Lithium ion battery

Abstract

A lithium ion battery, comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte. The positive electrode comprises a positive current collector and a positive electrode material layer arranged on a surface of the positive current collector. The positive electrode material layer comprises a positive electrode active material. The positive electrode active material is selected from one or more of ternary positive electrode active materials Li1+xNimConM1-m-nO2-yAy. The negative electrode comprises a negative electrode current collector and a negative electrode material layer arranged on a surface of the negative electrode current collector, and the negative electrode material layer comprises a silicon-based material. The non-aqueous electrolyte comprises a non-aqueous organic solvent, an additive, and a lithium salt. The additive comprises an FEC. The lithium salt comprises lithium hexafluorophosphate and lithium fluorosulfonyl imide. The lithium ion battery meets the following conditions: 100≤(b+c)*d / a≤200, 5≤a≤15, 1≤b≤15, 0.5≤c≤10, and 90≤d≤140. By means of optimizing the composition of the lithium ion battery, the types and the amount of raw materials of the battery meet specific requirements and relational expressions, so that the lithium ion battery can have both a high energy density and an excellent cycle life.

Description

A lithium-ion battery Technical Field

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

[0002] With the expansion of the new energy vehicle market such as electric vehicles and hybrid electric vehicles and the rapid development of portable electronic devices such as mobile phones and laptops, the requirements for the capacity and service life of the batteries used in them are becoming increasingly higher. Lithium-ion secondary batteries have attracted much attention and are developing rapidly due to their high theoretical energy and long cycle life.

[0003] Currently, the negative electrode active materials used in lithium-ion secondary batteries are primarily carbon-based materials, which offer advantages in terms of charge-discharge cycle life and cost. Silicon-based materials have rapidly developed due to their higher theoretical capacity and ability to achieve high energy density. However, during the absorption and desorption of lithium ions, the active materials in silicon-based negative electrodes expand and contract significantly, resulting in large volume changes. This causes the SEI film (solid electrolyte interphase) to continuously break down and reorganize. The active material particles then break apart during repeated charge and discharge, exposing new active surfaces. This new active surface easily decomposes the electrolyte solvent, thereby degrading the battery's cycling characteristics.

[0004] In addition, when silicon-based negative electrode active materials and high-nickel ternary positive electrode (Ni ≥ 60 mol%) active materials are used together, metal ions are easily dissolved in the high-nickel ternary positive electrode active materials, which hinders the formation of a stable SEI film on the negative electrode surface, further deteriorating the negative electrode performance.

[0005] Therefore, there is a need to develop lithium-ion secondary batteries that have excellent cycle life while achieving high energy density.

[0006] Summary of the Invention

[0007] Based on this, the purpose of this application is to provide a lithium-ion battery with both high energy density and excellent cycle life.

[0008] In order to achieve the above purpose, this application adopts the following technical solutions:

[0009] A lithium-ion battery comprises a positive electrode, a negative electrode and a non-aqueous electrolyte; the positive electrode comprises a positive electrode current collector and a positive electrode material layer arranged on the surface of the positive electrode current collector, the positive electrode material layer contains a positive electrode active material, and the positive electrode active material is selected from a ternary positive electrode active material Li 1+x Ni m Co n M 1-m-n O 2-y A yOne or more of them, where -0.1 ≤ x ≤ 0.2; 0.6 ≤ m < 1; 0 < n < 0.2; 0 < m + n < 1; 0 ≤ y < 0.2; M includes one or both of Mn or Al, and includes zero, one or more of Sr, Mg, Ti, Ca, Zr, Zn, Si, Fe, B, Ga, Cr, W, V, Nb, Ce; A includes one or more of S, N, F, B, Cl, Br and I; the negative electrode includes a negative electrode current collector and a negative electrode material layer provided on the surface of the negative electrode current collector, and the negative electrode material layer contains a silicon-based material; the non-aqueous electrolyte contains a non-aqueous organic solvent, an additive and a lithium salt, the additive includes fluoroethylene carbonate; the lithium salt includes lithium hexafluorophosphate and lithium fluorosulfonylimide;

[0010] The lithium ion battery satisfies the following conditions:

[0011] 100 ≤ (b + c) * d / a ≤ 200, and 5 ≤ a ≤ 15, 1 ≤ b ≤ 15, 0.5 ≤ c ≤ 10, 90 ≤ d ≤ 140;

[0012] Where, a represents the mass percentage of silicon element in the negative electrode material layer, and the unit is %;

[0013] b represents the mass percentage of fluoroethylene carbonate in the non-aqueous electrolyte, and the unit is %;

[0014] c represents the mass percentage of lithium fluorosulfonylimide in the non-aqueous electrolyte, and the unit is %;

[0015] d represents the thickness of the negative electrode material layer, and the unit is μm.

[0016] In some embodiments, the lithium ion battery satisfies the following conditions: 120 ≤ (b + c) * d / a ≤ 180.

[0017] In some embodiments, the mass percentage a of silicon element in the negative electrode material layer is 6% to 10%.

[0018] In some embodiments, the mass percentage b of fluoroethylene carbonate in the non-aqueous electrolyte is 3% to 10%.

[0019] In some embodiments, the mass percentage c of lithium fluorosulfonylimide in the non-aqueous electrolyte is 1% to 6%.

[0020] In some embodiments, the thickness d of the negative electrode material layer is 110 μm to 130 μm.

[0021] In some embodiments, the silicon-based material is selected from one or more of silicon materials, silicon oxide materials, silicon-carbon composite materials and silicon alloy materials.

[0022] In some embodiments, the lithium fluorosulfonyl imide is selected from one or more of LiFSI and LiTFSI.

[0023] In some embodiments, the non-aqueous electrolyte further includes an auxiliary additive, wherein the auxiliary additive is selected from one or more of cyclic carbonate compounds, cyclic sulfate compounds, sultone compounds, phosphate compounds, borate compounds, and nitrile compounds; based on the total mass of the non-aqueous electrolyte as 100%, the content of the auxiliary additive is 0.01% to 5%;

[0024] Preferably, the cyclic carbonate compound is selected from one or more of vinylene carbonate, ethylene carbonate, methylene carbonate, fluoroethylene carbonate, trifluoromethylethylene carbonate, bisfluoroethylene carbonate or the compound represented by the following structural formula 1:

[0025] 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;

[0026] The cyclic sulfate compound is selected from one or more of vinyl sulfate, 4-methylvinyl sulfate, and propylene sulfate;

[0027] The sultone compound is selected from one or more of 1,3-propane sultone, 1,4-butane sultone, and propenyl-1,3-sultone;

[0028] The phosphate compound is selected from tris(trimethylsilyl)phosphate, tris(triethylsilyl)phosphate and the compound shown in the following structural formula 2:

[0029] 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;

[0030] The borate compound is selected from one or more of tris(trimethylsilyl)borate and tris(triethylsilyl)borate;

[0031] The nitrile compound is selected from one or more of succinonitrile, glutaronitrile, ethylene glycol bis(propionitrile) ether, hexanetrionitrile, adiponitrile, pimelonitrile, suberonitrile, azelaic acid dinitrile and sebacononitrile.

[0032] In some embodiments, the non-aqueous organic solvent is selected from one or more of cyclic carbonates, linear carbonates, carboxylates, and ethers;

[0033] Preferably, the cyclic carbonate is selected from one or more of ethylene carbonate, vinylene carbonate, propylene carbonate and butylene carbonate;

[0034] The chain carbonate is selected from one or more of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate and methyl propyl carbonate;

[0035] The carboxylic acid ester is selected from one or more of methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, methyl butyrate, methyl isobutyrate, pivalic acid methyl ester and pivalic acid ethyl ester;

[0036] The ethers are selected from one or more of ethylene glycol dimethyl ether, 1,3-dioxolane and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether.

[0037] The present application provides a lithium-ion battery, wherein the positive electrode comprises a high-nickel ternary positive electrode active material, the negative electrode comprises a silicon-based negative electrode active material, the additive in the non-aqueous electrolyte comprises fluoroethylene carbonate, and the lithium salt comprises lithium hexafluorophosphate and lithium fluorosulfonyl imide. By optimizing the composition of the lithium-ion battery and ensuring that the mass percentage a of the silicon element in the negative electrode material layer, the mass percentage b of fluoroethylene carbonate in the non-aqueous electrolyte, the mass percentage c of lithium fluorosulfonyl imide in the non-aqueous electrolyte, and the thickness d of the negative electrode material layer meet the following conditions: 100≤(b+c)*d / a≤200, and 5≤a≤15, 1≤b≤15, 0.5≤c≤10, 90≤d≤140, the influence of metal ions dissolved in the high-nickel ternary positive electrode active material on the formation of the SEI film on the negative electrode surface and the volume change of the negative electrode silicon-based active material during the battery charge and discharge process can be effectively solved, thereby forming a stable SEI film, reducing the migration path of lithium ions, and reducing the change of the electrode structure during the charge and discharge cycle, so that the lithium-ion battery has both high energy density and excellent cycle performance, and improves service life. DETAILED DESCRIPTION

[0038] 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.

[0039] Unless otherwise defined, all technical and scientific terms used in this application have the same meaning as commonly understood by those skilled in the technical field to which this application belongs. The terms used in the specification of this application are only for the purpose of describing specific embodiments and do not limit this application.

[0040] The terms "comprising" and "having" in this application and any variations thereof are intended to cover non-exclusive inclusion. For example, a process, method, device, product or equipment that includes a series of steps is not limited to the listed steps or modules, but may optionally further include unlisted steps, or may optionally further include other steps inherent to these processes, methods, products or equipment.

[0041] As mentioned in this application, "multiple" means two or more.

[0042] This embodiment provides a lithium-ion battery, including a positive electrode, a negative electrode and a non-aqueous electrolyte; the positive electrode includes a positive electrode current collector and a positive electrode material layer provided on the surface of the positive electrode current collector, the positive electrode material layer contains a positive electrode active material, and the positive electrode active material is selected from one or more of the ternary positive electrode active substances Li 1+x Ni m Co n M 1-m-n O 2-y A y where -0.1 ≤ x ≤ 0.2; 0.6 ≤ m < 1; 0 < n < 0.2; 0 < m + n < 1; 0 ≤ y < 0.2; M includes one or both of Mn or Al, and includes zero, one or more of Sr, Mg, Ti, Ca, Zr, Zn, Si, Fe, B, Ga, Cr, W, V, Nb, Ce; A includes one or more of S, N, F, B, Cl, Br and I; the negative electrode includes a negative electrode current collector and a negative electrode material layer provided on the surface of the negative electrode current collector, the negative electrode material layer contains a silicon-based material; the non-aqueous electrolyte contains a non-aqueous organic solvent, an additive and a lithium salt, the additive includes fluoroethylene carbonate (FEC); the lithium salt includes lithium hexafluorophosphate (LiPF6) and lithium fluorosulfonimide;

[0043] The lithium-ion battery satisfies the following conditions:

[0044] 100 ≤ (b + c) * d / a ≤ 200, and 5 ≤ a ≤ 15, 1 ≤ b ≤ 15, 0.5 ≤ c ≤ 10, 90 ≤ d ≤ 140;

[0045] where, a represents the mass percentage of silicon element in the negative electrode material layer, with the unit of %;

[0046] b represents the mass percentage of fluoroethylene carbonate in the non-aqueous electrolyte, with the unit of %;

[0047] c represents the mass percentage of lithium fluorosulfonyl imide in the non-aqueous electrolyte, in %;

[0048] d represents the thickness of the negative electrode material layer, in μm.

[0049] The inventors, based on their own experience and extensive research, found that when the mass percentage a of the silicon element in the negative electrode material layer of the lithium ion battery, the mass percentage b of the FEC in the non-aqueous electrolyte, the mass percentage c of the lithium fluorosulfonyl imide in the non-aqueous electrolyte, and the thickness d of the negative electrode material layer satisfy 100≤(b+c)*d / a≤200, and 5≤a≤15, 1≤b≤15, 0.5≤c≤10, and 90≤d≤140, the influence of metal ions dissolved in the high-nickel ternary positive electrode active material on the formation of the SEI film on the negative electrode surface, as well as the volume change of the negative electrode silicon-based active material during the battery charge and discharge process can be effectively solved, thereby forming a stable SEI film, reducing the migration path of lithium ions, and reducing the change of the electrode structure during the charge and discharge cycle, so that the lithium ion battery has both high energy density and excellent cycle performance, and improves the service life.

[0050] Specifically, the (b+c)*d / a can be, but is not limited to, 100, 105, 110, 115, 120, 125, 130, 135, 140, 145, 150, 155, 160, 165, 170, 175, 180, 185, 190, 195, or 200.

[0051] In some preferred embodiments, the lithium-ion battery satisfies the following condition: 120≤(b+c)*d / a≤180. Within this range, the lithium-ion battery has better comprehensive performance.

[0052] Specifically, the mass percentage b% of the FEC in the non-aqueous electrolyte can be, but is not limited to, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, 10.5%, 11%, 11.5%, 12%, 12.5%, 13%, 13.5%, 14%, 14.5% or 15%.

[0053] In some preferred embodiments, the mass percentage b% of the FEC in the non-aqueous electrolyte is 3% to 10%.

[0054] The secondary lithium-ion battery provided by the present application adopts a high-nickel ternary positive electrode and a silicon-based active material negative electrode, which can effectively improve the capacity of the lithium-ion battery, and the higher the Si element content, the higher its theoretical capacity. However, since the volume change of the Si-based active material during the charging and discharging process of the lithium-ion battery is very large (100% to 300%) accompanying the insertion / extraction of lithium ions, it is easy to cause degradation problems such as disconnection of the electron conduction path in the electrode and particle micronization. The micronization of particles will cause the exposure of new surfaces with high activity, and their surfaces will react with the electrolyte to cause the surface deterioration of the active material, resulting in problems such as a decrease in the capacity of the active material and deterioration of the battery cycle performance. In addition, the higher the silicon element content in the negative electrode active material, the greater the volume change caused by the insertion / extraction of lithium ions. The additive FEC is an excellent film-forming additive for the negative electrode containing silicon-based active materials. FEC is added to the electrolyte to form a more stable SEI film. Insufficient FEC concentration during the cycle process will cause the cycle life of the silicon-based active material negative electrode to suddenly drop, but too high FEC content may aggravate the gas production problem of the battery, which will also cause the battery cycle life to decline, and excessive FEC will increase the charge exchange impedance of the interface, causing an increase in battery impedance and affecting the electrochemical performance of the battery. Therefore, it is necessary to control the amount of additive FEC according to the silicon content, so as to effectively extend the cycle life of the silicon-based active material negative electrode. In the lithium-ion battery of the present application, when the mass percentage b of the FEC in the non-aqueous electrolyte is 1% to 15%, the electrochemical performance of the battery can be effectively balanced, especially when the mass percentage b of the FEC in the non-aqueous electrolyte is 3% to 10%, the battery can obtain better comprehensive performance.

[0055] Specifically, the mass percentage c% of the lithium fluorosulfonyl imide in the non-aqueous electrolyte can be, but is not limited to, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, and 10%.

[0056] In some preferred embodiments, the mass percentage c% of the lithium fluorosulfonyl imide in the non-aqueous electrolyte is 1% to 6%.

[0057] In the present application, by using a fluorosulfonyl structure (-SO2F) of lithium fluorinated sulfonyl imide as the second lithium salt, the relative content of the F element is low and the thermal stability is good, the HF produced is small, the dissolution of the transition metal ions of the positive electrode material can be effectively suppressed, and excellent battery safety can be provided. And the lithium fluorinated sulfonyl imide forms an inorganic SEI film based on LiF on the negative electrode, which can enhance the stability of the silicon-based active material negative electrode during the cycle. In addition, after the fluorinated sulfonyl imide lithium salt is prepared into an electrolyte, its conductivity is higher than that of the lithium hexafluorophosphate electrolyte, and it shows obvious advantages in both cycle and storage life. However, when the concentration of lithium fluorinated sulfonyl imide is too high, it will cause the viscosity of the electrolyte to increase and the fluidity to deteriorate, affecting the widespread use of the substance in lithium-ion batteries, and excessive lithium fluorinated sulfonyl imide is easy to corrode the aluminum current collector, so it is necessary to control the lithium fluorinated sulfonyl imide to take into account its effect on the stability of the positive and negative electrodes and the comprehensive performance of the electrolyte and the current collector. In the lithium-ion battery of the present application, when the mass percentage c% of the lithium fluorosulfonyl imide in the non-aqueous electrolyte is 0.5% to 10%, the stability of the positive and negative electrodes, as well as the overall performance of the electrolyte and current collector, are excellent. In particular, when the mass percentage c% of the lithium fluorosulfonyl imide in the non-aqueous electrolyte is 1% to 6%, the overall performance of the battery is even better.

[0058] Specifically, the mass percentage a% of the silicon element in the negative electrode material layer can be but is not limited to 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, 10.5%, 11%, 11.5%, 12%, 12.5%, 13%, 13.5%, 14%, 14.5% or 15%.

[0059] In some preferred embodiments, the mass percentage a% of silicon in the negative electrode material layer is 6% to 10%.

[0060] Specifically, the thickness d of the negative electrode material layer in the negative electrode can be, but is not limited to, 90 μm, 95 μm, 100 μm, 105 μm, 110 μm, 115 μm, 120 μm, 125 μm, 130 μm, 135 μm, or 140 μm.

[0061] In some preferred embodiments, the thickness d of the negative electrode material layer in the negative electrode is 110 μm to 130 μm.

[0062] By controlling the mass percentage content of silicon element in the negative electrode material layer and the thickness of the negative electrode material layer, while increasing the silicon element content, the thickness of the negative electrode material layer can be reduced, the migration path of lithium ions can be shortened, and the changes in the structure of the electrode caused by the continuous insertion and extraction of lithium ions during charge and discharge cycles can be minimized, thereby improving its cycling performance. When the mass percentage content a of silicon element in the negative electrode material layer is 5% - 15%, and the thickness d of the negative electrode material layer in the negative electrode is 90μm - 140μm, the energy density and cycling performance of the battery can be balanced; especially when the mass percentage content a of silicon element in the negative electrode material layer is 6% - 10%, and the thickness d of the negative electrode material layer in the negative electrode is 110μm - 130μm, better energy density and cycling performance can be obtained.

[0063] In some preferred embodiments, the positive electrode active material may be selected from ternary positive electrode active material LiNi m Co n M 1-m-n O2, where 0.6 ≤ m < 1; 0 < n < 0.2; 0 < m + n < 1; M includes one or both of Mn or Al, and includes zero, one or more of Sr, Mg, Ti, Ca, Zr, Zn, Si, Fe, B, Ga, Cr, W, V, Nb, Ce.

[0064] Specifically, the positive electrode active material may be selected from at least one of 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 0.8 Co 0.15 Al 0.05 O2, LiNi 0.9 Co 0.05 Mn 0.05 O2.

[0065] In some embodiments, the molar concentration of LiPF6 in the non-aqueous electrolyte is 0.8 mol / L - 1.2 mol / L.

[0066] In some embodiments, the silicon-based material is selected from one or more of silicon materials, silicon oxide materials, silicon-carbon composite materials, and silicon alloy materials. Preferably, the silicon material is selected from silicon-carbon composite materials.

[0067] In some embodiments, the silicon material is a nano-silicon material; the silicon oxide material is a SiOx material, where 0 < x < 2; the silicon-carbon composite material is a silicon-based material containing silicon and carbon materials, and / or a silicon-based material containing SiOy and carbon materials, where 0 < y < 2; the silicon alloy material is a Mg2Si alloy material and / or an Fe2Si alloy material.

[0068] In some embodiments, the non-aqueous electrolyte further includes an auxiliary additive, and the auxiliary additive is selected from one or more of cyclic carbonate compounds, cyclic sulfate compounds, sultone compounds, phosphate compounds, borate compounds, and nitrile compounds; based on the total mass of the non-aqueous electrolyte being 100%, the content of the auxiliary additive is 0.01% - 5%.

[0069] Preferably, the cyclic carbonate compounds are selected from one or more of vinylene carbonate, ethylene ethylenecarbonate, ethylene methylene carbonate, fluoroethylene carbonate, trifluoromethyl ethylene carbonate, difluoroethylene carbonate, or the compound shown in the following structural formula 1:

[0070] In the structural formula 1, R 21 、R 22 、R 23 、R 24 、R 25 、R 26 are each independently selected from a hydrogen atom, a halogen atom, or a C1-C5 group;

[0071] The cyclic sulfate compounds are selected from one or more of ethylene sulfate, 4-methyl ethylene sulfate, and propylene sulfate;

[0072] The sultone compounds are selected from one or more of 1,3-propane sultone, 1,4-butane sultone, and allyl-1,3-sultone;

[0073] The phosphate compounds are selected from tris(trimethylsilyl) phosphate, tris(triethylsilyl) phosphate, and the compound shown in the following structural formula 2:

[0074] In the structural formula 2, R 31 、R 32 、R 33 are 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 33At least one of them is an unsaturated hydrocarbon group;

[0075] The borate compound is selected from one or more of tris(trimethylsilyl)borate and tris(triethylsilyl)borate;

[0076] The nitrile compound is selected from one or more of succinonitrile, glutaronitrile, ethylene glycol bis(propionitrile) ether, hexanetrionitrile, adiponitrile, pimelonitrile, suberonitrile, azelaic acid dinitrile and sebacononitrile.

[0077] In a preferred embodiment, the phosphate compound shown in Structural Formula 2 may be at least one of tripropargyl phosphate, dipropargyl methyl phosphate, dipropargyl ethyl phosphate, dipropargyl propyl phosphate, dipropargyl trifluoromethyl phosphate, dipropargyl-2,2,2-trifluoroethyl phosphate, dipropargyl-3,3,3-trifluoropropyl phosphate, dipropargyl hexafluoroisopropyl phosphate, triallyl phosphate, diallyl methyl phosphate, diallyl ethyl phosphate, diallyl propyl phosphate, diallyl trifluoromethyl phosphate, diallyl-2,2,2-trifluoroethyl phosphate, diallyl-3,3,3-trifluoropropyl phosphate, and diallyl hexafluoroisopropyl phosphate.

[0078] The use of auxiliary additives in non-aqueous electrolytes can further improve the cycle performance of batteries.

[0079] In some embodiments, the lithium salt further comprises LiBOB, LiDFOB, LiDFOP, LiPO2F2, LiBF4, LiSbF6, LiAsF6, LiN(SO2C2F5)2, LiC(SO2CF3)3, LiClO4, LiAlCl4, LiCF3SO3, LiSO3F, Li2B 10 Cl 10 , lithium chloroborane, lithium tetrafluorooxalophosphate, lithium trioxalophosphate, a lower aliphatic lithium carboxylate having 4 or fewer carbon atoms, or lithium tetraphenylborate. In a specific embodiment, the concentration of the above lithium salt is 0.1 mol / L-4 mol / L. In a preferred embodiment, the concentration of the above lithium salt is 0.5 mol / L-2.5 mol / L. Specifically, the concentration of the above lithium salt can be 0.5 mol / L, 1 mol / L, 1.5 mol / L, 2 mol / L, or 2.5 mol / L.

[0080] In some embodiments, the non-aqueous organic solvent is selected from one or more of cyclic carbonates, linear carbonates, carboxylates, and ethers;

[0081] Preferably, the cyclic carbonate is selected from one or more of ethylene carbonate, vinylene carbonate, propylene carbonate and butylene carbonate;

[0082] The chain carbonate is selected from one or more of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate and methyl propyl carbonate;

[0083] The carboxylic acid ester is selected from one or more of methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, methyl butyrate, methyl isobutyrate, pivalic acid methyl ester and pivalic acid ethyl ester;

[0084] The ethers are selected from one or more of ethylene glycol dimethyl ether, 1,3-dioxolane and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether.

[0085] In some embodiments, the positive electrode current collector is selected from a metal material that can conduct electrons. Preferably, the positive electrode current collector includes 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.

[0086] In some embodiments, the positive electrode 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.

[0087] 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.

[0088] The positive electrode conductive agent includes at least one of conductive carbon black, conductive carbon balls, conductive graphite, conductive carbon fibers, carbon nanotubes, graphene, or reduced graphene oxide.

[0089] In some embodiments, the material of the negative electrode current collector may be the same as that of the positive electrode current collector, which will not be described in detail 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 secondary 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] Example 1

[0095] This embodiment is used to illustrate the lithium-ion battery and its preparation method disclosed in this application, including the following steps:

[0096] Preparation of positive electrode: Mix high nickel ternary positive electrode active material NCM811 (LiNi 0.8 Co 0.1 Mn 0.1 O2), conductive carbon black and binder polyvinylidene fluoride are dispersed in N-methyl-2-pyrrolidone to obtain a positive electrode slurry, which is evenly coated on both sides of an aluminum foil. A positive electrode material layer is formed on the aluminum foil after drying, calendering and vacuum drying, and an aluminum lead wire is welded with an ultrasonic welder to obtain a positive electrode sheet.

[0097] Negative electrode preparation: A silicon-carbon composite (a mixture of silicon dioxide and graphite), conductive carbon black, binder styrene-butadiene rubber, and carboxymethyl cellulose were mixed in a mass ratio of 94.2:1.2:3.0:1.5 and dispersed in deionized water to produce a negative electrode slurry. The slurry was then coated on both sides of a copper foil. After drying, rolling, and vacuum drying, a negative electrode material layer was formed on the copper foil. The silicon content and thickness of the negative electrode material layer are shown in Table 1. Nickel lead wires were then welded to the negative electrode sheet using an ultrasonic welder. The thickness of the negative electrode material layer in the negative electrode sheet (μm) = the thickness of the negative electrode sheet (μm) - the thickness of the negative electrode current collector (μm). The negative electrode sheet surface capacity test method is as follows: the negative electrode sheet is cut into a 12 mm diameter disc (only one side contains the negative electrode material layer), and the disc is assembled with a 16 mm diameter lithium sheet, using an electrolyte of EC / EMC=30 / 70 (w / w), LiPF6:1M, FEC:5%, to form a button battery. The assembled button battery is placed on a test cabinet for charge and discharge, and the discharge capacity C is recorded. dis The electrode surface capacity (single side) S is calculated according to the formula:

[0098] S=C dis / A

[0099] S is the negative electrode surface capacity, in mA·h / cm 2 ;

[0100] C dis is the discharge capacity of the button battery, in mA·h;

[0101] A is the area of ​​the negative electrode in the button battery, in cm 2 .

[0102] Preparation of electrolyte: Ethylene carbonate, diethyl carbonate and ethyl methyl carbonate were mixed in a volume ratio of EC:DEC:EMC=20:30:50. After mixing, LiFSI, FEC and LiPF6 were added. The concentration of LiPF6 in the electrolyte was 1.1 mol / L. The contents of LiFSI and FEC are shown in Table 1.

[0103] Preparation of battery cells: Place an isolation film between the positive and negative electrodes to assemble them into a laminated soft-pack battery cell.

[0104] Liquid injection and formation: In a glove box with a dew point controlled below -40°C, the prepared electrolyte was injected into the battery cell, vacuum-sealed, and left to stand for 48 hours. Then, the first charge was performed at 45°C hot pressing according to the following steps: 0.05C constant current charging for 3 hours, upper limit voltage 4.0V, pressure 3kg / cc; 0.1C constant current charging for 2 hours, upper limit voltage 4.0V, pressure 5kg / cc; 0.2C constant current charging for 2 hours, upper limit voltage 4.0V, pressure 5kg / cc, secondary vacuum sealing, and then further charged at 0.02C constant current for 30 minutes, 0.05C constant current charging for 30 minutes, 0.1C constant current charging for 120 minutes, 0.2C constant current charging for 240 minutes, the cut-off voltage was set to 3.85V, left for 1 hour, and left at room temperature for 24 hours (12 hours each on the forward and reverse sides), then charged at 0.5C constant current to 4.2V, and discharged at 0.2C constant current to 2.75V.

[0105] Examples 2 to 32

[0106] Examples 2 to 32 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, except that the battery parameters shown in Table 1 are used, and the lithium fluorosulfonyl imide in the non-aqueous electrolyte of Examples 28 and 32 is selected from LiTFSI.

[0107] Comparative Examples 1 to 23

[0108] Comparative Examples 1 to 23 are used to illustrate the lithium-ion battery and the preparation method thereof disclosed in the present application, including most of the operating steps in Example 1, except that the battery parameters shown in Table 1 are used, wherein the non-aqueous electrolyte in Comparative Example 23 does not contain LiPF6.

[0109] Table 1

[0110] Performance Testing

[0111] The following properties of the lithium-ion batteries in the above examples and comparative examples were tested:

[0112] (1) 25°C cycle performance test: At 25°C, the formed battery was charged to 4.2V using a 1C constant current and constant voltage test, and then discharged to 2.75V using a 1C constant current test. After 800 charge / discharge cycles, the 800th cycle capacity retention rate was calculated. The calculation formula is as follows: 800th cycle capacity retention rate (%) = (800th cycle discharge capacity / first cycle discharge capacity) × 100%;

[0113] (2) 45°C Cycling Performance Test: At 45°C, the formed battery was charged to 4.2V using a 1C constant current and constant voltage test, and then discharged to 2.75V using a 1C constant current test. After 800 charge / discharge cycles, the capacity retention rate and volume expansion rate at the 800th cycle were calculated. The calculation formula is as follows: 800th cycle capacity retention rate (%) = (800th cycle discharge capacity / first cycle discharge capacity) × 100%.

[0114] Fill in the performance test results in Table 2:

[0115] Table 2

[0116] The above results show that the lithium-ion battery of the present application has excellent cycle performance, which indicates that by optimizing the composition of the lithium-ion battery and making the mass percentage a of the silicon element in the negative electrode material layer, the mass percentage b of fluoroethylene carbonate in the non-aqueous electrolyte, the mass percentage c of lithium fluorosulfonyl imide in the non-aqueous electrolyte and the thickness d of the negative electrode material layer meet the following conditions: 100≤(b+c)*d / a≤200, and 5≤a≤15, 1≤b≤15, 0.5≤c≤10, 90≤d≤140, it can effectively solve the influence of metal ions dissolved in the high-nickel ternary positive electrode active material on the formation of the SEI film on the negative electrode surface, and the volume change of the negative electrode silicon-based active material during the battery charging and discharging process, so that the lithium-ion battery has both high energy density and excellent cycle performance, and improves the service life.

[0117] In particular, when the mass percentage a of the silicon element in the negative electrode material layer, the mass percentage b of fluoroethylene carbonate in the non-aqueous electrolyte, the mass percentage c of lithium fluorosulfonyl imide in the non-aqueous electrolyte, and the thickness d of the negative electrode material layer meet the preferred ranges of 120≤(b+c)*d / a≤180, and 6≤a≤10, 3≤b≤10, 1≤c≤6, and 110≤d≤130, the overall performance of the battery is better (for example, Examples 1, 2, 5, 6, 12, 13, 17, 18, 21, 24, and 28). When one or more of a, b, c, d, and (b+c)*d / a is not within the preferred range, the relevant performance of the battery will be slightly deteriorated. For example, when a is lower than the preferred range, the cycle performance and energy density of the battery both decrease (Example 13 vs. Example 14); when a is higher than the preferred range, although the energy density of the battery increases, the cycle performance decreases (Example 9 vs. Example 17). When b is lower than the preferred range, the cycle performance of the battery decreases (Example 23 vs Example 24); when b is higher than the preferred range, the cycle performance of the battery also decreases slightly (Example 17 vs Example 22). When c is lower than the preferred range, the cycle performance of the battery decreases (Example 18 vs Example 19) and when b is higher than the preferred range (Example 20 vs Example 21), the cycle performance of the battery decreases slightly. When (b+c)*d / a is not in the preferred range, the cycle performance of the battery decreases slightly (Example 25 and Example 26). In particular, when a, b, c, d and (b+c)*d / a are all outside the preferred range, the relevant performance degradation of the battery is more obvious (Example 27).

[0118] The lithium fluorosulfonyl imide described in this application can achieve the application effect when it is selected from LiFSI or LiTFSI (Example 28, Example 32).

[0119] When the non-aqueous electrolyte of the lithium-ion battery of the present application further contains other auxiliary additives, the cycle performance of the battery can be further improved. For example, compared with Example 2, the cycle performance of the lithium-ion batteries in Example 29 (using the auxiliary additive LiPO2F2), Examples 30 and 32 (using the auxiliary additive DTD), and Example 31 (using the auxiliary additive VC) is further improved.

[0120] The present application optimizes the composition of the lithium-ion battery and ensures that the mass percentage a of the silicon element in the negative electrode material layer, the mass percentage b of FEC in the non-aqueous electrolyte, the mass percentage c of lithium fluorosulfonyl imide in the non-aqueous electrolyte, and the thickness d of the negative electrode material layer meet specific requirements and relationships, thereby enabling the lithium-ion battery to have both high energy density and excellent cycle life. When the type or amount of raw materials of the lithium-ion battery does not meet the requirements, or the relationship between the amounts of raw materials does not meet the requirements, the performance of the battery will be severely deteriorated. For example, compared with Example 2, the non-aqueous electrolyte of the lithium-ion batteries in Comparative Examples 1 to 4 does not contain FEC, and a stable SEI film cannot be formed, resulting in a sudden drop in the cycle life of the silicon-based active material negative electrode. Even if other types of auxiliary additives are added, the drop phenomenon cannot be avoided. When FEC is added to the non-aqueous electrolyte, but the FEC content is not within the scope of this application, it will also lead to deterioration of battery performance. When the FEC content is too high (Comparative Examples 9-10), the excessive FEC will increase the charge exchange impedance of the interface, causing an increase in the battery impedance and affecting the battery electrochemical performance; when the FEC content is too low (Comparative Example 21), a stable SEI film cannot be formed, and even if other types of additives are added, the problem of battery cycle performance degradation cannot be solved (Comparative Example 22).

[0121] When the mass percentage of silicon in the negative electrode material layer is not within the scope of this application and the content is too low (Comparative Example 5), it is necessary to increase the thickness of the negative electrode material layer to maintain the energy density. This increases the migration path of lithium ions, easily forming a concentration difference inside the battery, increasing polarization, and affecting the battery cycle performance. When the content is too high (Comparative Example 6), the volume change of the Si-based active material is very large during the charge and discharge process of the lithium-ion battery, which easily leads to deterioration problems such as disconnection of the electron conduction path in the electrode and micronization of particles, thereby deteriorating the battery cycle performance. When the mass percentage of lithium fluorosulfonyl imide in the non-aqueous electrolyte is too low, the inorganic SEI film stability is poor, and more positive electrode transition metal ions are dissolved, affecting the battery cycle performance (Comparative Example 7); when the mass percentage of lithium fluorosulfonyl imide in the non-aqueous electrolyte is too high, the viscosity of the electrolyte increases and the fluidity deteriorates. Excessive lithium fluorosulfonyl imide easily corrodes the aluminum current collector, deteriorating the battery performance (Comparative Example 8).

[0122] When the thickness of the negative electrode material layer is not within the scope of this application, when the thickness is too low (Comparative Example 19), the energy density is reduced; when the thickness is too high (Comparative Example 20), the migration path of lithium ions is increased, which easily forms a concentration difference inside the battery, increases polarization, and affects the battery cycle performance.

[0123] When the battery raw materials and dosage meet the requirements of this application, but the relationship between the raw material dosage does not satisfy 100≤(b+c)*d / a≤200, it is still impossible to take into account both the energy density and cycle performance of the battery (Comparative Examples 11 to 18).

[0124] When the non-aqueous electrolyte does not contain LiPF6 (Comparative Example 23), the positive electrode current collector aluminum foil lacks the passivation film generated by the LiPF6 reaction and is easily corroded by LiFSI, causing battery performance degradation.

[0125] In summary, the present application optimizes the composition of the lithium-ion battery and makes the mass percentage a of the silicon element in the negative electrode material layer, the mass percentage b of fluoroethylene carbonate in the non-aqueous electrolyte, the mass percentage c of lithium fluorosulfonyl imide in the non-aqueous electrolyte and the thickness of the negative electrode material layer d meet the following conditions: 100≤(b+c)*d / a≤200, and 5≤a≤15, 1≤b≤15, 0.5≤c≤10, 90≤d≤140, so that the lithium-ion battery has both high energy density and excellent cycle life.

[0126] 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.

[0127] 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: It includes a positive electrode, a negative electrode and a non-aqueous electrolyte; the positive electrode includes a positive electrode current collector and a positive electrode material layer provided on the surface of the positive electrode current collector, the positive electrode material layer contains a positive electrode active material, and the positive electrode active material is selected from ternary positive electrode active substances Li 1+x Ni m Co n M 1-m-n O 2-y A y or more of them, where, -0.1 ≤ x ≤ 0.2; 0.6 ≤ m < 1; 0 < n < 0.2; 0 < m + n < 1; 0 ≤ y < 0.2; M includes one or both of Mn or Al, and includes zero, one or more of Sr, Mg, Ti, Ca, Zr, Zn, Si, Fe, B, Ga, Cr, W, V, Nb, Ce; A includes one or more of S, N, F, B, Cl, Br and I; the negative electrode includes a negative electrode current collector and a negative electrode material layer provided on the surface of the negative electrode current collector, the negative electrode material layer contains a silicon-based material; the non-aqueous electrolyte contains a non-aqueous organic solvent, an additive and a lithium salt, the additive includes fluorinated ethylene carbonate; the lithium salt includes lithium hexafluorophosphate and lithium fluorosulfonimide; The lithium-ion battery meets the following conditions: 100≤(b+c)*d / a≤200, and 5≤a≤15, 1≤b≤15, 0.5≤c≤10, 90≤d≤140; Wherein, a represents the mass percentage of silicon element in the negative electrode material layer, in %; b represents the mass percentage of fluoroethylene carbonate in the non-aqueous electrolyte, in %; c represents the mass percentage of lithium fluorosulfonyl imide in the non-aqueous electrolyte, in %; d represents the thickness of the negative electrode material layer, in μm.

2. The lithium-ion battery according to claim 1, characterized in that The lithium ion battery meets the following condition: 120≤(b+c)*d / a≤180.

3. The lithium ion battery according to claim 1, characterized in that The mass percentage a of silicon element in the negative electrode material layer is 6% to 10%.

4. The lithium ion battery according to claim 1, characterized in that The mass percentage b of the fluoroethylene carbonate in the non-aqueous electrolyte is 3% to 10%.

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

6. The lithium ion battery according to claim 1, characterized in that The thickness d of the negative electrode material layer is 110 μm to 130 μm.

7. The lithium ion battery according to claim 1, characterized in that The silicon-based material is selected from one or more of silicon materials, silicon oxide materials, silicon-carbon composite materials and silicon alloy materials.

8. The lithium ion battery according to claim 1, characterized in that The lithium fluorosulfonyl imide is selected from one or more of LiFSI and LiTFSI.

9. The lithium ion battery according to any one of claims 1 to 8, characterized in that: The non-aqueous electrolyte further includes an auxiliary additive, and the auxiliary additive is selected from one or more of cyclic carbonate compounds, cyclic sulfate compounds, sultone compounds, phosphate compounds, borate compounds and nitrile compounds.

10. The lithium ion battery according to claim 9, characterized in that Based on the total mass of the non-aqueous electrolyte being 100%, the content of the auxiliary additive is 0.01% to 5%.

11. The lithium ion battery according to claim 9, characterized in that The cyclic carbonate compound is selected from one or more of vinylene carbonate, ethylene carbonate, methylene carbonate, fluoroethylene carbonate, trifluoromethylethylene 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.

12. The lithium ion battery according to claim 9, characterized in that The cyclic sulfate ester compound is selected from one or more of vinyl sulfate, 4-methylvinyl sulfate, and propylene sulfate.

13. The lithium ion battery according to claim 9, characterized in that The sultone compound is selected from one or more of 1,3-propane sultone, 1,4-butane sultone and propenyl-1,3-sultone.

14. The lithium ion battery according to claim 9, characterized in that The phosphate compound is selected from 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.

15. The lithium ion battery according to claim 9, characterized in that The borate ester compound is selected from one or more of tris(trimethylsilyl)borate and tris(triethylsilyl)borate.

16. The lithium ion battery according to claim 9, characterized in that The nitrile compound is selected from one or more of succinonitrile, glutaronitrile, ethylene glycol bis(propionitrile) ether, hexanetrinitrile, adiponitrile, pimelonitrile, suberonitrile, azelaic acid dinitrile and sebaconitrile.

17. The lithium ion battery according to any one of claims 1 to 8, characterized in that: The non-aqueous organic solvent is selected from one or more of cyclic carbonates, linear carbonates, carboxylates and ethers.

18. The lithium ion battery according to claim 17, wherein: The cyclic carbonate is selected from one or more of ethylene carbonate, vinylene carbonate, propylene carbonate and butylene carbonate.

19. The lithium ion battery according to claim 17, wherein: The chain carbonate is selected from one or more of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate and methyl propyl carbonate.

20. The lithium ion battery according to claim 17, wherein: The carboxylic acid ester is selected from one or more of methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, methyl butyrate, methyl isobutyrate, methyl trimethylacetate and ethyl trimethylacetate.

21. The lithium ion battery according to claim 17, wherein: The ethers are selected from one or more of ethylene glycol dimethyl ether, 1,3-dioxolane and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether.

Images