Lithium-ion battery

Abstract

Provided is a lithium-ion battery, which comprises a positive electrode sheet, a negative electrode sheet and a non-aqueous electrolyte. The positive electrode sheet comprises a positive electrode material layer containing a positive electrode active material, wherein the positive electrode active material comprises lithium manganese iron phosphate LiMnxFeyM1-x-yPO4 coated with a carbon coating layer, where 0.1≤x≤0.8, 0.2≤y≤0.9, 0≤1-x-y≤0.1, and M is selected from at least one element of Co, B, Ga, F, W, Zr, Mg, Na, Pb, K, Al, Cr, Ba, Ca, Ni, Sr, Ti, Zn, Si, V, Mo and Nb. The non-aqueous electrolyte comprises a non-aqueous organic solvent, LiFSI and VC. The lithium-ion battery satisfies the following condition: 0.1≤a(c+d) / b≤1.7, wherein 1.5≤a≤4.5, 25≤b≤40, 1≤c≤10, and 0.01≤d≤1.5; a is the mass percentage content of the carbon coating layer in the positive electrode material layer, with the unit thereof being wt%; b is the porosity of the positive electrode sheet, with the unit thereof being %; c is the mass percentage content of LiFSI in the non-aqueous electrolyte, with the unit thereof being wt%; and d is the mass percentage content of vinylene carbonate in the non-aqueous electrolyte, with the unit thereof being wt%. The lithium-ion battery can give full play to the synergistic effect between LiFSI and VC and the carbon-coated positive electrode active material, and therefore the battery has improved impedance, and also has good high-temperature cycling performance.

Description

A lithium-ion battery

[0001] This disclosure is based on the Chinese patent application with application number 202311712214.7 and application date December 13, 2023, and claims the priority of this Chinese patent application. The entire content of this Chinese patent application is hereby introduced into this application as a reference. Technical Field

[0002] The present application belongs to the technical field of secondary batteries, and specifically relates to a lithium-ion battery. Background Art

[0003] Lithium-ion secondary batteries have always been considered the most promising energy conversion and energy storage devices. Among them, lithium manganese iron phosphate (LMFP) has strong safety and stable chemical properties. At the same time, the manganese element doped in LMFP can increase the voltage platform of the material, raising the voltage platform from 3.4V of LFP to 4.1V, which increases the theoretical energy density of LMFP batteries by 15-20%. However, the presence of manganese makes it more difficult for lithium ions to be deintercalated and moved, resulting in poor conductivity of the material and, in turn, poor rate performance. Moreover, during the reaction, Mn 3+ The resulting Jahn-Teller effect causes Mn to dissolve and deposit on the surface of the negative electrode, destroying its SEI film and reducing the cycle life of the battery. Therefore, in order to improve the electrochemical performance of lithium-ion secondary batteries with lithium manganese iron phosphate positive electrodes, lithium manganese iron phosphate is usually carbon-coated during the preparation stage to form a conductive network to increase the conductivity of the material. However, the carbon material of the coating layer is prone to defects during the preparation process. These defects act as active sites in lithium-ion batteries and aggravate the side reactions of the electrolyte on the surface of the lithium manganese iron phosphate material, leading to an increase in the battery's impedance in the later stages. At the same time, side reactions can also cause the battery's capacity to decay rapidly at high temperatures, deteriorating its high-temperature cycle performance.

[0004] Therefore, it is necessary to provide a lithium manganese iron phosphate lithium-ion battery that takes into account both improved impedance and high-temperature cycle performance.

[0005] Application Contents

[0006] Based on this, the purpose of this application is to provide a lithium-ion battery that improves impedance while also having good high-temperature cycle performance.

[0007] In order to achieve the above objectives, this application adopts the following technical solutions.

[0008] A lithium-ion battery comprising a positive electrode sheet, a negative electrode sheet and a non-aqueous electrolyte; the positive electrode sheet comprises a positive electrode material layer comprising a positive electrode active material, the positive electrode active material comprises lithium manganese iron phosphate LiMn coated with a carbon coating layer x Fe y M1-x-y PO4, wherein 0.1≤x≤0.8, 0.2≤y≤0.9, 0≤1-xy≤0.1, and M is at least one element selected from Co, B, Ga, F, W, Zr, Mg, Na, Pb, K, Al, Cr, Ba, Ca, Ni, Sr, Ti, Zn, Si, V, Mo, and Nb; the non-aqueous electrolyte comprises a non-aqueous organic solvent, lithium bis(fluorosulfonyl)imide (LiFSI), and vinylene carbonate (VC);

[0009] The lithium-ion battery meets the following conditions:

[0010] 0.1≤a(c+d) / b≤1.7, and 1.5≤a≤4.5, 25≤b≤40, 1≤c≤10, 0.01≤d≤1.5;

[0011] Wherein, a is the mass percentage of the carbon coating layer in the positive electrode material layer, in wt%;

[0012] b is the porosity of the positive electrode sheet, in %;

[0013] c is the mass percentage of LiFSI in the non-aqueous electrolyte, in wt%;

[0014] d is the mass percentage of vinylene carbonate in the non-aqueous electrolyte, in wt%.

[0015] In some embodiments, the lithium-ion battery satisfies the following condition: 0.2≤a(c+d) / b≤0.7.

[0016] In some embodiments, the mass percentage a of the carbon coating layer in the positive electrode material layer is 2 wt % to 3.5 wt %.

[0017] In some embodiments, the porosity b of the positive electrode sheet is 28% to 36%.

[0018] In some embodiments, the mass percentage c of the LiFSI in the non-aqueous electrolyte is 2 wt % to 6 wt %.

[0019] In some embodiments, the mass percentage d of the vinylene carbonate in the non-aqueous electrolyte is 0.1 wt % to 1 wt %.

[0020] In some embodiments, the non-aqueous electrolyte further includes an auxiliary additive; the auxiliary additive includes at least one of a cyclic carbonate compound, a cyclic sulfate compound, a sultone compound, a phosphate compound, a borate compound, and a nitrile compound.

[0021] In some embodiments, based on the total mass of the non-aqueous electrolyte being 100%, the content of the auxiliary additive is 0.01% to 30%.

[0022] In some preferred embodiments, the cyclic carbonate compound includes at least one of vinyl ethylene carbonate, methylene carbonate, trifluoromethyl ethylene carbonate, bisfluoroethylene carbonate, or the compound represented by the following structural formula 1:

[0023] In the structural formula 1, R 21 、R 22 、R 23 、R 24 、R 25 、R 26 Each is independently selected from a hydrogen atom, a halogen atom, and a C1-C5 group.

[0024] In some preferred embodiments, the cyclic sulfate ester compound includes at least one of vinyl sulfate, 4-methylvinyl sulfate, and propylene sulfate.

[0025] In some preferred embodiments, the sultone compound includes at least one of 1,3-propane sultone, 1,4-butane sultone, and propenyl-1,3-sultone.

[0026] In some preferred embodiments, the phosphate compound includes at least one of tris(trimethylsilyl)phosphate, tris(triethylsilyl)phosphate and the compound represented by the following structural formula 2:

[0027] In the structural formula 2, R 31 、R 32 、R 33 Each independently selected from C1-C5 saturated hydrocarbon group, unsaturated hydrocarbon group, halogenated hydrocarbon group, -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.

[0028] In some preferred embodiments, the borate compound includes at least one of tris(trimethylsilyl)borate and tris(triethylsilyl)borate.

[0029] In some preferred embodiments, the nitrile compound includes at least one of succinonitrile, glutaronitrile, ethylene glycol bis(propionitrile) ether, hexanetrionitrile, adiponitrile, pimelonitrile, suberonitrile, azelaic acid dinitrile, and sebaconitrile.

[0030] In some embodiments, the non-aqueous electrolyte further comprises a lithium salt, and the lithium salt comprises LiPF6, LiBOB, LiDFOB, LiDFOP, LiPO2F2, LiBF4, LiSbF6, LiAsF6, LiN(SO2C2F5)2, LiC(SO2CF3)3, LiClO4, LiAlCl4, LiCF3SO3, LiSO3F, Li2B 10 Cl 10 , at least one of lithium chloroborane, lithium tetrafluorooxalophosphate, lithium trioxalophosphate, a lower aliphatic carboxylic acid lithium having 4 or less carbon atoms, and lithium tetraphenylborate.

[0031] In some embodiments, the concentration of the lithium salt in the non-aqueous electrolyte is 0.1 mol / L to 4 mol / L.

[0032] In some preferred embodiments, the concentration of the lithium salt in the non-aqueous electrolyte is 0.5 mol / L to 2.5 mol / L.

[0033] In some embodiments, the non-aqueous organic solvent includes at least one of a cyclic carbonate solvent, a chain carbonate solvent, a carboxylate solvent, and an ether solvent.

[0034] In some preferred embodiments, the cyclic carbonate includes at least one of ethylene carbonate, propylene carbonate, and butylene carbonate.

[0035] In some preferred embodiments, the linear carbonate solvent includes at least one of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, and methyl propyl carbonate.

[0036] In some preferred embodiments, the carboxylate solvent includes at least one of methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, methyl butyrate, methyl isobutyrate, methyl trimethylacetate, and ethyl trimethylacetate.

[0037] In some preferred embodiments, the ether solvent includes at least one of ethylene glycol dimethyl ether, 1,3-dioxolane, and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether.

[0038] The present application provides a lithium ion battery, wherein the lithium ion battery comprises lithium manganese iron phosphate LiMn coated with a carbon coating layer. x Fe y M 1-x-y PO4 is used as the positive electrode active material, the carbon coating content and the porosity of the positive electrode sheet are controlled, and an appropriate amount of LiFSI and VC are added to the non-aqueous electrolyte. x Fe y M 1-x-yPO4 has strong safety and stable chemical properties, while lithium manganese iron phosphate LiMn x Fe y M 1-x-y The manganese element doped in PO4 can effectively improve the battery charge and discharge platform and thus improve the battery energy density, but the electrical conductivity is poor. Carbon coating of the positive electrode active material can increase the conductivity of the material, and the initial impedance is small, but it can easily lead to an increase in the impedance of the battery in the later stage and rapid capacity decay at high temperatures, deteriorating the high-temperature cycle performance. To this end, the present application optimizes the carbon coating content and improves the porosity of the positive electrode sheet, which helps to enhance the wettability of the electrolyte and the degree of ion diffusion, thereby improving the high-temperature cycle performance. In addition, the inventors found that adding an appropriate amount of LiFSI and VC to the non-aqueous electrolyte helps to form a stable, high-ion conductivity interface film on the surface of the positive and negative electrode materials optimized in this application, thereby further improving the battery performance degradation caused by the carbon coating layer. In particular, when the mass percentage a of the carbon coating layer in the positive electrode material layer, the porosity b of the positive electrode sheet, the mass percentage c of LiFSI in the non-aqueous electrolyte, and the mass percentage d of vinylene carbonate in the non-aqueous electrolyte meet the following conditions: 0.1≤a(c+d) / b≤1.7, and 1.5≤a≤4.5, 25≤b≤40, 1≤c≤10, 0.01≤d≤1.5, the synergistic effect between LiFSI and VC and the carbon-coated positive electrode active material can be fully exerted, so that the lithium manganese iron phosphate lithium ion secondary battery has both low impedance and good high-temperature cycle performance. DETAILED DESCRIPTION

[0039] The experimental methods in the following examples of this application, where specific conditions are not specified, are generally carried out under conventional conditions or conditions recommended by the manufacturers. The various commonly used chemical reagents used in the examples are all commercially available products.

[0040] Unless otherwise defined, all technical and scientific terms used in this application have the same meaning as commonly understood by those skilled in the art to which this application belongs. The terms used in the specification of this application are only for the purpose of describing specific embodiments and are not intended to limit this application.

[0041] As used herein, the terms "comprise," "comprising," and "having," and any variations thereof, are intended to cover non-exclusive inclusions. For example, a process, method, apparatus, product, or device comprising a series of steps is not limited to the listed steps or modules but may optionally include steps not listed, or other steps inherent to the process, method, product, or device.

[0042] In this application, "at least one" refers to one or more than one. "And / or" describes the relationship between related objects, indicating that three relationships can exist. For example, "A and / or B" can mean: A exists alone, A and B exist simultaneously, and B exists alone.

[0043] This embodiment provides a lithium-ion battery, including a positive electrode plate, a negative electrode plate and a non-aqueous electrolyte; the positive electrode plate includes a positive electrode material layer containing a positive electrode active material, and the positive electrode active material includes lithium manganese iron phosphate LiMn coated with a carbon coating layer. x Fe y M 1-x-y PO4, wherein 0.1≤x≤0.8, 0.2≤y≤0.9, 0≤1-xy≤0.1, and M is at least one element selected from Co, B, Ga, F, W, Zr, Mg, Na, Pb, K, Al, Cr, Ba, Ca, Ni, Sr, Ti, Zn, Si, V, Mo, and Nb; the non-aqueous electrolyte comprises a non-aqueous organic solvent, LiFSI, and VC;

[0044] The lithium-ion battery meets the following conditions:

[0045] 0.1≤a(c+d) / b≤1.7, and 1.5≤a≤4.5, 25≤b≤40, 1≤c≤10, 0.01≤d≤1.5;

[0046] Wherein, a is the mass percentage of the carbon coating layer in the positive electrode material layer, in wt%;

[0047] b is the porosity of the positive electrode sheet, in %;

[0048] c is the mass percentage of LiFSI in the non-aqueous electrolyte, in wt%;

[0049] d is the mass percentage of vinylene carbonate in the non-aqueous electrolyte, in wt%.

[0050] This application optimizes the composition of a lithium-ion battery, using carbon-coated lithium iron manganese phosphate as the positive electrode active material. The carbon coating content and the porosity of the positive electrode sheet are controlled, and appropriate amounts of LiFSI and VC are added to the non-aqueous electrolyte. Lithium iron manganese phosphate has strong safety and stable chemical properties. The manganese doped in the lithium iron manganese phosphate effectively improves the battery's charge and discharge platform, thereby increasing the battery's energy density. However, its conductivity is poor. Carbon coating of the positive electrode active material can increase the material's conductivity and reduce initial impedance, but it can easily lead to increased impedance in the later stages of the battery and rapid capacity decay at high temperatures, degrading high-temperature cycling performance. To this end, this application optimizes the carbon coating content and improves the porosity of the positive electrode sheet, which helps enhance electrolyte wettability and ion diffusion, thereby improving high-temperature cycling performance. Furthermore, the inventors discovered that adding appropriate amounts of LiFSI and VC to the non-aqueous electrolyte helps form a stable, highly ionic conductive interface film on the surface of the positive and negative electrode materials optimized in this application, further improving the battery performance degradation caused by the carbon coating. In particular, when the mass percentage a of the carbon coating layer in the positive electrode material layer, the porosity b of the positive electrode sheet, the mass percentage c of LiFSI in the non-aqueous electrolyte, and the mass percentage d of vinylene carbonate in the non-aqueous electrolyte meet the following conditions: 0.1≤a(c+d) / b≤1.7, and 1.5≤a≤4.5, 25≤b≤40, 1≤c≤10, 0.01≤d≤1.5, the synergistic effect between LiFSI and VC and the carbon-coated positive electrode active material can be fully exerted, so that the lithium manganese iron phosphate lithium ion secondary battery has both low impedance and good high-temperature cycle performance.

[0051] In the description of this application, the positive electrode active material may include only the lithium iron manganese phosphate material, or a mixture of the lithium iron manganese phosphate material and other positive electrode active materials. Specifically, based on the total mass of the positive electrode active material, the mass proportion of the lithium iron manganese phosphate is 50% or more. More preferably, based on the total mass of the positive electrode active material, the mass proportion of the lithium iron manganese phosphate is 60% or more, which can further improve the safety and kinetic performance of the lithium-ion battery.

[0052] In a specific embodiment, the lithium manganese iron phosphate LiMn x Fe y M 1-x-y The ratio x of manganese in PO4 can be 0.1, 0.2, 0.3, 0.4, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75 or 0.8, where x refers to the molar ratio of manganese, based on the total molar mass of manganese, iron and M in the lithium manganese iron phosphate being 1. In a preferred embodiment, the ratio x of manganese in the lithium manganese iron phosphate is 0.5 to 0.8.

[0053] Replacing some of the iron in lithium manganese iron phosphate with manganese helps improve the material's charge-discharge performance and boost the battery's energy density. However, excessive manganese reduces the iron ion content, which in turn lowers the material's conductivity. Furthermore, manganese ions are more easily dissolved than iron ions and catalyze electrolyte decomposition, exacerbating side reactions and degrading battery performance. Excessive manganese content results in low energy density for lithium-ion batteries based on lithium manganese iron phosphate systems, making them unsuitable for commercial applications.

[0054] In some preferred embodiments, the lithium manganese iron phosphate LiMn x Fe y M 1-x-y PO4 is also doped with M elements, M is selected from at least one element of Co, B, Ga, F, W, Zr, Mg, Na, Pb, K, Al, Cr, Ba, Ca, Ni, Sr, Ti, Zn, Si, V, Mo, Nb, doping can cause defects in the material, these defects are conducive to Li + Diffusion, and due to the different charge valence states, a charge difference is generated, and cation vacancies are formed through the charge compensation mechanism, which improves the conductivity of the material and enhances the rate performance of the material.

[0055] Specifically, the value of a(c+d) / b can be, but is not limited to, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 1, 1.2, 1.4, 1.5, 1.7 or any range thereof.

[0056] In some preferred embodiments, the lithium-ion battery satisfies the following condition: 0.2≤a(c+d) / b≤0.7. Under this condition, the effects of manganese doping and the carbon coating on battery performance in the lithium manganese iron phosphate material can be better addressed, thereby improving the battery's energy density while maintaining low impedance and good high-temperature cycling performance.

[0057] Specifically, the mass percentage a of the carbon coating layer in the positive electrode material layer can be but is not limited to 1.5wt%, 1.7wt%, 1.9wt%, 2wt%, 2.2wt%, 2.4wt%, 2.6wt%, 2.8wt%, 3wt%, 3.2wt%, 3.4wt%, 3.6wt%, 3.8wt%, 4wt%, 4.1wt%, 4.2wt%, 4.3wt%, 4.4wt%, 4.5wt% or the range consisting of any of the above values.

[0058] When the outer layer of the lithium manganese iron phosphate material is coated with carbon, if the carbon content is too low, the positive electrode active material cannot be completely coated, resulting in poor conductivity of the material; when the carbon content is too high, the content of the positive electrode active material will be reduced. Since carbon does not contribute to the capacity, the capacity of the material will be reduced, affecting the energy density of the battery. At the same time, if the carbon content is too high, the active sites will increase, which will aggravate the side reactions of the electrolyte on the surface of the lithium manganese iron phosphate material, leading to an increase in the impedance of the battery in the later stage; the side reactions will also cause the battery capacity to decay rapidly at high temperatures, deteriorating the high-temperature cycle performance. When a is 1.5wt% to 4.5wt%, combined with the optimization of other battery parameters, it is possible to take into account conductivity, impedance performance and high-temperature cycle performance. Preferably, a is 2wt% to 3.5wt%.

[0059] Specifically, the porosity b of the positive electrode sheet can be, but is not limited to, 25%, 26%, 27%, 28%, 29%, 3%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40% or any range consisting of the above values.

[0060] Porosity reflects the compaction density of the electrode material on the electrode sheet, which affects the battery energy density, the wettability of the electrolyte in the electrode sheet, and the difficulty of ion diffusion. Among them, the wettability of the electrolyte in the electrode sheet has a great influence on the cycle performance of the battery: the better the wettability of the electrolyte to the electrode sheet, the smaller the initial impedance of the battery, the more complete the electrolyte diffusion, the better the film forming effect, and the better the cycle performance of the battery. If the electrode sheet porosity is too small, it means that the electrode sheet compaction density is large, the electrolyte infiltration and diffusion become difficult, and the cycle performance is affected; on the other hand, if the electrode sheet porosity is too high, it will lead to too little active material loaded per unit area. In order to achieve the designed capacity of the battery, the battery will be thickened, and the amount of reaction between the electrolyte and the auxiliary material will also increase, affecting the cycle performance. After research, the inventor found that the porosity of the positive electrode sheet of this application is preferably 25% to 40%, preferably 28% to 36%.

[0061] Specifically, the mass percentage c of the LiFSI in the non-aqueous electrolyte is 1 wt%, 1.5 wt%, 2 wt%, 2.2 wt%, 2.5 wt%, 2.7 wt%, 3 wt%, 3.2 wt%, 3.5 wt%, 3.7 wt%, 4 wt%, 4.2 wt%, 4.5 wt%, 4.7 wt%, 5 wt%, 5.2 wt%, 5.5 wt%, 5.7 wt%, 6 wt%, 6.2 wt%, 6.5 wt%, 6.7 wt%, 7 wt%, 7.2 wt%, 7.5 wt%, 7.7 wt%, 8 wt%, 8.2 wt%, 8.5 wt%, 8.7 wt%, 9 wt%, 9.2 wt%, 9.5 wt%, 9.7 wt%, 10 wt% or a range consisting of any of the above values.

[0062] Adding LiFSI to the non-aqueous electrolyte of the present invention increases the number of lithium ion migration in the non-aqueous electrolyte. + Increasing the number of LiFSI can reduce concentration polarization in the battery and improve the reversibility of the electrode reaction. Furthermore, the addition of LiFSI helps form a stable, ion-conductive passivation film on the surface of the positive electrode active material of the present application. The preferred mass percentage c of LiFSI in the non-aqueous electrolyte is 2 wt% to 6 wt%.

[0063] Specifically, the mass percentage d of the vinylene carbonate in the non-aqueous electrolyte is 0.01wt%, 0.05wt%, 0.1wt%, 0.15wt%, 0.2wt%, 0.25wt%, 0.3wt%, 0.35wt%, 0.4wt%, 0.45wt%, 0.5wt%, 0.55wt%, 0.6wt%, 0.65wt%, 0.7wt%, 0.75wt%, 0.8wt%, 0.85wt%, 0.9wt%, 0.95wt%, 1wt%, 1.05wt%, 1.1wt%, 1.15wt%, 1.2wt%, 1.25wt%, 1.3wt%, 1.35wt%, 1.4wt%, 1.45wt%, 1.5wt% or any range consisting of the above values.

[0064] Vinylene carbonate can undergo free radical polymerization on the surface of the carbon negative electrode, effectively inhibiting the co-insertion reaction of solvent molecules. It also exhibits good compatibility with the cathode material of the present application, no side effects, excellent high and low temperature performance, and anti-flatulence properties, thereby improving the capacity and cycle life of the lithium-ion battery of the present application. Preferably, the mass percentage (d) of the vinylene carbonate in the non-aqueous electrolyte is 0.1 wt% to 1 wt%.

[0065] After research, the inventors found that when the non-aqueous electrolyte of the lithium-ion battery of the present application contains LiFSI and VC at the same time, it helps to form a stable, high-ionic conductivity interface film on the surface of the positive and negative electrode materials of the present application, thereby improving the shortcomings brought by the carbon coating layer, while improving the electrochemical performance of the battery and ensuring low impedance and good high-temperature cycle performance.

[0066] In some embodiments, the non-aqueous electrolyte further includes an auxiliary additive; the auxiliary additive includes at least one of a cyclic carbonate compound, a cyclic sulfate compound, a sultone compound, a phosphate compound, a borate compound, and a nitrile compound. The use of the auxiliary additive can further enhance the performance of the lithium-ion battery.

[0067] In some embodiments, based on the total mass of the non-aqueous electrolyte as 100%, the content of the auxiliary additive is 0.01% to 30%. Preferably, the content of the auxiliary additive is 0.1% to 5%, and more preferably, the content of the auxiliary additive is 0.1% to 3%. Specifically, the content of any optional substance in the auxiliary additive can be, but is not limited to, 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%, 10% or a range consisting of any of the above values.

[0068] In some preferred embodiments, the cyclic carbonate compound includes at least one of vinyl ethylene carbonate, methylene carbonate, trifluoromethyl ethylene carbonate, bisfluoroethylene carbonate, or the compound represented by the following structural formula 1:

[0069] In the structural formula 1, R 21 、R 22 、R 23 、R 24 、R 25 、R 26 Each is independently selected from a hydrogen atom, a halogen atom, and a C1-C5 group.

[0070] In some preferred embodiments, the cyclic sulfate ester compound includes at least one of vinyl sulfate, 4-methylvinyl sulfate, and propylene sulfate.

[0071] In some preferred embodiments, the sultone compound includes at least one of 1,3-propane sultone, 1,4-butane sultone, and propenyl-1,3-sultone.

[0072] In some preferred embodiments, the phosphate compound includes at least one of tris(trimethylsilyl)phosphate, tris(triethylsilyl)phosphate and the compound represented by the following structural formula 2:

[0073] In the structural formula 2, R 31 、R 32 、R 33 Each independently selected from C1-C5 saturated hydrocarbon group, unsaturated hydrocarbon group, halogenated hydrocarbon group, -Si(C m H 2m+1 )3, m is a natural number from 1 to 3, and R 31 、R 32 、R33 At least one of them is an unsaturated hydrocarbon group.

[0074] In some preferred embodiments, the borate compound includes at least one of tris(trimethylsilyl)borate and tris(triethylsilyl)borate.

[0075] In some preferred embodiments, the nitrile compound includes at least one of succinonitrile, glutaronitrile, ethylene glycol bis(propionitrile) ether, hexanetrionitrile, adiponitrile, pimelonitrile, suberonitrile, azelaic acid dinitrile, and sebaconitrile.

[0076] In some embodiments, the non-aqueous electrolyte includes a lithium salt, and the lithium salt includes LiPF6, LiBOB, LiDFOB, LiDFOP, LiPO2F2, LiBF4, LiSbF6, LiAsF6, LiN(SO2C2F5)2, LiC(SO2CF3)3, LiClO4, LiAlCl4, LiCF3SO3, LiSO3F, Li2B 10 Cl 10 , at least one of lithium chloroborane, lithium tetrafluorooxalophosphate, lithium trioxalophosphate, a lower aliphatic carboxylic acid lithium having 4 or less carbon atoms, and lithium tetraphenylborate.

[0077] In some embodiments, the concentration of the lithium salt in the non-aqueous electrolyte is 0.1 mol / L to 4 mol / L. Preferably, the concentration of the lithium salt in the non-aqueous electrolyte is 0.5 mol / L to 2.5 mol / L. Specifically, the concentration of the lithium salt in the non-aqueous electrolyte may be, but is not limited to, 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, 4 mol / L, or any range thereof.

[0078] In some embodiments, the non-aqueous organic solvent includes at least one of a cyclic carbonate solvent, a chain carbonate solvent, a carboxylate solvent, and an ether solvent.

[0079] In some preferred embodiments, the cyclic carbonate includes at least one of ethylene carbonate, propylene carbonate, and butylene carbonate.

[0080] In some preferred embodiments, the linear carbonate solvent includes at least one of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, and methyl propyl carbonate.

[0081] In some preferred embodiments, the carboxylate solvent includes at least one of methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, methyl butyrate, methyl isobutyrate, methyl trimethylacetate, and ethyl trimethylacetate.

[0082] In some preferred embodiments, the ether solvent includes at least one of ethylene glycol dimethyl ether, 1,3-dioxolane, and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether.

[0083] In some embodiments, the positive electrode sheet further comprises a positive electrode current collector, and the positive electrode material layer is disposed on the surface of the positive electrode current collector. The positive electrode current collector is selected from an electron-conducting metal material. Preferably, the positive electrode current collector comprises at least one of Al, Ni, tin, copper, and stainless steel. In a more preferred embodiment, the positive electrode current collector is selected from aluminum foil.

[0084] In some embodiments, the positive electrode active material layer further includes a positive electrode binder and a positive electrode conductor, and the positive electrode active material, the positive electrode binder and the positive electrode conductor are blended to obtain the positive electrode material layer.

[0085] The positive electrode binder includes polyvinylidene fluoride, a copolymer of vinylidene fluoride, polytetrafluoroethylene, a copolymer of vinylidene fluoride-hexafluoropropylene, a copolymer of tetrafluoroethylene-hexafluoropropylene, a copolymer of tetrafluoroethylene-perfluoroalkyl vinyl ether, a copolymer of ethylene-tetrafluoroethylene, a copolymer of vinylidene fluoride-tetrafluoroethylene, a copolymer of vinylidene fluoride-trifluoroethylene, a copolymer of vinylidene fluoride-trichloroethylene, a copolymer of vinylidene fluoride-fluoroethylene, a copolymer of vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene, thermoplastic polyimide, a thermoplastic resin such as polyethylene and polypropylene; an acrylic resin; and at least one of styrene butadiene rubber.

[0086] The positive electrode conductive agent includes at least one of graphite carbon materials such as acetylene black, Super P, graphene, Ketjen black, SFG-6, carbon nanotubes, and graphyne.

[0087] In some embodiments, the negative electrode plate includes a negative electrode material layer, and the negative electrode material layer includes a negative electrode active material. The type and content of the negative electrode active material are not particularly limited and can be selected according to actual needs.

[0088] In a preferred embodiment, the negative electrode active material comprises at least one of a carbon-based negative electrode, a silicon-based negative electrode, a tin-based negative electrode, and a lithium negative electrode. Carbon-based negative electrodes may include graphite, hard carbon, soft carbon, graphene, mesocarbon microbeads, and the like; silicon-based negative electrodes may include silicon materials, silicon oxides, silicon-carbon composites, and silicon alloys; tin-based negative electrodes may include tin, tin-carbon, tin-oxygen, and tin metal compounds; and lithium negative electrodes may include metallic lithium or a lithium alloy. Specifically, the lithium alloy may be at least one of a lithium-silicon alloy, a lithium-sodium alloy, a lithium-potassium alloy, a lithium-aluminum alloy, a lithium-tin alloy, and a lithium-indium alloy.

[0089] In some embodiments, the negative electrode plate further includes a negative electrode current collector, and the negative electrode material layer is disposed on the surface of the negative electrode current collector. The material of the negative electrode current collector can be the same as that of the positive electrode current collector, which will not be repeated here.

[0090] In some embodiments, the negative electrode material layer further includes a negative electrode binder and a negative electrode conductive agent. The negative electrode active material, the negative electrode binder, and the negative electrode conductive agent are blended together to form the negative electrode material layer. The negative electrode binder and the negative electrode conductive agent may be the same as the positive electrode binder and the positive electrode conductive agent, respectively, and are not further described here.

[0091] In some embodiments, the lithium-ion battery further includes a separator, and the separator is located between the positive electrode and the negative electrode.

[0092] The diaphragm can be an existing conventional diaphragm, which can be a ceramic diaphragm, a polymer diaphragm, a non-woven fabric, an inorganic-organic composite diaphragm, etc., including but not limited to single-layer PP (polypropylene), single-layer PE (polyethylene), double-layer PP / PE, double-layer PP / PP and three-layer PP / PE / PP diaphragms.

[0093] The following describes the details in conjunction with specific embodiments.

[0094] Table 1

[0095] Example 1

[0096] This embodiment is used to illustrate the lithium-ion battery and its preparation method disclosed in this application, including the following steps:

[0097] 1) Preparation of positive electrode sheet

[0098] Step 1: Add PVDF as a binder to NMP solvent and stir thoroughly to obtain PVDF glue.

[0099] Step 2: Add the conductive agent (super P+CNT) and the positive electrode active material to the PVDF glue and stir them thoroughly to obtain the positive electrode slurry. The mass ratio of the positive electrode active material, the conductive carbon black Super-P and the positive electrode binder is 96:2:2. The positive electrode active material is LiMn coated with a carbon coating layer. 0.5 Fe 0.5 The contents of PO4 active material and carbon coating layer in the positive electrode material layer are shown in Table 1.

[0100] The content of the carbon coating layer in the positive electrode material layer was detected by the following method: the positive electrode sheet was taken out, and then about 5 g of the positive electrode material layer was scraped with a spoon, and the carbon content (%) was tested using a carbon-sulfur analyzer (Wuxi Chuangxiang Analytical Instrument Co., Ltd.).

[0101] Step 3: Evenly coat the prepared positive electrode slurry on a positive electrode current collector (e.g., aluminum foil), dry, roll-press, die-cut, or slit to obtain a positive electrode sheet. The porosity of the positive electrode sheet is controlled to 26% by the coating weight and rolling pressure.

[0102] 2) Preparation of negative electrode sheet

[0103] Step 1: Weigh each material according to the negative electrode sheet ratio of graphite: conductive carbon (super P): carboxymethyl cellulose (CMC): styrene-butadiene rubber (SBR) = 96.3:1.0:1.2:1.5 (mass ratio).

[0104] Step 2: First, add CMC into pure water at a solid content of 1.5%, stir thoroughly (for example, stirring time 120 minutes) to prepare a transparent CMC glue solution.

[0105] Step 3: Add conductive carbon (super P) to the CMC glue solution and stir thoroughly (for example, stirring time 90 minutes) to prepare a conductive glue.

[0106] Step 4: Continue to add graphite and stir thoroughly to obtain the required negative electrode slurry.

[0107] Step 5: Evenly coat the prepared negative electrode slurry on the copper foil, and obtain the negative electrode sheet by drying, rolling, die-cutting or striping.

[0108] 3) Preparation of non-aqueous electrolyte

[0109] Ethylene carbonate (EC), diethyl carbonate (DEC) and ethyl methyl carbonate (EMC) were mixed in a mass ratio of EC:DEC:EMC=1:1:1, LiFSI and VC were added in the mass percentages shown in Table 1, and then lithium hexafluorophosphate (LiPF6) was added to a molar concentration of 1 mol / L.

[0110] 4) Lithium-ion battery cell preparation

[0111] The prepared positive electrode sheet and the negative electrode sheet are assembled into a laminated soft-pack battery cell.

[0112] 5) Battery filling and formation

[0113] In a glove box maintained at a dew point below -40°C, the prepared electrolyte was injected into the cell, vacuum-sealed, and left to rest for 72 hours. The cells were then subjected to conventional formation for the first charge, following the following steps: 180 minutes of constant-current charging at 0.05C, 120 minutes of constant-current charging at 0.1C, and 120 minutes of constant-current charging at 0.2C. The cells were then vacuum-sealed again, followed by a further full charge at 0.2C (100% SOC). After 72 hours of room-temperature storage, the cells were fully discharged at 0.2C (0% SOC).

[0114] Examples 2 to 26

[0115] Examples 2 to 26 are used to illustrate the lithium-ion batteries and preparation methods disclosed in this application, and include most of the operating steps in Example 1, with the difference being that the battery composition shown in Table 1 is used.

[0116] Comparative Examples 1 to 16

[0117] Comparative Examples 1 to 16 illustrate the lithium-ion batteries and preparation methods disclosed herein, and include most of the steps in Example 1, except that the battery compositions shown in Table 1 are used. In Comparative Example 12, an equal amount of lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) is used instead of LiFSI, and in Comparative Example 13, an equal amount of vinyl ethylene carbonate (VEC) is used instead of VC.

[0118] Performance Testing

[0119] 1. 25℃ DCIR test

[0120] At 25°C, place the lithium-ion battery for 4 hours, charge it at a constant current rate of 0.5C to the upper cutoff voltage (e.g., 4.2V), then charge it at a constant voltage rate until the current is less than or equal to 0.05C. At this point, the battery's state of charge (SOC) is 100%. Then, discharge it at a constant current rate of 0.5C to the battery's lower limit voltage (e.g., 2.5V). Record the room temperature discharge capacity as C0. Then, charge the battery to 100% SOC using the same charging method, then discharge it at a constant current rate of 0.5C to the end capacity of C0 / 2. At this point, the battery's state of charge (SOC) is 50%. Perform the following tests:

[0121] 0.1C constant current charging for 10s and then rest for 40s;

[0122] Discharge at a constant current of 0.1C for 10 seconds, then rest for 40 seconds, and record the final voltage V1;

[0123] Charge at 0.2C constant current for 10s and then rest for 40s; discharge at 0.2C constant current for 10s and then rest for 40s, and record the end voltage V2;

[0124] Charge at 0.5C constant current for 10s and then rest for 40s; discharge at 0.5C constant current for 10s and then rest for 40s, and record the end voltage V3;

[0125] Draw a straight line with current as the horizontal axis and discharge termination voltage as the vertical axis. The slope of the straight line is 25℃DCIR.

[0126] 2. High temperature cycle performance test

[0127] Place the lithium-ion battery in a constant temperature environment of 45°C, charge it to 4.3V at a constant current of 1C, then charge it at a constant voltage until the current drops to 0.02C, test the internal resistance of the battery, and then discharge it to 3.0V at a constant current of 2C. Repeat this cycle 1000 times, record the first discharge capacity and the last discharge capacity, and also record the internal resistance of the battery when it is fully charged for the first time and the internal resistance of the battery after it is fully charged for the last time.

[0128] The capacity retention rate and internal resistance growth rate of the cycle are calculated according to the following formula: Capacity retention rate (%) = last discharge capacity / first discharge capacity × 100%; Internal resistance growth rate (%) = (battery internal resistance after the last full charge - battery internal resistance after the first full charge) / battery internal resistance after the first full charge × 100%.

[0129] (1) The test results of Examples 1 to 19 and Comparative Examples 1 to 16 are shown in Table 2.

[0130] Table 2

[0131] The above results show that the lithium iron manganese phosphate lithium ion battery of the present application has both low impedance and good high temperature cycle performance. The present application optimizes the composition of the lithium ion battery, and the lithium iron manganese phosphate LiMn coated with a carbon coating layer is x Fe y M 1-x-y PO4 is used as the positive electrode active material, the carbon coating content and the porosity of the positive electrode are adjusted, and an appropriate amount of LiFSI and VC are added to the non-aqueous electrolyte. x Fe y M 1-x-y PO4 has strong safety and stable chemical properties, while lithium manganese iron phosphate LiMn x Fe y M 1-x-yThe manganese element doped in PO4 can effectively improve the battery charge and discharge platform and thus improve the battery energy density, but the electrical conductivity is poor. Carbon coating of the positive electrode active material can increase the conductivity of the material, but it can easily lead to an increase in battery impedance and rapid capacity decay at high temperatures, deteriorating high-temperature cycle performance. To this end, the present application optimizes the carbon coating content and improves the porosity of the positive electrode sheet, which helps to enhance the wettability of the electrolyte and the degree of ion diffusion, thereby improving high-temperature cycle performance. In addition, the inventors found that adding an appropriate amount of LiFSI and VC to the non-aqueous electrolyte helps to form a stable, high-ion conductivity interface film on the surface of the positive and negative electrode materials optimized in this application, thereby further improving the battery performance degradation caused by the carbon coating layer. In particular, when the mass percentage a of the carbon coating layer in the positive electrode material layer, the porosity b of the positive electrode sheet, the mass percentage c of LiFSI in the non-aqueous electrolyte, and the mass percentage d of vinylene carbonate in the non-aqueous electrolyte meet the following conditions: 0.1≤a(c+d) / b≤1.7, and 1.5≤a≤4.5, 25≤b≤40, 1≤c≤10, 0.01≤d≤1.5, the synergistic effect between LiFSI and VC and the carbon-coated positive electrode active material can be fully exerted, so that the lithium manganese iron phosphate lithium ion secondary battery has both low impedance and good high-temperature cycle performance.

[0132] When the mass percentage a of the carbon coating layer in the positive electrode material layer, the porosity b of the positive electrode sheet, the mass percentage c of LiFSI in the non-aqueous electrolyte, and the mass percentage d of vinyl carbonate in the non-aqueous electrolyte meet the following conditions: 0.2≤a(c+d) / b≤0.7, and 2≤a≤3.5, 28≤b≤36, 2≤c≤6, 0.1≤d≤1, the lithium ion battery has a higher high temperature cycle capacity retention rate, a lower high temperature cycle internal resistance increase rate, and a lower 25°C DCIR (for example, Examples 6, 7, 9, 16, and 19). When at least one of the mass percentage a of the carbon coating layer in the positive electrode material layer, the porosity b of the positive electrode sheet, the mass percentage c of LiFSI in the non-aqueous electrolyte, the mass percentage d of vinyl carbonate in the non-aqueous electrolyte, and the value of a(c+d) / b is not within the preferred range, the relevant performance of the lithium ion battery will be slightly deteriorated. When the above parameters do not meet the preferred ranges, the relevant performance degradation of the battery is more obvious (such as Example 18).

[0133] When the raw material selection or dosage of the lithium-ion battery does not meet the requirements of this application, the relevant performance of the battery will be seriously deteriorated:

[0134] Compared with Example 19, the mass percentage a of the carbon coating layer in the positive electrode material layer of the lithium ion battery in Comparative Example 1 is too high; the mass percentage a of the carbon coating layer in the positive electrode material layer of the lithium ion battery in Comparative Example 2 is too low; and the positive electrode active material of the lithium ion battery in Comparative Example 3 is not carbon-coated. Without carbon coating, the 25°C DCIR of the battery increases significantly, and the battery experiences a dive and cannot test the capacity retention rate and internal resistance increase rate of 1000 cycles at 45°C (Comparative Example 3). Although carbon coating can improve the battery's 25°C DCIR, high-temperature cycle internal resistance increase rate, and high-temperature cycle capacity retention rate to a certain extent, the mass percentage a of the carbon coating layer has a significant impact on performance. When a is too high, although it can increase conductivity and reduce the initial impedance of the battery at 25°C, it will also lead to an increase in active sites, aggravating the side reactions of the electrolyte on the surface of the lithium manganese iron phosphate material, resulting in an increase in the later impedance of the battery, as well as rapid capacity decay at high temperatures, deteriorating high-temperature cycle performance (Comparative Example 1). When a is too low, the conductive properties of the material cannot be effectively improved, the 25°C DCIR increases significantly, and the high-temperature performance deteriorates (Comparative Example 2).

[0135] Compared with Example 19, the porosity of the positive electrode sheet of the lithium-ion battery in Comparative Example 4 was higher than the range of this application, and the battery's 25°C DCIR decreased, but the internal resistance increase rate during high-temperature cycling increased, and the high-temperature cycling capacity retention rate decreased. The porosity of the positive electrode sheet of the lithium-ion battery in Comparative Example 5 was lower than the range of this application, the battery's 25°C DCIR increased, and the battery experienced a water drop, making it impossible to test the capacity retention rate and internal resistance increase rate after 1000 cycles at 45°C.

[0136] Compared with Example 19, the mass percentage of LiFSI in the lithium ion battery non-aqueous electrolyte of Comparative Example 6 is too high, and the mass percentage of LiFSI in the lithium ion battery non-aqueous electrolyte of Comparative Example 7 is too low, both of which lead to deterioration of the battery's room temperature impedance and high temperature cycle performance, and an increase in the high temperature cycle internal resistance increase rate.

[0137] Compared with Example 19, the mass percentage of VC in the non-aqueous electrolyte of the lithium ion battery in Comparative Example 8 is too high, resulting in an increase in the battery's 25°C DCIR, a decrease in the high-temperature cycle capacity retention rate, and an increase in the high-temperature cycle internal resistance increase rate; the non-aqueous electrolyte of the lithium ion battery in Comparative Example 9 does not contain VC, resulting in the battery diving and the inability to test the capacity retention rate and internal resistance increase rate after 1000 cycles at 45°C.

[0138] Compared with Example 19, the LiFSI and VC contents in the non-aqueous electrolyte of the lithium-ion battery in Comparative Example 10 do not meet the requirements of this application, resulting in the ineffective synergy between the non-aqueous electrolyte and the carbon-coated positive electrode active material, severe deterioration of the high-temperature cycle performance of the battery, increased rate of increase of the high-temperature cycle internal resistance, and increased DC internal resistance.

[0139] Compared with Example 19, although the selection of raw materials for the lithium-ion battery of Example 11 and the amount of a single raw material used meet the requirements of this application, the amount of raw materials used is not satisfied with the relationship 0.1≤a(c+d) / b≤1.7, which still leads to degradation of the battery-related performance. In this case, even if other commonly used types of additives are added (Comparative Examples 14 to 16), the relevant performance of the battery cannot be improved well. This shows that the optimization of the overall composition of the lithium-ion battery of this application, the control of the types of raw materials and the dosage ratio of key raw materials in the positive electrode and non-aqueous electrolyte can effectively achieve the synergy of the positive electrode and non-aqueous electrolyte, and improve the positive electrode active material lithium manganese iron phosphate LiMn x Fe y M 1-x-y Effects of manganese doping and carbon coating in PO4 on related properties.

[0140] Compared with Example 19, an equal amount of lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) was used in place of LiFSI in Comparative Example 12, and an equal amount of vinyl ethylene carbonate (VEC) was used in place of VC in Comparative Example 13. The non-aqueous electrolytes of the lithium-ion batteries in Comparative Examples 12-13 do not contain both LiFSI and VC, resulting in ineffective improvement in the impedance and high-temperature cycle performance of the batteries. This indicates that a non-aqueous electrolyte containing both LiFSI and VC can better synergize with the positive electrode active material of the present application, enabling the battery to have both low impedance and good high-temperature cycle performance.

[0141] (2) The performance test results of Examples 19 to 22 are entered in Table 3.

[0142] Table 3

[0143] The results in Table 3 show that, based on the lithium-ion battery of the present application, conventional additives in the field can be further added to the non-aqueous electrolyte as auxiliary additives, such as vinyl sulfate (DTD), 1,3-propane sultone (PS), tris(trimethylsilyl) phosphate (TMSP), etc., which can further improve the corresponding performance of the lithium-ion battery.

[0144] (3) The performance test results of Examples 19 and 23 to 26 are entered in Table 4.

[0145] Table 4

[0146] The test results of Examples 19 and 23-25 ​​show that the value of x affects the 25°C DCIR of the lithium-ion battery. When 0<x≤0.8, the battery can have a lower 25°C DCIR. In particular, when 0.5≤x≤0.8, the battery's 25°C DCIR is even lower.

[0147] From the test results of Example 19 and Example 26, it can be seen that when lithium manganese iron phosphate LiMn x Fe y M 1-x-y When PO4 is doped with Mg, the battery can have a lower 25°C DCIR and improve high-temperature cycle performance, with a lower high-temperature cycle internal resistance growth rate and a higher high-temperature cycle capacity retention rate.

[0148] In summary, the present invention optimizes the composition of lithium-ion batteries and uses carbon-coated lithium manganese iron phosphate LiMn x Fe y M 1-x-y PO4 is used as the positive electrode active material, the content of the carbon coating layer and the porosity of the positive electrode sheet are controlled, and an appropriate amount of LiFSI and VC are added to the non-aqueous electrolyte, so that the mass percentage a of the carbon coating layer in the positive electrode material layer, the porosity b of the positive electrode sheet, the mass percentage c of LiFSI in the non-aqueous electrolyte, and the mass percentage d of vinylene carbonate in the non-aqueous electrolyte meet the following conditions: 0.1≤a(c+d) / b≤1.7, and 1.5≤a≤4.5, 25≤b≤40, 1≤c≤10, 0.01≤d≤1.5, the synergistic effect between LiFSI and VC and the carbon-coated positive electrode active material can be fully exerted, so that the battery has low impedance, low high-temperature cycle internal resistance growth rate and high high-temperature cycle capacity retention rate at high energy density.

[0149] The technical features of the above-described embodiments can be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0150] The above-described embodiments merely represent several implementation methods of the present application. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person of ordinary skill in the art may make various modifications and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be determined by the appended claims.

Claims

1. A lithium ion battery, characterized in that: The invention comprises a positive electrode sheet, a negative electrode sheet and a non-aqueous electrolyte; the positive electrode sheet comprises a positive electrode material layer comprising a positive electrode active material, and the positive electrode active material comprises lithium manganese iron phosphate LiMn coated with a carbon coating layer. x Fe y M 1-x-y PO4, wherein 0.1≤x≤0.8, 0.2≤y≤0.9, 0≤1-xy≤0.1, M is selected from at least one element of Co, B, Ga, F, W, Zr, Mg, Na, Pb, K, Al, Cr, Ba, Ca, Ni, Sr, Ti, Zn, Si, V, Mo, Nb; the non-aqueous electrolyte comprises a non-aqueous organic solvent, LiFSI and vinylene carbonate; The lithium-ion battery meets the following conditions: 0.1≤a(c+d) / b≤1.7, and 1.5≤a≤4.5, 25≤b≤40, 1≤c≤10, 0.01≤d≤1.5; Wherein, a is the mass percentage of the carbon coating layer in the positive electrode material layer, in wt%; b is the porosity of the positive electrode sheet, in %; c is the mass percentage of LiFSI in the non-aqueous electrolyte, in wt%; d is the mass percentage of vinylene carbonate in the non-aqueous electrolyte, in wt%.

2. The lithium-ion battery according to claim 1, characterized in that The lithium ion battery satisfies the following condition: 0.2≤a(c+d) / b≤0.

7.

3. The lithium ion battery according to claim 1, characterized in that The mass percentage a of the carbon coating layer in the positive electrode material layer is 2wt% to 3.5wt%.

4. The lithium ion battery according to claim 1, characterized in that The porosity b of the positive electrode plate is 28% to 36%.

5. The lithium ion battery according to claim 1, characterized in that The mass percentage c of the LiFSI in the non-aqueous electrolyte is 2 wt % to 6 wt %.

6. The lithium ion battery according to claim 1, characterized in that The mass percentage d of the vinylene carbonate in the non-aqueous electrolyte is 0.1 wt % to 1 wt %.

7. The lithium ion battery according to claim 1, characterized in that The non-aqueous electrolyte further includes an auxiliary additive, wherein the auxiliary additive includes at least one of a cyclic carbonate compound, a cyclic sulfate compound, a sultone compound, a phosphate compound, a borate compound, and a nitrile compound; Based on the total mass of the non-aqueous electrolyte being 100%, the content of the auxiliary additive is 0.01% to 30%.

8. The lithium ion battery according to claim 7, characterized in that The cyclic carbonate compound includes at least one of vinyl ethylene carbonate, methylene carbonate, trifluoromethyl vinyl carbonate, bisfluoroethylene carbonate or the compound shown in the following structural formula 1: In the structural formula 1, R 21 , R 22 , R 23 , R 24 , R 25 , R 26 Each is independently selected from a hydrogen atom, a halogen atom, and a C1-C5 group.

9. The lithium ion battery according to claim 7, characterized in that The cyclic sulfate ester compound includes at least one of vinyl sulfate, 4-methyl vinyl sulfate, and propylene sulfate.

10. The lithium ion battery according to claim 7, characterized in that The sultone compound includes at least one of 1,3-propane sultone, 1,4-butane sultone and propenyl-1,3-sultone.

11. The lithium ion battery according to claim 7, characterized in that: The phosphate compound includes at least one of tris(trimethylsilyl)phosphate, tris(triethylsilyl)phosphate and the compound shown in the following structural formula 2: In the structural formula 2, R 31 , R 32 , R 33 Each independently selected from a C1-C5 saturated hydrocarbon group, an unsaturated hydrocarbon group, a halogenated hydrocarbon group, -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.

12. The lithium ion battery according to claim 7, characterized in that The borate ester compound includes at least one of tris(trimethylsilyl)borate and tris(triethylsilyl)borate.

13. The lithium ion battery according to claim 7, characterized in that The nitrile compound includes at least one of succinonitrile, glutaronitrile, ethylene glycol bis(propionitrile) ether, hexanetrinitrile, adiponitrile, pimelonitrile, suberonitrile, azelaic acid dinitrile and sebaconitrile.

14. The lithium ion battery according to claim 1, wherein: The non-aqueous electrolyte also includes a lithium salt, and the lithium salt includes LiPF6, LiBOB, LiDFOB, LiDFOP, LiPO2F2, LiBF4, LiSbF6, LiAsF6, LiN(SO2C2F5)2, LiC(SO2CF3)3, LiClO4, LiAlCl4, LiCF3SO3, LiSO3F, Li2B 10 Cl 10 , lithium chloroborane, lithium tetrafluorooxalate phosphate, lithium trioxalate phosphate, a low-level aliphatic carboxylic acid lithium having 4 or less carbon atoms, and lithium tetraphenylborate; the concentration of the lithium salt in the non-aqueous electrolyte is 0.1 mol / L to 4 mol / L.

15. The lithium ion battery according to claim 1, wherein: The non-aqueous organic solvent includes at least one of a cyclic carbonate solvent, a chain carbonate solvent, a carboxylate solvent and an ether solvent; The cyclic carbonate includes at least one of ethylene carbonate, propylene carbonate and butylene carbonate; The chain carbonate solvent includes at least one of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, and methyl propyl carbonate; The carboxylate solvent includes at least one of methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, methyl butyrate, methyl isobutyrate, methyl trimethylacetate, and ethyl trimethylacetate; The ether solvent includes at least one of ethylene glycol dimethyl ether, 1,3-dioxolane, and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether.

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