Composite positive electrode material, positive electrode plate, lithium ion battery as well as preparation method and application of lithium ion battery

Abstract

The invention provides a composite positive electrode material, a positive electrode plate, a lithium ion battery and a preparation method and application thereof, the composite positive electrode material is composed of a lithium iron manganese phosphate material and a nickel-cobalt-manganese ternary material, and the weight ratio of the lithium iron manganese phosphate material to the nickel-cobalt-manganese ternary material is (4-7): (3-6); wherein the molecular formula of the lithium manganese iron phosphate material is LiMnzFe1-zPO4, and z is more than 0 and less than 1; the molecular formula of the nickel-cobalt-manganese ternary material is LiNi < 1-x-y > Co < x > Mn < y > O2, x is greater than or equal to 0.1 and less than or equal to 0.5, and y < lt > is greater than or equal to 0.1; 1-x-y is greater than 0. The composite positive electrode material compounded in the manner can effectively improve the conductivity, stability and other properties of the positive electrode material. When the composite material is used in the lithium ion battery, the diffusion kinetics, the structural stability, the interface stability, the cycle performance, the energy density and the like in the charging and discharging process of the lithium ion battery can be improved, and a new path is provided for developing the high-performance and high-safety fast-charging lithium ion battery.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium batteries, in particular to a composite positive electrode material, a positive electrode sheet, a lithium ion battery and a preparation method and application thereof. BACKGROUND

[0002] In recent years, electric vehicles as a clean, environmentally friendly means of transportation, its market acceptance and application range is rapidly expanding. However, compared with traditional fuel vehicles, electric vehicles have obvious gap in the range and charging time, and this "range anxiety" problem has become one of the main resistances restricting the development of electric vehicles. The improvement of fast charging capacity is regarded as the key way to solve the above problems, which not only can shorten the charging time and improve the convenience of electric vehicles, but also can alleviate the range anxiety to some extent and enhance the confidence of users to electric vehicles. As the core power component of electric vehicles, the performance of lithium ion batteries directly affects the endurance and charging efficiency of electric vehicles. Therefore, improving the fast charging capacity of lithium ion batteries has become the common goal pursued by battery manufacturers and automobile manufacturers.

[0003] However, the development of fast charging technology faces a series of technical challenges. First, under the conditions of low temperature and high rate charging, the electrochemical performance of lithium ion batteries will decrease significantly. Studies have shown that during high-rate charging, the rapid intercalation and deintercalation of lithium ions will cause stress changes in the positive and negative electrode materials, accelerating the capacity decay and internal resistance increase of the battery, and thus leading to a decrease in output power. In addition, high-rate charging will also cause a large amount of Joule heat to be generated inside the battery. If this part of heat energy cannot be effectively dissipated, it will not only accelerate the performance decay of the battery, but also may cause thermal runaway of the battery, causing more serious safety problems.

[0004] The modification of the positive electrode material in lithium ion batteries is one of the methods to improve the fast charging and capacity of lithium ion batteries, and there have been many reports on related research. However, the current fast charging lithium ion battery technology usually sacrifices the fast charging ability and safety of the battery to improve the energy density, and the measures to enhance safety often lead to a decrease in the energy density and fast charging performance of the battery. It is impossible to ensure that the charging rate, energy density, safety performance and cycle life of lithium ion batteries are at a good level at the same time. Therefore, how to further modify the positive electrode material in lithium ion batteries to shorten the charging time of lithium ion batteries while further improving the energy density, safety performance and cycle life of lithium ion batteries has become the top priority in the development of current fast charging lithium ion battery technology. SUMMARY

[0005] The main objective of this invention is to provide a composite cathode material, cathode sheet, lithium-ion battery, and its preparation method and application, in order to solve the problem that existing lithium-ion batteries cannot simultaneously guarantee that the charging rate, energy density, safety performance and cycle life of lithium-ion batteries are all at a good level.

[0006] This application provides a composite cathode material composed of lithium manganese iron phosphate and nickel-cobalt-manganese ternary materials in a weight ratio of (4-7):(3-6); wherein the molecular formula of the lithium manganese iron phosphate material is: LiMn z Fe 1-z PO4, 0 < z < 1; The molecular formula of the nickel-cobalt-manganese ternary material is: LiNi 1-x-y Co x Mn y O2, 0.1≤x≤0.5, 0.1≤y<1, and 1-xy>0.

[0007] Furthermore, in the composite cathode material, the weight ratio of lithium manganese iron phosphate material to nickel-cobalt-manganese ternary material is (6-7):(3-4); preferably, the molecular formula of lithium manganese iron phosphate material is: LiMn z Fe 1-z PO4, wherein 0 < z < 1, and the molar ratio of Mn to Fe in the lithium manganese iron phosphate material is (1-1.5):1; more preferably, the molecular formula of the lithium manganese iron phosphate material is: LiMn 0.5 Fe 0.5 PO4; The molecular formula of the nickel-cobalt-manganese ternary material is: LiNi 0.7 Co 0.2 Mn 0.1 O2; preferably, the nickel-cobalt-manganese ternary material is a single crystal material.

[0008] According to a second aspect of the present invention, a positive electrode sheet is also provided, the positive electrode sheet comprising a first current collector and a positive electrode active layer located on one side surface of the first current collector, the positive electrode active layer being made of the aforementioned composite positive electrode material, a first conductive agent and a first binder.

[0009] Further, by weight percentage, the composite positive electrode material comprises 95-98% of the positive electrode active layer material, the first conductive agent comprises 1-3% of the first conductive agent, and the first binder comprises 1-3% of the first conductive agent; preferably, by weight percentage, the composite positive electrode material comprises 96.5-97% of the positive electrode active layer material, the first conductive agent comprises 1.2-2% of the first conductive agent, and the first binder comprises 1.5-2% of the first conductive agent; preferably, the first conductive agent is one or more of carbon nanotubes, conductive carbon black, and graphene; more preferably, the first conductive agent is a composite of carbon nanotubes, conductive carbon black, and graphene; preferably, the weight ratio of conductive carbon black, graphene, and carbon nanotubes is (0.8-1.5):(0.1-0.5):(0.01-0.1); preferably, the first binder is one or more of polyvinylidene fluoride, polyacrylonitrile, and polyimide; preferably, the first current collector is at least one of carbon-coated aluminum foil current collector or aluminum foil current collector; preferably, the thickness of the first current collector is 8-15 μm.

[0010] According to a third aspect of the present invention, a lithium-ion battery is also provided, the lithium-ion battery comprising a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the positive electrode is the aforementioned positive electrode.

[0011] Furthermore, the negative electrode includes a second current collector and a negative electrode active layer located on one side surface of the second current collector. The material of the negative electrode active layer includes a negative electrode active material, a second conductive agent, a second binder, and a thickener. The positive electrode, the separator, and the negative electrode are alternately stacked and encapsulated in a metal shell, and the positive electrode, the separator, and the negative electrode are wetted by electrolyte.

[0012] Further, by weight percentage, the negative electrode active layer material comprises 93-97% negative electrode active material, 0.5-3% second conductive agent, 1-2.5% second binder, and 0.1-0.5% thickener; preferably, by weight percentage, the negative electrode active layer material comprises 95-96% negative electrode active material, 1-2% second conductive agent, 1.2-2% second binder, and 0.2-0.3% thickener; preferably, the negative electrode active material is artificial graphite; preferably, the artificial graphite is carbon-coated secondary single particles; and / or, the second conductive agent is conductive carbon black and / or aqueous carbon nanotubes; and / or, the second binder is styrene-butadiene rubber and / or acrylic binder; more preferably, the second binder is an acrylic binder, or, the second binder is a blend of styrene-butadiene rubber and acrylic binder; preferably, the acrylic binder is polyacrylic acid or polyacrylate; and / or, the thickener is sodium methyl cellulose and / or a copolymer of butadiene-styrene.

[0013] Further, the porosity of the separator is ≥46%, and the air permeability is ≥90s / 100mL; the thickness of the separator is 8-15μm; preferably, the porosity of the separator is 36-48%, and the air permeability is 120-180s / 100mL; preferably, the separator is a polyethylene separator; more preferably, the separator is a ceramic-coated polyethylene separator; preferably, the electrolyte includes an organic solvent, a lithium salt, a positive electrode film-forming additive, and a negative electrode film-forming additive, and the conductivity of the electrolyte is ≥8ms / cm; preferably, the concentration of the lithium salt is 0.8-1.5mol / L; preferably, the lithium salt is lithium hexafluorophosphate and / or lithium difluorosulfonyl imide; preferably, the weight content of the positive electrode film-forming agent in the electrolyte is 1-3%; preferably, the weight content of the negative electrode film-forming additive in the electrolyte is 1-3%; preferably, the positive electrode film-forming additive is vinyl sulfate, lithium difluoroborate, and tris(trimethyl)sulfonate. The electrolyte comprises one or more of silicon-based phosphates; preferably, the negative electrode film-forming additive is vinylene carbonate; preferably, the electrolyte also includes a low-resistance additive, more preferably, the low-resistance additive is at least one of lithium difluorophosphate or lithium difluorooxalate borate; preferably, the organic solvent is an organic carbonate solvent; more preferably, the organic solvent is one or more of ethylene carbonate, methyl ethyl carbonate and diethyl carbonate; preferably, ethylene carbonate, methyl ethyl carbonate and diethyl carbonate are used in combination; more preferably, the weight ratio of ethylene carbonate, methyl ethyl carbonate and diethyl carbonate is (20-40):(40-70):(10-30); preferably, the second current collector is at least one of copper foil current collector or copper alloy current collector; preferably, the thickness of the first current collector is 5-8 μm; preferably, the metal shell is made of aluminum; more preferably, the thickness of the metal shell is 0.2-0.8 mm.

[0014] According to a fourth aspect of the present invention, a method for preparing the above-mentioned lithium-ion battery is also provided. The method includes the following steps: mixing and dissolving a positive electrode active material, a first conductive agent, and a first binder in a first solvent to obtain a first slurry; coating the first slurry onto one side of a first current collector and drying it for the first time to obtain a positive electrode sheet; mixing and dissolving a negative electrode active material, a second conductive agent, a second binder, and a thickener in a second solvent to obtain a second slurry; coating the second slurry onto one side of a second current collector and drying it for the second time to obtain a negative electrode sheet; and subjecting the positive electrode sheet, the separator, and the negative electrode sheet to rolling, die-cutting, slitting, stacking, electrolyte injection, and formation processes to obtain a lithium-ion battery.

[0015] Further, the first drying temperature is 100-150°C, and the time is 1-20 min; preferably, the second drying temperature is 40-80°C, and the time is 1-20 min; preferably, the first solvent is N-methylpyrrolidone; preferably, the second solvent is deionized water; preferably, the solid content of the first slurry is 57-62%; and the solid content of the second slurry is 50-56%.

[0016] According to a fifth aspect of the present invention, a battery module is also provided, the battery module comprising a plurality of the above-described lithium-ion batteries.

[0017] According to a sixth aspect of the present invention, a battery pack is also provided, which includes a plurality of the above-described battery modules.

[0018] According to a seventh aspect of the present invention, an electrical device is also provided, the electrical device comprising the aforementioned battery pack.

[0019] According to an eighth aspect of the present invention, an energy storage system is also provided, the energy storage system comprising the aforementioned battery pack.

[0020] In summary, this application, by compounding lithium manganese iron phosphate and nickel-cobalt-manganese ternary materials and controlling their weight ratio, effectively improves the overall performance of composite cathode materials, including conductivity. When used in lithium-ion batteries, it improves various aspects of lithium-ion battery performance, such as diffusion kinetics, structural stability, interface stability, cycle performance, and energy density during charging and discharging. This results in enhanced overall battery performance under fast charging conditions, providing a new pathway for developing high-performance, high-safety fast-charging lithium-ion batteries. Attached Figure Description

[0021] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0022] Figure 1 The diagram shows the fast charging capability of the three-electrode test at different rates for lithium-ion batteries in Embodiment 5 of the present invention.

[0023] Figure 2 The diagram shows the performance test results of the fast charging cycle of the corresponding lithium-ion battery in Embodiment 5 of the present invention. Detailed Implementation

[0024] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0025] As described in the background section, how to further modify the cathode material in lithium-ion batteries to shorten the charging time while improving the energy density, safety performance, and cycle life of lithium-ion batteries has become the top priority in the development of fast-charging lithium-ion battery technology.

[0026] To address the aforementioned problems, this invention provides a composite cathode material composed of lithium manganese iron phosphate and nickel-cobalt-manganese ternary materials in a weight ratio of (4-7):(3-6); wherein the molecular formula of the lithium manganese iron phosphate material is: LiMn z Fe 1-z PO4, 0 < z < 1; The molecular formula of the nickel-cobalt-manganese ternary material is: LiNi 1-x-y Co x Mn y O2, 0.1≤x≤0.5, 0.1≤y<1, and 1-xy>0.

[0027] The composite cathode material provided by this invention is composed of lithium manganese iron phosphate and nickel-cobalt-manganese ternary materials. By compounding lithium manganese iron phosphate and nickel-cobalt-manganese ternary materials with the above molecular formula and controlling their weight ratio at (4-7):(3-6), this invention, when used in lithium-ion batteries, not only enables the lithium-ion batteries to have a better charging rate but also achieves better energy density, safety performance, and cycle life. The reasons for this are presumably due to the following factors:

[0028] Firstly, the composite cathode material is a combination of lithium manganese iron phosphate and nickel-cobalt-manganese ternary materials. The molecular formula of lithium manganese iron phosphate is LiMn. z Fe 1-z PO4, where 0 < z < 1; the molecular formula of the nickel-cobalt-manganese ternary material is: LiNi 1-x- y Co x Mn y O2, where 0.1≤x≤0.5, 0.1≤y<1, and 1-xy>0. In the above-mentioned lithium manganese iron phosphate material and nickel cobalt manganese ternary material, Mn and Fe elements affect the migration path and diffusion rate of lithium ions in the positive electrode active material, while Ni content affects the energy density of the battery. By compounding lithium manganese iron phosphate material with the above molecular formula and nickel cobalt manganese ternary material and controlling their weight ratio within the above range, the synergistic effect of various elements in the two materials at their contents can enable the lithium-ion battery to maintain high energy density while ensuring the stability and thermal safety of the battery during fast charging.

[0029] Secondly, lithium manganese iron phosphate materials typically have low electronic conductivity but high ionic conductivity, while nickel-cobalt-manganese ternary materials have high electronic conductivity. Combining these two materials, especially in proportions within the aforementioned range, can fully leverage their advantages, effectively improving the diffusion kinetics of lithium ions in the cathode material, reducing resistance during lithium ion diffusion, and making the migration of lithium ions under high-current charge and discharge conditions more efficient, thereby enhancing the battery's fast-charging performance.

[0030] Thirdly, lithium-ion batteries generate a large amount of heat during fast charging. Lithium manganese iron phosphate (MFP) material has a unique olivine structure, thus exhibiting good thermal and cycle stability. The lithium-ion battery provided in this application utilizes MFP as the positive electrode active material to suppress heat accumulation within the battery, reducing the risk of thermal runaway. The nickel-cobalt-manganese ternary material in the positive electrode active material has a high energy density, improving the specific capacity of the lithium-ion battery. By combining these two materials in the aforementioned ratio, their synergistic effect fully leverages their respective advantages, enabling the lithium-ion battery to maintain high energy density while further improving its stability and thermal safety during fast charging.

[0031] Fourth, during fast charging, the positive electrode material in the positive electrode active layer undergoes interfacial chemical reactions with the electrolyte, adversely affecting the interfacial stability and safety of the lithium-ion battery. The lithium-ion battery provided in this application combines lithium manganese iron phosphate and nickel-cobalt-manganese ternary materials in the aforementioned proportions. This improves the interfacial stability of the positive electrode material under high voltage during fast charging, reduces the negative impact of interfacial chemical reactions, and minimizes internal side reactions, thereby contributing to the formation of a more stable SEI film and further enhancing safety and stability during fast charging. Furthermore, this solution can further reduce the degradation and performance decay of the positive electrode active material during high-speed charge and discharge, enabling the lithium-ion battery to maintain a high capacity retention rate during fast charging cycles and extending battery life.

[0032] In summary, this application, by combining lithium manganese iron phosphate and nickel-cobalt-manganese ternary materials and adjusting their weight ratios, effectively improves the overall performance of composite cathode materials, including conductivity. When used in lithium-ion batteries, it improves various aspects of lithium-ion battery performance, such as diffusion kinetics, structural stability, interface stability, cycle performance, and energy density during charging and discharging. This results in enhanced overall battery performance under fast-charging conditions, providing a new pathway for developing high-performance, high-safety fast-charging lithium-ion batteries.

[0033] In a preferred embodiment, the weight ratio of lithium manganese iron phosphate (LFP) to nickel cobalt manganese (MCM) ternary materials in the composite cathode material is (6-7):(3-4). As mentioned above, the blending and weight ratio of LFP and MCM ternary materials in the cathode active material can affect various aspects of lithium-ion batteries, including diffusion kinetics, structural stability, interface stability, cycle performance, and energy density during charging and discharging. Controlling the weight ratio of LFP to MCM ternary materials in the cathode active material of lithium-ion batteries within the above-mentioned range can improve the electrochemical performance of lithium-ion batteries, such as charging rate, energy density, safety performance, and cycle life.

[0034] Preferably, the molecular formula of lithium manganese iron phosphate material is: LiMn z Fe 1-z PO4, where 0 < z < 1, and the molar ratio of Mn to Fe in the lithium manganese iron phosphate material is (1-1.5):1. As mentioned above, in lithium manganese iron phosphate materials, Mn and Fe elements affect the migration path and diffusion rate of lithium ions in the positive electrode active material; in nickel-cobalt-manganese ternary materials, the Ni content affects the energy density of the battery. Controlling the ratio of Mn to Fe elements in the lithium manganese iron phosphate material within the above range can improve the distribution of Mn and Fe elements in the lithium manganese iron phosphate material, and under the synergistic effect with nickel-cobalt-manganese ternary materials, can improve the migration path and diffusion rate of lithium ions and the energy density. This is beneficial to further improve the energy density of lithium-ion batteries and further ensure the stability and thermal safety of batteries during fast charging. Preferably, the molecular formula of lithium manganese iron phosphate material is: LiMn 0.5 Fe 0.5 PO4; The molecular formula of the nickel-cobalt-manganese ternary material is: LiNi 0.7 Co 0.2 Mn 0.1 O2. Using lithium manganese iron phosphate and nickel-cobalt-manganese ternary materials with the above molecular formulas can further improve the comprehensive electrochemical performance of lithium-ion batteries, including charging rate, energy density, safety performance, and cycle life. Preferably, the nickel-cobalt-manganese ternary material is a single-crystal material. Single-crystal nickel-cobalt-manganese ternary material has a more uniform and complete crystal structure with fewer grain boundaries. Its overall performance and consistency after being combined with lithium manganese iron phosphate material are better, thus enabling it to interact better with the positive electrode active material, improve the lithium-ion conductivity, and enhance the battery's charge / discharge rate and fast-charging performance.

[0035] According to another aspect of the present invention, a positive electrode sheet is also provided, the positive electrode sheet comprising a first current collector and a positive electrode active layer located on one side surface of the first current collector, the material of the positive electrode active layer comprising the above-mentioned composite positive electrode material, a first conductive agent and a first binder.

[0036] In a preferred embodiment, the composite positive electrode material comprises 95-98% of the positive electrode active layer material, the first conductive agent comprises 1-3% of the first conductive agent, and the first binder comprises 1-3% of the first binder. Controlling the addition ratio of the composite positive electrode material, the first conductive agent, and the first binder within the above-mentioned range allows for better utilization of the composite positive electrode material, resulting in improved conductivity and stability of the positive electrode sheet. Preferably, by weight percentage, the composite positive electrode material comprises 96.5-97% of the positive electrode active layer material, the first conductive agent comprises 1.2-2% of the first conductive agent, and the first binder comprises 1.5-2% of the first binder. Controlling the addition ratio of the composite positive electrode material, the first conductive agent, and the first binder within the above-mentioned preferred range further enhances the aforementioned effects.

[0037] Preferably, the first conductive agent is one or more of carbon nanotubes, conductive carbon black, and graphene; more preferably, the first conductive agent is a composite of carbon nanotubes, conductive carbon black, and graphene; preferably, the weight ratio of conductive carbon black, graphene, and carbon nanotubes is (0.8–1.5):(0.1–0.5):(0.01–0.1); preferably, the first binder is one or more of polyvinylidene fluoride, polyacrylonitrile, and polyimide. The above-mentioned conductive agents and binders can produce excellent effects on improving the overall electrochemical performance of lithium-ion batteries. In particular, when carbon nanotubes are used as conductive agents, they can better synergize with the positive electrode active material, providing a line-to-line conductive network for the positive electrode active layer, which can further improve the rate performance of lithium-ion batteries. In practical applications, multiple conductive materials can be blended to form a composite conductive slurry, which can then be used as a conductive agent for the positive electrode sheet. This further improves the battery's conductivity, flexibility, and adhesion. A combination of three conductive agents results in better performance of the positive electrode sheet. In particular, controlling the proportions of the three within the aforementioned range can further enhance the performance of the positive electrode sheet. Preferably, the first current collector is at least one of a carbon-coated aluminum foil current collector or an aluminum foil current collector; preferably, the thickness of the first current collector is 8–15 μm. Using the above-mentioned current collector as the current collector for the positive electrode sheet, and controlling the thickness of the current collector within the aforementioned range, can improve the performance of the positive electrode sheet.

[0038] According to a third aspect of the present invention, a lithium-ion battery is also provided, comprising a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the positive electrode is the aforementioned positive electrode. Using the composite positive electrode material provided in this application in a lithium-ion battery can improve various aspects of the lithium-ion battery, including diffusion kinetics, structural stability, interface stability, cycle performance, and energy density during charging and discharging. This achieves a comprehensive performance improvement of the battery under fast charging conditions, providing a new path for developing high-performance, high-safety fast-charging lithium-ion batteries.

[0039] In a preferred embodiment, the negative electrode includes a second current collector and a negative electrode active layer located on one side surface of the second current collector. The material of the negative electrode active layer includes a negative electrode active material, a second conductive agent, a second binder, and a thickener. The positive electrode, the separator, and the negative electrode are alternately stacked and encapsulated in a metal shell, and the positive electrode, the separator, and the negative electrode are wetted by electrolyte.

[0040] In a preferred embodiment, by weight percentage, the negative electrode active layer material comprises 93-97% negative electrode active material, 0.5-3% second conductive agent, 1-2.5% second binder, and 0.1-0.5% thickener. Controlling the proportions of active material, conductive agent, and binder in the negative electrode active layer material within the above-mentioned range allows for better interaction with the positive electrode, which is beneficial for further improving the overall performance of the lithium-ion battery. Preferably, by weight percentage, the negative electrode active layer material comprises 95-96% negative electrode active material, 1-2% second conductive agent, 1.2-2% second binder, and 0.2-0.3% thickener. Controlling the proportions of active material, conductive agent, and binder in the negative electrode active layer material within the above-mentioned preferred range further enhances the aforementioned effect.

[0041] Preferably, the negative electrode active material is artificial graphite; more preferably, the artificial graphite is carbon-coated secondary single-particle material. Selecting carbon-coated secondary single-particle artificial graphite as the negative electrode active material helps to further improve the overall performance of lithium-ion batteries. This is because carbon-coated secondary single-particle artificial graphite has a smaller particle size and OI value, which can effectively reduce the migration path of lithium ions, lower the migration resistance of lithium ions, and accelerate the insertion and extraction speed of lithium ions, thereby improving the fast-charging capability of the battery. And / or, the second conductive agent is conductive carbon black and / or aqueous carbon nanotubes; and / or, the second binder is styrene-butadiene rubber and / or acrylic binder; more preferably, the second binder is an acrylic binder, or, the second binder is a blend of styrene-butadiene rubber and acrylic binder; preferably, the acrylic binder is polyacrylic acid or polyacrylate; and / or, the thickener is sodium methyl cellulose and / or a copolymer of butadiene-styrene. The above-mentioned conductive agents, binders, and thickeners all have excellent effects on improving the overall electrochemical performance of lithium-ion batteries. Aqueous carbon nanotubes, with their high dispersibility, can be better dispersed in the negative electrode active layer, enhancing the conductivity of the negative electrode sheet. Acrylic binders can effectively suppress the negative electrode expansion caused by the rapid embedding of lithium ions into graphite and other negative electrode active materials during charging and discharging, thus contributing to improved fast-charge cycle life and high-temperature performance. In practical applications, multiple conductive materials can be blended to form a composite conductive slurry as a conductive agent for the negative electrode sheet, further improving the battery's electrochemical performance.

[0042] In a preferred embodiment, the separator has a porosity ≥46% and an air permeability ≥90 s / 100 mL; the separator thickness is 8–15 μm. These characteristics not only facilitate better migration of lithium-ion batteries but also improve battery safety and thermal stability, offering significant performance advantages for fast-charging lithium-ion batteries. In particular, the synergistic effect of the separator with the aforementioned porosity and air permeability, combined with the lithium manganese iron phosphate and nickel-cobalt-manganese ternary materials in the positive electrode active material, further enhances electrolyte penetration and ion conduction within the battery, improving efficiency and performance. It also further avoids localized overheating and overpressure caused by unsuitable separator porosity and air permeability, thus further improving battery safety and extending battery life. Preferably, the separator porosity is 36–48%, and the air permeability is 120–180 s / 100 mL. By controlling the porosity and permeability of the separator within the aforementioned ranges, the aforementioned functions can be better performed, thereby improving battery performance. Preferably, the separator is a polyethylene separator; more preferably, the separator is a ceramic-coated polyethylene separator; the above types of separators are more effective in improving the electrochemical performance of lithium-ion batteries.

[0043] Preferably, the electrolyte comprises an organic solvent, a lithium salt, a positive electrode film-forming additive, and a negative electrode film-forming additive, and the conductivity of the electrolyte is ≥8 mS / cm; preferably, the concentration of the lithium salt is 0.8–1.5 mol / L; preferably, the lithium salt is lithium hexafluorophosphate and / or lithium difluorosulfonyl imide; preferably, the weight content of the positive electrode film-forming agent in the electrolyte is 1–3%; preferably, the weight content of the negative electrode film-forming additive in the electrolyte is 1–3%; preferably, the positive electrode film-forming additive is one or more of vinyl sulfate, lithium difluoroborate, and tris(trimethyl)silyl phosphate; preferably, the negative electrode film-forming additive is vinylene carbonate; preferably, the electrolyte also includes a low-resistance additive, preferably at least one of lithium difluorophosphate or lithium difluorooxalate borate; an electrolyte with the above parameters is beneficial for better synergy with the positive electrode in the lithium-ion battery, and is beneficial for improving the overall performance of the lithium-ion battery, such as charging rate, energy density, safety performance, and cycle life. In particular, the low impedance properties of sulfur-based (such as vinyl sulfate) and phosphorus-based (such as tris(trimethyl)silyl phosphate) additives in the aforementioned positive electrode film-forming additives can significantly suppress the dissolution of the positive electrode transition metal and reduce interfacial impedance, thereby enhancing the migration ability of lithium ions and improving fast charging performance. Preferably, the weight content of the positive electrode film-forming agent and the negative electrode film-forming additive in the electrolyte is within the above-mentioned range, which further enhances the above effects.

[0044] Preferably, the organic solvent is an organic carbonate solvent; more preferably, the organic solvent is one or more of ethylene carbonate, methyl ethyl carbonate, and diethyl carbonate; preferably, ethylene carbonate, methyl ethyl carbonate, and diethyl carbonate are used in combination; more preferably, the weight ratio of ethylene carbonate, methyl ethyl carbonate, and diethyl carbonate is (20-40):(40-70):(10-30). The above-mentioned organic solvent enables the electrolyte to better synergize with the active material layer in the positive electrode, which is beneficial to further improving the overall performance of the lithium-ion battery. Preferably, the second current collector is at least one of a copper foil current collector or a copper alloy current collector; preferably, the thickness of the first current collector is 5-8 μm; preferably, the metal casing is made of aluminum; more preferably, the thickness of the metal casing is 0.2-0.8 mm.

[0045] According to a fourth aspect of the present invention, a method for preparing the above-mentioned lithium-ion battery is also provided. This method includes the following steps: mixing and dissolving a positive electrode active material, a first conductive agent, and a first binder in a first solvent to obtain a first slurry; coating the first slurry onto one side of a first current collector and drying it first to obtain a positive electrode sheet; mixing and dissolving a negative electrode active material, a second conductive agent, a second binder, and a thickener in a second solvent to obtain a second slurry; coating the second slurry onto one side of a second current collector and drying it second to obtain a negative electrode sheet; and subjecting the positive electrode sheet, separator, and negative electrode sheet to rolling, die-cutting, slitting, stacking, electrolyte injection, and formation processes to obtain a lithium-ion battery. The lithium-ion battery prepared by this method has better performance.

[0046] In a preferred embodiment, the first drying temperature is 100–150°C and the time is 1–20 min; preferably, the second drying temperature is 40–80°C and the time is 1–20 min; preferably, the first solvent is N-methylpyrrolidone; preferably, the second solvent is deionized water; preferably, the solid content of the first slurry is 57–62%; and the solid content of the second slurry is 50–56%.

[0047] According to a fifth aspect of the present invention, a battery module is also provided, the battery module comprising a plurality of the above-described lithium-ion batteries.

[0048] According to a sixth aspect of the present invention, a battery pack is also provided, which includes a plurality of the above-described battery modules.

[0049] According to a seventh aspect of the present invention, an electrical device is also provided, the electrical device comprising the aforementioned battery pack.

[0050] According to an eighth aspect of the present invention, an energy storage system is also provided, the energy storage system comprising the aforementioned battery pack.

[0051] The present application will be further described in detail below with reference to specific embodiments, which should not be construed as limiting the scope of protection claimed in the present application.

[0052] Example 1

[0053] Positive electrode sheet: The positive electrode active material, the first conductive agent, and the first binder are mixed in a weight ratio of 96.5:1.5:2 and dissolved in the first solvent N-methylpyrrolidone to obtain a first slurry with a solid content of 58%; the first slurry is coated on the surface of the first current collector with a thickness of 150 μm, and then dried to obtain the positive electrode sheet; wherein, the positive electrode active material is lithium manganese iron phosphate (LiMn). 0.5 Fe 0.5 PO4) and nickel-cobalt-manganese ternary materials (LiNi 0.7 Co 0.2 Mn 0.1 O2 (single crystal material) is compounded in a weight ratio of 7:3, the first conductive agent is a compound of conductive carbon black and carbon nanotubes in a weight ratio of 3:2, the first binder is polyvinylidene fluoride, and the first current collector is a carbon-coated aluminum foil current collector with a thickness of 12μm.

[0054] Negative electrode sheet: The negative electrode active material, the second conductive agent, the second binder and the thickener are mixed in a weight ratio of 96.3:0.8:2.3:0.6 and dissolved in a second solvent, water, to obtain a second slurry; the second slurry is coated on one side of the second current collector with a thickness of 117 μm and then dried to obtain the negative electrode sheet; wherein, the negative electrode active material is carbon-coated secondary single particles, the second conductive agent is conductive carbon black, the second binder is a mixture of styrene-butadiene rubber and polyacrylate in a weight ratio of 14:9, the thickener is sodium carboxymethyl cellulose, and the second current collector is a copper foil with a thickness of 6 μm;

[0055] Diaphragm: A polyethylene diaphragm with a thickness of 12μm, a porosity of 46%, and an air permeability of 90s / 100mL;

[0056] Electrolyte: The electrolyte includes an organic solvent, lithium salt, positive electrode film-forming additive, and negative electrode film-forming additive; wherein, the organic solvent is a mixture of ethylene carbonate, methyl ethyl carbonate, and diethyl carbonate in a weight ratio of 30:60:10, the lithium salt is lithium hexafluorophosphate, the positive electrode film-forming additive is a mixture of ethylene sulfate, lithium difluoroborate, and tris(trimethyl)silyl phosphate in a weight ratio of 1:0.5:0.3, the negative electrode film-forming additive is vinylene carbonate, and the concentration of lithium salt in the electrolyte is 1.1 mol / L, the weight content of positive electrode film-forming additive is 2.5%, the weight content of negative electrode film-forming additive is 2%, and the conductivity of the electrolyte is 8.5 mS / cm;

[0057] Lithium-ion battery assembly: The above-mentioned positive electrode, separator and negative electrode are packaged in a metal shell, and the lithium-ion battery is obtained by rolling, die cutting, slitting, stacking, electrolyte injection and formation processes. The thickness of the metal shell is 0.5 mm and the material of the metal shell is aluminum.

[0058] Example 2

[0059] The difference between Example 2 and Example 1 is that in the positive electrode sheet, the first conductive agent is a mixture of conductive carbon black, graphene and carbon nanotubes in a weight ratio of 1.2:0.2:0.05.

[0060] Example 3

[0061] The difference between Example 3 and Example 1 is that in the material of the negative electrode active layer of the negative electrode sheet, the negative electrode active material, the second conductive agent, the second binder and the thickener are in a weight ratio of 96.3:0.8:2.5:0.6, wherein the second binder is polyacrylate.

[0062] Example 4

[0063] The difference between Example 4 and Example 1 is that the diaphragm is a polyethylene diaphragm with a thickness of 12 μm, a porosity of 48%, and an air permeability of 110 s / 100 mL.

[0064] Example 5

[0065] The difference between Example 5 and Example 1 is that the diaphragm is a ceramic-coated polyethylene diaphragm with a thickness of 12 μm, a porosity of 48%, and an air permeability of 120 s / 100 mL.

[0066] Example 6

[0067] The difference between Example 6 and Example 1 is that the diaphragm is a ceramic-coated polyethylene diaphragm with a thickness of 12 μm, a porosity of 48%, and an air permeability of 180 s / 100 mL.

[0068] Example 7

[0069] The difference between Example 7 and Example 1 is that the electrolyte includes: an organic solvent, a lithium salt, a positive electrode film-forming additive, and a negative electrode film-forming additive; wherein, the organic solvent is a mixture of ethylene carbonate, methyl ethyl carbonate, and diethyl carbonate in a weight ratio of 30:50:20, the lithium salt is a mixture of lithium hexafluorophosphate and lithium difluorosulfonyl imide in a molar ratio of 7:3, the positive electrode film-forming additive is a mixture of ethylene sulfate, lithium difluoroborate, and tris(trimethyl)silyl phosphate in a weight ratio of 1.5:1:0.5, the negative electrode film-forming additive is vinylene carbonate, and in the electrolyte, the concentration of lithium salt is 1.15 mol / L, the weight content of the positive electrode film-forming additive is 3%, the weight content of the negative electrode film-forming additive is 3.5%, and the conductivity of the electrolyte is 9.2 mS / cm.

[0070] The lithium-ion battery prepared in this embodiment was subjected to three-electrode tests at different rates, and the corresponding fast charging capability graph is shown below. Figure 1 As shown in the figure, it can be seen that when the negative electrode potential is >0V, the SOC of direct charging at a 4C rate can reach 57.06%, and the SOC of direct charging at a 6C rate can reach 26.69%. This indicates that the battery in this embodiment has good charging capability at high rates.

[0071] The lithium-ion battery prepared in this embodiment was subjected to fast-charge cycle performance testing, and the corresponding fast-charge cycle performance graph is shown below. Figure 2 As shown in the figure, this embodiment, following the fast charging strategy, retains 85% of its capacity after 600 cycles, indicating that this embodiment has good fast charging cycle capability and can support the fast charging lifespan requirements throughout its entire life cycle.

[0072] Example 8

[0073] The difference between Example 8 and Example 1 is that the positive electrode active material is lithium manganese iron phosphate (LiMn). 0.5 Fe 0.5 PO4) and nickel-cobalt-manganese ternary materials (LiNi 0.7 Co 0.2 Mn 0.1 O2 (single crystal material), and the weight ratio of the two is 4:6.

[0074] Example 9

[0075] The difference between Example 9 and Example 1 is that the lithium manganese iron phosphate material is LiMn. 0.4 Fe 0.6 PO4.

[0076] Example 10

[0077] The difference between Example 10 and Example 1 is that the positive electrode active material is lithium manganese iron phosphate (LiMn). 0.5 Fe 0.5 PO4) and nickel-cobalt-manganese ternary materials (LiNi 0.7 Co 0.2 Mn 0.1 O2 (single crystal material), and the weight ratio of the two is 6:4.

[0078] Example 11

[0079] The difference between Example 11 and Example 1 is that the positive electrode active material is lithium manganese iron phosphate (LiMn). 0.4 Fe 0.6 PO4) and nickel-cobalt-manganese ternary materials (LiNi 0.8 Co 0.1 Mn 0.1O2 (single crystal material), and the weight ratio of the two is 7:3.

[0080] Example 12

[0081] The difference between Example 12 and Example 1 is that the lithium manganese iron phosphate material is LiMn. 0.6 Fe 0.4 PO4.

[0082] Example 13

[0083] The difference between Example 13 and Example 1 is that in the negative electrode active layer, the negative electrode active material is graphite, the second conductive agent is conductive carbon black, the second binder is styrene-butadiene rubber, and the thickener is sodium carboxymethyl cellulose, and the negative electrode active material, the second conductive agent, the second binder and the thickener are in a weight ratio of 96.4:0.8:1.8:1.2.

[0084] Example 14

[0085] The difference between Example 14 and Example 1 is that the diaphragm is a polyethylene diaphragm with a thickness of 12 μm, a porosity of 42%, and an air permeability of 80 s / 100 mL.

[0086] Example 15

[0087] The difference between Example 15 and Example 1 is that the organic solvent in the electrolyte is a mixture of ethylene carbonate, methyl ethyl carbonate and diethyl carbonate in a weight ratio of 30:40:30, the lithium salt is lithium hexafluorophosphate, and the conductivity of the electrolyte is 7.5 mS / cm.

[0088] Comparative Example 1

[0089] The difference between Comparative Example 1 and Example 1 is that the positive electrode active material is a mixture of lithium manganese iron phosphate and nickel cobalt manganese ternary materials in a weight ratio of 3:7, the first conductive agent is conductive carbon black, and the organic solvent in the electrolyte is a mixture of ethylene carbonate, ethyl methyl carbonate and diethyl carbonate in a weight ratio of 30:40:30.

[0090] Comparative Example 2

[0091] The difference between Comparative Example 2 and Example 1 is that the positive electrode active material is a mixture of lithium manganese iron phosphate and nickel cobalt manganese ternary materials in a weight ratio of 1:9.

[0092] Comparative Example 3

[0093] The difference between Comparative Example 3 and Example 1 is that the positive electrode active material is only lithium manganese iron phosphate.

[0094] Comparative Example 4

[0095] The difference between Comparative Example 4 and Example 1 is that the positive electrode active material is only a nickel-cobalt-manganese ternary material.

[0096] The safety and electrochemical performance of the lithium-ion batteries corresponding to the above embodiments and comparative examples were tested, and the results are shown in Table 1. The test methods are explained below:

[0097] Safety performance testing: The testing methods for safety performance refer to GB 38031-2020 Safety Requirements and Test Methods for Power Batteries for Electric Vehicles, with the addition of a single-cell thermal runaway test. Specifically, the single-cell thermal runaway test method includes: attaching a constant power heating plate (600W) to the surface of a single cell, connecting the circuit, and continuously heating the cell until thermal runaway is triggered. After triggering thermal runaway, heating is stopped, and the cell is observed for 1 hour. If the battery remains intact without tearing, the corresponding battery is considered to have passed the single-cell thermal runaway test; otherwise, the corresponding battery is considered to have failed the single-cell thermal runaway test.

[0098] Fast charging capability test: The lithium-ion battery in Example 5 was fabricated with three electrodes. After fabrication, the cell underwent normal process flow until it passed the capacity grading and was deemed qualified. The three-electrode cell was lithium-plated, and then the lithium-plated cell was charged at 0.33C constant current and constant voltage to 4.3V, with a cutoff current of 0.05C, and allowed to rest for 30 minutes. It was then discharged at 0.33C constant current to 2.5V and allowed to rest for 30 minutes; this process was repeated 3 times. The discharge capacity and nominal capacity were compared in the first 3 weeks, and the lower capacity was used as the rate C0 for subsequent tests. The C0 constant current charging was performed at 0.33 / 0.5 / 1 / 1.5 / 2 / 2.5 / 3 / 3.5 / 4 / 4.5 / 5 / 5.5 / 6 to the negative electrode potential reaching 0V or the battery voltage reaching 4.3V, followed by a 30-minute rest; then a 1C0 constant current discharge was performed to 2.5V and allowed to rest for 30 minutes. The test results are shown below. Figure 1 .

[0099] Fast charging time test: The corresponding lithium-ion battery is charged synchronously according to the fast charging strategy. When the negative electrode potential reaches 0V or the battery voltage reaches 4.3V, the charging is cut off. The time taken is the time it takes for the battery state to go from 10% to 80% SOC, which is the fast charging time.

[0100] Capacity retention test after 600 fast charging cycles at 25℃: The lithium-ion batteries in the examples and comparative examples were subjected to a 2.5-4.3V cycle test in a 25℃ constant temperature chamber. The test procedure was as follows: 4C constant current and constant voltage charging to 4.3V, resting for 30 minutes; 1C constant current discharging to 2.5V, resting for 30 minutes; repeat the charge and discharge cycle 600 times, and calculate the capacity retention rate.

[0101] High-temperature storage test: The lithium-ion batteries in the examples and comparative examples were subjected to charge-discharge tests from 2.5 to 4.3V in a 55℃ constant temperature chamber. The test procedure was as follows: charge at 0.33C constant current and constant voltage to 4.3V, cut off current at 0.05C, let stand for 30 minutes, discharge at 0.33C constant current to 2.5V, let stand for 30 minutes; repeat this step 3 times. The discharge capacity in the third week was recorded as C1. Charge at 0.33C to 4.3V at room temperature, let stand in a 55℃ constant temperature chamber for 7 days, and after 7 days, discharge the cell at 0.33C to 2.5V and record this discharge capacity as C2. Then charge at 0.33C constant current and constant voltage to 4.3V, cut off current at 0.05C, let stand for 30 minutes, discharge at 0.33C constant current to 2.5V, let stand for 30 minutes; repeat this step 3 times. The discharge capacity in week 3 was recorded as C3. The capacity retention rate after 7 days at 55℃ was calculated as C2 / C1 × 100%, and the capacity recovery rate after 7 days at 55℃ was calculated as C3 / C1 × 100%.

[0102] Table 1

[0103]

[0104] As can be seen from the above description, the embodiments of the present invention achieve the following technical effects:

[0105] Examples 1 to 15 utilize the lithium-ion battery provided in this application. In this lithium-ion battery, lithium manganese iron phosphate and nickel-cobalt-manganese ternary materials are combined as the positive electrode active material in the positive electrode active layer, and the ratio of the two is controlled. According to the fast-charging capability test, fast-charging cycle test, and high-temperature storage test data in Table 1, the lithium-ion batteries corresponding to Examples 1 to 15 not only have good safety but also good fast-charging speed and fast-charging cycle stability; furthermore, after being stored at high temperatures for a long time, they still maintain good capacity retention and capacity recovery rates. In particular, controlling the parameters in the lithium-ion battery within the preferred range further enhances these effects.

[0106] In Comparative Examples 1 and 2, the proportions of lithium manganese iron phosphate and nickel-cobalt-manganese ternary materials in the positive electrode active layer are outside the range specified in this application. While the electrochemical performance of the corresponding lithium-ion batteries is acceptable, the crucial safety test fails to meet basic usage requirements. In Comparative Example 3, only lithium manganese iron phosphate is used as the positive electrode active material in the positive electrode active layer; however, the fast-charging chemical performance of the corresponding lithium-ion battery is significantly different from that of the embodiments in this application. In Comparative Example 4, only nickel-cobalt-manganese ternary materials are used as the positive electrode active material in the positive electrode active layer; due to the high nickel content, the corresponding lithium-ion battery not only failed the safety performance test but also exhibited significantly different electrochemical performance compared to the embodiments in this application.

[0107] This application also tests the fast charging capability of the lithium-ion battery corresponding to Example 5 at different rates, and the test results are shown in [link to test results]. Figure 1 The fast-charge cycle performance of the lithium-ion battery corresponding to Example 5 was tested, and the test results are shown in [the table below]. Figure 2 .according to Figure 1 It is evident that the lithium-ion battery in this application still exhibits good fast-charging performance at different rate settings. According to... Figure 2 The results show that the lithium-ion battery in this application has good fast-charge cycle performance.

[0108] In summary, the composite cathode sheet in this application improves the performance of lithium-ion batteries in various aspects, including diffusion kinetics, structural stability, interface stability, cycle performance, and energy density, by combining lithium manganese iron phosphate and nickel-cobalt-manganese ternary materials as the positive active material in the positive active layer and controlling their ratio. This not only enables the lithium-ion battery to have a better charging rate but also achieves better energy density, safety performance, and cycle life, realizing a comprehensive performance improvement of the battery under fast charging conditions and providing a new path for developing high-performance, high-safety fast-charging lithium-ion batteries.

[0109] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A composite cathode material, characterized in that, The composite cathode material is composed of lithium manganese iron phosphate and nickel-cobalt-manganese ternary materials, with a weight ratio of (4-7):(3-6); wherein, The molecular formula of the lithium manganese iron phosphate material is: LiMn z Fe 1-z PO4, 0 < z < 1; The molecular formula of the nickel-cobalt-manganese ternary material is: LiNi 1-x-y Co x Mn y O2, 0.1≤x≤0.5, 0.1≤y<1, and 1-xy>0.

2. The composite cathode material according to claim 1, characterized in that, In the composite cathode material, the weight ratio of the lithium manganese iron phosphate material to the nickel cobalt manganese ternary material is (6-7):(3-4); Preferably, the molecular formula of the lithium manganese iron phosphate material is: LiMn z Fe 1-z PO4, wherein 0 < z < 1, and the molar ratio of Mn to Fe in the lithium manganese iron phosphate material is (1 ~ 1.5): 1; More preferably, the molecular formula of the lithium manganese iron phosphate material is: LiMn 0.5 Fe 0.5 PO4; The molecular formula of the nickel-cobalt-manganese ternary material is: LiNi 0.7 Co 0.2 Mn 0.1 O2; Preferably, the nickel-cobalt-manganese ternary material is a single-crystal material.

3. A positive electrode sheet, characterized in that, The positive electrode includes a first current collector and a positive active layer located on one side of the surface of the first current collector. The material of the positive active layer includes the composite positive electrode material as described in claim 1 or 2, a first conductive agent, and a first binder.

4. The positive electrode sheet according to claim 3, characterized in that, By weight percentage, the composite positive electrode material comprises 95-98% of the positive electrode active layer material, the first conductive agent comprises 1-3% of the first conductive agent, and the first binder comprises 1-3% of the first conductive agent. Preferably, by weight percentage, the composite positive electrode material comprises 96.5-97% of the positive electrode active layer material, the first conductive agent comprises 1.2-2% of the first conductive agent, and the first binder comprises 1.5-2% of the first conductive agent. Preferably, the first conductive agent is one or more of carbon nanotubes, conductive carbon black, and graphene; More preferably, the first conductive agent is a composite of the carbon nanotubes, the conductive carbon black, and the graphene; preferably, the weight ratio of the conductive carbon black, the graphene, and the carbon nanotubes is (0.8–1.5):(0.1–0.5): (0.01～0.1)； Preferably, the first adhesive is one or more of polyvinylidene fluoride, polyacrylonitrile, and polyimide; Preferably, the first current collector is at least one of a carbon-coated aluminum foil current collector or an aluminum foil current collector; Preferably, the thickness of the first current collector is 8–15 μm.

5. A lithium-ion battery, the lithium-ion battery comprising a positive electrode, a negative electrode, a separator, and an electrolyte, characterized in that, The positive electrode is the positive electrode as described in claim 3 or 4.

6. The lithium-ion battery according to claim 5, characterized in that, The negative electrode sheet includes a second current collector and a negative electrode active layer located on one side surface of the second current collector. The material of the negative electrode active layer includes a negative electrode active material, a second conductive agent, a second binder, and a thickener. The positive electrode, the separator, and the negative electrode are alternately stacked and encapsulated in a metal casing, and the positive electrode, the separator, and the negative electrode are wetted by the electrolyte.

7. The lithium-ion battery according to claim 6, characterized in that, By weight percentage, the negative electrode active layer comprises 93-97% negative electrode active material, 0.5-3% second conductive agent, 1-2.5% second binder, and 0.1-0.5% thickener; Preferably, by weight percentage, the negative electrode active layer comprises 95-96% negative electrode active material, 1-2% second conductive agent, 1.2-2% second binder, and 0.2-0.3% thickener; Preferably, the negative electrode active material is artificial graphite; preferably, the artificial graphite is carbon-coated secondary single particles; And / or, the second conductive agent is conductive carbon black and / or aqueous carbon nanotubes; And / or, the second adhesive is styrene-butadiene rubber and / or an acrylic adhesive; more preferably, the second adhesive is an acrylic adhesive, or, the second adhesive is a blend of the styrene-butadiene rubber and the acrylic adhesive; preferably, the acrylic adhesive is polyacrylic acid or polyacrylate; And / or, the thickener is sodium methylcellulose and / or a copolymer of butadiene-styrene.

8. The lithium-ion battery according to any one of claims 5 to 7, characterized in that, The porosity of the diaphragm is ≥46%, the air permeability of the diaphragm is ≥90s / 100mL, and the thickness of the diaphragm is 8~15μm; Preferably, the porosity of the diaphragm is 36-48%, and the air permeability of the diaphragm is 120-180 s / 100 mL; Preferably, the diaphragm is a polyethylene diaphragm; more preferably, the diaphragm is a ceramic-coated polyethylene diaphragm. Preferably, the electrolyte comprises an organic solvent, a lithium salt, a positive electrode film-forming additive, and a negative electrode film-forming additive, and the conductivity of the electrolyte is ≥8 mS / cm; Preferably, the concentration of the lithium salt is 0.8–1.5 mol / L; Preferably, the lithium salt is lithium hexafluorophosphate and / or lithium difluorosulfonyl imide; Preferably, the weight content of the positive electrode film-forming agent in the electrolyte is 1-3%; Preferably, the negative electrode film-forming additive in the electrolyte contains 1-3% by weight. Preferably, the positive electrode film-forming additive is one or more selected from vinyl sulfate, lithium difluoroborate, and tris(trimethyl)silyl phosphate; Preferably, the negative electrode film-forming additive is vinylene carbonate; Preferably, the electrolyte further includes a low-resistance additive, and the low-resistance additive is at least one of lithium difluorophosphate or lithium difluorooxalate borate. Preferably, the organic solvent is an organic carbonate solvent; more preferably, the organic solvent is one or more selected from ethylene carbonate, methyl ethyl carbonate, and diethyl carbonate. Preferably, the ethylene carbonate, methyl ethyl carbonate, and diethyl carbonate are used in combination; more preferably, the weight ratio of the ethylene carbonate, methyl ethyl carbonate, and diethyl carbonate is (20-40):(40-70). (10～30)； Preferably, the second current collector is at least one of copper foil current collector or copper alloy current collector; preferably, the thickness of the first current collector is 5-8 μm; Preferably, the metal casing is made of aluminum; more preferably, the thickness of the metal casing is 0.2 to 0.8 mm.

9. A method for preparing a lithium-ion battery according to any one of claims 5 to 8, characterized in that, The preparation method includes the following steps: The positive electrode active material, the first conductive agent and the first binder are mixed and dissolved in the first solvent to obtain the first slurry; the first slurry is coated on one side of the first current collector and dried to obtain the positive electrode sheet; The negative electrode active material, the second conductive agent, the second binder and the thickener are mixed and dissolved in the second solvent to obtain the second slurry; the second slurry is coated on one side of the second current collector and dried to obtain the negative electrode sheet; The positive electrode, the separator, and the negative electrode are subjected to rolling, die-cutting, slitting, stacking, electrolyte injection, and formation processes to obtain the lithium-ion battery.

10. The method for preparing a lithium-ion battery according to claim 9, characterized in that, The first drying temperature is 100-150℃, and the time is 1-20 min; Preferably, the second drying temperature is 40–80°C, and the time is 1–20 min; Preferably, the first solvent is N-methylpyrrolidone; Preferably, the second solvent is deionized water; Preferably, the solid content of the first slurry is 57-62%; and the solid content of the second slurry is 50-56%.

11. A battery module, characterized in that, The battery module includes a plurality of lithium-ion batteries as described in any one of claims 5 to 8.

12. A battery pack, characterized in that, The battery pack comprises the battery module as described in claim 11.

13. An electrical appliance, characterized in that, The electrical equipment includes the battery pack as described in claim 12.

14. An energy storage system, characterized in that, The energy storage system includes the battery pack of claim 12.

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