A lithium-ion battery

Abstract

To overcome the problems of serious gas generation and poor high-temperature cycle performance existing in existing high-nickel high-voltage lithium-ion batteries, the present invention provides a lithium-ion battery, which includes a positive electrode, a negative electrode and a non-aqueous electrolyte. The positive electrode includes a positive electrode material layer, and the positive electrode material layer includes a positive electrode active material. The positive electrode active material includes LiNi x Co y Mn z L (1‑x‑y‑z) O2, where L is Al, Sr, Mg, Ti, Ca, Zr, Zn, Si, Cu, V or Fe, 0.5 ≤ x ≤ 1, 0 ≤ y ≤ 0.5, 0 ≤ z ≤ 0.5, 0 ≤ x + y + z ≤ 1, and the upper limit voltage of the lithium-ion battery ≥ 4.2 V; the non-aqueous electrolyte includes a solvent, an electrolyte salt and a compound shown in Structural Formula 1: A-D-B-E-C Structural Formula 1 Based on the total mass of the non-aqueous electrolyte being 100%, the addition amount of the compound shown in Structural Formula 1 is 0.01-5.0%. The present invention uses the compound shown in Structural Formula 1 in combination with a high-nickel ternary material to obtain a ternary high-nickel lithium-ion battery with a relatively high high-temperature cycle capacity retention rate and relatively small cycle gas generation.

Description

Technical Field

[0001] The present invention belongs to the technical field of secondary batteries, and particularly relates to a lithium-ion battery. Background Art

[0002] Lithium-ion batteries are widely used in life and production due to their excellent performance. In recent years, with the development of consumer electronic products and new energy vehicles, people have put forward higher requirements for the performance of lithium-ion batteries, especially the cycle performance under high-temperature conditions needs to be further improved. During the cycle of lithium-ion batteries, especially in the high-nickel high-voltage ternary battery system, when the nickel content and working voltage in the ternary cathode material are both high, the cycle gas generation phenomenon of lithium-ion batteries is more serious. The possible reasons are as follows: on the one hand, with the increase of nickel content, the content of the original alkaline compounds on the surface of the cathode material increases, especially the content of lithium carbonate. During the battery cycle, lithium carbonate will decompose to generate gas; on the other hand, in the high-nickel ternary material, a larger proportion of lithium ions can be deintercalated. At this time, the structure of the cathode material is extremely prone to change or even collapse, which will cause the rupture of the cathode protective film, resulting in the direct exposure of the cathode material to the electrolyte to occur side reactions to generate a large amount of gas. At the same time, nickel ions have high activity, and the electrolyte is more likely and faster to oxidize and decompose on the surface of the cathode material with a high nickel content, further increasing the cycle gas generation and deteriorating the high-temperature cycle performance. Summary of the Invention

[0003] Aiming at the problems of serious gas generation and poor high-temperature cycle performance existing in the existing high-nickel lithium-ion batteries, the present invention provides a lithium-ion battery.

[0004] The technical solutions adopted by the present invention to solve the above technical problems are as follows:

[0005] The present invention provides a lithium-ion battery, including a positive electrode, a negative electrode, and a non-aqueous electrolyte. 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 LiNi x Co y Mn z L (1-x-y-z) O2, where L is Al, Sr, Mg, Ti, Ca, Zr, Zn, Si, Cu, V or Fe, 0.5 ≤ x ≤ 1, 0 ≤ y ≤ 0.5, 0 ≤ z ≤ 0.5, 0 ≤ x + y + z ≤ 1, and the upper limit voltage of the lithium-ion battery ≥ 4.2V;

[0006] The non-aqueous electrolyte includes a solvent, an electrolyte salt, and a compound shown in Structural Formula 1:

[0007] A-D-B-E-C

[0008] Structural Formula 1

[0009] Among them, A, B, and C are each independently selected from groups containing a cyclic carbonate group, a cyclic sulfate group, a cyclic sulfite group, a cyclic sulfonate group, a cyclic sulfone group, a cyclic sulfoxide group, a cyclic carboxylate group, or a cyclic anhydride group;

[0010] D and E are each independently selected from a single bond, or a group containing an alkylene group, an ether bond, a sulfur-oxygen double bond, or a carbon-oxygen double bond;

[0011] Based on the total mass of the non-aqueous electrolyte being 100%, the addition amount of the compound shown in the structural formula 1 is 0.01 to 5.0%.

[0012] Optionally, the number of cyclic carbonate groups, cyclic sulfate groups, cyclic sulfite groups, cyclic sulfonate groups, cyclic sulfone groups, cyclic sulfoxide groups, cyclic carboxylate groups, or cyclic anhydride groups contained in A, B, and C independently is 1 to 5, and the total number of cyclic carbonate groups, cyclic sulfate groups, cyclic sulfite groups, cyclic sulfonate groups, cyclic sulfone groups, cyclic sulfoxide groups, cyclic carboxylate groups, or cyclic anhydride groups of A, B, and C is less than or equal to 10.

[0013] Optionally, A and C are each independently selected from the groups shown in the structural formula 2:

[0014]

[0015] Among them, n is selected from an integer of 0 to 4, and R1 is selected from hydrogen, a halogen, or a C1-C5 halogenated hydrocarbon group; R2, R3, R4, R5, R6, and R7 are each independently selected from a C1-C3 alkylene group, a C1-C3 alkoxy group, an oxygen atom, At least one of R2, R3, and R4 is selected from and at least one of R2, R3, and R4 is selected from an oxygen atom, and at least one of R5, R6, and R7 is selected from and at least one of R5, R6, and R7 is selected from an oxygen atom.

[0016] Optionally, B is selected from the group shown in the structural formula 3:

[0017]

[0018] Among them, m is selected from an integer of 1 to 4, and R8, R9, R 10 are each independently selected from a C1-C3 alkylene group, a C1-C3 alkoxy group, an oxygen atom, R8, R9, R 10 Among them, at least one is selected from and at least one of R8, R9, R 10 is selected from an oxygen atom.

[0019] Optionally, D and E are each independently selected from the groups represented by Structural Formula 4:

[0020]

[0021] wherein z is selected from integers from 0 to 4, R 11 and R 13 are each independently selected from a single bond or a C1-C5 alkylene group, and R 12 is selected from a single bond,

[0022] Optionally, D and E are each independently selected from a single bond or a C1-C5 alkylene group, and A, B, and C are each independently selected from a substituted or unsubstituted cyclic carbonate group, cyclic sulfate group, cyclic sulfite group, cyclic sulfonate group, cyclic sulfone group, cyclic sulfoxide group, cyclic carboxylate group, or cyclic anhydride group;

[0023] Optionally, when A, B, or C is substituted, the substituent is selected from a halogen, a hydrocarbon group, or a halogenated hydrocarbon group.

[0024] Optionally, when A, B, or C is substituted, the substituent is selected from a halogen, an alkyl group, or a halogenated alkyl group.

[0025] Optionally, A and C are the same as each other, A and B are the same or different from each other, and D and E are the same as each other.

[0026] Optionally, the compound represented by Structural Formula 1 is selected from one or more of the following compounds:

[0027]

[0028]

[0029]

[0030]

[0031]

[0032]

[0033]

[0034] Optionally, the positive electrode active material is selected from LiNi 0.5 Co 0.2 Mn 0.3 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.7 Co 0.1 Mn0.2 O2, LiNi 0.8 Co 0.15 Al 0.05 O2, LiNi 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.6 Mn 0.4 O2 and LiNi 0.8 Mn 0.2 One or more of O2.

[0035] Optionally, the non-aqueous electrolyte further comprises an auxiliary additive, and the auxiliary additive comprises at least one of an unsaturated cyclic carbonate compound, a fluorinated cyclic carbonate compound, an aromatic additive, a fluorinated anisole compound, a dicarboxylic anhydride, lithium difluorophosphate, and lithium bis(fluorosulfonyl)imide (LiFSI).

[0036] For the lithium ion battery provided by the present invention, the inventors found that when the compound shown in Structural Formula 1 is used in combination with a high-nickel ternary material, a ternary high-nickel lithium ion battery with a relatively high high-temperature cycle capacity retention rate and relatively small cycle gas generation can be obtained. Among them, the compound shown in Structural Formula 1 decomposes on the surface of the positive electrode to form a protective film, which uniformly covers the surface of the positive electrode material. On the one hand, it inhibits the decomposition of alkaline oxides such as lithium carbonate on the surface of the positive electrode material and reduces gas generation. On the other hand, it can well protect the stability of the positive electrode structure. It is speculated that the decomposition product of Structural Formula 1 on the surface of the positive electrode forms a relatively stable protective film by complexing with nickel ions, restricting its dissolution. At the same time, the formed film has a certain elasticity and will expand and contract correspondingly with the expansion and contraction of the positive electrode material, realizing the protection of the positive electrode and being not easily broken during charge and discharge cycles. Description of the Drawings

[0037] Figure 1 is the TEM image of the positive electrode after cycling provided in Example 7 of the present invention;

[0038] Figure 2 is the TEM image of the positive electrode after cycling provided in Comparative Example 1 of the present invention. Detailed Embodiments

[0039] In order to make the technical problems, technical solutions and beneficial effects solved by the present invention clearer, the present invention will be further described in detail below with reference to the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0040] An embodiment of the present invention provides a lithium ion battery, including a positive electrode, a negative electrode and a non-aqueous electrolyte. 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 LiNi xCo y Mn z L (1-x-y-z) O₂, where L is Al, Sr, Mg, Ti, Ca, Zr, Zn, Si, Cu, V or Fe, 0.5 ≤ x ≤ 1, 0 ≤ y ≤ 0.5, 0 ≤ z ≤ 0.5, 0 ≤ x + y + z ≤ 1, and the upper limit voltage of the lithium-ion battery ≥ 4.2 V;

[0041] The non-aqueous electrolyte includes a solvent, an electrolyte salt, and a compound represented by Structural Formula 1:

[0042] A-D-B-E-C

[0043] Structural Formula 1

[0044] Wherein, A, B, and C are each independently selected from groups containing a cyclic carbonate group, a cyclic sulfate group, a cyclic sulfite group, a cyclic sulfonate group, a cyclic sulfone group, a cyclic sulfoxide group, a cyclic carboxylate group, or a cyclic anhydride group;

[0045] D and E are each independently selected from a single bond, or a group containing an alkylene group, an ether bond, a sulfur-oxygen double bond, or a carbon-oxygen double bond;

[0046] Based on the total mass of the non-aqueous electrolyte being 100%, the addition amount of the compound represented by Structural Formula 1 is 0.01 - 5.0%.

[0047] In the lithium-ion battery provided by the present invention, the compound represented by Structural Formula 1 decomposes on the surface of the positive electrode to form a protective film, which uniformly covers the surface of the positive electrode material. On the one hand, it inhibits the decomposition of alkaline oxides such as lithium carbonate on the surface of the positive electrode material and reduces the generation of gas. On the other hand, it can well protect the stability of the positive electrode structure. It is speculated that the decomposition product of Structural Formula 1 on the surface of the positive electrode complexes with nickel ions to form a relatively stable protective film, restricting its dissolution. At the same time, the formed film has a certain elasticity and will expand and contract correspondingly with the expansion and contraction of the positive electrode material to achieve the protection of the positive electrode and is not easily broken during charge and discharge cycles.

[0048] It should be noted that the performance of the battery is related to the nickel content in the positive electrode active material and the content of the compound shown in Structural Formula 1 in the non-aqueous electrolyte. When the nickel content in the positive electrode active material is too low, although adding the compound shown in Structural Formula 1 can improve the high-temperature cycle performance of the battery to a certain extent, its improvement effect is relatively low. However, when the nickel content in the positive electrode active material is relatively high (0.5 ≤ x ≤ 1), the compound shown in Structural Formula 1 has an extremely excellent improvement effect on the high-temperature cycle performance of the battery, indicating that there is a clear correlation between the presence of nickel in the positive electrode active material and the compound shown in Structural Formula 1. As the nickel content increases, the compound shown in Structural Formula 1 can better play its improvement role on the battery. At the same time, when the addition amount of the compound shown in Structural Formula 1 is too low, it cannot play a film-forming protection role, and the improvement effect on the battery performance is not obvious; when the addition amount of the compound shown in Structural Formula 1 is too high, not only will the film be too thick resulting in an increase in impedance, but also the viscosity of the electrolyte will be significantly increased, affecting the performance of the battery. Therefore, adding an appropriate amount of the compound shown in Structural Formula 1 can have a better matching effect with the high-nickel ternary material.

[0049] When the upper charging limit voltage of the lithium-ion battery is relatively high, its electrolyte is more likely to decompose, and the compound shown in Structural Formula 1 can effectively inhibit the decomposition of the electrolyte under high-voltage conditions. Therefore, it is particularly suitable for high-voltage lithium-ion batteries with an upper limit voltage ≥ 4.2V.

[0050] In some embodiments, x is selected from 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.83, 0.85, 0.88, 0.90, 0.95.

[0051] In some embodiments, the positive electrode active material is selected from LiNi 0.5 Co 0.2 Mn 0.3 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.7 Co 0.1 Mn 0.2 O2, LiNi 0.8 Co 0.15 Al 0.05 O2, LiNi 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.6 Mn 0.4 O2 and LiNi 0.8 Mn 0.2 One or more of O2.

[0052] In some embodiments, element L is introduced into the positive electrode active material by doping, where L is Al, Sr, Mg, Ti, Ca, Zr, Zn, Si, Cu, V or Fe. The doped element L can provide a stronger A-O chemical bond than active transition metals such as Ni, Co, and Mn, inhibit the precipitation of lattice oxygen at high voltages, and improve the stability of the material structure.

[0053] In some embodiments, the number of cyclic carbonate groups, cyclic sulfate groups, cyclic sulfite groups, cyclic sulfonate groups, cyclic sulfone groups, cyclic sulfoxide groups, cyclic carboxylate groups or cyclic anhydride groups contained in A, B, and C independently of each other is 1 to 5, and the total number of cyclic carbonate groups, cyclic sulfate groups, cyclic sulfite groups, cyclic sulfonate groups, cyclic sulfone groups, cyclic sulfoxide groups, cyclic carboxylate groups or cyclic anhydride groups of A, B, and C is less than or equal to 10.

[0054] In some embodiments, A and C independently of each other are selected from the groups shown in Structural Formula 2:

[0055]

[0056] Among them, n is an integer selected from 0 to 4, and R1 is selected from hydrogen, halogen or a C1-C5 halogenated hydrocarbon group; R2, R3, R4, R5, R6, and R7 are independently selected from a C1-C3 alkylene group, a C1-C3 alkoxy group, an oxygen atom, At least one of R2, R3, and R4 is selected from And at least one of R2, R3, and R4 is selected from an oxygen atom, and at least one of R5, R6, and R7 is selected from And at least one of R5, R6, and R7 is selected from an oxygen atom.

[0057] In a preferred embodiment, the combined groups of -R3-R2-R4- and -R7-R5-R6- are independently selected from

[0058] In some embodiments, B is selected from the group shown in Structural Formula 3:

[0059]

[0060] Among them, m is an integer selected from 1 to 4, and R8, R9, and R 10 are independently selected from a C1-C3 alkylene group, a C1-C3 alkoxy group, an oxygen atom, R8, R9, and R 10 At least one of them is selected from And at least one of R8, R9, and R 10 is selected from an oxygen atom.

[0061] In a preferred embodiment, the combined group -R9-R8-R 10 - are each independently selected from

[0062] In some embodiments, D and E are each independently selected from the groups represented by Structural Formula 4:

[0063]

[0064] wherein z is an integer selected from 0 to 4, R 11 and R 13 are each independently selected from a single bond or a C1-C5 alkylene group, and R 12 is selected from a single bond,

[0065] In some embodiments, A and C are the same as each other, A and B are the same or different from each other, and D and E are the same as each other.

[0066] When A and C are the same as each other and D and E are the same as each other, the compound represented by Structural Formula 1 has a symmetric structure. Compared with the asymmetric structure, the compound represented by Structural Formula 1 with a symmetric structure is more convenient in synthesis, has a higher product yield, and is beneficial to reducing production costs.

[0067] In some embodiments, D and E are each independently selected from a single bond or a C1-C5 alkylene group, and A, B, and C are each independently selected from a substituted or unsubstituted cyclic carbonate group, cyclic sulfate group, cyclic sulfite group, cyclic sulfonate group, cyclic sulfone group, cyclic sulfoxide group, cyclic carboxylate group, or cyclic anhydride group. Preferably, when A, B, or C is substituted, the substituent is selected from a halogen, a hydrocarbon group, or a halogenated hydrocarbon group. More preferably, when A, B, or C is substituted, the substituent is selected from a halogen, an alkyl group, or a halogenated alkyl group.

[0068] As an example, the compound represented by Structural Formula 1 may be selected from one or more of the following compounds:

[0069]

[0070]

[0071]

[0072]

[0073] In some embodiments, D and E are each independently selected from the groups represented by Structural Formula 4:

[0074]

[0075] wherein, z is an integer selected from 1 to 4, and R 11 and R 13 each independently selected from a single bond or a C1-C5 alkylene group, and R 12 is selected from

[0076]

[0077] A, B, and C each independently selected from a substituted or unsubstituted cyclic carbonate group, a cyclic sulfate group, a cyclic sulfite group, a cyclic sulfonate group, a cyclic sulfone group, a cyclic sulfoxide group, a cyclic carboxylate group, or a cyclic anhydride group. Preferably, when A, B, or C is substituted, the substituent is selected from a halogen, a hydrocarbon group, or a halogenated hydrocarbon group. More preferably, when A, B, or C is substituted, the substituent is selected from a halogen, an alkyl group, or a halogenated alkyl group.

[0078] As an example, the compound shown in Structural Formula 1 may be selected from one or more of the following compounds:

[0079]

[0080]

[0081]

[0082] In some embodiments, the compound shown in Structural Formula 1 may also be selected from one or more of the following compounds:

[0083]

[0084]

[0085] It should be noted that the above are some of the compounds claimed in the present invention, but are not limited thereto, and should not be construed as a limitation of the present invention.

[0086] Those skilled in the art can know the preparation methods of the above compounds according to the common general knowledge in the field of chemical synthesis when knowing the structural formula of the compound of Structural Formula 1. For example:

[0087] Compound 1 can be prepared by the following method:

[0088] Sorbitol, dimethyl carbonate, methanol basic substance catalyst potassium hydroxide, and an organic solvent such as DMF are placed in a reaction vessel, and the reaction is carried out under heating conditions for several hours. Then, a certain amount of oxalic acid is added to adjust the pH to neutral, and after filtration and recrystallization, Intermediate Product 1 can be obtained. Subsequently, Intermediate Product 1, a carbonate, thionyl chloride, etc. are subjected to an esterification reaction under high temperature conditions to obtain Intermediate Product 2, and then Intermediate Product 2 is oxidized using an oxidant such as sodium periodate to obtain Compound 1.

[0089] Compound 2 can be prepared by the following method:

[0090] React diacetone-D-mannitol, dimethyl carbonate, methanol, potassium carbonate, dioxane, etc. under heating and stirring for several hours, then add a certain amount of oxalic acid to adjust the pH of the solution to neutral, filter and concentrate to obtain intermediate 3; add appropriate amounts of pure water, carbonate, acid, etc. to intermediate 3 for hydrolysis reaction to obtain intermediate 4; then react intermediate 4, thionyl chloride and carbonate solvent under heating conditions to prepare intermediate 5; finally, oxidize intermediate 5 with an oxidant such as sodium periodate to obtain compound 2.

[0091] In some embodiments, the solvent includes one or more of an ether solvent, a nitrile solvent, a carbonate solvent, and a carboxylate solvent.

[0092] Among them, the ether solvent includes a cyclic ether or a chain ether.

[0093] Examples of the cyclic ether can include, for example, one or more of 1,3-dioxolane (DOL), 1,4-dioxane (DX), crown ether, tetrahydrofuran (THF), 2-methyltetrahydrofuran (2-CH3-THF), 2-trifluoromethyltetrahydrofuran (2-CF3-THF).

[0094] Examples of the chain ether can include, for example, one or more of dimethoxymethane (DMM), 1,2-dimethoxyethane (DME), diethylene glycol dimethyl ether (TEGDME).

[0095] Among them, examples of the nitrile solvent can include, for example, one or more of acetonitrile, glutarodinitrile, and malononitrile.

[0096] Among them, the carbonate solvent includes a cyclic carbonate or a chain carbonate.

[0097] Examples of the cyclic carbonate can include, for example, one or more of ethylene carbonate (EC), propylene carbonate (PC), γ-butyrolactone (GBL), and butylene carbonate (BC).

[0098] Examples of the chain carbonate can include, for example, one or more of dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), methyl n-propyl carbonate, ethyl n-propyl carbonate, and dipropyl carbonate (DPC).

[0099] Among them, the carboxylate solvent includes a cyclic carboxylate or a chain carbonate.

[0100] Examples of the cyclic carboxylic acid ester include one or more of γ-butyrolactone, γ-valerolactone, and δ-valerolactone.

[0101] Examples of the chain carbonate include one or more of methyl acetate (MA), ethyl acetate (EA), propyl acetate (EP), butyl acetate, propyl propionate (PP), and butyl propionate.

[0102] In some embodiments, the electrolyte salt is selected from lithium salts. In a preferred embodiment, the electrolyte salt is selected from LiPF6, LiBF4, LiBOB, LiDFOB, LiN(SO2CF3)2, LiN(SO2C2F5)2, LiC(SO2CF3)3, LiN(SO2F)2, LiClO4, LiAsF6, LiSbF6, LiCF3SO3, Li2B 10 Cl 10 , lithium salts of lower aliphatic carboxylic acids, and one or more of LiAlCl4.

[0103] In some embodiments, in the non-aqueous electrolyte, the concentration of the electrolyte salt is 0.1 mol / L - 8 mol / L.

[0104] In a preferred embodiment, in the non-aqueous electrolyte, the concentration of the electrolyte salt is 0.5 mol / L - 4 mol / L. Specifically, the concentration of the electrolyte salt can be 0.5 mol / L, 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L, 3 mol / L, 3.5 mol / L, or 4 mol / L.

[0105] In some embodiments, the non-aqueous electrolyte further includes an auxiliary additive, and the auxiliary additive includes at least one of an unsaturated cyclic carbonate compound, a fluorinated cyclic carbonate compound, an aromatic additive, a fluorinated anisole compound, a dicarboxylic anhydride, lithium difluorophosphate, and lithium bis(fluorosulfonyl)imide (LiFSI).

[0106] In some embodiments, the unsaturated cyclic carbonate compound includes at least one of vinylene carbonate (VC), ethylene vinylene carbonate (VEC), 4,5-dimethyl vinylene carbonate, phenyl vinylene carbonate, and 4,5-divinyl ethylene carbonate;

[0107] When the non-aqueous electrolyte contains an unsaturated cyclic carbonate compound, based on the total mass of the non-aqueous electrolyte being 100%, the content of the unsaturated cyclic carbonate compound is 0.1 - 5%.

[0108] In some embodiments, the fluorinated cyclic carbonate compounds include one or more of fluoroethylene carbonate (FEC), 4,4-difluoroethylene carbonate, 4,5-difluoroethylene carbonate, 4-fluoro-4-methyl ethylene carbonate, 4,5-difluoro-4-methyl ethylene carbonate, 4-fluoro-5-methyl ethylene carbonate, 4,4-difluoro-5-methyl ethylene carbonate, 4-(fluoromethyl) ethylene carbonate, 4-(difluoromethyl) ethylene carbonate, 4-(trifluoromethyl) ethylene carbonate, 4-(fluoromethyl)-4-fluoroethylene carbonate, 4-(fluoromethyl)-5-fluoroethylene carbonate, 4-fluoro-4,5-dimethyl ethylene carbonate, 4,5-difluoro-4,5-dimethyl ethylene carbonate, 4,4-difluoro-5,5-dimethyl ethylene carbonate.

[0109] When the non-aqueous electrolyte contains fluorinated cyclic carbonate compounds, based on the total mass of the non-aqueous electrolyte being 100%, the content of the fluorinated cyclic carbonate compounds is 0.1 - 30%;

[0110] In some embodiments, the aromatic additives include aromatic compounds such as biphenyl, alkyl biphenyl, terphenyl, partial hydrides of terphenyl, cyclohexylbenzene, tert-butylbenzene, tert-amylbenzene, diphenyl ether, dibenzofuran; one or more of 2-fluorobiphenyl, o-cyclohexylfluorobenzene, p-cyclohexylfluorobenzene.

[0111] When the non-aqueous electrolyte contains aromatic additives, based on the total mass of the non-aqueous electrolyte being 100%, the mass percentage content of the aromatic additives is 0.1 - 5%.

[0112] In some embodiments, the fluorinated anisole compounds include one or more of 2,4-difluoroanisole, 2,5-difluoroanisole, 2,6-difluoroanisole. When the non-aqueous electrolyte contains fluorinated anisole compounds, based on the total mass of the non-aqueous electrolyte being 100%, the mass percentage content of the fluorinated anisole compounds is 0.1 - 5%.

[0113] In some embodiments, the dicarboxylic anhydrides include one or more of succinic anhydride, maleic anhydride, phthalic anhydride. When the non-aqueous electrolyte contains dicarboxylic anhydrides, based on the total mass of the non-aqueous electrolyte being 100%, the mass percentage content of the dicarboxylic anhydrides is 0.1 - 5%.

[0114] In some embodiments, when the non-aqueous electrolyte contains lithium difluorophosphate, based on the total mass of the non-aqueous electrolyte being 100%, the mass percentage content of the lithium difluorophosphate is 0.1 - 2%;

[0115] In some embodiments, when the non-aqueous electrolyte contains lithium bis(fluorosulfonyl)imide (LiFSI), based on the total mass of the non-aqueous electrolyte being 100%, the mass percentage of lithium bis(fluorosulfonyl)imide (LiFSI) is 0.1-5%.

[0116] In some embodiments, the auxiliary additive further includes nitrogen-containing compounds such as 1-methyl-2-pyrrolidone, 1-methyl-2-piperidone, 3-methyl-2-oxazolidinone, 1,3-dimethyl-2-imidazolidinone, N-methylsuccinimide; hydrocarbon compounds such as heptane, octane, cycloheptane; fluorinated aromatic compounds such as fluorobenzene, difluorobenzene, trifluorotoluene, etc.

[0117] It should be noted that, unless otherwise specified, generally, the mass percentage range of any optional substance in the auxiliary additive in the non-aqueous electrolyte is 10% or less, preferably, the mass percentage is 0.1-5%.

[0118] In a preferred embodiment, the positive electrode active material is selected from LiNi 0.5 Co 0.2 Mn 0.3 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.7 Co 0.1 Mn 0.2 O2, LiNi 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.6 Mn 0.4 O2 and LiNi 0.8 Mn 0.2 One or more of O2.

[0119] In some embodiments, the positive electrode further includes a positive electrode current collector, and the positive electrode material layer covers the surface of the positive electrode current collector. The positive electrode current collector is selected from metal materials that can conduct electrons. Preferably, the positive electrode current collector includes one or more of Al, Ni, and stainless steel. In a more preferred embodiment, the positive electrode current collector is selected from aluminum foil.

[0120] 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.

[0121] The positive electrode binder includes one or more of thermoplastic resins such as polyvinylidene fluoride, copolymers of vinylidene fluoride, polytetrafluoroethylene, copolymers of vinylidene fluoride - hexafluoropropylene, copolymers of tetrafluoroethylene - hexafluoropropylene, copolymers of tetrafluoroethylene - perfluoroalkyl vinyl ether, copolymers of ethylene - tetrafluoroethylene, copolymers of vinylidene fluoride - tetrafluoroethylene, copolymers of vinylidene fluoride - trifluoroethylene, copolymers of vinylidene fluoride - trichloroethylene, copolymers of vinylidene fluoride - fluoroethylene, copolymers of vinylidene fluoride - hexafluoropropylene - tetrafluoroethylene, thermoplastic polyimide, polyethylene, and polypropylene; acrylic resins; and styrene - butadiene rubber.

[0122] The positive electrode conductive agent includes one or more of conductive carbon black, conductive carbon spheres, conductive graphite, conductive carbon fibers, carbon nanotubes, graphene, or reduced graphene oxide.

[0123] In some embodiments, the negative electrode includes a negative electrode material layer, the negative electrode material layer includes a negative electrode active material, and the negative electrode active material includes one or more of a silicon - based negative electrode, a carbon - based negative electrode, a tin - based negative electrode, and a lithium negative electrode. Among them, the silicon - based negative electrode includes one or more of silicon materials, silicon oxides, silicon - carbon composite materials, and silicon alloy materials; the carbon - based negative electrode includes one or more of graphite, hard carbon, soft carbon, graphene, and mesophase carbon microspheres; the tin - based negative electrode includes one or more of tin, tin - carbon, tin - oxygen, and tin metal compounds; the lithium negative electrode includes one or more of metallic lithium or lithium alloys. The lithium alloy may specifically be at least one of lithium - silicon alloy, lithium - sodium alloy, lithium - potassium alloy, lithium - aluminum alloy, lithium - tin alloy, and lithium - indium alloy.

[0124] In some embodiments, the negative electrode further includes a negative electrode current collector, and the negative electrode material layer covers the surface of the negative electrode current collector. The negative electrode current collector is selected from metal materials that can conduct electrons. Preferably, the negative electrode current collector includes one or more of Cu, Ni, and stainless steel. In a more preferred embodiment, the negative electrode current collector is selected from copper foil.

[0125] In some embodiments, the negative electrode 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 material layer.

[0126] The negative electrode binder includes one or more of thermoplastic resins such as polyvinylidene fluoride, copolymers of vinylidene fluoride, polytetrafluoroethylene, copolymers of vinylidene fluoride - hexafluoropropylene, copolymers of tetrafluoroethylene - hexafluoropropylene, copolymers of tetrafluoroethylene - perfluoroalkyl vinyl ether, copolymers of ethylene - tetrafluoroethylene, copolymers of vinylidene fluoride - tetrafluoroethylene, copolymers of vinylidene fluoride - trifluoroethylene, copolymers of vinylidene fluoride - trichloroethylene, copolymers of vinylidene fluoride - fluoroethylene, copolymers of vinylidene fluoride - hexafluoropropylene - tetrafluoroethylene, thermoplastic polyimide, polyethylene, and polypropylene; acrylic resins; and styrene - butadiene rubber.

[0127] The negative electrode conductive agent includes one or more of conductive carbon black, conductive carbon spheres, conductive graphite, conductive carbon fibers, carbon nanotubes, graphene, or reduced graphene oxide.

[0128] In some embodiments, the battery further includes a separator located between the positive electrode and the negative electrode.

[0129] The separator can be an existing conventional separator, which can be a ceramic separator, a polymer separator, a non - woven fabric, an inorganic - organic composite separator, etc., 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 separators.

[0130] The present invention is further illustrated by the following examples.

[0131] I. Examples 1 - 42 and Comparative Examples 1 - 9

[0132] 1) Preparation of the electrolyte

[0133] Ethylene carbonate (EC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC) were mixed at a mass ratio of EC:DEC:EMC = 1:1:1, and then lithium hexafluorophosphate (LiPF6) was added to a molar concentration of 1 mol / L, and then the following additives were added according to the respective tables. The dosage of the additives is calculated as a percentage of the total mass of the electrolyte.

[0134] 2) Preparation of the positive electrode plate

[0135] The positive electrode active material, conductive carbon black Super - P, and binder polyvinylidene fluoride (PVDF) were mixed at a mass ratio of 93:4:3, and then they were dispersed in N - methyl - 2 - pyrrolidone (NMP) to obtain a positive electrode slurry. The positive electrode active material is as shown in the following respective tables. The positive electrode slurry was uniformly coated on both sides of the aluminum foil, dried, calendered, and vacuum - dried, and then an aluminum lead wire was welded with an ultrasonic welder to obtain a positive electrode plate, and the thickness of the plate is 120 - 150 μm.

[0136] 3) Preparation of the negative electrode plate

[0137] Mix the negative electrode active material graphite, conductive carbon black Super - P, binder styrene - butadiene rubber (SBR) and carboxymethyl cellulose (CMC) in a mass ratio of 94:1:2.5:2.5, and then disperse them in deionized water to obtain a negative electrode slurry. Coat the negative electrode slurry on both sides of the copper foil, and after drying, rolling and vacuum drying, weld the nickel lead - out wire with an ultrasonic welder to obtain the negative electrode plate, and the thickness of the plate is 120 - 150 μm.

[0138] 4) Preparation of the battery cell

[0139] Place a three - layer separator with a thickness of 20 μm between the positive electrode plate and the negative electrode plate, then wind the sandwich structure composed of the positive electrode plate, the negative electrode plate and the separator, flatten the wound body and put it into an aluminum foil packaging bag, and bake it in vacuum at 75 °C for 48 h to obtain the battery cell to be injected with electrolyte.

[0140] 5) Injection of electrolyte and formation of the battery cell

[0141] In a glove box with the water and oxygen content below 20 ppm and 50 ppm respectively, inject the above - prepared electrolyte into the battery cell, carry out vacuum packaging, and leave it standing at 45 °C for 24 h.

[0142] Then carry out the conventional formation of the first charge according to the following steps: constant - current charge at 0.05C for 180 min, constant - current charge at 0.1C for 180 min, constant - current charge at 0.2C for 120 min, age at 45 °C for 48 h, then carry out secondary vacuum sealing, and then further constant - current charge at a current of 0.2C until 4.4V (LiNi 0.5 Co 0.2 Mn 0.3 O2 / AG) or 4.2V (LiNi 0.8 Co 0.15 Al 0.05 O2 / AG) or 4.2V (LiNi 0.8 Co 0.1 Mn 0.1 O2 / AG) or 4.25V (LiNi 0.7 Co 0.1 Mn 0.2 O2 / AG) or 4.35V (LiNi 0.6 Co 0.2 Mn 0.2 O2 / AG), and then constant - current discharge at a current of 0.2C until 3.0V.

[0143] II. Performance testing

[0144] Carry out the following performance tests on the lithium - ion batteries prepared in Examples 1 - 42 and Comparative Examples 1 - 9:

[0145] High-temperature cycle performance test

[0146] Place the prepared lithium-ion battery in an oven at a constant temperature of 45°C and charge it at a constant current of 1C to 4.4V (LiNi 0.5 Co 0.2 Mn 0.3 O2 / AG) or 4.2V (LiNi 0.8 Co 0.15 Al 0.05 O2 / AG) or 4.2V (LiNi 0.8 Co 0.1 Mn 0.1 O2 / AG) or 4.25V (LiNi 0.7 Co 0.1 Mn 0.2 O2 / AG) or 4.35V (LiNi 0.6 Co 0.2 Mn 0.2 O2 / AG), then charge at a constant current and constant voltage until the current drops to 0.05C, and then discharge at a constant current of 1C to 3.0V. Repeat this cycle, record the discharge capacity of the first time and the last time, and measure the initial volume of the battery and the volume after 1000 cycles.

[0147] Calculate the capacity retention rate of the high-temperature cycle according to the following formula:

[0148] Capacity retention rate = Discharge capacity of the last time / Discharge capacity of the first time × 100%.

[0149] Calculate the volume expansion rate of the high-temperature cycle according to the following formula:

[0150] Volume expansion rate (%) = (Volume of the battery after cycling - Initial volume of the battery) / Initial volume of the battery × 100%.

[0151] For the batteries used in the following data tests, other conditions are the same except for the differences listed in each table.

[0152] 1. Fill in the test results obtained from Examples 1 to 10 and Comparative Examples 1 to 4 in Table 1.

[0153] Table 1

[0154]

[0155]

[0156] From the test results in Table 1, it can be seen that when the positive electrode active material is LiNi 0.5 Co 0.2 Mn 0.3When it is O2, by comparing Examples 1-10 with Comparative Example 1, it can be seen that adding the compound shown in Structural Formula 1 can significantly inhibit gas generation during high-temperature cycling. When the content of the compound shown in Structural Formula 1 is 1% - 2%, the minimum volume expansion rate of the battery during high-temperature cycling is 7.2% - 8.2%, and at this time, it has the optimal high-temperature cycling capacity retention rate of 75.2% - 77.2%. By comparing Examples 1-10 with Comparative Examples 2-3, it can be seen that when the content of the compound shown in Structural Formula 1 is less than 0.01% or greater than 5%, the cyclic gas generation amount of the battery increases significantly, and the high-temperature cycling performance also decreases significantly. This shows that in high-nickel ternary lithium-ion batteries, the reasonable addition amount of the compound shown in Structural Formula 1 is 0.01% - 5%, and too much or too little is not conducive to improving the battery performance.

[0157] 2. Fill in the test results obtained from Examples 7, 11-14 and Comparative Examples 1, 4-9 in Table 2.

[0158] Table 2

[0159]

[0160]

[0161] By comparing Examples 7, 11-14 with Comparative Examples 1, 4-9, it can be found that when the nickel content of the positive electrode active material is low, the cyclic volume expansion rate in Comparative Example 5 is still 48.4%. The improvement range compared with Comparative Example 4 is much smaller than the improvement range between Example 7 and Comparative Example 1, and is also significantly smaller than the improvement range between Examples 11-14 and Comparative Examples 6-9. Moreover, the cyclic performance of the low-nickel battery system in Comparative Example 5 has no obvious improvement. That is, the improvement effect of the compound shown in Structural Formula 1 on the battery performance is significantly related to the nickel content in the positive electrode active material. When the nickel content in the positive electrode active material is higher than a certain value, the compound shown in Structural Formula 1 can play a better cooperative role.

[0162] 3. Fill in the test results obtained from Examples 15-24 and Comparative Example 6 in Table 3.

[0163] Table 3

[0164]

[0165] From the test data in Table 3, when the positive electrode active material is LiNi 0.6 Co 0.2 Mn 0.2 O2, by comparing Examples 15-24 with Comparative Example 6, it can be seen that adding the compound shown in Structural Formula 1 can significantly reduce the cyclic gas generation of the battery and improve the high-temperature cycling performance. At the same time, using different compounds shown in Structural Formula 1 can all improve the high-temperature cycling performance of the battery to varying degrees.

[0166] 4. Fill the test results obtained from Examples 25 - 31 and Comparative Example 7 into Table 4.

[0167] Table 4

[0168]

[0169]

[0170] From the test data in Table 4, it can be seen that when the positive electrode active material is LiNi 0.7 Co 0.1 Mn 0.2 O₂, by comparing Examples 25 - 30 and Comparative Example 7, it can be known that adding the compounds shown in Structural Formula 1 can significantly reduce the cyclic gas generation of the battery and improve the high - temperature cyclic performance. At the same time, using different compounds shown in Structural Formula 1 can all improve the high - temperature cyclic performance of the battery to varying degrees.

[0171] 5. Fill the test results obtained from Examples 32 - 35 and Comparative Example 8 into Table 5.

[0172] Table 5

[0173]

[0174] From the test data in Table 5, it can be seen that when the positive electrode active material is LiNi 0.8 Co 0.15 Al 0.05 O₂, by comparing Examples 32 - 35 and Comparative Example 8, it can be known that adding different compounds shown in Structural Formula 1 can significantly reduce the cyclic gas generation of the battery, and at the same time, the high - temperature cyclic capacity retention rate also has a significant improvement.

[0175] 6. Fill the test results obtained from Examples 36 - 42 and Comparative Example 9 into Table 6.

[0176] Table 6

[0177]

[0178]

[0179] From the test data in Table 6, it can be seen that when the positive electrode active material is LiNi 0.8 Co 0.1 Al 0.1 O₂, by comparing Examples 36 - 42 and Comparative Example 9, it can be known that adding different compounds shown in Structural Formula 1 can significantly reduce the cyclic gas generation of the battery, and at the same time, the high - temperature cyclic capacity retention rate also has a significant improvement.

[0180] 7. Place the lithium-ion batteries obtained in Example 7 and Comparative Example 1 in an oven at a constant temperature of 45 °C and charge them at a constant current of 1C to 4.4V (LiNi 0.5 Co 0.2 Mn 0.3 O2 / AG), then charge at a constant current and constant voltage until the current drops to 0.05C, and then discharge at a constant current of 1C to 3.0V. After 1000 cycles, disassemble the lithium-ion battery, take out the positive electrode and observe it by transmission electron microscopy. The TEM image of the positive electrode of Example 7 is as shown in Figure 1 , and the TEM image of the positive electrode of Comparative Example 1 is as shown in Figure 2 .

[0181] Comparing Figure 1 and Figure 2 of the transmission electron microscopy images, when the electrolyte does not contain the compound shown in Structural Formula 1, it is observed that the lattice fringes of the positive electrode material in Comparative Example 1 after cycling become significantly disordered, that is, the structure of the positive electrode material has changed. Combining the battery performance data in Table 1, it can be seen that the volume expansion rate of Comparative Example 1 after cycling is 57.4%; while Figure 2 in Example 7, the lattice fringes of the positive electrode material are still orderly distributed, and the volume expansion rate of Example 7 after cycling is only 7.2%, indicating that adding the additive shown in Structural Formula 1 can indeed protect the positive electrode material and inhibit gas generation during cycling.

[0182] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A lithium-ion battery, characterized in that, It includes a positive electrode, a negative electrode and a non-aqueous electrolyte. 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 LiNi x Co y Mn z L (1-x-y-z) O2, where L is Al, Sr, Mg, Ti, Ca, Zr, Zn, Si, Cu, V or Fe, 0.5 ≤ x ≤ 1, 0 ≤ y ≤ 0.5, 0 ≤ z ≤ 0.5, 0 ≤ x + y + z ≤ 1, and the upper limit voltage of the lithium-ion battery ≥ 4.2V; The non-aqueous electrolyte includes a solvent, an electrolyte salt, and a compound represented by Structural Formula 1: A-D-B-E-C Structural Formula 1 The compound represented by Structural Formula 1 is selected from one or more of the following compounds: ； Based on the total mass of the non-aqueous electrolyte being 100%, the addition amount of the compound represented by Structural Formula 1 is 0.5% to 3.0%.

2. The lithium ion battery according to claim 1, characterized in that, The positive electrode active material is selected from LiNi 0.5 Co 0.2 Mn 0.3 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.7 Co 0.1 Mn 0.2 O2, LiNi 0.8 Co 0.15 Al 0.05 O2, LiNi 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.6 Mn 0.4 O2 and LiNi 0.8 Mn 0.2 One or more of O2.

3. The lithium ion battery according to claim 1, characterized in that, The non-aqueous electrolyte further includes an auxiliary additive, and the auxiliary additive includes at least one of an unsaturated cyclic carbonate compound, a fluorinated cyclic carbonate compound, an aromatic additive, a fluorinated anisole compound, a dicarboxylic anhydride, lithium difluorophosphate, and lithium bis(fluorosulfonyl)imide (LiFSI).

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