Lithium ion battery

Abstract

The invention belongs to the technical field of new energy batteries, and relates to a lithium ion battery. The lithium ion battery comprises a positive plate, a negative plate, a diaphragm and a non-aqueous electrolyte, wherein the negative plate comprises a negative current collector and a negative material layer arranged on the negative current collector; the negative electrode current collector is a copper foil or a composite copper foil, and the negative electrode material layer comprises a silicon-containing material; the non-aqueous electrolyte comprises a non-aqueous organic solvent, a lithium salt, a first additive and a second additive; the first additive is 1, 3, 6-hexane trinitrile; the second additive comprises a compound as shown in a structural formula 1; the lithium ion battery satisfies the following conditions: 0.1 < = 10 (d + c) * a / b < = 100, 8 < = a < = 30, 20 < = b < = 800, 0.5 < = c < = 4, and 0.1 < = d < = 4. According to the lithium ion battery provided by the invention, the silicon negative electrode is stable in structure, high in energy density and stable in cycle performance.

Description

Technical Field

[0001] The present invention belongs to the technical field of new energy batteries and relates to a lithium-ion battery, in particular to a lithium-ion battery with a stable silicon negative electrode structure, high energy density and stable cycle performance. Background Art

[0002] Lithium-ion batteries are widely used in 3D digital products and electric vehicles. As market demands for longer battery life continue to increase, there's an urgent need to further improve battery energy density. The energy density of a lithium battery is primarily determined by the positive electrode's gram capacity, the negative electrode's gram capacity, and the potential difference between the positive and negative electrodes. Currently, the reversible specific capacity of graphite anode materials is close to the theoretical specific capacity of 372 mAh / g. Therefore, to increase the energy density of lithium batteries, it's necessary to develop anode materials with higher specific capacities. Silicon anode materials, which have a different lithium storage mechanism than graphite anode materials, have a theoretical specific capacity of up to 4200 mAh / g, approximately 10 times that of graphite anodes, making them the lithium-ion battery anode material with the highest known specific capacity. Using silicon-containing anode materials can increase the energy density of lithium batteries by over 8%, while reducing the cost per kilowatt-hour by at least 3%.

[0003] When silicon is fully lithiated, its volume expands by over 300%. This dramatic volume change can lead to a series of problems. First, the volume expansion effect causes high internal stress in the battery, which can easily squeeze the electrode sheets and cause cracks or even pulverization of the silicon anode material. Second, the volume expansion effect makes it easy for the electrode material to lose contact with the current collector, causing the active material to detach from the electrode sheet, leading to rapid battery capacity decay. Finally, the volume expansion effect easily forms an unstable solid electrolyte interface (SEI) film. As the silicon volume changes, the SEI film ruptures, and the newly exposed silicon on the surface produces a new SEI film, which continuously consumes lithium ions in the electrolyte, resulting in irreversible capacity loss and low initial charge efficiency. Furthermore, the SEI film thickness increases with electrochemical cycling. Excessively thick SEI layers hinder electron transfer and lithium ion diffusion, leading to increased impedance. Therefore, it is necessary to develop a lithium-ion battery that can effectively suppress the volume expansion of the silicon anode and exhibit stable cycling performance. Summary of the Invention

[0004] Based on this, the purpose of the present invention is to provide a lithium-ion battery that can effectively inhibit the expansion of the silicon negative electrode, stabilize the silicon negative electrode structure, and improve the battery cycle stability.

[0005] To achieve the above-mentioned purpose, the present invention adopts the following technical solutions.

[0006] The present invention provides a lithium-ion battery, comprising a positive electrode sheet, a negative electrode sheet, a separator and a non-aqueous electrolyte; the negative electrode sheet comprises a negative electrode current collector and a negative electrode material layer disposed on the negative electrode current collector; the negative electrode current collector is copper foil or composite copper foil, and the negative electrode material layer comprises a silicon-containing material; The non-aqueous electrolyte includes a non-aqueous organic solvent, a lithium salt, a first additive and a second additive; The first additive is 1,3,6-hexanetrinitrile; The second additive includes a compound shown in structural formula 1: ; Wherein, X is selected from or , R1, R2 are each independently selected from H, ,or , R1 and R2 are not simultaneously selected from H, and X, R1 and R2 contain at least one sulfur atom; The lithium-ion battery meets the following conditions: 0.1≤10(d+c)×a / b≤100, and 8≤a≤30, 20≤b≤800, 0.5≤c≤4, 0.1≤d≤4; Wherein, a is the mass percentage of silicon element in the negative electrode material layer, and the unit is %; b is the mass content of Cr element relative to Cu element in the negative electrode current collector, in ppm; c is the mass percentage of the first additive in the non-aqueous electrolyte, in %; d is the mass percentage of the second additive in the non-aqueous electrolyte, in %.

[0007] The lithium-ion battery provided by the present invention uses a silicon-containing material as the negative electrode, limits the silicon content in the negative electrode material layer, adds Cr to the negative electrode current collector, and uses 1,3,6-hexanetrinitrile as a first additive in the non-aqueous electrolyte, along with a compound represented by Structural Formula 1 as a second additive. After extensive research, the inventors discovered that when the relationship between the mass percentage a of the silicon element in the negative electrode material layer, the mass percentage b of the Cr element relative to the Cu element in the negative electrode current collector, the mass percentage c of the first additive in the non-aqueous electrolyte, and the mass percentage d of the second additive in the non-aqueous electrolyte satisfies 0.1≤10(d+c)×a / b≤100, 8≤a≤30, 20≤b≤800, 0.5≤c≤4, and 0.1≤d≤4, a lithium-ion battery with a stable silicon negative electrode structure, high energy density, and good cycle performance can be obtained. The reason is speculated to be that the use of silicon-containing negative electrode materials in the negative electrode material layer improves the energy density of the battery, while the Cr element in the negative electrode current collector improves the volume expansion of the negative electrode caused by the high silicon content in the silicon-containing negative electrode and stabilizes the negative electrode structure; due to the addition of the first additive, metal ions such as Cr are well complexed, the dissolution of metal ions is suppressed, and the stability of the positive and negative electrode structures of the battery is protected, thereby improving the cycle performance of the battery; in addition, the second additive, as a better negative electrode film-forming additive, also forms a dense SEI film at the negative electrode, reducing the aggravated effect of the use of the first additive on the negative electrode interface side reaction, better protecting the negative electrode, and also contributing to the improvement of battery performance. In summary, the present invention achieves a synergistic effect between the various parameters by limiting the content of the silicon element in the negative electrode material layer, the mass content of the Cr element relative to the Cu element in the negative electrode current collector, the content of the first additive in the non-aqueous electrolyte, and the content of the second additive in the non-aqueous electrolyte within a certain range, thereby obtaining a lithium-ion battery with a stable silicon negative electrode structure, high energy density, and good cycle performance. Preferably, the lithium-ion battery satisfies 0.8≤10(d+c)×a / b≤24.

[0008] The use of silicon-containing negative electrodes is one of the main methods to improve battery energy density. The content of silicon in the negative electrode has a significant impact on the performance of the battery. When the silicon content a% in the negative electrode material layer is too low, it has little effect on improving the battery energy density and cannot effectively improve the battery energy density. When the silicon content a% in the negative electrode material layer is too high, the volume of silicon expands significantly, which will cause the battery negative electrode material to rupture and easily lose contact with the current collector, causing the active material to detach from the electrode, causing rapid decay of the battery capacity and forming an unstable solid electrolyte interface membrane SEI membrane. As the volume of silicon changes, the SEI membrane will rupture, and the newly exposed silicon on the surface will generate a new SEI membrane, while continuously consuming lithium ions in the electrolyte, resulting in irreversible capacity loss and low initial charging efficiency. In addition, the SEI thickness will continue to increase with the electrochemical cycle. An excessively thick SEI membrane will hinder electron transfer and Li + Diffusion leads to increased impedance. Specifically, the silicon content a% in the negative electrode material layer is 8%, 10%, 12%, 14%, 16%, 18%, 20%, 22%, 24%, 26%, 28%, 30%, or a range consisting of any two of these values; preferably, the silicon content a% in the negative electrode material layer is 10≤a≤25. Within this range, while significantly improving energy density, the volume expansion of silicon can be well controlled by designing other battery structures, thereby significantly improving the battery's electrochemical performance.

[0009] Specifically, in some embodiments of the present invention, the problem of high-silicon-content silicon-containing anodes experiencing significant volume expansion and contraction during charge and discharge, which can lead to structural damage, exacerbate solid / liquid interfacial reactions, and alter the electrode microstructure, resulting in degraded battery performance, is overcome by doping the copper foil used as the anode current collector with an appropriate amount of chromium. Chromium is a common trace element that significantly impacts the performance of copper foil. An appropriate amount of chromium can improve the hardness and wear resistance of the copper foil, stabilize the anode structure, and mitigate the volume expansion of the anode caused by the high silicon content in silicon-containing anodes. Chromium also improves the copper foil's oxidation resistance, reducing its reactivity with environmental factors such as oxygen and moisture. However, when the mass content of Cr in the anode current collector is excessive relative to the mass content of Cu, the excess Cr may dissolve during charge and discharge, catalyzing side reactions between the electrolyte and the electrode at the anode interface, thereby degrading battery performance. Furthermore, excessive chromium can cause copper to become brittle, reducing its ductility and mechanical properties, and hindering electrode production. When the mass content b of the Cr element relative to the Cu element in the negative electrode current collector is too low, the hardness and wear resistance of the copper foil are poor, it is easy to break, and the negative electrode structure is damaged. Therefore, it is necessary to accurately control the chromium content in the copper foil to ensure that the performance of the copper foil reaches the best state. Specifically, the mass content b of the Cr element relative to the Cu element in the negative electrode current collector is 20ppm, 50ppm, 100ppm, 150ppm, 200ppm, 230ppm, 250ppm, 280ppm, 300ppm, 330ppm, 350ppm, 380ppm, 400ppm, 450ppm, 500ppm, 650ppm, 700ppm, 750ppm, 800ppm or a range consisting of any two of these values; preferably, the mass content b of the Cr element relative to the Cu element in the negative electrode current collector is 50ppm~500ppm. Within this range, the addition of Cr can significantly improve the hardness and wear resistance of the copper foil, stabilize the negative electrode structure, and mitigate the negative electrode volume expansion caused by the high silicon content in silicon-containing negative electrodes. Furthermore, this range can significantly reduce the probability of side reactions between the catalytic electrolyte and the electrode, improving battery performance. The Cr content in the negative electrode current collector of the present invention can be determined by inductively coupled plasma (ICP) testing, where the mass content of Cr relative to Cu in the negative electrode current collector (b) is the mass of Cr divided by the mass of Cu.

[0010] Specifically, in some embodiments of the present invention, since the Cr doped in the negative electrode current collector may be dissolved during the charge and discharge process, it may catalyze the side reaction between the electrolyte and the electrode at the negative electrode interface, thereby deteriorating the battery performance. Therefore, by adding the first additive 1,3,6-hexanetrinitrile to the non-aqueous electrolyte, metal ions such as Cr and Co can be well complexed, the dissolution of metal ions can be inhibited, and the stability of the positive and negative electrode structures of the battery can be protected, thereby improving the cycle performance of the battery. However, when the mass percentage c% of the first additive in the non-aqueous electrolyte is too high, the high content of the first additive will affect the electrolyte solvation structure, affect the film formation of the electrolyte at the negative electrode, lead to the aggravation of the side reaction at the negative electrode interface, and deteriorate the battery performance. When the mass percentage c% of the first additive in the non-aqueous electrolyte is too low, the complexing effect on the metal ions is limited, affecting the integrity of the electrolyte film formation at the negative electrode, or the film thickness is insufficient, deteriorating the battery cycle performance. Specifically, the mass percentage c% of the first additive in the non-aqueous electrolyte is 0.5%, 0.8%, 1.0%, 1.2%, 1.4%, 1.6%, 1.8%, 2.0%, 2.2%, 2.4%, 2.6%, 2.8%, 3.0%, 3.2%, 3.4%, 3.6%, 3.8%, 4.0%, or a range consisting of any two of these values; preferably, the mass percentage c% of the first additive in the non-aqueous electrolyte is 1% to 3%. Within this range, the first additive can effectively complex transition metal ions and inhibit ion dissolution without destroying the electrolyte solvation structure or the battery negative electrode interface, thereby ensuring good cycle performance of the battery.

[0011] Specifically, in some embodiments of the present invention, since the first additive affects the electrolyte solvation structure and affects the electrolyte film formation at the negative electrode, it leads to aggravated negative electrode interface side reactions and deterioration of battery performance; while the second additive is a better negative electrode film-forming additive, which can preferentially form a dense SEI film at the negative electrode, protect the negative electrode interface from negative electrode damage caused by the addition of the first additive, reduce interface side reactions, and improve battery performance. However, the addition of the second additive will increase the internal resistance of the battery and deteriorate the low temperature and fast charging performance of the battery, so the addition amount of the second additive needs to be strictly controlled. Specifically, the mass percentage content d% of the second additive in the non-aqueous electrolyte is 0.1%, 0.3%, 0.5%, 0.8%, 1%, 1.3%, 1.5%, 1.8%, 2%, 2.3%, 2.5%, 2.8%, 3%, 3.3%, 3.5%, 3.8%, 4% or a range consisting of any two of these values; preferably, the mass percentage content d% of the second additive in the non-aqueous electrolyte is 0.5%~2%. Within this range, a dense SEI film can be effectively formed at the negative electrode, reducing interfacial side reactions and improving battery cycle performance. At the same time, it will not cause a significant increase in the internal resistance of the battery, ensuring that the battery has good low-temperature and fast-charging performance.

[0012] Specifically, in some embodiments of the present invention, in the compound represented by structural formula 1, X is selected from or , R1, R2 are each independently selected from H, ,or , R1 and R2 are not selected from H at the same time, X, R1 and R2 contain at least one sulfur atom, and X, R, and R2 do not contain sulfur atoms at the same time.

[0013] As an example, the second additive is selected from one or more of the following compounds: .

[0014] The first additive includes both a sulfur-containing cyclic structure and a carbonate-containing cyclic structure. The interface film component formed by the carbonate cyclic structure and the sulfur-containing cyclic structure is more stable and dense.

[0015] In some embodiments of the present invention, in the compound represented by structural formula 1, X is selected from , R1, R2 are each independently selected from H or , R1 and R2 are not selected from H at the same time.

[0016] As an example, the second additive is selected from one or more of the following compounds: .

[0017] The second additive has a multi-ring structure. Compared with the single-ring structure of vinyl sulfate, the multi-ring structure opens each ring to participate in the formation of the interface film on the electrode surface. The formed interface film components are more stable and dense, which has the effect of improving the strength of the interface film structure, thereby helping to improve its high-temperature stability.

[0018] Specifically, in some embodiments of the present invention, the non-aqueous organic solvent includes at least one of a cyclic carbonate solvent, a linear carbonate solvent, a carboxylate solvent, and an ether solvent.

[0019] In some preferred embodiments, the cyclic carbonate solvent includes at least one of ethylene carbonate, propylene carbonate, fluoroethylene carbonate, vinylene carbonate and butylene carbonate.

[0020] In some preferred embodiments, the linear carbonate solvent includes at least one of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate and methyl propyl carbonate.

[0021] In some preferred embodiments, the carboxylate solvent includes at least one of ethyl acetate, ethyl propionate, propyl propionate, ethyl difluoroacetate, methyl acetate, methyl propionate, methyl butyrate, methyl isobutyrate, methyl trimethylacetate and ethyl trimethylacetate.

[0022] 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.

[0023] Specifically, in some embodiments of the present invention, the lithium salt includes lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, LiPO2F2, LiBF4, LiBOB, LiSbF6, LiAsF6, LiCF3SO3, LiDFOB, LiDFOP, LiC(SO2CF3)3, LiN(SO2C2F5)2, LiCl, LiBr, LiI, LiClO4, LiB 10 Cl 10 , LiAlCl4, lithium chloroborane, and lithium tetraphenylborate.

[0024] In a specific embodiment, the total molar content of the lithium salt is 0.5 mol / L to 3.5 mol / L. In a preferred embodiment, the total molar content of the lithium salt is 0.8 mol / L to 2.0 mol / L. Specifically, the total molar content of the lithium salt can be 0.5 mol / L, 0.55 mol / L, 0.6 mol / L, 0.65 mol / L, 0.7 mol / L, 0.8 mol / L, 0.85 mol / L, 0.9 mol / L, 0.95 mol / L, 1.0 mol / L, 1.1 mol / L, 1.15 mol / L, 1.2 mol / L, 1.3 mol / L, 1.4 mol / L, 1.45 mol / L, 1.5 mol / L, 1.6 mol / L, 1.7mol / L, 1.8mol / L, 1.9mol / L, 2.0mol / L, 2.1mol / L, 2.2mol / L, 2.3mol / L, 2.4mol / L, 2.5mol / L, 2.6mol / L, 2.7mol / L, 2.8mol / L, 2.9mol / L, 3.0mol / L, 3.1mol / L, 3.2mol / L, 3.3mol / L, 3.4mol / L, 3.5mol / L or a range consisting of any two of these values.

[0025] Specifically, in some preferred embodiments of the present invention, the lithium salt includes at least LiPF6. In the non-aqueous electrolyte, the concentration of the lithium salt is 0.1mol / L~2mol / L. In a preferred embodiment, in the non-aqueous electrolyte, the concentration of the lithium salt is 0.5mol / L~1.5mol / L. Specifically, in the non-aqueous electrolyte, the concentration of the lithium salt can be 0.5mol / L, 0.6mol / L, 0.7mol / L, 0.8mol / L, 0.9mol / L, 1.0mol / L, 1.2mol / L, 1.3mol / L, 1.4mol / L, 1.5mol / L or a range consisting of any two of these values.

[0026] In some embodiments of the present invention, the non-aqueous electrolyte further includes an auxiliary additive, and the auxiliary additive includes at least one of a cyclic sulfate compound, a sultone compound, a cyclic carbonate compound, a phosphate compound, and a borate compound.

[0027] In some preferred embodiments, the cyclic sulfate ester compound includes at least one of 4-methylvinyl sulfate, vinyl sulfate, and propylene sulfate.

[0028] 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.

[0029] In some preferred embodiments, the cyclic carbonate compound includes at least one of vinylene carbonate, ethylene carbonate, methylene carbonate, fluoroethylene carbonate, trifluoromethylethylene carbonate, bisfluoroethylene carbonate and the compound represented by the following structural formula 2: ; In the structural formula 2 shown, 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.

[0030] In some preferred embodiments, the compound represented by structural formula 2 includes at least one of the following compounds represented by compounds 2-1 to 2-6: ; In some preferred embodiments, the phosphate compound includes at least one of the compounds shown in the following structural formula 3: ; In the structural formula 3, 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 of 1 to 3; more preferably, the compound represented by structural formula 3 includes at least one of tris(trimethylsilane) phosphate, tris(triethylsilane) phosphate, 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.

[0031] In some preferred embodiments, the borate ester compound includes at least one of tris(trimethylsilyl)borate and tris(triethylsilyl)borate.

[0032] In some embodiments of the present invention, based on the total mass of the non-aqueous electrolyte as 100%, the content of the auxiliary additive is 0.01% to 10%. Preferably, the content is 0.1% to 5%; more preferably, the content is 0.1% to 2%. Specifically, the content of any one of the optional substances in the auxiliary additive can be 0.01%, 0.05%, 0.08%, 0.1%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, 2.8%, 3%, 3.2%, 3.5%, 3.8%, 4%, 4.5%, 5%, or a range consisting of any two of these values.

[0033] Specifically, in some embodiments of the present invention, the silicon-containing material is a silicon-containing material containing silicon and carbon material, and / or a silicon-containing material containing SiO y and a silicon-containing material of a carbon material, wherein 0≤y<2.

[0034] Specifically, in some embodiments of the present invention, the negative electrode sheet further includes a negative electrode binder and a negative electrode conductor. The negative electrode binder includes polyvinylidene fluoride, a copolymer of vinylidene fluoride, polytetrafluoroethylene, a copolymer of vinylidene fluoride and hexafluoropropylene, a copolymer of tetrafluoroethylene and hexafluoropropylene, a copolymer of tetrafluoroethylene and perfluoroalkyl vinyl ether, a copolymer of ethylene and tetrafluoroethylene, a copolymer of vinylidene fluoride and tetrafluoroethylene, a copolymer of vinylidene fluoride and trifluoroethylene, a copolymer of vinylidene fluoride and trichloroethylene, a copolymer of vinylidene fluoride and fluoroethylene, a copolymer of vinylidene fluoride and hexafluoropropylene and tetrafluoroethylene, thermoplastic polyimide, a thermoplastic resin such as polyethylene and polypropylene; an acrylic resin; and one or more of styrene butadiene rubber. The negative electrode conductor includes one or more of conductive carbon black, conductive carbon spheres, conductive graphite, conductive carbon fibers, carbon nanotubes, graphene, or reduced graphene oxide.

[0035] Specifically, in some embodiments of the present invention, the positive electrode sheet includes a positive electrode material layer, the positive electrode material layer includes a positive electrode active material, and the positive electrode active material may include at least one of a ternary material, a phosphate material, a lithium cobalt oxide material, a lithium manganese-rich material, or a lithium nickel manganese oxide material.

[0036] In some preferred embodiments of the present invention, the ternary material comprises a chemical formula of Li q Ni x Co y M 1-x-y O 2-g R g The material or the surface of the Li q Ni x Co y M 1-x-y O 2-g R g At least one of the materials, wherein 0.9≤q≤1.2, 0.01≤x≤0.96, y>0, 1-xy>0, 0≤g≤1, M includes one or two of Mn and Al, and zero, one or more of Sr, Mg, Ti, Ca, Zr, Zn, Si, Fe, B, Ga, Cr, W, V, Nb, and Ce, and R includes one or more of N, F, S, and Cl.

[0037] In some preferred embodiments of the present invention, the phosphate material includes a molecular formula of Li r Mn α Fe β A 1-α-β PO 4-n G n The material or the surface of the Li r Mn α Fe βA 1-α-β PO 4-n G n At least one of the materials, wherein 0.9≤r≤1.1, 0≤α≤0.8, 0.2≤β≤1, 0≤n≤0.1, A is selected from one or more of Ti, Mg, V, Cr, Zr, Nb, Zn, Al, Na, K, Mo, W, Ni, Co, Ga, Sn, Sb, Ge and W, and G includes one or more of N, F, S and Cl.

[0038] In some preferred embodiments of the present invention, the lithium cobalt oxide material includes lithium cobalt oxide or lithium cobalt oxide modified by doping and / or coating with any one or more elements of Ni, Mn, Mg, Al, Zr, W, F, B, Cr, Mo and rare earth elements.

[0039] In some preferred embodiments of the present invention, the lithium nickel manganese oxide material comprises a molecular formula of LiNi x' L' y’ Mn （2-x'-y'） O4, or LiNi with a coating layer on the surface x' L' y’ Mn （2-x'-y'） At least one of the O4 materials, 0.3≤x'≤0.6, 0.01≤y'≤0.2, and L' is selected from one or more of Co, Al, Sr, Mg, Ti, Ca, Zr, Zn, Si and Fe.

[0040] In a more preferred embodiment of the present invention, the positive electrode active material may include LiCoO2, LiFePO4, LiFe 0.4 Mn 0.6 PO4, LiMn2O4, LiNi 0.5 Co 0.2 Mn 0.3 O2、LiNi 0.6 Co 0.2 Mn 0.2 O2、LiNi 0.7 Co 0.1 Mn 0.2 O2、LiNi 0.8 Co 0.1 Mn 0.1 O2、LiNi 0.8 Co 0.15 Al 0.05 O2、LiNi 0.9 Co 0.05 Mn 0.05 O2、LiNi 0.5 Co 0.2 Mn 0.2 Al 0.1 O2、LiNi0.5 Co 0.2 Al 0.3 One or more of O2.

[0041] Specifically, in some embodiments of the present invention, the positive electrode sheet further includes a positive electrode current collector, and the positive electrode material layer is disposed on a surface of the positive electrode current collector. The positive electrode current collector includes an electron-conducting metal material, preferably, the positive electrode current collector includes one or more of aluminum, nickel, tin, copper, and stainless steel.

[0042] Specifically, in some embodiments of the present invention, the positive electrode material layer further includes a positive electrode binder and a positive electrode conductive agent. The positive electrode active material, the positive electrode binder, and the positive electrode conductive agent are blended together to form the positive electrode material layer. The positive electrode binder and the positive electrode conductive agent may be the same as the negative electrode binder and the negative electrode conductive agent, respectively, and are not further described here.

[0043] Specifically, in some embodiments of the present invention, the lithium-ion battery further includes a separator, and the separator is located between the positive electrode and the negative electrode.

[0044] The separator is a conventional separator selected from one or more of a ceramic separator, a polymer separator, a non-woven fabric, and an inorganic-organic composite separator, for example, a single-layer polypropylene (PP) separator, a single-layer polyethylene (PE) separator, a double-layer PP / PE separator, a double-layer PP / PP separator, and a triple-layer PP / PE / PP separator.

[0045] The lithium-ion battery of the present invention uses a silicon-containing material in its negative electrode sheet and dopes the negative electrode current collector with Cr. In addition, 1,3,6-hexanetrinitrile is used as a first additive in the non-aqueous electrolyte, and a compound represented by structural formula 1 is used as a second additive. Furthermore, the relationship between the mass percentage a of the silicon element in the negative electrode material layer, the mass percentage b of the Cr element relative to the Cu element in the negative electrode current collector, the mass percentage c of the first additive in the non-aqueous electrolyte, and the mass percentage d of the second additive in the non-aqueous electrolyte is defined as satisfying 0.1≤10(d+c)×a / b≤100, 8≤a≤30, 20≤b≤800, 0.5≤c≤4, and 0.1≤d≤4. This achieves a synergistic effect among the various parameters, effectively improves the battery energy density, improves the negative electrode volume expansion caused by high silicon content, inhibits metal ion dissolution, and forms a stable interface film, thereby obtaining a lithium-ion battery with a stable silicon negative electrode structure, high energy density, and stable cycle performance. DETAILED DESCRIPTION

[0046] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0047] Example 1-1 The method for preparing a lithium-ion battery in this embodiment includes the following steps: (1) Preparation of non-aqueous electrolyte: Ethylene carbonate (EC), propylene carbonate (PC), ethyl propionate (EP), and propyl propionate (PP) were mixed in a volume ratio of EC:PC:EP:PP = 15:10:55:20. Lithium hexafluorophosphate (LiPF6) was then added to a molar concentration of 1.01 mol / L. The first additive, the second additive, and other additives were then added. Based on the total weight of the non-aqueous electrolyte as 100%, the mass percentage of the first additive (1,3,6-hexanetricarbonitrile) in the non-aqueous electrolyte was 2%, and the mass percentage of the second additive (Compound 1) in the non-aqueous electrolyte was 2%.

[0048] (2) Preparation of positive electrode: The cathode active material, lithium cobalt oxide (LiCoO2), conductive carbon black Super-P, and binder polyvinylidene fluoride (PVDF), are mixed in a mass ratio of 93:4:3 and then dispersed in N-methyl-2-pyrrolidone (NMP) to create a cathode slurry. The slurry is evenly coated on both sides of aluminum foil, dried, rolled, and vacuum-dried, and then ultrasonically welded to aluminum lead wires to form the cathode sheet.

[0049] (3) Preparation of negative electrode sheet: The negative electrode material (graphite and silicon oxide), conductive carbon black Super-P, binder styrene-butadiene rubber (SBR), and carboxymethyl cellulose (CMC) were mixed in a mass ratio of 94:1:2.5:2.5 and dispersed in deionized water to create a negative electrode slurry. The slurry was coated on both sides of a copper foil, dried, rolled, and vacuum-dried, and then ultrasonically welded with nickel lead wires to form the negative electrode sheet. The silicon content in the negative electrode material layer was 15% by weight, and the chromium content relative to the copper content in the copper foil was 60 ppm by weight.

[0050] (4) Preparation of battery cells: A separator is placed between the positive electrode sheet and the negative electrode sheet, and then the sandwich structure consisting of the positive electrode sheet, the negative electrode sheet and the separator are stacked, and then placed in an aluminum foil packaging bag and vacuum-baked at 75°C for 48 hours to obtain a battery cell ready for liquid injection.

[0051] (5) Injection and formation of battery cells: 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 24 hours.

[0052] Then, the conventional formation of the first charge was carried out according to the following steps: 0.05d constant current charging for 180min, 0.2d constant current charging to 3.95V, secondary vacuum sealing, and then further 0.2d constant current charging to 4.5V, after being placed at room temperature for 24h, and then discharged to 3.0V at 0.2d constant current.

[0053] Examples 1-2 to 1-26 and Comparative Examples 1-1 to 1-18 This embodiment and comparative example are used to compare and illustrate the lithium-ion battery disclosed in the present invention, including most of the operating steps in the above embodiment 1-1, and the differences are: the content of silicon in the negative electrode material layer, the mass content of Cr element relative to Cu element in the negative electrode current collector, the mass percentage of the first additive in the non-aqueous electrolyte, the mass percentage of the second additive in the non-aqueous electrolyte, and the content of the auxiliary additive, as shown in Tables 1 to 3.

[0054] The lithium-ion batteries prepared in each embodiment and comparative example were subjected to the following performance tests: 1. 60℃ storage test The formed lithium-ion battery was charged at room temperature at a constant current and constant voltage of 1C to 4.5V (LiCoO2 / silicon-carbon battery), and then charged at a constant voltage until the current dropped to 0.02C. The initial battery volume was measured. After storage at 60°C for 30 days, the battery was discharged at 1C to 3V, and the post-storage battery volume was measured.

[0055] Battery expansion rate (%) = (battery volume after storage - battery volume before storage) / battery volume before storage × 100%.

[0056] 2. Cycle performance test The lithium-ion battery was placed in a constant temperature environment of 45°C, charged at a constant current of 1C to 4.5V (LiCoO2 / silicon-carbon battery), then charged at a constant voltage until the current dropped to 0.02C, and then discharged at a constant current of 1C to 3.0 V. This cycle was repeated for 800 times. The discharge capacity of the first cycle (initial discharge capacity) and the discharge capacity of the 800th cycle were recorded. The volume of the battery before and after the cycle was recorded, and the capacity retention rate and gas expansion rate were calculated.

[0057] The capacity retention rate of the cycle is calculated as follows: Battery capacity retention rate (%) = discharge capacity at the 800th cycle / discharge capacity at the 1st cycle × 100%; Battery expansion rate (%) = (battery volume after cycling - battery volume before cycling) / battery volume before cycling × 100%.

[0058] Test results: As shown in Table 1, the parameters required for preparing lithium-ion batteries in Examples 1-1 to 1-19 and Comparative Examples 1-1 to 1-12 are shown; the differences between Examples 1-2 to 1-19 and Comparative Examples 1-1 to 1-12 and Example 1-1 are the relevant parameters in Table 1, and the remaining parameters and preparation steps are the same as those described in Example 1-1, with the specific differences being: the silicon element content a in the negative electrode material layer, the mass content b of Cr relative to Cu in the negative electrode current collector, the mass percentage c of the first additive in the non-aqueous electrolyte, the mass percentage d of the second additive in the non-aqueous electrolyte, and the value of the relationship 10(c+d)×a / b.

[0059] Table 1 also shows the test results of initial discharge capacity, 60°C storage 30D expansion rate, 45°C cycle 800 cycle expansion rate and 45°C cycle 800 cycle capacity retention rate of Examples 1-1 to 1-19 and Comparative Examples 1-1 to 1-12.

[0060] Table 1 Group Silicon content in the negative electrode material layer a / % Mass content of Cr relative to Cu in the negative electrode current collector (b / ppm) Mass percentage of the first additive in the non-aqueous electrolyte c / % Mass percentage of the second additive in the non-aqueous electrolyte d / % 10(c+d)×a / b Initial discharge capacity / mAh Storage at 60℃ for 30 days, inflation rate / % 45℃ cycle 800 cycles inflation rate / % Capacity retention rate after 800 cycles at 45℃ / % Example 1-1 15 60 2 2 10.00 4825 10.5 10.6 88.5 Example 1-2 20 100 3 2 10.00 4900 13.2 12.8 87.7 Examples 1-3 10 50 1 0.5 3.00 4750 8.7 15.3 87.3 Examples 1-4 25 300 1.5 1 2.08 4975 12.5 14.6 87.5 Examples 1-5 23 400 2.5 1.5 2.30 4945 12.8 13.1 87.9 Examples 1-6 13 500 1.8 1.3 0.81 4795 7.4 11.9 88.0 Examples 1-7 8 20 0.5 0.1 2.40 4720 15.6 19.5 84.2 Examples 1-8 9 30 0.8 0.3 3.30 4735 16.1 20 84.5 Examples 1-9 27 700 3.5 3 2.51 5005 23.7 25.8 85.3 Examples 1-10 30 800 4 4 3.00 5050 25.5 28.1 85.1 Examples 1-11 8 600 0.6 0.2 0.11 4715 14.3 16.5 84.0 Examples 1-12 25 300 4 4 6.67 4961 23 26.1 84.5 Examples 1-13 15 50 4 4 24.00 4812 13.5 16.1 84.6 Examples 1-14 25 20 4 4 100.00 4958 24.3 27.5 84.1 Examples 1-15 16 25 3 2 32.00 4840 20.8 26.3 85.1 Examples 1-16 24 35 0.7 0.1 5.49 4960 25 28.8 84.2 Examples 1-17 28 450 4 3 4.36 5020 24.8 28.2 84.1 Examples 1-18 22 55 3 4 28.00 4930 24.5 28.5 85.4 Examples 1-19 25 25 4 3 70.00 4963 25.3 29.3 84.4 Comparative Example 1-1 15 60 / 2 / 4818 33.1 33.8 80.1 Comparative Example 1-2 15 60 2 / / 4835 36.1 38.0 79.5 Comparative Examples 1-3 7 20 1 1 7.00 4705 26.7 29.3 82.5 Comparative Examples 1-4 31 800 3 2 1.94 5065 30.5 32.3 81.9 Comparative Examples 1-5 20 18 0.5 0.3 8.89 4913 24.8 27.7 82.3 Comparative Examples 1-6 26 810 3.5 3 2.09 4990 24.3 27.1 82.7 Comparative Examples 1-7 28 35 0.4 0.2 4.80 5036 25.9 28.8 82.6 Comparative Examples 1-8 25 40 4.2 2.5 41.88 4975 24.7 27.3 82.9 Comparative Examples 1-9 29 45 4 0.05 26.10 5035 25.4 27.0 83.3 Comparative Examples 1-10 8 700 0.8 4.1 0.56 4732 22.3 25.6 82.2 Comparative Examples 1-11 30 23 4 4 104.35 5048 31.2 33.5 81.7 Comparative Examples 1-12 8 700 0.6 0.1 0.08 4718 29.8 30.4 81.3

[0061] Note: “ / ” in the table means that there is no such item.

[0062] The test results of Examples 1-1 to 1-19 and Comparative Examples 1-1 to 1-12 show that the lithium ion battery provided by the present invention uses a silicon-containing material as the negative electrode, limits the content of silicon in the negative electrode material layer, adds Cr to the negative electrode current collector, uses 1,3,6-hexanetrinitrile as the first additive in the non-aqueous electrolyte, and uses a compound of a specific structure as the second additive; at the same time, the relationship between the mass percentage a of the silicon element in the negative electrode material layer, the mass content b of the Cr element relative to the Cu element in the negative electrode current collector, the mass percentage c of the first additive in the non-aqueous electrolyte, and the mass percentage d of the second additive in the non-aqueous electrolyte is also defined to satisfy 0.1≤10(d+c)×a / b≤100, 8≤a≤30, 20≤b≤800, 0.5≤c≤4, and 0.1≤d≤4. A lithium ion battery with a stable silicon negative electrode structure, high energy density, and good cycle performance can be obtained.

[0063] It can be seen from the test results of Examples 1-1 to 1-19 and Comparative Examples 1-1 to 1-12 that when any one of the mass percentage a of the silicon element in the negative electrode material layer, the mass content b of the Cr element relative to the Cu element in the negative electrode current collector, the mass percentage c of the first additive in the non-aqueous electrolyte, and the mass percentage d of the second additive in the non-aqueous electrolyte does not satisfy the range or the value of the relationship 10(d+c)×a / b is too large or too small, the parameters cannot achieve a synergistic effect, the negative electrode volume expansion caused by the high silicon content in the silicon-containing negative electrode cannot be well improved, and a dense SEI film cannot be formed on the negative electrode to protect the negative electrode. Therefore, a lithium-ion battery with a stable silicon negative electrode structure, high energy density, and good cycle performance cannot be obtained.

[0064] When the mass percentage a of the silicon element in the negative electrode material layer, the mass content b of the Cr element relative to the Cu element in the negative electrode current collector, the mass percentage c of the first additive in the non-aqueous electrolyte, and the mass percentage d of the second additive in the non-aqueous electrolyte further satisfy 0.8≤10(d+c)×a / b≤24, and 10≤a≤25, 50≤b≤500, 1≤c≤3, and 0.5≤d≤2, the prepared lithium-ion battery can significantly improve the energy density while better controlling the volume expansion of silicon. The first additive and the second additive can also better synergize with each other on the negative electrode of the battery to protect the negative electrode of the battery, making the performance of the lithium-ion battery more stable.

[0065] Table 2 shows the test results of the initial discharge capacity, 60°C storage 30D expansion rate, 45°C cycle 800 cycle expansion rate, and 45°C cycle 800 cycle capacity retention rate of the lithium ion batteries prepared in Example 1-1 and Examples 1-20 to 1-23. The difference between Examples 1-20 to 1-23 and Example 1-1 lies in the type of the second additive shown in Table 2. The remaining parameters and preparation steps are the same as those described in Example 1-1.

[0066] Table 2

[0067] From the test results in Table 2, it can be seen that when the mass percentage a of the silicon element in the negative electrode material layer, the mass content b of the Cr element relative to the Cu element in the negative electrode current collector, the mass percentage c of the first additive in the non-aqueous electrolyte, and the mass percentage d of the second additive in the non-aqueous electrolyte and the relationship 10(d+c)×a / b meet the relevant requirements, adding any one of the compounds containing both sulfate groups and carbonate groups as the second additive can obtain a lithium-ion battery with a stable silicon negative electrode structure, high energy density, and good cycle performance, indicating that the battery system of the present invention is universal for different types of second additives.

[0068] Table 3 shows the test results of the initial discharge capacity, 60°C storage 30D expansion rate, 45°C cycle 800 cycle expansion rate, and 45°C cycle 800 cycle capacity retention rate of the lithium ion batteries prepared in Example 1-1, Examples 1-24 to 1-26, and Comparative Examples 1-13 to 1-18. The differences between Examples 1-24 to 1-26 and Comparative Examples 1-13 to 1-18 and Example 1-1 are the mass percentage of the first additive in the non-aqueous electrolyte, the mass percentage of the second additive in the non-aqueous electrolyte, and the type and content of the auxiliary additives shown in Table 3. The remaining parameters and preparation steps are the same as those described in Example 1-1.

[0069] Table 3

[0070] Note: “ / ” in the table means that there is no such item.

[0071] The test results in Table 3 show that the lithium-ion battery of the present invention, when used in combination with the auxiliary additive, still has a significant effect on improving the high-temperature storage performance and high-temperature cycling performance of the lithium-ion battery. The test results of Examples 1-1, 1-24 to 1-26, and Comparative Examples 1-13 to 1-18 show that when different amounts of the auxiliary additive are used to replace the second additive, the auxiliary additive and the other components do not form a good synergistic effect, resulting in poor improvement in the energy density and cycling performance of the lithium-ion battery.

[0072] As shown in Table 4, the various parameters required for preparing lithium-ion batteries in Examples 2-1 to 2-19 and Comparative Examples 2-1 to 2-12 are shown; the differences between Examples 2-1 to 2-19 and Comparative Examples 2-1 to 2-12 and Example 1-1 are the relevant parameters and the type of the second additive in Table 4, and the remaining parameters and preparation steps are the same as those described in Example 1-1. The specific differences are: in Examples 2-1 to 2-19 and Comparative Examples 2-1 to 2-12, the second additive is compound 6, the silicon element content a in the negative electrode material layer, the mass content b of Cr relative to Cu in the negative electrode current collector, the mass percentage c of the first additive in the non-aqueous electrolyte, the mass percentage d of the second additive in the non-aqueous electrolyte, and the value of the relationship 10(c+d)×a / b are shown in Table 4.

[0073] Table 4 also shows the test results of initial discharge capacity, 60°C storage 30D expansion rate, 45°C cycle 800 cycle expansion rate and 45°C cycle 800 cycle capacity retention rate for Examples 2-1 to 2-19 and Comparative Examples 2-1 to 2-12.

[0074] Table 4 Group Silicon content in the negative electrode material layer a / % Mass content of Cr relative to Cu in the negative electrode current collector (b / ppm) Mass percentage of the first additive in the non-aqueous electrolyte c / % Mass percentage of the second additive in the non-aqueous electrolyte d / % 10(c+d)×a / b Initial discharge capacity / mAh Storage at 60℃ for 30 days, inflation rate / % 45℃ cycle 800 cycles expansion rate / % Capacity retention rate after 800 cycles at 45℃ / % Example 2-1 15 60 2 2 10.00 4830 9.5 11.7 88.1 Example 2-2 20 100 3 2 10.00 4907 11.7 14 87.2 Example 2-3 10 50 1 0.5 3.00 4758 6.5 16.6 86.7 Examples 2-4 25 300 1.5 1 2.08 4982 13.7 17 87 Examples 2-5 23 400 2.5 1.5 2.30 4951 14.1 14.6 87.5 Examples 2-6 13 500 1.8 1.3 0.81 4800 6.5 13.5 87.7 Examples 2-7 8 20 0.5 0.1 2.40 4726 16.8 21.2 83.8 Examples 2-8 9 30 0.8 0.3 3.30 4742 17.9 21.8 84 Examples 2-9 27 700 3.5 3 2.51 5010 25.1 27.7 84.7 Example 2-10 30 800 4 4 3.00 5058 27 29.9 84.6 Example 2-11 8 600 0.6 0.2 0.11 4724 16.4 18.2 83.6 Example 2-12 25 300 4 4 6.67 4971 25.3 27.7 84 Example 2-13 15 50 4 4 24.00 4821 16.1 27.6 84 Examples 2-14 25 20 4 4 100.00 4966 26.2 28.9 83.5 Example 2-15 16 25 3 2 32.00 4847 22.4 27.5 84.6 Example 2-16 24 35 0.7 0.1 5.49 4966 26.7 29.9 83.8 Example 2-17 28 450 4 3 4.36 5025 26.1 29.4 83.7 Example 2-18 22 55 3 4 28.00 4936 25.8 29.8 84.9 Example 2-19 25 25 4 3 70.00 4970 27.4 30.7 83.8 Comparative Example 2-1 15 60 / 2 / 4826 34.9 35.4 79.7 Comparative Example 2-2 15 60 2 / / 4835 36.1 38.0 79.5 Comparative Examples 2-3 7 20 1 1 7.00 4715 28 31.1 82 Comparative Examples 2-4 31 800 3 2 1.94 5074 32 34.2 81.3 Comparative Examples 2-5 20 18 0.5 0.3 8.89 4921 26.5 29.5 81.7 Comparative Examples 2-6 26 810 3.5 3 2.09 4997 26.4 28.8 82.2 Comparative Examples 2-7 28 35 0.4 0.2 4.80 5042 27.3 30.4 82.3 Comparative Examples 2-8 25 40 4.2 2.5 41.88 4980 26.4 28.8 82.5 Comparative Examples 2-9 29 45 4 0.05 26.10 5041 26.9 28.4 82.8 Comparative Examples 2-10 8 700 0.8 4.1 0.56 4739 23.6 26.9 81.6 Comparative Examples 2-11 30 23 4 4 104.35 5056 33.2 34.7 81.1 Comparative Examples 2-12 8 700 0.6 0.1 0.08 4727 31.1 31.5 80.8

[0075] Note: “ / ” in the table means that there is no such item.

[0076] The test results of Examples 2-1 to 2-19 and Comparative Examples 2-1 to 2-12 show that the lithium ion battery provided by the present invention uses a silicon-containing material as the negative electrode, limits the content of silicon in the negative electrode material layer, adds Cr to the negative electrode current collector, uses 1,3,6-hexanetrinitrile as the first additive in the non-aqueous electrolyte, and uses a tricyclic compound containing only sulfate groups as the second additive; at the same time, the mass percentage a of the silicon element in the negative electrode material layer, the mass content b of the Cr element relative to the Cu element in the negative electrode current collector, the mass percentage c of the first additive in the non-aqueous electrolyte, and the mass percentage d of the second additive in the non-aqueous electrolyte are also defined. When the relationship satisfies 0.1≤10(d+c)×a / b≤100, 8≤a≤30, 20≤b≤800, 0.5≤c≤4, and 0.1≤d≤4, a lithium ion battery with a stable silicon negative electrode structure, high energy density, and good cycle performance can be obtained.

[0077] It can be seen from the test results of Example 2-1 and Comparative Examples 2-1 to Comparative Examples 2-12 that when any one of the mass percentage a of the silicon element in the negative electrode material layer, the mass content b of the Cr element relative to the Cu element in the negative electrode current collector, the mass percentage c of the first additive in the non-aqueous electrolyte, and the mass percentage d of the second additive in the non-aqueous electrolyte does not meet the range or the value of the relationship 10(d+c)×a / b is too large or too small, the parameters cannot achieve a synergistic effect, the negative electrode volume expansion caused by the high silicon content in the silicon-containing negative electrode cannot be well improved, and a dense SEI film cannot be formed on the negative electrode to protect the negative electrode. Therefore, a lithium-ion battery with a stable silicon negative electrode structure, high energy density, and good cycle performance cannot be obtained.

[0078] When the mass percentage a of the silicon element in the negative electrode material layer, the mass content b of the Cr element relative to the Cu element in the negative electrode current collector, the mass percentage c of the first additive in the non-aqueous electrolyte, and the mass percentage d of the second additive in the non-aqueous electrolyte further satisfy 0.8≤10(d+c)×a / b≤24, and 10≤a≤25, 50≤b≤500, 1≤c≤3, and 0.5≤d≤2, the prepared lithium-ion battery can significantly improve the energy density while better controlling the volume expansion of silicon. The first additive and the second additive can also better synergize with each other on the negative electrode of the battery to protect the negative electrode of the battery, making the performance of the lithium-ion battery more stable.

[0079] Table 5 shows the test results of the initial discharge capacity, 60°C storage 30D expansion rate, 45°C cycle 800 cycle expansion rate, and 45°C cycle 800 cycle capacity retention rate of the lithium ion batteries prepared in Example 2-1, Example 2-20, and Comparative Example 2-13. The difference between Example 2-20 and Comparative Example 2-13 and Example 2-1 lies in the type of the second additive shown in Table 5. The remaining parameters and preparation steps are the same as those described in Example 2-1.

[0080] Table 5

[0081] From the test results in Table 5, it can be seen that when the mass percentage a of the silicon element in the negative electrode material layer, the mass content b of the Cr element relative to the Cu element in the negative electrode current collector, the mass percentage c of the first additive in the non-aqueous electrolyte, and the mass percentage d of the second additive in the non-aqueous electrolyte and the relationship 10(d+c)×a / b meet the relevant requirements, adding any tricyclic or bicyclic compound containing only sulfate groups as the second additive can obtain a lithium-ion battery with a stable silicon negative electrode structure, high energy density, and good cycle performance, indicating that the battery system of the present invention is universal for different types of second additives.

[0082] It can be seen from the test results of Example 2-1, Example 2-20 and Comparative Example 2-13 that when DTD is used to replace the second additive, the cycle performance of Comparative Example 2-13 is significantly lower than that of Example 2-1 and Example 2-20, and the cycle inflation rate and storage inflation rate are both increased, indicating that the second additive of the present application has a better effect on improving battery performance than the single-ring structure of vinyl sulfate. This is because the polycyclic structures of the first additive of the present application are each opened to participate in the formation of the interface film on the electrode surface, and the formed interface film components are more stable and dense, which has the effect of improving the strength of the interface film structure, and thus is beneficial to improving its high-temperature stability. However, the single-ring structure of DTD cannot form a good synergistic effect with other components, and has a poor effect on improving the structural stability, energy density and cycle performance of the silicon negative electrode of the lithium-ion battery.

[0083] Table 6 shows the test results of the initial discharge capacity, 60°C storage 30D expansion rate, 45°C cycle 800 cycle expansion rate, and 45°C cycle 800 cycle capacity retention rate of the lithium ion batteries prepared in Example 2-1, Examples 2-21 to 2-23, and Comparative Examples 2-14 to 2-19. The differences between Examples 2-21 to 2-23 and Comparative Examples 2-14 to 2-19 and Example 2-1 are the mass percentage of the first additive in the non-aqueous electrolyte, the mass percentage of the second additive in the non-aqueous electrolyte, and the auxiliary additives and their contents shown in Table 6. The remaining parameters and preparation steps are the same as those described in Example 2-1.

[0084] Table 6

[0085] Note: “ / ” in the table means that there is no such item.

[0086] The test results in Table 6 show that the lithium-ion battery of the present invention, when used in combination with the auxiliary additive, still has a significant effect on improving the high-temperature storage performance and high-temperature cycling performance of the lithium-ion battery. The test results of Examples 2-1, 2-21 to 2-23, and Comparative Examples 2-14 to 2-19 show that when different amounts of the auxiliary additive are used to replace the second additive, the auxiliary additive and the other components do not form a good synergistic effect, resulting in poor improvement in the energy density and cycling performance of the lithium-ion battery.

[0087] The above-described embodiments merely illustrate several implementations of the present invention, and while their 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 skilled in the art would be able to make numerous variations 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, a separator and a non-aqueous electrolyte; the negative electrode sheet comprises a negative electrode current collector and a negative electrode material layer provided on the negative electrode current collector; the negative electrode current collector is a copper foil or a composite copper foil, and the negative electrode material layer comprises a silicon-containing material; The non-aqueous electrolyte includes a non-aqueous organic solvent, a lithium salt, a first additive and a second additive; The first additive is 1,3,6-hexanetrinitrile; The second additive includes a compound shown in structural formula 1: ； Wherein, X is selected from or , R1, R2 are each independently selected from H, ,or , R1 and R2 are not simultaneously selected from H, and X, R1 and R2 contain at least one sulfur atom; The lithium ion battery satisfies the following conditions: 1≤10(d+c)×a / b≤100, and 8≤a≤30, 20≤b≤800, 0.5≤c≤4, 0.1≤d≤4; Wherein, a is the mass percentage of silicon element in the negative electrode material layer, and the unit is %; b is the mass content of Cr element relative to Cu element in the negative electrode current collector, in ppm; c is the mass percentage of the first additive in the non-aqueous electrolyte, in units of %; d is the mass percentage of the second additive in the non-aqueous electrolyte, in %.

2. The lithium-ion battery according to claim 1, wherein The lithium ion battery satisfies: 0.8≤10(d+c)×a / b≤24.

3. The lithium-ion battery according to claim 1, wherein The mass percentage a% of silicon element in the negative electrode material layer is 10% to 25%.

4. The lithium-ion battery according to claim 1, wherein The mass content (b ppm) of the Cr element relative to the Cu element in the negative electrode current collector is 50 ppm to 500 ppm.

5. The lithium-ion battery according to claim 1, wherein The mass percentage c% of the first additive in the non-aqueous electrolyte is 1% to 3%.

6. The lithium-ion battery according to claim 1, wherein The mass percentage d% of the second additive in the non-aqueous electrolyte is 0.5%-2%.

7. The lithium-ion battery according to claim 1, wherein The compound represented by the structural formula 1 includes one or more of the following compounds: 。 8. The lithium-ion battery according to claim 1, wherein The non-aqueous organic solvent includes one or more of cyclic carbonates, linear carbonates, carboxylates and ethers; and / or, The cyclic carbonate includes one or more of vinylene carbonate, propylene carbonate, ethylene carbonate and butylene carbonate; and / or, The linear carbonate comprises one or more of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate and methyl propyl carbonate; and / or, The carboxylic acid ester includes one or more of methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, methyl butyrate, methyl isobutyrate, methyl trimethylacetate and ethyl trimethylacetate; and / or, The ethers include one or more of ethylene glycol dimethyl ether, 1,3-dioxolane and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether.

9. The lithium-ion battery according to claim 1, wherein The lithium salts include lithium hexafluorophosphate, lithium bis(fluorosulfonyl imide), lithium bis(trifluoromethanesulfonyl imide), LiPO2F2, LiBF4, LiBOB, LiSbF6, LiAsF6, LiCF3SO3, LiDFOB, LiDFOP, LiC(SO2CF3)3, LiN(SO2C2F5)2, LiCl, LiBr, LiI, LiClO4, LiB 10 Cl 10 , LiAlCl4, lithium chloroborane, and lithium tetraphenylborate.

10. The lithium-ion battery according to claim 1, wherein The non-aqueous electrolyte further includes an auxiliary additive, wherein the auxiliary additive includes at least one of a cyclic sulfate compound, a sultone compound, a cyclic carbonate compound, a phosphate compound, and a borate compound; and / or, Based on the total mass of the non-aqueous electrolyte as 100%, the content of the auxiliary additive is 0.01% to 10%; and / or, The cyclic sulfate compound includes at least one of 4-methylvinyl sulfate, vinyl sulfate, and propylene sulfate; and / or, The sultone compound includes at least one of 1,3-propane sultone, 1,4-butane sultone, and propenyl-1,3-sultone; and / or, The cyclic carbonate compound includes at least one of vinylene carbonate, vinyl ethylene carbonate, methylene carbonate, fluoroethylene carbonate, trifluoromethylethylene carbonate, bisfluoroethylene carbonate and the compound represented by the following structural formula 2: ； In the structural formula 2 shown, R 21 、R 22 、R 23 、R 24 、R 25 、R 26 are each independently selected from a hydrogen atom, a halogen atom, a C1-C5 group; and / or, The phosphate compound includes at least one of the compounds shown in the following structural formula 3: ； In the structural formula 3, 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 / or, The borate ester compound includes at least one of tris(trimethylsilyl)borate and tris(triethylsilyl)borate.

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