Electrolyte for lithium ion secondary battery and application thereof

Abstract

To provide an electrolyte for a lithium ion secondary battery and its application.SOLUTION: The electrolyte solution contains a nonaqueous solvent, a lithium salt, and an additive. The additive is a specific compound containing a nitrogen atom, and examples thereof include pyrimidine and 2, 6-difluoropyridine.EFFECT: The provided electrolyte for a lithium ion secondary battery and the application thereof can prevent the dissolution of transition metal ions on the positive electrode side, improve the problems of initial dynamics and gas generation, and improve the performance of the lithium ion secondary battery.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 secondary batteries and its applications. [Background technology]

[0002] With the ever-expanding demand for electric vehicles and portable devices, the development of lithium-ion secondary batteries is also progressing rapidly. In commercially available lithium-ion secondary batteries, the cathode material accounts for more than 50% of the total mass and cost, and is a key factor in determining the energy density and cost of the battery.

[0003] Among various cathode materials, high-nickel cathode materials have the potential to achieve high energy density, are maturely developed, and offer considerable cycle life. However, due to issues such as the decomposition of lithium-related compounds within the battery, side reactions occurring in the acidic environment of the battery case and system, oxidation reactions between the electrolyte and the high-nickel cathode, and the leaching of transition metal ions from the cathode material, high-nickel cathode materials suffer from serious gas generation. Gas accumulation can lead to battery swelling, mechanical failure of the battery case, and even battery explosion, posing a certain degree of hidden risk to safety performance. To address the high-temperature gas generation issue in high-nickel cathode materials, coating the material or adding cathode film-forming additives, transition metal ion scavengers, or stabilizers have been primarily employed. However, these methods still suffer from issues such as poor energy density, initial dynamics, and performance of the battery system. Summary of the Invention [Problem to be solved by the invention]

[0004] The present invention provides an electrolyte for a lithium ion secondary battery and its application. The electrolyte for a lithium ion secondary battery provided by the present invention and its application can prevent the elution of transition metal ions from the positive electrode side, prevent the transition metal ions from diffusing to the negative electrode and reducing, which can cause an internal short circuit, and at the same time, improve the initial dynamics and reduce the H generated by the system. + This can neutralize the gas generation problem in lithium ion secondary batteries and improve the performance of lithium ion secondary batteries. [Means for solving the problem]

[0005] In order to solve the above-mentioned technical problems, the present invention provides an electrolyte for a lithium ion secondary battery, which comprises: a non-aqueous solvent; A lithium salt, Additives and Including, The additive comprises a compound represented by any one of formulas (I) to (III), [ka] Here, R1, R2, R3, and R4 are each a substituent having 1 to 3 carbon atoms, 0 to 3 heteroatoms, and a degree of unsaturation of 0 to 4. R5, R6, and R7 are each a substituent having 1 to 3 carbon atoms, 0 to 3 heteroatoms, and a degree of unsaturation of 0 to 4. R8 is a cyclic substituent having 0 to 4 unsaturation, and has 0 to 5 heteroatoms. When the degree of unsaturation of R8 is 0, R9 is a vinyl group, propenyl group, butenyl group, 1,3-butadienyl group, ethynyl group, or propynyl group. When the degree of unsaturation of R8 is 1 to 4, no R9 group substituent is present. The heteroatom is at least one selected from nitrogen, fluorine, and oxygen, 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, a carbonyl group, an ester group, or an amino group, and R5, R6, and R7 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 solution is 0.05 wt % to 3 wt %.

[0008] In one embodiment of the present invention, the content of the additive in the electrolyte solution is 0.1 wt % to 0.5 wt %.

[0009] In one embodiment of the present invention, the additive is at least one selected from the following compounds: [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, diethyl carbonate, or fluoroethylene 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 a content of the non-aqueous solvent in the electrolytic solution 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 methanesulfonate, and lithium trifluoromethanesulfonate, and the content of the lithium salt in the electrolyte solution is 12 wt % to 16 wt %.

[0012] The present invention further provides a lithium-ion secondary battery. The lithium-ion secondary battery includes at least a positive electrode sheet, a negative electrode sheet, and an electrolytic solution and includes the electrolytic solution is selected from the electrolytic solutions for lithium-ion secondary batteries described above.

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

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

Advantages of the Invention

[0015] To sum up, the electrolytic solution for a lithium-ion secondary battery and its application according to the present invention can introduce an unsaturated functional group with excellent lithium-ion conductivity on the positive electrode side, and utilize the ability of the lone pair electrons of nitrogen atoms to bind to the D orbit of the vacancy of transition metal ions after adsorption to capture the transition metal ions that may escape, prevent the elution of transition metal ions on the positive electrode side, prevent the occurrence of internal short circuits caused by the diffusion and reduction of transition metal ions to the negative electrode, and improve the safety performance of the battery. At the same time, it can also improve the initial dynamics and avoid the collapse of the positive electrode due to the overflow of transition metal ions. The H generated by the system +It can neutralize the HF content, reduce the HF content, solve the gas generation problem of lithium ion secondary batteries, improve the performance of lithium ion secondary batteries, and improve the safety of lithium ion secondary batteries. DETAILED DESCRIPTION OF THE INVENTION

[0016] The following describes how the present invention is implemented using certain specific embodiments. 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 using 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.

[0017] It is 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. It is obvious that the described embodiments 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.

[0019] The present invention provides a lithium-ion secondary battery. The lithium-ion secondary 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 particularly limit the type of lithium-ion secondary battery. Here, a specific embodiment of the present invention will be described using a prismatic battery as an example. In one embodiment of the present invention, the lithium-ion secondary 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. To ensure that the separator is evenly positioned between the positive electrode sheet and the negative electrode sheet, the positive electrode sheet, the separator, and the negative electrode sheet are stacked in this order. The bare cell is obtained by winding or stacking, and then inserted into a battery casing. Then, an electrolyte is injected into the casing one or more times to completely immerse 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 after surface treatment of nickel, titanium, aluminum, silver, stainless steel, or carbon. In addition to foil materials, the positive electrode current collector may be in one or a combination of various forms, such as film, mesh, porous, foam, or nonwoven fabric. 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, a conductive material, etc. The positive electrode active material may be a nickel-cobalt-manganese ternary positive electrode active material, such as the positive electrode active material of the chemical formula Li x [Ni y Co z Mn t M (1-y-z-t) ]O 2-δIt may be represented by [formula], where M is one or more 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. Among the substances shown here, when the blending ratio of the nickel content exceeds 0.9, compared with the conventional ternary cathode active material with a nickel content of less than 0.8, the energy density and cycle life of the lithium-ion secondary battery can be further improved. 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, 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. The mass ratio of the cathode active material, conductive agent, and adhesive in the cathode active material layer is, for example, (90 - 98):(1 - 5):(1 - 5).

[0022] In one embodiment of the present invention, the cathode active material is, for example, LiNi 0.9 Mn 0.05 Co 0.05 O2. The adhesive is, for example, polyvinylidene fluoride. The conductive agent is, for example, conductive carbon black. The cathode active material, conductive agent, and adhesive are, for example, mixed at a mass ratio of 98:1:1, then an organic solvent is added, and stirred with a vacuum mixer until the system becomes uniform to obtain a cathode slurry. Among them, the organic solvent is, for example, N-methylpyrrolidone (NMP). The cathode slurry is uniformly coated on an aluminum foil, then air-dried at room temperature and then transferred to an oven for drying, and a cathode sheet is obtained through processes such as cold pressing and slitting. In other embodiments, the cathode sheet may be obtained by selecting any other cathode sheet forming method.

[0023] 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, 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, etc. 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, a copper foil, and the thickness of the copper foil is, for example, 13 μm.

[0024] 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 thickening agent, 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. When the negative electrode active material includes a silicon material or a silicon carbon material, the mass ratio of it to graphite is, for example, 5:95 to 10:90. 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 thickening agent 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. The mass ratio of the negative electrode active material, the conductive agent, the adhesive, and the thickening agent 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, for example, graphite and a silicon carbon material, and the mass ratio of the silicon carbon material to the graphite is, for example, 6:94. The conductive agent is conductive carbon black. The thickener is sodium carboxymethyl cellulose. The adhesive is styrene butadiene rubber. In one embodiment of the present invention, the negative electrode active material, the conductive agent, the adhesive, and the thickener are mixed in a mass ratio of, for example, 96:1:1:2, and deionized water is added. 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 selecting any other negative electrode sheet formation method.

[0026] The separator is, for example, polyethylene (PE), polypropylene (PP), a glass fiber film, a composite film, or the like, and the thickness of the separator is, for example, 9 μm to 15 μm.

[0027] Lithium-ion secondary batteries also contain an electrolyte solution, which is injected and fills the entire internal space of the battery. The positive electrode sheet, separator, and negative electrode sheet are completely immersed in the electrolyte solution. The electrolyte functions to conduct ions, provide ion channels, and maintain chemical stability. Depending on their function and added amount, the components of the electrolyte solution can be divided into nonaqueous solvents, lithium salts, and additives. The nonaqueous solvent dissolves the lithium salt and additives. The lithium salt primarily provides lithium ions to form ion channels. Electric power is generated through the directional movement of lithium ions and electrons in the entire electrochemical system of a battery. 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. There are many types, and each has a different function. For example, they can bring different improvements to the battery's high- and low-temperature performance, cycle performance, and membrane formation performance.

[0028] The present invention provides an electrolyte solution for a lithium ion secondary battery. The electrolyte solution for a lithium ion secondary battery includes at least a non-aqueous solvent, a lithium salt, an additive, etc. The additive includes a compound represented by any one of formulas (I) to (III). [ka] Here, 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. In one embodiment of the present invention, R1, R2, R3, and R4 are each a substituent such as an alkyl group, an alkenyl group, an alkynyl group, a carbonyl group, an ester group, or an amino group. R5, R6, and R7 are each a substituent having 1 to 3 carbon atoms, a degree of unsaturation of 0 to 4, and 0 to 3 heteroatoms. In one embodiment of the present invention, R5, R6, and R7 are each a substituent such as an alkyl group, an alkenyl group, an alkynyl group, or an amino group. R8 is a cyclic substituent having a degree of unsaturation of 0 to 4 and having 0 to 5 heteroatoms. When the degree of unsaturation of R8 is 0, R9 is a vinyl group, a propenyl group, a butenyl group, a 1,3-butadienyl group, an ethynyl group, a propynyl group, or the like. When the degree of unsaturation of R8 is 1 to 4, the R9 group substituent is absent. The heteroatom contained in formulas (I) to (III) is at least one selected from nitrogen, fluorine, and oxygen, and n in formulas (I) to (II) is 0 to 2. In a fully charged state, the activity of the transition metal ions in the positive electrode is high, and the positive electrode structure is H + After being attacked by the ions, the additive disintegrates, and the transition metal ions are easily released from the positive electrode. In addition, the additive contains unsaturated bonds and nitrogen atoms, which can complex the nickel ions in the positive electrode, and the H + This can neutralize the ions and improve the safety of the lithium ion secondary battery.

[0029] In one embodiment of the present invention, the additive is selected from, for example, at least one of Compounds 1 to 5. [ka]

[0030] In one embodiment of the present invention, the molecular weight of the additive is, for example, 200 or less. The additive provided by the present invention uses unsaturated bonds in the additive to preferentially adsorb the additive to the positive electrode side, introducing unsaturated functional groups with excellent lithium ion conductivity to the positive electrode side. After adsorption, the lone pair of electrons in the nitrogen atom can bond with the vacant D orbital of the transition metal ion, capturing potentially escaping transition metal ions and preventing the elution of transition metal ions on the positive electrode side. This prevents the transition metal ions from diffusing to the negative electrode and being reduced, thereby preventing internal short circuits and improving the safety performance of the battery. At the same time, it is also possible to avoid the collapse of the positive electrode due to the overflow of transition metal ions. At the same time, the nitrogen atom in the additive has a lone pair of electrons, which prevents the H generated by the system from being released. + It can neutralize the HF content, reduce the HF content, improve the gas generation problem of lithium ion secondary batteries, and improve the performance of lithium ion secondary batteries.

[0031] In one embodiment of the present invention, the content of the additive in the electrolyte is 0.05 wt% to 3 wt%, inclusive. If the additive content is low, its neutralizing ability is insufficient, and the performance of the lithium-ion secondary battery is not sufficiently improved. If the additive content is high, an excessive amount of the 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 deterioration of the battery's dynamics and high-temperature performance. In one embodiment of the present invention, the content of the additive in the electrolyte is selected to be 0.1 wt% to 0.5 wt%. Within this range, battery performance such as initial energy, accumulation of generated gas at high temperatures, and open-circuit voltage after storage can be simultaneously improved. Therefore, controlling the additive content ensures the overall performance improvement of the lithium-ion secondary battery.

[0032] 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 solution is, for example, 12 wt% to 16 wt%. In one embodiment of the present invention, the lithium salt is 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 14:4.

[0033] 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, nitriles, etc. Among them, the carbonate ester is at least one selected from ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), fluoroethylene carbonate (FEC), etc. The carboxylic acid ester is at least one selected from ethyl formate (EF), ethyl acetate (EA), propyl acetate (PA), ethyl propionate (EP), etc. The ether is at least one selected from 1,2-dimethoxyethane (DME), ethylene glycol diethyl ether, etc. The nitrile is at least one selected from acetonitrile (AN), propionitrile, butyronitrile (BN), valeronitrile (VN), etc. The content of the non-aqueous solvent in the electrolyte solution 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.

[0034] 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 thorough drying, and additives are added to prepare the non-aqueous electrolyte for the lithium ion secondary battery. The content of the lithium salt and additives other than the non-aqueous solvent is expressed in weight percent based on the total weight of the electrolyte.

[0035] In one embodiment of the present invention, the positive electrode sheet, separator, and negative electrode sheet are arranged in this order. The separator positioned 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 through at least steps such as leaving, chemical formation, and capacity separation.

[0036] The present invention will be explained in more 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 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, ethyl methyl carbonate, and dimethyl carbonate were uniformly mixed in a mass ratio of 3:5:2 to obtain a mixed solvent. Then, dried lithium hexafluorophosphate and Compound 1 were added to the mixed solvent and mixed uniformly to obtain an electrolyte solution. The resulting electrolyte solution contained 12 wt% of lithium salt and 0.05 wt% of Compound 1. Preparation of positive electrode sheet: LiNi 0.9 Mn 0.05 Co 0.05O2, 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. 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. Separator selection: 12 μm polyethylene film was selected as the separator. Battery preparation: The positive electrode sheet, separator, and negative electrode sheet were stacked in this order. The separator located between the positive and negative electrode sheets acted as an insulator, and the sheets were stacked to obtain a bare cell. The cell was then placed in a housing and dried in a vacuum oven. After that, the electrolyte obtained above was poured into the housing, sealed, and the electrolyte was converted to form a lithium-ion secondary battery (hereafter referred to as the battery).

[0038] Example 2 The additive was changed to Compound 2, and other steps were the same as in Example 1.

[0039] Example 3 The additive was changed to Compound 4, and the content of Compound 4 was 3 wt%, and other steps were consistent with Example 1.

[0040] Example 4

[0041] The additive was changed to Compound 2, and the content of Compound 2 was 3 wt%, and other steps were consistent with Example 1.

[0042] Example 5 The additive was changed to Compound 2, and the content of Compound 2 was 0.1 wt%, and other steps were consistent with Example 1.

[0043] Example 6 The additive was changed to Compound 2, and the content of Compound 2 was 0.3 wt%, and other steps were consistent with Example 1.

[0044] Example 7 The additive was changed to Compound 2, and the content of Compound 2 was 0.5 wt%, and other steps were consistent with Example 1.

[0045] Example 8 The additive was changed to Compound 2, and the content of Compound 2 was 1 wt%, and other steps were consistent with Example 1.

[0046] Comparative Example 1 No additives were added, and other steps were consistent with Example 1.

[0047] Comparative Example 2 The additive was changed to Compound 2, and the content of Compound 2 was 5 wt%, and other steps were consistent with Example 1.

[0048] Comparative Example 3 The additive was changed to the following compound 6, and the content of compound 6 was 0.3 wt%, and the other steps were the same as in Example 1. [ka]

[0049] Comparative Example 4 The additive was changed to the following compound 7, and the content of compound 7 was 0.3 wt%, and the other steps were the same as in Example 1. [ka]

[0050] In the present invention, lithium ion secondary batteries were prepared using different electrolyte solution distribution ratios in the above-described Examples 1 to 8 and Comparative Examples 1 to 4, and the performance of each lithium ion secondary battery was measured as follows.

[0051] Initial (BOL) DC Resistance (DCR) Test The specific test method for testing direct current resistance (DCR) in the beginning of life (BOL) state was as follows. After adjusting the thermostat temperature to 25°C, the battery was placed in the thermostat and allowed to stand for 10 minutes. The battery was charged at a constant current of 0.33 C to 4.25 V, then charged at a constant voltage of 0.05 C at 4.25 V, allowed to stand for 30 minutes, and then discharged at a constant current of 0.33 C to 2.5 V and allowed to stand for 10 minutes. This charge-discharge cycle was repeated twice, and the discharge capacity of the final cycle was recorded as C0. The battery was then charged at a constant current of 0.33 C to 4.25 V, charged at a constant voltage of 0.05 C, allowed to stand for 30 minutes, and then discharged at a constant current of 0.33 C to 50% C0. The battery was allowed to stand for 1 hour, and the static terminal voltage at this time was recorded as V0. Finally, the battery was discharged again to 50% C0, and then discharged at a constant current of 4 C0 for 30 seconds, and the voltage at this time was recorded as V1. BOL DCR = (V0 - V1) / 4 C0.

[0052] Gas generation test and open circuit voltage test when stored at 60℃ The specific steps for the gas generation test during storage at 60°C were as follows: After adjusting the thermostat temperature to 25°C, the battery was placed in the thermostat and allowed to stand for 2 hours. It was then charged at a constant current of 0.33C to 4.25V, then at a constant voltage of 0.05C, and allowed to stand for 30 minutes. The volume of the battery at this time was measured and recorded as V1. V1 is the volume of the battery when fully charged before storage. The same battery used to obtain V1 was discharged at a constant current of 0.33C to 2.5V. The thermostat temperature was then adjusted to 60°C, allowed to stand for 30 minutes, then charged at a constant current of 0.33C to 4.25V, then at a constant voltage of 0.05C. After storage for 2 months (referred to as 2M in Table 1 below), the measured volume of the battery was recorded as V2. The gas generation volume expansion rate after 2 months of storage can be calculated as (V2 - V1) / V1 × 100%. At the same time as measuring the battery volume, the voltage across the positive and negative electrodes of the battery was recorded as the open circuit voltage (OCV), thereby obtaining the open circuit voltage after storage at 60°C for 2 months.

[0053] [Table 1]

[0054] As can be seen from Table 1 and comparing Examples 1 to 8 with Comparative Example 1, adding the additives provided by the present invention to the electrolyte can improve the initial dynamics of lithium-ion secondary batteries, significantly improving gas generation during high-temperature storage and open-circuit voltage after storage. Comparing Examples 1 to 4, selecting different compounds conforming to the formula of the present invention as additives can uniformly improve the performance of lithium-ion secondary batteries. This is believed to be due to the following reasons. Adding a compound conforming to the formula of the present invention, which contains both an unsaturated bond and a nitrogen atom, to the electrolyte complexes the transition metal ions in the positive electrode and neutralizes the H+ generated by the system, thereby improving the initial dynamics of the battery, gas generation during high-temperature storage, and open-circuit voltage after storage. However, additives with different structures have different performance-improving effects. As shown in Table 1, Compound 2 does not deteriorate the initial dynamics of the battery, and it most significantly improves gas generation during high-temperature storage and open-circuit voltage after storage.

[0055] Referring to Table 1 and comparing Examples 2, 5-8 with Comparative Example 2, when the content of the specific compound in the additive is within the range of 0.05 wt% to 3 wt%, both the initial dynamics and high-temperature storage performance of the battery are improved. With increasing additive content, the DCR of the lithium-ion secondary battery first decreases and then increases, gas generation during high-temperature storage first decreases and then increases, and the high-temperature storage OCV first increases and then decreases. Therefore, controlling the additive content can optimize the overall performance of the lithium-ion secondary battery. When the additive content exceeds 3 wt%, a thick SEI film forms on the negative electrode, resulting in deterioration of lithium-ion secondary battery performance.

[0056] Furthermore, as can be seen from a comparison between Examples 1 to 8 and Comparative Examples 3 and 4, when the compound in the additive has only an unsaturated bond or only a nitrogen atom, no significant improvement in the performance of the lithium ion secondary battery is observed, and it is explained that only when the additive contains a compound with a specific structure that simultaneously contains an unsaturated bond and a nitrogen atom can the performance of the battery, such as initial dynamics, gas generation during high-temperature storage, and open-circuit voltage after storage, be improved.

[0057] 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 is, for example, a new energy vehicle, which may be an electric vehicle, a hybrid vehicle, or an extended-range vehicle. The airplane includes an airplane, a rocket, a space shuttle, a spaceship, or the like. The electric toy includes stationary or mobile electric toys, such as game consoles, electric car toys, electric boat toys, and electric airplane toys. The electric tool includes 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 planes. The electronic device includes the above-described lithium ion secondary battery and thus incorporates the advantages of the above-described lithium ion secondary battery, but these will not be described in detail again here. [Industrial Applicability]

[0058] In summary, the present invention provides an electrolyte for lithium-ion secondary batteries and its applications. By adding a compound with a specific structure containing both an unsaturated bond and a nitrogen atom to the electrolyte, an unsaturated functional group with excellent lithium ion conductivity can be introduced to the positive electrode. After adsorption, the lone electron pair of the nitrogen atom can bond with the vacant D orbital of a transition metal ion, capturing potentially escaping transition metal ions and preventing their elution from the positive electrode. This prevents the transition metal ions from diffusing to the negative electrode and reducing them, thereby preventing internal short circuits and improving the safety performance of the battery. At the same time, the initial dynamics can be improved, preventing the collapse of the positive electrode due to the overflow of transition metal ions. The H generated by the system + This can neutralize the gas generation problem of the lithium ion secondary battery, improve the performance of the lithium ion secondary battery, and improve the safety of the lithium ion secondary battery.

[0059] 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.

[0060] 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.

Claims

1. An electrolyte for a lithium ion secondary battery, the components of which include at least a non-aqueous solvent; A lithium salt, Additives and Including, The additive contains a compound represented by any one of formulas (I) to (III). Electrolyte for lithium-ion secondary batteries, 【Transformation 7】 Here, R １ , R ２ , R ３ , R ４ are each a substituent having 1 to 3 carbon atoms, 0 to 3 heteroatoms, and a degree of unsaturation of 0 to 4, and R ５ , R ６ , R ７ are each a substituent having 1 to 3 carbon atoms, 0 to 3 heteroatoms, and a degree of unsaturation of 0 to 4, and R ８ is a cyclic substituent having a degree of unsaturation of 0 to 4 and having 0 to 5 heteroatoms; R ８ When the degree of unsaturation of R is 0, ９ is a vinyl group, a propenyl group, a butenyl group, a 1,3-butadienyl group, an ethynyl group, or a propynyl group, and R ８ When the degree of unsaturation of R is 1 to 4, ９ is absent, the heteroatom is at least one selected from nitrogen, fluorine and oxygen, and n is 0 to 2.

2. R １ , R ２ , R ３ , R ４ are each an alkyl group, an alkenyl group, an alkynyl group, a carbonyl group, an ester group, or an amino group, and R ５ , R ６ , R ７ are each an alkyl group, an alkenyl group, an alkynyl group, or an amino group. characterized in that The electrolyte solution for a lithium ion secondary battery according to claim 1.

3. The content of the additive in the electrolyte is 0.05 wt % to 3 wt %. characterized in that The electrolyte solution for a lithium ion secondary battery according to claim 1.

4. The content of the additive in the electrolyte is 0.1 wt % to 0.5 wt %. characterized in that The electrolyte solution for a lithium ion secondary battery according to claim 3.

5. The additive is at least one selected from the following compounds: The electrolyte solution for a lithium ion secondary battery according to claim 1 . 【Transformation 8】 。

6. 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, diethyl carbonate, and fluoroethylene 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; The content of the non-aqueous solvent in the electrolyte solution is 70 wt % to 85 wt %. characterized in that The electrolyte solution for a lithium ion secondary battery according to claim 1.

7. 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 trifluoromethanesulfonate; The content of the lithium salt in the electrolyte solution is 12 wt % to 16 wt %. characterized in that The electrolyte solution for a lithium ion secondary battery according to claim 1.

8. A positive electrode sheet; A negative electrode sheet; Electrolyte and At least The electrolyte solution is selected from the electrolyte solutions for lithium ion secondary batteries according to any one of claims 1 to 7. characterized in that Lithium-ion secondary battery.

9. The positive electrode active material on 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, or 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; The negative electrode active material on the negative electrode sheet includes at least one of graphite, a silicon material, or a silicon carbon material. characterized in that The lithium ion secondary battery according to claim 8.

10. The lithium ion secondary battery according to claim 8 or 9 is included. characterized in that Electrochemical equipment.

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