Electrolyte and lithium ion battery

Abstract

The invention relates to an electrolyte and a lithium ion battery in the technical field of lithium battery production. The electrolyte comprises a first compound, a second compound and a third compound, the electrolyte contains the first compound, the second compound and the third compound at the same time, the stability of the electrolyte under high voltage can be effectively improved, gas production of the electrolyte is inhibited, and the wettability of the electrolyte to a pole piece is improved, so that the dynamics is improved. Furthermore, halogen groups contained in the three components participate in the formation of a CEI film, so that the damage of dissolution of nickel in the ternary material to a negative electrode can be effectively inhibited, and the cycle stability at high temperature and high pressure is improved.

Description

Technical Field

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

[0002] Lithium-ion batteries, due to their high energy density, long cycle life, and excellent safety, are widely used in consumer electronics, electric vehicles, and energy storage systems. The electrolyte is a crucial component of lithium-ion batteries, not only responsible for the conduction of lithium ions but also directly affecting the battery's overall performance and stability. The selection and characteristics of the electrolyte have a profound impact on the battery's efficiency, lifespan, and safety.

[0003] Existing electrolytes are prone to decomposition and gas production under high temperature and high pressure environments, and have many side reactions with electrodes, resulting in poor battery cycle performance. Carbonate solvents can improve the stability of the electrolyte, but will increase the gas production problem of the electrolyte. Adding additives that inhibit gas production and using them in combination with carbonate solvents will increase the viscosity of the electrolyte, reduce the wettability, and limit the improvement in the battery cycle performance.

[0004] Furthermore, when the positive electrode of the battery uses a ternary positive electrode material, the positive electrode is prone to dissolution of transition metal elements, which causes capacity decay and thus affects the charge and discharge performance of the battery. Therefore, improving the stability of the electrode-electrolyte interface film is crucial to improving the high-temperature cycle performance of lithium-ion batteries with ternary positive electrodes as the core. In summary, the role of the electrolyte in lithium batteries cannot be ignored. Improving the stability of the electrode-electrolyte interface film through the electrolyte will be one of the key factors in improving the high-temperature performance of the battery.

[0005] To this end, the present invention proposes a technical solution to solve the above problem. Summary of the Invention

[0006] In order to solve the above problems, the present invention discloses an electrolyte and a lithium-ion battery. The present invention uses a compound of three electrolyte components, which synergistically helps to improve the oxidative stability of the solvent, improve the components of the SEI membrane and the CEI membrane, and improve the lithium ion conduction kinetics, thereby improving the performance of high-temperature cycles.

[0007] The technical solution of the present invention is implemented as follows: A first aspect of the present invention provides an electrolyte, comprising 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 Including one of CF3, CHF2, CH2F, CH2Cl, CH2Br; The structural formula of the second compound is as follows: ; In the above formula, R 2 Including one of H, F, Cl, Br; The structural formula of the third compound is as follows: .

[0008] Preferably, in the electrolyte, the content of the third compound is 0.01 wt%-10 wt%.

[0009] Preferably, in the electrolyte, the content of the third compound is 0.01 wt%-2 wt%.

[0010] Preferably, the first compound includes at least one of compound A-1, compound A-2, and compound A-3: Among them, 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: .

[0011] Preferably, in the electrolyte, the content of the first compound is 5wt%-30wt%.

[0012] Preferably, the second compound includes at least one of compound B-1, compound B-2, and compound B-3: Among them, the molecular formula of B-1 compound is as follows: ; The molecular formula of compound B-2 is as follows: ; The molecular formula of compound B-3 is as follows: .

[0013] Preferably, in the electrolyte, the content of the second compound is 0.01 wt%-10 wt%.

[0014] Preferably, 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.

[0015] The second aspect of the present invention discloses a lithium-ion battery, which includes the electrolyte disclosed in the first aspect of the present invention, and also includes a positive electrode, a separator, and a negative electrode.

[0016] Preferably, the positive electrode comprises a positive electrode active material; The positive electrode active material includes a ternary material.

[0017] The advantages of the present invention are as follows: The electrolyte of the present application contains a first compound, a second compound, and a third compound, which can effectively improve the stability of the electrolyte at high voltages, inhibit gas production, and improve the wettability of the electrolyte to the electrode, thereby enhancing the kinetics and improving the electrolyte's room-temperature and high-temperature cycling performance. Furthermore, all three components contain halogen groups that participate in the formation of the CEI film, effectively inhibiting the dissolution of nickel from the ternary material and damaging the negative electrode, thereby improving cycling stability under high temperature and high pressure. DETAILED DESCRIPTION

[0018] The following will clearly and completely describe the technical solutions of the present invention in conjunction with the embodiments of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts shall fall within the scope of protection of the present invention.

[0019] Unless otherwise defined, all technical and scientific terms used in the present invention have the same meanings as those commonly understood by technicians in the technical field to which the present invention belongs; the terms used in the specific embodiments are only for the purpose of describing specific embodiments and are not intended to limit the present invention; the terms "including" and "having" in the description and claims of the present invention and any variations thereof are intended to cover non-exclusive inclusions.

[0020] In the description of the specific embodiments of the present invention, the technical terms "first" and "second" are used only to distinguish different objects and should not be understood to indicate or imply relative importance or implicitly specify the quantity, specific order, or primary and secondary relationship of the technical features indicated. In the description of the embodiments of the present invention, the meaning of "plurality" is more than two, unless otherwise specifically defined.

[0021] References to "embodiments" in this disclosure mean that a particular feature, structure, or characteristic described in connection with the embodiment may be included in at least one embodiment of the disclosure. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor does it constitute an independent or alternative embodiment that is mutually exclusive of other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0022] In the description of the embodiments of the present invention, the term "and / or" is simply a description of the association relationship between associated objects, indicating that three possible relationships exist. For example, A and / or B can represent the following three situations: A exists alone, A and B exists simultaneously, and B exists alone. In addition, the character " / " in this invention generally indicates that the associated objects are in an "or" relationship.

[0023] Throughout this disclosure, numerical values ​​represent approximate measures or limits of ranges to encompass minor deviations from a given value, as well as embodiments having approximately the stated value and embodiments having the exact value stated. Except for the working examples provided at the end of the detailed description, all numerical values ​​for parameters (e.g., amounts, or conditions) in this specification (including the appended claims) should be understood as being modified in all instances by the term "about," regardless of whether "about" actually precedes the value. "About" indicates that the stated value allows for some minor imprecision (some close to the exact value of the stated value; approximately or reasonably close to the stated value; nearly). If the imprecision provided by "about" is not otherwise understood in this ordinary sense in the art, "about," as used herein, at least indicates the variation that can occur due to ordinary methods of measuring and using such parameters. For example, "about" may encompass variations of less than or equal to 5%, alternatively less than or equal to 4%, alternatively less than or equal to 3%, alternatively less than or equal to 2%, alternatively less than or equal to 1%, alternatively less than or equal to 0.5%, and in certain aspects, optionally less than or equal to 0.1%.

[0024] Additionally, disclosure of ranges includes disclosure of all values ​​within the entire range and further divided ranges, including endpoints and sub-ranges stated for such ranges.

[0025] Existing electrolytes are prone to decomposition and gas production under high temperature and high pressure environments, and have many side reactions with electrodes, resulting in poor battery cycle performance. Carbonate solvents can improve the stability of the electrolyte, but will increase the gas production problem of the electrolyte. Adding additives that inhibit gas production and using them in combination with carbonate solvents will increase the viscosity of the electrolyte, reduce the wettability, and limit the improvement in the battery cycle performance.

[0026] Furthermore, when a ternary cathode material is used for the positive electrode of a battery, transition metal elements are easily dissolved in the positive electrode, thereby causing capacity decay and affecting the charge and discharge performance of the battery. In order to solve the above problem, the present invention proposes a technical solution.

[0027] A first aspect of the present invention provides an electrolyte, comprising 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 Including one of CF3, CHF2, CH2F, CH2Cl, CH2Br; The structural formula of the second compound is as follows: ; In the above formula, R 2 Including one of H, F, Cl, Br; The structural formula of the third compound is as follows: .

[0028] The electrolyte of the present application contains a first compound, a second compound, and a third compound, which can effectively improve the stability of the electrolyte at high voltages, inhibit gas production, and improve the wettability of the electrolyte to the electrode, thereby improving kinetics. Furthermore, the three components contain halogen groups that participate in the formation of the CEI film, which can effectively inhibit the dissolution of nickel in the ternary material and damage to the negative electrode, thereby improving cycling stability under high temperature and high pressure.

[0029] It is understandable that the first compound contains electron-withdrawing and carbonate groups, which improve the stability of the electrolyte under high voltage conditions. However, the first compound is prone to gassing in the battery, which affects the cycling stability of the lithium battery at high temperatures. Therefore, a second compound with a sulfonate group is used. The sulfonate group can effectively inhibit gassing of the electrolyte, but the simultaneous use of the first and second compounds increases the viscosity of the electrolyte, thereby affecting its dynamics. To address this issue, the third compound is introduced to improve the wettability of the electrolyte to the electrode, thereby improving the dynamics.

[0030] In the electrolyte, the content of the third compound is 0.01 wt %-10 wt %.

[0031] In specific applications, the content of the third compound in the electrolyte can be 0.01 wt%, 0.05 wt%, 0.08 wt%, 1 wt%, 2 wt%, 3 wt%, 5 wt%, 8 wt%, 10 wt%, etc. The above values ​​are for illustrative purposes only and are not intended to be limiting. Those skilled in the art may freely implement any value within the range of 0.01 wt% to 10 wt% without departing from the scope of understanding of those skilled in the art.

[0032] In some preferred embodiments, the content of the third compound in the electrolyte is 0.01 wt %-2 wt % to prevent the occurrence of side reactions in the electrolyte.

[0033] In some embodiments, the first compound includes at least one of compound A-1, compound A-2, and compound A-3: Among them, 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: .

[0034] The term "at least one" as used in the present invention means that one element can be selected from the multiple elements listed above, or a combination of two or more elements can be selected from the multiple elements listed above, as long as the combination does not exceed the scope of understanding of those skilled in the art, and the multiple elements do not chemically react with each other and do not affect each other's physical and chemical properties.

[0035] In some embodiments, in the electrolyte, the content of the first compound is 5 wt %-30 wt %.

[0036] In specific applications, the content of the first compound in the electrolyte can be 5wt%, 6wt%, 8wt%, 10wt%, 12wt%, 15wt%, 18wt%, 20wt%, 22wt%, 23wt%, 25wt%, 28wt%, 30wt%, etc. The above values ​​are only examples and are not limiting. Those skilled in the art can freely implement any value within the range of 5wt%-30wt% without exceeding the scope of understanding of those skilled in the art.

[0037] In some embodiments, the second compound includes at least one of compound B-1, compound B-2, and compound B-3: Among them, the molecular formula of B-1 compound is as follows: ; The molecular formula of compound B-2 is as follows: ; The molecular formula of compound B-3 is as follows: .

[0038] In some embodiments, in the electrolyte, the content of the second compound is 0.01 wt %-10 wt %.

[0039] In specific applications, the content of the second compound in the electrolyte can be 0.01 wt%, 0.05 wt%, 0.08 wt%, 1 wt%, 2 wt%, 3 wt%, 5 wt%, 8 wt%, 10 wt%, etc. The above values ​​are only examples and are not limiting. Those skilled in the art can freely implement any value within the range of 0.01 wt%-10 wt% without exceeding the scope of understanding.

[0040] In some embodiments, the electrolyte further includes a second solvent; the second solvent is a non-aqueous organic solvent.

[0041] In the present invention, the second solvent refers to other solvents in the electrolyte except the first compound.

[0042] 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 above-listed values ​​are examples and not limitations. Without exceeding the scope of understanding of those skilled in the art, those skilled in the art can freely implement any value in the range of 1wt%-90wt%.

[0043] In a specific application, the non-aqueous organic solvent includes one or both of carbonates or carboxylates.

[0044] In some preferred embodiments, the carbonate includes at least one of dimethyl carbonate, fluoroethylene carbonate, diethyl carbonate, ethylene carbonate, propylene carbonate or ethyl methyl carbonate, bisfluoropropylene carbonate, trichloroethyl methyl carbonate, 4-trichloromethylethylene carbonate, trifluoromethylethylene carbonate, chloroethylene carbonate, 1,1,1,3,3,3-hexafluoroisopropyl acrylate or di(2,2,2-trifluoroethyl)carbonate.

[0045] In specific applications, carbonate can select one of the elements listed above, or a mixture of two or more elements. The above elements will not chemically react with each other and will not affect their respective physical and chemical properties.

[0046] The carboxylic acid ester includes any one or a combination of at least two of propyl fluorobutyrate, propyl chloroacetate, ethyl fluoroacetate, 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.

[0047] In specific applications, the carboxylic acid ester can be selected from one of the elements listed above, or a mixture of two or more elements. The above elements will not chemically react with each other and will not affect their respective physical and chemical properties.

[0048] In some embodiments, the electrolyte further includes an electrolyte salt.

[0049] 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(oxalatoborate) (LiBOB), lithium difluorooxalatoborate (LiDFOB) and lithium difluorophosphate (LiPO2F2).

[0050] In the electrolyte, the mass proportion of the electrolyte salt is 0.5%-20%.

[0051] In specific applications, the mass proportion of the electrolyte salt in the electrolyte can be 0.5%, 0.8%, 1%, 2%, 5%, 8%, 10%, 12%, 15%, 18%, 20%, etc. The above values ​​are only examples and are not limiting. Any value within the range of 0.5%-20% can be freely implemented without exceeding the scope of understanding of those skilled in the art.

[0052] In some embodiments, the electrolyte further includes a second additive.

[0053] In the present invention, the second additive refers to additives other than the second compound and the third compound.

[0054] For example, the second additive may be one or a combination of at least two of cyclic sulfate, phosphate, borate, borate, and silane compounds.

[0055] The second aspect of the present invention discloses a lithium-ion battery, which includes the electrolyte disclosed in the first aspect of the present invention, and also includes a positive electrode, a separator, and a negative electrode.

[0056] In some embodiments, the positive electrode includes a positive electrode active material and a positive electrode current collector; The positive electrode active material includes a ternary material (lithium nickel cobalt manganese oxide or lithium nickel cobalt aluminum oxide) or a combination of one or at least two of lithium iron phosphate, lithium cobalt oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium-rich manganese-based materials, and lithium vanadium phosphate; In some embodiments, the positive electrode active material layer further includes a binder, which 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.

[0057] In some embodiments, non-limiting examples of binders include polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, and the like.

[0058] 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 chemical changes. Non-limiting examples of conductive materials include carbon-based materials (e.g., natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, etc.), metal-based materials (e.g., metal powder, metal fiber, etc., including, for example, copper, nickel, aluminum, silver, etc.), conductive polymers (e.g., polyphenylene derivatives), and mixtures thereof.

[0059] In some embodiments, non-limiting examples of the positive electrode current collector include one of aluminum (Al), aluminum alloy, stainless steel, titanium, titanium alloy, and nickel-plated steel, but are not limited thereto.

[0060] In some embodiments, the negative electrode comprises a negative electrode sheet.

[0061] In some embodiments, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector.

[0062] In the present invention, the specific types of negative electrode active materials are not subject to specific restrictions and can be selected according to needs. Specifically, the negative electrode active material is selected from natural graphite, artificial graphite, mesophase microcarbon beads (MCMB), hard carbon, soft carbon, silicon, silicon-carbon composite, Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, spinel structured lithiated TiO2-Li4Ti5O 12 , Li-Al alloy. Non-limiting examples of carbon materials include crystalline carbon, amorphous carbon, and mixtures thereof. Crystalline carbon can be amorphous or flake-shaped, platelet-shaped, spherical, or fibrous natural graphite or artificial graphite. Amorphous carbon can be soft carbon, hard carbon, mesophase pitch carbide, calcined coke, etc.

[0063] In some embodiments, metal elements and metal compounds can 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.

[0064] In some embodiments, the negative electrode material layer may include a binder; the binder improves the bonding between the negative electrode active material particles and the bonding between the negative electrode active material and the current collector.

[0065] In some embodiments, non-limiting examples of binders include polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, and the like.

[0066] In some embodiments, the negative electrode active material layer can be formed by coating a negative electrode slurry on a negative electrode current collector, followed by drying and other operations. 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, a thickener is preferably used for slurrying. The thickener is generally used to adjust the viscosity of the slurry.

[0067] In some embodiments, the aforementioned viscosity enhancer may be one or more of the following: carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, oxidized starch, phosphorylated starch, casein, and salts thereof.

[0068] 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 chemical changes. Non-limiting examples of conductive materials include carbon-based materials (e.g., natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, etc.), metal-based materials (e.g., metal powder, metal fiber, etc., such as copper, nickel, aluminum, silver, etc.), conductive polymers (e.g., polyphenylene derivatives), and mixtures thereof.

[0069] In some embodiments, the negative electrode current collector can be selected from copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, and combinations thereof.

[0070] In some embodiments, the separator is a polyolefin separator or a glass fiber separator.

[0071] Hereinafter, embodiments of the present invention will be described in more detail through examples and comparative examples.

[0072] It should be noted that the embodiments of the present invention are not limited to these examples. The number of samples in all examples and comparative examples is 40, the test results are averaged, and some results are rounded off.

[0073] To minimize the impact of variables on the comparative experiments, the organic solvent system in Examples 1-6 and Comparative Examples 1-5 was a 3:5:2 ratio of (ethylene carbonate) EC: (ethyl methyl carbonate) EMC: (diethyl carbonate) DEC. The above ratios are by volume. The organic solvent usage (wt%) was 100 wt% - lithium salt electrolyte (wt%) - first compound (wt%) - second compound (wt%) - third compound (wt%) - other film-forming aids (wt%).

[0074] The lithium salt is LiPF6, accounting for 14 wt.% of the electrolyte. Other film-forming agents include 2 wt.% VC and 2 wt.% LiPO2F2.

[0075] The experiments for Examples 1-6 and Comparative Examples 1-5 were conducted in a glove box filled with high-purity argon. The glove box conditions were: O₂ ≤ 0.01 ppm, H₂O ≤ 0.01 ppm. All electrolyte materials were battery-grade and were subjected to standard procedures such as dehydration and drying prior to preparation.

[0076] 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 diaphragm is also the same, as follows: 1. 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 form a positive electrode slurry, and 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, and then cold pressed, trimmed, cut into pieces, and slit, and the slit is made into a lithium-ion battery positive electrode.

[0077] 2. Preparation of negative electrode: The negative electrode slurry is prepared by mixing the negative electrode active material graphite, the conductive agent superconducting carbon black (Super~P), the binder sodium carboxymethyl cellulose (CMC), and the binder styrene-butadiene rubber (SBR) in a mass ratio of 96.5:1.0:1.0:1.5, coating it on the current collector copper foil and drying it at 90°C to form a negative electrode active material layer. It is then cold pressed, trimmed, cut into pieces, and slit into strips to produce the lithium-ion battery negative electrode.

[0078] 3. Selection of diaphragm: PE membrane is selected as the separator of lithium battery.

[0079] Example 1: Preparation of electrolyte: A lithium salt electrolyte is added to the organic solvent system. After the lithium salt electrolyte is completely dissolved, the first compound (A-2 compound) and other film-forming additives are added in sequence, followed by the second compound (B-2 compound). After stirring until uniform and fully dissolved, the third compound is added to prepare an electrolyte.

[0080] In this embodiment, the first compound is selected as compound A-2, and the specific molecular formula is as follows: ; The second compound is selected as compound B-2, and the specific molecular formula is as follows: ; The molecular formula of the third compound is as follows: ; In this embodiment, the mass proportion of the first compound in the electrolyte is 20wt%, the mass proportion of the second compound in the electrolyte is 3wt%, and the mass proportion of the third compound in the electrolyte is 0.1wt%. 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 in sequence to obtain a bare cell. The bare cell is placed in an outer packaging shell and injected with the electrolyte prepared in this embodiment. After vacuum packaging, standing, formation, and shaping, a lithium-ion battery is obtained.

[0081] Example 2: The electrolyte preparation process and lithium-ion battery preparation process of this example are basically the same as those in Example 1, with the only difference being that, in this example, the mass proportion of the third compound in the electrolyte is 1 wt %.

[0082] Example 3: The electrolyte preparation process and lithium-ion battery preparation process of this example are basically the same as those in Example 1, with the only difference being that, in this example, the mass proportion of the third compound in the electrolyte is 2 wt %.

[0083] Example 4: The electrolyte preparation process and lithium-ion battery preparation process of this example are basically the same as those in Example 1, with the only difference being that, in this example, the mass proportion of the third compound in the electrolyte is 5 wt %.

[0084] Example 5: The electrolyte preparation process and lithium-ion battery preparation process of this embodiment are basically the same as those in Example 1, except that, in this embodiment, 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: ; The molecular formula of compound B-1 is as follows: .

[0085] Example 6: The electrolyte preparation process and lithium-ion battery preparation process of this example are basically the same as those in Example 1, except that, in this example, the second compound in the electrolyte is selected as compound B-1; The molecular formula of compound B-1 is as follows: .

[0086] Example 7: The electrolyte preparation process and lithium-ion battery preparation process of this example are basically the same as those in Example 1, with the only difference being that, in this example, the mass proportion of the first compound of the electrolyte in the electrolyte is 5 wt%.

[0087] Example 8: The electrolyte preparation process and lithium-ion battery preparation process of this example are basically the same as those in Example 1, with the only difference being that, in this example, the mass proportion of the first compound of the electrolyte in the electrolyte is 30 wt%.

[0088] Example 9: The electrolyte preparation process and lithium-ion battery preparation process of this example are basically the same as those in Example 1, with the only difference being that, in this example, the mass proportion of the second compound of the electrolyte in the electrolyte is 0.01 wt%.

[0089] Example 10: The electrolyte preparation process and lithium-ion battery preparation process of this example are basically the same as those in Example 1, with the only difference being that, in this example, the mass proportion of the second compound of the electrolyte in the electrolyte is 10 wt%.

[0090] Example 11: The electrolyte preparation process and lithium-ion battery preparation process of this example are basically the same as those in Example 1, with the only difference being that, in this example, the mass proportion of the third compound in the electrolyte is 0.01 wt%.

[0091] Example 12: The electrolyte preparation process and lithium-ion battery preparation process of this example are basically the same as those in Example 1, with the only difference being that, in this example, the mass proportion of the third compound in the electrolyte is 10 wt %.

[0092] Comparative Example 1: The electrolyte preparation process and lithium-ion battery preparation process of this comparative example are basically the same as those in Example 1, with the only difference being that the electrolyte of this example does not include the third compound.

[0093] Comparative Example 2: The electrolyte preparation process and lithium-ion battery preparation process of this comparative example are basically the same as those in Example 1, with the only difference being that the electrolyte in this example does not include the first compound.

[0094] 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, with the only difference being that the electrolyte of this example does not include the second compound.

[0095] 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, with the only difference being that, in this example, the third compound of the electrolyte is replaced with HFE with a mass percentage of 0.1 wt%.

[0096] HFE is 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether.

[0097] 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 0.1 wt% of FB. FB is fluorobenzene.

[0098] Comparative Experiment: 11 groups of samples, including Examples 1-6 and Comparative Examples 1-5, were collected and tested as follows: Cycle 1: At 25°C (room temperature), charge at 1C to a charge cutoff voltage of 4.25V. Switch to constant voltage charging to a cutoff current of 0.05C, wait for 0.5h, then discharge at 1C to a cutoff voltage of 2.5V. Wait for 0.5h before entering the next charge-discharge cycle. Repeat this cycle, and record the number of cycles required for the battery capacity retention rate to reach 80%. Capacity retention rate = discharge capacity after cycle / initial discharge capacity.

[0099] Cycle 2 test: At 45°C (room temperature), charge at a current of 1C to a charge cut-off voltage of 4.25V, switch to constant voltage charging to a cut-off current of 0.05C, let stand for 0.5h, then discharge at a current of 1C to a cut-off voltage of 2.5V, let stand for 0.5h, and enter the next charge and discharge cycle. Repeat this cycle and record the number of cycles when the battery capacity retention rate is 80%.

[0100] The test results are shown in the following table:

[0101] As can be seen from the above table, by adding the first compound, the second compound, and the third compound to the electrolyte at the same time, the three work synergistically to effectively improve the cycle performance of the battery at room temperature and high temperature.

[0102] Comparing Examples 1 to 4, it can be seen that when the mass ratio of the third compound is 0.1-2, the battery cycle performance improvement effect is better. This may be because as the content of the third compound in the electrolyte increases, the electrolyte's wettability to the positive and negative electrodes increases, the contact angle decreases, and the electrolyte retention capacity increases, thereby improving the cycle performance. However, when the content of the third compound in the electrolyte continues to increase, side reactions occur within the battery, resulting in a decrease in the cycle performance improvement effect.

[0103] Comparison of Example 1 and Comparative Examples 1 to 3 shows that the first compound, the second compound and the third compound are indispensable.

[0104] By comparing Example 1 with Comparative Examples 4-5, it can be seen that, compared with fluoroether and fluorobenzene, the cycle performance of the battery prepared by adding the third compound to the electrolyte is more significantly improved.

[0105] It should be pointed out that the above 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 in the scope of protection 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 Including one of CF3, CHF2, CH2F, CH2Cl, CH2Br; The structural formula of the second compound is as follows: ; R 2 Including one of H, F, Cl, and Br; the third compound has the following structural formula: ; 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 In the electrolyte, the content of the third compound is 0.01 wt %-2 wt %.

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. 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. 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: Also includes the electrolyte according to any 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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