Electrolyte and lithium ion battery

Abstract

The application relates to an electrolyte and a lithium ion battery in the technical field of lithium battery production, which comprises a first compound, a second compound and a third compound; the electrolyte of the application simultaneously contains the first compound, the second compound and the third compound, can effectively improve the stability of the electrolyte under high voltage, inhibit electrolyte gas production, improve the wettability of the electrolyte to the pole piece, and thus improve the kinetics. Further, the three components contain halogen groups to participate in the formation of a CEI film, can effectively inhibit the damage of the dissolution of nickel in the ternary material to the negative electrode, and thus improve the cycle stability under high temperature and high pressure.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium battery production, and particularly relates to an electrolyte and a lithium ion battery. BACKGROUND

[0002] Ion batteries are widely used in consumer electronics, electric vehicles and energy storage systems due to their high energy density, long cycle life and good safety. In the composition of lithium batteries, electrolyte is a crucial component, which is responsible for the conduction of lithium ions and directly affects the overall performance and stability of the battery. The selection and properties of electrolyte have a profound impact on the efficiency, life and safety of the battery.

[0003] The existing electrolyte has the problems of easy decomposition, gas production, and more side reactions with the electrode under high temperature and high pressure environment, resulting in poor cycle performance of the battery. Carbonate solvents can improve the stability of the electrolyte, but will increase the gas production problem of the electrolyte. Adding gas production inhibiting additives and using them with carbonate solvents will increase the viscosity of the electrolyte and reduce the wettability, and the cycle performance of the battery is improved limitedly.

[0004] Further, when the positive electrode of the battery uses a ternary positive electrode material, the positive electrode is prone to transition metal element dissolution, thereby causing capacity attenuation and affecting the charge and discharge performance of the battery. Therefore, improving the stability of the electrode-electrolyte interface film is one of the key factors to improve the high-temperature cycle performance of lithium ion batteries with ternary positive electrodes as the core. In summary, the role of electrolyte in lithium batteries cannot be ignored, and improving the stability of the electrode-electrolyte interface film through electrolyte will be one of the key factors to improve the high-temperature performance of the battery.

[0005] Therefore, the present application proposes a technical solution to solve the above problems. SUMMARY

[0006] To solve the above problems, an electrolyte and a lithium ion battery are disclosed in the present application. The present application improves the oxidation stability of the solvent, improves the components of the SEI film and the CEI film, and improves the lithium ion conduction kinetics through the synergistic effect of the combination of three electrolyte components, thereby improving the high-temperature cycle performance.

[0007] The technical solution of the present application is implemented as follows:

[0008] The present application proposes an electrolyte in the first aspect, which comprises a first compound, a second compound and a third compound.

[0009] The structure of the first compound is as follows:

[0010] ;

[0011] In the above formula, R1 comprises one of CF3, CHF2, CH2F, CH2Cl, CH2Br;

[0012] The second compound has the following structural formula:

[0013] ;

[0014] In the above formula, R 2 comprises one of H, F, Cl, Br;

[0015] The third compound has the following structural formula:

[0016] .

[0017] Preferably, the content of the third compound in the electrolyte is 0.01wt%-10wt%.

[0018] Preferably, the content of the third compound in the electrolyte is 0.01wt%-2wt%.

[0019] Preferably, the first compound comprises at least one of A-1 compound, A-2 compound, A-3 compound:

[0020] The molecular formula of the A-1 compound is as follows:

[0021] ;

[0022] The molecular formula of the A-2 compound is as follows:

[0023] ;

[0024] The molecular formula of the A-3 compound is as follows:

[0025] .

[0026] Preferably, the content of the first compound in the electrolyte is 5wt%-30wt%.

[0027] Preferably, the second compound comprises at least one of B-1 compound, B-2 compound, B-3 compound:

[0028] The molecular formula of the B-1 compound is as follows:

[0029] ;

[0030] The molecular formula of the B-2 compound is as follows:

[0031] ;

[0032] The molecular formula of the B-3 compound is as follows:

[0033] .

[0034] Preferably, the content of the second compound in the electrolyte is 0.01wt%-10wt%.

[0035] Preferably, the electrolyte further comprises a second solvent; the second solvent is a non-aqueous organic solvent; and / or, the electrolyte further comprises a second additive.

[0036] The second aspect of the present application discloses a lithium ion battery, which comprises the electrolyte disclosed in the first aspect of the present application, and further comprises a positive electrode, a separator and a negative electrode.

[0037] Preferably, the positive electrode comprises a positive electrode active material.

[0038] The positive electrode active material comprises a ternary material.

[0039] The advantages of the present application are as follows:

[0040] The electrolyte of the present application contains the first compound, the second compound and the third compound, which can effectively improve the stability of the electrolyte at high voltage, inhibit the electrolyte gas production, improve the wettability of the electrolyte to the electrode sheet, thereby improving the kinetics, and improving the room temperature cycle performance and high temperature cycle performance of the electrolyte. Further, the three components all contain halogen groups to participate in the formation of CEI film, which can effectively inhibit the damage of the dissolution of nickel in the ternary material to the negative electrode, thereby improving the cycle stability at high temperature and high pressure. DETAILED DESCRIPTION

[0041] The technical solutions of the present application will be described clearly and completely below in combination with the embodiments of the present application. Obviously, the described embodiments are only some 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.

[0042] Unless otherwise defined, all technical and scientific terms used in the present application have the same meanings as commonly understood by those skilled in the art to which the present application belongs; the terms used in the specific embodiments are only for the purpose of describing the specific embodiments, and are not intended to limit the present application; the terms "include" and "have" and any variations thereof in the specification and claims of the present application are intended to cover non-exclusive inclusion.

[0043] In the description of the embodiments of the application, the technical terms "first", "second", and the like are used only to distinguish different objects, and cannot be understood as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features. In the description of the embodiments of the application, the meaning of "a plurality of" is two or more, unless otherwise explicitly and specifically limited.

[0044] In the present application, the phrase "embodiments" means that the specific features, structures or properties described in conjunction with the embodiments can be included in at least one embodiment of the present application. The appearance of this phrase at various places in the specification does not necessarily refer to the same embodiment, nor is it independent or alternative to other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described in the present application can be combined with other embodiments.

[0045] In the description of the embodiments of the application, the term "and / or" is only a description of the association relationship of the associated objects, which means that there can be three relationships, for example, A and / or B, which can represent the three cases of A alone, A and B together, and B alone. In addition, the character " / " in the present application generally represents an "or" relationship between the front and rear associated objects.

[0046] Throughout the present application, numerical values represent approximate measures or limits of ranges to encompass minor deviations from given values and embodiments with about the mentioned values and embodiments with the mentioned exact values. Except for the working examples provided at the end of the specific embodiments, all numerical values of parameters (e.g. amounts or conditions) in the specification (including the appended claims) should be understood in all cases to be modified by the term "about", whether or not the term "about" actually precedes the numerical value. "About" indicates that some minor inaccuracy exists in the stated numerical value (is close to the exact value of the stated value to some extent; is approximately or reasonably close to the stated value; is almost). If the inaccuracy provided by "about" is not otherwise understood in the art in this ordinary meaning, "about" as used in the present application at least indicates the variation that can be produced by ordinary methods of measuring and using such parameters. For example, "about" can include a variation of less than or equal to 5%, optionally less than or equal to 4%, optionally less than or equal to 3%, optionally less than or equal to 2%, optionally less than or equal to 1%, optionally less than or equal to 0.5%, and in some aspects, optionally less than or equal to 0.1%.

[0047] In addition, the disclosure of a range includes all values within the range and the disclosure of a further divided range, including the endpoints and subranges given for these ranges.

[0048] The existing electrolyte has problems of easy decomposition, gas production, and more side reactions with the electrode under high temperature and high pressure environment, resulting in poor cycle performance of the battery. The carbonate solvent can improve the stability of the electrolyte, but will increase the gas production problem of the electrolyte. The addition of an additive for inhibiting gas production, in combination with the carbonate solvent, will increase the viscosity of the electrolyte and reduce the wettability, and the cycle performance of the battery is limitedly improved.

[0049] Further, when the positive electrode of the battery is selected as a ternary positive electrode material, the positive electrode is prone to transition metal element dissolution, thereby causing capacity attenuation and affecting the charge-discharge performance of the battery. In order to solve the above problems, the present application proposes a technical scheme.

[0050] The first aspect of the present application proposes an electrolyte, which comprises a first compound, a second compound and a third compound.

[0051] The structure of the first compound is as follows:

[0052] ;

[0053] In the above formula, R 1 including one of CF3, CHF2, CH2F, CH2Cl and CH2Br;

[0054] The structure of the second compound is as follows:

[0055] ;

[0056] In the above formula, R 2 including one of H, F, Cl and Br;

[0057] The structure of the third compound is as follows:

[0058] .

[0059] The electrolyte of the present application contains the first compound, the second compound and the third compound, which can effectively improve the stability of the electrolyte under high voltage, inhibit the gas production of the electrolyte, improve the wettability of the electrolyte to the electrode sheet, and thus improve the kinetics. Further, the three components contain halogen groups to participate in the formation of CEI film, which can effectively inhibit the damage of the dissolution of nickel in the ternary material to the negative electrode, thereby improving the cycle stability under high temperature and high pressure.

[0060] Understandably, the first compound contains electron-withdrawing groups and carbonate groups, which improve the stability of the electrolyte under high voltage conditions. However, the first compound is prone to gas generation in the battery, thus affecting the cycle stability of the lithium battery at high temperatures. Therefore, a second compound with sulfonate groups is used, as sulfonate groups can effectively suppress electrolyte gas generation. However, using the first and second compounds simultaneously increases the viscosity of the electrolyte, thus affecting its kinetics. To solve these problems, a third compound is introduced to improve the wettability of the electrolyte to the electrode, thereby improving the kinetics.

[0061] The content of the third compound in the electrolyte is 0.01wt%-10wt%.

[0062] In specific applications, the content of the third compound in the electrolyte can be selected as 0.01wt%, 0.05wt%, 0.08wt%, 1wt%, 2wt%, 3wt%, 5wt%, 8wt%, 10wt%, etc. The values ​​listed above are merely examples and not limitations. Without exceeding the understanding of those skilled in the art, any value within the range of 0.01wt%-10wt% can be freely implemented.

[0063] In some preferred embodiments, the content of the third compound in the electrolyte is 0.01wt%-2wt% to prevent side reactions from occurring in the electrolyte.

[0064] In some embodiments, the first compound includes at least one of compound A-1, compound A-2, and compound A-3:

[0065] The molecular formula of compound A-1 is as follows:

[0066] ;

[0067] The molecular formula of compound A-2 is as follows:

[0068] ;

[0069] The molecular formula of compound A-3 is as follows:

[0070] .

[0071] The term "at least one" as used in this invention refers to the selection of one element from the plurality of elements listed above, or the selection of a combination of two or more elements from the plurality of elements listed above, as long as such combination does not exceed the understanding of those skilled in the art, and the plurality of elements do not chemically react with each other or affect each other's physicochemical properties.

[0072] In some embodiments, the content of the first compound in the electrolyte is 5wt%-30wt%.

[0073] In specific applications, the content of the first compound in the electrolyte can be selected as 5wt%, 6wt%, 8wt%, 10wt%, 12wt%, 15wt%, 18wt%, 20wt%, 22wt%, 23wt%, 25wt%, 28wt%, 30wt%, etc. The values ​​listed above are merely examples and not limitations. Those skilled in the art can freely implement any value within the range of 5wt%-30wt% without exceeding their understanding.

[0074] In some embodiments, the second compound includes at least one of compound B-1, compound B-2, and compound B-3:

[0075] The molecular formula of compound B-1 is as follows:

[0076] ;

[0077] The molecular formula of compound B-2 is as follows:

[0078] ;

[0079] The molecular formula of compound B-3 is as follows:

[0080] .

[0081] In some embodiments, the content of the second compound in the electrolyte is 0.01wt%-10wt%.

[0082] In specific applications, the content of the second compound in the electrolyte can be selected as 0.01wt%, 0.05wt%, 0.08wt%, 1wt%, 2wt%, 3wt%, 5wt%, 8wt%, 10wt%, etc. The values ​​listed above are merely examples and not limitations. Without exceeding the understanding of those skilled in the art, any value within the range of 0.01wt%-10wt% can be freely implemented.

[0083] In some embodiments, the electrolyte further includes a second solvent; the second solvent is a non-aqueous organic solvent.

[0084] In this invention, the second solvent refers to any solvent in the electrolyte other than the first compound.

[0085] In the electrolyte, the content of the second solvent can be selected as 1wt%, 2wt%, 5wt%, 8wt%, 10wt%, 15wt%, 20wt%, 25wt%, 30wt%, 35wt%, 40wt%, 50wt%, 60wt%, 70wt%, 80wt%, 90wt%, etc.; the values ​​listed above are examples and not limitations. Without exceeding the understanding of those skilled in the art, those skilled in the art can freely implement any value in the range of 1wt%-90wt%.

[0086] In specific applications, the non-aqueous organic solvent includes one or both of carbonates or carboxylic acid esters.

[0087] In some preferred embodiments, the carbonate includes at least one of dimethyl carbonate, fluoroethylene carbonate, diethyl carbonate, ethylene carbonate, propylene carbonate or methyl ethyl carbonate, difluoropropylene carbonate, trichloroethyl methyl carbonate, 4-trichloromethyl ethylene carbonate, trifluoromethyl ethylene carbonate, chloroethylene carbonate, 1,1,1,3,3,3-hexafluoroisopropyl acrylate or di(2,2,2-trifluoroethyl) carbonate.

[0088] In practical applications, carbonates can be selected from one of the elements listed above, or a mixture of two or more. These elements will not react chemically with each other, nor will they affect their respective physicochemical properties.

[0089] The carboxylic acid esters include any one or a combination of at least two of the following: propyl fluorobutyrate, propyl chloroacetate, ethyl fluorobutyrate, methyl fluoropropionate, ethyl fluoropropionate, isopropyl acetate, methyl propionate, isopropyl propionate, propyl fluoropropionate, isopropyl fluoroacetate, butyl fluoropropionate, propyl acetate, ethyl acetate, methyl acetate, propyl butyrate, isopropyl fluoropropionate, ethyl chlorobutyrate, butyl propionate, ethyl butyrate, ethyl propionate, or propyl propionate.

[0090] In practical applications, carboxylic acid esters can be selected from one of the elements listed above, or a mixture of two or more. These elements will not react chemically with each other, nor will they affect their respective physicochemical properties.

[0091] In some embodiments, the electrolyte also includes electrolyte salts.

[0092] In specific applications, the electrolyte salts include lithium hexafluorophosphate (LiPF6), lithium perchlorate (LiClO4), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), bis(fluorosulfonyl)imide electrolyte salt (LiFSI), lithium tetrafluoroborate (LiBF4), lithium hexafluoroarsenate (LiAsF6), lithium bis(oxalateborate)borate (LiBOB), lithium difluorooxalateborate (LiDFOB), and lithium difluorophosphate (LiPO2F2).

[0093] In the electrolyte, the mass percentage of the electrolyte salt is 0.5%-20%.

[0094] In specific applications, the mass percentage of the electrolyte salt in the electrolyte can be selected as 0.5%, 0.8%, 1%, 2%, 5%, 8%, 10%, 12%, 15%, 18%, 20%, etc. The values ​​listed above are merely examples and are not limitations. Any value within the range of 0.5% to 20% can be freely implemented without exceeding the understanding of those skilled in the art.

[0095] In some embodiments, the electrolyte also includes a second additive.

[0096] In this invention, the second additive refers to any additive other than the second compound and the third compound.

[0097] For example, the second additive may be one or a combination of at least two of cyclic sulfates, phosphates, borate esters, borates, and silane compounds.

[0098] A second aspect of the present invention discloses a lithium-ion battery, the lithium-ion battery comprising the electrolyte disclosed in the first aspect of the present invention, and further comprising a positive electrode, a separator, and a negative electrode.

[0099] In some embodiments, the positive electrode includes a positive electrode active material and a positive electrode current collector;

[0100] The positive electrode active material includes ternary materials (lithium nickel cobalt manganese oxide or lithium nickel cobalt aluminum oxide) or one or at least two combinations of lithium iron phosphate, lithium cobalt oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium-rich manganese-based materials, and lithium vanadium phosphate.

[0101] In some embodiments, the positive electrode active material layer further includes a binder. The binder improves the bonding between the composite positive electrode active material particles and also improves the bonding between the positive electrode material layer and the positive electrode current collector.

[0102] In some embodiments, non-limiting examples of adhesives include polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, etc.

[0103] In some embodiments, the positive electrode active material layer further includes a conductive agent to impart conductivity to the electrode. The conductive agent may include any conductive material as long as it does not cause a chemical change. Non-limiting examples of conductive materials include carbon-based materials (e.g., natural graphite, synthetic graphite, carbon black, acetylene black, Ketjen black, carbon fiber, etc.), metal-based materials (e.g., metal powders, metal fibers, etc., including, for example, copper, nickel, aluminum, silver, etc.), conductive polymers (e.g., polyphenylene derivatives), and mixtures thereof.

[0104] In some embodiments, non-limiting examples of the positive current collector include, but are not limited to, aluminum (Al), aluminum alloy, stainless steel, titanium, titanium alloy, and nickel-plated steel.

[0105] In some implementations, the negative electrode includes a negative electrode sheet.

[0106] In some embodiments, the negative electrode sheet includes a negative current collector and a negative active material layer disposed on the negative current collector.

[0107] In this invention, the specific type of negative electrode active material is not specifically limited and can be selected according to requirements. Specifically, the negative electrode active material is selected from natural graphite, artificial graphite, mesophase microcarbon spheres (MCMB), hard carbon, soft carbon, silicon, silicon-carbon composites, Li-Sn alloys, Li-Sn-O alloys, Sn, SnO, SnO2, and spinel-structured lithiated TiO2-Li4Ti5O. 12 One or more of Li-Al alloys. Non-limiting examples of carbon materials include crystalline carbon, amorphous carbon, and mixtures thereof. Crystalline carbon can be amorphous or flake-shaped, small flake-shaped, spherical, or fibrous natural or artificial graphite. Amorphous carbon can be soft carbon, hard carbon, mesophase pitch carbides, calcined coke, etc.

[0108] In some embodiments, elemental metals and metal compounds may also be selected as negative electrode active materials, such as compounds containing metals or metalloids such as Li, Ag, Al, Bi, Cu, Ga, Ge, In, Ni, Pb, Sb, Si, Sn, Sr, and Zn.

[0109] In some embodiments, the negative electrode material layer may include a binder; the binder enhances the bonding between the negative electrode active material particles and the bonding between the negative electrode active material and the current collector.

[0110] In some embodiments, non-limiting examples of adhesives include polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, etc.

[0111] In some embodiments, the negative electrode active material layer can be obtained by coating a negative electrode slurry onto a negative electrode current collector and then performing operations such as drying. The negative electrode slurry includes at least a negative electrode active material and a negative electrode binder. When an aqueous solvent is used as the liquid medium for forming the negative electrode slurry, it is preferable to use a thickener for slurry formation. The thickener is typically used to adjust the viscosity of the slurry.

[0112] In some embodiments, the aforementioned thickener may be one or more of the following: carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, oxidized starch, phosphorylated starch, casein and their salts, etc.

[0113] In some embodiments, the negative electrode active material layer includes a conductive material, thereby making the electrode conductive. The conductive material may include any conductive material as long as it does not cause a chemical change. Non-limiting examples of conductive materials include carbon-based materials (e.g., natural graphite, synthetic graphite, carbon black, acetylene black, Ketjen black, carbon fiber, etc.), metal-based materials (e.g., metal powders, metal fibers, such as copper, nickel, aluminum, silver, etc.), conductive polymers (e.g., polyphenylene derivatives), and mixtures thereof.

[0114] In some embodiments, the negative current collector may be selected from copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, polymer substrate coated with conductive metal, and combinations thereof.

[0115] In some embodiments, the diaphragm is a polyolefin diaphragm or a glass fiber diaphragm.

[0116] The embodiments of the present invention will be described in more detail below through examples and comparative examples.

[0117] It should be noted that the embodiments of the present invention are not limited to these examples. The sample size of all examples and comparative examples is 40, the test results are averaged, and some results are rounded.

[0118] In addition, to reduce the influence of variables on the comparative experiments, the organic solvent system in Examples 1-6 and Comparative Examples 1-5 of this invention is (ethylene carbonate) EC: (methyl ethyl carbonate) EMC: (diethyl carbonate) DEC = 3:5:2, and the above ratio is a volume ratio. The amount of organic solvent used (wt.%) = 100 wt.% - lithium salt electrolyte (wt.%) - first compound (wt.%) - second compound (wt.%) - third compound (wt.%) - other film-forming aids (wt.%).

[0119] The lithium salt is LiPF6, accounting for 14 wt.% of the electrolyte. Other film-forming agents are 2 wt.% VC + 2 wt.% LiPO2F2.

[0120] The experimental environment for Examples 1-6 and Comparative Examples 1-5 was as follows: The experiments were conducted in a glove box filled with high-purity argon gas, with the following environmental conditions: O2 ≤ 0.01 ppm, H2O ≤ 0.01 ppm. All raw materials used in the preparation of the electrolyte were battery-grade, and routine operations such as dehydration and drying were performed on the raw materials before preparation.

[0121] The preparation processes of the positive and negative electrodes in Examples 1-6 and Comparative Examples 1-5 are the same, and the selection of the separator is also the same, as follows: I. Preparation of the positive electrode: The positive electrode active material ternary material lithium nickel cobalt manganese oxide, the conductive agent superconducting carbon black (Super~P), and the binder polyvinylidene fluoride (PVDF) are mixed evenly in a mass ratio of 90:7:3 to prepare a positive electrode slurry. The positive electrode slurry is coated on both surfaces of the current collector aluminum foil and dried at 100°C to form a positive electrode active material layer. Then, it is cold pressed, trimmed, cut into sheets, and slit. After slitting, a lithium-ion battery positive electrode is made.

[0122] II. Preparation of the negative electrode:

[0123] A negative electrode slurry is prepared by mixing graphite (a negative electrode active material), superconducting carbon black (SuperP) (a conductive agent), sodium carboxymethyl cellulose (CMC) (a binder), and styrene-butadiene rubber (SBR) (a binder) in a mass ratio of 96.5:1.0:1.0:1.5. The slurry is coated onto copper foil (a current collector) and dried at 90°C to form a negative electrode active material layer. The slurry is then cold-pressed, trimmed, cut into sheets, and slit. The slits are then used to produce the negative electrode for lithium-ion batteries.

[0124] III. Selection of Diaphragm:

[0125] PE separator was chosen as the separator for lithium batteries.

[0126] Example 1: Preparation of electrolyte:

[0127] Lithium salt electrolyte is added to an organic solvent system. After the lithium salt electrolyte is completely dissolved, the first compound (compound A-2) and other film-forming additives are added in sequence, followed by the second compound (compound B-2). After stirring until homogeneous and fully dissolved, the third compound is added to obtain the electrolyte.

[0128] In this embodiment, the first compound is selected as compound A-2, with the following molecular formula:

[0129] ;

[0130] The second compound was chosen as compound B-2, with the following molecular formula:

[0131] ;

[0132] The molecular formula of the third compound is as follows:

[0133] ;

[0134] In this embodiment, the first compound accounts for 20 wt% of the electrolyte, the second compound accounts for 3 wt% of the electrolyte, and the third compound accounts for 0.1 wt% of the electrolyte. Lithium-ion battery assembly: After preparing the electrolyte, the positive electrode prepared in the first step, the separator selected in the third step, and the negative electrode prepared in the second step are stacked sequentially to obtain a bare cell. The bare cell is placed in an outer packaging shell, and the electrolyte prepared in this embodiment is injected. After vacuum sealing, settling, formation, and shaping processes, a lithium-ion battery is obtained.

[0135] Example 2: The electrolyte preparation process and lithium-ion battery preparation process in this example are basically the same as those in Example 1. The only difference is that in this example, the mass percentage of the third compound in the electrolyte is 1 wt%.

[0136] Example 3: The electrolyte preparation process and lithium-ion battery preparation process in this example are basically the same as those in Example 1. The only difference is that in this example, the mass percentage of the third compound in the electrolyte is 2wt%.

[0137] Example 4: The electrolyte preparation process and lithium-ion battery preparation process in this example are basically the same as those in Example 1. The only difference is that in this example, the mass percentage of the third compound in the electrolyte is 5 wt%.

[0138] Example 5: The electrolyte preparation process and lithium-ion battery preparation process in this example are basically the same as those in Example 1, except that in this example, the first compound of the electrolyte is selected as compound A-1, and the second compound is selected as compound B-1. The molecular formula of compound A-1 is as follows:

[0139] ;

[0140] The molecular formula of compound B-1 is as follows:

[0141] .

[0142] Example 6: The electrolyte preparation process and lithium-ion battery preparation process in this example are basically the same as those in Example 1, except that in this example, the second compound in the electrolyte is compound B-1.

[0143] The molecular formula of compound B-1 is as follows:

[0144] .

[0145] Example 7: The electrolyte preparation process and lithium-ion battery preparation process in this example are basically the same as those in Example 1, except that in this example, the mass percentage of the first compound in the electrolyte is 5 wt%.

[0146] Example 8: The electrolyte preparation process and lithium-ion battery preparation process in this example are basically the same as those in Example 1. The only difference is that in this example, the mass percentage of the first compound in the electrolyte is 30 wt%.

[0147] Example 9: The electrolyte preparation process and lithium-ion battery preparation process in this example are basically the same as those in Example 1. The only difference is that in this example, the mass percentage of the second compound in the electrolyte is 0.01 wt%.

[0148] Example 10: The electrolyte preparation process and lithium-ion battery preparation process in this example are basically the same as those in Example 1. The only difference is that in this example, the mass percentage of the second compound in the electrolyte is 10 wt%.

[0149] Example 11: The electrolyte preparation process and lithium-ion battery preparation process in this example are basically the same as those in Example 1. The only difference is that in this example, the mass percentage of the third compound in the electrolyte is 0.01 wt%.

[0150] Example 12: The electrolyte preparation process and lithium-ion battery preparation process in this example are basically the same as those in Example 1. The only difference is that in this example, the mass percentage of the third compound in the electrolyte is 10 wt%.

[0151] Comparative Example 1: The electrolyte preparation process and lithium-ion battery preparation process in this comparative example are basically the same as those in Example 1, except that the electrolyte in this example does not include the third compound.

[0152] Comparative Example 2: The electrolyte preparation process and lithium-ion battery preparation process in this comparative example are basically the same as those in Example 1, except that the electrolyte in this example does not include the first compound.

[0153] Comparative Example 3: The electrolyte preparation process and lithium-ion battery preparation process of this comparative example are basically the same as those in Example 1, except that the electrolyte in this example does not include the second compound.

[0154] Comparative Example 4: The electrolyte preparation process and lithium-ion battery preparation process of this comparative example are basically the same as those in Example 1. The only difference is that in this example, the third compound of the electrolyte is replaced with HFE with a mass ratio of 0.1 wt%.

[0155] HFE is 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether.

[0156] Comparative Example 5: The electrolyte preparation process and lithium-ion battery preparation process in this comparative example are basically the same as those in Example 1, except that in this example, the third compound in the electrolyte is replaced with FB at a mass ratio of 0.1 wt%. FB is fluorobenzene.

[0157] Comparative Experiment: A total of 11 groups of samples were taken from Examples 1-6 and Comparative Examples 1-5. Half of each group was used for the following tests: Cycle Count 1 Test: At 25℃ (room temperature), the battery was charged at 1C to the charging cutoff voltage of 4.25V, then switched to constant voltage charging to the cutoff current of 0.05C, allowed to stand for 0.5h, and then discharged at 1C to the cutoff voltage of 2.5V. After standing for 0.5h, the battery entered the next charge-discharge cycle, and so on. The number of cycles when the battery capacity retention rate was 80% was recorded. Capacity retention rate = Discharge capacity after cycles / Initial discharge capacity.

[0158] Cycle count 2 test: At a temperature of 45℃ (room temperature), charge at a current of 1C to the charging cutoff voltage of 4.25V, switch to constant voltage charging to the cutoff current of 0.05C, let stand for 0.5h, then discharge at a current of 1C to the cutoff voltage of 2.5V, let stand for 0.5h, and enter the next charge-discharge cycle, and so on, and record the number of cycles when the battery capacity retention rate is 80%.

[0159] The test results are shown in the table below:

[0160]

[0161] As shown in the table above, by simultaneously adding the first compound, the second compound, and the third compound to the electrolyte, the synergistic effect of the three compounds can effectively improve the cycle performance of the battery at both room temperature and high temperature.

[0162] Comparing Examples 1-4, it can be seen that when the mass percentage of the third compound is 0.1-2%, the battery cycle performance is improved more effectively. This may be because as the content of the third compound in the electrolyte increases, the wettability of the electrolyte on the positive and negative electrodes increases, the contact angle decreases, and the electrolyte retention increases, thus improving cycle performance. However, if the content of the third compound in the electrolyte continues to increase, side reactions will occur inside the battery, causing a decrease in the improvement in cycle performance.

[0163] As can be seen from Comparative Example 1 and Comparative Examples 1-3, the first compound, the second compound, and the third compound are all indispensable.

[0164] Comparative Examples 1 and 4-5 show that, compared with fluoroethers and fluorobenzenes, the addition of a third compound to the electrolyte results in a more significant improvement in the cycle performance of the prepared battery.

[0165] It should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An electrolyte, characterized in that, It includes a first compound, a second compound, and a third compound; the structural formula of the first compound is as follows: In the above formula, R 1 Includes one of CF3, CHF2, CH2F, CH2Cl, and CH2Br; The structural formula of the second compound is as follows: ;R 2 It includes one of H, F, Cl, and Br; the structural formula of the third compound is as follows: In the electrolyte, the content of the third compound is 0.01wt%-10wt%, the content of the second compound is 0.01wt%-10wt%, and the content of the first compound is 5wt%-30wt%.

2. The electrolyte according to claim 1, characterized in that, The content of the third compound in the electrolyte is 0.01wt%-2wt%.

3. The electrolyte according to claim 1, characterized in that, The first compound includes at least one of compound A-1, compound A-2, and compound A-3: wherein the molecular formula of compound A-1 is as follows: The molecular formula of compound A-2 is as follows: The molecular formula of compound A-3 is as follows: .

4. The electrolyte according to claim 1, characterized in that, The second compound includes at least one of compound B-1, compound B-2, and compound B-3: wherein the molecular formula of compound B-1 is as follows: The molecular formula of compound B-2 is as follows: The molecular formula of compound B-3 is as follows: .

5. The electrolyte according to claim 1, characterized in that, The electrolyte further includes a second solvent; the second solvent is a non-aqueous organic solvent; and / or, the electrolyte further includes a second additive.

6. A lithium-ion battery, comprising a positive electrode, a separator, and a negative electrode, characterized in that, It also includes the electrolyte as described in any one of claims 1-5.

7. The lithium-ion battery according to claim 6, characterized in that, The positive electrode includes a positive electrode active material; the positive electrode active material includes a ternary material.

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