A lithium-ion battery

Abstract

To overcome the problems of positive electrode current collector corrosion and solid electrolyte interface film damage during the cycling process of existing lithium iron phosphate batteries, this invention provides a lithium-ion battery, comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte. The positive electrode includes a positive electrode current collector and a positive electrode material layer disposed on the positive electrode current collector. The positive electrode material layer includes a positive electrode active material, which includes a lithium phosphate material. The positive electrode current collector contains Si element, and the mass percentage of Si element in the positive electrode current collector is 0.01%-0.2%. The non-aqueous electrolyte includes lithium salt, additives, and a non-aqueous organic solvent. The additives include fluoroethylene carbonate and sulfur-containing additives. The sulfur-containing additives include one or two of the following compounds:

Description

Technical Field

[0001] This invention belongs to the field of electrochemical technology, specifically relating to a lithium-ion battery. Background Technology

[0002] With the booming development of the new energy industry, lithium iron phosphate batteries have been widely used in new energy vehicles and energy storage due to their advantages such as high safety, absence of precious metals, and long lifespan. However, compared with ternary materials, lithium iron phosphate does not have an advantage in energy density. Therefore, the cell manufacturing process has been continuously improved and advanced, such as increasing the compaction density of the electrode sheets, thickening the coated positive electrode active material layer (hereinafter referred to as thick coating), and reducing the mass ratio of inactive materials such as current collectors. However, this also poses challenges to the wetting of the battery and the corrosion resistance of the current collector. To improve wetting characteristics and compensate for the power degradation caused by high compaction and thick electrode sheets, low viscosity and low melting point solvents are generally selected for the electrolyte. However, this also degrades the high-temperature performance of the battery, leading to a decrease in calendar life and an increase in battery gas production. The thick coating process and the treatment of thinning the current collector also reduce the mechanical strength and corrosion resistance of the current collector, especially the positive electrode current collector aluminum foil which is under high potential for a long time. If left untreated, the active material layer may detach from the current collector during battery use, causing an increase in electron transfer impedance. Under high-temperature conditions, the active material layer separated from the current collector may also undergo side reactions with the electrolyte, further causing high-temperature gas generation and capacity decay. In addition, the free acid generated by the electrolyte will also corrode the current collector, dissolve aluminum ions into the electrolyte, and may deposit on the negative electrode, damaging the solid electrolyte interface film on the negative electrode surface, further aggravating battery failure. Summary of the Invention

[0003] To address the problems of capacity decay and high gas production caused by corrosion of the positive electrode current collector and damage to the solid electrolyte interface film in existing lithium iron phosphate batteries under high temperature conditions, this invention provides a lithium-ion battery.

[0004] The technical solution adopted by the present invention to solve the above-mentioned technical problems is as follows: This invention provides a lithium-ion battery, comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte. The positive electrode includes a positive electrode current collector and a positive electrode material layer disposed on the positive electrode current collector. The positive electrode material layer includes a positive electrode active material, which includes a lithium phosphate-containing material. The positive electrode current collector contains silicon (Si) element, and the mass percentage of Si element in the positive electrode current collector is 0.01%-0.2%. The non-aqueous electrolyte includes a lithium salt, additives, and a non-aqueous organic solvent. The additives include fluoroethylene carbonate and a sulfur-containing additive, and the sulfur-containing additive includes one or two of the following compounds: Based on the weight of the non-aqueous electrolyte as 100%, the mass percentage of the sulfur-containing additive is 0.05% to 2%, and the mass percentage of the fluoroethylene carbonate is 0.05% to 3%.

[0005] Optionally, the sulfur-containing additive has a mass percentage content of 0.2% to 1.5% based on 100% of the weight of the non-aqueous electrolyte.

[0006] Optionally, the mass percentage of the fluoroethylene carbonate is 0.2% to 2%, based on 100% of the weight of the non-aqueous electrolyte.

[0007] Optionally, the mass percentage of Si element in the positive electrode current collector is 0.02%-0.1%.

[0008] Optionally, the thickness of the positive electrode current collector is 8~20 μm; and / or, The thickness of the positive electrode material layer is 130~240μm.

[0009] Optionally, the ratio of the thickness of the positive electrode material layer to the thickness of the positive electrode current collector is 7 to 22.

[0010] Optionally, the positive current collector is an aluminum foil or an aluminum alloy foil.

[0011] Optionally, the lithium 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 β A 1-α-β PO 4-n G n At least one of the following materials, wherein 0.9≤r≤1.1, 0≤α≤0.8, 0.2≤β≤1, 0.2≤α+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, Ni, Co, Ga, Sn, Sb, Ge and W, and G includes one or more of N, F, S and Cl.

[0012] Optionally, the non-aqueous organic solvent includes linear carbonates and / or carboxylic acid esters, wherein the linear carbonates include one or more of dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, dipropyl carbonate, and methyltrifluoroethyl carbonate, and the carboxylic acid esters include one or more of methyl formate, ethyl formate, ethyl acetate, propyl acetate, butyl acetate, ethyl propionate, propyl propionate, butyl propionate, and ethyl difluoroacetate.

[0013] Optionally, the non-aqueous electrolyte further comprises auxiliary additives, which include one or more of the following: vinylene carbonate, vinyl sulfate, 1,3-propanesulfonate lactone, methanedisulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium difluorobis(oxalate) phosphate, lithium bis(oxalate) borate, lithium tetrafluoroborate, tris(trimethylsilyl) phosphate, tris(trimethylsilyl) borate, tripropynyl phosphate, tetravinylsilane, and divinyldimethylsilane.

[0014] The lithium-ion battery provided by this invention uses lithium phosphate material as the positive electrode active material. The positive electrode current collector contains Si element, which can form an extremely thin and dense amorphous silicon oxide layer on the surface of the positive electrode current collector, fundamentally isolating the positive electrode current collector from direct contact with the electrolyte, thereby inhibiting the corrosion of the positive electrode current collector by the non-aqueous electrolyte. However, this protection has a significant shortcoming: the amorphous silicon oxide layer is easily corroded by HF in the electrolyte, and the free aluminum ions caused by HF corrosion have a destructive effect on the solid electrolyte interface film on the negative electrode surface. To solve this problem, fluoroethylene carbonate and sulfur-containing additives are added to the non-aqueous electrolyte as additives. On the one hand, fluoroethylene carbonate can undergo a solid electrolyte-like film-forming reaction on the surface of the amorphous silicon oxide layer, constructing an additional protective film on the outside of the silicon oxide protective layer, inhibiting the corrosion of the positive electrode current collector by the non-aqueous electrolyte. HF corrodes the amorphous silicon oxide layer, improving the stability of the positive electrode current collector interface. On the other hand, sulfur-containing additives can preferentially form a film on the negative electrode, generating a stable solid electrolyte interface film component containing sulfur-containing lithium salts, improving the high-temperature stability of the solid electrolyte interface film, and further enhancing the high-temperature capacity retention rate of the battery. At the same time, it directly suppresses the gas generation problem caused by fluoroethylene carbonate, solving the performance side effects of fluoroethylene carbonate. Meanwhile, the stable solid electrolyte interface film can reduce the side reactions between lithium salts and the electrode interface in the electrolyte, indirectly reducing the amount of HF generated in the electrolyte, mitigating the corrosion of the amorphous silicon oxide layer of the positive electrode current collector from the source, forming a dual synergy with fluoroethylene carbonate, strengthening the high-temperature stability of the current collector interface and the solid electrolyte interface film, and improving the high-temperature storage performance and high-temperature fast charging performance of lithium iron phosphate batteries. Detailed Implementation

[0015] To make the technical problems solved, the technical solutions, and the beneficial effects of the present invention clearer, the present invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present invention and are not intended to limit the present invention.

[0016] This invention provides a lithium-ion battery, comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte. The positive electrode includes a positive electrode current collector and a positive electrode material layer disposed on the positive electrode current collector. The positive electrode material layer includes a positive electrode active material, which includes a lithium phosphate-containing material. The positive electrode current collector contains silicon (Si) element, and the mass percentage of Si element in the positive electrode current collector is 0.01%-0.2%. The non-aqueous electrolyte includes a lithium salt, additives, and a non-aqueous organic solvent. The additives include fluoroethylene carbonate and sulfur-containing additives. The sulfur-containing additives include one or two of the following compounds: Based on the weight of the non-aqueous electrolyte as 100%, the mass percentage of the sulfur-containing additive is 0.05% to 2%, and the mass percentage of the fluoroethylene carbonate is 0.05% to 3%.

[0017] In the lithium-ion battery, lithium phosphate material is used as the positive electrode active material, and the positive electrode current collector contains silicon (Si). Si can form an extremely thin and dense amorphous silicon oxide layer on the surface of the positive electrode current collector, fundamentally isolating the positive electrode current collector from direct contact with the electrolyte, thereby inhibiting corrosion of the positive electrode current collector by the non-aqueous electrolyte. However, this protection has a significant drawback: the amorphous silicon oxide layer is easily corroded by HF in the electrolyte, and the free aluminum ions caused by HF corrosion have a destructive effect on the solid electrolyte interface film on the negative electrode surface. To solve this problem, fluoroethylene carbonate and sulfur-containing additives are added to the non-aqueous electrolyte as additives. On the one hand, fluoroethylene carbonate can undergo a solid electrolyte-like film-forming reaction on the surface of the amorphous silicon oxide layer, constructing an additional protective film outside the silicon oxide protective layer, inhibiting HF corrosion. To mitigate the corrosion of the amorphous silicon oxide layer, the stability of the positive electrode current collector interface is improved. On the other hand, sulfur-containing additives can preferentially form a film on the negative electrode, generating a stable solid electrolyte interface film component containing sulfur-containing lithium salts, improving the high-temperature stability of the solid electrolyte interface film, and further enhancing the high-temperature capacity retention rate of the battery. At the same time, it directly suppresses the gas generation problem caused by fluoroethylene carbonate, solving the performance side effects of fluoroethylene carbonate. Meanwhile, the stable solid electrolyte interface film can reduce the side reactions between lithium salts and the electrode interface in the electrolyte, indirectly reducing the amount of HF generated in the electrolyte, mitigating the corrosion of the amorphous silicon oxide layer of the positive electrode current collector from the source, and forming a dual synergy with fluoroethylene carbonate, strengthening the high-temperature stability of the current collector interface and the solid electrolyte interface film, and improving the high-temperature storage performance and high-temperature fast charging performance of lithium iron phosphate batteries.

[0018] The sulfur-containing additive has multiple sulfate ester ring structures. Compared with the monocyclic structure of vinyl sulfate, the multiple sulfate ester ring structures each open their rings to participate in the formation of the interface film on the electrode surface. The resulting solid electrolyte interface film is more stable and dense, which can improve the strength of the interface film structure and thus help improve its high-temperature stability.

[0019] In some embodiments, the sulfur-containing additive has a mass percentage content of 0.05% to 2% based on 100% of the weight of the non-aqueous electrolyte.

[0020] In a specific embodiment, based on the weight of the non-aqueous electrolyte as 100%, the mass percentage of the sulfur-containing additive can be 0.05%, 0.15%, 0.2%, 0.36%, 0.46%, 0.56%, 0.66%, 0.77%, 0.87%, 0.97%, 1.08%, 1.18%, 1.28%, 1.38%, 1.48%, 1.5%, 1.69%, 1.79%, 1.89%, 2%, or any two of these ranges.

[0021] In a preferred embodiment, the sulfur-containing additive has a mass percentage content of 0.2% to 1.5% based on the weight of the non-aqueous electrolyte (100%).

[0022] The sulfur-containing additive is used during the battery formation stage to decompose and form a solid electrolyte interface film component containing sulfur-containing lithium salt on the surface of the negative electrode, suppressing side reactions at the interface between the non-aqueous electrolyte and the negative electrode, thereby inhibiting the high-temperature decomposition and gas production of fluoroethylene carbonate and suppressing HF production, avoiding corrosion of the positive electrode current collector, and improving the high-temperature storage performance of the battery. If the content of the sulfur-containing additive is too low, it will be difficult to significantly improve the high-temperature stability of the solid electrolyte interface film of the negative electrode; if the content of the sulfur-containing additive is too high, it will lead to an excessively thick film on the negative electrode, which will increase the impedance and is not conducive to the performance of the battery's fast charging.

[0023] In some embodiments, the mass percentage of the fluoroethylene carbonate is 0.05% to 3% based on 100% of the weight of the non-aqueous electrolyte.

[0024] In a specific embodiment, based on the weight of the non-aqueous electrolyte as 100%, the mass percentage content of the fluoroethylene carbonate can be 0.10%, 0.2%, 0.36%, 0.46%, 0.56%, 0.66%, 0.77%, 0.87%, 0.97%, 1.08%, 1.18%, 1.28%, 1.38%, 1.48%, 1.59%, 1.69%, 1.79%, 1.89%, 2%, 2.18%, 2.28%, 2.38%, 2.48%, 2.59%, 2.69%, 2.79%, 2.89%, 3.00%, or any two of these ranges.

[0025] In a preferred embodiment, the mass percentage of the fluoroethylene carbonate is 0.2% to 2%, based on the weight of the non-aqueous electrolyte as 100%.

[0026] Fluoroethylene carbonate readily undergoes a film-forming reaction on Si and its oxides, similar to that of a solid electrolyte, providing an additional protective layer for the silicon oxide protective layer of the positive electrode current collector, further isolating the non-aqueous electrolyte from contact with the aluminum foil or aluminum alloy foil. If the content of fluoroethylene carbonate is too low, it will be difficult to provide good protection for the positive electrode current collector. If the content of fluoroethylene carbonate is too high, the high-temperature decomposition and gas production of fluoroethylene carbonate itself will trigger high-temperature side reactions, leading to an increase in the expansion rate of the lithium-ion battery at high temperatures and affecting its high-temperature storage performance.

[0027] In a specific embodiment, the mass percentage of Si element in the positive electrode current collector can be 0.01%, 0.02%, 0.04%, 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.1%, or any two of these ranges.

[0028] In a preferred embodiment, the mass percentage of Si element in the positive electrode current collector is 0.02%-0.1%.

[0029] Introducing silicon (Si) into the positive electrode current collector can generate an extremely thin and dense amorphous silicon oxide layer on the surface, isolating the current collector from direct contact with the non-aqueous electrolyte. Furthermore, Si can improve the creep resistance of the aluminum foil, raise the critical point of metal fatigue, maintain contact with the positive electrode active material, effectively reduce separation and demolding, and suppress impedance growth. However, excessive Si content in the positive electrode current collector can lead to decreased ductility, making the aluminum foil brittle and prone to breakage during die-cutting or winding of the electrode, thus affecting its processing performance.

[0030] In some embodiments, the thickness of the positive current collector is 8~20μm.

[0031] In a specific embodiment, the thickness of the positive current collector can be 8.0 μm, 8.6 μm, 9.3 μm, 10 μm, 10.5 μm, 11.2 μm, 11.8 μm, 12.4 μm, 13.1 μm, 13.7 μm, 14.3 μm, 14.9 μm, 15 μm, 16.2 μm, 16.8 μm, 17.5 μm, 18.1 μm, 18.7 μm, 19.4 μm, 20 μm, or any two of these ranges.

[0032] In a preferred embodiment, the thickness of the positive current collector is 10~15μm. In some embodiments, the thickness of the positive electrode material layer is 130~240μm.

[0033] In a specific embodiment, the thickness of the positive electrode material layer can be 130μm, 140μm, 150μm, 160μm, 170μm, 180μm, 190μm, 200μm, 210μm, 220μm, 230μm, 240μm or any two of these ranges.

[0034] In a preferred embodiment, the thickness of the positive electrode material layer is 150~200μm.

[0035] In some embodiments, the ratio of the thickness of the positive electrode material layer to the thickness of the positive electrode current collector is 7 to 22.

[0036] In a preferred embodiment, the ratio of the thickness of the positive electrode material layer to the thickness of the positive electrode current collector is 10-18.

[0037] In the battery system provided by this invention, by further limiting the ratio of the thickness of the positive electrode material layer to the thickness of the positive electrode current collector to be within the above range, it is beneficial to maintain a stable bonding state between the positive electrode material layer and the positive electrode current collector. This prevents layer separation due to insufficient support caused by an excessively thin positive electrode current collector, and also prevents demolding due to excessive stress caused by an excessively thick positive electrode material layer. This avoids the impedance surge problem caused by demolding, extending the battery's high-temperature cycle life and long-term reliability. While avoiding thickness imbalance, the thickness of the positive electrode material layer is not excessively constrained. Under the premise of ensuring processing performance and stability, the battery energy density can be increased by reasonably thickening the positive electrode material layer, achieving a balance between energy density and high-temperature stability, which meets the core objective of cell optimization design.

[0038] In some embodiments, the positive current collector is aluminum foil or aluminum alloy foil. Aluminum and aluminum alloys are both good conductors of electricity, capable of effectively transporting electrons to meet the electron transport requirements during battery operation, reducing battery internal resistance, and improving battery charge and discharge efficiency.

[0039] In some embodiments, the lithium phosphate material comprises 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 β A 1-α-β PO 4-n G n At least one of the following materials, wherein 0.9≤r≤1.1, 0≤α≤0.8, 0.2≤β≤1, 0.2≤α+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, Ni, Co, Ga, Sn, Sb, Ge and W, and G includes one or more of N, F, S and Cl.

[0040] In a preferred embodiment, the phosphate material includes lithium iron phosphate and / or lithium manganese iron phosphate.

[0041] In some embodiments, the positive electrode material layer further includes a positive electrode binder and a positive electrode conductive agent, and the positive electrode active material, the positive electrode binder and the positive electrode conductive agent are blended to obtain the positive electrode material layer.

[0042] The positive electrode binder includes at least one 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.

[0043] The positive electrode conductive agent includes at least one of conductive carbon black, conductive carbon spheres, conductive graphite, conductive carbon fiber, carbon nanotubes, graphene, or reduced graphene oxide.

[0044] In some embodiments, the negative electrode includes a negative electrode material layer, the negative electrode material layer includes a negative electrode active material, and the negative electrode active material includes one or more of natural graphite, artificial graphite, graphene, hard carbon, elemental silicon, silicon-carbon materials, silicon-oxygen materials, silicon-nitrogen materials, or silicon alloys.

[0045] In some embodiments, the negative electrode further includes a negative electrode current collector, and the negative electrode material layer is disposed on the surface of the negative electrode current collector. The negative electrode current collector includes a metallic material capable of conducting electrons. Preferably, the negative electrode current collector includes at least one of Al, Ni, tin, copper, and stainless steel. In a more preferred embodiment, the negative electrode current collector is selected from copper foil.

[0046] In some embodiments, the negative electrode material layer further includes a negative electrode binder and a negative electrode conductive agent, and the negative electrode active material, the negative electrode binder and the negative electrode conductive agent are blended to obtain the negative electrode material layer.

[0047] The negative electrode binder includes at least one 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.

[0048] The negative electrode conductive agent includes at least one of conductive carbon black, conductive carbon spheres, conductive graphite, conductive carbon fiber, carbon nanotubes, graphene, or reduced graphene oxide.

[0049] In some embodiments, the non-aqueous electrolyte further comprises auxiliary additives, which include one or more of the following: vinylene carbonate, vinyl sulfate, 1,3-propanesulfonate lactone, methanedisulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium difluorobis(oxalate) phosphate, lithium bis(oxalate) borate, lithium tetrafluoroborate, tris(trimethylsilyl) phosphate, tris(trimethylsilyl) borate, tripropynyl phosphate, tetravinylsilane, and divinyldimethylsilane.

[0050] In the battery system provided by the present invention, the above-mentioned auxiliary additives are added to the non-aqueous electrolyte to further suppress the problems of gas generation, impedance increase and capacity degradation of the battery at high temperature.

[0051] It should be noted that, unless otherwise specified, the content of any one of the optional substances in the auxiliary additives in the non-aqueous electrolyte is generally less than 10%, preferably 0.01-5%, and more preferably 0.1% to 2%. Specifically, the content of any one of the optional substances in the auxiliary additives 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%, 5.5%, 6%, 6.5%, 7%, 7.5%, 7.8%, 8%, 8.5%, 9%, 9.5%, 10%, or any combination of these values.

[0052] In some embodiments, the non-aqueous organic solvent comprises linear carbonates and / or carboxylic acid esters, wherein the linear carbonates comprise one or more of dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, dipropyl carbonate, and methyltrifluoroethyl carbonate, and the carboxylic acid esters comprise one or more of methyl formate, ethyl formate, ethyl acetate, propyl acetate, butyl acetate, ethyl propionate, propyl propionate, butyl propionate, and ethyl difluoroacetate.

[0053] Compared to other solvents, linear carbonates and carboxylic esters can reduce the viscosity of the electrolyte, improve the penetration efficiency of non-aqueous electrolytes to the positive and negative electrodes, enhance the liquid phase transport kinetics of ions and additives, and promote the uniformity of the solid electrolyte interface film formation on the positive and negative electrode surfaces.

[0054] In some embodiments, the non-aqueous organic solvent further includes at least one of cyclic carbonates, ether solvents, nitrile solvents, and sulfone solvents.

[0055] In some embodiments, the cyclic carbonate may be, but is not limited to, at least one of ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC).

[0056] In some embodiments, the ether solvent includes cyclic ethers or chain ethers, preferably chain ethers with 3 to 10 carbon atoms and cyclic ethers with 3 to 6 carbon atoms. The cyclic ethers may specifically include, but are not limited to, at least one of 1,3-dioxane (DOL), 1,4-dioxane (DX), crown ethers, tetrahydrofuran (THF), 2-methyltetrahydrofuran (2-CH3-THF), and 2-trifluoromethyltetrahydrofuran (2-CF3-THF). The chain ethers may specifically include, but are not limited to, dimethoxymethane, diethoxymethane, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethoxymethoxymethane, ethylene glycol di-n-propyl ether, ethylene glycol di-n-butyl ether, and diethylene glycol dimethyl ether. Because chain ethers have high solvation ability with lithium ions and can improve ion dissociation, dimethoxymethane, diethoxymethane, and ethoxymethoxymethane, which have low viscosity and can impart high ionic conductivity, are particularly preferred. Ether compounds can be used alone or in any combination and ratio of two or more. There are no particular restrictions on the content of ether compounds; it is arbitrary as long as it does not significantly impair the performance of the high-pressure lithium-ion battery of this invention. Typically, the volume ratio is 1% or more, preferably 2% or more, and more preferably 3% or more, when the non-aqueous solvent volume ratio is 100%. Furthermore, the volume ratio is typically 30% or less, preferably 25% or less, and more preferably 20% or less.

[0057] In some embodiments, the nitrile solvent may be, but is not limited to, at least one of acetonitrile, glutaronitrile, and malononitrile.

[0058] In some embodiments, the sulfone solvent includes cyclic sulfones and chain sulfones. Preferably, in the case of cyclic sulfones, it is typically a compound with 3 to 6 carbon atoms, more preferably 3 to 5 carbon atoms; in the case of chain sulfones, it is typically a compound with 2 to 6 carbon atoms, more preferably 2 to 5 carbon atoms. The content of the sulfone solvent is not particularly limited and is arbitrary within a range that does not significantly impair the performance of the lithium-ion battery of the present invention. Relative to the total amount of solvent in the non-aqueous electrolyte, it is typically 0.3% or more by volume, preferably 0.5% or more by volume, more preferably 1% or more by volume. Furthermore, it is typically 40% or less by volume, preferably 35% or less by volume, more preferably 30% or less by volume. When using two or more sulfone solvents in combination, the total amount of sulfone solvent should satisfy the above range. When the content of the sulfone solvent is within the above range, a non-aqueous electrolyte with excellent high-temperature storage stability is preferred.

[0059] In some embodiments, the mass content of the non-aqueous organic solvent is 65% to 90% based on the total mass of the non-aqueous electrolyte being 100%.

[0060] Specifically, based on the total mass of the non-aqueous electrolyte as 100%, the mass content of the non-aqueous organic solvent can be 65%, 68%, 71%, 74%, 76%, 78%, 79%, 80%, 81.5%, 82%, 84%, 85%, 86%, 87%, 89%, 90%, or any combination of these values.

[0061] In some embodiments, the electrolyte salt is selected from lithium salts, including LiPF6, LiODFP, LiODFB, LiBOB, LiPO2F2, LiBF4, LiSbF6, LiAsF6, LiN(SO2F)2, LiN(SO2CF3)2, LiN(SO2C2F5)2, LiC(SO2CF3)3, LiClO4, LiAlCl4, LiCF3SO3, LiSO3F, and Li2B. 10 Cl 10 At least one of lithium chloroborane, lithium trioxazophosphate, lithium lower aliphatic carboxylic acid having four or fewer carbon atoms, or lithium tetraphenylborate.

[0062] In some embodiments, the concentration of the lithium salt in the non-aqueous electrolyte is 0.1 mol / L to 4 mol / L. In a preferred embodiment, the concentration of the lithium salt in the non-aqueous electrolyte is 0.5 mol / L to 2.5 mol / L. Specifically, in the non-aqueous electrolyte, the concentration 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, 1.7 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, or any combination of these values.

[0063] In some embodiments, the secondary battery further includes a separator located between the positive electrode and the negative electrode.

[0064] The diaphragm can be a conventional diaphragm, such as a ceramic diaphragm, a polymer diaphragm, a non-woven fabric, or an inorganic-organic composite diaphragm, including but not limited to single-layer PP (polypropylene), single-layer PE (polyethylene), double-layer PP / PE, double-layer PP / PP, and triple-layer PP / PE / PP diaphragms.

[0065] The present invention will be further illustrated by the following examples.

[0066] Table 1 Example 1 This embodiment illustrates the lithium-ion battery and its preparation method disclosed in this invention, and includes the following steps: (1) Preparation of positive electrode: 95.5% positive electrode active material LiFePO4, 2.5% conductive carbon black, 1.7% carbon nanotube conductive agent and 0.3% binder polyvinylidene fluoride are dispersed in N-methyl-2-pyrrolidone to obtain positive electrode slurry; aluminum foil containing Si element is used as positive electrode current collector. The mass percentage of Si element in the positive electrode current collector is shown in Table 1. The positive electrode slurry is uniformly coated on both sides of the aluminum foil. After drying, rolling and vacuum drying, and aluminum lead wires are welded on with an ultrasonic welding machine to obtain positive electrode plate. The thickness of the positive electrode material layer is 160 μm and the thickness of the positive electrode current collector is 12 μm.

[0067] (2) Anode preparation: 1.7% conductive carbon black, 2.8% binder styrene-butadiene rubber, 1.5% carboxymethyl cellulose and 94% artificial graphite are dispersed in deionized water to obtain anode slurry; the anode slurry is coated on both sides of copper foil, dried, rolled and vacuum dried, and nickel leads are welded on with an ultrasonic welding machine to obtain anode plate.

[0068] (3) Preparation of non-aqueous electrolyte: Ethyl carbonate, dimethyl carbonate, ethyl methyl carbonate and ethyl acetate were mixed in a volume ratio of EC:DMC:EMC:EA=30:20:20:30. After mixing, lithium hexafluorophosphate with a concentration of 0.8 mol / L and lithium bis(fluorosulfonylimide) with a concentration of 0.25 mol / L were added to the electrolyte. 3 wt% ethylene carbonate, 0.5 wt% tris(trimethylsilyl) phosphate and additives with the mass percentages shown in Table 1 were also added.

[0069] (4) Separator preparation: a separator membrane made of polypropylene, polyethylene and polypropylene three-layer base membrane with ceramic particles coated on the base membrane; (5) The battery assembly steps are as follows: three layers of ceramic separator are placed between the positive plate and the negative plate, and then the sandwich structure composed of the positive plate, the negative plate and the separator is wound up. The wound body is flattened and placed into a prefabricated aluminum-plastic shell. The lead wires of the positive and negative electrodes are welded to nickel tabs and aluminum tabs respectively. The shell is sealed and vacuumed to obtain the cell to be injected with electrolyte. The electrolyte prepared above is injected into the cell through the injection hole. The amount of electrolyte should be enough to fill the gaps in the cell.

[0070] Then, perform the first charge routine formation as follows: charge at a constant current of 0.05 C for 2 hours, charge at a constant current of 0.2 C to 3.65 V, then discharge at a constant current of 0.2 C to 2.5 V, vent the gas, shape and seal the container, then charge at a constant current of 0.2 C to 3.65 V, let it rest for 0.5 hours, and then discharge at a constant current of 0.2 C to 2.5 V.

[0071] Examples 2-31 Examples 2-31 illustrate the lithium-ion battery and its preparation method disclosed in this invention, including most of the operational steps in Example 1, with the following differences: The selection and content of additives, the mass percentage of Si element in the positive electrode current collector, and the thickness of the positive electrode material layer and the positive electrode current collector are shown in Examples 2 to 31 in Table 1.

[0072] Comparative Examples 1-10 Comparative Examples 1-10 are used to illustrate the lithium-ion battery and its preparation method disclosed in this invention, including most of the operation steps in Example 1, the difference being: The selection and content of additives, the mass percentage of Si element in the positive electrode current collector, and the thickness of the positive electrode material layer and the positive electrode current collector are shown in Comparative Examples 1 to 10 in Table 1. Comparative Example 7 did not contain vinylene carbonate or tris(trimethylsilyl)phosphate.

[0073] Performance testing The lithium-ion batteries prepared above were subjected to the following performance tests: (1) High-temperature storage performance At room temperature, the battery was discharged at a constant current of 0.5 C to 2.5 V, then charged at a constant current and voltage of 0.5 C to 3.65 V with a cutoff current of 0.05 C. After resting for 5 min, it was discharged at a constant current of 0.5 C to 2.5 V, and the discharge capacity was recorded as C0. After resting for 5 min, it was charged at a constant current of 0.5 C to 3.65 V with a cutoff current of 0.05 C. After resting for 10 min, it was discharged at a constant current of 0.5 C, with a cutoff capacity of 0.5 C. After resting for 30 min, it was discharged at a constant current of 2 C I for 10 s, and the discharge start voltage U1 and discharge cutoff voltage U2 were recorded. Subsequently, it was charged at a constant current and voltage of 0.5 C to 3.65 V with a cutoff current of 0.05 C. The initial volume V0 was measured, and then the battery was placed in a 60℃ constant temperature test chamber. After resting for 30 days, the battery was removed and the volume V at room temperature was measured. n Discharge from 0.5 C to 2.5 V, and record the discharge capacity as C. nAfter resting for 5 minutes, charge at a constant current to 0.5 C until reaching 3.65 V, with a cutoff current of 0.05 C. Rest for 10 minutes, then discharge at a constant current of 0.5 C until the cutoff capacity is 0.5 C. After resting for 30 minutes, discharge at a constant current of 2 C I for 10 seconds, and record the discharge initiation voltage U. n1 and discharge cutoff voltage U n2 , 30-day storage capacity retention rate (%) = (C0 - C) n ) / C0*100% Volume expansion rate (%) after 30 days of storage = (V n -V0) / V0*100% Initial DCIR: R0 = (U1 - U2) / I * 1000, unit: milliohms 30-day DCIR storage: R n =(U n1 -U n2 ) / I*1000, unit milliohms Impedance growth rate (%) = R n / R0*100% (2) High-temperature fast charging cycle The battery was placed in a 45°C constant temperature test chamber and charged at a constant current and voltage of 0.2 C to 3.65 V, with a cutoff current of 0.05 C. It was then allowed to rest for 5 minutes. Next, it was discharged at a constant current of 0.2 C to 2.5 V, and allowed to rest for 5 minutes. This cycle was repeated twice. Then, the battery was charged at a constant current of 3 C to 80% SOC, switched to a constant current and voltage of 1 C to 3.65 V, with a cutoff current of 0.05 C, and allowed to rest for 10 minutes. Finally, it was discharged at a constant current of 1 C to 2.5 V, and allowed to rest for 10 minutes. The discharge capacity was recorded as C0. This cycle was repeated, and the discharge capacity after 1000 cycles was recorded as C0. n .

[0074] High-temperature cycling capacity retention rate (%) after 1000 cycles = C n / C0*100%.

[0075] The test results obtained from Examples 1-31 and Comparative Examples 1-10 are filled in Table 2.

[0076] Table 2 The test results from Examples 1-22 and Comparative Examples 1-6 show that the positive electrode current collector contains 0.01%-0.2% Si element, and the non-aqueous electrolyte simultaneously adds sulfur-containing additives (0.05%-2%) and fluoroethylene carbonate (0.05%-3%) as shown in Structural Formula 1. The three components work synergistically to significantly improve the high-temperature storage capacity retention rate of lithium-ion batteries, reduce the volume expansion rate and impedance growth rate, and improve the stability of high-temperature fast charging cycles. If any key component is missing (does not contain Si element, sulfur-containing additives, or fluoroethylene carbonate), the high-temperature performance of the battery will deteriorate significantly, resulting in problems such as accelerated capacity decay, increased gas production, and a surge in impedance. Furthermore, the content of each key component must be controlled within an appropriate range. Exceeding the range (such as excessively high Si content, excessively high / low content of sulfur-containing additives or fluoroethylene carbonate) will lead to poor processing performance or impaired fast charging performance.

[0077] As can be seen from the test results of Example 1 and Comparative Example 7, in the battery system provided by the present invention, the addition of auxiliary additives such as vinylene carbonate and tris(trimethylsilyl)phosphate results in higher high-temperature storage capacity retention, lower volume expansion rate and impedance growth rate, and better high-temperature fast charging cycle capacity retention. This indicates that the auxiliary additives can further suppress gas generation, impedance increase and capacity degradation of the battery at high temperatures.

[0078] As can be seen from the test results of Examples 23-31 and Comparative Examples 8 and 9, when Compound 2 is used as a sulfur-containing additive, it can also effectively optimize the high-temperature performance of the battery, improve the high-temperature storage capacity retention rate, reduce the gas generation rate and impedance growth, and improve the high-temperature fast charging cycle stability when used in conjunction with Si-containing positive electrode current collectors and fluoroethylene carbonate, achieving a synergistic effect comparable to that of Compound 1.

[0079] The test results of Example 1 and Comparative Example 10 show that, compared with vinyl sulfate, the sulfur-containing additive shown in Structural Formula 1 of this invention has a higher high-temperature storage capacity retention rate, lower volume expansion rate and impedance growth rate, and better high-temperature fast-charge cycle capacity retention rate. This indicates that the sulfur-containing additive shown in Structural Formula 1 of this invention has a better synergistic effect with the Si element in the positive electrode current collector and the fluoroethylene carbonate in the electrolyte. It is speculated that this is because the sulfur-containing additive of this application has a polycyclic structure. Compared with the monocyclic structure of vinyl sulfate, the polycyclic structure opens its rings and participates in the formation of the interface film on the electrode surface. The resulting interface film composition is 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.

[0080] Examples 32-38, Comparative Examples 11-12 Examples 32-38 and Comparative Examples 11-12 are used to illustrate the lithium-ion battery and its preparation method disclosed in this invention, including most of the operation steps in Example 1, the difference being: The thickness of the positive electrode current collector, the thickness of the positive electrode material layer, and the ratio of the thickness of the positive electrode material layer to the thickness of the positive electrode current collector are shown in Examples 32-38 in Table 3.

[0081] Performance testing The lithium-ion batteries prepared in the above embodiments were subjected to performance tests according to the performance test method of Example 1, and the test results were filled in Table 3.

[0082] Table 3 The test results from Examples 1, 32-38, and Comparative Examples 11-12 show that in the battery system provided by this invention, the thickness ratio of the positive electrode material layer to the positive electrode current collector affects the processing performance and high-temperature performance of the lithium-ion battery. When this ratio is within the suitable range of 7-22, the battery can maintain excellent high-temperature storage performance (manifested as high capacity retention, low volume expansion rate, and impedance growth rate) and stable high-temperature fast-charging cycle performance, and can successfully complete electrode processing and battery assembly. If the ratio is lower than 7, the electrode processing performance will deteriorate, resulting in winding breakage and making it impossible to manufacture batteries normally. If the ratio exceeds 22, the electrode processing performance will drop significantly, making it impossible to manufacture batteries. Even if batteries can be manufactured, their high-temperature performance is not better than that of products within the suitable ratio range, making it difficult to achieve a good balance between structural stability and high-temperature performance.

[0083] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A lithium-ion battery, characterized in that, The electrolyte comprises a positive electrode, a negative electrode, and a non-aqueous electrolyte. The positive electrode includes a positive electrode current collector and a positive electrode material layer disposed on the positive electrode current collector. The positive electrode material layer includes a positive electrode active material, which includes a lithium phosphate-containing material. The positive electrode current collector contains silicon (Si) element, and the mass percentage of Si element in the positive electrode current collector is 0.01%-0.2%. The non-aqueous electrolyte includes a lithium salt, additives, and a non-aqueous organic solvent. The additives include fluoroethylene carbonate and sulfur-containing additives. The sulfur-containing additives include one or two of the following compounds: Based on the weight of the non-aqueous electrolyte as 100%, the mass percentage of the sulfur-containing additive is 0.05% to 2%, and the mass percentage of the fluoroethylene carbonate is 0.05% to 3%.

2. The lithium-ion battery according to claim 1, characterized in that, Based on the weight of the non-aqueous electrolyte as 100%, the mass percentage of the sulfur-containing additive is 0.2% to 1.5%.

3. The lithium-ion battery according to claim 1 or 2, characterized in that, Based on the weight of the non-aqueous electrolyte as 100%, the mass percentage of the fluoroethylene carbonate is 0.2% to 2%.

4. The lithium-ion battery according to any one of claims 1 to 3, characterized in that, The mass percentage of Si element in the positive electrode current collector is 0.02%-0.1%.

5. The lithium-ion battery according to any one of claims 1 to 3, characterized in that, The thickness of the positive electrode current collector is 8~20μm; and / or, The thickness of the positive electrode material layer is 130~240μm.

6. The lithium-ion battery according to any one of claims 1 to 3, characterized in that, The ratio of the thickness of the positive electrode material layer to the thickness of the positive electrode current collector is 7~22.

7. The lithium-ion battery according to any one of claims 1 to 3, characterized in that, The positive current collector is aluminum foil or aluminum alloy foil.

8. The lithium-ion battery according to any one of claims 1 to 3, characterized in that, The lithium 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 β A 1-α-β PO 4-n G n At least one of the following materials, wherein 0.9≤r≤1.1, 0≤α≤0.8, 0.2≤β≤1, 0.2≤α+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, Ni, Co, Ga, Sn, Sb, Ge and W, and G includes one or more of N, F, S and Cl.

9. The lithium-ion battery according to any one of claims 1 to 3, characterized in that, The non-aqueous organic solvent includes linear carbonates and / or carboxylic acid esters, wherein the linear carbonates include one or more of dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, dipropyl carbonate, and methyltrifluoroethyl carbonate, and the carboxylic acid esters include one or more of methyl formate, ethyl formate, ethyl acetate, propyl acetate, butyl acetate, ethyl propionate, propyl propionate, butyl propionate, and ethyl difluoroacetate.

10. The lithium-ion battery according to any one of claims 1 to 3, characterized in that, The non-aqueous electrolyte also contains auxiliary additives, which include one or more of the following: vinylene carbonate, vinyl sulfate, 1,3-propanesulfonate lactone, methanedisulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium difluorobis(oxalate) phosphate, lithium bis(oxalate) borate, lithium tetrafluoroborate, tris(trimethylsilyl) phosphate, tris(trimethylsilyl) borate, tripropynyl phosphate, tetravinylsilane, and divinyldimethylsilane.

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