A lithium-ion battery

Abstract

This invention relates to the field of energy storage electronic components, specifically to a lithium-ion battery. The lithium-ion battery includes a positive electrode, a negative electrode, and a separator. The negative electrode includes a negative electrode current collector and a negative electrode active material layer disposed on the surface of the current collector. The non-aqueous electrolyte includes a lithium salt, an organic solvent, and a first additive. The organic solvent includes dimethyl carbonate and a low-viscosity solvent, wherein the low-viscosity solvent is composed of at least one of methyl acetate, ethyl acetate, and ethyl propionate. The lithium-ion battery satisfies the following conditions: 0.05 ≤ 4, 0.01 ≤ a ≤ 2, 25 ≤ b ≤ 55, 4 ≤ c ≤ 30, 10 ≤ d ≤ 30. The lithium-ion battery of this invention can fully utilize the advantages of carboxylic acid ester solvents in increasing battery power, while greatly suppressing their degradation of high-temperature performance and thermal runaway, achieving a balance between high power performance and high safety performance.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and more specifically to a lithium-ion battery that combines high power and high safety. Background Technology

[0002] Lithium-ion batteries, with their advantages of high energy density, lightweight design, and long cycle life, have become the core energy carrier for portable electronic devices, new energy vehicles, and large-scale energy storage systems. With the rapid development of the new energy industry, end-use applications are placing increasingly higher demands on the performance of lithium-ion batteries, especially in high-power scenarios where fast charging and discharging capabilities have become a key indicator for evaluating battery performance.

[0003] To improve the power performance of lithium-ion batteries (the charge / discharge rate of a lithium-ion battery directly reflects its power performance, and internal resistance is one of the most critical indicators determining power performance), existing technologies typically optimize the following aspects: Material optimization: improving the microstructure of positive and negative electrode materials (such as high-nickel ternary positive electrodes and silicon-carbon composite negative electrodes), enhancing the ionic conductivity and thermal stability of the electrolyte, or using highly conductive additives to reduce internal resistance; Structural design: optimizing electrode coating processes, current collector designs (such as ultra-thin copper foil), or internal battery heat dissipation structures to improve current distribution and thermal management performance; Process improvement: such as precisely controlling electrode compaction density and optimizing electrolyte injection processes to enhance electrolyte wettability.

[0004] However, during fast charge and discharge cycles, the degradation of the battery's internal structure becomes particularly prominent, mainly manifested as: lithium dendrite growth: lithium is easily deposited on the negative electrode surface during high-current charging, leading to the rupture and regeneration of the SEI film and accelerating the loss of active lithium; increased heat generation: ohmic heat and polarization heat accumulate during high-rate charging and discharging, which may cause local overheating or even thermal runaway; mechanical stress damage: repeated expansion / contraction of electrode materials leads to particle pulverization and current collector deformation, which in turn causes an increase in internal resistance and capacity decay.

[0005] These problems not only shorten battery cycle life but may also cause safety hazards such as internal short circuits and gas bulging, severely limiting the application of lithium-ion batteries in high-power scenarios. Therefore, how to achieve a synergistic improvement in fast charging and discharging, long life, and high safety while ensuring high energy density has become a key challenge that current lithium-ion battery technology urgently needs to overcome. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention provides a lithium-ion battery that combines low-temperature high power and high safety.

[0007] The present invention adopts the following technical solution:

[0008] A lithium-ion battery includes a positive electrode, a negative electrode, and a non-aqueous electrolyte;

[0009] The negative electrode includes a negative electrode current collector and a negative electrode material layer disposed on the surface of the negative electrode current collector, wherein the porosity of the negative electrode material layer is d%

[0010] The non-aqueous electrolyte comprises lithium salt, organic solvent, and a first additive;

[0011] The organic solvent includes dimethyl carbonate and a low-viscosity solvent, wherein the low-viscosity solvent is composed of at least one of methyl acetate, ethyl acetate and ethyl propionate;

[0012] The first additive comprises a compound represented by structural formula 1:

[0013]

[0014] Structural Formula 1

[0015] 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;

[0016] Based on the mass of the non-aqueous electrolyte, the mass percentage of the first additive is a%, the mass percentage of the dimethyl carbonate is b%, and the mass percentage of the low-viscosity solvent is c%.

[0017] The lithium-ion battery meets the following conditions:

[0018] 0.05≤ ≤4, 0.01≤a≤2, 25≤b≤55, 4≤c≤30, 10≤d≤30.

[0019] In the lithium-ion battery provided by this invention, a sulfur-containing compound with a specific structure is used as the first additive, and dimethyl carbonate and a low-viscosity solvent are used as non-aqueous organic solvents. Through extensive research, the inventors discovered that by controlling the mass percentages of the first additive (a), dimethyl carbonate (b), and low-viscosity solvent (c) in the non-aqueous electrolyte, and ensuring the porosity (d) of the negative electrode material layer satisfies 0.05 ≤ When the values ​​are ≤4, 0.01≤a≤2, 25≤b≤55, 4≤c≤30, and 10≤d≤30, the synergistic effect between additives, solvents, and negative electrode materials can be fully utilized, enabling lithium-ion batteries to possess both high power performance and high safety performance. It is speculated that low-viscosity solvents selected from methyl acetate, ethyl acetate, and ethyl propionate have lower freezing points and viscosities compared to linear carbonates, which can significantly improve battery power performance. However, ethyl acetate and ethyl propionate have lower boiling points, which degrades high-temperature performance and further triggers thermal runaway. To address this issue, on the one hand, by controlling the content of DMC and low-viscosity solvents in the non-aqueous electrolyte, good power performance of the battery is ensured. On the other hand, by introducing an appropriate amount of excellent positive and negative electrode film-forming additives as the first additive, a protective film with excellent thermal stability is formed on the surface of the positive and negative electrodes. This film can suppress side reactions generated by the electrolyte at the positive and negative electrodes, thereby protecting the stability of the structure of the positive and negative electrode active materials and preventing corrosion and oxidation of the electrode materials at high temperatures. It also reduces the continuous rise in temperature during charging and discharging, thereby reducing the risk of thermal runaway. Furthermore, by controlling the porosity of the negative electrode material layer, the heat generated during battery charging and discharging is promptly conducted and dissipated.

[0020] when When <0.05, the interface film is incomplete, electrolyte decomposition is accelerated, and battery safety performance is insufficient; when When the value is greater than 4, the interface impedance is too high, the electrode structure is loose, and the battery power performance is insufficient.

[0021] Preferably, the mass percentages of the first additive (a), dimethyl carbonate (b), low-viscosity solvent (c), and the porosity (d) of the negative electrode material layer in the non-aqueous electrolyte satisfy a0.05 ≤ 0.05. ≤1.8.

[0022] The power performance of lithium-ion batteries is closely related to their kinetic processes. During charging, the Li... + The electrolyte, acting as the "blood" of the lithium-ion battery, transports energy from the positive electrode to the negative electrode via the electrolyte. +Transport, interface stability, SEI film formation, and desolvation processes are inextricably linked. High-kinetic solvent design of the electrolyte can significantly improve the power performance of lithium-ion batteries. Dimethyl carbonate (DMC), due to its low viscosity and high dielectric constant, exhibits good power performance at both room and high temperatures; however, its high melting point (2-4°C) makes it prone to solidification at low temperatures, degrading the battery's low-temperature power performance. Methyl acetate, ethyl acetate, and ethyl propionate, on the other hand, have lower melting points and viscosities, resulting in excellent low-temperature power performance, but poor high-temperature performance. This invention addresses this by compounding DMC with methyl acetate, ethyl acetate, and ethyl propionate, and by studying and controlling their proportions within a suitable range, specifically enabling the battery to achieve excellent power performance over a wide temperature range. When the mass percentage of DMC (b) in the non-aqueous electrolyte, and the mass percentage of the low-viscosity solvent (c) (b / c < 1) are related, it indicates that the DMC content is too low or the ethyl acetate and ethyl propionate content is too high, leading to a decrease in high-temperature performance. If the b-value is too small, it will be detrimental to the processing of lithium-ion batteries. Dimethyl carbonate, as a low-viscosity, high-dielectric solvent, mainly plays a role in regulating the overall fluidity and ion conduction efficiency of the electrolyte. When the dimethyl carbonate content is insufficient, the viscosity of the electrolyte will increase significantly, leading to a decrease in the liquid penetration rate during the injection process. Especially in the lithium-ion battery winding process, the electrolyte will have difficulty in quickly and uniformly wetting the microporous structure of the electrode material and the separator, which may cause problems such as electrode drying and increased interfacial impedance. In addition, the low boiling point of dimethyl carbonate can help the electrolyte achieve a moderate evaporation balance during the drying process. When its content is insufficient, the solvent system will be unbalanced, which may lead to abnormal solvent residue in the electrode after drying, thereby affecting the dimensional stability and interfacial adhesion during the lithium-ion battery winding process. If the c value is too high, it will threaten the safety performance of lithium-ion batteries. Methyl acetate, ethyl acetate, and ethyl propionate usually have high volatility and low thermal stability. When the proportion of these components in the electrolyte system is too high, the amount of evaporation of the electrolyte may surge due to changes in ambient temperature during the electrolyte injection process, leading to loss of control over the injection volume. During the battery charging and discharging process, excessive amounts of methyl acetate, ethyl acetate, and ethyl propionate will exacerbate the thermal decomposition reaction of the electrolyte and reduce the battery's safety threshold.

[0023] A sulfur-containing compound with a specific structure is used as the first additive. This additive is a high-performance film-forming additive for both positive and negative electrodes. During the first charge and discharge of the battery, it can form a uniform, moderately thick, and thermally stable interfacial film on the surfaces of the positive and negative electrodes, thereby suppressing the temperature rise of the battery during charge and discharge. When the mass percentage a% of the first additive is too high, the resulting interfacial film is thicker, and the cell interface impedance increases simultaneously. This not only negatively impacts the battery's rate performance but also generates more Joule heat. When the mass percentage a% of the first additive is too low, it is difficult to form a complete interfacial film on the surfaces of the positive and negative electrodes, failing to effectively protect the positive and negative electrode interfaces. Specifically, in some embodiments of the present invention, the mass percentage a% of the first additive in the non-aqueous electrolyte is 0.01%, 0.015%, 0.02%, 0.025%, 0.03%, 0.05%, 0.07%, 0.09%, 0.1%, 0.2%, 0.3%, 0.5%, 0.7%, 0.9%, 1%, 1.1%, 1.3%, 1.5%, 1.7%, 1.9%, 2%, or a range of any two of these values. Preferably, the mass percentage a% of the first additive satisfies: 0.1 ≤ a ≤ 1.

[0024] Dimethyl carbonate (DMC) is an organic solvent with low viscosity and high dielectric constant used in lithium-ion batteries. It exhibits good power performance at both room and high temperatures, but its high melting point results in insufficient power performance at low temperatures. When the mass percentage (b%) of DMC in the electrolyte is too high, the overall thermal stability of the electrolyte decreases significantly. Under overcharge or high-temperature conditions, excess DMC will undergo a chain decomposition reaction first, decomposing into highly active intermediates that may react with the positive electrode to cause thermal runaway, leading to a significant decrease in the thermal runaway initiation temperature. Simultaneously, high DMC content can dissolve the protective film on the positive electrode surface, directly exposing active metal sites and accelerating the dissolution of transition metals, ultimately resulting in poor battery safety performance. When the mass percentage (b%) of dimethyl carbonate in the electrolyte is too low, it is detrimental to the processing of lithium-ion batteries. As a low-viscosity, high-dielectric solvent, dimethyl carbonate mainly functions to regulate the overall fluidity and ion conduction efficiency of the electrolyte. When the dimethyl carbonate content is insufficient, the viscosity of the electrolyte will increase significantly, leading to a decrease in the liquid penetration rate during the injection process. Especially in the lithium-ion battery winding process, the electrolyte will have difficulty quickly and uniformly wetting the microporous structure of the electrode material and the separator, which may cause problems such as electrode drying and increased interfacial impedance. In addition, the low boiling point of dimethyl carbonate can help the electrolyte achieve a moderate evaporation balance during drying. When its content is insufficient, the solvent system will be unbalanced, which may lead to abnormal solvent residue after the electrode is dried, thereby affecting the dimensional stability and interfacial adhesion during the lithium-ion battery winding process. Specifically, in some embodiments of the present invention, the mass percentage b% of dimethyl carbonate solvent in the non-aqueous electrolyte is 25%, 28%, 30%, 32%, 34%, 35%, 36%, 38%, 40%, 41%, 43%, 45%, 47%, 49%, 50%, 51%, 53%, 55%, or any combination of these values. Preferably, the mass percentage b% of dimethyl carbonate satisfies: 30 ≤ b ≤ 45.

[0025] Methyl acetate, ethyl acetate, and ethyl propionate are commonly used organic solvents with low melting points and viscosities in battery electrolytes, exhibiting excellent power performance at low temperatures. However, when the mass percentage (c%) of these low-viscosity solvents in the electrolyte is too high, it poses a threat to the safety performance of lithium-ion batteries. Methyl acetate, ethyl acetate, and ethyl propionate typically have high volatility and low thermal stability. When these components constitute a high proportion in the electrolyte system, the amount of evaporation may surge during the electrolyte injection process due to changes in ambient temperature, leading to loss of accuracy in the injection volume. During battery charging and discharging, excessive carboxylic acid esters can exacerbate the thermal decomposition reaction of the electrode solution, especially under overcharge or high-temperature conditions. The carbon dioxide and methane gases produced during decomposition may accelerate the gas generation rate inside the battery, leading to risks such as battery casing expansion and separator rupture, thus lowering the battery's safety threshold. When the mass percentage (c%) of the low-viscosity solvent in the electrolyte is too low, the low-temperature power performance of the lithium-ion battery will significantly decrease. This is because the overall polarity of the solvent in the non-aqueous electrolyte decreases, leading to a reduction in lithium salt dissociation efficiency, a sharp decrease in the concentration of free lithium ions and ionic conductivity, and a significant increase in charge transfer resistance. Simultaneously, the electrolyte viscosity increases, reducing the ability to wet the negative electrode pores, lengthening the lithium-ion diffusion path, and exacerbating concentration polarization. Furthermore, it results in an excessively high proportion of rigid inorganic phase in the SEI film, making it prone to embrittlement and cracking at low temperatures, triggering continuous electrolyte permeation side reactions. Specifically, in some embodiments of the present invention, the mass percentage (c%) of the low-viscosity solvent in the non-aqueous electrolyte is 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, or any combination of these values. Preferably, the mass percentage c% of the low viscosity solvent satisfies: 8 ≤ c ≤ 20.

[0026] Compared to other carboxylic acid esters, methyl acetate, ethyl acetate, and ethyl propionate not only have lower viscosity, which reduces the resistance to lithium ion movement and helps improve the ionic conductivity of the electrolyte, but also help stabilize the cathode structure. Therefore, while improving the fast-charging performance of lithium-ion batteries, they can also improve their high-temperature performance, thereby enhancing the overall performance of electrochemical devices.

[0027] In a preferred embodiment of the present invention, the mass ratio of dimethyl carbonate to low-viscosity solvent in the non-aqueous electrolyte is (1~8):1. By controlling the mass ratio of dimethyl carbonate to low-viscosity solvent to meet the above requirements, the battery can still maintain good power performance at low temperatures. When the mass ratio of dimethyl carbonate to low-viscosity solvent in the non-aqueous electrolyte is less than 1:1, it indicates that the content of dimethyl carbonate (DMC) is too low and the content of low-viscosity solvent is too high, resulting in a decrease in high-temperature performance. When the mass ratio of dimethyl carbonate to low-viscosity solvent in the non-aqueous electrolyte is greater than 8:1, it indicates that the content of dimethyl carbonate (DMC) is too high and the content of low-viscosity solvent is too low. Dimethyl carbonate has a high melting point (2~4°C) and is prone to solidification at low temperatures. Methyl acetate, ethyl acetate, and ethyl propionate, which are used as low-viscosity solvents, have lower melting points and viscosities and excellent low-temperature power performance. Therefore, too much dimethyl carbonate or too little low-viscosity solvent will lead to a deterioration in the low-temperature power performance of lithium-ion batteries. By controlling the mass ratio of dimethyl carbonate to low-viscosity solvent in the non-aqueous electrolyte to (1~8):1, the high-temperature and low-temperature power performance of lithium-ion batteries can be balanced, and the operating temperature range of the batteries can be broadened. Specifically, in some embodiments of the present invention, the mass ratio of dimethyl carbonate to low-viscosity solvent in the non-aqueous electrolyte is (1~8):1, which is 1:1, 1.1:1, 1:2, 1.4:1, 1.5:1, 1.7:1, 1.9:1, 2:1, 2.5:1, 2.8:1, 3:1, 3.2:1, 3.5:1, 3.8:1, 4.1:1, 4.3:1, 4.8:1, 5:1, 5.2:1, 5.6:1, 5.8:1, 6:1, 6.3:1, 6.5:1, 6.8:1, 7.1:1, 7.5:1, 8:1, or any combination of these values. Preferably, the mass ratio of dimethyl carbonate to low-viscosity solvent in the non-aqueous electrolyte is (1.5~6):1.

[0028] The porosity (d%) of the negative electrode material layer in a lithium-ion battery is between 10% and 30%. If the negative electrode porosity is too low, the heat generated during battery charging and discharging is difficult to dissipate and conduct; conversely, if the negative electrode porosity is too high, the contact between the negative electrode active material particles decreases, the battery energy density decreases, and the wettability of the electrolyte also decreases. By controlling the porosity of the negative electrode material layer between 10 ≤ d ≤ 30, both good safety performance and high energy density can be achieved. Specifically, the porosity (d%) of the negative electrode material layer of the lithium-ion battery is 10%, 12%, 15%, 18%, 20%, 21%, 23%, 25%, 27%, 29%, 30%, or any combination of these values; preferably, the porosity (d%) of the negative electrode material layer satisfies: 15 ≤ d ≤ 25.

[0029] 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.

[0030] As an example, the first additive is selected from one or more of the following compounds:

[0031]

[0032] 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.

[0033] In some embodiments, 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.

[0034] As an example, the first additive is selected from one or more of the following compounds:

[0035]

[0036] The first 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 can improve the strength of the interface film structure and thus help improve its high-temperature stability.

[0037] Specifically, in some embodiments of the present invention, the non-aqueous electrolyte further includes auxiliary additives, which include at least one of the following: cyclic sulfate compounds, sulfonyl lactone compounds, cyclic carbonate compounds, phosphate compounds, borate compounds, and nitrile compounds, other than the compound shown in structural formula 1.

[0038] In some preferred embodiments, the cyclic sulfate compounds other than those shown in structural formula 1 include at least one of 4-methyl vinyl sulfate, vinyl sulfate, and propylene sulfate.

[0039] 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.

[0040] 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:

[0041]

[0042] Structural Formula 2

[0043] 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;

[0044] In some preferred embodiments, the compound represented by structural formula 2 includes at least one of the compounds represented by compounds 2-1 to 2-6 below:

[0045]

[0046] In some preferred embodiments, the phosphate ester compound includes at least one of the compounds represented by structural formula 3:

[0047]

[0048] Structural Formula 3

[0049] 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; 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 preferred embodiments, the nitrile compound includes at least one selected from succinic anhydride, glutaronitrile, ethylene glycol bis(propionitrile) ether, hexanetrionitrile, adiponitrile, heptanonitrile, octanilide, nonadionitrile, and sebacate.

[0052] In some embodiments, the content of the auxiliary additive is 0.01% to 10% based on the mass of the non-aqueous electrolyte. 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%, 6%, 7%, 8%, 9%, 10%, or any combination of these values.

[0053] Specifically, in some embodiments of the present invention, the lithium salt includes LiPF6, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, LiPO2F2, LiBF4, LiBOB, LiSbF6, LiAsF6, LiCF3SO3, LiDFOB, LiDFOP, LiN(SO2CF3)2, LiC(SO2CF3)3, LiN(SO2C2F5)2, LiCl, LiBr, LiI, LiClO4, and LiB 10 Cl 10 At least one of LiAlCl4, lithium chloroborane, and lithium tetraphenylborate.

[0054] 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.

[0055] The negative electrode material layer includes a negative electrode active material. Specifically, in some embodiments of the present invention, the negative electrode active material is any one or more of silicon-based materials and carbon materials. The silicon-based material is selected from one or more of silicon materials, silicon oxide materials, silicon-carbon materials, and silicon alloy materials; preferably, the silicon material is nano-silicon material; preferably, the silicon oxide material is SiOx material, wherein 0≤x<2; preferably, the silicon-carbon material is: a silicon-based material containing silicon and carbon materials, and / or a silicon-based material containing SiOy and carbon materials, wherein 0≤y<2; preferably, the silicon alloy material is Mg2Si alloy material and / or Fe2Si alloy material. The carbon material is selected from one or more of artificial graphite, natural graphite, composite graphite, graphene, and hard carbon; preferably, the carbon material is artificial graphite material.

[0056] Specifically, in some embodiments of the present invention, the negative electrode material layer further includes a negative electrode binder and a negative electrode conductive agent.

[0057] 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.

[0058] The negative electrode conductive agent includes one or more of conductive carbon black, conductive carbon spheres, conductive graphite, conductive carbon fiber, carbon nanotubes, graphene, or reduced graphene oxide.

[0059] Specifically, in some embodiments of the present invention, the negative electrode current collector includes a metallic material capable of conducting electrons, preferably, the negative electrode current collector includes one or more of aluminum, nickel, tin, copper, and stainless steel.

[0060] Specifically, in some embodiments of the present invention, the positive electrode includes a positive electrode material layer comprising a positive electrode active material, wherein the positive electrode active material is a lithium transition metal oxide. More specifically, the lithium transition metal oxide includes at least one of a nickel-containing ternary material, a phosphate material, and a lithium cobalt oxide material, wherein:

[0061] The nickel-containing ternary material includes materials with the molecular formula Li. q Ni x Co y M 1-x-y O 2-g Rg 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 following materials, wherein 0.9≤q≤1.2, 0.5≤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;

[0062] 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 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≤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;

[0063] The lithium cobalt oxide material includes lithium cobalt oxide or lithium cobalt oxide modified by doping and / or coating with any one or more elements selected from Ni, Mn, Mg, Al, Zr, W, F, B, Cr, Mo and rare earth elements.

[0064] Preferably, the positive electrode active material includes LiCoO2, LiFePO4, and 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 0.1O2, 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, LiNi 0.5 Co 0.2 Al 0.3 One or more of O2.

[0065] Specifically, in some embodiments of the present invention, the positive electrode further includes a positive electrode current collector, and the positive electrode material layer is disposed on the surface of the positive electrode current collector. The positive electrode current collector includes a metallic material capable of conducting electrons. Preferably, the positive electrode current collector includes one or more of aluminum, nickel, tin, copper, and stainless steel.

[0066] Specifically, in some embodiments of the present invention, the positive electrode 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 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 positive 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.

[0067] Specifically, in some embodiments of the present invention, in the lithium-ion battery, the positive electrode and the negative electrode are stacked, and a separator is disposed between the positive electrode and the negative electrode for isolation. The separator can be a conventional separator, such as a ceramic separator, a polymer separator, a non-woven fabric separator, an inorganic-organic composite separator, etc., 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 separators.

[0068] Specifically, in some embodiments of the present invention, the battery casing is selected from one of steel casing, aluminum casing, polypropylene (PP) plastic casing, polycarbonate (PC) plastic casing, or carbon fiber composite casing.

[0069] The lithium-ion battery provided by this invention comprehensively considers electrolyte additives, organic solvents, and battery design. It incorporates a first additive, dimethyl carbonate, ethyl acetate, and ethyl propionate solvents into a non-aqueous electrolyte. Furthermore, by adjusting the relationship between the mass percentages (a) of the first additive, (b) of dimethyl carbonate, (c) of the low-viscosity solvent, and (d) of the porosity of the negative electrode material layer in the non-aqueous electrolyte, the desired result is 0.05 ≤ ≤4, 0.01≤a≤2, 25≤b≤55, 4≤c≤30, 10≤d≤30; This allows for the full utilization of the synergistic effect between the first additive, dimethyl carbonate, ethyl acetate, and ethyl propionate solvents, and the negative electrode porosity, enabling lithium-ion batteries to possess both high power performance and high safety performance. Dimethyl carbonate exhibits good power performance at both room and high temperatures, while methyl acetate, ethyl acetate, and ethyl propionate demonstrate excellent power performance at low temperatures. Combining dimethyl carbonate with ethyl acetate and ethyl propionate can achieve good power performance over a wide temperature range. Furthermore, by adding the first additive to the non-aqueous electrolyte and adjusting the amount of the first additive and the porosity of the negative electrode material layer, a suitable match is achieved. This ensures that the electrolyte easily penetrates the pores while forming a complete and dense interfacial film on the positive and negative electrode surfaces, guaranteeing timely heat dissipation with appropriate negative electrode porosity, thus balancing power and safety performance. Detailed Implementation

[0070] 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.

[0071] Example 1-1

[0072] The method for preparing the lithium-ion battery in this embodiment includes the following steps:

[0073] (1) Cathode preparation: High-nickel ternary cathode active material NCM811 (LiNi) was mixed at a mass ratio of 97:1.5:1.5. 0.8 Co 0.1 Mn 0.1 O2), conductive carbon black Super-P, and binder polyvinylidene fluoride (PVDF) are then dispersed in N-methyl-2-pyrrolidone (NMP) to obtain a positive electrode slurry. The slurry is uniformly coated on both sides of an aluminum foil, and after drying, calendering, and vacuum drying, a positive electrode material layer is formed on the aluminum foil. Aluminum leads are then welded on using an ultrasonic welding machine to obtain a positive electrode plate with a thickness between 120-150 μm.

[0074] (2) Anode preparation: Silicon-carbon composite material (silicon suboxide + graphite mixture), conductive carbon black Super-P, styrene-butadiene rubber (SBR) binder, and sodium carboxymethyl cellulose were mixed in a mass ratio of 94.2:1.2:3.0:1.5, and then dispersed in deionized water to obtain anode slurry. The slurry was coated on both sides of copper foil, and after drying, rolling, and vacuum drying, anode material layer (with Si content of 6%) was formed on the copper foil. Nickel leads were then welded on using an ultrasonic welding machine to obtain anode plate with a thickness of 120-150 μm. The porosity of thenode material layer was 20%.

[0075] (3) Electrolyte preparation: Ethyl carbonate (EC), dimethyl carbonate (DMC), and ethyl acetate (EA) are mixed in a certain mass ratio, and then lithium hexafluorophosphate (LiPF6) is added to a molar concentration of 1 mol / L. Then, additive compound 4 is added. Based on the mass of the non-aqueous electrolyte as 100%, the mass percentage of compound 4 is 1%, the mass percentage of dimethyl carbonate (DMC) is 45%, and the mass percentage of ethyl acetate (EA) is 20%.

[0076] (4) Membrane preparation: A three-layer membrane of polypropylene, polyethylene and polypropylene is used, with a thickness of 20 μm;

[0077] (5) Battery assembly: Place a separator between the positive plate and the negative plate, then wind the sandwich structure consisting of the positive plate, the negative plate and the separator, and then put the wound body into a cylindrical steel metal shell.

[0078] (6) Electrolyte injection and formation: The electrolyte prepared above is injected into the cell, vacuum sealed, and left to stand for 36 hours. Then, the first charge is carried out according to the following steps: 0.02C constant current charging for 30 minutes, 0.05C constant current charging for 30 minutes, 0.1C constant current charging for 120 minutes, 0.2C constant current charging for 240 minutes, with the cutoff voltage set at 3.85V for all. After resting for 1 hour and resting at room temperature for 24 hours (12 hours each in both directions), the cell is charged to 4.2V with 0.5C constant current and discharged to 2.75V with 0.2C constant current.

[0079] Examples 1-2 to 1-33 and Comparative Examples 1-1 to 1-16

[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, but differ in the following aspects: the mass percentage of the first additive in the non-aqueous electrolyte, the mass percentage of dimethyl carbonate in the non-aqueous electrolyte, the mass percentage and selection of the low-viscosity solvent in the non-aqueous electrolyte, the content of auxiliary additives in the non-aqueous electrolyte, and the porosity of the negative electrode material layer, as shown in the table below.

[0081] The performance of the lithium-ion batteries prepared in each embodiment and comparative example was tested according to the following method:

[0082] 1. 0℃ Battery DCIR Test

[0083] After the prepared battery was charged to SOC=50% by constant current at 0.5C, it was kept at constant voltage for 10 min, transferred to a high and low temperature chamber at 0℃ and left to stand for 6 h. The room temperature DCIR (0.1 / 0.2 / 0.5C) was tested according to the following steps: 0.1C constant current charging for 10s, rest for 40s, 0.1C constant current discharging for 10s, rest for 40s, 0.2C constant current charging for 10s, rest for 40s, 0.2C constant current discharging for 10s, rest for 40s, 0.5C constant current charging for 10s, rest for 40s, 0.5C constant current discharging for 10s, rest for 40s.

[0084] 2. 130℃ Hot Box Test

[0085] The fully charged battery was placed in the GX-3020-BL40 thermal shock test chamber. The chamber operated according to the set program of "heating from 25°C to 130°C at a rate of 5°C / min and then holding for 30 minutes". At the same time, the temperature and voltage channels of the "data acquisition instrument" panel began to record real-time data of the cell surface.

[0086] 3. Battery capacity retention rate at -20℃ / 3C discharge (%)

[0087] The prepared battery was charged to 4.2V at a constant current and constant voltage of 0.5C, with a cutoff current of 0.05C. It was then discharged to 2.5V at a constant current of 3C, and the discharge capacity Q1 was recorded. The battery was then charged to 4.2V at a constant current and constant voltage of 0.5C, with a cutoff current of 0.05C. It was then transferred to a high and low temperature chamber at -20℃ and left to stand for 6 hours. It was then discharged to 2.5V at a constant current of 3C, and the discharge capacity Q2 was recorded. The capacity retention rate (%) was calculated as: discharge capacity Q2 / discharge capacity Q1 * 100%.

[0088] The 0℃ battery DCIR test result reflects the battery's power performance; generally, the smaller the DCIR, the better the power performance. The 130℃ hot box test result reflects the battery's safety performance; generally, the lower the temperature, i.e., the closer to the ambient temperature (130℃), the better the safety performance. The battery's -20℃ / 3C discharge capacity retention rate reflects the battery's low-temperature performance; generally, the higher the capacity retention rate, the better the low-temperature performance.

[0089] Test results:

[0090] Table 1 shows the parameters required for the lithium-ion batteries prepared in Examples 1-1 to 1-23 and Comparative Examples 1-1 to 1-9. The differences between Examples 1-2 to 1-23 and Comparative Examples 1-1 to 1-9 and Example 1-1 lie in the relevant parameters in Table 1. The remaining parameters and preparation steps are the same as those described in Example 1-1. The specific differences are: the mass percentage of the first additive in the non-aqueous electrolyte (a%), the mass percentage of dimethyl carbonate in the non-aqueous electrolyte (b%), the mass percentage of the low-viscosity solvent in the non-aqueous electrolyte (c%), and the relationship. And the selection of low-viscosity solvents.

[0091] Table 1 also shows the test results of the initial 0°C DCIR (mΩ), 130°C hot box battery surface temperature (°C), and -20°C / 3C discharge capacity retention (%) of the batteries in Examples 1-1 to 1-23 and Comparative Examples 1-1 to 1-9.

[0092] Table 1

[0093]

[0094]

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

[0096] As can be seen from the test results of Examples 1-1 to 1-23 and Comparative Examples 1-1 to 1-9 in Table 1, the lithium-ion battery provided in this invention uses a compound with a specific structure as the first additive in its non-aqueous electrolyte, and dimethyl carbonate and a low-viscosity solvent as the non-aqueous organic solvent. Furthermore, by controlling the mass percentages of the first additive (a), dimethyl carbonate (b), and low-viscosity solvent (c) in the non-aqueous electrolyte, and the porosity (d) of the negative electrode material layer, the battery satisfies 0.05 ≤ When the values ​​are ≤4, 0.01≤a≤2, 25≤b≤55, 4≤c≤30, and 10≤d≤30, the synergistic effect between additives, solvents, and negative electrode materials can be fully utilized, enabling lithium-ion batteries to achieve both high power performance and high safety performance.

[0097] As can be seen from the test results of Examples 1-1 and Comparative Examples 1-1 to 1-9, when any one or more of the following parameters in the non-aqueous electrolyte—a) the mass percentage of the first additive, b) the mass percentage of dimethyl carbonate, c) the mass percentage of the low-viscosity solvent, and d) the porosity of the negative electrode material layer—do not meet the specified range, or the relationship between them is not met, the test results will be affected. If the values ​​are too high or too low, the various parameters cannot achieve a synergistic effect, and the risk of thermal runaway cannot be effectively mitigated. Therefore, it is impossible to balance the high power and high safety performance of lithium-ion batteries.

[0098] When the mass percentages of the first additive (a), dimethyl carbonate (b), and low-viscosity solvent (c) in the non-aqueous electrolyte further satisfy 0.05 ≤ When the values ​​are ≤1.8, 0.1≤a≤1, 25≤b≤50, 8≤c≤20, and 15≤d≤25, the resulting lithium-ion battery can significantly improve battery power performance while better reducing the risk of thermal runaway caused by continuous temperature rise during battery charging and discharging. The first additive can also better provide a stable, complete, and excellent positive and negative electrode interface film, protecting the positive and negative electrodes of the battery, thereby further improving the power performance and safety performance of the lithium-ion battery.

[0099] A comparison of the test results from Examples 1-1 to 1-21 and Examples 1-22 to 1-23 shows that further limiting the mass ratio of dimethyl carbonate to low-viscosity solvent to (1~8):1 enables lithium-ion batteries to achieve excellent power performance over a wide temperature range, especially maintaining good power performance at low temperatures. Furthermore, when the mass ratio of dimethyl carbonate to a low-viscosity solvent containing both sulfate and carbonate esters is further satisfied to (1.5~6):1, the battery's power performance at low temperatures is even more outstanding.

[0100] Table 2 shows the test results of the initial 0°C DCIR (mΩ), 130°C hot box battery surface temperature (°C), and -20°C / 3C discharge capacity retention (%) of the lithium-ion batteries prepared in Examples 1-1 and Examples 1-24 to 1-27. The difference between Examples 1-24 to 1-27 and Example 1-1 is that the first additive type shown in Table 2 is the same as that in Example 1-1.

[0101] Table 2

[0102]

[0103] As shown in Table 2, when the mass percentages of the first additive (a), dimethyl carbonate (b), low-viscosity solvent (c), and negative electrode material layer (d) in the non-aqueous electrolyte of the lithium-ion battery meet the corresponding conditions, using any compound containing both sulfate and carbonate groups as the first additive can ensure a high addition amount of low-viscosity solvent, improve battery power performance, prevent corrosion and oxidation of the electrode material at high temperatures, and prevent the battery from continuously heating up during charging and discharging, allowing the generated heat to be dissipated and conducted in a timely manner. This enables the lithium-ion battery to possess both high power performance and high safety performance. This demonstrates that the lithium-ion battery system of the present invention is universally applicable to different compounds containing both sulfate and carbonate groups as the first additive.

[0104] Table 3 shows the test results of the initial 0°C DCIR (mΩ), 130°C hot box battery surface temperature (°C), and -20°C / 3C discharge capacity retention rate (%) of the lithium-ion batteries prepared in Examples 1-1 and Examples 1-28 to 1-30. The difference between Examples 1-28 to 1-30 and Example 1-1 is that the auxiliary additives and their contents are shown in Table 3, while the other parameters and preparation steps are the same as those described in Example 1-1.

[0105] Table 3

[0106]

[0107] As shown in Table 3, when the mass percentages of the first additive (a), dimethyl carbonate (b), low viscosity solvent (c), and anode material layer (d) in the non-aqueous electrolyte of the lithium-ion battery meet the corresponding conditions, adding VC or DTD as auxiliary additives will significantly improve the safety performance, although the initial DCIR of the battery at 0℃ will increase and the low-temperature performance will deteriorate. However, adding FEC as an auxiliary additive will not significantly improve the safety performance, but it can further improve the low-temperature performance.

[0108] Table 4 shows the test results of the initial 0°C DCIR (mΩ), 130°C hot box battery surface temperature (°C), and -20°C / 3C discharge capacity retention (%) of the lithium-ion batteries prepared in Examples 1-1 and Comparative Examples 1-10 to 1-13. The difference between Comparative Examples 1-10 to 1-13 and Example 1-1 is the type of carboxylic acid ester shown in Table 4. The other parameters and preparation steps are the same as those described in Example 1-1.

[0109] Table 4

[0110]

[0111] As can be seen from the test results of Examples 1-1 and Comparative Examples 1-10 to 1-13 in Table 4, when other carboxylic acid ester solvents are used to replace low-viscosity solvents for non-aqueous electrolytes, although the surface temperature of the battery in the 130°C hot box is lower, the initial DCIR at 0°C is greater for other carboxylic acid ester solvents, and the low-temperature discharge capacity retention rate is significantly reduced, making it impossible to simultaneously achieve high power and high safety performance of lithium-ion batteries.

[0112] Table 5 shows the test results of the initial 0°C DCIR (mΩ), 130°C hot box battery surface temperature (°C), and -20°C / 3C discharge capacity retention rate (%) of the lithium-ion batteries prepared in Examples 1-1, 1-31 to 1-33, Comparative Examples 1-1, 1-14 to 1-16. The difference between Examples 1-31 to 1-33 and Example 1-1 is the type of positive electrode active material shown in Table 5. The other parameters and preparation steps are the same as those described in Example 1-1. The difference between Comparative Examples 1-1 and Comparative Examples 1-14 to 1-16 and Example 1-1 is the type of positive electrode active material shown in Table 5 and the absence of the first additive. The other parameters and preparation steps are the same as those described in Example 2-1.

[0113] Table 5

[0114]

[0115] Note: " / " in the table indicates that the item does not exist.

[0116] The results in Table 5 show that when the mass percentages of the first additive (a), dimethyl carbonate (b), low viscosity solvent (c), and the porosity (d) of the negative electrode material layer in the non-aqueous electrolyte satisfy 0.05 ≤ When the values ​​are ≤4, 0.01≤a≤2, 25≤b≤55, 4≤c≤30, and 10≤d≤30, the synergistic effect between the additives, solvents, and negative electrode materials can be fully utilized, enabling lithium-ion batteries to achieve both high power performance and high safety performance. This demonstrates that the battery system of the present invention has universal applicability to different polarity materials.

[0117] Table 6 shows the parameters required for the lithium-ion batteries prepared in Examples 2-1 to 2-23 and Comparative Examples 2-1 to 2-9. The differences between Examples 2-1 to 2-23 and Comparative Examples 2-1 to 2-9 and Example 1-1 lie in the relevant parameters in Table 1 and the type of the first additive. The remaining parameters and preparation steps are the same as those described in Example 1-1. Specifically, Examples 2-1 to 2-23 and Comparative Examples 2-1 to 2-9 use compound 6 containing only sulfate ester groups as the first additive. The mass percentage of the first additive in the non-aqueous electrolyte is a%, the mass percentage of dimethyl carbonate in the non-aqueous electrolyte is b%, the mass percentage of low viscosity solvent in the non-aqueous electrolyte is c%, and the relationship is... The selection of low-viscosity solvents is shown in Table 6.

[0118] Table 6 also shows the test results of the initial 0°C DCIR (mΩ), 130°C hot box battery surface temperature (°C), and -20°C / 3C discharge capacity retention rate (%) of the batteries in Examples 2-1 to 2-23 and Comparative Examples 2-1 to 2-9.

[0119] Table 6

[0120]

[0121]

[0122] As can be seen from the test results of Examples 2-1 to 2-23 and Comparative Examples 2-1 to 2-9 in Table 6, the lithium-ion battery provided in this invention uses a compound with a specific structure as the first additive in its non-aqueous electrolyte, and dimethyl carbonate and a low-viscosity solvent as the non-aqueous organic solvent. Furthermore, by controlling the mass percentages of the first additive (a), dimethyl carbonate (b), and low-viscosity solvent (c) in the non-aqueous electrolyte, and the porosity (d) of the negative electrode material layer, the battery satisfies 0.05 ≤ When the values ​​are ≤4, 0.01≤a≤2, 25≤b≤55, 4≤c≤30, and 10≤d≤30, the synergistic effect between additives, solvents, and negative electrode materials can be fully utilized, enabling lithium-ion batteries to achieve both high power performance and high safety performance.

[0123] As can be seen from the test results of Examples 2-1 and Comparative Examples 2-1 to 2-9, when any one or more of the following parameters in the non-aqueous electrolyte—a, b, c, and d—do not meet the specified range, or the relationship between them is not met, the following conditions will be met: If the values ​​are too high or too low, the various parameters cannot achieve a synergistic effect, and the risk of thermal runaway cannot be effectively mitigated. Therefore, it is impossible to balance the high power and high safety performance of lithium-ion batteries.

[0124] When the mass percentages of the first additive (a), dimethyl carbonate (b), and low-viscosity solvent (c) in the non-aqueous electrolyte further satisfy 0.05 ≤ When the values ​​are ≤1.8, 0.1≤a≤1, 25≤b≤50, 8≤c≤20, and 15≤d≤25, the resulting lithium-ion battery can significantly improve battery power performance while better reducing the risk of thermal runaway caused by continuous temperature rise during battery charging and discharging. The first additive can also better provide a stable, complete, and excellent positive and negative electrode interface film, protecting the positive and negative electrodes of the battery, thereby further improving the power performance and safety performance of the lithium-ion battery.

[0125] A comparison of the test results from Examples 2-1 to 2-21 and Examples 2-22 to 2-23 shows that further limiting the mass ratio of dimethyl carbonate to a low-viscosity solvent to (1~8):1 enables the lithium-ion battery to achieve excellent power performance over a wide temperature range, especially maintaining good power performance at low temperatures. Furthermore, when the mass ratio of dimethyl carbonate to a low-viscosity solvent containing both sulfate and carbonate esters is further satisfied to (1.5~6):1, the battery's power performance at low temperatures is even more outstanding.

[0126] Table 7 shows the test results of the initial 0°C DCIR (mΩ), 130°C hot box battery surface temperature (°C), and -20°C / 3C discharge capacity retention (%) of the lithium-ion batteries prepared in Examples 2-1 and 2-24. The difference between Example 2-24 and Example 2-1 is the type of the first additive shown in Table 7. The other parameters and preparation steps are the same as those described in Example 2-1.

[0127] Table 7

[0128]

[0129] As shown in Table 7, when the mass percentages of the first additive (a), dimethyl carbonate (b), low-viscosity solvent (c), and negative electrode material layer (d) in the non-aqueous electrolyte of the lithium-ion battery meet the corresponding conditions, using any compound containing only sulfate groups as the first additive can ensure a high addition amount of low-viscosity solvent, improve battery power performance, prevent corrosion and oxidation of the electrode material at high temperatures, and prevent the battery from continuously heating up during charging and discharging, allowing the generated heat to be dissipated and conducted in a timely manner. This enables the lithium-ion battery to possess both high power performance and high safety performance. This demonstrates that the lithium-ion battery system of the present invention is universally applicable to different compounds containing only sulfate groups as the first additive.

[0130] Table 8 shows the test results of the initial 0°C DCIR (mΩ), 130°C hot box battery surface temperature (°C), and -20°C / 3C discharge capacity retention (%) of the lithium-ion batteries prepared in Examples 2-1, 2-25 to 2-27, and Comparative Example 2-11. The difference between Examples 2-25 to 2-27 and Example 2-1 is the auxiliary additives and their contents shown in Table 8. The difference between Comparative Example 2-11 and Example 2-1 is that 1% DTD is used to replace the first additive in Comparative Example 2-11. The remaining parameters and preparation steps are the same as those described in Example 2-1.

[0131] Table 8

[0132] Group First type of additive Auxiliary additives and their content Battery initial 0℃ DCIR (mΩ) Surface temperature of the battery in a 130℃ hot box (°C) Battery capacity retention rate at -20℃ / 3C discharge (%) Example 2-1 Compound 6 / 68.2 139.5 93.1 Example 2-25 Compound 6 VC: 1% 73.6 136.7 89.3 Example 2-26 Compound 6 DTD: 1% 71.7 137.3 90.1 Example 2-27 Compound 6 FEC: 1% 69.7 139.3 94.0 Comparative Examples 2-10 DTD / 70.0 150.4 86.3

[0133] As shown in Table 8, when the mass percentages of the first additive (a), dimethyl carbonate (b), low viscosity solvent (c), and the porosity (d) of the negative electrode material layer in the non-aqueous electrolyte of the lithium-ion battery meet the corresponding conditions, adding VC or DTD as an auxiliary additive results in a slight increase in the DCIR of the battery at 0°C and a slight deterioration in low-temperature performance, but a significant improvement in safety performance. However, adding FEC as an auxiliary additive does not significantly improve safety performance, but it can further improve low-temperature performance.

[0134] As can be seen from the test results of Examples 2-1 and Comparative Examples 2-10, when DTD is used to replace the first additive, the low-temperature power performance of Comparative Example 2-10 is significantly worse, and the surface temperature of the battery in the 130°C hot box is even higher, resulting in even worse safety performance. This indicates that the first 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 its own open rings. 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 energy density and cycle performance of lithium-ion batteries is not good.

[0135] Table 9 shows the test results of the initial 0°C DCIR (mΩ), 130°C hot box battery surface temperature (°C), and -20°C / 3C discharge capacity retention (%) of the lithium-ion batteries prepared in Examples 2-1 and Comparative Examples 2-11 to 2-14. The difference between Comparative Examples 2-11 to 2-14 and Example 2-1 is the type of carboxylic acid ester shown in Table 9. The other parameters and preparation steps are the same as those described in Example 2-1.

[0136] Table 9

[0137]

[0138] As can be seen from the test results of Examples 2-1 and Comparative Examples 2-11 to 2-14 in Table 9, when other carboxylic acid ester solvents are used to replace low-viscosity solvents for non-aqueous electrolytes, although the surface temperature of the battery in the 130°C hot box is lower, the initial DCIR at 0°C is greater for other carboxylic acid ester solvents, and the low-temperature discharge capacity retention rate is significantly reduced, making it impossible to simultaneously achieve high power and high safety performance of lithium-ion batteries.

[0139] Table 10 shows the test results of the initial 0°C DCIR (mΩ), 130°C hot box battery surface temperature (°C), and -20°C / 3C discharge capacity retention rate (%) of the lithium-ion batteries prepared in Examples 2-1, 2-28 to 2-30, Comparative Examples 2-1, 2-15 to 2-17. The difference between Examples 2-28 to 2-30 and Example 2-1 is the type of positive electrode active material shown in Table 10; the other parameters and preparation steps are the same as those described in Example 2-1. The difference between Comparative Examples 2-1 and Comparative Examples 2-16 to 2-18 and Example 2-1 is the type of positive electrode active material shown in Table 10 and the absence of the first additive; the other parameters and preparation steps are the same as those described in Example 2-1.

[0140] Table 10

[0141]

[0142] The results in Table 10 show that when the mass percentages of the first additive (a), dimethyl carbonate (b), low viscosity solvent (c), and the porosity (d) of the negative electrode material layer in the non-aqueous electrolyte satisfy 0.05 ≤ When the values ​​are ≤4, 0.01≤a≤2, 25≤b≤55, 4≤c≤30, and 10≤d≤30, the synergistic effect between the additives, solvents, and negative electrode materials can be fully utilized, enabling lithium-ion batteries to achieve both high power performance and high safety performance. This demonstrates that the battery system of the present invention has universal applicability to different positive electrode active materials.

[0143] The present invention has been further described above with reference to specific embodiments. However, it should be understood that the specific description herein should not be construed as limiting the nature and scope of the present invention. Various modifications made to the above embodiments by those skilled in the art after reading this specification are all within the scope of protection of the present invention.

Claims

1. A lithium-ion battery, characterized in that, Includes positive electrode, negative electrode, and non-aqueous electrolyte; The negative electrode includes a negative electrode current collector and a negative electrode material layer disposed on the surface of the negative electrode current collector, wherein the porosity of the negative electrode material layer is d% The non-aqueous electrolyte comprises lithium salt, organic solvent, and a first additive; The organic solvent includes dimethyl carbonate and a low-viscosity solvent, wherein the low-viscosity solvent is composed of at least one of methyl acetate, ethyl acetate, and ethyl propionate; the mass ratio of dimethyl carbonate to low-viscosity solvent in the non-aqueous electrolyte is (1~8):

1. The first additive comprises a compound represented by structural formula 1: 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; Based on the mass of the non-aqueous electrolyte, the mass percentage of the first additive is a%, the mass percentage of the dimethyl carbonate is b%, and the mass percentage of the low-viscosity solvent is c%. The lithium-ion battery meets the following condition: 0.05 ≤ ≤4, 0.01≤a≤2, 25≤b≤55, 4≤c≤30, 10≤d≤30.

2. The lithium-ion battery according to claim 1, characterized in that, The lithium-ion battery meets the following condition: 0.05 ≤ ≤1.

8.

3. The lithium-ion battery according to claim 1, characterized in that, The mass percentage a% of the first additive satisfies: 0.1≤a≤1.

4. The lithium-ion battery according to claim 1, characterized in that, The mass percentage b% of the dimethyl carbonate satisfies: 30 ≤ b ≤ 45.

5. The lithium-ion battery according to claim 1, characterized in that, The mass percentage (c%) of the low-viscosity solvent satisfies: 8 ≤ c ≤ 20.

6. The lithium-ion battery according to claim 1, characterized in that, The porosity d% of the negative electrode material layer satisfies: 15≤d≤25.

7. The lithium-ion battery according to claim 1, characterized in that, The first additive includes at least one of the following compounds:

8. The lithium-ion battery according to claim 1, characterized in that, The non-aqueous electrolyte further includes auxiliary additives, which include at least one of the following: cyclic sulfate compounds, sulfonyl lactone compounds, cyclic carbonate compounds, phosphate compounds, borate ester compounds, and nitrile compounds, other than the compound shown in structural formula 1; and / or, Based on the mass of the non-aqueous electrolyte, the content of the auxiliary additive is 0.01% to 10%; and / or, The cyclic sulfate compounds other than those shown in structural formula 1 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: 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: Structural Formula 3 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 ester compounds include at least one of tris(trimethylsilane)borate and tris(triethylsilane)borate; and / or, The nitrile compounds include at least one of butadionitrile, glutaronitrile, ethylene glycol bis(propionitrile) ether, hexanetrionitrile, adiponitrile, heptanonitrile, octadionitrile, nonadionitrile, and sebaconitol.

9. The lithium-ion battery according to claim 1, characterized in that, The positive electrode includes a positive electrode material layer containing a positive electrode active material, wherein the positive electrode active material is a lithium transition metal oxide, and the lithium transition metal oxide includes at least one of nickel-containing ternary materials, phosphate materials, and lithium cobalt oxide materials.

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