Electrolyte for lithium-ion battery, lithium-ion battery, and electrochemical

Abstract

To provide an electrolyte for a lithium-ion battery, a lithium-ion battery, and an electrochemical device that simultaneously achieve low-temperature performance, high-temperature performance, and gas generation performance.SOLUTION: The electrolyte solution contains additives including a first additive selected from compounds represented by formula (I) and a second additive containing lithium difluorobis (oxalato) phosphate.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to the technical field of power batteries, and in particular to lithium ion battery electrolytes, lithium ion batteries, and electrochemical devices. [Background technology]

[0002] With the depletion of fossil fuels and the worsening of environmental pollution, the automotive industry faces unprecedented challenges and urgently needs to find new, environmentally friendly and efficient energy sources. Among the many potential options, lithium-ion batteries have attracted attention due to their excellent performance and wide application prospects. Lithium-ion batteries have characteristics such as high energy density, low self-discharge rate, and high voltage, allowing them to store large amounts of energy in a relatively small volume and maintain high power even when not in use for long periods of time, providing powerful power output for automobiles.

[0003] Although lithium-ion batteries boast superior performance, their safety is not negligible. During the charge and discharge process, complex chemical reactions generate large amounts of gas inside the battery. The accumulation of this gas can cause the battery to expand, potentially leading to misalignment between the electrode sheet and separator, increased risk of battery polarization, and potential problems such as battery explosion and fire. These unpredictable events during battery use pose a significant threat to the safety of life and property. Currently, commonly used electrolytes, which combine lithium hexafluorophosphate as a lithium salt with a mixed organic solvent of cyclic and chain carbonate esters, suffer from severe gas generation and are unable to fully balance performance in high and low temperature environments, limiting their application range. Summary of the Invention [Problem to be solved by the invention]

[0004] The present invention provides a lithium ion battery electrolyte, a lithium ion battery, and an electrochemical device, which effectively reduce the impedance of the battery and improve the low-temperature performance of the battery, while simultaneously achieving high-temperature performance and gas generation performance. [Means for solving the problem]

[0005] In order to solve the above technical problems, the present invention provides an electrolyte for a lithium ion battery, which contains at least the following components: a non-aqueous solvent; A lithium salt, An additive comprising a first additive selected from the compounds represented by formula (I) and a second additive comprising lithium difluorobis(oxalato)phosphate. [ka] (R1, R2, R3, and R4 are each a substituent having 1 to 3 carbon atoms, a degree of unsaturation of 0 to 4, and 0 to 3 heteroatoms. The heteroatom is at least one selected from nitrogen, phosphorus, and sulfur, and n is 0 to 2.)

[0006] In one embodiment of the present invention, R1, R2, R3, and R4 are each an alkyl group, an alkenyl group, an alkynyl group, or an amino group.

[0007] In one embodiment of the present invention, the content of the first additive in the electrolytic solution is 0.1 wt% to 3 wt%, and the content of the second additive in the electrolytic solution is 0.1 wt% to 3 wt%.

[0008] In one embodiment of the present invention, the content of the first additive in the electrolyte solution is 0.1 wt% to 0.5 wt%, the content of the second additive in the electrolyte solution is 0.5 wt% to 1 wt%, and the mass ratio of the second additive to the first additive is 1.5:1 to 2:1.

[0009] In one embodiment of the present invention, the first additive is at least one selected from the group consisting of Compound 1, Compound 2, Compound 3, and Compound 4 below. [ka]

[0010] In one embodiment of the present invention, the non-aqueous solvent is at least one selected from a carbonate ester, a carboxylic acid ester, an ether, or a nitrile, the carbonate ester is at least one selected from ethylene carbonate, propylene carbonate, dimethyl carbonate, ethyl methyl carbonate, or diethyl carbonate, the carboxylic acid ester is at least one selected from ethyl formate, ethyl acetate, propyl acetate, or ethyl propionate, the ether is at least one selected from 1,2-dimethoxyethane or ethylene glycol diethyl ether, the nitrile is at least one selected from acetonitrile, propionitrile, butyronitrile, or valeronitrile, and the content of the non-aqueous solvent in the electrolyte is 70 wt % to 85 wt %.

[0011] In one embodiment of the present invention, the lithium salt is at least one selected from lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethyl)sulfonylimide, lithium acetate, lithium methylsulfonate, and lithium trifluoromethylsulfonate, and the content of the lithium salt in the electrolyte solution is 12 wt% to 16 wt%.

[0012] The present invention also provides a lithium-ion battery comprising at least: A positive electrode sheet; A negative electrode sheet; An electrolyte selected from the electrolytes for the lithium ion battery described above.

[0013] In one embodiment of the present invention, the positive electrode active material in the positive electrode sheet is Lix [Ni y Co z Mn t M (1-y-z-t) O 2-δ which contains, where M is at least one of Cr, Zr, Ca, Mg, Cu, Ti, Al, Mo, W, or Zn, and 0.9 < x < 1.1, 0.65 ≤ y < 1.0, 0 ≤ z < 0.5, 0 ≤ t < 0.5, 0 ≤ δ ≤ 0.1. The negative electrode active material in the negative electrode sheet contains at least one of graphite, silicon oxide material, or silicon carbon material.

[0014] The present invention further provides an electrochemical device including the above-described lithium-ion battery. [Advantages of the Invention]

[0015] In summary, the present invention provides an electrolyte for a lithium-ion battery, a lithium-ion battery, and an electrochemical device. By sharing lithium difluorobis(oxalato)phosphate as the first additive and the second additive, the solubility of lithium difluorobis(oxalato)phosphate can be enhanced through intermolecular interaction. The unsaturated bond in the first additive captures F - generated by the cleavage of the P-F bond, forms a C-F covalent bond, and further causes a chain addition reaction on the positive electrode side, improving the stability of the positive electrode interface. H + in the electrolyte is neutralized, avoiding the acidification of the electrolyte, reducing gas generation due to the decomposition of the non-aqueous solvent, further preventing the elution and structural collapse of transition metals from the positive electrode, and protecting transition metal ions in the positive electrode from HF corrosion. By using the first additive and lithium difluorobis(oxalato)phosphate in combination, the advantages of both can be fully exerted, improving the quality of the positive electrode-electrolyte interface and the negative electrode-electrolyte interface, effectively reducing the low-temperature impedance of the lithium-ion battery, improving the low-temperature performance of the battery, and at the same time achieving both high-temperature performance and gas generation performance. [Embodiments for Carrying Out the Invention]

[0016] While the present invention will be described below with reference to specific examples, those skilled in the art will readily understand other advantages and effects of the present invention from the disclosure of this specification. The present invention may also be implemented or applied through other different specific embodiments, and various details in this specification may be modified or changed in various ways based on different perspectives and applications without departing from the spirit of the present invention.

[0017] It should be understood that the present invention may be embodied in different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

[0018] The technical solutions of the present invention will be described in more detail below in combination with the embodiments, but it is clear that the described embodiments are only some examples of the present invention, and are not all examples. Based on the embodiments of the present invention, all other examples obtained by those skilled in the art without any creative work fall within the scope of protection of the present invention.

[0019] The present invention provides a lithium-ion battery. The lithium-ion battery may be, for example, a primary battery or a secondary battery. The secondary battery may be, for example, a pouch-type battery, a prismatic-case battery, or a cylindrical battery. However, the present invention is not limited to this type of lithium-ion battery. Here, a cylindrical battery is used as an example to explain specific embodiments of the present invention. In one embodiment of the present invention, the lithium-ion battery includes a housing and a bare cell disposed within the housing. The bare cell includes a positive electrode sheet, a separator, and a negative electrode sheet. The positive electrode sheet, the separator, and the negative electrode sheet are stacked in this order, with a separator disposed between each of the positive and negative electrode sheets. The multilayer stack is then wound to obtain a bare cell, which is then assembled into a battery housing. Finally, an electrolyte is injected into the housing in one or more batches, completely immersing the bare cell in the electrolyte.

[0020] The positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer coated on at least one surface of the positive electrode current collector. The positive electrode current collector is, for example, a foil material formed by surface-treating nickel, titanium, aluminum, silver, stainless steel, or carbon. In addition to foil materials, the positive electrode current collector may also be in various forms, such as film, mesh, porous, foam, or nonwoven fabric, either alone or in combination. The thickness of the positive electrode current collector is, for example, 8 μm to 15 μm. In this embodiment, the positive electrode current collector is, for example, aluminum foil, and the thickness of the aluminum foil is, for example, 13 μm.

[0021] The positive electrode active material layer includes a positive electrode active material, an adhesive, and a conductive agent. Here, the positive electrode active material may be a nickel-cobalt-manganese ternary positive electrode active material. This positive electrode active material may be expressed by the following chemical formula, for example: Li x [Ni y Co z Mn t M (1-y-z-t) ]O 2-δHere, M is one or more selected from Cr, Zr, Ca, Mg, Cu, Ti, Al, Mo, W, Zn, etc., where 0.9 < x < 1.1, 0.65 ≤ y < 1.0, 0 ≤ z < 0.5, 0 ≤ t < 0.5, and 0 ≤ δ ≤ 0.1. The adhesive is, for example, any one or more selected from Polyvinylidene Fluoride (PVDF), Poly(ethylene oxide) (PEO), Polyamide (PA), Polyacrylonitrile (PAN), Polyacrylate, Polyvinylether, Polymethyl Methacrylate (PMMA), Ethylene·Propylene·Diene Terpolymer (EPDM), Polyhexafluoropropylene, and Polymerized Styrene Butadiene Rubber (SBR). The conductive agent is, for example, any one or more selected from Super P, acetylene black, carbon nanotubes, and graphene. In the positive electrode active material layer, the mass ratio of the positive electrode active material, the conductive agent, and the adhesive is, for example, (90 - 98):(1 - 5):(1 - 5).

[0022] In one embodiment of the present invention, the positive electrode active material is, for example, LiNi 0.9 Mn 0.05 Co 0.05The positive electrode active material is O2, the adhesive is selected from, for example, polyvinylidene fluoride, and the conductive agent is selected from, for example, conductive carbon black. The positive electrode active material, conductive agent, and adhesive are mixed, for example, in a mass ratio of 98:1:1, and then an organic solvent is added. The mixture is stirred under a vacuum mixer until the system becomes homogeneous, yielding a positive electrode slurry. The organic solvent is, for example, N-methylpyrrolidone (NMP). The positive electrode slurry is uniformly applied to an aluminum foil, dried at room temperature, and then transferred to an oven for drying. A positive electrode sheet is obtained through processes such as cold pressing and slitting. In other embodiments, the positive electrode sheet may be obtained using any other method for forming a positive electrode sheet. In this embodiment, the nickel content is, for example, 0.9, which can further improve the energy density and cycle life of lithium-ion batteries compared to conventional ternary positive electrode active materials with a nickel content of less than 0.8.

[0023] The negative electrode sheet includes, for example, a negative electrode current collector and a negative electrode active material layer applied to at least one surface of the negative electrode current collector. The negative electrode current collector is, for example, one selected from a copper foil current collector, a composite copper foil current collector, a carbon current collector, a foamed copper current collector, and a stainless steel current collector. The thickness of the negative electrode current collector is, for example, 8 μm to 15 μm. In this embodiment, the negative electrode current collector is, for example, selected from copper foil, and the thickness of the copper foil is, for example, 13 μm.

[0024] The negative electrode active material layer includes a negative electrode active material, a conductive agent, an adhesive, a thickener, etc. Here, the negative electrode active material is a compound capable of absorbing and releasing lithium ions. In one embodiment of the present invention, the negative electrode active material is, for example, graphite, a silicon oxide material (SiO x, (0 < x < 2), and at least one selected from silicon-carbon materials. When the negative electrode active material contains a silicon oxide material or a silicon-carbon material, the mass ratio thereof to graphite is, for example, 2:98 to 10:90. The adhesive is selected from, for example, polyvinylidene fluoride, poly(ethylene oxide), polyamide, polypropylene, polyacrylate, polyvinyl ether, poly(methyl methacrylate), polyhexafluoropropylene, and styrene-butadiene rubber. The thickener is selected from, for example, sodium carboxymethyl cellulose (Carboxymethyl Cellulose Sodium, CMC-Na). The conductive agent is any one or more selected from, for example, conductive carbon black, acetylene black, ketjen black, carbon nanotubes, and graphene. The mass ratio of the negative electrode active material, conductive agent, adhesive, and thickener in the negative electrode active material layer is, for example, (90 to 96):(1 to 2):(1 to 3):(2 to 5).

[0025] In one embodiment of the present invention, the negative electrode active material is selected from, for example, graphite and a silicon oxide material, the mass ratio of the silicon oxide material to graphite is, for example, 3.5:96.5, the conductive agent is selected from, for example, conductive carbon black, the thickener is selected from, for example, sodium carboxymethyl cellulose, and the adhesive is selected from, for example, styrene-butadiene rubber. In one embodiment of the present invention, the negative electrode active material, conductive agent, adhesive, and thickener are mixed, for example, at a mass ratio of 96:1:1:2, deionized water is added, and they are uniformly mixed under the action of a vacuum mixer to obtain a negative electrode slurry. The negative electrode slurry is applied to a copper foil, dried at room temperature, then transferred to an oven for drying, and a negative electrode sheet is obtained through processes such as cold pressing and slitting. In other embodiments, the negative electrode sheet may be obtained by selecting any other method for forming the negative electrode sheet.

[0026] In one embodiment of the present invention, the separator is, for example, a polyethylene film (PE), a polypropylene film (PP), a glass fiber film, or a composite film. The thickness of the separator is, for example, 9 μm to 15 μm. In one embodiment of the present invention, the separator is obtained by selecting, for example, an 8 μm to 10 μm polyethylene base film, and coating a 2 μm to 4 μm nano-aluminum oxide layer on the base film. In one embodiment of the present invention, the separator is, for example, SEMCORP separator SCB9-018.

[0027] In one embodiment of the present invention, the lithium-ion battery further includes an electrolyte that fills the entire battery interior space. The positive electrode sheet, separator, and negative electrode sheet are completely immersed in the electrolyte. The electrolyte functions to conduct ions, provide ion channels, and maintain chemical stability. The various components in the electrolyte are classified into non-aqueous solvents, lithium salts, additives, etc., depending on their functions and amounts. The non-aqueous solvent is used to dissolve the lithium salt and additives. The lithium salt is primarily used to provide lithium ions and form ion channels. In the entire electrochemical system of a battery, electricity is generated through the directional movement of lithium ions and electrons. Lithium salts significantly affect the energy density, power density, wide potential window, cycle life, and safety performance of lithium batteries. Additives are substances added in small amounts to the electrolyte. There are many types, each with different functions, and they each provide different improvements in, for example, high and low-temperature performance, cycle performance, and membrane formation performance.

[0028] The present invention provides an electrolyte for a lithium ion battery, which includes at least a non-aqueous solvent, a lithium salt, and additives including a first additive and a second additive selected from the group consisting of compounds represented by formula (I).

[0029] [ka] Here, R1, R2, R3, and R4 are each substituents having 1 to 3 carbon atoms, a degree of unsaturation of 0 to 4, and a heteroatom number of 0 to 3. The heteroatom is at least one selected from nitrogen, phosphorus, sulfur, etc., and n is 0 to 2.

[0030] In one embodiment of the present invention, R1, R2, R3, and R4 are each an alkyl group, an alkenyl group, an alkynyl group, or an amino group. The second additive is lithium difluorobis(oxalato)phosphate (LiODFP), which has the ability to form films on positive and negative electrodes, improves the quality of the cathode-electrolyte interphase (CEI) and the anode-electrolyte solid electrolyte interface (SEI), effectively reduces the direct current resistance (DCR) of the lithium ion battery, and improves the low-temperature performance of the battery.

[0031] In one embodiment of the present invention, the first additive is at least one selected from the compounds shown in Compound 1, Compound 2, Compound 3, and Compound 4 below.

[0032] [ka]

[0033] The first additive is a Lewis base substance with an unsaturated bond, so it + The first additive effectively neutralizes the acidity of the electrolyte, thereby preventing the electrolyte from becoming acidic and preventing the elution of transition metals and structural collapse in the positive electrode active material. When the first additive is used in combination with LiODFP, a remarkable synergistic effect is produced. The first additive's strong polarity significantly improves the solubility of LiODFP in the electrolyte through intermolecular forces. In addition, the unsaturated bond in the first additive can effectively neutralize the acidity of the electrolyte, thereby preventing the elution of transition metals and structural collapse in the positive electrode active material. -The first additive captures ions, forming stable C—F covalent bonds, and then undergoes a chain addition reaction on the positive electrode side, forming a dense C—E—I film, improving the stability of the positive electrode interface and effectively reducing gas generation due to decomposition of the non-aqueous solvent, while protecting the transition metal ions in the positive electrode from HF corrosion. The combined use of the first additive and lithium difluorobis(oxalato)phosphate fully exploits the benefits of both, improving the battery's low-temperature performance while simultaneously achieving high-temperature performance and gas generation performance.

[0034] In one embodiment of the present invention, the content of the first additive in the electrolyte is, for example, 0.1 wt% to 3 wt%, and the content of lithium difluorobis(oxalato)phosphate as the second additive in the electrolyte is, for example, 0.1 wt% to 3 wt%. In another embodiment of the present invention, the content of the first additive in the electrolyte is, for example, 0.1 wt% to 0.5 wt%, the content of lithium difluorobis(oxalato)phosphate in the electrolyte is, for example, 0.5 wt% to 1 wt%, and the mass ratio of lithium difluorobis(oxalato)phosphate to the first additive is, for example, 1.5:1 to 2:1. If the content of the first additive is too low, the stability of the formed CEI film will be poor, resulting in poor high-temperature storage and gas generation performance. If the content of the first additive is too high, the CEI film will be too thick, which will be detrimental to the battery capacity. If the content of lithium difluorobis(oxalato)phosphate is too low, the high-temperature storage capacity recovery rate will be high, and if the content of lithium difluorobis(oxalato)phosphate is too high, the low-temperature performance of the lithium-ion battery will be improved, but gas generation from the electrolyte will be deteriorated, resulting in poor high-temperature storage performance and gas generation performance. Therefore, by controlling the contents of the first additive and lithium difluorobis(oxalato)phosphate, the high-temperature and low-temperature performance of the lithium-ion battery can be comprehensively improved and gas generation can be reduced.

[0035] In one embodiment of the present invention, the additive further includes a third additive, which is at least one selected from the group consisting of fluoroethylene carbonate (FEC), ethylene sulfate (1,3,2-dioxathiolane 2,2-dioxide (DTD)), 1,3-propanesultone (PS), and vinylene carbonate (VC). The third additive may be added singly or in combination. The content of a single third additive in the electrolyte is, for example, 0.1 wt% to 2 wt%, and the total content of the third additives in the electrolyte is, for example, 1 wt% to 10 wt%. The first additive, the second additive, and the third additive act in combination to form a stable SEI film on the negative electrode, preventing continued decomposition of the electrolyte and improving the cycling stability of the lithium-ion battery.

[0036] In one embodiment of the present invention, the lithium salt is at least one selected from the group consisting of lithium hexafluorophosphate (LiPF), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethyl)sulfonylimide lithium (LiTFSI), lithium acetate, lithium methylsulfonate, and lithium trifluoromethylsulfonate (CFSOLi). The content of the lithium salt in the electrolyte is, for example, 12 wt% to 16 wt%. The present application does not limit the type of lithium salt, and a single lithium salt or a mixture of lithium salts can be used. In one embodiment of the present invention, the lithium salt is, for example, selected from a mixture of lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide, and the mass ratio of lithium hexafluorophosphate to lithium bis(fluorosulfonyl)imide is, for example, 14:1 to 13:2.

[0037] In one embodiment of the present invention, the non-aqueous solvent is at least one selected from, for example, carbonate esters, carboxylic acid esters, ethers, and nitriles. Here, the carbonate ester is at least one selected from ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC). The carboxylic acid ester is at least one selected from ethyl formate (EF), ethyl acetate (EA), n-propyl acetate (PA), and ethyl propionate (EP). The ethers are 1,2-dimethoxyethane (DME) and ethylene glycol diethyl ether. The non-aqueous solvent is at least one selected from the group consisting of acetonitrile (AN), propionitrile, butyronitrile (BN), and valeronitrile (VN). The content of the non-aqueous solvent in the electrolyte is, for example, 70 wt% to 85 wt%. In one specific embodiment of the present invention, the non-aqueous solvent is, for example, a mixture of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate.

[0038] In one embodiment of the present invention, when preparing the electrolyte, the content of a stable gas such as nitrogen or argon in a glove box is 99.999%, the actual oxygen content in the glove box is 0.1 ppm or less, and the water content is 0.1 ppm or less. After uniformly mixing the non-aqueous solvent by mass, a sufficiently dried lithium salt is added to the non-aqueous solvent, and additives are added to prepare a non-aqueous electrolyte for a lithium ion battery. Here, the contents of the lithium salt and additives, excluding the non-aqueous solvent, are expressed as weight percentages calculated based on the total weight of the electrolyte.

[0039] In one embodiment of the present invention, the positive electrode sheet, separator, and negative electrode sheet are arranged in this order. The separator is positioned between the positive electrode sheet and the negative electrode sheet to provide insulation. A bare cell is obtained by rolling or stacking. The bare cell is placed in a housing, dried in a vacuum oven, and then sealed after the electrolyte solution prepared in the present invention is injected. A lithium-ion battery is obtained by at least performing steps such as standing, chemical conversion, and grading.

[0040] The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to these examples. Appropriate modifications can be made within the scope of the present invention, and all such modifications are within the technical scope of the present invention.

[0041] Example 1

[0042] Preparation of electrolyte solution: In an argon glove box with a water content of less than 0.1 ppm and an oxygen content of less than 0.1 ppm, ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate were mixed uniformly in a mass ratio of 3:5:2 to obtain a mixed solvent. Battery-grade lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, and Compound 1 were then added to the mixed solvent and mixed uniformly to obtain an electrolyte solution. The resulting electrolyte solution contained 14 wt% lithium hexafluorophosphate, 1 wt% lithium bis(fluorosulfonyl)imide, and 0.5 wt% Compound 1.

[0043] Preparation of positive electrode sheet: LiNi 0.9 Mn 0.05 Co 0.05 O2, polyvinylidene fluoride, and conductive carbon black were mixed in a mass ratio of 98:1:1, and then N-methylpyrrolidone was added. The mixture was stirred under a vacuum mixer until the mixture was homogeneous, yielding a positive electrode slurry. The positive electrode slurry was evenly applied to aluminum foil, dried at room temperature, and then transferred to an oven for drying. The positive electrode sheet was obtained through processes such as cold pressing and slitting.

[0044] Preparation of negative electrode sheet: The negative electrode active material, conductive carbon black, sodium carboxymethylcellulose, and styrene-butadiene rubber were mixed in a mass ratio of 96:1:1:2. The negative electrode active material was a mixture of silicon oxide material and graphite, with a mass ratio of silicon oxide material to graphite of 3.5:96.5. Deionized water was added and uniformly mixed under the action of a vacuum mixer to obtain negative electrode slurry. The negative electrode slurry was applied to copper foil, dried at room temperature, and then transferred to an oven for drying. The negative electrode sheet was obtained through processes such as cold pressing and slitting.

[0045] Separator selection: 8 μm polyethylene was selected as the base film, and a 3 μm thick nano-aluminum oxide layer was coated on the base film.

[0046] Battery preparation: The positive electrode sheet, separator, and negative electrode sheet were wound in this order so that the separator was positioned between the positive electrode sheet and the negative electrode sheet to provide insulation, and a bare cell was obtained. The bare cell was then placed in a cylindrical case and dried in a vacuum oven. The electrolyte prepared above was then poured into the case, sealed, and subjected to a chemical conversion process to obtain a lithium-ion battery.

[0047] Example 2

[0048] The additives included Compound 1 and lithium difluorobis(oxalato)phosphate (referred to as LiODFP in Table 1), with the content of Compound 1 being 0.5 wt% and the content of lithium difluorobis(oxalato)phosphate being 0.1 wt%. The other steps were the same as in Example 1.

[0049] Example 3

[0050] The additives included Compound 1 and lithium difluorobis(oxalato)phosphate, the content of Compound 1 was 0.5 wt%, the content of lithium difluorobis(oxalato)phosphate was 0.5 wt%, and the other steps were the same as in Example 1.

[0051] Example 4

[0052] The additives included Compound 1 and lithium difluorobis(oxalato)phosphate, the content of Compound 1 was 0.5 wt%, the content of lithium difluorobis(oxalato)phosphate was 1 wt%, and the other steps were the same as in Example 1.

[0053] Example 5

[0054] The additives included Compound 1 and lithium difluorobis(oxalato)phosphate, the content of Compound 1 was 0.5 wt%, the content of lithium difluorobis(oxalato)phosphate was 3 wt%, and the other steps were the same as in Example 1.

[0055] Example 6

[0056] The additives included Compound 1 and lithium difluorobis(oxalato)phosphate, the content of Compound 1 was 0.1 wt%, the content of lithium difluorobis(oxalato)phosphate was 0.5 wt%, and the other steps were the same as in Example 1.

[0057] Example 7

[0058] The additives included Compound 1 and lithium difluorobis(oxalato)phosphate, the content of Compound 1 was 1 wt%, the content of lithium difluorobis(oxalato)phosphate was 0.5 wt%, and the other steps were the same as in Example 1.

[0059] Example 8

[0060] The additives included Compound 1 and lithium difluorobis(oxalato)phosphate, the content of Compound 1 was 3 wt%, the content of lithium difluorobis(oxalato)phosphate was 0.5 wt%, and the other steps were the same as in Example 1.

[0061] Example 9

[0062] The additive contains Compound 3, and the content of Compound 3 is 0.5 wt %, and the other steps are the same as those in Example 1.

[0063] Example 10

[0064] The additives included Compound 3 and lithium difluorobis(oxalato)phosphate, the content of Compound 3 was 0.5 wt%, the content of lithium difluorobis(oxalato)phosphate was 0.5 wt%, and the other steps were the same as in Example 1.

[0065] Example 11

[0066] The additives included Compound 3 and lithium difluorobis(oxalato)phosphate, the content of Compound 3 was 0.5 wt%, the content of lithium difluorobis(oxalato)phosphate was 1 wt%, and the other steps were the same as in Example 1.

[0067] Comparative Example 1

[0068] The electrolyte solution does not contain the first additive and lithium difluorobis(oxalato)phosphate, and the other steps are the same as in Example 1.

[0069] Comparative Example 2

[0070] The additive includes lithium difluorobis(oxalato)phosphate, and the content of lithium difluorobis(oxalato)phosphate is 0.5 wt %, and the other steps are the same as those in Example 1.

[0071] Comparative Example 3

[0072] The additives included Compound 1 and lithium difluorobis(oxalato)phosphate, the content of Compound 1 was 0.05 wt%, and the content of lithium difluorobis(oxalato)phosphate was 0.05 wt%, and the other steps were the same as in Example 1.

[0073] Comparative Example 4

[0074] The additives included Compound 1 and lithium difluorobis(oxalato)phosphate, the content of Compound 1 was 5 wt%, the content of lithium difluorobis(oxalato)phosphate was 5 wt%, and the other steps were the same as in Example 1.

[0075] In the present invention, lithium ion batteries were manufactured by changing the ratio of the electrolyte solution in Examples 1 to 11 and Comparative Examples 1 to 4, and the performance of the lithium ion batteries was tested. The test results are shown in Table 1.

[0076] In one embodiment of the present invention, low-temperature DC impedance measurements were performed by adjusting the temperature of the thermostatic chamber to -20°C and allowing the lithium-ion battery to stand in the chamber for two hours. The battery was then charged at a constant current of 0.33 C to 4.25 V, further charged at a constant voltage of 4.25 V to 0.05 C, allowed to stand for 30 minutes, and then discharged at a constant current of 0.33 C to 2.5 V. This charge-discharge cycle was repeated twice, and the final discharge capacity was recorded as C. After allowing the battery to stand for 30 minutes, the battery was again discharged at 0.33 C to 50% of C, and the state of charge (SOC) of the battery was adjusted to 50%. After allowing the battery to stand for 30 minutes, the voltage V at the end of the discharge was recorded. The battery was then discharged for another 30 seconds at a constant current of C, and the voltage V and current I at the end of the discharge were recorded. From this, DCR = (V - V) / I was calculated.

[0077] In one embodiment of the present invention, the high-temperature storage capacity recovery test was performed by charging a lithium-ion battery at 25°C at a constant current of 0.33C to 4.25V, then charging at a constant voltage until the current reached 0.05C. After allowing the battery to stand for 30 minutes, this process was repeated two or three times, and the final discharge capacity C1 at 0.33C was recorded. Next, the fully charged lithium-ion battery was stored in a thermostatic chamber at 60°C for 30 days (denoted as "1M" in Table 1), after which the battery was cooled, the temperature of the thermostatic chamber was adjusted to 25°C, and the battery was allowed to stand for 10 minutes. After this, the battery was discharged at a constant current of 0.33C to 2.5V. The battery was then charged and discharged at 0.33C over a voltage range of 2.5V to 4.25V. This cycle was repeated twice, and the final discharge capacity C2 was recorded. The capacity recovery rate of the lithium-ion battery stored at high temperature was calculated as (C2 / C1) × 100%.

[0078] In one embodiment of the present invention, the gas generation increase rate test was performed by fully charging a lithium ion battery, storing it in a thermostatic chamber at 60°C, measuring its volume every seven days, and recording and calculating the volume increase rate, i.e., the gas generation increase rate.

[0079] Table 1 shows the performance test results of the lithium ion batteries of Examples 1 to 11 and Comparative Examples 1 to 4.

[0080] [Table 1]

[0081] As shown in Table 1, when Examples 1 to 11 are compared, when only the first additive is added, H in the electrolyte +The first additive effectively neutralizes the electrolyte, thereby preventing deterioration of its acidity and reducing gas generation, but the low-temperature impedance is high and the capacity recovery rate after high-temperature storage is low. This indicates that adding only the first additive can improve the gas generation issue but does not significantly improve the high-temperature and low-temperature performance of the lithium-ion battery. Comparing Examples 1 to 5, when the first additive and lithium difluorobis(oxalato)phosphate are used in combination, as the content of lithium difluorobis(oxalato)phosphate increases, the high-temperature gas generation and low-temperature impedance tend to initially decrease and then increase, and the high-temperature storage capacity recovery rate tends to initially increase and then decrease. Therefore, the content of lithium difluorobis(oxalato)phosphate should be controlled to 0.1 wt% to 3 wt%, with an optimal content being, for example, 0.5 wt% to 1 wt%.

[0082] As shown in Table 1, comparing Examples 3, 6 to 8, when the first additive and lithium difluorobis(oxalato)phosphate are used in combination, as the content of the first additive increases, the high-temperature gas generation and low-temperature impedance tend to initially decrease and then increase, and the high-temperature storage capacity recovery rate initially increases and then decreases. Therefore, the optimal content of the first additive is, for example, 0.1 wt% to 0.5 wt%. This is because the unsaturated bonds in the structure of the first additive are broken down into F, which is generated by the cleavage of PF bonds. - The first additive acts to capture C₈O₁₀, form C₄ covalent bonds, and induce a chain addition reaction on the positive electrode side, improving the stability of the positive electrode interface and thereby improving high-temperature performance. On the other hand, if too much of the first additive is used, the CEI film will become too thick during high-temperature storage, which will be detrimental to the capacity of the lithium-ion battery.

[0083] As shown in Table 1, comparing Examples 1, 3-4, and 9-11, when a first additive with a different structure is selected, by using it in combination with lithium difluorobis(oxalato)phosphate and controlling the content within a reasonable range, it is possible to improve the low-temperature effect of the lithium ion battery while simultaneously achieving high-temperature storage performance and gas generation performance. Furthermore, when the content of a first additive with a different structure is changed, the change tendency is the same, so that the performance of a lithium ion battery can be improved by using a first additive with a different specific structure in combination with lithium difluorobis(oxalato)phosphate.

[0084] As shown in Table 1, comparing Examples 1-11 with Comparative Example 1, it can be seen that when the first additive and lithium difluorobis(oxalato)phosphate are not included in the electrolyte, the high-temperature gas generation, low-temperature impedance, and high-temperature storage capacity recovery rate of the lithium-ion battery are significantly worsened. Comparing Examples 1-11 with Comparative Example 2, it can be seen that when the first additive is not added, on the one hand, lithium difluorobis(oxalato)phosphate does not help to exhibit better low-temperature performance, and on the other hand, the gas generation and high-temperature performance of the lithium-ion battery are also significantly reduced. Comparing Examples 1-11 with Comparative Examples 3 and 4, it can be seen that when the contents of the first additive and lithium difluorobis(oxalato)phosphate are both less than 0.1 wt% or more than 3 wt%, the performance of the lithium-ion battery is also deteriorated. Therefore, it can be seen that controlling the contents of the first additive and lithium difluorobis(oxalato)phosphate within an appropriate range can improve the overall performance of the lithium-ion battery.

[0085] The present invention further provides an electronic device including the above-described lithium ion battery used to supply at least one type of electrical energy. The electronic device includes vehicles, mobile phones, portable devices, laptops, boats, aerospace equipment, electric toys, power tools, etc. In one embodiment of the present invention, the vehicle is, for example, a new energy vehicle, such as a pure electric vehicle, a hybrid vehicle, or a range-extended vehicle. The aerospace equipment includes airplanes, rockets, space shuttles, spacecraft, etc. The electric toys include game consoles, electric car toys, electric boat toys, electric airplane toys, and other stationary or mobile electric toys. The electric tools include metal cutting power tools, grinding power tools, assembly power tools, and railway power tools, such as electric drills, electric grinders, electric wrenches, electric screwdrivers, electric hammers, impact drills, concrete vibrators, and electric planers. Since the electronic device includes the above-described lithium ion battery, it has the advantages of the above-described lithium ion battery, but these will not be described in detail here.

[0086] In summary, the present invention provides an electrolyte for a lithium ion battery, a lithium ion battery, and an electrochemical device. The use of a first additive in combination with lithium difluorobis(oxalato)phosphate can enhance the solubility of lithium difluorobis(oxalato)phosphate through intermolecular interaction. The unsaturated bond in the first additive is converted into F, which is generated by cleavage of the P-F bond. - The H in the electrolyte solution forms a C—F covalent bond, and then a chain addition reaction occurs on the positive electrode side, improving the stability of the positive electrode interface. + This neutralizes the electrolyte, prevents acidification of the electrolyte, reduces gas generation due to decomposition of the non-aqueous solvent, and prevents transition metal ions from leaching from the positive electrode and structural collapse, protecting the transition metal ions in the positive electrode from HF corrosion. The combined use of the first additive and lithium difluorobis(oxalato)phosphate fully exploits the benefits of both additives, improving the quality of the positive electrode-electrolyte interface and the negative electrode-electrolyte interface, effectively reducing the low-temperature impedance of lithium-ion batteries and improving the battery's low-temperature performance, while simultaneously achieving high-temperature performance and gas generation.

[0087] The above description is merely a more preferred embodiment of the present application and merely describes the technical principles used. Those skilled in the art should understand that the scope of the present invention is not limited to the technical solution formed by the specific combination of the above technical features, but also includes other technical solutions formed by any combination of the above technical features or equivalent features, for example, by replacing the above features with technical features having similar functions disclosed in the present application (but not limited to).

[0088] Except for the technical features described in the specification, the remaining technical features are well-known to those skilled in the art, so in order to highlight the innovative features of the present invention, the remaining technical features will not be described in detail here. [Industrial Applicability]

[0089] The lithium ion battery electrolyte, lithium ion battery, and electrochemical device of the present invention can be applied in the field of power battery technology.

Claims

1. An electrolyte for a lithium ion battery, a non-aqueous solvent; A lithium salt, an additive comprising a first additive selected from the compounds represented by formula (I) and a second additive comprising lithium difluorobis(oxalato)phosphate; An electrolyte for a lithium ion battery, comprising at least 【Chemistry 1】 (R １ , R ２ , R ３ , R ４ are each a substituent having 1 to 3 carbon atoms, a degree of unsaturation of 0 to 4, and 0 to 3 heteroatoms. The heteroatom is at least one selected from nitrogen, phosphorus, and sulfur, and n is 0 to 2.

2. R １ , R ２ , R ３ , R ４ and each are an alkyl group, an alkenyl group, an alkynyl group, or an amino group.

3. The content of the first additive in the electrolytic solution is 0.1 wt % to 3 wt %; 2. The electrolyte of claim 1, wherein the content of the second additive in the electrolyte is 0.1 wt% to 3 wt%.

4. The content of the first additive in the electrolyte solution is 0.1 wt % to 0.5 wt %; The content of the second additive in the electrolyte solution is 0.5 wt % to 1 wt %; 2. The electrolyte of claim 1, wherein the mass ratio of the second additive to the first additive is 1.5:1 to 2:

1.

5. The electrolyte solution of a lithium ion battery according to claim 1, wherein the first additive is at least one selected from the group consisting of Compound 1, Compound 2, Compound 3, and Compound 4 below. 【Chemistry 2】

6. the non-aqueous solvent is at least one selected from carbonate esters, carboxylic acid esters, ethers, and nitriles; the carbonate ester is at least one selected from ethylene carbonate, propylene carbonate, dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate; the carboxylic acid ester is at least one selected from ethyl formate, ethyl acetate, propyl acetate, and ethyl propionate; the ether is at least one selected from 1,2-dimethoxyethane and ethylene glycol diethyl ether; the nitrile is at least one selected from acetonitrile, propionitrile, butyronitrile, and valeronitrile; 2. The electrolyte for a lithium ion battery according to claim 1, wherein the content of the non-aqueous solvent in the electrolyte is 70 wt % to 85 wt %.

7. the lithium salt is at least one selected from lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethyl)sulfonylimide, lithium acetate, lithium methylsulfonate, and lithium trifluoromethylsulfonate; 2. The electrolyte solution for a lithium ion battery according to claim 1, wherein the content of the lithium salt in the electrolyte solution is 12 wt % to 16 wt %.

8. A lithium-ion battery, A positive electrode sheet; A negative electrode sheet; An electrolyte selected from the electrolytes for lithium ion batteries according to any one of claims 1 to 7; A lithium ion battery comprising at least

9. The positive electrode active material in the positive electrode sheet is Li ｘ [Ni ｙ Co ｚ Mn ｔ M （１－ｙ－ｚ－ｔ） ]O ２－δ wherein M is at least one of Cr, Zr, Ca, Mg, Cu, Ti, Al, Mo, W, and Zn, and 0.9<x<1.1, 0.65≦y<1.0, 0≦z<0.5, 0≦t<0.5, and 0≦δ≦0.1; 9. The lithium ion battery according to claim 8, wherein the negative electrode active material in the negative electrode sheet includes at least one of graphite, a silicon oxide material, and a silicon carbon material.

10. 9. An electrochemical device comprising the lithium ion battery according to claim 8.

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