Modified lithium ion battery negative electrode material and preparation method and application thereof

Abstract

The application provides a modified lithium ion battery negative electrode material and a preparation method and application thereof, relates to the technical field of battery energy storage, and the negative electrode material takes graphite as a core, an outer layer of the graphite is coated with a polymethyl methacrylate layer and a polydopamine layer from the outer surface of the graphite outward in sequence; wherein the mass fraction of the polymethyl methacrylate is 0.5-2% of the graphite; and the mass fraction of the polydopamine is 0.5-2% of the graphite. The application adopts a composite coating layer of PMMA and polydopamine to modify the graphite negative electrode material to form an artificial SEI. The composite coating layer not only retains the excellent electrochemical stability of PMMA and the good wettability of polydopamine, but also significantly improves the comprehensive performance of the graphite negative electrode through the synergistic effect between PMMA and polydopamine.

Description

Technical Field

[0001] This invention relates to the field of battery energy storage technology, and in particular to a modified lithium-ion battery anode material, its preparation method, and its application. Background Technology

[0002] Graphite has been widely used as an anode material in lithium-ion batteries, particularly in portable devices, energy storage batteries, and power batteries. However, graphite anode materials have limitations in cycle stability, fast charging, and rate performance, especially in energy storage. Long-term cycling causes the solid electrolyte interphase (SEI) on the anode surface to continuously break down and regenerate, leading to increased battery resistance, capacity decay, and reduced cycle life. To address these issues, researchers have attempted to improve the performance of graphite anodes by forming artificial SEIs through surface coating. In existing technologies, single polymer nanomaterial artificial SEIs can improve the performance of graphite anodes to some extent, but they generally suffer from problems such as single coating layer, uneven coating, and high repetition rate, resulting in limited performance improvement. Summary of the Invention

[0003] To address the shortcomings of existing technologies, the present invention aims to provide a modified lithium-ion battery anode material, its preparation method, and its application. The method involves modifying graphite anode materials by forming an artificial SEI (Sediment-Insulated Layer) using a composite coating layer of PMMA and polydopamine. This composite coating layer not only retains the excellent electrochemical stability of PMMA and the good wettability of polydopamine, but also significantly improves the overall performance of the graphite anode through the synergistic effect between the two.

[0004] To achieve the above objectives, the present invention adopts the following technical solution:

[0005] This invention provides a modified lithium-ion battery anode material, wherein the anode material uses graphite as a core, and the outer layer of the graphite is sequentially coated with a polymethyl methacrylate layer and a polydopamine layer from the outer surface of the graphite to the outside.

[0006] The mass fraction of polymethyl methacrylate is 0.5-2% of graphite.

[0007] The mass fraction of polydopamine is 0.5-2% of graphite.

[0008] Furthermore, based on the above technical solution, the thickness of both the polymethyl methacrylate layer and the polydopamine layer is 2-20 μm.

[0009] Furthermore, based on the above technical solution, the mass fraction of polymethyl methacrylate is 0.5-1% of graphite;

[0010] And / or, the mass fraction of polydopamine is 0.5-1% of graphite.

[0011] Furthermore, based on the above technical solution, the graphite is artificial graphite prepared from graphite raw material coke;

[0012] Among them, graphite raw material coke includes one or more of petroleum coke, pitch coke, and needle coke;

[0013] Artificial graphite includes single-particle and secondary-particle graphite;

[0014] Among them, the mass ratio of secondary particles to single particles is x, where 1≤x≤4;

[0015] The D50 of secondary particles is 12-16 μm, and the D50 of single particles is 10-15 μm;

[0016] And / or, the graphite has a D50 of 10-16 μm and a specific surface area of ​​1.2-1.8 m². 2 / g.

[0017] The present invention also provides a method for preparing the modified lithium-ion battery anode material as described above, comprising the following steps:

[0018] S1: Graphite powder is mixed with methyl methacrylate ethanol solution, and the mixture is obtained after preliminary heating to evaporate the ethanol;

[0019] S2: In a protective atmosphere, an initiator is added to the mixture, followed by heat treatment to obtain PMMA-coated graphite material;

[0020] S3: The PMMA-coated graphite material is dispersed in an alkaline aqueous solution containing dopamine, and a polydopamine coating layer is formed on the outside of the PMMA layer through the self-polymerization reaction of dopamine. After the reaction is completed, the modified lithium-ion battery anode material is obtained by washing and drying.

[0021] Furthermore, based on the above technical solution, in step S1, the mass ratio of the graphite powder to the methyl methacrylate in the methyl methacrylate ethanol solution is (98-99.5):(2-0.5).

[0022] And / or, the mass concentration of methyl methacrylate in the methyl methacrylate ethanol solution is 25-55 wt%;

[0023] And / or, in step S1, the initial heating temperature is 40-50℃, and the heating time is 2-3 hours.

[0024] Furthermore, based on the above technical solution, in step S2, the heat treatment temperature is 50-60℃ and the time is 3-4h;

[0025] And / or, the initiator includes one or more of azobisisobutyronitrile, azobisisoheptanenitrile, and benzoyl peroxide;

[0026] And / or, in step S2, the protective atmosphere includes one or more of argon, helium, nitrogen, or xenon.

[0027] Furthermore, based on the above technical solution, in step S3, the mass concentration of dopamine in the alkaline aqueous solution containing dopamine is 0.5-1 g / L;

[0028] And / or, the base used in the alkaline aqueous solution containing dopamine includes Tris-HCl buffer or NaOH;

[0029] And / or, the pH of the alkaline aqueous solution containing dopamine is 8-10;

[0030] And / or, in step S3, the mass ratio of graphite powder to dopamine in the PMMA-coated graphite material is (98-99.5):(2-0.5);

[0031] And / or, in step S3, the temperature of the self-polymerization reaction is 25-60°C, and the time is 24-48h.

[0032] The present invention also provides a negative electrode sheet, the negative electrode sheet comprising the modified lithium-ion battery negative electrode material as described above or the modified lithium-ion battery negative electrode material prepared by the preparation method of the modified lithium-ion battery negative electrode material as described above.

[0033] The present invention also provides a lithium-ion battery comprising the negative electrode sheet as described above, or comprising the modified lithium-ion battery negative electrode material as described above, or comprising the modified lithium-ion battery negative electrode material prepared by the preparation method of the modified lithium-ion battery negative electrode material as described above.

[0034] The present invention provides a modified lithium-ion battery anode material, its preparation method, and its application, with the following beneficial effects:

[0035] 1. Improved fast charging capability: The composite coating significantly improves the wettability of the graphite anode and the electrolyte, reduces the resistance to lithium-ion transport, and enables the graphite anode to maintain a high capacity even at high current densities.

[0036] 2. Enhanced cycle stability: The PMMA layer effectively inhibits the decomposition of the electrolyte and the formation of lithium dendrites, while the polydopamine layer further enhances the mechanical stability of the graphite anode and extends the cycle life of the battery.

[0037] 3. Optimized electrochemical performance: The composite coating also improves the first coulombic efficiency and rate performance of the graphite anode, making the overall battery performance more excellent. Attached Figure Description

[0038] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0039] Figure 1 A schematic diagram of the structure of the modified lithium-ion battery anode material provided by the present invention;

[0040] Icons: 1. Graphite; 2. PMMA layer; 3. PDA layer. Detailed Implementation

[0041] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Those skilled in the art should understand that the embodiments described are merely illustrative of the invention and should not be considered as specific limitations thereof. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention. Process parameters not specifically specified in the following embodiments are generally performed under conventional conditions.

[0042] The endpoints and any values ​​of the ranges disclosed in this invention are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this invention.

[0043] According to a first aspect of the present invention, a modified lithium-ion battery anode material is provided, wherein the anode material has graphite as a core, and the outer layer of the graphite is sequentially coated with a polymethyl methacrylate (PMMA) layer and a polydopamine (PDA) layer from the outer surface of the graphite outward.

[0044] The mass fraction of polymethyl methacrylate is 0.5-2% of graphite (e.g., 0.8%, 1%, 1.2%, 1.4%, 1.6%, 1.8%, etc.).

[0045] The mass fraction of polydopamine is 0.5-2% of graphite (e.g., 0.8%, 1%, 1.2%, 1.4%, 1.6%, 1.8%, etc.).

[0046] Specifically, such as Figure 1As shown, this invention sequentially coats the surface of graphite 1 with a PMMA layer 2 and a PDA layer 3. PMMA is selected as the first coating material because its excellent electrochemical stability and mechanical strength can effectively protect the graphite anode and inhibit electrolyte decomposition and lithium dendrite formation. A polydopamine layer is then coated outside the PMMA layer. The strong adhesion and good wettability of polydopamine further improve the interfacial contact between the graphite anode and the electrolyte, and promote the rapid transport of lithium ions.

[0047] This invention improves the cycle stability of graphite anodes during long-term cycling and enhances the liquid retention capacity of graphite, making it less prone to rapid decline in battery capacity retention in the later stages of cycling. Furthermore, PMMA is inexpensive and has good dielectric properties, while polydopamine has strong liquid retention capacity. The combination of these two can improve the cycle stability and rate performance of graphite anodes.

[0048] As an optional embodiment of the present invention, the thickness of both the polymethyl methacrylate (PMMA) layer and the polydopamine (PDA) layer is 2μm-20μm (e.g., 4μm, 6μm, 8μm, 10μm, 12μm, 14μm, 16μm, 18μm, etc.).

[0049] Specifically, a polymethyl methacrylate (PMMA) layer and a polydopamine (PDA) layer are uniformly coated sequentially around the core graphite. The inventors' research revealed that the mass fraction of both PMMA and PDA in the outer coating is 0.5-2% of the graphite. The thickness or amount of these two outer coating layers significantly impacts the performance of the graphite anode material. Too much or too little artificial SEI will affect performance; too little or too thin an outer coating will result in uneven coating, increasing anode side reactions and affecting battery cycle stability, liquid retention capacity, and rate performance. Excessive or excessively thick outer coatings will affect the specific capacity of the graphite anode and thus the Li-C content. + Diffusion can affect the cycle stability of the battery.

[0050] As an optional embodiment of the present invention, the mass fraction of polymethyl methacrylate is 0.5-1% of graphite (e.g., 0.6%, 0.7%, 0.8%, 0.9%, etc.), preferably 1%.

[0051] The mass fraction of polydopamine is 0.5-1% of graphite (e.g., 0.6%, 0.7%, 0.8%, 0.9%, etc.), preferably 1%.

[0052] As an optional embodiment of the present invention, the graphite used in the present invention is artificial graphite commonly used in the art, such as being prepared from one or more of petroleum coke, pitch coke, and needle coke, including single particles and secondary particles.

[0053] Among them, the mass ratio of secondary particles to single particles is x, where 1≤x≤4;

[0054] The D50 of secondary particles is 12-16μm (e.g., 13μm, 14μm, 15μm, etc.), while the D50 of single particles is 10-15μm (e.g., 11μm, 12μm, 13μm, 14μm, etc.).

[0055] Specifically, this invention limits the secondary particles to a mass ratio of single particles of x, where 1 ≤ x ≤ 4. This is because within this range, mixing single and secondary particles is beneficial for improving battery cycle performance and addressing processing performance issues such as wetting and sedimentation. If the range of 1 ≤ x ≤ 4 is exceeded, the battery's processing and electrical performance will be poor. If the proportion of single particles is greater than that of secondary particles, or if all particles are single particles, insufficient wetting of the cell may lead to insufficient electrical performance due to the poorer wetting properties of single particles compared to secondary particles. If the proportion of single particles is less than 1 / 4 of that of secondary particles, or if all particles are secondary particles, processing difficulties will arise, leading to more side reactions and a rapid decline in battery capacity retention during later stages of cycling.

[0056] Specifically, the secondary particle granulation method is called pre-granulation. Pre-granulation refers to granulation carried out before graphitization, with graphitization as the node. Granulation carried out after graphitization is called post-granulation.

[0057] The graphite used in this invention can have a particle size within the conventional range in the art. As an optional embodiment of this invention, the graphite has a D50 of 10-16 μm (e.g., 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, etc.) and a specific surface area of ​​1.2-1.8 m². 2 / g.

[0058] According to a second aspect of the present invention, a method for preparing the above-mentioned modified lithium-ion battery anode material is provided, comprising the following steps:

[0059] S1: Graphite powder is mixed with methyl methacrylate ethanol solution, and the mixture is obtained after preliminary heating to evaporate the ethanol;

[0060] S2: In a protective atmosphere, an initiator is added to the mixture, followed by heat treatment to obtain PMMA-coated graphite material;

[0061] S3: The PMMA-coated graphite material is dispersed in an alkaline aqueous solution containing dopamine, and a polydopamine coating layer is formed on the outside of the PMMA layer through the self-polymerization reaction of dopamine. After the reaction is completed, the modified lithium-ion battery anode material is obtained by washing and drying.

[0062] As an optional embodiment of the present invention, the graphite powder is prepared from graphite raw material coke, which is one or more of petroleum coke, pitch coke, and needle coke.

[0063] Specifically, graphite coke is an important raw material in the graphite production process, mainly including petroleum coke, pitch coke, and needle coke. Among them, petroleum coke is a by-product of petroleum processing and has advantages such as high fixed carbon and low volatile matter, making it an important raw material for graphite production. Needle coke has a significant fibrous structure, is easy to graphitize, and is often used to produce high-performance graphite products. Pitch coke is used as a binder and impregnating agent to improve the mechanical strength and conductivity of graphite products. According to actual needs, the above-mentioned graphite coke is selected and subjected to crushing and shaping, pitch air jet milling, granulation, crushing and grading, graphitization, mixing, sieving, and demagnetization in sequence to obtain artificial graphite. If necessary, the graphite can be coated.

[0064] As an optional embodiment of the present invention, in step S1, the mass ratio of the graphite powder to the methyl methacrylate (MMA) ethanol solution is (98-99.5):(2-0.5), such as 98.3:1.7, 98.5:1.5, 98.7:1.3, 99:1, 99.3:0.7, 99.5:0.5, etc.

[0065] Furthermore, the mass concentration of methyl methacrylate in the methyl methacrylate ethanol solution is 25-55 wt% (e.g., 30 wt%, 35 wt%, 40 wt%, 45 wt%, etc.).

[0066] As an optional embodiment of the present invention, in step S1, the initial heating temperature is 40-50℃ and the heating time is 2-3h.

[0067] As an optional embodiment of the present invention, in step S2, the temperature of the heat treatment is 50-60°C and the time is 3-4 hours;

[0068] The initiator includes one or more of azobisisobutyronitrile (AIBN), azobisisoheptanenitrile, and benzoyl peroxide (BPO);

[0069] In step S2, the protective atmosphere includes one or more of argon, helium, nitrogen, or xenon.

[0070] Specifically, the purpose of initially heating the graphite powder and MMA ethanol solution is to evaporate the ethanol solution. It is important to control the heating temperature to avoid premature polymerization of MMA or oxidation of graphite. As the temperature rises, the ethanol gradually evaporates, eventually yielding a mixture containing graphite powder and MMA. The mixture is then heat-treated at high temperature in an inert gas atmosphere. The inert gas atmosphere provides an oxygen-free or low-oxygen environment, which can prevent oxidation of graphite and MMA at high temperatures. High-temperature heat treatment can promote the polymerization reaction of MMA, and the initiator can accelerate the polymerization process, allowing PMMA to uniformly coat the graphite surface.

[0071] As an optional embodiment of the present invention, in step S3, the mass concentration of dopamine in the alkaline aqueous solution containing dopamine is 0.5-1 g / L (e.g., 0.6 g / L, 0.7 g / L, 0.8 g / L, 0.9 g / L, etc.).

[0072] The base used in the alkaline aqueous solution containing dopamine includes Tris-HCl buffer or NaOH;

[0073] The pH value of the alkaline aqueous solution containing dopamine is 8-10, preferably 8.

[0074] As an optional embodiment of the present invention, in step S3, the mass ratio of graphite powder to dopamine in the PMMA-coated graphite material is (98-99.5):(2-0.5), such as 98.3:1.7, 98.5:1.5, 98.7:1.3, 99:1, 99.3:0.7, 99.5:0.5, etc.

[0075] As an optional embodiment of the present invention, in step S3, the temperature of the self-polymerization reaction is 25-60°C and the time is 24-48h.

[0076] Specifically, PMMA-coated graphite material is dispersed and impregnated in an alkaline aqueous solution containing dopamine. A polydopamine coating layer is formed on the outside of the PMMA layer through the self-polymerization reaction of dopamine. The material is then washed multiple times with deionized water and dried in a drying oven at 60-70°C to obtain a modified lithium-ion battery anode material.

[0077] According to a third aspect of the present invention, a negative electrode sheet is provided, the negative electrode sheet comprising the modified lithium-ion battery negative electrode material as described above or the modified lithium-ion battery negative electrode material prepared by the preparation method of the modified lithium-ion battery negative electrode material as described above.

[0078] According to a fourth aspect of the present invention, a lithium-ion battery is provided, comprising the negative electrode sheet as described above, or comprising the modified lithium-ion battery negative electrode material as described above, or the modified lithium-ion battery negative electrode material prepared by the preparation method of the modified lithium-ion battery negative electrode material as described above.

[0079] The present invention will now be described in further detail with reference to specific embodiments and comparative examples.

[0080] The graphite secondary or single particles involved in this invention can be purchased from the following manufacturers: BTR New Materials, Shanghai Shanshan, Jiangxi Zichen, Xiangfenghua, or Hebei Kuntian.

[0081] Example 1

[0082] The modified anode material prepared in this embodiment uses graphite as the core, with PMMA and polydopamine layers sequentially coated on the outside of the core. The mass fraction of PMMA is 0.5% of graphite, and the mass fraction of polydopamine is 0.5% of graphite.

[0083] S1: Mix graphite powder with MMA ethanol solution and heat at 45°C for 3 hours to obtain a mixture;

[0084] The graphite powder includes single particles and secondary particles, with the ratio of secondary particles (D50 = 13 μm) to single particles (D50 = 10 μm) being 1:1.

[0085] The mass ratio of added graphite powder to methyl methacrylate (MMA) ethanol solution is 99.5:0.5.

[0086] The mass concentration of methyl methacrylate in the methyl methacrylate ethanol solution is 40%.

[0087] S2: Add initiator AIBN to the mixture, and then perform heat treatment in an argon atmosphere at a temperature of 60°C for 4 hours to obtain PMMA-coated graphite material.

[0088] S3: At a temperature of 25°C, the PMMA-coated graphite material is dispersed in an alkaline aqueous solution containing dopamine for 24 hours. A polydopamine coating layer is formed on the outside of the PMMA layer through the self-polymerization reaction of dopamine. After the reaction is completed, the material is washed multiple times with deionized water and then dried in a drying oven at 60°C to obtain the modified lithium-ion battery anode material.

[0089] The dopamine-containing alkaline aqueous solution has a dopamine concentration of 1 g / L, the alkali used in the dopamine-containing alkaline aqueous solution is Tris-HCl solution, the mass ratio of graphite powder to dopamine is 99.5:0.5, and the pH value of the dopamine-containing alkaline aqueous solution is 8.0.

[0090] The thicknesses of the PMMA layer and the polydopamine layer in the modified lithium-ion battery anode material prepared in this embodiment are 3 μm and 2 μm, respectively.

[0091] Example 2

[0092] The modified anode material prepared in this embodiment uses graphite as the core, with PMMA and polydopamine layers sequentially coated on the outside of the core. The mass fraction of PMMA is 1% of the graphite, and the mass fraction of polydopamine is 0.5% of the graphite.

[0093] S1: Mix graphite powder with MMA ethanol solution and heat at 45°C for 3 hours to obtain a mixture;

[0094] The graphite powder includes single particles and secondary particles, with the ratio of secondary particles (D50 = 13 μm) to single particles (D50 = 10 μm) being 1:1.

[0095] The mass ratio of the added graphite powder to the methyl methacrylate (MMA) ethanol solution is 99.0:1.0.

[0096] The mass concentration of methyl methacrylate in the methyl methacrylate ethanol solution is 40%.

[0097] S2: Add initiator AIBN to the mixture, and then perform heat treatment in an argon atmosphere at a temperature of 60°C for 4 hours to obtain PMMA-coated graphite material.

[0098] S3: At a temperature of 25°C, the PMMA-coated graphite material is dispersed in an alkaline aqueous solution containing dopamine for 24 hours. A polydopamine coating layer is formed on the outside of the PMMA layer through the self-polymerization reaction of dopamine. After the reaction is completed, the material is washed multiple times with deionized water and then dried in a drying oven at 60°C to obtain the modified lithium-ion battery anode material.

[0099] The dopamine-containing alkaline aqueous solution has a dopamine concentration of 1 g / L, the alkali used in the dopamine-containing alkaline aqueous solution is Tris-HCl solution, the mass ratio of graphite powder to dopamine is 99.5:0.5, and the pH value of the dopamine-containing alkaline aqueous solution is 8.0.

[0100] The thicknesses of the PMMA layer and the polydopamine layer in the modified lithium-ion battery anode material prepared in this embodiment are 6 μm and 2 μm, respectively.

[0101] Example 3

[0102] The modified anode material prepared in this embodiment uses graphite as the core, with PMMA and polydopamine layers sequentially coated on the outside of the core. The mass fraction of PMMA is 0.5% of graphite, and the mass fraction of polydopamine is 1% of graphite.

[0103] S1: Mix graphite powder with MMA ethanol solution and heat at 45°C for 3 hours to obtain a mixture;

[0104] The graphite powder includes single particles and secondary particles, with the ratio of secondary particles (D50 = 13 μm) to single particles (D50 = 10 μm) being 1:1.

[0105] The mass ratio of added graphite powder to methyl methacrylate (MMA) ethanol solution is 99.5:0.5.

[0106] The mass concentration of methyl methacrylate in the methyl methacrylate ethanol solution is 40%.

[0107] S2: Add initiator AIBN to the mixture, and then perform heat treatment in an argon atmosphere at a temperature of 60°C for 4 hours to obtain PMMA-coated graphite material.

[0108] S3: At a temperature of 25°C, the PMMA-coated graphite material is dispersed in an alkaline aqueous solution containing dopamine for 24 hours. A polydopamine coating layer is formed on the outside of the PMMA layer through the self-polymerization reaction of dopamine. After the reaction is completed, the material is washed multiple times with deionized water and then dried in a drying oven at 60°C to obtain the modified lithium-ion battery anode material.

[0109] The dopamine-containing alkaline aqueous solution has a dopamine concentration of 1 g / L, the alkali used in the dopamine-containing alkaline aqueous solution is Tris-HCl solution, the mass ratio of graphite powder to dopamine is 99:1, and the pH value of the dopamine-containing alkaline aqueous solution is 8.0.

[0110] The thicknesses of the PMMA layer and the polydopamine layer in the modified lithium-ion battery anode material prepared in this embodiment are 3 μm and 4 μm, respectively.

[0111] Example 4

[0112] The modified anode material prepared in this embodiment uses graphite as the core, with PMMA and polydopamine layers sequentially coated on the outside of the core. The mass fraction of PMMA is 1% of the graphite, and the mass fraction of polydopamine is 1% of the graphite.

[0113] S1: Mix graphite powder with MMA ethanol solution and heat at 45°C for 3 hours to obtain a mixture;

[0114] The graphite powder includes single particles and secondary particles, with the ratio of secondary particles (D50 = 13 μm) to single particles (D50 = 10 μm) being 1:1.

[0115] The mass ratio of added methyl methacrylate in the graphite powder and methyl methacrylate (MMA) ethanol solution is 99:1.

[0116] The mass concentration of methyl methacrylate in the methyl methacrylate ethanol solution is 40%.

[0117] S2: Add initiator AIBN to the mixture, and then perform heat treatment in an argon atmosphere at a temperature of 60°C for 4 hours to obtain PMMA-coated graphite material.

[0118] S3: At a temperature of 25°C, the PMMA-coated graphite material is dispersed in an alkaline aqueous solution containing dopamine for 24 hours. A polydopamine coating layer is formed on the outside of the PMMA layer through the self-polymerization reaction of dopamine. After the reaction is completed, the material is washed multiple times with deionized water and then dried in a drying oven at 60°C to obtain the modified lithium-ion battery anode material.

[0119] The dopamine-containing alkaline aqueous solution has a dopamine concentration of 1 g / L, the alkali used in the dopamine-containing alkaline aqueous solution is Tris-HCl solution, the mass ratio of graphite powder to dopamine is 99:1, and the pH value of the dopamine-containing alkaline aqueous solution is 8.0.

[0120] The thicknesses of the PMMA layer and the polydopamine layer in the modified lithium-ion battery anode material prepared in this embodiment are 6 μm and 4 μm, respectively.

[0121] Example 5

[0122] The modified anode material prepared in this embodiment uses graphite as the core, with PMMA and polydopamine layers sequentially coated on the outside of the core. The mass fraction of PMMA is 2% of graphite, and the mass fraction of polydopamine is 1% of graphite.

[0123] S1: Mix graphite powder with MMA ethanol solution in a certain proportion, and heat at 45°C for 3 hours to obtain a mixture;

[0124] The graphite powder includes single particles and secondary particles, with the ratio of secondary particles (D50 = 13 μm) to single particles (D50 = 10 μm) being 1:1.

[0125] The mass ratio of added methyl methacrylate in the graphite powder and methyl methacrylate (MMA) ethanol solution is 98:2.

[0126] The mass concentration of methyl methacrylate in the methyl methacrylate ethanol solution is 40%.

[0127] S2: Add initiator AIBN to the mixture, and then perform heat treatment in an argon atmosphere at a temperature of 60°C for 4 hours to obtain PMMA-coated graphite material.

[0128] S3: At a temperature of 25°C, the PMMA-coated graphite material is dispersed in an alkaline aqueous solution containing dopamine for 24 hours. A polydopamine coating layer is formed on the outside of the PMMA layer through the self-polymerization reaction of dopamine. After the reaction is completed, the material is washed multiple times with deionized water and then dried in a drying oven at 60°C to obtain the modified lithium-ion battery anode material.

[0129] The dopamine-containing alkaline aqueous solution has a dopamine concentration of 1 g / L, the alkali used in the dopamine-containing alkaline aqueous solution is Tris-HCl solution, the mass ratio of graphite powder to dopamine is 99:1, and the pH value of the dopamine-containing alkaline aqueous solution is 8.0.

[0130] The thicknesses of the PMMA layer and the polydopamine layer in the modified lithium-ion battery anode material prepared in this embodiment are 12 μm and 4 μm, respectively.

[0131] Example 6

[0132] The modified anode material prepared in this embodiment uses graphite as the core, with PMMA and polydopamine layers sequentially coated on the outside of the core. The mass fraction of PMMA is 1% of the graphite, and the mass fraction of polydopamine is 2% of the graphite.

[0133] S1: Mix graphite powder with MMA ethanol solution and heat at 45°C for 3 hours to obtain a mixture;

[0134] The graphite powder includes single particles and secondary particles, with the ratio of secondary particles (D50 = 13 μm) to single particles (D50 = 10 μm) being 1:1.

[0135] The mass ratio of added methyl methacrylate in the graphite powder and methyl methacrylate (MMA) ethanol solution is 99:1.

[0136] The mass concentration of methyl methacrylate in the methyl methacrylate ethanol solution is 40%.

[0137] S2: Add initiator AIBN to the mixture, and then perform heat treatment in an argon atmosphere at a temperature of 60°C for 4 hours to obtain PMMA-coated graphite material.

[0138] S3: At a temperature of 25°C, the PMMA-coated graphite material is dispersed in an alkaline aqueous solution containing dopamine for 24 hours. A polydopamine coating layer is formed on the outside of the PMMA layer through the self-polymerization reaction of dopamine. After the reaction is completed, the material is washed multiple times with deionized water and then dried in a drying oven at 60°C to obtain the modified lithium-ion battery anode material.

[0139] The dopamine concentration in the alkaline aqueous solution is 1 g / L, the alkali used in the dopamine-containing alkaline aqueous solution is Tris-HCl solution, the mass ratio of graphite powder to dopamine is 98:2, and the pH value of the dopamine-containing alkaline aqueous solution is 8.0.

[0140] The thicknesses of the PMMA layer and the polydopamine layer in the modified lithium-ion battery anode material prepared in this embodiment are 6 μm and 8 μm, respectively.

[0141] Example 7

[0142] The modified anode material prepared in this embodiment uses graphite as the core, with PMMA and polydopamine layers sequentially coated on the outside of the core. The mass fraction of PMMA is 2% of the graphite, and the mass fraction of polydopamine is 2% of the graphite.

[0143] S1: Mix graphite powder with MMA ethanol solution and heat at 45°C for 3 hours to obtain a mixture;

[0144] The graphite powder includes single particles and secondary particles, with the ratio of secondary particles (D50 = 13 μm) to single particles (D50 = 10 μm) being 1:1.

[0145] The mass ratio of added methyl methacrylate in the graphite powder and methyl methacrylate (MMA) ethanol solution is 98:2.

[0146] The mass concentration of methyl methacrylate in the methyl methacrylate ethanol solution is 40%.

[0147] S2: Add initiator AIBN to the mixture, and then perform heat treatment in an argon atmosphere at a temperature of 60°C for 4 hours to obtain PMMA-coated graphite material.

[0148] S3: At a temperature of 25°C, the PMMA-coated graphite material is dispersed in an alkaline aqueous solution containing dopamine for 24 hours. A polydopamine coating layer is formed on the outside of the PMMA layer through the self-polymerization reaction of dopamine. After the reaction is completed, the material is washed multiple times with deionized water and then dried in a drying oven at 60°C to obtain the modified lithium-ion battery anode material.

[0149] The dopamine concentration in the alkaline aqueous solution is 1 g / L, the alkali used in the dopamine-containing alkaline aqueous solution is Tris-HCl solution, the mass ratio of graphite powder to dopamine is 98:2, and the pH value of the dopamine-containing alkaline aqueous solution is 8.0.

[0150] The thicknesses of the PMMA layer and the polydopamine layer in the modified lithium-ion battery anode material prepared in this embodiment are 12 μm and 8 μm, respectively.

[0151] Comparative Example 1

[0152] The main difference between this comparative example and Examples 1-7 is that no PMMA and PDA layers are coated on the graphite surface; that is, the mass fraction of PMMA and polydopamine is 0% of the graphite. The graphite powder produced from the selected graphite raw materials—petroleum coke, pitch coke, and needle coke—is directly used as the negative electrode material for performance testing, as shown in Table 1. The powder includes single particles and secondary particles, with a ratio of secondary particles (D50 = 13 μm) to single particles (D50 = 10 μm) of 1:1, consistent with the graphite powder used in Examples 1-7.

[0153] Comparative Example 2

[0154] The main difference between this comparative example and Example 1 is that a PDA layer is not coated on the graphite surface; that is, the mass fraction of PMMA is 0.5% of the graphite and the mass fraction of polydopamine is 0% of the graphite.

[0155] S1: Mix graphite powder with MMA ethanol solution and heat at 45°C for 3 hours to obtain a mixture;

[0156] The graphite powder includes single particles and secondary particles, with the ratio of secondary particles (D50 = 13 μm) to single particles (D50 = 10 μm) being 1:1.

[0157] The mass ratio of added graphite powder to methyl methacrylate (MMA) ethanol solution is 99.5:0.5.

[0158] The mass concentration of methyl methacrylate in the methyl methacrylate ethanol solution is 40%.

[0159] S2: Add initiator AIBN to the mixture, and then perform heat treatment in an argon atmosphere at a temperature of 60°C for 4 hours to obtain PMMA-coated graphite material.

[0160] The PMMA-coated graphite material obtained in step S2 was washed multiple times with deionized water and then dried in a drying oven at 60°C. The performance tests are shown in Table 1.

[0161] The PMMA layer in the battery anode material prepared in this comparative example has a thickness of 3 μm.

[0162] Comparative Example 3

[0163] The main difference between this comparative example and Example 1 is that no PMMA layer is coated on the graphite surface; that is, the mass fraction of PMMA is 0% of the graphite and the mass fraction of polydopamine is 0.5% of the graphite.

[0164] Graphite powder was dispersed in an alkaline aqueous solution containing dopamine at 25°C for 24 hours. A polydopamine coating layer was formed on the outside of the graphite powder through the self-polymerization reaction of dopamine. After the reaction was completed, the powder was washed multiple times with deionized water and then dried in a drying oven at 60°C to obtain PDA-coated graphite material.

[0165] The graphite powder includes single particles and secondary particles, with a ratio of secondary particles (D50 = 13 μm) to single particles (D50 = 10 μm) of 1:1; the dopamine concentration in the alkaline aqueous solution is 1 g / L, the alkali used in the alkaline aqueous solution is Tris-HCl solution, the mass ratio of graphite powder to dopamine is 99.5:0.5, and the pH value of the alkaline aqueous solution is 8.0.

[0166] The performance of the obtained PDA-coated graphite material was tested, as shown in Table 1.

[0167] The thickness of the polydopamine layer in the battery anode material prepared in this comparative example is 2 μm.

[0168] Comparative Example 4

[0169] The main difference between this comparative example and Example 1 is that the mass fraction of PMMA in this comparative example is 2.5% of graphite, and the mass fraction of polydopamine is 0.5% of graphite; the remaining technical parameters and operating steps are the same as in Example 1, and the performance tests are shown in Table 1.

[0170] The thicknesses of the PMMA layer and the polydopamine layer in the battery anode material prepared in this comparative example are 15 μm and 2 μm, respectively.

[0171] Comparative Example 5

[0172] The main difference between this comparative example and Example 1 is that the mass fraction of PMMA in this comparative example is 0.5% of graphite, and the mass fraction of polydopamine is 2.5% of graphite; the remaining technical parameters and operating steps are the same as in Example 1, and the performance tests are shown in Table 1.

[0173] The thicknesses of the PMMA layer and the polydopamine layer in the battery anode material prepared in this comparative example are 3 μm and 10 μm, respectively.

[0174] Comparative Example 6

[0175] The main difference between this comparative example and Example 1 is that the mass fraction of PMMA in this comparative example is 2.5% of graphite, and the mass fraction of polydopamine is 2.5% of graphite; the remaining technical parameters and operating steps are the same as in Example 1, and the performance tests are shown in Table 1.

[0176] The thicknesses of the PMMA layer and the polydopamine layer in the battery anode material prepared in this comparative example are 15 μm and 15 μm, respectively.

[0177] Comparative Example 7

[0178] The main difference between this comparative example and Example 1 is that the ratio of secondary particles to single particles in this comparative example is 5:1; the remaining technical parameters and operating steps are the same as in Example 1, and the performance tests are shown in Table 1.

[0179] The thicknesses of the PMMA layer and the polydopamine layer in the battery anode material prepared in this comparative example are 3 μm and 2 μm, respectively.

[0180] Comparative Example 8

[0181] The modified anode material prepared in this comparative example uses graphite as the core, with polydopamine and PMMA layers sequentially coated around the core. The mass fraction of PMMA is 0.5% of the graphite, and the mass fraction of polydopamine is 0.5% of the graphite.

[0182] S1: At a temperature of 25℃ (self-polymerization reaction temperature), graphite powder is dispersed in an alkaline aqueous solution containing dopamine for 24 hours (self-polymerization reaction time). Through the self-polymerization reaction of dopamine, a polydopamine coating layer is formed on the outside of the graphite powder. After the reaction is completed, the powder is washed multiple times with deionized water and then dried in a drying oven at 60℃ to obtain polydopamine-coated graphite material.

[0183] The graphite powder includes single particles and secondary particles, with the ratio of secondary particles (D50 = 13 μm) to single particles (D50 = 10) being 1:1.

[0184] The dopamine concentration in the alkaline aqueous solution is 1 g / L, the alkali used in the alkaline aqueous solution is Tris-HCl solution, the mass ratio of graphite powder to dopamine is 99.5:0.5, and the pH value of the alkaline aqueous solution is 8.0.

[0185] S2: Mix polydopamine-coated graphite material with MMA ethanol solution and heat at 45°C for 3 hours to obtain a mixture;

[0186] The mass ratio of added graphite powder to methyl methacrylate (MMA) ethanol solution is 99.5:0.5.

[0187] The mass concentration of methyl methacrylate in the ethanol solution is 40%.

[0188] S3: Add initiator AIBN to the mixture, and then perform heat treatment in an argon atmosphere at a temperature of 60°C for 4 hours to obtain a modified lithium-ion battery anode material sequentially coated with a polydopamine layer and a PMMA layer.

[0189] The thicknesses of the PMMA layer and the polydopamine layer in the battery anode material prepared in this comparative example are 3 μm and 2 μm, respectively.

[0190] Performance testing

[0191] 1. Preparation of button half-cells

[0192] Preparation of the positive electrode: Lithium iron phosphate positive electrode material, PVDF, SP, and CNT were mixed uniformly in a ratio of 96.5:2.0:1.0:0.5 and coated evenly on a 13μm carbon-coated aluminum foil to obtain an areal density of 190mg / 10cm³. 2 The positive electrode plate;

[0193] Preparation of the negative electrode: The modified graphite negative electrode material, SP, CMC, and SBR prepared in the embodiments or comparative examples of the present invention are mixed uniformly in a ratio of 94:2:1.5:2.5, and then uniformly coated onto a 6μm copper foil to obtain an areal density of 90mg / 10cm. 2 The negative electrode plate;

[0194] A coin cell with model number CR2032 is obtained by assembling and injecting electrolyte into the positive electrode shell, gasket, positive electrode plate, separator, negative electrode plate, and negative electrode shell.

[0195] 2. The initial reversible capacity refers to the delithiation specific capacity of a coin cell after lithium insertion and delithiation.

[0196] The adhesive preparation involves a CMC: ultrapure water ratio of 1:49 (to prepare a 2% CMC adhesive solution);

[0197] Test standard: GB / T 24533-2009.

[0198] 2. 500-cycle retention rate: refers to the ratio of the discharge capacity to the initial capacity after 500 cycles, with one charge-discharge cycle being 2.5-3.65V.

[0199] 3. Electrolyte retention coefficient: refers to the ratio of the mass of electrolyte retained inside the battery to its capacity after the battery is sealed twice.

[0200] 4. 2C / 0.5C capacity retention rate: This refers to the ratio of the battery's capacity when discharged at twice the nominal capacity to its capacity when discharged at 0.5 times the nominal capacity.

[0201] Results data

[0202] Following the above testing methods, three groups of batteries were prepared according to the preparation methods in Examples 1-7 and Comparative Examples 1-8, respectively. The average value was taken after testing, and the data are shown in Table 1.

[0203] Table 1

[0204]

[0205] As shown in Table 1, compared with Example 1, Comparative Example 1 does not have a PMMA layer and a PDA layer coated on the graphite surface, so the graphite cannot be effectively protected. The graphite comes into contact with the electrolyte, which weakens the negative electrode cycle performance and rate performance of the graphite, thus affecting the battery performance.

[0206] As shown in Table 1, compared with Example 1, Comparative Example 2 does not have a PDA layer coated on the graphite surface, resulting in a decrease in the bonding performance between the PMMA layer and the graphite. This affects the negative electrode cycle performance and rate performance of the graphite, further impacting the battery performance.

[0207] As shown in Table 1, compared with Example 1, Comparative Example 3 did not have a PMMA layer coated on the graphite surface, resulting in a decrease in the stability and mechanical properties of the graphite anode, which ultimately affected the performance of the battery.

[0208] As shown in Table 1, compared with Example 1, Comparative Example 4 has an excessive amount of PMMA, which affects the specific capacity of the graphite anode and the cycle stability of the battery because the mass fraction of PMMA in Comparative Example 4 is 2.5% of graphite and the mass fraction of polydopamine is 0.5% of graphite.

[0209] As shown in Table 1, compared with Example 1, Comparative Example 5 has an excessive amount of polydopamine, which affects the specific capacity of the graphite anode and the cycle stability of the battery because the mass fraction of PMMA in Comparative Example 5 is 0.5% of graphite and the mass fraction of polydopamine is 2.5% of graphite.

[0210] As shown in Table 1, compared with Example 1, Comparative Example 6 has a PMMA mass fraction of 2.5% and a polydopamine mass fraction of 2.5% of graphite. The contents of polydopamine and PMMA both exceed the limits of this invention, which seriously affects the specific capacity of the graphite anode and the cycle stability of the battery.

[0211] As shown in Table 1, compared with Example 1, Comparative Example 7 has a 5:1 ratio of secondary particles to single particles. Due to the higher content of secondary particles, the battery capacity retention rate drops rapidly in the later stages of battery cycling, ultimately affecting the battery performance.

[0212] As shown in Table 1, compared with Example 1, Comparative Example 8 has a different effect. The modified negative electrode material prepared in Comparative Example 8 uses graphite as the core, and then coats the core with a polydopamine layer and a PMMA layer in sequence. The mass fraction of PMMA is 0.5% of graphite, and the mass fraction of polydopamine is 0.5% of graphite. Comparative Example 8 changed the coating order, coating the polydopamine layer first and then the PMMA layer. This will affect the binding force between polydopamine and graphite due to the adhesion and hydrophilicity of polydopamine, reduce the electrochemical stability, weaken the protective effect of PMMA, affect the liquid retention capacity, reduce the lithium-ion transport efficiency, and may increase the processing difficulty. The combined effect of these factors leads to a decrease in the cycle stability and rate performance of the battery.

[0213] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A modified lithium-ion battery anode material, characterized in that, The negative electrode material uses graphite as its core, and the outer layer of the graphite is coated with a polymethyl methacrylate layer and a polydopamine layer from the outer surface of the graphite to the outside. The mass fraction of polymethyl methacrylate is 0.5-2% of graphite. The mass fraction of polydopamine is 0.5-2% of graphite; The graphite is artificial graphite prepared from graphite raw material coke; Artificial graphite includes single-particle and secondary-particle graphite. Secondary particles: The mass ratio of single particles is x, where 1 ≤ x ≤ 4; The preparation method of modified lithium-ion battery anode material includes the following steps: S1: Graphite powder is mixed with methyl methacrylate ethanol solution, and the mixture is obtained after preliminary heating to evaporate the ethanol; The initial heating temperature is 40-50℃, and the heating time is 2-3 hours; S2: In a protective atmosphere, an initiator is added to the mixture, followed by heat treatment to obtain PMMA-coated graphite material; S3: The PMMA-coated graphite material is dispersed in an alkaline aqueous solution containing dopamine, and a polydopamine coating layer is formed on the outside of the PMMA layer through the self-polymerization reaction of dopamine. After the reaction is completed, the modified lithium-ion battery anode material is obtained by washing and drying. The mass ratio of graphite powder to dopamine in the PMMA-coated graphite material is (98-99.5):(2-0.5).

2. The modified lithium-ion battery anode material according to claim 1, characterized in that, The thickness of both the polymethyl methacrylate layer and the polydopamine layer is 2-20 μm.

3. The modified lithium-ion battery anode material according to claim 1, characterized in that, The mass fraction of polymethyl methacrylate is 0.5-1% of graphite; And / or, the mass fraction of polydopamine is 0.5-1% of graphite.

4. The modified lithium-ion battery anode material according to claim 1, characterized in that, Graphite raw material coke includes one or more of petroleum coke, pitch coke, and needle coke; And / or, the D50 of secondary particles is 12-16 μm, and the D50 of single particles is 10-15 μm; And / or, the graphite has a D50 of 10-16 μm and a specific surface area of ​​1.2-1.8 m². 2 / g.

5. The modified lithium-ion battery anode material according to claim 1, characterized in that, In step S1, the mass ratio of the graphite powder to the methyl methacrylate in the methyl methacrylate ethanol solution is (98-99.5):(2-0.5). And / or, the mass concentration of methyl methacrylate in the methyl methacrylate ethanol solution is 25-55 wt%.

6. The modified lithium-ion battery anode material according to claim 1, characterized in that, In step S2, the heat treatment temperature is 50-60℃ and the time is 3-4 hours; And / or, the initiator includes one or more of azobisisobutyronitrile, azobisisoheptanenitrile, and benzoyl peroxide; And / or, in step S2, the protective atmosphere includes one or more of argon, helium, nitrogen, or xenon.

7. The modified lithium-ion battery anode material according to claim 1, characterized in that, In step S3, the mass concentration of dopamine in the alkaline aqueous solution containing dopamine is 0.5-1 g / L; And / or, the base used in the alkaline aqueous solution containing dopamine includes Tris-HCl buffer or NaOH; And / or, the pH of the alkaline aqueous solution containing dopamine is 8-10; And / or, in step S3, the temperature of the self-polymerization reaction is 25-60°C, and the time is 24-48h.

8. A negative electrode sheet, said negative electrode sheet comprising the modified lithium-ion battery negative electrode material as described in any one of claims 1-7.

9. A lithium-ion battery comprising the negative electrode sheet as described in claim 8, or comprising the modified lithium-ion battery negative electrode material as described in any one of claims 1-7.

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