Non-aqueous electrolyte and secondary battery

Abstract

To overcome the problems of insufficient cycle stability and high-temperature performance in existing high-voltage lithium-ion batteries, this invention provides a non-aqueous electrolyte and a secondary battery. The non-aqueous electrolyte comprises a non-aqueous organic solvent, an electrolyte salt, and additives. The additives include the compound shown in structural formula 1, succinic anionylene, the compound shown in structural formula 2, and the compound shown in structural formula 3. The non-aqueous electrolyte of structural formulas 1, 2, and 3 satisfies the following conditions: 0.24 ≤ x / (a+b+c) ≤ 2; and 1 ≤ x ≤ 4, 0.5 ≤ a ≤ 3, 1 ≤ b ≤ 4, and 0.01 ≤ c ≤ 0.2. The non-aqueous electrolyte provided by this invention is suitable for lithium cobalt oxide batteries, and can improve the density and stability of the solid electrolyte film on the positive and negative electrode surfaces, which is beneficial for improving the high-temperature performance and rate performance of the battery.

Description

Technical Field

[0001] This invention belongs to the field of battery material technology, specifically relating to a non-aqueous electrolyte and a secondary battery. Background Technology

[0002] Lithium-ion batteries are currently used in various electronic products, electric vehicles, and energy storage devices due to their irreplaceable advantages, including high operating voltage, long cycle life, high energy density, and environmental friendliness. With the development of the lithium-ion battery industry, higher demands are being placed on lithium-ion batteries: they need to be thinner, lighter, smaller, and have higher energy density. Increasing the charging cut-off voltage is one of the effective methods to improve the energy density of lithium-ion batteries.

[0003] Theoretically, increasing the charging cutoff voltage from 4.3 V to 4.7 V can increase battery capacity by 15% to 35%. However, as the voltage of commercially available lithium-ion batteries further increases to above 4.5 V, their high-temperature cycle performance and high-temperature storage performance face increasing challenges. This is due to the low oxidation stability of conventional carbonate electrolytes and their poor passivation ability on the delithiated cathode. At high voltages, numerous side reactions occur between the delithiated cathode and the electrolyte, leading to the dissolution of transition metal ions from the positive electrode and damage to the cathode structure. Oxidation byproducts are reduced and deposited at the negative electrode, increasing negative electrode polarization and thus degrading battery performance. To further realize the widespread application of lithium-ion batteries above 4.5 V, it is necessary to develop more effective additives to further improve the cycle stability and high-temperature performance of high-voltage lithium-ion batteries, thereby achieving large-scale commercialization of high-energy-density batteries. Summary of the Invention

[0004] To address the issues of insufficient cycle stability and high-temperature performance in existing high-voltage lithium-ion batteries, this invention provides a non-aqueous electrolyte.

[0005] The technical solution adopted by the present invention to solve the above-mentioned technical problems is as follows: This invention provides a non-aqueous electrolyte comprising a non-aqueous organic solvent, an electrolyte salt, and additives, wherein the additives include a compound represented by structural formula 1, succinic anion, a compound represented by structural formula 2, and a compound represented by structural formula 3. Structural Formula 1 Where n is 0 or 1, A is selected from C or O, and X is selected from... or R1 and R2 are each independently selected from H, , , , or R1 and R2 are not both selected from H, and X, R1 and R2 contain at least one sulfur atom; Structural Formula 2 R3 is selected from C1-C4 alkylene groups; Structural Formula 3 In this group, R4 is selected from functional groups with lone pairs of electrons, R5 is selected from C1-C3 carboxylic acid ester groups or amide groups, and R6 is selected from -(CH2). n CN, 1≤n≤3; The non-aqueous electrolyte meets the following conditions: 0.24≤x / (a+b+c)≤ 2; and 1≤x≤4, 0.5≤a≤3, 1≤b≤4, 0.01≤c≤0.2; Where x is the mass percentage of the compound represented by structural formula 1 in the non-aqueous electrolyte; a represents the mass percentage of succinic acid in the non-aqueous electrolyte; b represents the mass percentage of the compound represented by structural formula 2 in the non-aqueous electrolyte; c represents the mass percentage of the compound represented by structural formula 3 in the non-aqueous electrolyte.

[0006] Optionally, the non-aqueous electrolyte meets the following conditions: 0.24 ≤x / (a+b+c)≤ 0.75.

[0007] Optionally, the mass percentage x of the compound represented by structural formula 1 in the non-aqueous electrolyte is 1% to 3%.

[0008] Optionally, the mass percentage a of succinic acid in the non-aqueous electrolyte is 0.5% to 2%.

[0009] Optionally, the mass percentage b of the compound represented by structural formula 2 in the non-aqueous electrolyte is 1% to 2%.

[0010] Optionally, the mass percentage c of the compound represented by structural formula 3 in the non-aqueous electrolyte is 0.01% to 0.1%.

[0011] Optionally, the compound represented by structural formula 1 includes one or more of the following compounds:

[0012] Optionally, the compound represented by structural formula 2 includes one or more of the following compounds: And / or, in the compounds represented by structural formula 3, R4 is selected from C1-C3 alkyl chains containing cyano, carbonyl, alkoxy, or -P=O.

[0013] Optionally, the compound represented by structural formula 3 includes one or more of the following compounds: .

[0014] Optionally, the additive further includes at least one of cyclic sulfate compounds, sulfonyl lactone compounds, cyclic carbonate compounds, phosphate compounds, and borate compounds; The cyclic sulfate compounds include at least one of vinyl sulfate, propylene sulfate, and methyl vinyl sulfate; and / or The sulfonyl lactone compounds include at least one of 1,3-propanesulfonyl lactone, 1,4-butanesulfonyl lactone, and 1,3-propenesulfonyl lactone; and / or The cyclic carbonate compounds include at least one of vinylene carbonate, ethylene ethylene carbonate, methylene ethylene carbonate, or the compound shown in structural formula 3: Structural Formula 3 In structural formula 3, R 21 R 22 R 23 R 24 R 25 R 26 Each is independently selected from one of the following: hydrogen atom, halogen atom, C1-C5 group; and / or The phosphate ester compounds include at least one of tris(trimethylsilane) phosphate, tris(triethylsilane) phosphate, or the compound shown in structural formula 4: Structural Formula 4 In structural formula 4, R 31 R 32 R 33 Each is independently selected from C1-C5 saturated hydrocarbon groups, C1-C5 unsaturated hydrocarbon groups, C1-C5 halohydrocarbon groups, and -Si(C m H 2m+1 )3, m is a natural number from 1 to 3, and R 31 R 32 R 33 At least one of them is an unsaturated hydrocarbon group; and / or The borate esters include at least one of tris(trimethylsilane)borate and tris(triethylsilane)borate.

[0015] In another aspect, the present invention provides a secondary battery, comprising a positive electrode, a negative electrode and a non-aqueous electrolyte as described above, wherein the positive electrode comprises a positive electrode material layer, the positive electrode material layer comprises a positive electrode active material, and the positive electrode active material is selected from lithium cobalt oxide.

[0016] According to the non-aqueous electrolyte provided by the present invention, compounds represented by structural formula 1, succinic acid, structural formula 2, and structural formula 3 are added as additives. Through extensive research, the inventors discovered that when the amounts of compounds represented by structural formula 1, succinic acid, structural formula 2, and structural formula 3 added to the non-aqueous electrolyte satisfy the condition 0.24 ≤ x / (a+b+c) ≤ 2; and when 1≤x≤4, 0.5≤a≤3, 1≤b≤4, 0.01≤c≤0.2, the resulting lithium-ion battery exhibits lower impedance growth and higher cycle life under high operating voltage and high temperature conditions. It is speculated that this is because the compounds shown in structural formula 1, succinic anion, structural formula 2, and structural formula 3 jointly participate in the formation of the solid electrolyte film on the positive and negative electrode surfaces. Among them, succinic anion, structural formula 2, and structural formula 3 can complex with high-valence transition metal ions on the high-voltage positive electrode surface, thereby protecting the positive electrode and preventing the dissolution of the transition metal. Through the combination of various nitrile substances, a multi-site protection effect can be formed on the positive electrode. The film-forming mechanism of the compound shown in structural formula 1 is different from that of succinic anion, structural formula 2, and structural formula 3, which can form a complementary effect. The compound shown in structural formula 1 decomposes on the positive and negative electrode surfaces to form sulfur-containing components, which can improve the density and stability of the solid electrolyte film on the positive and negative electrode surfaces, which is beneficial to improving the high-temperature performance and rate performance of the battery. Detailed Implementation

[0017] To make the technical problems solved, the technical solutions, and the beneficial effects of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0018] This invention provides a non-aqueous electrolyte, comprising a non-aqueous organic solvent, an electrolyte salt, and additives, wherein the additives include the compound shown in structural formula 1, succinic anion, the compound shown in structural formula 2, and the compound shown in structural formula 3; Structural Formula 1 Where n is 0 or 1, A is selected from C or O, and X is selected from... or R1 and R2 are each independently selected from H, , , , or R1 and R2 are not both selected from H, and X, R1 and R2 contain at least one sulfur atom; Structural Formula 2 R3 is selected from C1-C4 alkylene groups; Structural Formula 3 In this group, R4 is selected from functional groups with lone pairs of electrons, R5 is selected from C1-C3 carboxylic acid ester groups or amide groups, and R6 is selected from -(CH2). n CN, 1≤n≤3; The non-aqueous electrolyte meets the following conditions: 0.24≤x / (a+b+c)≤ 2; and 1≤x≤4, 0.5≤a≤3, 1≤b≤4, 0.01≤c≤0.2; Where x is the mass percentage of the compound represented by structural formula 1 in the non-aqueous electrolyte; a represents the mass percentage of succinic acid in the non-aqueous electrolyte; b represents the mass percentage of the compound represented by structural formula 2 in the non-aqueous electrolyte; c represents the mass percentage of the compound represented by structural formula 3 in the non-aqueous electrolyte.

[0019] Through extensive research, the inventors discovered that when the amounts of the compound shown in structural formula 1, succinic anionyl nitrile, the compound shown in structural formula 2, and the compound shown in structural formula 3 in the non-aqueous electrolyte meet the condition 0.24 ≤ x / (a+b+c) ≤ 2; and when 1≤x≤4, 0.5≤a≤3, 1≤b≤4, 0.01≤c≤0.2, the resulting lithium-ion battery exhibits lower impedance growth and higher cycle life under high operating voltage and high temperature conditions. It is speculated that this is because the compounds shown in structural formula 1, succinic anion, structural formula 2, and structural formula 3 jointly participate in the formation of the solid electrolyte film on the positive and negative electrode surfaces. Among them, succinic anion, structural formula 2, and structural formula 3 can complex with high-valence transition metal ions on the high-voltage positive electrode surface, thereby protecting the positive electrode and preventing the dissolution of the transition metal. Through the combination of various nitrile substances, a multi-site protection effect can be formed on the positive electrode. The film-forming mechanism of the compound shown in structural formula 1 is different from that of succinic anion, structural formula 2, and structural formula 3, which can form a complementary effect. The compound shown in structural formula 1 decomposes on the positive and negative electrode surfaces to form sulfur-containing components, which can improve the density and stability of the solid electrolyte film on the positive and negative electrode surfaces, which is beneficial to improving the high-temperature performance and rate performance of the battery.

[0020] In a preferred embodiment, the non-aqueous electrolyte satisfies the following conditions: 0.24 ≤ x / (a+b+c) ≤ 0.75 When the mass percentages x of the compound shown in structural formula 1, a of the succinic anion, b of the compound shown in structural formula 2, and c of the compound shown in structural formula 3 further satisfy the above conditions, it is beneficial to further improve the high-temperature stability of the solid electrolyte membrane on the positive and negative electrode surfaces, thereby improving the high-temperature cycle performance of the battery.

[0021] In specific embodiments, the mass percentage x of the compound represented by structural formula 1 in the non-aqueous electrolyte can be 1.0%, 1.2%, 1.4%, 1.6%, 1.8%, 2.0%, 2.2%, 2.4%, 2.6%, 2.8%, 3.0%, 3.2%, 3.4%, 3.6%, 3.8%, or 4.0%.

[0022] In a preferred embodiment, the mass percentage x of the compound represented by structural formula 1 in the non-aqueous electrolyte is 1% to 3%.

[0023] The sulfur-containing component formed by the decomposition of the compound shown in Formula 1 can significantly improve the thermal stability of the negative electrode solid electrolyte membrane and has a good ion migration rate. It can inhibit the damage of electrolyte decomposition products to the solid electrolyte membrane in both positive and negative electrode film formation. When the mass percentage x of the compound shown in Formula 1 in the non-aqueous electrolyte is too low, it is difficult to show the enhancing effect on the solid electrolyte membrane. When the mass percentage x of the compound shown in Formula 1 in the non-aqueous electrolyte is too high, it will lead to an excessive amount of sulfur-containing component in the solid electrolyte membrane, which will affect the complexation effect on transition metal ions.

[0024] In specific embodiments, the mass percentage 'a' of succinic acid in the non-aqueous electrolyte can be 0.5%, 0.7%, 0.9%, 1.1%, 1.3%, 1.5%, 1.7%, 1.9%, 2.1%, 2.3%, 2.5%, 2.7%, 2.9%, or 3.0%.

[0025] In a preferred embodiment, the mass percentage 'a' of succinic acid in the non-aqueous electrolyte is 0.5% to 2%.

[0026] In a specific embodiment, the mass percentage b of the compound represented by structural formula 2 in the non-aqueous electrolyte can be 1.0%, 1.2%, 1.4%, 1.6%, 1.8%, 2.0%, 2.2%, 2.4%, 2.6%, 2.8%, 3.0%, 3.2%, 3.4%, 3.6%, 3.8%, or 4.0%.

[0027] In a preferred embodiment, the mass percentage b of the compound represented by structural formula 2 in the non-aqueous electrolyte is 1% to 2%.

[0028] The succinic anhydride and the compound shown in Formula 2 contain multiple cyano groups, which can form a complex protection on the surface of the high-voltage positive electrode material layer. Their decomposition products have a good complexing effect on the transition metal ions dissolved from the positive electrode active material. Furthermore, the compound shown in Formula 2 has cyano-branched chains that can form multidimensional cross-linking sites, improving the stability of the solid electrolyte membrane. When the mass percentage of succinic anhydride or the compound shown in Formula 2 in the non-aqueous electrolyte is too low, the protection effect on the positive electrode is insufficient. The transition metal ions in the positive electrode active material are easily dissolved during cycling, leading to a loss of positive electrode capacity. Moreover, the dissolved transition metal ions catalyze the side reactions of the non-aqueous electrolyte, resulting in the consumption of the non-aqueous electrolyte. When the mass percentage of succinic anhydride or the compound shown in Formula 2 in the non-aqueous electrolyte is too high, it will lead to an excessively thick solid electrolyte membrane on the negative electrode surface, thereby increasing the battery impedance and affecting the rate performance.

[0029] In a specific embodiment, the mass percentage c of the compound represented by structural formula 3 in the non-aqueous electrolyte can be 0.01%, 0.02%, 0.03%, 0.04%, 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.10%, 0.11%, 0.12%, 0.13%, 0.14%, 0.15%, 0.16%, or 0.20%.

[0030] In a preferred embodiment, the mass percentage c of the compound represented by structural formula 3 in the non-aqueous electrolyte is 0.01% to 0.1%.

[0031] The compound shown in structural formula 3 has a similar structure to the compound shown in structural formula 2, but it also includes carboxylic acid ester groups or amide groups. In addition to forming a complex structure with the compound shown in structural formula 2, the compound shown in structural formula 3 has carboxylic acid ester groups or amide groups that form cross-linking sites, thereby improving the density and stability of the solid electrolyte film on the negative electrode surface, preventing the solid electrolyte film on the negative electrode surface from cracking and continuously thickening during cycling, and extending the battery cycle life. When the mass percentage c of the compound shown in structural formula 3 in the non-aqueous electrolyte is too low, the improvement on the battery cycle life is not significant. When the mass percentage c of the compound shown in structural formula 3 in the non-aqueous electrolyte is too high, it will increase the risk of gas generation during high-temperature storage of the battery and affect the high-temperature performance of the battery.

[0032] In some embodiments, the compound represented by structural formula 1 includes one or more of the following compounds:

[0033] In some embodiments, the compound represented by structural formula 2 includes one or more of the following compounds: .

[0034] In some embodiments, in the compound represented by structural formula 3, R4 is selected from alkyl chains of C1 to C3 containing cyano, carbonyl, alkoxy, or -P=O.

[0035] In some embodiments, in the compound represented by structural formula 3, R4 is selected from a C1-C3 alkyl chain with a cyano or alkoxy group, and R5 is selected from a C1-C3 carboxylic acid ester group.

[0036] In some embodiments, the compound represented by structural formula 3 includes one or more of the following compounds: .

[0037] The compound represented by structural formula 3 can be prepared by the following method: Using carboxylic acid esters with dicyano groups or carboxylic acid esters with methoxy and cyano groups as raw materials, acrylonitrile is reacted with triethylamine in the presence of a catalyst at a reaction temperature of 40-60℃ to obtain the compound shown in structural formula 3.

[0038] Taking compound 26 as an example, ethyl 2,3-dicyanopropionate, dimethyl carbonate, and triethylamine are added to a reaction vessel, and the temperature is raised to 40-60°C. Acrylonitrile is then added dropwise, with the reaction solution temperature controlled to not exceed 70°C. After the addition is complete, the reaction is maintained at atmospheric pressure for 2-4 hours. After the reaction is complete, the target compound 26 is obtained by separation and purification from the reaction solution. Similarly, the preparation of compound 29 requires replacing the raw material with ethyl 2-methoxy-3-cyanopropionate.

[0039] In some embodiments, the electrolyte salt includes LiPF6, LiTFSI, LiBOB, LiDFOB, LiDFOP, LiPO2F2, LiBF4, LiSbF6, LiAsF6, LiN(SO2CF3)2, LiN(SO2C2F5)2, LiC(SO2CF3)3, LiClO4, LiAlCl4, LiCF3SO3, LiSO3F, and Li2B. 10 Cl 10 At least one lithium salt selected from lithium chloroborane, lithium tetrafluorooxalate phosphate, lithium trioxalate phosphate, lithium lower aliphatic carboxylic acids having four or fewer carbon atoms, or lithium tetraphenylborate.

[0040] In some embodiments, the concentration of the lithium salt in the non-aqueous electrolyte is 0.1 mol / L to 4 mol / L. In a preferred embodiment, the concentration of the lithium salt in the non-aqueous electrolyte is 0.5 mol / L to 2.5 mol / L. Specifically, in the non-aqueous electrolyte, the concentration of the lithium salt can be 0.5 mol / L, 0.55 mol / L, 0.6 mol / L, 0.65 mol / L, 0.7 mol / L, 0.8 mol / L, 0.85 mol / L, 0.9 mol / L, 0.95 mol / L, 1.0 mol / L, 1.1 mol / L, 1.15 mol / L, 1.2 mol / L, 1.3 mol / L, 1.4 mol / L, 1.45 mol / L, 1.5 mol / L, 1.6 mol / L, 1.7 mol / L, 1.8 mol / L, 1.9 mol / L, 2.0 mol / L, 2.1 mol / L, 2.2 mol / L, 2.3 mol / L, 2.4 mol / L, or 2.5 mol / L.

[0041] In some embodiments, the mass content of the non-aqueous organic solvent is 65% to 90% based on the total mass of the non-aqueous electrolyte being 100%.

[0042] Specifically, based on the total mass of the non-aqueous electrolyte as 100%, the mass content of the non-aqueous organic solvent can be 65%, 68%, 71%, 74%, 76%, 78%, 79%, 80%, 81.5%, 82%, 84%, 85%, 86%, 87%, 89%, or 90%.

[0043] In some embodiments, the non-aqueous organic solvent includes at least one of ether solvents, carbonate solvents, carboxylic acid ester solvents, and sulfone solvents.

[0044] In some embodiments, the ether solvent includes cyclic ethers or chain ethers, preferably chain ethers with 3 to 10 carbon atoms and cyclic ethers with 3 to 6 carbon atoms. The cyclic ethers may specifically include, but are not limited to, at least one of 1,3-dioxolane (DOL), 1,4-dioxane (Da), crown ethers, tetrahydrofuran (THF), 2-methyltetrahydrofuran (2-CH3-THF), and 2-trifluoromethyltetrahydrofuran (2-CF3-THF). The chain ethers may specifically include, but are not limited to, dimethoxymethane, diethoxymethane, ethoxymethoxymethane, ethylene glycol di-n-propyl ether, ethylene glycol di-n-butyl ether, and diethylene glycol dimethyl ether. Because chain ethers have high solvation ability with lithium ions and can improve ion dissociation, dimethoxymethane, diethoxymethane, and ethoxymethoxymethane, which have low viscosity and can impart high ionic conductivity, are particularly preferred. Ether compounds can be used alone or in any combination and ratio of two or more. There are no particular restrictions on the amount of ether compounds added, and it can be arbitrary as long as it does not significantly impair the effect of the high-pressure lithium-ion battery of the present invention. When the volume ratio of non-aqueous solvent is 100%, the volume ratio is usually 1% or more, preferably 2% or more, and more preferably 3% or more. In addition, the volume ratio is usually 30% or less, preferably 25% or less, and more preferably 20% or less.

[0045] In some embodiments, the carbonate solvent includes cyclic carbonates or chain carbonates. Cyclic carbonates may specifically include, but are not limited to, at least one of ethylene carbonate (EC), propylene carbonate (PC), γ-butyrolactone (GBL), and butylene carbonate (BC); chain carbonates may specifically include, but are not limited to, at least one of dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), and dipropyl carbonate (DPC). The content of cyclic carbonates is not particularly limited and is arbitrary within a range that does not significantly impair the performance of the lithium-ion battery of the present invention. However, when using only one type, its content is typically 3% or more, preferably 5% or more, by volume relative to the total amount of solvent in the non-aqueous electrolyte. By setting this range, a decrease in conductivity due to a decrease in the dielectric constant of the non-aqueous electrolyte can be avoided, making it easier to achieve good high-current discharge characteristics, stability relative to the negative electrode, and cycle characteristics of the non-aqueous electrolyte battery. Furthermore, the upper limit is typically 90% or less by volume, preferably 85% or less, and more preferably 80% or less by volume. By setting this range, the oxidation / reduction resistance of the non-aqueous electrolyte can be improved, thereby contributing to enhanced stability during high-temperature storage. The content of the chain carbonate is not particularly limited, but relative to the total amount of solvent in the non-aqueous electrolyte, it is typically 15% or more by volume, preferably 20% or more, and more preferably 25% or more. Furthermore, it is typically 90% or less by volume, preferably 85% or less, and more preferably 80% or less. By keeping the chain carbonate content within the above range, it is easier to achieve an appropriate viscosity for the non-aqueous electrolyte, suppressing the decrease in ionic conductivity, and thus contributing to achieving a good range of output characteristics for the non-aqueous electrolyte battery. When using two or more chain carbonates in combination, it is sufficient to ensure that the total amount of chain carbonate meets the above range.

[0046] In some embodiments, fluorine-containing chain carbonates (hereinafter referred to as "fluorinated chain carbonates") are also preferably used. There is no particular limitation on the number of fluorine atoms in a fluorinated chain carbonate as long as it is 1 or more, but it is generally 6 or less, preferably 4 or less. When a fluorinated chain carbonate has multiple fluorine atoms, these fluorine atoms can be bonded to the same carbon atom or to different carbon atoms. Examples of fluorinated chain carbonates include dimethyl fluorinated carbonate derivatives, methyl ethyl fluorinated carbonate derivatives, and diethyl fluorinated carbonate derivatives.

[0047] Carboxylic acid ester solvents include cyclic carboxylic acid esters and / or chain carbonates. Examples of cyclic carboxylic acid esters include at least one of γ-butyrolactone, γ-valerolactone, and δ-valerolactone. Examples of chain carbonates include at least one of methyl acetate (MA), ethyl acetate (EA), propyl acetate (EP), butyl acetate, propyl propionate (PP), and butyl propionate.

[0048] In some embodiments, the sulfone solvent includes cyclic sulfones and chain sulfones. Preferably, in the case of cyclic sulfones, it is typically a compound with 3 to 6 carbon atoms, more preferably 3 to 5 carbon atoms; in the case of chain sulfones, it is typically a compound with 2 to 6 carbon atoms, more preferably 2 to 5 carbon atoms. There are no particular limitations on the amount of sulfone solvent added, and it is arbitrary within a range that does not significantly impair the performance of the lithium-ion battery of the present invention. Relative to the total amount of solvent in the non-aqueous electrolyte, it is typically 0.3% or more by volume, preferably 0.5% or more by volume, more preferably 1% or more by volume. Furthermore, it is typically 40% or less by volume, preferably 35% or less by volume, more preferably 30% or less by volume. When using two or more sulfone solvents in combination, the total amount of sulfone solvent should satisfy the above range. When the amount of sulfone solvent added is within the above range, a non-aqueous electrolyte with excellent high-temperature storage stability is tended to be obtained.

[0049] In some embodiments, the additive further includes at least one of cyclic sulfate compounds, sulfonyl lactone compounds, cyclic carbonate compounds, phosphate compounds, and borate compounds.

[0050] In some embodiments, the content of the additive is 0.01% to 10% based on the total mass of the non-aqueous electrolyte as 100%.

[0051] In some embodiments, the cyclic sulfate compound includes at least one of vinyl sulfate, propylene sulfate, and methyl vinyl sulfate.

[0052] In some embodiments, the sulfonyl lactone compound includes at least one of 1,3-propanesulfonyl lactone, 1,4-butanesulfonyl lactone, and 1,3-propenesulfonyl lactone.

[0053] In some embodiments, the cyclic carbonate compound includes at least one of vinylene carbonate, ethylene ethylene carbonate, methylene ethylene carbonate, or the compound shown in structural formula 3: Structural Formula 3 In structural formula 3, R 21 R 22 R 23 R 24 R 25 R 26 Each is independently selected from one of the following: hydrogen atom, halogen atom, or C1-C5 group.

[0054] In some embodiments, the phosphate compound includes at least one of tris(trimethylsilane) phosphate, tris(triethylsilane) phosphate, or the compound shown in structural formula 4: Structural Formula 4 In structural formula 4, R 31 R 32 R 33 Each is independently selected from C1-C5 saturated hydrocarbon groups, C1-C5 unsaturated hydrocarbon groups, C1-C5 halohydrocarbon groups, and -Si(C m H 2m+1 )3, m is a natural number from 1 to 3, and R 31 R 32 R 33 At least one of them is an unsaturated hydrocarbon group.

[0055] In a preferred embodiment, the phosphate ester compound represented by structural formula 4 may be at least one of the following: triargyl phosphate, diallyl methyl phosphate, diallyl ethyl phosphate, diallyl propyl phosphate, diallyl trifluoromethyl phosphate, diallyl-2,2,2-trifluoroethyl phosphate, diallyl-3,3,3-trifluoropropyl phosphate, diallyl hexafluoroisopropyl phosphate, triallyl phosphate, diallyl methyl phosphate, diallyl ethyl phosphate, diallyl propyl phosphate, diallyl trifluoromethyl phosphate, diallyl-2,2,2-trifluoroethyl phosphate, diallyl-3,3,3-trifluoropropyl phosphate, and diallyl hexafluoroisopropyl phosphate.

[0056] In some embodiments, the borate ester compound includes at least one of tris(trimethylsilane)borate and tris(triethylsilane)borate.

[0057] In other embodiments, the additive may also include other additives that can improve battery performance: for example, additives that improve battery safety performance, such as flame retardant additives like fluorophosphates and cyclophosphonitriles, or overcharge prevention additives like tert-amylbenzene and tert-butylbenzene.

[0058] It should be noted that, unless otherwise specified, the content of any optional substance in the additive in the non-aqueous electrolyte is generally less than 10%, preferably 0.01-5%, and more preferably 0.1% to 2%. Specifically, the content of any optional substance in the additive can be 0.01%, 0.05%, 0.08%, 0.1%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, 2.8%, 3%, 3.2%, 3.5%, 3.8%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 7.8%, 8%, 8.5%, 9%, 9.5%, or 10%.

[0059] In some embodiments, the additive includes fluoroethylene carbonate, and the amount of fluoroethylene carbonate added is 0.01% to 30% based on 100% of the total mass of the non-aqueous electrolyte.

[0060] Another embodiment of the present invention provides a battery including a positive electrode, a negative electrode and a non-aqueous electrolyte as described above.

[0061] In some embodiments, the positive electrode includes a positive electrode material layer, the positive electrode material layer includes a positive electrode active material, and the positive electrode active material includes at least one of lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium cobalt manganese oxide, lithium iron phosphate, or lithium manganese iron phosphate.

[0062] In some preferred embodiments, the positive electrode active material includes at least lithium cobalt oxide.

[0063] In some embodiments, the positive electrode material layer further includes a positive electrode binder and a positive electrode conductive agent, and the positive electrode active material, the positive electrode binder and the positive electrode conductive agent are blended to obtain the positive electrode material layer.

[0064] The positive electrode binder includes at least one of the following: polyvinylidene fluoride (PVDF), copolymers of PVDF, polytetrafluoroethylene (PTFE), copolymers of PVDF-hexafluoropropylene, copolymers of tetrafluoroethylene-hexafluoropropylene, copolymers of tetrafluoroethylene-perfluoroalkyl vinyl ethers, copolymers of ethylene-tetrafluoroethylene, copolymers of PVDF-tetrafluoroethylene, copolymers of PVDF-trifluoroethylene, copolymers of PVDF-trichloroethylene, copolymers of PVDF-fluorinated vinylidene, copolymers of PVDF-hexafluoropropylene-tetrafluoroethylene, thermoplastic polyimide, polyethylene, and polypropylene; acrylic resins; and styrene-butadiene rubber.

[0065] The positive electrode conductive agent includes at least one of conductive carbon black, conductive carbon spheres, conductive graphite, conductive carbon fiber, carbon nanotubes, graphene, or reduced graphene oxide.

[0066] In some embodiments, the positive current collector comprises a metallic material capable of conducting electrons. Preferably, the positive current collector comprises at least one of Al, Ni, tin, copper, and stainless steel. In a more preferred embodiment, the positive current collector is selected from aluminum foil.

[0067] In some embodiments, the negative electrode includes a negative electrode active material layer, which includes a negative electrode active material, and the negative electrode active material includes at least one of carbon-based negative electrode, silicon-based negative electrode, tin-based negative electrode, and lithium negative electrode. The carbon-based negative electrode may include graphite, hard carbon, soft carbon, graphene, mesophase carbon microspheres, etc.; the silicon-based negative electrode may include silicon materials, silicon oxides, silicon-carbon composite materials, and silicon alloy materials, etc.; the silicon material is one or more of silicon nanoparticles, silicon nanowires, silicon nanotubes, silicon thin films, 3D porous silicon, and hollow porous silicon. The tin-based negative electrode may include tin, tin-carbon, tin-oxygen, and tin metal compounds; the lithium negative electrode may include metallic lithium or lithium alloys. Specifically, the lithium alloy may be at least one of lithium-silicon alloy, lithium-sodium alloy, lithium-potassium alloy, lithium-aluminum alloy, lithium-tin alloy, and lithium-indium alloy.

[0068] In some preferred embodiments, the negative electrode active material includes at least graphite.

[0069] In some embodiments, the negative electrode further includes a negative electrode current collector, and the negative electrode active material layer covers the surface of the negative electrode current collector. The negative electrode current collector includes a metallic material capable of conducting electrons; preferably, the negative electrode current collector includes at least one of Al, Ni, tin, copper, and stainless steel; in a more preferred embodiment, the negative electrode current collector is selected from copper foil.

[0070] In some embodiments, the negative electrode active material layer further includes a negative electrode binder and a negative electrode conductive agent, and the negative electrode active material, the negative electrode binder, and the negative electrode conductive agent are blended to obtain the negative electrode active material layer. The negative electrode binder and the negative electrode conductive agent can be the same as the positive electrode binder and the positive electrode conductive agent, respectively, and will not be described in detail here.

[0071] In some embodiments, the battery further includes a separator located between the positive electrode and the negative electrode.

[0072] The diaphragm can be a conventional diaphragm, such as a ceramic diaphragm, a polymer diaphragm, a non-woven fabric, or an inorganic-organic composite diaphragm, including but not limited to single-layer PP (polypropylene), single-layer PE (polyethylene), double-layer PP / PE, double-layer PP / PP, and triple-layer PP / PE / PP diaphragms.

[0073] The present invention will be further illustrated by the following examples.

[0074] Table 1 Example 1 This embodiment illustrates the preparation method of the lithium-ion battery disclosed in this invention, including the following steps: 1) Preparation of non-aqueous electrolyte: Ethylene carbonate (EC), diethyl carbonate (DEC), and methyl ethyl carbonate (EMC) were mixed in a mass ratio of EC:DEC:EMC = 1:1:1. Then, lithium hexafluorophosphate (LiPF6) was added to a molar concentration of 1 mol / L. Additives were added based on the total weight of the non-aqueous electrolyte as 100%. The types and contents of each additive are shown in Table 1.

[0075] 2) Preparation of the positive electrode: Lithium cobalt oxide, conductive carbon black Super-P, and polyvinylidene fluoride (PVDF) binder are mixed in a mass ratio of 95:2:3, and then dispersed in N-methyl-2-pyrrolidone (NMP) to obtain a positive electrode slurry. The slurry is uniformly coated on both sides of an aluminum foil, dried, calendered, and vacuum dried, and then aluminum leads are welded on using an ultrasonic welder to obtain a positive electrode sheet with a thickness between 120-150 μm.

[0076] 3) Preparation of the negative electrode: Artificial graphite, conductive carbon black Super-P, styrene-butadiene rubber (SBR), and carboxymethyl cellulose (CMC) were mixed in a mass ratio of 95:1:2:2 and then dispersed in deionized water to obtain a negative electrode slurry. The slurry was coated on both sides of a copper foil, dried, calendered, and vacuum dried, and then nickel leads were welded on using an ultrasonic welder to obtain a negative electrode plate with a thickness between 120-150 μm.

[0077] 4) Cell fabrication: A three-layer separator with a thickness of 20 μm is placed between the positive and negative plates. Then, the sandwich structure composed of the positive plate, negative plate and separator is wound up. The wound body is flattened and placed in an aluminum foil packaging bag. It is then vacuum baked at 75°C for 48 hours to obtain the cell to be injected with electrolyte.

[0078] 5) Electrolyte injection and formation of the battery cell: In a glove box where the dew point is controlled below -40°C, the electrolyte prepared above is injected into the battery cell, vacuum sealed, and left to stand for 24 hours.

[0079] Then, the first charging process was carried out according to the following steps: constant current charging at 0.05C for 180 minutes, constant current charging at 0.2C to 3.95V, vacuum sealing for the second time, and then further constant current charging at 0.2C to 4.5V. After being left at room temperature for 24 hours, constant current discharge at 0.2C to 3.0V was obtained to obtain a lithium cobalt oxide / artificial graphite lithium-ion battery.

[0080] Examples 2-18 Examples 2-18 illustrate the non-aqueous electrolyte and its battery disclosed in this invention, including most of the operating steps in Example 1, with the following differences: In the preparation of non-aqueous electrolytes, the types and contents of additives vary, as shown in Table 1.

[0081] Comparative Examples 1-14 Comparative Examples 1-14 are used to compare and illustrate the non-aqueous electrolyte and its battery disclosed in this invention, including most of the operating steps in Example 1, with the following differences: In the preparation of non-aqueous electrolytes, the types and contents of additives vary, as shown in Table 1.

[0082] Performance testing The lithium-ion batteries prepared in Examples 1-18 and Comparative Examples 1-14 were subjected to the following performance tests: After capacity grading, the batteries were placed in a 45°C oven and charged at a constant current and constant voltage of 0.7C to 4.5V, with a cutoff current of 0.03C. After resting for 5 minutes, they were discharged at a constant current of 1.5C to 3.0V and rested for 5 minutes. Then, 500 charge-discharge cycles were performed at the above rates. The discharge capacity, DC internal resistance of the first discharge cycle, discharge capacity of the 500th cycle, and DC internal resistance of the 500th cycle were recorded. The capacity retention rate was calculated as (discharge capacity of the 500th cycle / discharge capacity of the first cycle) * 100%, and the internal resistance growth rate was calculated as (DC internal resistance of the 500th cycle / DC internal resistance of the first cycle) * 100%. (1) The test results obtained from Examples 1-14 and Comparative Examples 1-14 are filled in Table 2.

[0083] Table 2 The test results of Examples 1-14 and Comparative Examples 1-14 show that the compounds shown in Structural Formula 1, succinic anionylene, Structural Formula 2, and Structural Formula 3 have a significant correlation in their impact on the formation quality of the solid electrolyte interfacial film on the positive and negative electrode surfaces. When the amounts of the compounds shown in Structural Formula 1, succinic anionylene, Structural Formula 2, and Structural Formula 3 added to the non-aqueous electrolyte satisfy the following relationship: 0.24≤x / (a+b+c)≤2; and 1≤x≤4, 0.5≤a≤3, 1≤b≤4, 0.01≤c≤0.2, the resulting lithium-ion battery exhibits a lower internal resistance growth rate and a higher cycle capacity retention rate during battery charge-discharge cycles. This is presumably because the compounds shown in Structural Formula 1, succinic anionylene, Structural Formula 2, and Structural Formula 3 all play important roles in the formation of the solid electrolyte film on the positive and negative electrode surfaces of the battery. Specifically, succinic anhydride, the compound shown in Formula 2, and the compound shown in Formula 3 can undergo a complexation reaction on the surface of the high-voltage positive electrode. This complexation effectively captures high-valence transition metal ions, thereby forming a protective barrier on the positive electrode surface and effectively preventing the dissolution of transition metal ions. The compound shown in Formula 1 decomposes on the surfaces of both the positive and negative electrodes, producing sulfur-containing components. The presence of these sulfur-containing components can significantly improve the density and stability of the solid electrolyte film on the positive and negative electrode surfaces, thus playing a positive role in improving the high-temperature performance and rate performance of the battery. By combining multiple nitrile substances, a multi-site protective effect on the positive electrode can be achieved, greatly enhancing the comprehensiveness and effectiveness of the protection. At the same time, the film-forming mechanism of the compound shown in Formula 1 is significantly different from that of succinic anhydride, the compound shown in Formula 2, and the compound shown in Formula 3. This difference allows them to form a good complementary effect.

[0084] The test results of Examples 1-14 show that when the amounts of the compound shown in structural formula 1, succinic anion, compound shown in structural formula 2, and compound shown in structural formula 3 added to the non-aqueous electrolyte further satisfy the conditions 0.24≤x / (a+b+c)≤0.75; and 1≤x≤3, 0.5≤a≤2, 1≤b≤2, and 0.01≤c≤0.1, the resulting lithium-ion battery has the best overall performance.

[0085] The test results of Comparative Examples 9-14 show that when the values ​​of a, b, c, and x do not meet the constraint 0.24≤x / (a+b+c)≤2, it will lead to the deterioration of battery cycle performance and the decrease in cycle life. This indicates that there is an interaction between the compound shown in structural formula 1, succinic anion, compound shown in structural formula 2, and compound shown in structural formula 3 in the non-aqueous electrolyte. Only when the four reach a good balance can they significantly improve the high-temperature performance and cycle performance of lithium-ion batteries. The test results from Comparative Examples 1 to 8 show that when any of the parameters a, b, c, and x exceed the specified range of 1≤x≤4, 0.5≤a≤3, 1≤b≤4, and 0.01≤c≤0.2, even if the requirement of the relationship 0.24≤x / (a+b+c)≤2 is met, the lithium-ion battery still exhibits poor cycle performance and a significant increase in impedance. This indicates that when the values ​​of a, b, c, and x are too high or too low, they will affect the stability of the solid electrolyte interface film on the positive and negative electrode surfaces during charge and discharge cycles, leading to its rupture and recombination, and thus continuously increasing the battery impedance.

[0086] (2) The test results obtained in Examples 1, 15-18 are filled in Table 3.

[0087] Table 2 As shown in the test results of Examples 1 and 15-18, in the battery system provided by this invention, the addition amounts of the compound shown in structural formula 1, succinic anion, compound shown in structural formula 2, and compound shown in structural formula 3 in the non-aqueous electrolyte satisfy the following relationship: 0.24≤x / (a+b+c)≤2; and 1≤x≤4, 0.5≤a≤3, 1≤b≤4, 0.01≤c≤0.2. Under the premise that different compounds shown in structural formula 1, different compounds shown in structural formula 2, and different compounds shown in structural formula 3 are used, the resulting lithium-ion batteries all have good cycle capacity retention and low impedance. This indicates that the battery system provided by this invention has universality for different compounds shown in structural formula 1, different compounds shown in structural formula 2, and different compounds shown in structural formula 3.

[0088] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A non-aqueous electrolyte, characterized in that, It includes non-aqueous organic solvents, electrolyte salts, and additives, wherein the additives include the compound shown in structural formula 1, succinic acid, the compound shown in structural formula 2, and the compound shown in structural formula 3; Structural Formula 1 Where n is 0 or 1, A is selected from C or O, and X is selected from... or R1 and R2 are each independently selected from H, , , , or R1 and R2 are not both selected from H, and X, R1 and R2 contain at least one sulfur atom; Structural Formula 2 R3 is selected from C1-C4 alkylene groups; Structural Formula 3 In this group, R4 is selected from functional groups with lone pairs of electrons, R5 is selected from C1-C3 carboxylic acid ester groups or amide groups, and R6 is selected from -(CH2). n CN, 1≤n≤3; The non-aqueous electrolyte meets the following conditions: 0.24≤x / (a+b+c)≤ 2; and 1≤x≤4, 0.5≤a≤3, 1≤b≤4, 0.01≤c≤0.2; Where x is the mass percentage of the compound represented by structural formula 1 in the non-aqueous electrolyte; a represents the mass percentage of succinic acid in the non-aqueous electrolyte; b represents the mass percentage of the compound represented by structural formula 2 in the non-aqueous electrolyte; c represents the mass percentage of the compound represented by structural formula 3 in the non-aqueous electrolyte.

2. The non-aqueous electrolyte according to claim 1, characterized in that, The non-aqueous electrolyte meets the following conditions: 0.24 ≤x / (a+b+c)≤ 0.

75.

3. The non-aqueous electrolyte according to claim 1, characterized in that, The mass percentage (x) of the compound represented by structural formula 1 in the non-aqueous electrolyte is 1% to 3%.

4. The non-aqueous electrolyte according to claim 1, characterized in that, The mass percentage (a) of succinic acid in the non-aqueous electrolyte is 0.5% to 2%.

5. The non-aqueous electrolyte according to claim 1, characterized in that, The mass percentage b of the compound represented by structural formula 2 in the non-aqueous electrolyte is 1% to 2%.

6. The non-aqueous electrolyte according to claim 1, characterized in that, The mass percentage c of the compound represented by structural formula 3 in the non-aqueous electrolyte is 0.01% to 0.1%.

7. The non-aqueous electrolyte according to claim 1, characterized in that, The compound represented by structural formula 1 includes one or more of the following compounds: 。 8. The non-aqueous electrolyte according to claim 1, characterized in that, The compound represented by structural formula 2 includes one or more of the following compounds: And / or, in the compound shown in structural formula 3, R4 is selected from C1 to C3 alkyl chains containing cyano, carbonyl, alkoxy or -P=O; Preferably, the compound represented by structural formula 3 includes one or more of the following compounds: 。 9. The non-aqueous electrolyte according to claim 1, characterized in that, The additives also include at least one of cyclic sulfate compounds, sulfonyl lactone compounds, cyclic carbonate compounds, phosphate compounds, and borate ester compounds; The cyclic sulfate compounds include at least one of vinyl sulfate, propylene sulfate, and methyl vinyl sulfate; and / or The sulfonyl lactone compounds include at least one of 1,3-propanesulfonyl lactone, 1,4-butanesulfonyl lactone, and 1,3-propenesulfonyl lactone; and / or The cyclic carbonate compound includes at least one of vinylene carbonate, ethylene ethylene carbonate, methylene ethylene carbonate, or the compound shown in structural formula 3: Structural Formula 3 In structural formula 3, R 21 R 22 R 23 R 24 R 25 R 26 Each is independently selected from one of the following: hydrogen atom, halogen atom, C1-C5 group; and / or The phosphate ester compounds include at least one of tris(trimethylsilane) phosphate, tris(triethylsilane) phosphate, or the compound shown in structural formula 4: Structural Formula 4 In structural formula 4, R 31 R 32 R 33 Each is independently selected from C1-C5 saturated hydrocarbon groups, C1-C5 unsaturated hydrocarbon groups, C1-C5 halohydrocarbon groups, and -Si(C m H 2m+1 )3, m is a natural number from 1 to 3, and R 31 R 32 R 33 At least one of them is an unsaturated hydrocarbon group; and / or The borate esters include at least one of tris(trimethylsilane)borate and tris(triethylsilane)borate.

10. A secondary battery, characterized in that, The device includes a positive electrode, a negative electrode, and a non-aqueous electrolyte as described in any one of claims 1 to 9, wherein the positive electrode includes a positive electrode material layer, the positive electrode material layer includes a positive electrode active material, and the positive electrode active material is selected from lithium cobalt oxide.

Images