Electrolyte for lithium ion battery and application thereof

Abstract

To provide an electrolyte for a lithium ion battery and its application.SOLUTION: The electrolytic solution for a lithium ion battery contains at least a nonaqueous solvent, a lithium salt, and an additive containing a substance represented by the following general formula (I) as components. In the formula (I), R1, R2, and R3 are substituents each having a carbon atom number of 1 to 6, an unsaturation degree of 0 to 4, and a hetero atom number of 0 to 3, the hetero atom is at least one selected from the group consisting of N and O, n is 0 to 2, the content of the additive in the electrolytic solution is 0.05 to 3wt%, the electrolytic solution further comprises hydrogen fluoride, and the content of the hydrogen fluoride is 30 to 200ppm. The electrolyte for a lithium ion battery of the present invention and the application thereof can improve the high-temperature performance of the battery and effectively suppress the increase of acidity.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to the technical field of power batteries, and more particularly to an electrolyte for lithium ion batteries and its applications. [Background technology]

[0002] The total number of electric vehicles sold worldwide is increasing dramatically, and it is expected that electric vehicles will account for more than 30% of total vehicle sales by 2030. Accordingly, the demand for automotive lithium-ion batteries will be nearly 10 times the current global demand for electric vehicle battery capacity, and it is predicted that 89% of battery demand will come from electric vehicles by 2030. The direction of lithium-ion battery research and development will undoubtedly be influenced by the performance requirements of electric vehicles.

[0003] The main factors hindering the rapid commercialization of electric vehicles are the relatively high vehicle price and the short driving distance per charge. The bottlenecks are the high cost and insufficient energy density of electric vehicle battery packs. Currently, the energy density of lithium-ion batteries for electric vehicles needs to be further improved. To achieve a high energy density performance index, attention needs to be paid to the energy density and cost of nickel-based layered oxide cathode active materials. The industry trend is LiNi 1‐x‐y Mn x Co y The goal is to increase the nickel content of O2(NMC) to improve energy density. However, high-nickel layered oxide cathode active materials usually suffer from lattice and surface instability issues, resulting in reduced battery life. Although many dopants have been proven to effectively mitigate these adverse effects, different dopants have limited potential for improving the high-temperature performance of battery cells. Summary of the Invention [Problem to be solved by the invention]

[0004] The present invention provides an electrolyte for a lithium-ion battery and its applications, which can effectively suppress an increase in acidity, and the additive forms a dense CEI film at the interface, capturing dissolved transition metal ions at the interface and preventing the transition metal ions from diffusing to the negative electrode and causing an internal short circuit due to reduction, thereby improving the safety performance of the battery and improving the performance of the lithium-ion battery under high temperature conditions. [Means for solving the problem]

[0005] In order to solve the above technical problems, the present invention provides: a non-aqueous solvent; A lithium salt, an additive containing a substance represented by the following general formula (I); The present invention provides an electrolyte solution for a lithium ion battery, which contains at least the following as a component: [ka] In formula (I), R1, R2, and R3 each represent a substituent having 1 to 6 carbon atoms, a degree of unsaturation of 0 to 4, and 0 to 3 heteroatoms, the heteroatom being at least one selected from nitrogen and oxygen, n is 0 to 2, and the content of the additive in the electrolytic solution is 0.05 to 3 wt %; The electrolytic solution further contains hydrogen fluoride, and the content of the hydrogen fluoride is 30 to 200 ppm.

[0006] In one embodiment of the present invention, R1, R2 and R3 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 additive in the electrolyte is 0.1 to 0.5 wt %.

[0008] In one embodiment of the present invention, the substance represented by the general formula (I) includes at least one of the compounds represented by the following Compound 1, Compound 2, Compound 3, and Compound 4. [ka]

[0009] In one embodiment of the present invention, the non-aqueous solvent is at least one selected from a carbonate, a carboxylate, an ether, and a nitrile, the carbonate is at least one selected from ethylene carbonate, propylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, and fluoroethylene carbonate, the carboxylate is at least one selected from ethyl formate, ethyl acetate, propyl acetate, and ethyl propionate, the ether is at least one selected from ethylene glycol dimethyl ether and diethanol diethyl ether, and the nitrile is at least one selected from acetonitrile, propionitrile, butyronitrile, and valeronitrile, and the content of the non-aqueous solvent in the electrolyte is 70 to 85 wt %.

[0010] 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 methanesulfonate, and lithium trifluoromethylsulfonate, and the content of the lithium salt in the electrolyte solution is 12 to 16 wt %.

[0011] The present invention further provides a lithium ion battery containing the above-mentioned electrolyte solution for lithium ion batteries.

[0012] In one embodiment of the present invention, the positive electrode active material of the lithium ion battery is Li x [Ni y Co z Mn t M (1‐y‐z‐t) ]O 2‐δM is at least one selected from Cr, Zr, Ca, Mg, Cu, Ti, Al, Mo, W and Zn, and <x<1.1、0.65≦y<1.0,0≦z<0.5,0≦t<0.5,0≦δ≦0.1である。

[0013] The present invention further provides an electrochemical device comprising the above-described lithium ion battery. [Effects of the Invention]

[0014] In summary, the present invention provides an electrolyte for lithium ion batteries and its applications. By adding a compound having a specific structure containing both an unsaturated bond and a nitrogen atom to the electrolyte, protons H + The additive generates acid-base neutralization and forms a Lewis acid-base pair, effectively suppressing the increase in acidity and preventing the substitution of transition metal ions in the positive electrode active material. The additive contains electron-rich unsaturated bonds, which enable it to form an extremely dense CEI film at the interface, capturing dissolved transition metal ions at the interface and preventing them from diffusing to the negative electrode and causing internal short circuits due to reduction, thereby improving battery safety. It also suppresses the generation of HF in batteries under high-temperature operating conditions, alleviating gas generation issues and improving the performance of lithium-ion batteries under high-temperature conditions. DETAILED DESCRIPTION OF THE INVENTION

[0015] The following describes the implementation of the present invention through specific specific examples. Those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific implementation methods. Various changes or modifications can be made to the details of this specification based on different perspectives and applications without departing from the spirit of the present invention.

[0016] It is understood that the present invention may be embodied in many different forms and should not be construed as limited to the examples set forth herein. Rather, these examples 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.

[0017] The technical solutions of the present invention will be described in more detail below in combination with examples. It is obvious that the described examples are only a part, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without expending creative efforts fall within the protection scope of the present invention.

[0018] 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 soft-pack battery, a prismatic battery, or a cylindrical battery. The present invention does not limit the type of lithium-ion battery. A specific embodiment of the present invention will be described below using a prismatic battery as an example. In one embodiment of the present invention, the lithium-ion battery includes a casing and a bare cell disposed within the casing. The bare cell includes a positive electrode sheet, a separator, and a negative electrode sheet. The positive electrode sheet, separator, and negative electrode sheet are stacked in this order to ensure that the separator is evenly positioned between the positive electrode sheet and the negative electrode sheet. The multilayer stack is obtained by winding or stacking, and is then assembled into a battery casing as a bare cell. Finally, an electrolyte is injected into the casing one or more times to completely immerse the bare cell in the electrolyte.

[0019] In one embodiment of the present invention, 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. Among them, the positive electrode current collector is, for example, a foil material formed after surface treatment of nickel, titanium, aluminum, silver, stainless steel, carbon, or the like. In addition to the foil material, the positive electrode current collector may adopt the use of one or a combination of a plurality of various forms such as film, mesh, porous, foam, non-woven fabric, etc. Among them, 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.

[0020] In one embodiment of the present invention, the positive electrode active material layer includes a positive electrode active material, an adhesive, a conductive agent, and the like. Among them, a layered oxide with high energy density may be selected as the positive electrode active material. In one embodiment of the present invention, the positive electrode active material is, for example, Li x [Ni y Co z Mn t M (1-y-z-t) O 2-δ where M is at least one selected from Cr, Zr, Ca, Mg, Cu, Ti, Al, Mo, W, Zn, etc., 0.9 < x < 1.1, 0.65 ≤ y < 1.0, 0 ≤ z < 0.5, 0 ≤ t < 0.5, 0 ≤ δ ≤ 0.1, which improves the energy density and cycle life of the battery. The adhesive is, for example, one or more arbitrarily selected from polyvinylidene fluoride (PVDF), polyethylene oxide (PEO), polyamide (PA), polyacrylonitrile (PAN), polyacrylate, polyvinyl ether, polymethyl methacrylate (PMMA), ethylene-propylene-diene terpolymer (EPDM), polyhexafluoropropylene, and styrene-butadiene rubber (SBR), etc. The conductive agent is, for example, one or more arbitrarily selected from conductive carbon black (Super P), acetylene black, carbon nanotubes, graphene, etc.

[0021] In one embodiment of the present invention, the positive electrode active material is, for example, LiNi 0.9 Mn 0.05 Co 0.05It is O2. The adhesive is selected from, for example, polyvinylidene fluoride. The conductive agent is selected from, for example, conductive carbon black. The positive electrode active material, the conductive agent, and the adhesive are mixed, for example, in a mass ratio of (90 to 98):(1 to 5):(1 to 5), and then an organic solvent is added and stirred with a vacuum mixer until the system becomes uniform to obtain a positive electrode slurry. Among them, the organic solvent is selected from, for example, N-methylpyrrolidone (NMP). The positive electrode slurry is uniformly coated on an aluminum foil, and then air-dried at room temperature and then transferred to an oven for drying, and a positive electrode sheet is obtained through processes such as cold pressing and slitting. In other embodiments, the positive electrode sheet may be obtained by selecting any other positive electrode sheet forming method.

[0022] In one embodiment of the present invention, the negative electrode sheet includes, for example, a negative electrode current collector and a negative electrode active material layer coated on at least one surface of the negative electrode current collector. The negative electrode current collector is selected from, for example, one of a copper foil current collector, a composite copper foil current collector, a carbon current collector, a foamed copper current collector, or 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 selected from, for example, copper foil, and the thickness of the copper foil is, for example, 13 μm.

[0023] In one embodiment of the present invention, the negative electrode active material layer includes a negative electrode active material, a conductive agent, an adhesive, a thickener, etc. Among them, the negative electrode active material is a compound capable of inserting and desorbing lithium ions. In one embodiment of the present invention, the negative electrode active material includes, for example, at least one of graphite, a silicon material (SiOx, 0 < x < 2), or a silicon carbon material. The adhesive is arbitrarily selected from one or more of polyvinylidene fluoride, polyethylene oxide, polyamide, polyacrylonitrile, polyacrylate, polyvinyl ether, polymethyl methacrylate, polyhexafluoropropylene, styrene butadiene rubber, etc. The thickener is, for example, sodium carboxymethyl cellulose (CMC-Na), etc. The conductive agent is selected from, for example, one or more of conductive carbon black, acetylene black, ketjen black, carbon nanotubes, graphene, etc.

[0024] In one embodiment of the present invention, the negative electrode active material is selected from graphite and a silicon carbon material, and the mass ratio of the silicon carbon material to the graphite is, for example, 5:95 to 10:90. The conductive agent is selected from conductive carbon black. The thickener is selected from sodium carboxymethyl cellulose. The adhesive is selected from styrene butadiene rubber. In one embodiment of the present invention, the negative electrode active material, conductive agent, adhesive, and thickener are mixed in a mass ratio of, for example, (90-96):(1-2):(1-3):(2-5), and deionized water is added and the mixture is uniformly stirred in a vacuum mixer to obtain a negative electrode slurry. The negative electrode slurry is uniformly coated on a copper foil, dried in the shade at room temperature, transferred to an oven, and then subjected to processes such as cold pressing and slitting to obtain a negative electrode sheet. In other embodiments, the negative electrode sheet may be obtained by any other negative electrode sheet formation method.

[0025] In one embodiment of the present invention, the separator is, for example, polyethylene (PE), polypropylene (PP), a glass fiber film, or a composite film, and the thickness of the separator is, for example, 9 μm to 15 μm.

[0026] In one embodiment of the present invention, the lithium-ion battery further includes an electrolyte solution injected and filling the entire internal space of the battery, with the positive electrode sheet, separator, and negative electrode sheet completely immersed in the electrolyte solution. The electrolyte solution functions to conduct ions, provide ion channels, maintain chemical stability, etc. The components of the electrolyte solution can be divided into non-aqueous solvents, lithium salts, and additives, 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 supply lithium ions and form ion channels. In the entire electrochemical system of a battery, power is generated by the directional movement of lithium ions and electrons. Lithium salts have a significant impact on the energy density, power density, wide electrochemical window, cycle life, and safety performance of lithium batteries. Additives are substances added in small amounts to the electrolyte solution, and there are many types, each with different functions. For example, they can bring different improvements to the battery's high- and low-temperature performance, cycle performance, and membrane formation performance.

[0027] The present invention provides an electrolyte solution for a lithium ion battery, which contains at least a non-aqueous solvent, a lithium salt, an additive, and the like, wherein the additive contains a substance represented by formula (I). [ka] Here, R1, R2, and R3 are substituents having 1 to 6 carbon atoms, a degree of unsaturation of 0 to 4, and 0 to 3 heteroatoms, where the heteroatom is, for example, at least one of nitrogen and oxygen, and n is, for example, 0 to 2. In a specific embodiment of the present invention, R1, R2, and R3 are each a substituent such as alkyl, alkenyl, alkynyl, or amino. In an acidic environment, proton hydrogen replaces the transition metal ion in the positive electrode active material, promoting the transition metal ion to dissolve from the positive electrode structure. The dissolved transition metal ion further destroys the cathode-electrolyte interface (CEI) of the battery. After the additive having the structure of formula (I) is added, the nitrogen atom in the additive acts as a Lewis base, and due to the presence of a lone electron pair, proton H +The additive undergoes acid-base neutralization with the additive to form a Lewis acid-base pair, thereby effectively suppressing the increase in acidity and preventing the replacement of transition metal ions in the positive electrode active material. Even if a small amount of transition metal ions leach out of the positive electrode structure, the additive contains unsaturated bonds, and due to the electron-rich nature of the unsaturated bonds, the additive forms a very dense CEI film at the interface, capturing the transition metal ions at the interface, thus achieving a comprehensive effect of improving the high-temperature performance of the battery and suppressing the increase in acidity.

[0028] In one embodiment of the present invention, the substance represented by general formula (I) includes at least one of compounds represented by, for example, Compound 1, Compound 2, Compound 3, and Compound 4. [ka]

[0029] The additives provided by the present invention allow H + This can react with the transition metal ions, trapping any transition metal ions that may escape, preventing the elution of the transition metal ions from the positive electrode, and preventing the transition metal ions from diffusing to the negative electrode and being reduced, thereby improving the safety performance of the battery.

[0030] In one embodiment of the present invention, the additive content in the electrolyte is, for example, 0.05 to 3 wt %, or, for example, 0.1 to 0.5 wt %, including the endpoints. If the additive content is low, its neutralizing ability is insufficient and the performance of the lithium-ion battery is not improved. If the additive content is high, an excessive amount of additive is likely to act as a nucleophilic attacking agent, causing ring-opening polymerization with cyclic substances in the system, such as ethylene carbonate or fluoroethylene carbonate in the non-aqueous solvent, resulting in excessive consumption of the non-aqueous solvent and degrading the battery's dynamics and high-temperature performance. Therefore, controlling the additive content ensures improved lithium-ion battery performance.

[0031] 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 (LiTFSI), lithium acetate, lithium methanesulfonate, and lithium trifluoromethanesulfonate (CFSOLi). The content of the lithium salt in the electrolyte is, for example, 12 to 16 wt%. The present invention does not limit the type of lithium salt, and a single lithium salt or a mixed lithium salt may be used.

[0032] 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. The carbonate ester is at least one selected from, for example, ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), and fluoroethylene carbonate (FEC). The carboxylic acid ester is at least one selected from, for example, ethyl formate (EF), ethyl acetate (EA), propyl acetate (PA), and ethyl propionate (EP). The ether is at least one selected from, for example, 1,2-dimethoxyethane (DME), ethylene glycol diethyl ether, and the like. The nitrile is at least one selected from, for example, 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 and ethyl methyl carbonate. In one specific embodiment of the present invention, the non-aqueous solvent is, for example, a mixture of ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate.

[0033] In one embodiment of the present invention, when preparing the electrolyte, the content of a stable gas such as nitrogen gas or argon in the glove box is 99.999%. When the actual oxygen content in the glove box is 0.1 ppm or less and the water content is 0.1 ppm or less, the non-aqueous solvent is uniformly mixed according to the mass ratio, and then the lithium salt is added to the non-aqueous solvent after being thoroughly dried, and additives are added to prepare the non-aqueous electrolyte for the lithium ion battery. The content of the lithium salt and additives other than the non-aqueous solvent is calculated as a weight percent based on the total weight of the electrolyte.

[0034] In one embodiment of the present invention, hydrogen fluoride is contained in the electrolyte due to factors such as impurities present in raw materials during the production process of the electrolyte, for example, the presence of hydrogen-containing impurities. The initial hydrogen fluoride content in the initial electrolyte is, for example, 5 to 50 ppm. In one embodiment of the present invention, the impurities are, for example, derived from the non-aqueous solvent, and the impurities are at least one of ethylene glycol, ethylene oxide, and glyoxal. In this embodiment, the type and content of the impurities in the electrolyte are measured, for example, by a gas chromatograph mass spectrometer (GC-MS) or other device. By adding the additive to the electrolyte, after a battery containing the electrolyte is cycled at 45°C a predetermined number of times, the hydrogen fluoride content in the electrolyte is, for example, 30 to 200 ppm, and the predetermined number of times is, for example, 10 to 50 times. The addition of an additive having a specific structure of formula (I) can suppress the generation of HF in the battery under high-temperature operating conditions, alleviate the gas generation problem, and improve the performance of lithium-ion batteries under high-temperature environments.

[0035] In one embodiment of the present invention, the positive electrode sheet, separator, and negative electrode sheet are arranged in this order. The separator, located between the positive electrode sheet and the negative electrode sheet, acts as an insulator. A bare cell is obtained by winding or stacking. The bare cell is placed in a casing, dried in a vacuum oven, and sealed after the electrolyte prepared in the present invention is poured in. A lithium-ion secondary battery is obtained by at least the following steps: leaving it, chemical formation, and capacity separation.

[0036] The present invention will be further explained in detail below by introducing examples. These examples should not be understood as limiting the present invention. Appropriate modifications can be made within the scope consistent with the spirit of the present invention, and they are equally included in the technical scope of the present invention.

[0037] Example 1 Preparation of electrolyte: 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, ethyl methyl carbonate, and dimethyl carbonate were uniformly mixed in a mass ratio of 3:5:2 to obtain a mixed solvent. Dried lithium hexafluorophosphate and compound 4 were then added to the mixed solvent and mixed uniformly to obtain an electrolyte. The resulting electrolyte contained 12 wt% lithium salt and 0.05 wt% compound 4. The impurity in the electrolyte was ethylene glycol, and the initial ethylene glycol content was 5 ppm.

[0038] 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 in a vacuum mixer until the system was homogeneous, yielding a positive electrode slurry. The positive electrode slurry was evenly applied to aluminum foil, dried in the shade at room temperature, then transferred to an oven for drying, and subjected to processes such as cold pressing and slitting to obtain a positive electrode sheet.

[0039] Negative electrode sheet preparation: The negative electrode active material, conductive carbon black, sodium carboxymethyl cellulose, 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 carbon material and graphite, with a mass ratio of silicon carbon material to graphite of 6:94. Deionized water was added and the mixture was uniformly mixed in a vacuum mixer to obtain negative electrode slurry. The negative electrode slurry was evenly applied to copper foil, dried in the shade at room temperature, then transferred to an oven for drying. The negative electrode sheet was obtained through processes such as cold pressing and slitting.

[0040] Separator selection: 12 μm polyethylene film was selected as the separator.

[0041] Battery preparation: The positive electrode sheet, separator, and negative electrode sheet were stacked in this order. The separator located between the positive electrode sheet and the negative electrode sheet served as an insulator, and the sheets were stacked to obtain a bare cell. The cell was then placed in a casing and dried in a vacuum oven. The electrolyte obtained above was then poured into the casing, which was then sealed. The electrolyte was then converted to form a lithium-ion secondary battery.

[0042] Example 2 The additive was changed to Compound 2, and other steps were the same as in Example 1.

[0043] Example 3 The additive was changed to Compound 1, and the content of Compound 1 was 3 wt %. The impurity was ethylene glycol, and the initial amount of ethylene glycol was 50 ppm. The other steps were consistent with Example 1.

[0044] Example 4 The additive was changed to Compound 2, and the content of Compound 2 was 3 wt%, the impurity was ethylene glycol, and the initial amount of ethylene glycol was 50 ppm. The other steps were consistent with Example 1.

[0045] Example 5 The additive was changed to Compound 2, and the content of Compound 2 was 0.3 wt%, the impurity was ethylene oxide, and the initial amount of ethylene oxide was 20 ppm, and the other steps were consistent with Example 1.

[0046] Example 6 The additive was changed to Compound 2, and the content of Compound 2 was 0.3 wt%, the impurity was ethylene glycol, and the initial amount of ethylene glycol was 20 ppm. The other steps were consistent with Example 1.

[0047] Example 7 The additive was changed to Compound 2, and the content of Compound 2 was 0.1 wt%, the impurity substance was glyoxal, and the initial amount of glyoxal was 20 ppm. The other steps were consistent with Example 1.

[0048] Example 8 The additive was changed to Compound 2, and the content of Compound 2 was 0.5 wt%, the impurity substance was glyoxal, and the initial amount of glyoxal was 20 ppm. The other steps were consistent with Example 1.

[0049] Example 9 The additive was changed to Compound 2, and the content of Compound 2 was 1 wt%, the impurity substance was glyoxal, and the initial amount of glyoxal was 20 ppm, and the other steps were consistent with Example 1.

[0050] Example 10 The additive was changed to Compound 2, and the content of Compound 2 was 2 wt%, the impurity substance was glyoxal, and the initial amount of glyoxal was 20 ppm, and the other steps were consistent with Example 1.

[0051] Comparative Example 1 No additives were added, and other steps were consistent with Example 1.

[0052] Comparative Example 2 The additive was changed to Compound 2, and the impurity was ethylene glycol. The initial amount of ethylene glycol was 200 ppm, and the other steps were the same as in Example 1.

[0053] Comparative Example 3 The additive was changed to Compound 2, and the content of Compound 2 was 8 wt%, and other steps were consistent with Example 1.

[0054] Comparative Example 4 The additive was changed to the following compound 5, and the content of compound 5 was 0.3 wt%, the impurity was ethylene glycol, and the initial amount of ethylene glycol was 20 ppm, and the other steps were the same as in Example 1. [ka]

[0055] Comparative Example 5 The additive was changed to the following compound 6, and the content of compound 6 was 0.3 wt%, the impurity was ethylene glycol, and the initial amount of ethylene glycol was 20 ppm. The other steps were the same as in Example 1. [ka]

[0056] In the present invention, lithium ion batteries were prepared using different electrolyte distribution ratios in Examples 1 to 10 and Comparative Examples 1 to 5, and the performance of each lithium ion secondary battery was measured. The measurement results are shown in Table 1.

[0057] In one embodiment of the present invention, the high-temperature storage test was performed by adjusting the thermostat temperature to 25°C and placing the battery in the thermostat for two hours. The battery was charged at a constant current of 0.33C to 4.25V, then charged at a constant voltage to 0.05C, and left for 30 minutes. After two cycles, the initial battery capacity C0 was recorded. The thermostat temperature was adjusted to 60°C, left for 30 minutes, and then stored for one month (referred to as 1M in Table 1 below). The battery was charged at a constant current of 0.33C to 4.25V, then charged at a constant voltage to 0.05C, and left for 30 minutes. After two cycles, the battery capacity C1 was recorded again. Capacity recovery rate = C1 / C0 × 100%.

[0058] In one embodiment of the present invention, the HF content test after cycling was performed by adjusting the thermostat temperature to 45°C, placing the battery in the thermostat for 30 minutes, charging it at a constant current of 1C to 4.25V, and then charging it at a constant voltage of 0.05C. After leaving it for 10 minutes, the battery was discharged at a constant current of 1C to 2.5V. This charge-discharge cycle was repeated 10 times, after which the battery was removed, discharged, and disassembled to measure the HF content in the electrolyte. After cycling, if there was residual electrolyte, the electrolyte in the battery was directly removed. If there was no residual electrolyte, the battery cell was protected with aluminum plastic film and removed using a large press (≥10 MPa). The hydrogen fluoride content was tested using triethylamine titration, using bromomethylphenol blue as an indicator during the test.

[0059] Table 1: Performance test results of lithium ion batteries of Examples 1 to 10 and Comparative Examples 1 to 5 [Table 1]

[0060] As shown in Table 1, a comparison of Examples 1-10 and Comparative Examples 1-2 reveals that adding the additive provided by the present invention to the electrolyte can reduce the HF content of lithium-ion batteries after high-temperature cycling and improve the high-temperature storage capacity recovery rate of lithium-ion batteries, indicating that the additive has excellent acid inhibition ability and improves the high-temperature performance of lithium-ion batteries. A comparison of Examples 1-4 reveals that the performance of lithium-ion batteries can be improved by selecting different additives, and Compound 2 has a better acidity inhibition effect and a better storage capacity recovery rate than Compounds 1 and 4. The addition of a compound with a specific structure containing an unsaturated bond and a nitrogen atom to the electrolyte forms a complex with the transition metal ions in the positive electrode, neutralizing the system and reducing H + The additives can produce hydroxybenzoates, inhibit the increase in acidity, and improve high-temperature performance, but additives with different structures have different effects on improving performance.

[0061] Comparing Examples 5 to 7 with Table 1 reveals that even when the acidity of the electrolyte is caused by different factors, excellent acid suppression and good storage capacity recovery performance are possible as long as the additive amount of Compound 2 is appropriately controlled. Comparative Examples 7 to 10 reveal that when the additive content is in the range of 0.05 to 3 wt%, as the additive content increases, the HF content decreases first after cycling and then increases, and storage capacity recovery increases first and then decreases. The optimal additive content range is 0.1 to 0.5 wt%. Therefore, the additive content can be controlled to optimize the overall performance of the lithium-ion battery.

[0062] Comparing Comparative Examples 1 to 3 with Table 1, we found that excessively high initial amounts of additive and HF resulted in poor battery storage capacity recovery. Without the addition of compounds such as Compound 2, acidity rapidly increased after cycling. Adding excessive amounts of Compound 2 had a certain inhibitory effect on the increase in acidity, but the overall effect was not significant. This indicates that optimizing the performance of lithium-ion batteries requires controlling the initial amounts of additive and HF in the electrolyte. Comparing Example 6 with Comparative Examples 4 and 5, we found that additives containing only nitrogen atoms only inhibit the increase in acidity and do not provide any benefit to the performance of the battery cell. Additives containing only unsaturated bonds not only fail to inhibit the increase in acidity, but also cause a decrease in electrical performance due to the increased acidity. Therefore, only additives containing a specific structure containing both unsaturated bonds and nitrogen atoms can inhibit the increase in acidity and improve high-temperature storage performance.

[0063] The present invention also provides an electronic device. The electronic device includes at least one of the above-described lithium ion secondary batteries, which are used to provide electrical energy. The electronic device may be a vehicle, a mobile phone, a portable device, a notebook computer, a boat, an airplane, an electric toy, or an electric tool. In one embodiment of the present invention, the vehicle may be, for example, a new energy vehicle, which may be an electric vehicle, a hybrid vehicle, or an extended-range vehicle. The airplane may include an airplane, a rocket, a space shuttle, a spaceship, or the like. The electric toy may include a stationary or mobile electric toy, such as a game console, an electric car toy, an electric boat toy, or an electric airplane toy. The electric tool may include a metal cutting power tool, a grinding power tool, an assembly power tool, or a railway power tool, such as an electric drill, an electric grinder, an electric wrench, an electric screwdriver, an electric hammer, an impact drill, a concrete vibrator, an electric plane, or the like. The electronic device includes the above-described lithium ion secondary battery and thus includes the advantages of the above-described lithium ion secondary battery, but these will not be described in detail again here.

[0064] In summary, the present invention provides an electrolyte for lithium ion batteries and its applications. By adding a compound having a specific structure containing both an unsaturated bond and a nitrogen atom to the electrolyte, protons H + The additive generates acid-base neutralization and forms a Lewis acid-base pair, effectively suppressing the increase in acidity and preventing the substitution of transition metal ions in the positive electrode active material. The additive contains electron-rich unsaturated bonds, allowing it to form an extremely dense CEI film at the interface, capturing leached transition metal ions at the interface, achieving the combined effect of improving the battery's high-temperature performance and preventing the increase in acidity. It also suppresses the generation of HF in the battery under high-temperature operating conditions, alleviating gas generation issues and improving the performance of lithium-ion batteries under high-temperature conditions. It also prevents the leaching of transition metal ions from the positive electrode and prevents the transition metal ions from diffusing to the negative electrode, which can cause internal short circuits due to reduction, thereby improving the safety performance of the battery.

[0065] The above description is merely a description of the preferred embodiments of the present invention and the technical principles utilized. Those skilled in the art will understand that the scope of the present invention is not limited to the technical solution consisting of the specific combination of the above-mentioned technical features, but also encompasses other technical solutions formed by any combination of the above-mentioned technical features or their equivalent features without departing from the spirit of the present invention, for example, by replacing the above-mentioned features with (but not limited to) technical features having similar functions disclosed in the present invention.

[0066] Except for the technical features described in this specification, the remaining technical features are well known to those skilled in the art, and in order to highlight the innovative features of the present invention, the remaining technical features will not be described in detail again here. [Industrial Applicability]

[0067] The electrolyte for lithium ion batteries and its applications of the present invention can be applied to the technical field of power batteries.

Claims

1. a non-aqueous solvent; A lithium salt, an additive containing a substance represented by the following general formula (I); An electrolyte for a lithium ion battery, comprising at least the following as a component: 【Chemistry 1】 In formula (I), R １ , R ２ and R ３ are each a substituent having 1 to 6 carbon atoms, a degree of unsaturation of 0 to 4, and a number of heteroatoms of 0 to 3, the heteroatom being at least one selected from nitrogen and oxygen, n is 0 to 2, the content of the additive in the lithium ion battery electrolyte is 0.05 to 3 wt %, The lithium ion battery electrolyte further contains hydrogen fluoride, and the content of the hydrogen fluoride is 30 to 200 ppm.

2. R １ , R ２ and R ３ 2. The electrolyte for a lithium ion battery according to claim 1, wherein each of the groups is an alkyl group, an alkenyl group, an alkynyl group, or an amino group.

3. 2. The lithium ion battery electrolyte according to claim 1, wherein the content of the additive in the lithium ion battery electrolyte is 0.1 to 0.5 wt %.

4. 2. The electrolyte solution for a lithium ion battery according to claim 1, wherein the substance represented by the general formula (I) contains at least one of compounds represented by the following compounds 1, 2, 3, and 4: 【Chemistry 2】

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

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

7. A lithium ion battery comprising the electrolyte solution for lithium ion batteries according to any one of claims 1 to 6.

8. The positive electrode active material of the lithium ion battery is Li ｘ [Ni ｙ Co ｚ Mn ｔ M （１‐ｙ‐ｚ‐ｔ） ]O ２‐δ 8. The lithium ion battery according to claim 7, wherein M is at least one selected from 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, 0≦δ≦0.

1.

9. An electrochemical device comprising the lithium ion battery of claim 7.

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