A lithium-ion battery

Abstract

This invention belongs to the field of new energy battery technology and relates to a lithium-ion battery. The lithium-ion battery includes a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte. The negative electrode includes a negative current collector and a negative electrode material layer disposed on the negative current collector. The negative current collector is copper foil or composite copper foil, and the negative electrode material layer includes 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-hexanetrionitrile; the second additive includes a compound shown in structural formula 1. The lithium-ion battery satisfies 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. The lithium-ion battery provided by this invention has a stable silicon negative electrode structure, high energy density, and stable cycle performance.

Description

Technical Field

[0001] This invention belongs to the field of new energy battery technology, and relates to a lithium-ion battery, particularly a lithium-ion battery with a stable silicon anode structure, high energy density, and stable cycle performance. Background Technology

[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 is an urgent need to further improve battery energy density. The energy density of a lithium battery is primarily determined by the specific capacity of the positive electrode, the specific capacity of the negative electrode, 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 improve the energy density of lithium batteries, it is necessary to develop anode materials with higher specific capacities. Silicon anode materials have a different lithium storage mechanism than graphite anode materials, and their theoretical specific capacity is as high as 4200 mAh / g, about 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 more than 8%, while simultaneously reducing the cost per kilowatt-hour of battery by at least 3%.

[0003] When silicon is fully lithium-ionized, its volume expands by over 300%, a massive change that leads to a series of problems. First, the volume expansion results in high internal stress, easily compressing the electrodes and causing cracks or even pulverization of the silicon anode material. Second, the volume expansion makes it easy for the electrode material to lose contact with the current collector, causing the active material to detach from the electrode and resulting in rapid capacity decay. Finally, the volume expansion easily forms an unstable solid electrolyte interphase (SEI) film. Due to the change in silicon volume, the SEI breaks down, and the newly exposed silicon produces a new SEI film, continuously consuming lithium ions in the electrolyte, leading to irreversible capacity loss and low initial charging efficiency. Furthermore, the SEI film thickness increases with electrochemical cycling; an excessively thick SEI layer hinders electron transfer and lithium-ion diffusion, increasing impedance. Therefore, developing a lithium-ion battery that effectively suppresses the volume expansion of the silicon anode and possesses stable cycle performance is essential. Summary of the Invention

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

[0005] To achieve the above objectives, the present invention adopts the following technical solution.

[0006] This invention provides a lithium-ion battery, comprising a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte; the negative electrode includes a negative electrode current collector and a negative electrode material layer disposed 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 includes a silicon-containing material;

[0007] The non-aqueous electrolyte includes a non-aqueous organic solvent, a lithium salt, a first additive, and a second additive.

[0008] The first additive is 1,3,6-hexanetrionitrile;

[0009] The second additive includes the compound shown in structural formula 1:

[0010] ;

[0011] Where X is selected from or R1 and R2 are each independently selected from H, ,or R1 and R2 are not both selected from H, and X, R1 and R2 contain at least one sulfur atom;

[0012] The lithium-ion battery meets the following conditions:

[0013] 0.1≤10(d+c)×a / b≤100, and 8≤a≤30, 20≤b≤800, 0.5≤c≤4, 0.1≤d≤4;

[0014] Where 'a' represents the mass percentage of silicon in the negative electrode material layer, expressed in % %.

[0015] b represents the mass content of Cr relative to Cu in the negative electrode current collector, in ppm.

[0016] c represents the mass percentage of the first additive in the non-aqueous electrolyte, expressed in % .

[0017] d represents the mass percentage of the second additive in the non-aqueous electrolyte, in units of .

[0018] The lithium-ion battery provided by this invention uses a silicon-containing material as the negative electrode, and limits the silicon content in the negative electrode material layer. Cr is added to the negative electrode current collector, and 1,3,6-hexanetrionitrile is used as the first additive in the non-aqueous electrolyte, while the compound shown in structural formula 1 is used as the second additive. Through extensive research, the inventors discovered that when the relationship between the mass percentage of silicon (a) in the negative electrode material layer, the mass percentage of Cr relative to Cu in the negative electrode current collector (b), the mass percentage of the first additive in the non-aqueous electrolyte (c), and the mass percentage of the second additive in the non-aqueous electrolyte (d) 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, a lithium-ion battery with a stable silicon negative electrode structure, high energy density, and good cycle performance can be obtained. The reasons for this are speculated to be as follows: the use of silicon-containing anode materials in the anode material layer increases the battery's energy density; simultaneously, the Cr element in the anode current collector mitigates the volume expansion caused by the high silicon content in the silicon-containing anode, stabilizing the anode structure; the addition of the first additive effectively complexes Cr and other metal ions, inhibiting metal ion dissolution and protecting the stability of the battery's positive and negative electrode structures, thereby improving the battery's cycle performance; furthermore, the second additive, as a better anode film-forming additive, forms a dense SEI film on the anode, reducing the exacerbating effect of the first additive on the anode interface side reactions, providing better protection for the anode, and also contributing to improved battery performance. In summary, this invention achieves a synergistic effect among various parameters by limiting the silicon content in the anode material layer, the Cr content relative to Cu in the anode 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 certain ranges, thus obtaining a lithium-ion battery with a stable silicon anode structure, high energy density, and good cycle performance. Preferably, the lithium-ion battery satisfies 0.8≤10(d+c)×a / b≤24.

[0019] Using silicon-containing anodes is one of the main methods to improve battery energy density. The silicon content in the anode has a significant impact on battery performance. When the silicon content (a%) in the anode material layer is too low, it has little effect on improving battery energy density and cannot effectively enhance it. When the silicon content (a%) in the anode material layer is too high, the volume expansion of silicon is significant, which can lead to the cracking of the battery anode material. This can cause it to lose contact with the current collector, resulting in the active material detaching from the electrode and causing rapid capacity decay. An unstable solid electrolyte interphase (SEI) film is formed. Due to the change in silicon volume, the SEI film will crack accordingly. Newly exposed silicon will generate a new SEI film, continuously consuming lithium ions in the electrolyte, leading to irreversible capacity loss and low initial charging efficiency. Furthermore, the SEI thickness will continuously increase with electrochemical cycling. An excessively thick SEI film hinders electron transfer and Li-ion exchange. + 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 any combination of these values; preferably, the silicon content (a%) in the negative electrode material layer is 10 ≤ a ≤ 25%. Within this range, a significant increase in energy density can be ensured, while the volume expansion of silicon can be well controlled through the design of other battery structures, thereby significantly improving the battery's electrochemical performance.

[0020] Specifically, in some embodiments of the present invention, the problem of significant volume expansion and contraction of high-silicon-content silicon-containing anodes during charge and discharge, leading to structural damage, exacerbating solid / liquid interface reactions and changes in electrode microstructure, and ultimately degrading battery performance, is overcome by doping an appropriate amount of chromium into the copper foil of the anode current collector. Chromium is a common trace element that has a significant impact on 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 high silicon content in silicon-containing anodes. Furthermore, chromium can improve the oxidation resistance of copper foil and reduce its reaction with external environmental factors such as oxygen and humidity. However, when the mass content (b) of Cr relative to Cu in the anode current collector is excessive, the excess Cr may dissolve during charge and discharge, catalyzing side reactions between the electrolyte and the electrode at the anode interface, thus degrading battery performance. Simultaneously, excessive chromium may cause copper to become brittle, reducing its ductility and mechanical properties, and affecting electrode production. When the mass content (b) of Cr relative to Cu in the negative electrode current collector is too low, the copper foil has poor hardness and wear resistance, making it prone to breakage and damaging the negative electrode structure. Therefore, it is necessary to precisely control the chromium content in the copper foil to ensure that the copper foil's performance reaches its optimal state. Specifically, the mass content (b) of Cr relative to Cu 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 any combination of these values; preferably, the mass content (b) of Cr relative to Cu in the negative electrode current collector is 50ppm to 500ppm. Within this range, the addition of Cr can significantly improve the hardness and wear resistance of copper foil, stabilize the negative electrode structure, and mitigate the volume expansion of the negative electrode caused by high silicon content in silicon-containing negative electrodes. Simultaneously, within this range, the probability of side reactions in the catalytic electrolyte and electrode sheets can be significantly reduced, improving battery performance. The Cr content in the negative electrode current collector of this invention can be obtained by inductively coupled plasma (ICP) testing, where the mass content b of Cr relative to Cu in the negative electrode current collector refers to the mass of Cr divided by the mass of Cu.

[0021] Specifically, in some embodiments of the present invention, since the Cr doped in the negative electrode current collector may dissolve during charging and discharging, it catalyzes side reactions between the electrolyte and the electrode at the negative electrode interface, degrading battery performance. Therefore, by adding a first additive, 1,3,6-hexanetrionitrile, to the non-aqueous electrolyte, Cr, Co, and other metal ions can be effectively complexed, inhibiting metal ion dissolution, protecting the stability of the positive and negative electrode structures, and thus improving the battery's cycle performance. 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, affecting the electrolyte film formation at the negative electrode, leading to aggravated side reactions at the negative electrode interface and degrading battery performance. When the mass percentage (c%) of the first additive in the non-aqueous electrolyte is too low, the complexation effect on metal ions is limited, affecting the integrity of the electrolyte film formation at the negative electrode, or the film thickness is insufficient, thus degrading the battery's 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 any combination 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, while not damaging the electrolyte solvation structure or the battery negative electrode interface, thereby ensuring good battery cycle performance.

[0022] Specifically, in some embodiments of the present invention, the first additive affects the solvation structure of the electrolyte, thus affecting the film formation of the electrolyte at the negative electrode, leading to intensified side reactions at the negative electrode interface and deterioration of battery performance. The second additive, however, is a better negative electrode film-forming additive, preferentially forming a dense SEI film at the negative electrode, protecting the negative electrode interface from damage caused by the addition of the first additive, reducing interfacial side reactions, and improving battery performance. However, the addition of the second additive increases the battery's internal resistance, deteriorating its low-temperature and fast-charging performance; therefore, the amount of the second additive added needs to be strictly controlled. Specifically, the mass percentage 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 any combination of these values; preferably, the mass percentage d% of the second additive in the non-aqueous electrolyte is 0.5% to 2%. Within this range, a dense SEI film can be effectively formed on the negative electrode, reducing interfacial side reactions and improving battery cycle performance, while not causing a significant increase in battery internal resistance, ensuring that the battery has good low-temperature and fast-charging performance.

[0023] Specifically, in some embodiments of the present invention, in the compound represented by structural formula 1, X is selected from... or R1 and R2 are each independently selected from H, ,or R1 and R2 are not both selected from H, and at least one sulfur atom is contained in X, R1 and R2, and X, R1 and R2 do not contain sulfur atoms at the same time.

[0024] As an example, the second additive is selected from one or more of the following compounds:

[0025] .

[0026] The first additive includes both sulfur-containing cyclic structures and carbonate-containing cyclic structures. The interfacial film component formed by the combination of carbonate cyclic structures and sulfur-containing cyclic structures is more stable and dense.

[0027] In some embodiments of the present invention, in the compound represented by structural formula 1, X is selected from... R1 and R2 are each independently selected from H or R1 and R2 are not both selected from H.

[0028] As an example, the second additive is selected from one or more of the following compounds:

[0029] .

[0030] The second additive has a polycyclic structure. Compared with the monocyclic structure of vinyl sulfate, the polycyclic structure allows each ring to open and participate in the formation of the interface film on the electrode surface. The resulting interface film is more stable and dense, which improves the strength of the interface film structure and thus helps to enhance its high-temperature stability.

[0031] Specifically, in some embodiments of the present invention, the non-aqueous organic solvent includes at least one of cyclic carbonate solvents, linear carbonate solvents, carboxylic acid ester solvents, and ether solvents.

[0032] In some preferred embodiments, the cyclic carbonate solvent includes at least one of ethylene carbonate, propylene carbonate, fluoroethylene carbonate, vinylene carbonate, and butene carbonate.

[0033] In some preferred embodiments, the linear carbonate solvent includes at least one of dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, and methyl propyl carbonate.

[0034] In some preferred embodiments, the carboxylic acid ester 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.

[0035] 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.

[0036] 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, and LiB₂. 10 Cl 10 At least one of LiAlCl4, lithium chloroborane, and lithium tetraphenylborate.

[0037] In specific embodiments, the total molar content of the lithium salt is 0.5 mol / L to 3.5 mol / L. In preferred embodiments, 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, etc. 1.7 mol / L, 1.8 mol / L, 1.9 mol / L, 2.0 mol / L, 2.1 mol / L, 2.2 mol / L, 2.3 mol / L, 2.4 mol / L, 2.5 mol / L, 2.6 mol / L, 2.7 mol / L, 2.8 mol / L, 2.9 mol / L, 3.0 mol / L, 3.1 mol / L, 3.2 mol / L, 3.3 mol / L, 3.4 mol / L, 3.5 mol / L, or any combination of these values.

[0038] 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 0.1 mol / L to 2 mol / L. In a preferred embodiment, the concentration of the lithium salt in the non-aqueous electrolyte is 0.5 mol / L to 1.5 mol / L. Specifically, the concentration of the lithium salt in the non-aqueous electrolyte can be 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1.0 mol / L, 1.2 mol / L, 1.3 mol / L, 1.4 mol / L, 1.5 mol / L, or any combination of these values.

[0039] In some embodiments of the present invention, the non-aqueous electrolyte further includes auxiliary additives, which include at least one of cyclic sulfate compounds, sulfonyl lactone compounds, cyclic carbonate compounds, phosphate compounds, and borate compounds.

[0040] In some preferred embodiments, the cyclic sulfate compound includes at least one of 4-methyl vinyl sulfate, vinyl sulfate, and propylene sulfate.

[0041] In some preferred embodiments, the sulfonyl lactone compound includes at least one of 1,3-propanesulfonyl lactone, 1,4-butanesulfonyl lactone, and propenyl-1,3-sulfonyl lactone.

[0042] In some preferred embodiments, the cyclic carbonate compound includes at least one of vinylene carbonate, ethylene ethylene carbonate, methylene carbonate, fluoroethylene carbonate, trifluoromethyl ethylene carbonate, difluoroethylene carbonate, and a compound represented by structural formula 2 below:

[0043] ;

[0044] In the structural formula 2 shown, R 21 R 22 R 23 R 24 R 25 R 26 Each is independently selected from one of the following: hydrogen atom, halogen atom, or C1-C5 group.

[0045] In some preferred embodiments, the compound shown in structural formula 2 includes at least one of the compounds shown in compounds 2-1 to 2-6 below:

[0046] ;

[0047] In some preferred embodiments, the phosphate ester compound includes at least one of the compounds represented by structural formula 3:

[0048] ;

[0049] In structural formula 3, R 31 R 32 R 33 Each independent group is selected from C1-C5 saturated hydrocarbon groups, unsaturated hydrocarbon groups, halohydrocarbon groups, and -Si(C m H 2m+1 )3, where m is a natural number from 1 to 3; more preferably, the compound represented by structural formula 3 includes at least one of tris(trimethylsilane) phosphate, tris(triethylsilane) phosphate, triargylpropyl phosphate, diargylpropylmethyl phosphate, diargylpropylethyl phosphate, diargylpropylpropyl phosphate, diargylpropyltrifluoromethyl phosphate, diargylpropyl-2,2,2-trifluoroethyl phosphate, diargylpropyl-3,3,3-trifluoropropyl phosphate, diargylpropylhexafluoroisopropyl 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.

[0050] In some preferred embodiments, the borate ester compound includes at least one of tris(trimethylsilane)borate and tris(triethylsilane)borate.

[0051] In some embodiments of the present invention, the content of the auxiliary additive is 0.01% to 10% based on the total mass of the non-aqueous electrolyte as 100%. Preferably, the content is 0.1% to 5%; more preferably, the content is 0.1% to 2%. Specifically, the content of any one optional substance 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 any combination of these values.

[0052] Specifically, in some embodiments of the present invention, the silicon-containing material is a silicon-containing material containing silicon and carbon materials, and / or containing SiO2. y Silicon-containing materials and carbon materials, wherein 0≤y<2.

[0053] Specifically, in some embodiments of the present invention, the negative electrode sheet further includes a negative electrode binder and a negative electrode conductive agent. The negative electrode binder includes one or more of the following: polyvinylidene fluoride (PVDF), copolymers of PVDF, polytetrafluoroethylene (PTFE), copolymers of PVDF-hexafluoropropylene, copolymers of tetrafluoroethylene-hexafluoropropylene, copolymers of tetrafluoroethylene-perfluoroalkyl vinyl ethers, copolymers of ethylene-tetrafluoroethylene, copolymers of PVDF-tetrafluoroethylene, copolymers of PVDF-trifluoroethylene, copolymers of PVDF-trichloroethylene, copolymers of PVDF-fluorinated vinylidene, copolymers of PVDF-hexafluoropropylene-tetrafluoroethylene, thermoplastic polyimide, polyethylene, and polypropylene; acrylic resins; and styrene-butadiene rubber. The negative electrode conductive agent includes one or more of the following: conductive carbon black, conductive carbon spheres, conductive graphite, conductive carbon fibers, carbon nanotubes, graphene, or reduced graphene oxide.

[0054] 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 ternary materials, phosphate materials, lithium cobalt oxide materials, lithium-rich manganese materials or nickel-manganese oxide materials.

[0055] In some preferred embodiments of the present invention, the ternary material includes materials with the chemical formula Li. q Ni x Co y M 1-x-y O 2-g R g Li materials or surfaces with a coating layer 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 or one or more of Sr, Mg, Ti, Ca, Zr, Zn, Si, Fe, B, Ga, Cr, W, V, Nb, Ce, and R includes one or more of N, F, S and Cl.

[0056] In some preferred embodiments of the present invention, the phosphate material includes materials with the molecular formula Li. r Mn α Fe β A 1-α-β PO 4-n G n Li materials or surfaces with a coating layer 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.

[0057] In some preferred embodiments of the present invention, the lithium cobalt oxide material includes lithium cobalt oxide or lithium cobalt oxide doped and / or coated with any one or more elements selected from Ni, Mn, Mg, Al, Zr, W, F, B, Cr, Mo and rare earth elements.

[0058] In some preferred embodiments of the present invention, the lithium nickel manganese oxide material comprises LiNi x' L' y’ Mn （2-x'-y'） O4, or LiNi with a coating layer on its 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.

[0059] In a more preferred embodiment of the present invention, the positive electrode active material may include LiCoO2, LiFePO4, or 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.

[0060] Specifically, in some embodiments of the present invention, the positive electrode sheet further includes a positive current collector, and the positive electrode material layer is disposed on the surface of the positive current collector. The positive current collector includes a metallic material capable of conducting electrons; preferably, the positive current collector includes one or more of aluminum, nickel, tin, copper, and stainless steel.

[0061] 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, and the positive electrode active material, the positive electrode binder, and the positive electrode conductive agent are blended to obtain the positive electrode material layer. The positive electrode binder and the positive electrode conductive agent can be the same as the negative electrode binder and the negative electrode conductive agent, respectively, and will not be described in detail here.

[0062] Specifically, in some embodiments of the present invention, the lithium-ion battery further includes a separator located between the positive electrode and the negative electrode.

[0063] The diaphragm is a conventional diaphragm, selected from one or more of ceramic diaphragms, polymer diaphragms, non-woven fabrics, and inorganic-organic composite diaphragms. For example, single-layer polypropylene (PP) diaphragms, single-layer polyethylene (PE) diaphragms, double-layer PP / PE diaphragms, double-layer PP / PP diaphragms, and triple-layer PP / PE / PP diaphragms.

[0064] The lithium-ion battery of the present invention uses a silicon-containing material for the negative electrode and does not contain Cr in the negative electrode current collector. Simultaneously, 1,3,6-hexanetrionitrile is used as the first additive in the non-aqueous electrolyte, and the compound shown in structural formula 1 is used as the second additive. The relationships between the mass percentage of silicon (a) in the negative electrode material layer, the mass percentage of Cr relative to Cu in the negative electrode current collector (b), the mass percentage of the first additive (c) in the non-aqueous electrolyte, and the mass percentage of the second additive (d) in the non-aqueous electrolyte satisfy the following: 0.1≤10(d+c)×a / b≤100, 8≤a≤30, 20≤b≤800, 0.5≤c≤4, 0.1≤d≤4. This achieves a synergistic effect among the parameters, effectively improving the battery's energy density and mitigating the negative electrode volume expansion caused by high silicon content. It also inhibits metal ion dissolution and forms a stable interface film, resulting in a lithium-ion battery with a stable silicon negative electrode structure, high energy density, and stable cycle performance. Detailed Implementation

[0065] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present invention.

[0066] Example 1-1

[0067] The method for preparing the lithium-ion battery in this embodiment includes the following steps:

[0068] (1) Preparation of non-aqueous electrolyte:

[0069] 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, followed by the addition of a first additive, a second additive, and other additives. Based on the total weight of the non-aqueous electrolyte (100%), the first additive (1,3,6-hexanetrionitrile) and the second additive (compound 1) each comprised 2% of the non-aqueous electrolyte by mass.

[0070] (2) Preparation of the positive electrode:

[0071] Lithium cobalt oxide (LiCoO2), conductive carbon black (Super-P), and polyvinylidene fluoride (PVDF) binder were mixed in a mass ratio of 93:4:3, and then dispersed in N-methyl-2-pyrrolidone (NMP) to obtain a positive electrode slurry. The slurry was uniformly coated on both sides of an aluminum foil, and after drying, calendering, and vacuum drying, aluminum leads were welded on using an ultrasonic welder to obtain the positive electrode sheet.

[0072] (3) Preparation of negative electrode:

[0073] A negative electrode material (graphite and silicon oxide), conductive carbon black Super-P, styrene-butadiene rubber (SBR) binder, and carboxymethyl cellulose (CMC) were mixed in a mass ratio of 94:1:2.5:2.5, and then dispersed in deionized water to obtain a negative electrode slurry. The slurry was coated on both sides of a copper foil, dried, rolled, and vacuum dried, and then nickel leads were soldered on using an ultrasonic welder to obtain the negative electrode sheet. The silicon content in the negative electrode material layer was 15% by mass; the chromium content relative to the copper content in the copper foil was 60 ppm.

[0074] (4) Cell fabrication:

[0075] A separator is placed between the positive and negative electrode plates. Then, the sandwich structure consisting of the positive electrode plate, negative electrode plate, and separator is stacked and placed in an aluminum foil packaging bag. The cells are then vacuum-baked at 75°C for 48 hours to obtain the cells to be injected with electrolyte.

[0076] (5) Electrolyte injection and formation of the battery cell:

[0077] In a glove box where the dew point is controlled below -40°C, the electrolyte prepared above is injected into the battery cell, vacuum sealed, and left to stand for 24 hours.

[0078] Then, perform the first charge routine formation as follows: charge at a constant current for 180 minutes with a current of 0.05d, charge at a constant current for 0.2d to 3.95V, vacuum seal for the second time, and then charge at a constant current of 0.2d to 4.5V. After resting at room temperature for 24 hours, discharge at a constant current of 0.2d to 3.0V.

[0079] Examples 1-2 to 1-26 and Comparative Examples 1-1 to 1-18

[0080] This embodiment and comparative example are used to illustrate the lithium-ion battery disclosed in this invention. They include most of the operating steps in the above embodiments 1-1. The differences are: the content of silicon in the negative electrode material layer, the mass content of Cr relative to Cu 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 auxiliary additives, as shown in Tables 1 to 3.

[0081] The lithium-ion batteries prepared in each embodiment and comparative example were subjected to the following performance tests:

[0082] 1. Storage test at 60℃

[0083] The formed lithium-ion battery was charged at 1C constant current and constant voltage to 4.5V (LiCoO2 / silicon-carbon battery) at room temperature, and then charged at constant voltage until the current dropped to 0.02C. The initial battery volume was measured, and then the battery was stored at 60℃ for 30 days. After that, it was discharged at 1C to 3V, and the battery volume after storage was measured.

[0084] Battery inflation rate (%) = (Battery volume after storage - Battery volume before storage) / Battery volume before storage × 100%.

[0085] 2. Cyclic performance test

[0086] The lithium-ion battery was placed in a constant temperature environment of 45℃ and charged to 4.5V (LiCoO2 / silicon-carbon battery) with a constant current of 1C. Then it was charged with a constant voltage until the current dropped to 0.02C. Then it was discharged to 3.0V with a constant current of 1C. This cycle was repeated 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.

[0087] Calculate the capacity retention rate of the cycle using the following formula:

[0088] Battery capacity retention rate (%) = Discharge capacity at 800th cycle / Discharge capacity at 1st cycle × 100%;

[0089] Battery inflation rate (%) = (Battery volume after cycle - Battery volume before cycle) / Battery volume before cycle × 100%.

[0090] Test results:

[0091] Table 1 shows the parameters required for preparing lithium-ion batteries in Examples 1-1 to 1-19 and Comparative Examples 1-1 to 1-12. 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. The other parameters and preparation steps are the same as those in Example 1-1. The specific differences are: the silicon 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 content c of the first additive in the non-aqueous electrolyte, the mass percentage content d of the second additive in the non-aqueous electrolyte, and the value of the relationship 10(c+d)×a / b.

[0092] Table 1 also shows the test results of the initial discharge capacity, 30D gas expansion rate at 60°C, gas expansion rate after 800 cycles at 45°C, and capacity retention rate after 800 cycles at 45°C for Examples 1-1 to 1-19 and Comparative Examples 1-1 to 1-12.

[0093] Table 1

[0094] Group Silicon content (a / %) in the anode material layer Mass content of Cr relative to Cu in negative electrode current collector (b / ppm) Mass percentage of the first additive in non-aqueous electrolyte (c / %) Mass percentage of the second additive in non-aqueous electrolytes (d / %) 10(c+d)×a / b Initial discharge capacity / mAh 60℃ storage, 30D air expansion rate / % 45℃, 800 cycles, air expansion 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 Examples 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 Examples 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

[0095] Note: " / " in the table indicates that the item does not exist.

[0096] 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 silicon-containing materials as the negative electrode, limits the silicon content in the negative electrode material layer, adds Cr to the negative electrode current collector, uses 1,3,6-hexanetrionitrile as the first additive in the non-aqueous electrolyte, and uses a compound with a specific structure as the second additive. Furthermore, the relationship between the mass percentage of silicon in the negative electrode material layer (a), the mass percentage of Cr relative to Cu in the negative electrode current collector (b), the mass percentage of the first additive in the non-aqueous electrolyte (c), and the mass percentage of the second additive in the non-aqueous electrolyte (d) is limited 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. This results in a lithium-ion battery with a stable silicon negative electrode structure, high energy density, and good cycle performance.

[0097] As can be seen from the test results of Examples 1-1 to 1-19 and Comparative Examples 1-1 to 1-12, when any one of the following parameters does not meet the range or the value of the relationship 10(d+c)×a / b is too large or too small, the synergistic effect between the parameters cannot be achieved. This cannot effectively improve the volume expansion of the negative electrode caused by the high silicon content in the silicon-containing negative electrode, nor can a dense SEI film be formed on the negative electrode to protect it. Therefore, it is impossible to obtain a lithium-ion battery with a stable silicon negative electrode structure, high energy density, and good cycle performance.

[0098] When the mass percentage of silicon (a) in the negative electrode material layer, the mass percentage of Cr relative to Cu in the negative electrode current collector (b), the mass percentage of the first additive in the non-aqueous electrolyte (c), and the mass percentage of the second additive in the non-aqueous electrolyte (d) 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 resulting lithium-ion battery can significantly improve energy density while better controlling the volume expansion of silicon. The first and second additives can also work synergistically with each other to protect the negative electrode, making the performance of the lithium-ion battery more stable.

[0099] Table 2 shows the test results of the initial discharge capacity, 30D gas expansion rate at 60°C, gas expansion rate after 800 cycles at 45°C, and capacity retention rate of the lithium-ion batteries prepared in Examples 1-1 and 1-20 to 1-23. The difference between Examples 1-20 to 1-23 and Example 1-1 is the type of the second additive shown in Table 2. The other parameters and preparation steps are the same as those described in Example 1-1.

[0100] Table 2

[0101]

[0102] As shown in Table 2, when the mass percentage of silicon in the negative electrode material layer (a), the mass percentage of Cr relative to Cu in the negative electrode current collector (b), the mass percentage of the first additive in the non-aqueous electrolyte (c), and the mass percentage of the second additive in the non-aqueous electrolyte (d), and the relationship 10(d+c)×a / b meet the relevant requirements, adding any one of the compounds containing both sulfate ester groups and carbonate groups as the second additive can result in a lithium-ion battery with a stable silicon negative electrode structure, high energy density, and good cycle performance. This indicates that the battery system of the present invention has universality for different types of second additives.

[0103] Table 3 shows the test results of the initial discharge capacity, 30D gas expansion rate at 60°C, gas expansion rate after 800 cycles at 45°C, and capacity retention rate of the lithium-ion batteries prepared in Examples 1-1, 1-24 to 1-26, and Comparative Examples 1-13 to 1-18. The difference between Examples 1-24 to 1-26 and Comparative Examples 1-13 to 1-18 and Example 1-1 is that the mass percentage content of the first additive in the non-aqueous electrolyte, the mass percentage content of the second additive in the non-aqueous electrolyte, and the types and contents of auxiliary additives are shown in Table 3. The other parameters and preparation steps are the same as those described in Example 1-1.

[0104] Table 3

[0105]

[0106] Note: " / " in the table indicates that the item does not exist.

[0107] As shown in Table 3, the lithium-ion battery of the present invention, when used in conjunction with auxiliary additives, still exhibits good improvement effects on the high-temperature storage performance and high-temperature cycle performance of lithium-ion batteries. However, the test results of Examples 1-1, 1-24 to 1-26, and Comparative Examples 1-13 to 1-18 indicate that when different amounts of auxiliary additives are used to replace the second additive, the auxiliary additives do not form a good synergistic effect with other components, resulting in poor improvement effects on the energy density and cycle performance of lithium-ion batteries.

[0108] Table 4 shows the parameters required for preparing lithium-ion batteries in Examples 2-1 to 2-19 and Comparative Examples 2-1 to 2-12. 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 in Table 4 and the type of the second additive. The other parameters and preparation steps are the same as those recorded in Example 1-1. The specific differences are as follows: the second additive in Examples 2-1 to 2-19 and Comparative Examples 2-1 to 2-12 is compound 6. The silicon 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.

[0109] Table 4 also shows the test results for the initial discharge capacity, 30D gas expansion rate at 60°C storage, gas expansion rate after 800 cycles at 45°C, and capacity retention rate after 800 cycles at 45°C for Examples 2-1 to 2-19 and Comparative Examples 2-1 to 2-12.

[0110] Table 4

[0111] Group Silicon content a / % in the anode material layer Mass content of Cr relative to Cu in negative electrode current collector (b / ppm) Mass percentage of the first additive in non-aqueous electrolyte (c / %) Mass percentage of the second additive in non-aqueous electrolytes (d / %) 10(c+d)×a / b Initial discharge capacity / mAh 60℃ storage, 30D air expansion rate / % 45℃, 800 cycles, air 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 Example 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 Example 2-11 30 23 4 4 104.35 5056 33.2 34.7 81.1 Comparative Example 2-12 8 700 0.6 0.1 0.08 4727 31.1 31.5 80.8

[0112] Note: " / " in the table indicates that the item does not exist.

[0113] 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 silicon-containing material as the negative electrode, limits the silicon content in the negative electrode material layer, adds Cr element to the negative electrode current collector, uses 1,3,6-hexanetrionitrile as the first additive in the non-aqueous electrolyte, and uses a tricyclic compound containing only sulfate ester groups as the second additive. Furthermore, the relationship between the mass percentage of silicon element 'a' in the negative electrode material layer, the mass percentage of Cr element relative to Cu element 'b' in the negative electrode current collector, the mass percentage of the first additive 'c' in the non-aqueous electrolyte, and the mass percentage of the second additive 'd' in the non-aqueous electrolyte is limited to satisfy the following: 0.1≤10(d+c)×a / b≤100, 8≤a≤30, 20≤b≤800, 0.5≤c≤4, 0.1≤d≤4. This results in a lithium-ion battery with a stable silicon negative electrode structure, high energy density, and good cycle performance.

[0114] As can be seen from the test results of Examples 2-1 and Comparative Examples 2-1 to 2-12, when any one of the following parameters does not meet the range or the value of the relationship 10(d+c)×a / b is too large or too small, the synergistic effect between the parameters cannot be achieved. This cannot effectively improve the volume expansion of the anode caused by the high silicon content in the silicon-containing anode, nor can a dense SEI film be formed on the anode to protect it. Therefore, it is impossible to obtain a lithium-ion battery with a stable silicon anode structure, high energy density, and good cycle performance.

[0115] When the mass percentage of silicon (a) in the negative electrode material layer, the mass percentage of Cr relative to Cu in the negative electrode current collector (b), the mass percentage of the first additive in the non-aqueous electrolyte (c), and the mass percentage of the second additive in the non-aqueous electrolyte (d) 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 resulting lithium-ion battery can significantly improve energy density while better controlling the volume expansion of silicon. The first and second additives can also work synergistically with each other to protect the negative electrode, making the performance of the lithium-ion battery more stable.

[0116] Table 5 shows the test results of the initial discharge capacity, 30D gas expansion rate at 60°C, gas expansion rate after 800 cycles at 45°C, and capacity retention rate of the lithium-ion batteries prepared in Examples 2-1, 2-20, and Comparative Example 2-13. The difference between Examples 2-20 and Comparative Example 2-1 and Example 2-1 is the type of the second additive shown in Table 5. The other parameters and preparation steps are the same as those described in Example 2-1.

[0117] Table 5

[0118]

[0119] As shown in Table 5, when the mass percentage of silicon in the negative electrode material layer (a), the mass percentage of Cr relative to Cu in the negative electrode current collector (b), the mass percentage of the first additive in the non-aqueous electrolyte (c), and the mass percentage of the second additive in the non-aqueous electrolyte (d), and the relationship 10(d+c)×a / b meet the relevant requirements, adding any tricyclic or bicyclic compound containing only sulfate ester groups as the second additive can result in a lithium-ion battery with a stable silicon negative electrode structure, high energy density, and good cycle performance. This indicates that the battery system of the present invention has universality for different types of second additives.

[0120] As can be seen from the test results of Examples 2-1, 2-20 and Comparative Example 2-13, when DTD is used to replace the second additive, the cycle performance of Comparative Example 2-13 is significantly lower than that of Examples 2-1 and 2-20, and both the cycle gas expansion rate and the storage gas expansion rate are increased. This indicates that the second additive of this application has a greater effect on improving battery performance than the monocyclic ethylene sulfate. This is because the multi-ring structure of the first additive of this application participates in the formation of the interface film on the electrode surface through ring opening, and the resulting interface film components are more stable and dense, which can improve the strength of the interface film structure and thus help improve its high-temperature stability. In contrast, the monocyclic DTD cannot form a good synergistic effect with other components, and its effect on improving the stability of the silicon anode structure, energy density and cycle performance of lithium-ion batteries is not good.

[0121] Table 6 shows the test results of the initial discharge capacity, 30D gas expansion rate at 60°C, gas expansion rate after 800 cycles at 45°C, and capacity retention rate of the lithium-ion batteries prepared in Examples 2-1, 2-21 to 2-23, and Comparative Examples 2-14 to 2-19. The difference between Examples 2-21 to 2-23 and Comparative Examples 2-14 to 2-19 and Example 2-1 is that the mass percentage content of the first additive in the non-aqueous electrolyte, the mass percentage content of the second additive in the non-aqueous electrolyte, and the auxiliary additives and their contents are shown in Table 6. The other parameters and preparation steps are the same as those described in Example 2-1.

[0122] Table 6

[0123]

[0124] Note: " / " in the table indicates that the item does not exist.

[0125] As shown in Table 6, the lithium-ion battery of the present invention, when used in conjunction with auxiliary additives, still exhibits good improvement effects on the high-temperature storage performance and high-temperature cycle performance of lithium-ion batteries. However, the test results of Examples 2-1, 2-21 to 2-23, and Comparative Examples 2-14 to 2-19 indicate that when different amounts of auxiliary additives are used to replace the second additive, the auxiliary additives do not form a good synergistic effect with other components, resulting in poor improvement effects on the energy density and cycle performance of lithium-ion batteries.

[0126] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A lithium-ion battery, characterized in that, The device includes a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte; the negative electrode includes a negative electrode current collector and a negative electrode material layer disposed 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 includes 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-hexanetrionitrile; The second additive includes the compound shown in structural formula 1: ； Where X is selected from or R1 and R2 are each independently selected from H, ,or R1 and R2 are not both selected from H, and X, R1 and R2 contain at least one sulfur atom; 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; Where 'a' represents the mass percentage of silicon in the negative electrode material layer, expressed in % %. b represents the mass content of Cr relative to Cu in the negative electrode current collector, in ppm. c represents the mass percentage of the first additive in the non-aqueous electrolyte, expressed in % (%). d represents the mass percentage of the second additive in the non-aqueous electrolyte, in units of %.

2. The lithium-ion battery as described in claim 1, characterized in that, The lithium-ion battery satisfies the following condition: 0.8≤10(d+c)×a / b≤24.

3. The lithium-ion battery as described in claim 1, characterized in that, The mass percentage (a%) of silicon in the negative electrode material layer is 10% to 25%.

4. The lithium-ion battery as described in claim 1, characterized in that, The mass content of Cr relative to Cu in the negative electrode current collector is 50ppm to 500ppm.

5. The lithium-ion battery as described in claim 1, characterized in that, The mass percentage (c%) of the first additive in the non-aqueous electrolyte is 1% to 3%.

6. The lithium-ion battery as described in claim 1, characterized in that, The mass percentage (d%) of the second additive in the non-aqueous electrolyte is 0.5% to 2%.

7. The lithium-ion battery as described in claim 1, characterized in that, The compound represented by structural formula 1 includes one or more of the following compounds: 。 8. The lithium-ion battery as described in claim 1, characterized in that, The non-aqueous organic solvent includes one or more of cyclic carbonates, linear carbonates, carboxylic esters, and ethers; and / or, The cyclic carbonates include one or more selected from vinylene carbonate, propylene carbonate, ethylene carbonate, and butene carbonate; and / or, The linear carbonate includes one or more of dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, and methyl propyl carbonate; and / or, The carboxylic acid ester includes one or more selected from 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 as described in claim 1, characterized in that, 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, and LiB₂. 10 Cl 10 At least one of LiAlCl4, lithium chloroborane, and lithium tetraphenylborate.

10. The lithium-ion battery as described in claim 1, characterized in that, The non-aqueous electrolyte further includes auxiliary additives, which include at least one of cyclic sulfate compounds, sulfonyl lactone compounds, cyclic carbonate compounds, phosphate compounds, and borate ester compounds; and / or, Based on the total mass of the non-aqueous electrolyte as 100%, the content of the auxiliary additives is 0.01%~10%; and / or, The cyclic sulfate compounds include at least one of 4-methylvinyl sulfate, vinyl sulfate, and propylene sulfate; and / or, The sulfonyl lactone compounds include at least one selected from 1,3-propanesulfonyl lactone, 1,4-butanesulfonyl lactone, and propenyl-1,3-sulfonyl lactone; and / or, The cyclic carbonate compounds include at least one of the following: vinylene carbonate, ethylene ethylene carbonate, methylene carbonate, fluoroethylene carbonate, trifluoromethyl ethylene carbonate, difluoroethylene carbonate, and a compound represented by 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 one of the following: hydrogen atom, halogen atom, C1-C5 group; and / or, The phosphate ester compounds include at least one of the compounds shown in structural formula 3 below: ； In structural formula 3, R 31 R 32 R 33 Each is independently selected from C1-C5 saturated hydrocarbon groups, unsaturated hydrocarbon groups, halohydrocarbon groups, and -Si(C m H 2m+1 )3, where m is a natural number from 1 to 3; and / or, The borate esters include at least one of tris(trimethylsilane)borate and tris(triethylsilane)borate.

Images