V constant voltage charging until the charging current is less than or equal to the given cutoff current 0.05C, and stand for 5 min; transfer the fully charged cell to a high-low temperature box, set -20°C, and after the temperature of the box reaches, stand for 120 min; then discharge it to the terminal voltage 2.8V at 1C, and stand for 5 min; then adjust the temperature of the high-low temperature box to 25°C±3°C, and after the temperature of the box reaches, stand for 60 min; charge it to 4.2V at 1C, and when the cell voltage reaches 4.2V, change it to 4.2V constant voltage charging until the charging current is less than or equal to the given cutoff current 0.05C; stand for 5 min; calculate the capacity retention rate of -20°C low-temperature discharge 2.8V. The calculation formula is as follows:

[0112] -20°C discharge 2.8V capacity retention rate (%) = (-20°C discharge to 2.8V discharge capacity / 25°C discharge to 2.8V discharge capacity) x 100%.

[0113] (3) 60°C, 30 days high-temperature storage test

[0114] Put the battery in room temperature to charge and discharge at 1C for 1 time (4.2V-2.8V), record the discharge capacity C0 before the battery storage, then charge the battery to 4.2V full state, use vernier caliper to test the thickness d1 of the battery before high-temperature storage (connect two opposite angles of the above battery by straight lines, and the intersection point of the two diagonal lines is the test point of the battery thickness), put the battery into 60°C constant temperature box for storage for 30 days, take out the battery after storage is completed and test the thickness d2 of the battery after storage, calculate the thickness expansion rate of the battery after 60°C storage for 30 days; after the battery is cooled at room temperature for 24h, discharge the battery to 2.8V at 1C constant current again, then charge it to 4.2V at 1C constant current and constant voltage, record the discharge capacity C1 and charge capacity C2 of the battery after storage, and calculate the capacity retention rate and recovery rate of the battery after 60°C storage for 30 days, the calculation formula is as follows:

[0115] 60°C storage for 30 days thickness expansion rate = (d2-d1) / d1*100%;

[0116] 60°C storage for 30 days residual capacity retention rate = C1 / C0*100%;

[0117] The recovery capacity retention rate after storage at 60°C for 30 days = C2 / C0*100%.

[0118] (4) 45°C floating for 100 hours

[0119] At (25±2) °C, 1C constant current discharge to cut-off voltage 2.8V, rest for 5min, 1C constant current constant voltage charge to cut-off voltage 4.2V, cut-off current 0.05C, test the thickness of the cell T0; put the cell in (45±2) °C environment for 4h to reach thermal equilibrium, at (45±2) °C, 1C constant current charge to 4.2V and constant voltage at 4.2V for 100 hours, take out the cell and put it in (25±2) °C environment for 4h to reach thermal equilibrium, at (25±2) °C, 1C constant current discharge to cut-off voltage (2.8V), rest for 5min, 1C constant current constant voltage charge to cut-off voltage 4.2V, cut-off current 0.05C, test the thickness of the cell T1.

[0120] 45°C floating for 100 hours thickness change rate = (T1-T0) / T0*100%

[0121] Table 2 Performance test results of lithium ion batteries of examples and comparative examples

[0122]

[0123]

[0124] According to the test results in Table 2, the electrolyte of the examples effectively improves the high-temperature storage performance, high-temperature cycle performance, high-temperature floating performance and low-temperature discharge performance of the lithium ion battery compared with the comparative examples.

[0125] Specifically, from the comparison of examples 1-17, it can be seen that when the specific structures of the first additive and the second additive are adjusted, the high-temperature storage performance, high-temperature cycle performance, high-temperature floating performance and low-temperature discharge performance of the battery can be improved, and the improvement effect of example 2 is the most outstanding.

[0126] From the comparison of Examples 1, 18-23, it can be seen that the content of the sulfonobenzothiazole compound affects the high-temperature storage performance, high-temperature cycle performance, high-temperature floating performance and low-temperature discharge performance of the battery. When the content of the sulfonobenzothiazole compound increases, it will cause the film forming resistance to be too large, the initial efficiency and capacity of the battery to be low, and the high and low temperature performance of the battery to be poor. When the content of the sulfonobenzothiazole compound decreases, it will cause the acid and water removal effect and the film forming effect to be poor, and also cause the high and low temperature performance of the battery to be poor. When the content of the sulfonobenzothiazole compound is in the range of 0.02-5wt%, the high and low temperature performance of the battery can be good, especially when the content of the sulfonobenzothiazole compound is in the range of 0.05-3wt%, the performance of the battery obtained is more prominent.

[0127] From the comparison of Examples 1, 24-28, it can be seen that the content of the oxazolone compound affects the high-temperature storage performance, high-temperature cycle performance, high-temperature floating performance and low-temperature discharge performance of the battery. When the addition amount of the oxazolone compound increases, it will cause the battery resistance to be too large, the initial efficiency and capacity to be low, the rate and low temperature performance to be poor, and the gas generation to increase during high-temperature storage, thereby increasing the volume expansion rate of the battery. When the addition amount of the oxazolone compound decreases, it will cause the film forming effect on the surface of the high-nickel positive electrode and the surface of the artificial graphite negative electrode to be poor, and cause the high-temperature cycle performance and high-temperature storage performance of the battery to be poor. When the content of the oxazolone compound is in the range of 0.1-8wt%, the high and low temperature performance of the battery can be good, especially when the content of the oxazolone compound is in the range of 0.2-5wt%, the performance of the battery obtained is more prominent.

[0128] From the comparison of Examples 29-33, it can be seen that the addition of the sulfonic acid lactone compound on the basis of Example 1 can improve the high and low temperature performance of the battery, especially the high-temperature floating performance of the battery.

[0129] When the content of the sulfonic acid lactone compound is in the range of 0.1-10wt%, the battery performance can be improved, especially when the content of the sulfonic acid lactone compound is in the range of 1-3.5wt%, the performance of the battery obtained is more prominent.

[0130] From the comparison of Examples 17-23, 34-36, it can be seen that when the battery satisfies the relationship of 5.0x10 -3 ≤A / B≤8.0x10 -2 and 1.5≤α≤1.8, the dynamics of the battery is significantly improved, the low temperature performance of the battery is improved, and the high energy density characteristics of the battery are also considered; when the battery does not satisfy the above relationship, due to the mismatch between the addition amount of the additive and the negative electrode active material, the low temperature performance of the battery is deteriorated, and the battery cannot simultaneously consider the low temperature performance and the high energy density.

[0131] As can be seen from the comparison of Examples 1 and Comparative Examples 1-5, when sulfonylbenzothiazolium compounds and oxazolone compounds are added to the electrolyte simultaneously, a synergistic effect is achieved, which can effectively improve the high-temperature storage performance, high-temperature cycle performance, high-temperature float charge performance, and low-temperature discharge performance of the lithium-ion battery. In particular, the further introduction of sulfonylbenzothiazolium compounds into the sulfonylbenzothiazolium and oxazolone compounds can significantly improve the high-temperature storage performance, high-temperature cycle performance, high-temperature float charge performance, and low-temperature discharge performance of the lithium-ion battery. The test results above show that the combined use of three different types of additives can significantly improve battery performance.

[0132] As can be seen from the comparison between Example 1 and Comparative Example 6, the sulfonylbenzothiazolium compounds of this application can achieve a synergistic effect when used in combination with oxazolone compounds, while the sulfonylpyridine compounds (or other sulfonyl heterocyclic compounds) cannot achieve a synergistic effect when combined with oxazolone compounds.

[0133] The exemplary embodiments of the present invention have been described above. However, the scope of protection of this application is not limited to the above embodiments. Any modifications, equivalent substitutions, improvements, etc., made by those skilled in the art within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. An electrolyte, characterized by, The electrolyte comprises an organic solvent, an electrolyte salt, a first additive and a second additive; the first additive comprises a sulfonated benzothi-oxazole compound, and the second additive comprises an oxazolone compound; The sulfonated benzothi-oxazole compound comprises at least one of the compounds shown in Formula I: wherein R1 is selected from hydrogen, halogen, substituted or unsubstituted alkyl, substituted or unsubstituted alkoxy; if substituted, the substituent is alkyl or halogen; R2 is selected from halogen, substituted or unsubstituted alkyl, substituted or unsubstituted alkenyl, substituted or unsubstituted alkoxy, substituted or unsubstituted aryl, substituted or unsubstituted heteroaryl; if substituted, the substituent is alkyl or halogen; Y is O element or S element; The second additive comprises at least one of the compounds shown in Formula II: wherein R3 is selected from substituted or unsubstituted alkyl, substituted or unsubstituted aryl, substituted or unsubstituted heteroaryl; if substituted, the substituent is alkoxy, alkyl or halogen.

2. The electrolyte according to claim 1, characterized in that, R1is selected from halogen, substituted or unsubstituted C 1-12 alkyl, substituted or unsubstituted C 1-12 alkyl, substituted or unsubstituted C 1-12 alkyl, substituted or unsubstituted C 1-12 alkyl, substituted or unsubstituted C 2-12 alkyl, substituted or unsubstituted C 1-12 alkyl, substituted or unsubstituted C 6-12 aryl, substituted or unsubstituted 5- to 12-membered heteroaryl; if substituted, substituted with C 1-12 alkyl, substituted or unsubstituted C Y is an O element or an S element.

3. The electrolyte according to claim 2, characterized in that, The first additive comprises at least one of the following compounds I-1 to I-11:

4. The electrolyte of claim 1, wherein The mass percentage of the first additive in the total mass of the electrolyte is 0.02wt%-5wt%.

5. The electrolyte according to claim 4, characterized in that, The mass percentage of the first additive in the total mass of the electrolyte is 0.05-3wt%.

6. The electrolyte of claim 1, wherein, R3is selected from substituted or unsubstituted C 1-12 alkyl, substituted or unsubstituted C 6-12 aryl, substituted or unsubstituted 5-12 membered heteroaryl; and if substituted, with C 1-12 alkoxy, C 1-12 alkyl or halogen.

7. The electrolyte of claim 6, wherein, The second additive comprises at least one of the following compounds II-1 to II-7:

8. The electrolyte of claim 1, wherein, The mass percentage of the second additive in the total mass of the electrolyte is 0.1wt%-8wt%.

9. The electrolyte of claim 8, wherein, The mass percentage of the second additive in the total mass of the electrolyte is 0.2wt%-5wt%.

10. The electrolyte according to any one of claims 1 to 9, characterized in that, The electrolyte comprises a third additive, and the third additive comprises a sulfonic acid lactone compound.

11. The electrolyte of claim 10, wherein, The sulfonic acid lactone compound comprises at least one of the compounds shown in Formula III: wherein R4, R5, R6 are the same or different, and are independently selected from hydrogen, halogen, substituted or unsubstituted alkyl; if substituted, the substituent is alkyl or halogen.

12. The electrolyte of claim 11, wherein, R4, R5, R6are the same or different, independently of one another, selected from the group consisting of hydrogen, halogen, substituted or unsubstituted C 1-12 alkyl; if substituted, the substituent is C 1-12 alkyl or halogen.

13. The electrolyte of claim 12, wherein, The sulfonic acid lactone compound is selected from at least one of the following compounds III-1 to III-10:

14. The electrolyte of claim 10, wherein, The mass percentage of the third additive in the total mass of the electrolyte is 0.1wt%-10wt%.

15. The electrolyte of claim 14, wherein, The mass percentage of the third additive in the total mass of the electrolyte is 1.0wt%-3.5wt%.

16. A battery comprising the electrolyte according to any one of claims 1-15.

17. The battery of claim 16, wherein, The battery further comprises a positive electrode sheet comprising a positive electrode active material, and the positive electrode active material comprises a high-nickel ternary material.

18. The battery of claim 17, wherein, Li z Ni x Co y Mn 1-x-y O2, wherein 0.75≤x≤0.85, 0.075≤y≤0.125, 1.0≤z≤1.1; or a chemical formula of Li z Ni x Co y Al 1-x-y O2, wherein 0.75≤x≤0.85, 0.075≤y≤0.125, 1.0≤z≤1.

1.

19. The battery of any one of claims 16-18, wherein, The battery satisfies: 5.0 x 10 -3 ≤ A / B ≤ 8.0 x 10 -2 ; 1.5≤α≤1.8； Wherein, A is the percentage of the mass of the first additive in the total mass of the electrolyte, in wt%; B is the hardness of the negative active material, in N / mm 2 ; and a is the compaction density of the negative plate, in g / cm 3 .

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