Negative electrode material, method for manufacturing the same, and lithium-ion battery

Abstract

This invention provides a negative electrode material, a method for manufacturing the same, and a lithium-ion battery. [Solution] The negative electrode material includes natural graphite and a coating layer covering the surface of the natural graphite. The compression index K of the negative electrode material is 30 ≤ K ≤ 80. The compression index K = 100(V0 - V F ) / V0, where V0 is the apparent volume per unit mass in the dispersed state, V F This is the tap volume per unit mass. The anode material of the present invention has appropriate powder fluidity, reduces the functional groups on the surface of the anode material particles, improves dispersibility during processing, and, because there are fewer functional groups on the surface, reduces side reactions during high-temperature storage, thereby improving the high-temperature storage performance of the anode material.

Description

[Technical Field]

[0001] This invention relates to the field of lithium-ion batteries, and more specifically to negative electrode materials, methods for manufacturing the same, and lithium-ion batteries. [Background technology]

[0002] Natural graphite possesses excellent kinetic properties, particularly at low temperatures, where it offers significant advantages. This is because its abundant porosity improves electrolyte wettability and facilitates end-face lithium intercalation, while the surface of natural graphite is rich in functional groups, promoting rapid desolvation of organolithium compounds. However, these factors lead to more reaction sites in natural graphite, significantly reducing its high-temperature storage performance.

[0003] Therefore, there is a need to provide an anode material that can improve the high-temperature storage performance of natural graphite while maintaining the advantages of natural graphite's dynamic performance. [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] In view of the problems present in the prior art, the present invention provides a negative electrode material, a method for producing the same, and a lithium-ion battery that improve upon the problem of deterioration of the high-temperature storage performance of natural graphite. [Means for solving the problem]

[0005] To achieve the above and other related objectives, a first aspect of the present invention provides a negative electrode material comprising natural graphite and a coating layer covering the surface of the natural graphite, wherein the compression index K of the negative electrode material is 30 ≤ K ≤ 80, and the compression index K = 100(V0 - V F ) / V0, where V0 is the apparent volume per unit mass in the dispersed state, V F This is the tap volume per unit mass.

[0006] In one embodiment of the present invention, the Young's modulus E of the negative electrode material is 17 GPa ≤ E ≤ 25 GPa.

[0007] In one embodiment of the present invention, the contact angle θ between the electrolyte and the surface of the negative electrode material is 82° ≤ θ ≤ 90°.

[0008] In one embodiment of the present invention, the mass of the coating layer accounts for 0.5% to 1% of the mass of the natural graphite; the material of the coating layer contains aluminum oxide or titanium oxide, and the particle size Dv50 of the aluminum oxide or titanium oxide is less than 0.1 μm.

[0009] In one embodiment of the present invention, the particle size Dv50 of the negative electrode material is 5 μm to 20 μm.

[0010] A second aspect of the present invention provides a method for manufacturing a negative electrode material. The manufacturing method is as follows: The first precursor is obtained by crushing and molding natural flake graphite raw material. The first precursor is heat-molded, and the surface functional groups are removed to obtain a second precursor. The second precursor is subjected to cold quenching, and a coating layer is formed on the surface of the precursor after cold quenching to obtain the negative electrode material. Includes.

[0011] In one embodiment of the present invention, the first precursor is heat-molded and the surface functional groups are removed. Heating the aforementioned first precursor to a first temperature, Subsequently, the first precursor is subjected to hydroxylation treatment using deionized water, wherein the amount of deionized water added accounts for 1% to 3% of the mass of the first precursor. Subsequently, the first precursor is peroxidized using an oxygen-containing gas, wherein the oxygen-containing gas is a mixture of nitrogen and oxygen, and the mass content of oxygen in the mixture is 10% to 40%. Afterward, it is heated to a second temperature, vented to the outside until the gas pressure drops below 0.2 atmospheres, and then kept warm for 4 hours. Includes, The first temperature is 450°C to 600°C, and the second temperature is 800°C to 1000°C.

[0012] In one embodiment of the present invention, forming a coating layer on the surface of a precursor after cold quenching includes ball milling the material after cold quenching treatment with γ-type aluminum oxide for 1 to 3 hours, then firing it in an inert atmosphere at 700°C to 900°C for 4 to 8 hours, and then cooling it to room temperature to obtain a negative electrode material; the particle size Dv50 of the γ-type aluminum oxide is less than 0.1 μm, and the amount of the γ-type aluminum oxide is 1% or less of the mass of the second precursor.

[0013] In one embodiment of the present invention, the cold quenching treatment is performed by cooling the second precursor using an inert gas, the temperature difference between the temperature of the cold quenching treatment and the temperature of the previous treatment is 400°C to 600°C, and the flow rate of the inert gas is 60 L / min or less; and / or, the particle size Dv50 of the first precursor is 15 μm to 25 μm, and the particle size distribution width (Dv90 - Dv10) / Dv50 < 1.1.

[0014] A third aspect of the present invention provides a lithium-ion battery. The lithium-ion battery includes a negative electrode sheet comprising the negative electrode material described in any of the above descriptions or the negative electrode material manufactured by any of the above manufacturing methods. [Effects of the Invention]

[0015] The anode material of the present invention has appropriate powder fluidity by adjusting the compression index. This means that the functional groups on the surface of the anode material particles are reduced, the interaction force between adjacent particles is reduced, dispersibility during processing is improved, and the possibility of particle aggregation is reduced. At the same time, because there are fewer functional groups on the surface, side reactions of the anode material during high-temperature storage are reduced, thereby improving the high-temperature storage performance of the anode material. Furthermore, by adjusting the Young's modulus of the anode material to give it a certain mechanical strength, the occurrence of microcracks during the cold pressing process is reduced, the specific surface area of ​​reaction activity during high-temperature storage is reduced, and the high-temperature storage performance of the anode material is further improved. In addition, by adjusting the contact angle between the anode material and the electrolyte, the wettability to the electrolyte is reduced, which reduces the specific surface area of ​​reaction activity during high-temperature storage and further improves the high-temperature storage performance of the anode material.

[0016] The present invention, when manufacturing a negative electrode material, uses natural flake graphite as a raw material and sequentially performs processes such as hot forming, removal of surface functional groups, and cold quenching. As a result, the negative electrode material maintains the advantages of the kinetic performance of natural graphite while having an appropriate compressibility index, thereby reducing the possibility of aggregation of the negative electrode material, reducing side reactions during high-temperature storage, and improving the high-temperature storage performance of the negative electrode material. The manufacturing method of the present invention can effectively solve the problem of the deterioration of the high-temperature storage performance of natural graphite, and because it is simple and easy to operate, it can significantly reduce the cost and energy consumption of the negative electrode.

[0017] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in describing the embodiments are briefly introduced below. Clearly, the drawings described below represent only a portion of the embodiments of the present invention. Those skilled in the art can obtain other embodiments based on these drawings without any creative effort. [Brief explanation of the drawing]

[0018] [Figure 1] This flowchart shows one embodiment of the method for manufacturing the negative electrode material of the present invention. [Modes for carrying out the invention]

[0019] The following specific examples are used to illustrate the implementation method of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments. Various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that unless otherwise specified, the following embodiments and features can be combined with each other. In the test methods in the following embodiments, when specific conditions are not specified, usually, they are implemented according to conventional conditions or the conditions recommended by each manufacturer.

[0020] Unless otherwise defined, all technical terms and scientific terms used in this specification have the same meaning as commonly understood by those skilled in the technical field related to the present invention. The terms used in this specification are only for the purpose of explaining specific embodiments and do not limit the present invention. The term "and / or" used in this specification includes any combination of one or more of the related listed items.

[0021] In the specification, when referring to a numerical range, unless otherwise specified, the distribution of selectable values within the numerical range is considered to be continuous and includes both endpoints (the minimum value and the maximum value) of the range and all values between these two endpoints. When multiple numerical ranges are provided to describe a feature or characteristic, these numerical ranges can be combined.

[0022] In the specification, the compression index is tested for the tap density and the bulk (loose) density by referring to GB / T 6609.25-2023, and then the apparent volume and the tap volume are calculated according to the formula ρ = m / v respectively, and further the compression index is calculated according to K = 100(V0 - V F ) / V0. The Young's modulus was tested by referring to GB / T 34186-2017. The contact angle was tested by referring to GB / T 36086-2018.

[0023] Natural graphite possesses a rich porous structure, which enhances the wettability of the electrolyte and provides a lithium intercalation space. Furthermore, the abundant functional groups on the surface of natural graphite promote the rapid desolvation of organolithium compounds. These properties give natural graphite excellent kinetic performance, but simultaneously increase the number of reaction sites and side reactions, potentially reducing its high-temperature storage properties. Existing techniques to improve the storage properties of natural graphite include methods such as filling natural graphite with impregnating pitch and then subjecting it to graphitization to reduce its porosity, and methods of passivating the graphite surface through ultra-high-temperature graphitization. All of these methods affect the kinetic performance of natural graphite.

[0024] Based on this, the present invention provides a negative electrode material, a method for manufacturing the negative electrode material, and a lithium-ion battery containing the negative electrode material. By controlling the compression index K of the negative electrode material to achieve appropriate powder fluidity, side reactions can be reduced while maintaining the kinetic advantages of natural graphite, and the high-temperature storage performance of natural graphite can be effectively improved.

[0025] A first aspect of the present invention provides a negative electrode material. The negative electrode material comprises natural graphite and a coating layer covering the surface of the natural graphite, wherein the compressibility index K of the negative electrode material is 30 ≤ K ≤ 80. Here, the compressibility index K = 100(V0-V F ) / V0, where V0 is the apparent volume per unit mass under the negative electrode material dispersion state, and V Fis the tap volume per unit mass. The compression index K is used as an indicator that reflects the fluidity of the anode material. The smaller the compression index K, the better the powder fluidity of the anode material. Macroscopically, this indicates that the interaction force between anode material particles is small, and microscopically, it indicates that there are fewer functional groups on the surface of the anode material particles. This improves dispersibility during processing and reduces the possibility of particle aggregation. At the same time, because there are fewer functional groups on the surface of the anode material particles, fewer side reactions occur during high-temperature storage, thereby improving the high-temperature storage performance of the anode material. Conversely, the larger the compression index K, the poorer the powder fluidity of the anode material. This means that there are more functional groups on the surface of the anode material particles, which leads to more side reactions during high-temperature storage and poor high-temperature storage performance. However, if the compression index is too small, the surface functional groups of the anode material are almost completely lost, which may affect the kinetic performance of the natural graphite itself. Therefore, in the present invention, by limiting the compression index K of the anode material to the range of 30 ≤ K ≤ 80, it is possible to reduce the functional groups on the surface of the anode material and improve its high-temperature storage performance while maintaining the kinetic performance of natural graphite. In some embodiments, the compression index K of the anode material may be, for example, 30, 50, 60, or 80.

[0026] In another embodiment, the Young's modulus E of the negative electrode material is 17 GPa ≤ E ≤ 25 GPa. Young's modulus represents the degree of change in the initial length per unit cross-sectional area of ​​powder under a constant tensile stress and reflects the deformation of the material under stress. The formula for Young's modulus is E = σ / ε, where σ is the stress per unit area of ​​the material and ε is the strain per unit length. From the formula for Young's modulus, it can be seen that when the stress σ per unit area of ​​the material is constant, the larger the Young's modulus E, the smaller the strain ε per unit length, meaning the material is less deformable, i.e., has higher mechanical strength. Conversely, the smaller the Young's modulus E, the larger the strain ε per unit length, meaning the material is more deformable, i.e., has lower mechanical strength. During the charging and discharging process of a lithium-ion battery, the negative electrode material undergoes insertion and removal of lithium ions. If the mechanical strength of the negative electrode material is low (the material is relatively soft), the volume deforms significantly during the insertion and removal of lithium ions and does not recover, which is unfavorable for the lithium-ion battery cycle. On the other hand, if the negative electrode material has high mechanical strength (has a certain hardness), the fine crystalline structure can be better maintained during the insertion and removal of lithium ions, resulting in less irreversible deformation and improved cycle characteristics of the lithium-ion battery. However, if the hardness of the negative electrode material is too high, it not only becomes difficult to compress, but microcracks may also occur, potentially increasing the reactive specific surface area during high-temperature storage. Therefore, by controlling the Young's modulus E of the negative electrode material to an appropriate range, it is possible to maintain good mechanical strength, reduce the occurrence of microcracks during the cold pressing process, reduce the reactive specific surface area during high-temperature storage, and improve cycle characteristics. In some embodiments, the Young's modulus E of the negative electrode material may be 17 GPa, 20 GPa, 22 GPa, or 25 GPa, etc.

[0027] In another embodiment, the contact angle θ between the electrolyte and the negative electrode material surface is 82° ≤ θ ≤ 90°. The contact angle θ is the reciprocal of the radius of curvature of the smallest surface formed by the liquid surface on the solid surface when the liquid comes into contact with the solid surface. This is an important parameter for measuring the wettability of a liquid on a solid surface. When the contact angle θ is less than 90°, the solid surface is hydrophilic, and the liquid can easily wet the solid. A smaller contact angle indicates better wettability, while a larger contact angle indicates worse wettability. In the present invention, the contact angle θ of the electrolyte on the negative electrode material surface is 82° ≤ θ ≤ 90°, which reduces the wettability of the electrolyte to the negative electrode material, decreases the specific surface area of ​​reaction activity during high-temperature storage, and further improves the high-temperature storage performance of the negative electrode material. Exemplaryly, the contact angle θ may be 82°, 85°, 88°, or 90°. The electrolyte used here is an electrolyte commonly used in lithium-ion batteries. The electrolyte solvent includes, but is not limited to, dimethyl carbonate. The electrolyte used in this invention is manufactured by Xinya Cancan New Materials Technology (Quzhou) Co., Ltd., model number: E3.

[0028] In another embodiment, the material of the coating layer may be aluminum oxide or titanium oxide. Furthermore, the coating layer material is aluminum oxide. By coating the surface of natural graphite with aluminum oxide, on the one hand, contact between the natural graphite and the electrolyte can be reduced, side reactions can be reduced, and the high-temperature stability of the anode material can be improved. On the other hand, because aluminum oxide has a relatively high true density, the Young's modulus and compressibility of the anode material can be further improved.

[0029] In another embodiment, the particle size Dv50 of the negative electrode material is 5 μm to 20 μm. Dv50 represents the particle size at which the cumulative volume distribution accounts for 50% of the particle size distribution. Exemplaryly, the particle size Dv50 of the negative electrode material may be, for example, 5 μm, 10 μm, 15 μm, or 20 μm.

[0030] A second aspect of the present invention provides a method for manufacturing a negative electrode material. The negative electrode material obtained by the manufacturing method has a low compressibility index, thereby giving the negative electrode material appropriate powder fluidity and reducing the possibility of particle aggregation and the possibility of side reactions occurring during high-temperature storage.

[0031] Referring to Figure 1, the method for manufacturing the above-mentioned negative electrode material includes at least the following steps: S1, obtaining a first precursor by crushing and molding a natural flake-like graphite raw material, S2, the first precursor is heated and molded, and the surface functional groups are removed to obtain the second precursor. S3. The second precursor is subjected to cold quenching, and a coating layer is formed on the surface of the precursor after cold quenching to obtain the negative electrode material.

[0032] Specifically, in process S1, natural flake graphite is used as the raw material. Before crushing and molding, pretreatment is required to remove impurity minerals from the raw material. Pretreatment includes washing and flotation. First, the natural flake graphite is washed with water to remove mud, dust, and other impurities from the graphite surface, preparing it for the subsequent flotation process. In flotation, a flotation agent is added to achieve selective adhesion of graphite particles to other impurity minerals, thereby separating the graphite from other minerals and improving the purity of the natural flake graphite.

[0033] Since the particle size of natural flake graphite is relatively large, sometimes reaching micrometers or even millimeters, it is necessary to crush and mold the natural flake graphite to obtain a first precursor with an appropriate particle size distribution. Specifically, this involves high-frequency molding of water-washed and flotation-treated natural flake graphite to reduce the natural flake graphite size Dv50 at the millimeter level to 15-25 μm, removing large and small particle sizes by classification, and ensuring that the particle size distribution width (Dv90-Dv10) / Dv50 < 1.1. The above high-frequency molding can employ conventional molding methods in this field, such as molding natural flake graphite at a high frequency of 90 Hz for 6 hours using a honeycomb mill. The honeycomb mill effectively disperses and de-aggregates aggregated graphite flakes, thereby reducing damage to large flake graphite and improving the quality of the graphite product. Note that Dv90 represents the particle size at which the cumulative volume distribution accounts for 90% of the particle size distribution. Dv10 represents the particle size at which the cumulative volume distribution in the particle size distribution is 10%. The particle size distribution width (Dv90-Dv10) / Dv50 is an index indicating the uniformity of particle size. A larger particle size distribution width indicates a wider particle size distribution and a larger difference between large and small particles. A particle size distribution width closer to 0 indicates uniform particle size and high size uniformity. In step S1, by reducing the particle size Dv50 of the natural flake graphite to 15-25 μm and setting the particle size distribution width (Dv90-Dv10) / Dv50 < 1.1, the final negative electrode material can satisfy its required particle size. For example, the Dv50 of the first precursor may be 15 μm, 20 μm, or 25 μm. The particle size distribution width (Dv90-Dv10) / Dv50 may be 1, 0.5, or 0.

[0034] In step S2, functional groups on the surface of the first precursor are removed. Specifically, this includes the following: First, the first precursor obtained in step S1 is recovered and transferred to an air jet mill where it is heated to a first temperature to remove crystal water from the first precursor. Here, the first temperature is 450°C to 600°C, and may be, for example, 450°C, 500°C, or 600°C. Next, deionized water is injected by pump to hydroxylate the first precursor and remove some impurity functional groups such as ester groups and acyl groups. Here, the amount of deionized water added accounts for 1% to 3% by mass of the first precursor, and exemplary, the amount of deionized water added may be 1%, 2%, or 3%. After that, while maintaining aeration, ultra-high frequency thermoforming is performed at a molding frequency of 100 Hz to 140 Hz, for example, 100 Hz, 120 Hz, or 140 Hz, and heat molding is performed for 0.5 hours to 2 hours, for example, 0.5 hours, 1 hour, 1.5 hours, or 2 hours. After hot forming, an oxygen-containing gas is introduced from the top of the air jet mill to peroxidize the first precursor, forming easily detachable oxygen-containing functional groups. Here, a mixture of nitrogen and oxygen is used as the oxygen-containing gas, and the mass content of oxygen in the mixed gas is 10% to 40%, for example, 10%, 20%, 30%, or 40%. The flow rate of the oxygen-containing gas is 2 L / min, and aeration is maintained for 4 hours simultaneously with forming. After stopping the aeration, the chamber is heated to a second temperature and exhausted to the outside to remove the oxygen-containing functional groups formed in the above step. The second temperature is 800 to 1000°C, and may be 800°C, 900°C, or 1000°C as an example. After the gas pressure in the chamber falls below 0.2 atmospheres, the temperature is maintained for 4 hours to stabilize the crystalline form and obtain the second precursor.

[0035] Subsequently, step S3 is performed to rapidly cool the second precursor obtained in step S2 to obtain a negative electrode material having a certain mechanical strength. In the cold rapid cooling process, the second precursor is gradient cooled using an inert gas. The inert gas may be, for example, nitrogen, helium, or argon. Gradient cooling means cooling to a certain temperature, holding it for a certain period of time, then cooling to another temperature, holding it for a certain period of time, and repeating this process until the set temperature is reached. The temperature difference between each cold rapid cooling process should not be too large. If the temperature difference is too large, microcracks are likely to form inside the graphite. In this invention, the temperature difference between the cold rapid cooling processes is 400 to 600°C, and specifically may be 400°C, 500°C, or 600°C. The number of cold rapid cooling processes is at least one. If the number of processes is too large, the performance will not improve significantly and will instead lead to increased energy consumption. The flow rate of the inert gas should be 60 L / min or less, preferably 30 L / min to 60 L / min, and may be, for example, 30 L / min, 40 L / min, 50 L / min, 60 L / min, etc. If the flow rate of the inert gas exceeds 60 L / min, instantaneous cooling will occur, causing defects such as microcracks inside the material.

[0036] After the cold quenching process is complete, a coating layer is formed on the surface of the precursor. In another embodiment, the material of the coating layer is aluminum oxide, and the aluminum oxide coating process is as follows. The material, after cold quenching using γ-type aluminum oxide, is ball-milled for 1 to 3 hours, then calcined at 700°C to 900°C for 4 to 8 hours in an inert atmosphere, and finally cooled to room temperature in an inert atmosphere to obtain a natural graphite anode material with a surface coated with aluminum oxide. The calcination temperature may be, for example, 700°C, 800°C, or 900°C, and the calcination time may be, for example, 4 hours, 6 hours, or 8 hours. γ-type aluminum oxide is used because it is unstable and can chemically adsorb onto the graphite surface, react with the dangling bonds on the graphite surface, and form stable α-type aluminum oxide. The particle size Dv50 of the γ-type aluminum oxide is less than 0.1 μm. The smaller the particle size, the easier it is to adsorb onto the graphite surface, allowing for the formation of a uniform aluminum oxide coating layer. The amount of γ-type aluminum oxide is 1% or less, more specifically 0.5 to 1%, and more specifically 0.8% relative to the mass of the second precursor. The negative electrode material consists of natural graphite coated with a layer of aluminum oxide. The aluminum oxide coating prevents direct contact between the natural graphite and the electrolyte, reducing side reactions and improving the stability of the negative electrode material. Furthermore, the removal of the functional groups significantly reduces the wettability between the electrolytes, which is detrimental to lithium ion transport within the battery. Therefore, the aluminum oxide coating improves the wettability between the electrolyte and the negative electrode material.

[0037] In other embodiments, the coating layer material may be replaced with titanium dioxide. The titanium dioxide coating process can be described in detail here by referring to conventional processes in the art.

[0038] The particle size Dv50 of the negative electrode material obtained after the above process is 5 μm to 20 μm, and as an example, the particle size Dv50 of the negative electrode material may be 5 μm, 10 μm, 15 μm, or 20 μm.

[0039] The negative electrode material produced by the above manufacturing method has a relatively low compression index, a relatively high Young's modulus, and an appropriate contact angle, and can maintain the dynamic performance of natural graphite while also possessing excellent high-temperature storage capabilities.

[0040] A third aspect of the present invention provides a lithium-ion battery. The lithium-ion battery includes non-aqueous electrolyte lithium batteries, solid-state lithium batteries, and the like. Taking a non-aqueous electrolyte lithium battery as an example, the lithium-ion battery includes a negative electrode sheet, a positive electrode sheet, and a separator disposed between the positive electrode sheet and the negative electrode sheet. Here, the negative electrode sheet includes the negative electrode material described above in the present invention or a negative electrode material manufactured by the above manufacturing method.

[0041] Specifically, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on at least one side surface of the negative electrode current collector. The negative electrode current collector can be made from materials conventionally used in the art, such as copper foil or carbon-coated copper foil. The negative electrode active material layer may be disposed on one side surface of the negative electrode current collector or on both sides. The negative electrode active material layer includes a negative electrode active material, a negative electrode conductive agent, and a negative electrode binder. Here, the negative electrode active material is selected from materials capable of intercalating and releasing lithium ions. In the present invention, the negative electrode active material is the above-mentioned negative electrode material. In other embodiments, the negative electrode active material may be selected from a combination of the above-mentioned negative electrode material and other materials. For example, a silicon-based negative electrode material is used. The silicon-based negative electrode material is a silicon oxide compound SiO x(0 < x < 2) includes silicon-carbon materials, elemental silicon, etc. However, the present invention is not limited to the materials listed above, and other conventional materials that can be used as the negative electrode active material can also be used. These negative electrode active materials can be used alone or in combination of two or more. The negative electrode conductive agent has the function of improving electron conductivity and collecting minute currents between the negative electrode active materials and between the negative electrode active material and the negative electrode current collector, reducing the contact resistance of the battery, and improving the electron transfer speed. In some embodiments, the negative electrode conductive agent includes at least one of conductive carbon black (SP), conductive graphite, carbon fiber, carbon nanotube, and graphene. Optionally, the negative electrode conductive agent can be selected from conductive carbon black, a composition of carbon fiber and conductive carbon black, or a composition of carbon nanotube and graphene, etc. The binder is used to adhere the negative electrode active material and the negative electrode conductive agent, impart a certain adhesive force to the negative electrode active material layer, and adhere it onto the negative electrode current collector. As an example, the negative electrode binder is selected from at least one of polyacrylic acid (PAA), polyvinylidene fluoride (PVDF), styrene-butadiene rubber (SBR), carboxymethyl cellulose (CMC), styrene acrylate, and acrylic multi-component copolymer. For example, the negative electrode binder is polyvinylidene fluoride, or a composition of styrene-butadiene rubber and carboxymethyl cellulose, etc. The ratios of the negative electrode active material, the negative electrode conductive agent, and the negative electrode binder can be set according to the conventions in the art.

[0042] The manufacturing process of the negative electrode sheet is as follows, for example. First, the negative electrode active material, the negative electrode conductive agent, and the negative electrode binder are uniformly mixed and stirred at a certain ratio in a solvent such as deionized water to form a negative electrode slurry. Further, the negative electrode slurry is applied onto the negative electrode current collector, and through processes such as drying, rolling, and cutting, a negative electrode sheet is obtained.

[0043] The positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer disposed on at least one side surface of the positive electrode current collector. The positive electrode current collector can be made from materials conventionally used in the art, such as aluminum foil or carbon-coated aluminum foil. The positive electrode active material layer may be disposed on one side surface of the positive electrode current collector or on both sides surface. The positive electrode active material layer includes a positive electrode active material, a positive electrode conductive agent, and a positive electrode binder. Here, the positive electrode active material can be any positive electrode material suitable for lithium-ion batteries, that is, any compound that allows for reversible insertion and removal of lithium ions can be used. For example, the positive electrode active material may be a ternary material such as nickel-cobalt-manganese ternary material (NCM), nickel-cobalt-aluminum ternary material (NCA), or an iron-lithium positive electrode material such as lithium iron phosphate (LFP) or lithium iron manganese phosphate (LMFP), or even a conventional material such as lithium cobalt oxide or lithium manganese oxide. These materials may be used individually or in combination. The positive electrode binder may be one or more of the following: polyvinylidene fluoride (PVDF), polyethylene oxide (PEO), polyamide (PA), polyacrylonitrile (PAN), polyacrylate, polyethylene ether, polymethyl methacrylate (PMMA), ethylene-propylene-diene ternary copolymer (EPDM), polyhexafluoropropylene, or styrene-butadiene rubber (SBR). The positive electrode conductive agent includes, but is not limited to, at least one of conductive carbon black (SP), conductive graphite, carbon fiber, carbon nanotubes, and graphene. Optionally, the conductive agent may be conductive carbon black, a composition of carbon fiber and conductive carbon black, or a composition of carbon nanotubes and graphene, etc. The ratio of the positive electrode active material, the positive electrode conductive agent, and the positive electrode binder can be set according to the conventions of the art.

[0044] The manufacturing process for a positive electrode sheet is as follows: First, the positive electrode active material, positive electrode conductive agent, and positive electrode binder are uniformly mixed and stirred in a constant ratio in a solvent such as N-methylpyrrolidone (NMP) to form a positive electrode slurry. Then, the positive electrode slurry is applied onto a positive electrode current collector, and a positive electrode sheet is obtained through processes such as drying, rolling, and cutting.

[0045] The separator is placed between the positive and negative electrode sheets to prevent short circuits inside the battery and allow lithium ions to pass and move between the positive and negative electrodes, thereby enabling the battery's charging and discharging process. The separator can be made from porous materials such as polyethylene (PE), polypropylene (PP), glass fiber film, or composite film. The separator thickness is 9-18 μm, the air permeability is 180 seconds / 100 mL to 380 seconds / 100 mL, and the porosity is 30-50%.

[0046] Lithium-ion batteries further contain an electrolyte, which plays a role in conducting lithium ions during the charging and discharging process of the battery. The electrolyte contains an organic solvent and a lithium salt, and the lithium salt may be one or more selected from lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalate borate (LiDFOB), lithium bisoxalate borate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorobisoxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP). Furthermore, as the lithium salt, a composition of lithium hexafluorophosphate or lithium hexafluorophosphate with other lithium salts that has superior overall performance is used, for example, a composition of lithium hexafluorophosphate with bis(fluorosulfonyl)imide lithium. The organic solvent may be one or more selected from fluoroethylene carbonate (FEC), ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), and ethyl propyl carbonate (EPC). The electrolyte may further contain functional additives such as fluoroethylene carbonate (FEC), propylene-1,3-sultone (PST), tetravinylsilane (TVSI), vinylene carbonate (VC), and ethylene sulfate (DTD), which can be added according to actual manufacturing requirements.

[0047] Battery assembly: The fabricated positive electrode sheet, separator, and negative electrode sheet are arranged in sequence, with the separator positioned between the positive and negative electrode sheets to act as an insulator. A bare cell is obtained by winding or laminating the sheets. The bare cell is placed in a battery case, and a lithium-ion battery is obtained through processes such as assembly, electrolyte injection, chemical conversion, and capacity adjustment.

[0048] In other embodiments, the lithium-ion battery may be a solid-state lithium-ion battery. The electrolyte of a solid-state lithium-ion battery is solid. Common solid electrolytes include oxide solid electrolytes, halide solid electrolytes, sulfide solid electrolytes, etc., but these will not be described in detail here. Those skilled in the art can select them according to the requirements of actual manufacturing.

[0049] Furthermore, the structures of the lithium-ion batteries described above, which are not explained in detail, can all be set up by referring to existing technologies, and therefore will not be explained in detail here.

[0050] The lithium-ion battery of the present invention can be used to supply power to electronic devices in the form of a single battery, a battery module, or a battery pack. Electronic devices include, but are not limited to, mobile phones, tablets, laptops, electric toys, electric vehicles, new energy vehicles, ships, and spacecraft. Electric toys include stationary or mobile electric toys such as game consoles, electric vehicle toys, electric ship toys, and electric airplane toys. Spacecraft include airplanes, rockets, space shuttles, and spaceships. New energy vehicles include pure electric vehicles, hybrid electric vehicles, and extended-range electric vehicles.

[0051] The technical solutions of the present invention will be described in detail below through several specific embodiments and comparative examples. Unless otherwise specified, all raw materials and reagents used in the following embodiments are commercially available or can be prepared by conventional methods in the art, and all equipment used in the embodiments is commercially available. [Examples]

[0052] Example 1 This embodiment provides a negative electrode material comprising natural graphite and aluminum oxide. The aluminum oxide is uniformly coated on the surface of the natural graphite, with the amount of aluminum oxide coating accounting for 1% of the mass of the natural graphite. The compression index K of the negative electrode material is 54, the Young's modulus E is 21 GPa, and the contact angle θ is 85°. The particle size Dv50 of the negative electrode material is 12.7 μm.

[0053] This embodiment further provides a method for manufacturing the negative electrode material, which includes the following steps. Step 1: After washing and flotation of the natural flake graphite, high-frequency molding at 90 Hz is performed using a honeycomb mill for 6 hours to reduce the millimeter-level natural flake graphite size Dv50 to 15-25 μm. Large and small particle sizes are removed by classification, and the particle size distribution width (Dv90-Dv10) / Dv50 < 1.1 is obtained to obtain the first precursor. Step 2: The powder of the first precursor is collected and transferred to an air jet mill, where it is heated to T1: 600°C. Deionized water is then injected by pump so that the mass ratio of the first precursor to the deionized water is 50:1 (the amount of deionized water added is 2% of the mass of the first precursor). After that, ultra-high frequency molding at 120Hz is performed for 2 hours. Then, a mixed gas of nitrogen and oxygen at 600°C (mass ratio 4:1, the mass percentage content of oxygen in the mixed gas is 20%) is introduced from the top of the air jet mill, and the flow rate of the mixed gas is set to L1:2L / min. Aeration is maintained for 4 hours simultaneously with molding. After stopping the aeration, it is heated to T2: 800°C and evacuated to the outside. After the gas pressure in the chamber falls below 0.2 atmospheres, it is kept warm for 4 hours to obtain the second precursor. Then, inert gas is introduced from the top of the air jet mill and cooled to T3: 200°C. The inert gas flow rate L2 was 60 L / min. After maintaining aeration for 2 hours, heating was stopped to obtain the spherical precursor. Step 3: The spherical precursor is ball-milled with γ-type aluminum oxide for 2 hours. The particle size of the γ-type aluminum oxide is less than 0.1 μm, and the amount added is 1% by weight. After 2 hours of ball-milling, the sphericity of the finished product is greater than 0.93. The product is calcined at 800°C for 6 hours under an inert atmosphere and then cooled to room temperature under an inert atmosphere to obtain a finished product with a particle size of 12.7 μm.

[0054] Referring to Table 1, the present invention also provides Examples 2-9 and Comparative Examples 1-5.

[0055] Example 2 The differences between this embodiment and Embodiment 1 are that the compression index K of the negative electrode material is 67, the Young's modulus E is 23 Gpa, the contact angle θ is 83°, and the particle size Dv50 of the negative electrode material is 13.1 μm. The amount of deionized water added during the hydroxide treatment in the manufacturing process remains 1%, and no other aspects are changed.

[0056] Example 3 The differences between this embodiment and Embodiment 1 are that the compression index K of the negative electrode material is 42, the Young's modulus E is 21 GPa, the contact angle θ is 88°, and the particle size Dv50 of the negative electrode material is 12.5 μm. The amount of deionized water added during the hydroxide treatment in the manufacturing process remains 3%, and no other aspects are changed.

[0057] Example 4 The differences between this embodiment and Embodiment 1 are that the compression index K of the negative electrode material is 75, the Young's modulus E is 25 Gpa, the contact angle θ is 82°, and the particle size Dv50 of the negative electrode material is 13.5 μm. In the peroxidation treatment during the manufacturing process, the oxygen content in the mixed gas is 40%.

[0058] Example 5 The differences between this embodiment and Embodiment 1 are that the compression index K of the negative electrode material is 35, the Young's modulus E is 20 Gpa, the contact angle θ is 90°, and the particle size Dv50 of the negative electrode material is 12.4 μm. In the peroxidation treatment during the manufacturing process, the oxygen content in the mixed gas is 10%.

[0059] Example 6 The differences between this embodiment and Embodiment 1 are that the compression index K of the negative electrode material is 30, the Young's modulus E is 17 GPa, the contact angle θ is 87°, and the particle size Dv50 of the negative electrode material is 12.3 μm. During the manufacturing process, the temperature T2 for exhausting to the outside is adjusted to 1000°C. In the cold quenching process, the system is first cooled with an inert gas at 600°C, aeration is maintained for 2 hours, and then it is cooled with an inert gas at 200°C, aeration is maintained for 2 hours.

[0060] Example 7 The differences between this embodiment and Embodiment 1 are that the compression index K of the negative electrode material is 30, the Young's modulus E is 17 Gpa, the contact angle θ is 88°, and the particle size Dv50 of the negative electrode material is 12.1 μm. The temperature at which the wastewater is exhausted to the outside during the manufacturing process is raised to 900°C, and the cold quenching temperature is 300°C.

[0061] Example 8 The differences between this embodiment and Embodiment 1 are that the compression index K of the negative electrode material is 80, the Young's modulus E is 19 GPa, the contact angle θ is 90°, and the particle size Dv50 of the negative electrode material is 13 μm. The amount of γ-type aluminum oxide used in step 3 of the manufacturing method is 0.5%.

[0062] Example 9 The differences between this embodiment and Embodiment 1 are that the compression index K of the negative electrode material is 68, the Young's modulus E is 21 Gpa, the contact angle θ is 87°, and the particle size Dv50 of the negative electrode material is 13.3 μm. The amount of γ-type aluminum oxide used in step 3 of the manufacturing method is 0.8%.

[0063] Comparative Example 1 The differences between this comparative example and Embodiment 1 are that the compression index K of the negative electrode material is 26, the Young's modulus E is 17 GPa, the contact angle θ is 90°, and the particle size Dv50 of the negative electrode material is 11.6 μm. In step 2 of the manufacturing process, the exhaust temperature is raised to 1250°C.

[0064] Comparative Example 2 The differences between this comparative example and Embodiment 1 are that the compression index K of the negative electrode material is 123, the Young's modulus E is 30 GPa, the contact angle θ is 102°, and the particle size Dv50 of the negative electrode material is 15.4 μm. In this manufacturing method, a heating step was not performed before the exhaust step.

[0065] Comparative Example 3 In this comparative example, commercially available 12 μm natural graphite was used. The compression index K of the negative electrode material in this comparative example was 138, the Young's modulus E was 2 Gpa, and the contact angle θ was 74°; the particle size Dv50 of the negative electrode material was 11.2 μm.

[0066] Comparative Example 4 The differences between this comparative example and Embodiment 1 are that the compression index K of the negative electrode material is 95, the Young's modulus E is 15 GPa, the contact angle θ is 81°, and the particle size Dv50 of the negative electrode material is 12.7 μm. The amount of γ-type aluminum oxide used in step 3 of the manufacturing method is 0.2%.

[0067] Comparative Example 5 The differences between this comparative example and Embodiment 1 are that the compression index K of the negative electrode material is 106, the Young's modulus E is 15 GPa, and the contact angle θ is 80°; the particle size Dv50 of the negative electrode material is 10.5 μm; and the surface of the natural graphite is not coated with aluminum oxide. Steps 3 and 4 are not included in this manufacturing method. The composition and parameters of the first and second solid electrolyte layers in each example and comparative example are as shown in Table 1.

[0068] Parameter characteristics and manufacturing method parameters of the negative electrode materials of Examples 1 to 9 and Comparative Examples 1 to 5 [Table 1]

[0069] To verify the performance of the negative electrode material of the present invention, the inventors applied the negative electrode materials of Examples 1 to 9 and Comparative Examples 1 to 5 to lithium-ion batteries respectively, and conducted performance tests on each lithium-ion battery. The configuration and test method of the lithium-ion battery are as follows, and the test results are shown in Table 2.

[0070] The lithium-ion battery includes a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte. The positive electrode sheet, the separator, and the negative electrode sheet are wound to form a cell, and then the cell is housed in a case and the electrolyte is injected to complete a pouch-type battery.

[0071] Here, preparation of the negative electrode sheet: The negative electrode material obtained in the example or comparative example, a conductive agent (SP), a binder (PAA and SBR, the mass ratio of both is 1.3:0.5), and carboxymethyl cellulose (CMC) as a thickener are mixed at a mass ratio of 97.2:0.5:1.8:0.5 (total 100 parts by mass), and then 82 parts by mass of deionized water is added and mixed uniformly to obtain a negative electrode slurry. Then, the negative electrode slurry is uniformly coated on a copper foil. Further, processes such as drying, rolling, and cutting are performed to prepare a negative electrode sheet.

[0072] Preparation of the positive electrode sheet: The positive electrode active material NCM622 (LiNi 0.6 Co 0.2 Mn 0.2 O2), PVDF, and SP are mixed at a mass ratio of 97:1.8:1.2 (total 100 parts by mass), and then 82 parts by mass of NMP is added to obtain a positive electrode slurry. The obtained positive electrode slurry is coated on at least one surface of an aluminum foil, dried, rolled and compressed to obtain a positive electrode sheet.

[0073] Separator: Polyethylene film, separator thickness 11 μm, separator air permeability 230 seconds / 100 mL, separator porosity 40%.

[0074] A commercially available electrolyte (manufactured by Xinya Sushan New Materials Technology (Quzhou) Co., Ltd., model number: E3) was used.

[0075] Battery performance testing method (1) Initial efficiency of all batteries Total battery charge capacity: The lithium-ion battery is charged to 4.35V with a current of 1C, and the charge capacity at this stage is recorded as c1. Then, it is charged at a constant voltage until the cutoff current reaches 0.05C, and the charge capacity at this stage is recorded as c2. The total charge capacity of all batteries is the sum of c1 and c2. Total battery discharge capacity: After fully charging the cells and letting them sit for 30 minutes, discharge them to 2.8V with a current of 1C. Record the discharge capacity at this stage as c3. This is the total discharge capacity of the batteries. Initial efficiency = Total battery discharge capacity c3 / Total battery charge capacity (c1 + c2) × 100%.

[0076] (2) Quick charging time The cell was directly charged to an 8% State of Charge (SOC) with a current of 0.33C. Then, based on the measured three-electrode windows of the cell (c1, c2, c3, c4, c5, c6, c7, c8 respectively), it was charged in stages up to 80% through charging windows of 10%, 20%, 30%, 40%, 50%, 60%, 70%, and 80%. That is, charging was performed using c1 from 8% to 10%, c2 from 10% to 20%, and so on. The charging time from 8% to 80% SOC was recorded as a criterion for measuring rapid charging capability. The formula is as follows: T(8%-80%) =(0.02 / c1+0.1 / c2+0.1 / c3+0.1 / c4+0.1 / c5+0.1 / c6+0.1 / c7+0.1 / c8)*60.

[0077] (3) Number of cycles at room temperature At 25°C, cycling was performed at a charge / discharge rate of 2.8–4.25V with a charge / discharge rate of 0.21A / g (calculated based on the mass of the positive electrode active material). The number of cycles at which 80% of the initial capacity was reached was recorded as the effect of the material's cycling properties.

[0078] (4) Number of storage days A constant capacity test was performed at 25°C using a current of 0.33C, and the capacity was recorded as C0. The cells were then stored at a high temperature of 60°C. Subsequently, as a measure of storage capacity, the cells were removed every 7 days, and their capacities were measured at room temperature and recorded as C1, C2, ..., Cn until Cn first fell below 80% of C0.

[0079] Performance of assembled batteries in Examples 1-9 and Comparative Examples 1-5 [Table 2]

[0080] As can be seen from Tables 1-2, the compression index, Young's modulus, and contact angle of the anode material can be adjusted by adjusting parameters such as the hydroxide treatment, peroxide treatment, cold quenching treatment, and amount of aluminum oxide coating in the manufacturing process. The compression index of the anode materials obtained in Examples 1-9 is significantly lower than that of commercially available natural graphite (Comparative Example 3), indicating that the anode material of the present invention has appropriate powder fluidity, reduces functional groups on the surface of the anode material particles, thereby reducing side reactions in processes such as battery cycling and storage, and improving the battery's cycling and storage performance. The assembled battery shows significant improvements in both room temperature cycling characteristics and high-temperature storage performance compared to Comparative Example 3. Although the rapid charging performance is slightly lower, the overall performance of the battery is significantly improved. The compression index of the anode materials in Comparative Examples 1-2 and Comparative Example 4 is not within the range defined in this application, and although the assembled batteries show improvements compared to Comparative Example 3, the initial efficiency, rapid charging time, cycling characteristics, and storage characteristics are all inferior to those of Examples 1-9. The negative electrode material in Comparative Example 5 contains natural graphite, and the surface of the natural graphite is not coated with aluminum oxide. Because the functional groups on the surface of the natural graphite are completely exposed, the powder has poor fluidity and a relatively high compressibility index. The exposure of surface functional groups leads to an increase in side reactions, resulting in relatively poor high-temperature storage characteristics. [Industrial applicability]

[0081] The anode material provided by the present invention has appropriate powder fluidity by adjusting the compression index, reduces the functional groups on the surface of the anode material, decreases the interaction force between adjacent particles, improves dispersibility during processing, reduces the possibility of particle aggregation, and simultaneously reduces side reactions during high-temperature storage due to the fewer functional groups on the surface, thereby improving the high-temperature storage performance of the anode material. Furthermore, the anode material has a relatively high Young's modulus and a certain level of mechanical strength, reduces the occurrence of microcracks during the cold pressing process, reduces the specific surface area of ​​reaction activity during high-temperature storage, and further improves the high-temperature storage performance of the anode material. Moreover, because the anode material has a relatively large contact angle with the electrolyte, the wettability of the electrolyte to the anode material is reduced, which further reduces the specific surface area of ​​reaction activity during high-temperature storage and further improves the high-temperature storage performance of the anode material.Therefore, the present invention effectively overcomes several practical problems in the prior art and has high utility value and significance.

[0082] The embodiments described above are merely illustrative of the principles and effects of the present invention and do not limit it. Those skilled in the art can modify or change the embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or changes made by those skilled in the art without departing from the spirit and technical idea disclosed herein are still included within the claims of the present invention. [Explanation of Symbols]

[0083] S1~S3: Process

Claims

1. It is a negative electrode material, Natural graphite and A coating layer covering the surface of the aforementioned natural graphite, Includes, The compression index K of the anode material is 30 ≤ K ≤ 80. The compression index K = 100 (V ０ -V Ｆ ) / V ０ And in the formula V ０ V is the apparent volume per unit mass in the dispersed state. Ｆ This is the tap volume per unit mass. A negative electrode material characterized by the following features.

2. The Young's modulus E of the anode material is 17 GPa ≤ E ≤ 25 GPa. The negative electrode material according to claim 1, characterized in that...

3. The contact angle θ between the electrolyte and the surface of the negative electrode material is 82° ≤ θ ≤ 90°. The negative electrode material according to claim 1 or 2, characterized in that

4. The mass of the coating layer accounts for 0.5% to 1% of the mass of the natural graphite. The material of the coating layer includes aluminum oxide or titanium oxide. The particle size Dv50 of the aluminum oxide or titanium oxide is less than 0.1 μm. The negative electrode material according to claim 1, characterized in that...

5. The particle size Dv50 of the negative electrode material is 5 μm to 20 μm. The negative electrode material according to claim 1, characterized in that...

6. The first precursor is obtained by crushing and molding natural flaky graphite raw material, The first precursor is heat-molded, and the surface functional groups are removed to obtain a second precursor. The second precursor is subjected to cold quenching, and a coating layer is formed on the surface of the precursor after cold quenching to obtain the negative electrode material. A method for producing a negative electrode material according to claim 1, characterized by including the following:

7. Heat molding the first precursor and removing the surface functional groups is Heating the first precursor to a first temperature, Subsequently, the first precursor is subjected to hydroxylation treatment using deionized water, wherein the amount of deionized water added accounts for 1% to 3% of the mass of the first precursor. Subsequently, the first precursor is peroxidized using an oxygen-containing gas, wherein the oxygen-containing gas is a mixture of nitrogen and oxygen, and the mass content of oxygen in the mixture is 10% to 40%. Afterward, it is heated to a second temperature, vented to the outside until the gas pressure drops below 0.2 atmospheres, and then kept warm for 4 hours. Includes, The first temperature is 450°C to 600°C, and the second temperature is 800°C to 1000°C. A method for producing a negative electrode material according to claim 6, characterized in that

8. Forming a coating layer on the surface of a precursor after rapid cold cooling is After cold quenching using γ-type aluminum oxide, the material is subjected to ball milling for 1 to 3 hours. The process then includes firing in an inert atmosphere at 700°C to 900°C for 4 to 8 hours, followed by cooling to room temperature to obtain the negative electrode material. The particle size Dv50 of the γ-type aluminum oxide is less than 0.1 μm, and the amount of the γ-type aluminum oxide is 1% or less relative to the mass of the second precursor. A method for producing a negative electrode material according to claim 6, characterized in that

9. The cold quenching treatment involves cooling the second precursor using an inert gas, the temperature difference between the temperature of the cold quenching treatment and the temperature of the previous treatment is 400°C to 600°C, and the flow rate of the inert gas is 60 L / min or less. and / or, The particle size Dv50 of the first precursor is 15 μm to 25 μm, and the particle size distribution width (Dv90 - Dv10) / Dv50 < 1.

1. A method for producing a negative electrode material according to claim 6, characterized in that

10. The present invention includes a negative electrode sheet containing a negative electrode material manufactured by the negative electrode material manufacturing method described in any one of claims 1 to 5 or any one of claims 6 to 9. A lithium-ion battery characterized by the following features.

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