Negative electrode material, negative electrode sheet and secondary battery

Abstract

The present application relates to the technical field of secondary batteries. Disclosed are a negative electrode material, a negative electrode sheet and a secondary battery. The negative electrode material comprises an inner core and a coating layer, wherein the coating layer is located on the surface of the inner core, the inner core comprises natural graphite and first amorphous carbon that is filled into the pores of the natural graphite, and the coating layer comprises second amorphous carbon; the Raman spectrum of the negative electrode material has a peak D and a peak G, and the intensity ratio of the peak D to the peak G is ID / IG; the inner core comprises an inner-layer area and an outer-layer area located outside the inner-layer area, and the outer-layer area is adjacent to the coating layer; and the mean value of the ID / IG of the inner-layer area is Ka, and the mean value of the ID / IG ratio of the inner-layer area to the outer-layer area is K, the two satisfying: 0.4≤Ka≤0.7, and 0.5≤K<0.9. When the negative electrode material is applied to a secondary battery, the initial coulombic efficiency can be significantly improved, and the expansion rate can be significantly reduced.

Description

Negative electrode materials, negative electrode sheets and secondary batteries

[0001] This application claims priority to Chinese patent application 202411850893.9, filed on December 16, 2024. The entire contents of the aforementioned Chinese patent application are incorporated herein by reference. Technical Field

[0002] This application relates to the field of secondary battery technology, and more specifically, to a negative electrode material, a negative electrode sheet, and a secondary battery. Background Technology

[0003] Lithium-ion batteries are widely used in 3C products, power devices, and energy storage equipment due to their advantages such as low self-discharge rate, high charge-discharge efficiency, no memory effect, and long cycle life. Among these, the anode material is a crucial component of lithium-ion batteries, and its performance directly affects the battery's electrochemical performance. Natural anode materials have attracted widespread attention due to their high specific capacity, low charge-discharge plateau, and low cost. However, natural graphite has high anisotropy and internal defects. During lithium-ion intercalation, the volume expansion of graphite is mainly manifested in the thickness direction. Solvent molecules in the electrolyte enter the graphite interlayer along with lithium ions, further increasing the degree of graphite expansion. Simultaneously, the intercalation of solvent molecules not only increases the volume of graphite but may also lead to a less dense SEI film, affecting the battery's initial coulombic efficiency. Summary of the Invention

[0004] The main objective of this application is to provide a negative electrode material, a negative electrode sheet, and a secondary battery to solve the problem that existing negative electrode materials are difficult to balance expansion rate and initial coulombic efficiency.

[0005] To achieve the above objectives, according to one aspect of this application, a negative electrode material is provided, comprising a core and a coating layer, the coating layer being located on the surface of the core. The core comprises natural graphite and a first amorphous carbon filling the pores of the natural graphite, and the coating layer comprises a second amorphous carbon. The Raman spectrum of the negative electrode material exhibits a D peak and a G peak, with the intensity ratio of the D peak to the G peak being I. D / I G The kernel consists of an inner region and an outer region located outside the inner region, with the outer region immediately adjacent to the outer layer; the inner region's I... D / I G The mean is K a I of the inner and outer regions D / I G The mean of the ratio is K; satisfying: 0.4 ≤ K a ≤0.7, 0.5≤K<0.9.

[0006] A second aspect of this application provides a negative electrode sheet, which includes the negative electrode material provided in the first aspect.

[0007] A third aspect of this application provides a secondary battery, which includes the negative electrode provided in the second aspect.

[0008] By applying the technical solution of this application, the microstructure of the material is optimized and its electrochemical performance is improved by filling the pores of natural graphite with a first amorphous carbon and coating the surface with a second amorphous carbon. This is achieved by defining the inner layer region using I... D / I G The mean is K a I of the inner and outer regions D / I G The mean of the ratio is K; satisfying: 0.4 ≤ K a The values ​​≤0.7 and 0.5≤K<0.9 indicate that the first amorphous carbon can achieve dense filling and a reasonable distribution of the D and G peaks, which helps to improve the lithium-ion insertion and extraction efficiency, while effectively mitigating volume expansion during charge and discharge, thereby extending the service life of the secondary battery. Applying this negative electrode material to secondary batteries can achieve an initial coulombic efficiency ≥94% and an electrode expansion rate ≤25.7% after 20 cycles. Attached Figure Description

[0009] Figure 1 is a schematic diagram of the cross-sectional Raman mapping region of the negative electrode material particles in one embodiment of this application.

[0010] Figure 2 is a schematic diagram of the rectangular region in the cross-section of the negative electrode material particles in one embodiment of this application.

[0011] Figure 3 is a SEM image of the cross-sectional morphology of the negative electrode material particles in another embodiment of this application.

[0012] Figure 4 is a schematic diagram of the structure of a secondary battery provided in one embodiment of this application during charging.

[0013] Figure 5 is a schematic diagram of the structure of a secondary battery provided in one embodiment of this application during discharge.

[0014] Explanation of reference numerals in the attached figures: 100 - Electrode assembly; 101 - Positive electrode; 102 - Negative electrode; 103 - Separator. Detailed Implementation

[0015] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0016] As described in the background section of this application, existing anode materials suffer from high expansion rates and low initial coulombic efficiency. To address these issues, in a typical embodiment of this application, an anode material is provided. The anode material includes a core and a coating layer, with the coating layer located on the surface of the core. The core comprises natural graphite and a first amorphous carbon filling the pores of the natural graphite. The coating layer comprises a second amorphous carbon. The Raman spectrum of the anode material exhibits a D peak and a G peak, with the intensity ratio of the D peak to the G peak being I. D / I G The kernel consists of an inner region and an outer region located outside the inner region, with the outer region immediately adjacent to the outer layer; the inner region's I... D / I G The mean is K a I of the inner and outer regions D / I G The mean of the ratio is K; satisfying: 0.4 ≤ K a ≤0.7, 0.5≤K<0.9.

[0017] The negative electrode material of this application has a multilayer composite structure, including a core and a coating layer. The core comprises natural graphite and a first amorphous carbon filling the pores of the natural graphite. Through the filling of the core with the first amorphous carbon and the coating of the surface with a second amorphous carbon, the structure of the negative electrode material is significantly optimized. The coating layer includes the second amorphous carbon, which covers the surface of the core to form a protective film.

[0018] Specifically, on the one hand, the first amorphous carbon is a highly disordered carbon structure that can fill the internal pores of natural graphite, effectively reducing porosity and increasing particle density. Furthermore, the filling of the first amorphous carbon can reduce the anisotropy of the negative electrode material, making the diffusion of lithium ions in different directions more uniform and improving the Li-ion density. + The diffusion rate between graphite layers reduces Li + The structural strain generated during the insertion and extraction processes reduces the material's expansion rate and improves its structural stability. On the other hand, the coating of a second amorphous carbon helps reduce direct contact between natural graphite and the electrolyte, preventing solvent co-intercalation. Simultaneously, it facilitates the formation of a stable and dense SEI film during the initial charge-discharge process, improving the material's electrochemical stability and enhancing the initial coulombic efficiency. TEM detection can distinguish between the graphite core and the amorphous carbon.

[0019] The Raman spectrum of the negative electrode material contains D and G peaks. The diffraction peaks and their corresponding intensities can be obtained through Raman spectroscopy analysis. The D peak is located at approximately 1350 cm⁻¹. -1 The G peak is located at approximately 1580 cm. -1The intensity of the D peak is related to lattice defects, amorphous carbon, or disordered structure in the negative electrode material, while the intensity of the G peak is related to the degree of graphitization or orderliness of the graphite material. The intensity ratio of the D peak to the G peak (Ig) is... D / I G ) is an important parameter for measuring the distribution of amorphous carbon and the degree of graphitization within a material. It reflects the orderliness of the internal structure of the negative electrode material particles and the changes in surface properties. D / I G A higher value indicates that there is more amorphous carbon or defect structure in the material, while a lower value indicates that the material is more graphitized and has a more ordered structure.

[0020] The negative electrode material has multiple particles, with I in the inner layer region. D / I G It can be the inner layer region I of multiple particles D / I G The arithmetic mean of the inner and outer regions, I D / I G The mean of the ratio can be the ratio of the inner layer region to the outer layer region in multiple particles. D / I G The arithmetic mean of the ratios. I of the inner region. D / I G The mean is K a I of the inner and outer regions D / I G The mean of the ratio is K, K a K is used to characterize the overall structural properties of the negative electrode material.

[0021] K a The magnitude of the value reflects the average distribution of amorphous carbon in the inner region and the structural defect state of that region. This is achieved by limiting the value to 0.4 ≤ K. a A K value ≤0.7 ensures that the inner layers of graphite particles contain an appropriate amount of amorphous carbon. This amorphous carbon fills the pores between graphite layers, reducing the volume expansion of graphite during charging and discharging, improving the structural stability of the material, and delaying the shedding of graphite sheets, thereby improving the cycle life of the secondary battery; a suitable range of K... a A certain value helps to form a more optimized SEI film on the surface and inside the negative electrode material. The stability of the SEI film directly affects the first coulombic efficiency, and the amorphous carbon in the inner layer region can promote the formation of the SEI film and reduce electrolyte decomposition, thereby improving the first coulombic efficiency. Specifically, but not limitingly, 0.41 ≤ K a ≤0.68; or, 0.4≤K a ≤0.6; or, 0.45≤K a ≤0.7; or, K aThe range is 0.4, 0.41, 0.45, 0.5, 0.55, 0.6, 0.65, 0.68, 0.7 or any two of the aforementioned values.

[0022] By limiting K to 0.5 ≤ K < 0.9, it is evident that the inner and outer regions of the particle exhibit structural differences, with a relatively higher content of amorphous carbon in the inner region and a relatively lower content in the outer region. This indicates that the pores in the inner region are filled with primary amorphous carbon, while the outer region maintains a certain degree of order. Optimizing the distribution of amorphous carbon in the inner and outer layers can ensure a relative balance in the lithium-ion diffusion rates, avoiding performance issues caused by excessively fast or slow diffusion rates in the inner region. Secondly, it reduces lithium-ion loss during charging and discharging, improving the initial coulombic efficiency. Furthermore, it helps control the stress distribution within the material, reducing structural damage during charging and discharging, lowering the risk of graphite sheet detachment, and thus improving the material's structural stability and cycle life. Specifically, but not restrictively, 0.51≤K≤0.88; or 0.5≤K≤0.89; or 0.6≤K≤0.8; or K is a range of 0.5, 0.51, 0.6, 0.7, 0.8, 0.88, 0.89, or any two of the aforementioned values.

[0023] In some embodiments, K a Satisfy: 0.41≤K a ≤0.68, and K satisfies 0.51≤K≤0.88. Further constraints are made on K. a The range of values ​​for K is beneficial for further improving the initial Coulomb efficiency and reducing the expansion rate.

[0024] According to the research in this application, applying the above-mentioned negative electrode material to secondary batteries helps to balance improving the initial coulombic efficiency and reducing the expansion rate. This is because the microstructure of the material is optimized by filling the pores of natural graphite with a first amorphous carbon and coating the surface with a second amorphous carbon; and by defining the I in the inner and outer layer regions of the core... D / I G The mean of the ratio and the I of the inner region D / I G The mean of this special structure combined with I D / I GThe limitations ensure the stability of the overall material structure, resulting in minimal volume change during lithium-ion insertion and extraction. This reduces graphite sheet shedding and expansion, lowering the electrode's expansion rate during charge and discharge. Simultaneously, it ensures uniform amorphous carbon distribution on the surface and within the negative electrode material, forming a stable SEI film. This stable and uniformly distributed SEI film reduces direct contact between the electrolyte and graphite, thereby minimizing ineffective lithium-ion consumption during the initial charge and discharge cycle and improving the initial coulombic efficiency. Applying this negative electrode material to secondary batteries achieves an initial coulombic efficiency ≥93.5%, and further, an initial coulombic efficiency ≥94%. After 20 cycles, the electrode expansion rate is ≤27.3%, and further, it is ≤25.9%.

[0025] In the above embodiments of this application, the method for determining the inner and outer regions of the core is as follows: A negative electrode material particle is selected, and a rectangular region is selected on the core cross-section of the particle. The center of the rectangular region is either the center of the core cross-section or the center of the core cross-section falls within the rectangular region. Preferably, the two endpoints along the length direction or the two endpoints along the diagonal of the rectangular region are located on the edge of the core cross-section (i.e., the outer region is adjacent to the coating layer). This ensures that the rectangular region spans the entire core cross-section, guaranteeing that the obtained data is both accurate and representative, which is helpful for analyzing the distribution of amorphous carbon at different depths. The rectangular region is divided into four equal parts along its length direction; the two middle parts, combined, occupy 50% of the area of ​​the rectangular region, forming the inner region, where the center of the core cross-section falls; the regions at both ends, totaling 50% of the area of ​​the rectangular region, form the outer region.

[0026] For example, in Figure 1, region a represents the inner rectangular region, and region b represents the outer rectangular region. The two outer rectangular regions are located on either side of the inner rectangular region, meaning they are adjacent to its edge. These correspond to the structural characteristics of the inner and outer layers of the particle, respectively. By comparing these two regions, the distribution of amorphous carbon can be analyzed. Figure 2 shows a schematic diagram of the three types of rectangular regions.

[0027] The rectangular region is designed to more accurately analyze the distribution of amorphous carbon at different depths of the negative electrode material particles. In some embodiments, the width of the rectangular region is 1 μm to 6 μm and the length is 5 μm to 20 μm to ensure that the width of the rectangular region is small enough and that the rectangular region does not exceed the particle outline, so as to finely detect changes in the internal structure of the material.

[0028] Of course, in the cross-section of the particles of the negative electrode material, there may be some particles whose cross-section cannot be selected as a rectangular area with a width of 1μm to 6μm and a length of 5μm to 20μm due to shape and size issues. Alternatively, there may be some particles whose rectangular area does not cover the center of the core cross-section. In the actual test, these particles are discarded, and at least 15 particles that can define a rectangular area of ​​this size are randomly selected for testing. The average value can be used to represent the situation of the negative electrode material.

[0029] This application does not limit K. a The testing method for K can use conventional methods in the art, as long as the negative electrode material meets the above structural and parameter requirements. For example, in some embodiments, K a K is obtained through the following steps:

[0030] S11, select n particles in the negative electrode material, and select and delineate the i-th rectangular region on the core cross-section of the i-th particle; wherein, the center of the i-th rectangular region is the center of the core cross-section or the center of the core cross-section falls into the i-th rectangular region, 1≤i≤n, n≥15, and i and n are both positive integers.

[0031] S12, Raman surface scanning is performed on all defined rectangular regions. The obtained Raman mapping data is arranged in chronological order, and the test data corresponding to the inner rectangular region 'a' and the outer rectangular region 'b' are determined according to the set scanning rules. For example, when the scanning rule is set to scan horizontally first, then vertically layer by layer, the first 1 / 4 and the last 1 / 4 of the Raman mapping data are considered as the Raman data for the outer rectangular region 'b', and the middle portion is considered as the Raman data for the inner rectangular region 'a'.

[0032] S13, obtain the I values ​​of the inner rectangular region and the outer rectangular region in the i-th particle. D / I G Let them be denoted as K. ai and K bi .

[0033] S14, calculate K for n particles. ai The average value is used to obtain the I value of the inner region. D / I G The mean, i.e., K a .

[0034] S15, via K i =K ai / K bi Calculate K for the i-th particle i value.

[0035] S16, calculate K for n particles. iThe average value is used to obtain the I values ​​of the inner and outer regions. D / I G The mean of the ratios is K.

[0036] Specifically, in S11, n particles are randomly selected from the negative electrode material, where n is a sufficiently large sample size, typically a positive integer ≥15, to ensure the statistical significance and representativeness of the analytical results. Next, the i-th particle can be sliced ​​using a slicing or ion beam method to expose its core surface. An i-th rectangular region is selected on this core surface, and its center is set as the geometric center of the core surface, meaning this region encompasses the center of the particle. This selection ensures the representativeness of the analytical region and reflects the characteristics of the particle's core. The value of i ranges from 1 to m, both being positive integers.

[0037] In S12, the selected i-th rectangular region is further divided into three parts along its length: an inner rectangular region and two outer rectangular regions. For example, in Figure 1, a is the inner rectangular region and b is the outer rectangular region. The two outer rectangular regions are located on both sides of the inner rectangular region, that is, the outer rectangular regions are adjacent to the edges of the inner rectangular regions. They correspond to the structural characteristics of the inner and outer layers of the particle, respectively. By comparing these two regions, the distribution of amorphous carbon can be analyzed.

[0038] In S13, Raman spectroscopy is used to scan the inner and outer rectangular regions of the i-th particle to obtain Raman spectral data for these two regions. From the Raman spectra, the intensities of the D and G peaks can be extracted, and then I can be calculated. D / I G The values ​​are denoted as K. ai (I of the i-th inner layer region) D / I G (value) and K bi( I of the outer layer region of the i-th particle D / I G value).

[0039] In S14, for the inner rectangular region I of n particles D / I G The values ​​are averaged to obtain K. a The value represents the average I in the inner layer region of the negative electrode material. D / I G Value. K a The value reflects the average state of the relative content of amorphous carbon and the degree of structural disorder in the inner region.

[0040] In S15, for each particle, via K i =K ai / K biCalculations were performed to obtain the inner rectangular region and the outer rectangular region I in the i-th particle. D / I G The ratio of values, that is, the K of the i-th particle. i This ratio reflects the difference in structural characteristics between the inner and outer regions of the i-th particle.

[0041] In S16, K for n particles i The values ​​are averaged to obtain the K value, which is the sum of the values ​​of the inner and outer rectangular regions. D / I G The mean of the ratio. K reflects the ratio of the inner layer region to the outer layer region I in the entire negative electrode material. D / I G The mean of the ratios is used to represent the differences in property characteristics between the inner and outer layers of a particle.

[0042] The inner rectangular region represents the average state of the inner layer of the particle, and the outer rectangular region represents the average state of the outer layer of the particle. In some embodiments, the center of the inner rectangular region is the center of the core cross-section, ensuring that the inner rectangular region is the inner layer of the particle. This allows for a more accurate assessment of the uniformity of amorphous carbon filling within the particle. In some embodiments, the length of the inner rectangular region is equal to half the length of the i-th rectangular region. This ensures that the depth of the inner rectangular region is sufficient to reach the internal structure of the particle, and not just the surface or near-surface region.

[0043] In some embodiments, the percentage of pore area in the kernel is satisfy: By controlling the core pore area ratio between 2% and 5%, the volume change of the anode material during charge and discharge can be reduced, preventing particles from breaking due to excessive expansion. This improves the structural stability of the material, further enhancing the initial coulombic efficiency and reducing the expansion rate. It also helps construct a continuous conductive network, reducing resistance to electron and lithium-ion transport and improving the efficiency and safety of the secondary battery. (Specific, not limiting.) or, or, or, The range is 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, or any two of the aforementioned values.

[0044] In some embodiments, the core includes a central region and an edge region located around the periphery of the central region. The mean ratio of the pore area percentage of the central region to that of the edge region is A, where A satisfies: 1.2 ≤ A ≤ 2.0. By limiting the mean ratio of the pore area percentage of the central region to that of the edge region, a more uniform pore distribution is formed within the negative electrode material, which is beneficial for the uniform insertion and extraction of lithium ions, reduces local stress, and further improves structural stability and initial coulombic efficiency. In addition, a suitable pore area and uniform pore distribution can promote more efficient diffusion of lithium ions between graphite layers, shorten charge and discharge time, and increase the power density of the secondary battery. Specifically, but not limitingly, 1.2 ≤ A ≤ 1.8; or 1.2 ≤ A ≤ 1.6; or 1.4 ≤ A ≤ 1.9; or A is a range of 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, or any two of the aforementioned values.

[0045] In the above embodiments of this application, the method for determining the central region and the edge region located on the periphery of the central region is as follows: A negative electrode material particle is selected, and a circular or elliptical region is selected on the core cross-section of the particle. The intersection of the transverse median line and the longitudinal median line of the core cross-section of a single particle is taken as the center of the ellipse or circle. The major axis of the ellipse or circle is half the length of the transverse median line, and the minor axis is half the length of the longitudinal median line. The core cross-section is divided into a central region (a1) and an edge region (b1) by the outline of the ellipse. The transverse median line is the longest horizontal diameter of the cross-section in the test interface, and the longitudinal median line is perpendicular to the transverse median line, passes through the midpoint of the transverse median line, and intersects with the edge of the material cross-section.

[0046] As shown in Figure 3, the inner side of the ellipse's outline is the central region (a1), and the outer side of the ellipse's outline is the edge region (b1).

[0047] By selecting the shape described above, the central region can be located at the center of the cross-section as much as possible, and can be clearly distinguished from the edge region, thereby more accurately testing the porosity ratio of the central region and the edge region.

[0048] The central region represents the average state of the internal region of the particle, while the edge region represents the average state of the external region of the particle. In some embodiments, the central region is circular or elliptical, and its center is the intersection of the transverse median and the longitudinal median of the core section. The definition of the central region ensures that the analysis scope covers the central part of the particle's core section.

[0049] In this application, the exposed surface obtained by cutting the negative electrode material particles can be referred to as a cross-section, which reveals the internal structural features of the material. The cross-section can be made through the center of the particle and perpendicular to the length or width direction of the particle. The cross-section can be used for microstructure analysis, such as scanning electron microscopy (SEM) and Raman spectroscopy.

[0050] This application is not limited to The testing method for A can use conventional methods in the art, as long as the negative electrode material meets the above structural and parameter requirements. In some embodiments, A is obtained through the following steps:

[0051] S21, select m particles in the negative electrode material, select the core cross-section of the j-th particle, and delineate the central region and the edge region; wherein, the edge region is located on the outer periphery of the central region, 1≤j≤n, m≥20, and j and m are both positive integers;

[0052] S22, obtain the pore area ratio of the j-th particle, the pore area ratio of the central region, and the pore area ratio of the edge region, denoted as […]. and

[0053] S23, calculate the number of m particles. The average value is used to obtain the percentage of pore area in the kernel.

[0054] S24, via The A of the j-th particle was calculated. j value;

[0055] S25, calculate A for m particles. j The average value is the mean of the ratio of the percentage of pore area between the inner and outer regions, i.e., A.

[0056] Specifically, in S21, m particles are randomly selected from the negative electrode material. m is a sufficiently large sample size to ensure the representativeness of the statistical sample; typically, m is a positive integer ≥ 20. The j-th particle can be sliced ​​using a slicing or ion beam method, exposing its core surface and dividing it into two parts: a central region and an edge region. The edge region is located on the periphery of the central region. This division helps us analyze the distribution of pores in different regions, thereby assessing the consistency of the material's internal structure. The value of j ranges from 1 to m, both being positive integers.

[0057] In S22, SEM (Scanning Electron Microscopy) images can be used, and software tools can be used to identify and measure the pore area on the cross-section of the particle's core. Dividing the pore area by the total area of ​​the cross-section of the entire particle's core yields the pore area ratio of the j-th particle. It reflects the overall pore distribution of the particle. Similarly, by identifying and measuring the pore area of ​​the central region, and dividing the pore area of ​​the central region by the total area of ​​the central region, we can obtain the pore area ratio of the central region of the j-th particle, i.e. It reflects the pore distribution in the central region; by identifying and measuring the pore area of ​​the edge region, and dividing the pore area of ​​the edge region by the total area of ​​the edge region, the pore area ratio of the edge region of the j-th particle can be obtained, i.e. It reflects the pore distribution in the edge region. It can be understood that the pore area of ​​the j-th particle is equal to the sum of the pore areas of its central and edge regions, and the total area of ​​the j-th particle is equal to the sum of the areas of its central and edge regions.

[0058] In S23, for m particles By averaging, the percentage of pore area in the kernel is obtained, i.e. It reflects the proportion of the core pore area in the entire anode material.

[0059] S24, for each particle, via The calculation yields the ratio of the pore area percentage of the central region to the edge region of the j-th particle, which is the A of the j-th particle. j This ratio reflects the difference in pore structure characteristics between the inner and outer regions of the j-th particle.

[0060] S25, A for m particles j The average value A is obtained by averaging, which is the average ratio of the percentage of pore area in the central region to that in the edge region. A reflects the average ratio of the percentage of pore area in the inner layer region to that in the outer layer region of the entire negative electrode material, and is used to represent the difference in property characteristics between the inner and outer layer regions of the particle.

[0061] The D50 particle size is the particle size corresponding to a cumulative volume distribution percentage of 50% in a sample, reflecting the average particle size of the negative electrode material. In some embodiments, the D50 particle size of the negative electrode material is 5 μm to 20 μm. By limiting the D50 particle size of the negative electrode material to a suitable range, in addition to helping to further improve the initial coulombic efficiency and reduce the expansion rate of the secondary battery, it can also shorten the diffusion path of lithium ions, reduce the transport resistance of lithium ions during insertion and extraction, thereby improving the charge and discharge efficiency. Furthermore, it can reduce the porosity inside the electrode and increase the energy density of the secondary battery.

[0062] Regular particle shapes contribute to improved cycle stability and lifespan of secondary batteries. In some embodiments, the shape of the negative electrode material includes at least one of spherical, ellipsoidal, and quasi-spherical shapes. The shape of the negative electrode material essentially refers to the particle shape of the negative electrode material. By defining the shape of the negative electrode material, it is helpful to form more uniform electron and lithium-ion transport paths, reduce local stress concentration, and improve the power density of the secondary battery.

[0063] Specific surface area (SSA) refers to the total surface area per unit mass of material. In some embodiments, the specific surface area of ​​the negative electrode material is 2m². 2 / g~5m 2 / g. By limiting the specific surface area of ​​the negative electrode material to a suitable range, in addition to further improving the initial coulombic efficiency and reducing the expansion rate, a suitable diffusion path can also be provided. This avoids the performance degradation caused by the electrolyte penetrating deep into the pores of the material, and also facilitates the rapid and uniform diffusion of lithium ions during charge and discharge, thereby improving the rate performance and cycle stability of the secondary battery. In addition, it can reduce the contact between the electrolyte and the graphite material surface, reducing the possibility of side reactions, such as electrolyte decomposition and solvent molecule co-intercalation.

[0064] Tap density refers to the degree of compactness of a material under physical vibration. In some embodiments, the tap density of the negative electrode material is 0.9 g / cm³. 3 ~1.4g / cm 3 By limiting the tap density of the negative electrode material within a suitable range, it helps to improve the compaction density of the material during electrode fabrication, reduce internal porosity, and enhance the utilization rate of the negative electrode material and the energy density of the secondary battery. Simultaneously, it reduces the contact area between the electrolyte and graphite particles, thereby reducing SEI film formation, lowering irreversible capacity during the first charge-discharge cycle, and further improving the initial coulombic efficiency. It also helps to reduce volume expansion during cycling, lower mechanical stress between particles, and prevent crack formation. Furthermore, it helps maintain the integrity of the electrode structure, preventing active material from detaching from the current collector, and contributing to improved cycle performance.

[0065] In some embodiments, the average pore size of the negative electrode material is 10 nm to 20 nm. By limiting the average pore size of the negative electrode material to this range, firstly, it helps lithium ions to be more uniformly embedded in the graphite layer during the first charge and discharge process, thereby facilitating the formation of a stable and dense SEI film and further improving the first coulombic efficiency. Secondly, limiting the average pore size can reduce the volume change of the material during lithium ion insertion and extraction, further reducing the expansion rate of graphite particles during charge and discharge, which helps to improve the stability of the material structure, reduce stress accumulation inside the secondary battery, and extend the service life of the secondary battery. In addition, lithium ions can diffuse relatively easily and quickly between graphite layers, which helps to improve the charge and discharge rate and shorten the charge and discharge time.

[0066] In some embodiments, the average particle size of the core is 5 μm to 20 μm; the thickness of the coating layer is 2 nm to 100 nm. Controlling the thickness of the coating layer within the above range helps to balance the structural stability and electrochemical stability of the anode material, so that the battery prepared with this anode material has both good initial coulombic efficiency and low expansion rate.

[0067] In some embodiments, the mass ratio of the core to the coating layer is 100:(4 to 10), for example, a range consisting of 100:4, 100:5, 100:6, 100:7, 100:8, 100:9, 100:10 or any two thereof; the mass ratio of the first amorphous carbon to the second amorphous carbon is (5 to 10):3, for example, a range consisting of 5:3, 6:3, 7:3, 8:3, 9:3, 10:3 or any two thereof.

[0068] The negative electrode material of this application can be used as a negative electrode material in secondary batteries, which can effectively improve the initial coulombic efficiency and reduce the expansion rate of the secondary battery. For example, in some embodiments, the initial coulombic efficiency of the negative electrode material is ≥93.5%, and can be further achieved to be ≥94%, the electrode expansion rate after 20 cycles is ≤27.3%, and can be further achieved to be ≤25.9%, with a capacity ≥362mAh / g.

[0069] This application does not limit the specific preparation process of the negative electrode material, as long as the above parameters are met. In some embodiments, the preparation method of the above-mentioned negative electrode material includes the following steps:

[0070] S1, after the graphite raw material and the first part of the asphalt are subjected to the first mixing and coating and the first heat treatment in sequence, a composite is obtained;

[0071] S2, the composite is subjected to isostatic compaction, and then pulverized to obtain the first intermediate product;

[0072] S3, the first intermediate product is mixed with the second part of asphalt and coated in a second mixture to obtain a secondary coating;

[0073] S4, the secondary coating is subjected to compression molding to obtain the second intermediate product;

[0074] S5, the second intermediate product is subjected to a second heat treatment to obtain the negative electrode material.

[0075] In step S1, graphite raw material is mixed and coated with a first portion of asphalt. This can be understood as mixing the graphite raw material and asphalt at the softening point of the asphalt. During the first mixing and coating process, the first portion of asphalt is molten and uniformly mixed with the graphite raw material to obtain a primary coating. The primary coating then undergoes a first heat treatment, causing the molten first portion of asphalt to fill the pores inside the graphite, resulting in a composite. This mixing and coating process, along with the first heat treatment, helps improve the material's density. The graphite raw material can be spherical graphite with a D50 particle size of 1μm to 20μm.

[0076] The specific mixing ratio of graphite raw material and the first part of asphalt can be adjusted according to the material properties and requirements. The first part of asphalt is selected from at least one of petroleum asphalt, coal tar pitch, and mesophase asphalt, and the D50 particle size of the asphalt is 2mm to 3mm. The softening point of the first part of asphalt is 100℃ to 300℃. It can be understood that the mixing and coating temperature is 100℃ to 300℃, and the mixing and coating time is 10min to 60min. The first heat treatment can be carried out under a first inert atmosphere at a temperature 100℃ to 200℃ higher than the softening point of the asphalt. The first inert atmosphere is to prevent the material from oxidizing during the heat treatment process. Any inert gas can achieve this purpose, such as at least one of nitrogen, helium, and argon. The temperature of the first heat treatment is 200℃ to 600℃, and the time is 3h to 4h.

[0077] In step S2, the composite is subjected to isostatic pressing to obtain an isostatically pressed product. This product is then crushed to obtain the first intermediate product. The isostatic pressing process further achieves internal filling, effectively reducing the porosity of graphite, increasing the material's density, enhancing its structural compactness, and improving the pore-filling effect.

[0078] The specific pressure and time of isostatic pressing can be optimized according to the material performance requirements and equipment capabilities. For example, in some embodiments, the filling effect of asphalt inside graphite can be controlled by adjusting the pressure during isostatic pressing. For example, isostatic pressing can be carried out by cold isostatic pressing or warm isostatic pressing, with a pressure of 60MPa to 120MPa and a holding time of 1min to 60min.

[0079] In S3, the first intermediate product and the second part of asphalt are mixed and coated in a second way. This can be understood as mixing the first intermediate product and the second part of asphalt at the temperature of the asphalt softening point. During the second mixing and coating process, the second part of asphalt is in a molten state and is mixed evenly with the first intermediate product, so that the molten second part of asphalt coats the surface of the first intermediate product, resulting in a secondary coating.

[0080] In some embodiments, the mass ratio of graphite raw material to bitumen is 100:(8-12), for example, a range consisting of 100:8, 100:9, 100:10, 100:11, 100:12, or any two of these. The mass of bitumen refers to the sum of the masses of the first portion of bitumen and the second portion of bitumen, and the mass ratio of the first portion of bitumen to the second portion of bitumen is (5-10):3, for example, a range consisting of 5:3, 6:3, 7:3, 8:3, 9:3, 10:3, or any two of these.

[0081] In step S4, a hydraulic press can be used to press the secondary coating material to obtain the second intermediate product. The specific pressure, time, and number of cycles for the pressing process can be adjusted according to the actual equipment capacity and material requirements. For example, in some embodiments, the pressing conditions are: hydraulic press pressure of 10MPa to 40MPa, holding time of 0 to 2 minutes, and slow reciprocating 2 to 4 times after depressurization for 0.5 minutes. The short holding time ensures that the material quickly forms a dense structure under high pressure, while avoiding equipment wear and reduced production efficiency caused by long holding times. This is suitable for continuous production processes and can improve production efficiency and equipment utilization.

[0082] In step S5, the second intermediate product undergoes a second heat treatment under a second inert atmosphere to ensure the degree of graphitization of the material. After the second heat treatment, the material is dispersed, demagnetized, and sieved to obtain the negative electrode material. The second heat treatment transforms the first portion of pitch filling the pores inside the graphite into the first amorphous carbon, and the second portion of pitch coating the surface into the second amorphous carbon, resulting in a negative electrode material with the aforementioned special structure. The second heat treatment ensures stable carbonization of the material at high temperatures, improving its degree of graphitization. Appropriate heat treatment temperature and time can affect the crystallinity and microstructure of graphite, thereby influencing the Ig in different regions. D / I G The above requirements must be met.

[0083] The specific temperature and time of the second heat treatment can be adjusted according to the conditions of the heat treatment apparatus and the performance targets of the material. For example, in some embodiments, the temperature of the second heat treatment is higher than that of the first heat treatment, such as a temperature of 900–1500°C and a time of 1–24 hours. The second inert atmosphere is used to prevent oxidation of the material during the heat treatment process; any inert gas can achieve this purpose, such as at least one of nitrogen, helium, and argon.

[0084] A second aspect of this application provides a negative electrode sheet comprising the negative electrode material provided in the first aspect above.

[0085] The negative electrode sheet of this application includes a negative electrode current collector and a negative electrode material active layer disposed on at least one surface of the negative electrode current collector. The negative electrode material active layer includes the negative electrode material provided in the first aspect. The negative electrode current collector can be at least one of copper foil, nickel foil, stainless steel foil, titanium foil, or carbon-based current collector, or any composite current collector disclosed in the prior art, such as, but not limited to, current collectors formed by combining the aforementioned conductive foil and polymer substrate. Because it includes a negative electrode material with excellent performance, applying this negative electrode sheet to a secondary battery helps to improve the initial coulombic efficiency and reduce the expansion rate of the secondary battery.

[0086] The active layer of the negative electrode material also includes a binder to bond the negative electrode active material particles, thereby facilitating the formation of the film layer and improving the bonding force between the active layer of the negative electrode material and the negative electrode current collector. In some embodiments, the binder may include, but is not limited to, polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, or nylon, etc.

[0087] The active layer of the negative electrode material may further include a conductive material, which includes, but is not limited to, carbon-based materials, metal-based materials, conductive polymers, or any combination thereof. In some embodiments, carbon-based materials may include, but are not limited to, natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, or any combination thereof. In some embodiments, metal-based materials may include, but are not limited to, metal powders or metal fibers, such as copper, nickel, aluminum, or silver. In some embodiments, the conductive polymer may be a polyphenylene derivative.

[0088] In the specific preparation of the negative electrode sheet, the negative electrode material, conductive agent, and binder can be dispersed in an appropriate amount of solvent and thoroughly stirred to form a uniform negative electrode slurry. The negative electrode slurry is then uniformly coated onto the negative electrode current collector, and after drying, rolling, and slitting, the negative electrode sheet is obtained. In one specific embodiment, the negative electrode active layer comprises, by mass percentage, 70%–99% negative electrode material, 0.5%–15% conductive agent, and 0.5%–15% binder.

[0089] The conductive agent may be selected from at least one of natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, and graphene; the binder may be selected from at least one of carboxymethyl cellulose, styrene-butadiene rubber, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyvinyl alcohol, and sodium polyacrylate.

[0090] A third aspect of this application provides a secondary battery comprising the negative electrode provided in the second aspect above.

[0091] Due to the inclusion of the aforementioned high-performance negative electrode, this secondary battery exhibits excellent initial coulombic efficiency and low expansion rate.

[0092] Specifically, the secondary battery includes a casing, an electrode assembly, and an electrolyte. Both the electrode assembly and the electrolyte are located inside the casing.

[0093] The outer casing can be a packaging bag encapsulated with a film (such as aluminum-plastic film), for example, a pouch battery. In other embodiments, it can also be a steel-cased battery, an aluminum-cased battery, etc.

[0094] Referring to Figures 4 and 5, the electrode assembly 100 includes a positive electrode 101, a negative electrode 102, and a separator 103, with the separator 103 disposed between the positive electrode 101 and the negative electrode 102. During charging, as shown in Figure 4, active ions (such as lithium ions) are extracted from the lattice of the positive electrode material (such as a lithium-ion intercalated compound) of the positive electrode 101, pass through the separator 103 via the electrolyte, reach the negative electrode 102, and are inserted into the lattice of the negative electrode material. During discharging, as shown in Figure 5, active ions (such as lithium ions) are extracted from the lattice of the negative electrode material of the negative electrode 102, pass through the separator 103 via the electrolyte, reach the positive electrode 101, and are inserted into the lattice of the positive electrode material (such as a lithium-ion intercalated compound). Electrons are generated and travel from the negative electrode 102 to the positive electrode 101 via an external circuit. The reverse movement of these electrons forms an electric current, which can be used by electrical appliances.

[0095] In some embodiments, the electrode assembly 100 may be a stacked structure, which is formed by alternatingly stacking a positive electrode 101, a separator 103, and a negative electrode 102. In other embodiments, the electrode assembly 100 may also be a wound structure, which is formed by sequentially stacking and then winding the positive electrode 101, the separator 103, and the negative electrode 102.

[0096] The positive electrode 101 includes a positive current collector and a positive electrode material active layer disposed on at least one surface of the positive current collector. The positive current collector can be aluminum foil or nickel foil, or any composite current collector disclosed in the prior art, such as, but not limited to, current collectors formed by combining the aforementioned conductive foil and polymer substrate. The positive electrode material active layer includes a positive electrode active material, which includes a compound that reversibly inserts and extracts lithium ions (i.e., a lithiation intercalation compound). In some embodiments, the positive electrode active material may include a lithium transition metal composite oxide. This lithium transition metal composite oxide contains lithium and at least one element selected from cobalt, manganese, and nickel. In some embodiments, the positive electrode active material may include, but is not limited to, lithium cobalt oxide (LiCoO2), lithium nickel manganese cobalt ternary materials (NCM), lithium manganese oxide (LiMn2O4), and lithium nickel manganese oxide (LiNi).0.5 Mn 1.5 At least one of lithium iron phosphate (LiFePO4) or lithium iron phosphate (LiFePO4).

[0097] The positive electrode material active layer also includes an adhesive for bonding the positive electrode active material particles to facilitate the formation of the film layer, and also to improve the bonding force between the positive electrode material active layer and the positive electrode current collector. In some embodiments, the adhesive may include, but is not limited to, at least one of polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, or nylon.

[0098] The positive electrode material active layer may further include a conductive material, which includes, but is not limited to, carbon-based materials, metal-based materials, conductive polymers, or any combination thereof. In some embodiments, carbon-based materials may include, but are not limited to, natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, or any combination thereof. In some embodiments, metal-based materials may include, but are not limited to, metal powders or metal fibers, such as copper, nickel, aluminum, or silver. In some embodiments, the conductive polymer may be a polyphenylene derivative.

[0099] The separator 103 includes a membrane layer with a porous structure, and its material includes, but is not limited to, at least one of polyethylene, polypropylene, polyvinylidene fluoride, polyethylene terephthalate, polyimide, or aramid. For example, the separator 103 may be a polypropylene porous membrane, a polyethylene porous membrane, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric, or a polypropylene-polyethylene-polypropylene porous composite membrane, etc.

[0100] The electrolyte serves to conduct ions between the positive electrode 101 and the negative electrode 102. The electrolyte can be in one or more states, including gel, solid, and liquid. In some embodiments, the electrolyte is a liquid electrolyte solution. The liquid electrolyte solution serves to conduct active ions between the positive electrode 101 and the negative electrode 102. In some embodiments, the liquid electrolyte solution includes a lithium salt and an organic solvent. The lithium salt may be selected from, but is not limited to, one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium hexafluoroarsenate (LiAsF6), lithium perchlorate (LiClO4), lithium tetraphenylborate (LiB(C6H5)4), lithium methanesulfonate (LiCH3SO3), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiCF3SO3), lithium bis(trifluoromethanesulfonyl)imide (LiN(SO2CF3)2), lithium tri(trifluoromethanesulfonyl)methyllithium (LiC(SO2CF3)3), lithium dioxolaneborate (LiBOB), and lithium difluorophosphate (LiPO2F2). For example, LiPF6 is selected as the lithium salt because it provides high ionic conductivity and improves cycling characteristics. The organic solvent may be a carbonate compound, a carboxylic acid ester compound, an ether compound, a nitrile compound, other organic solvents, or combinations thereof. Examples of carbonate compounds include, but are not limited to, diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), butyl carbonate (BC), vinyl ethylene carbonate (VEC), fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, trifluoromethylethylene carbonate, or combinations thereof.

[0101] In the preparation of secondary batteries, positive electrode sheets, separators and negative electrode sheets are wound or stacked to obtain battery cells. The battery cells are then encapsulated in pre-stamped aluminum-plastic films. After the encapsulated batteries are dried, electrolyte is injected into the dried batteries. The secondary batteries are then placed, formed and resealed to complete the preparation of the secondary batteries.

[0102] The present application will be further described in detail below with reference to specific embodiments, which should not be construed as limiting the scope of protection claimed in the present application.

[0103] Example 1

[0104] The preparation method of the negative electrode material in this embodiment includes the following steps:

[0105] S1. 20 kg of graphite raw material (D50 particle size of 16 μm) and 1.6 kg of asphalt (softening point of 250℃) were added to a VC mixer and mixed for 25 min. After uniform mixing, the mixture was subjected to low-temperature heat treatment at 400℃ for 4 h under a nitrogen protective atmosphere. After cooling to room temperature, the composite was obtained.

[0106] S2, the composite is subjected to isostatic pressing to densify it. The maximum isostatic pressing pressure is 60 MPa. After holding the pressure for 15 min, the material is crushed to about 16 μm to obtain the first intermediate product.

[0107] S3, the first intermediate product and 0.6 kg of asphalt (softening point 250℃) are added to a VC mixer and mixed for 25 min to obtain a secondary coating;

[0108] S4. The secondary coating is pressed in a hydraulic press at a pressure of 30 MPa for 0.5 min, repeated 3 times to obtain the second intermediate product.

[0109] S5, the second intermediate product is subjected to high-temperature heat treatment, carbonized at 1250°C for 16 hours under a nitrogen protective atmosphere, and after carbonization, it is dispersed, demagnetized and sieved to obtain the negative electrode material of this embodiment.

[0110] Example 2

[0111] The preparation method of the negative electrode material in this embodiment includes the following steps:

[0112] S1. 20 kg of graphite raw material (D50 particle size of 16 μm) and 1.6 kg of asphalt (softening point of 180℃) were added to a VC mixer and mixed for 25 min. After uniform mixing, the mixture was heat-treated at 350℃ for 4 h under a nitrogen protective atmosphere. After cooling to room temperature, the composite was obtained.

[0113] S2, the composite is subjected to isostatic pressing to densify it. The maximum isostatic pressing pressure is 50 MPa. After holding the pressure for 15 min, the material is crushed to about 16 μm to obtain the first intermediate product.

[0114] S3, the first intermediate product and 0.6 kg of asphalt (softening point 180℃) are added to a VC mixer and mixed for 30 min to obtain a secondary coating;

[0115] S4. The secondary coating is pressed in a hydraulic press at a pressure of 30 MPa for 0.5 min, repeated 3 times to obtain the second intermediate product.

[0116] S5, the second intermediate product is subjected to high-temperature heat treatment, carbonized at 1150°C for 12 hours under a nitrogen protective atmosphere, and after carbonization, it is dispersed, demagnetized and sieved to obtain the negative electrode material of this embodiment.

[0117] Example 3

[0118] The preparation method of the negative electrode material in this embodiment includes the following steps:

[0119] S1. 20 kg of graphite raw material (D50 particle size of 16 μm) and 1.0 kg of asphalt (softening point of 180℃) were added to a VC mixer and mixed for 25 min. After uniform mixing, the mixture was subjected to low-temperature heat treatment at 350℃ for 4 h under nitrogen protection atmosphere. After cooling to room temperature, the composite was obtained.

[0120] S2, the composite is subjected to isostatic pressing to densify it. The maximum isostatic pressing pressure is 50 MPa. After holding the pressure for 15 min, the material is crushed to about 16 μm to obtain the first intermediate product.

[0121] S3, the first intermediate product is mixed with 0.6 kg of asphalt (softening point 180℃) in a VC mixer for 25 min to obtain the first intermediate product;

[0122] S4. The first intermediate product is pressed in a hydraulic press at a pressure of 25 MPa for 0.5 min, and repeated 3 times to obtain the second intermediate product.

[0123] S5, the second intermediate product is subjected to high-temperature heat treatment and carbonized at 1150°C for 10 hours under a nitrogen protective atmosphere. After carbonization, it is dispersed, demagnetized and sieved to obtain the negative electrode material of this embodiment.

[0124] Example 4

[0125] The preparation method of the negative electrode material in this embodiment includes the following steps:

[0126] S1. 20 kg of graphite raw material (D50 particle size of 14.5 μm) and 1.6 kg of asphalt (softening point of 250℃) were added to a VC mixer and mixed for 25 min. After uniform mixing, the mixture was heat-treated at 400℃ for 4 h under a nitrogen protective atmosphere. After cooling to room temperature, the composite was obtained.

[0127] S2, the composite is subjected to isostatic pressing to densify it. The maximum isostatic pressing pressure is 70 MPa. After holding the pressure for 15 min, the material is crushed to about 14.5 μm to obtain the first intermediate product.

[0128] S3, the first intermediate product and 0.6 kg of asphalt (softening point 250℃) are added to a VC mixer and mixed for 30 min to obtain a secondary coating;

[0129] S4, the secondary coating is pressed in a hydraulic press at a pressure of 30MPa for 0.5min, repeated 3 times, and the second intermediate product is obtained after coarse crushing;

[0130] S5, the second intermediate product is subjected to high-temperature heat treatment and carbonized at 1250°C for 16 hours under a nitrogen protective atmosphere. After carbonization, it is dispersed, demagnetized and sieved to obtain the negative electrode material of this embodiment.

[0131] Example 5

[0132] The preparation method of the negative electrode material in this embodiment includes the following steps:

[0133] S1, 20 kg of graphite raw material (D50 particle size of 12 μm) and 1.6 kg of asphalt (softening point of 250℃) were added to a VC mixer and mixed for 25 min. After uniform mixing, the mixture was subjected to low-temperature heat treatment at 400℃ for 4 h under nitrogen protection atmosphere. After cooling to room temperature, the composite was obtained.

[0134] S2, the composite is subjected to isostatic pressing to densify it. The maximum isostatic pressing pressure is 60 MPa. After holding the pressure for 15 min, the material is crushed to about 12 μm to obtain the first intermediate product.

[0135] S3, the first intermediate product and 0.6 kg of asphalt (softening point 250℃) are added to a VC mixer and mixed for 30 min to obtain a secondary coating;

[0136] S4. The secondary coating is pressed in a hydraulic press at a pressure of 30 MPa for 0.5 min, repeated 3 times. After coarse crushing, the second intermediate product is obtained.

[0137] S5, the second intermediate product is subjected to high-temperature heat treatment, carbonized at 1250°C for 14 hours under a nitrogen protective atmosphere, and after carbonization, it is dispersed, demagnetized and sieved to obtain the negative electrode material of this embodiment.

[0138] Example 6

[0139] The preparation method of the negative electrode material in this embodiment includes the following steps:

[0140] S1. 20 kg of graphite raw material (D50 particle size of 10 μm) and 1.6 kg of asphalt (softening point of 250℃) were added to a VC mixer and mixed for 25 min. After uniform mixing, the mixture was heat-treated at 400℃ for 4 h under a nitrogen protective atmosphere. After cooling to room temperature, the composite was obtained.

[0141] S2, the composite is subjected to isostatic pressing to densify it. The maximum isostatic pressing pressure is 60 MPa. After holding the pressure for 15 min, the material is crushed to about 10 μm to obtain the first intermediate product.

[0142] S3, the first intermediate product and 0.6 kg of asphalt (softening point 250℃) are added to a VC mixer and mixed for 25 min to obtain a secondary coating;

[0143] S4. The secondary coating is pressed in a hydraulic press at a pressure of 30 MPa for 0.5 min, repeated 3 times. After coarse crushing, the second intermediate product is obtained.

[0144] S5, the second intermediate product is subjected to high-temperature heat treatment, carbonized at 1250°C for 18 hours under a nitrogen protective atmosphere, and after carbonization, it is dispersed, demagnetized and sieved to obtain the negative electrode material of this embodiment.

[0145] Example 7

[0146] The preparation method of the negative electrode material in this embodiment includes the following steps:

[0147] S1. 20 kg of graphite raw material (D50 particle size of 16 μm) and 0.7 kg of asphalt (softening point of 180℃) were added to a VC mixer and mixed for 25 min. After uniform mixing, the mixture was subjected to low-temperature heat treatment at 350℃ for 4 h under nitrogen protection atmosphere. After cooling to room temperature, the composite was obtained.

[0148] S2, the composite is subjected to isostatic pressing to densify it. The maximum isostatic pressing pressure is 50 MPa. After holding the pressure for 15 min, the material is crushed to about 16 μm to obtain the first intermediate product.

[0149] S3, the first intermediate product is mixed with 0.3 kg of asphalt (softening point 180℃) in a VC mixer for 25 min to obtain the first intermediate product;

[0150] S4. The first intermediate product is pressed in a hydraulic press at a pressure of 25 MPa for 0.5 min, and repeated 3 times to obtain the second intermediate product.

[0151] S5, the second intermediate product is subjected to high-temperature heat treatment and carbonized at 1150°C for 12 hours under a nitrogen protective atmosphere. After carbonization, it is dispersed, demagnetized and sieved to obtain the negative electrode material of this embodiment.

[0152] Example 8

[0153] The preparation method of the negative electrode material in this embodiment includes the following steps:

[0154] S1. 20 kg of graphite raw material (D50 particle size of 16 μm) and 2.0 kg of asphalt (softening point of 180℃) were added to a VC mixer and mixed for 25 min. After uniform mixing, the mixture was heat-treated at 350℃ for 4 h under a nitrogen protective atmosphere. After cooling to room temperature, the composite was obtained.

[0155] S2, the composite is subjected to isostatic pressing to densify it. The maximum isostatic pressing pressure is 50 MPa. After holding the pressure for 15 min, the material is crushed to about 16 μm to obtain the first intermediate product.

[0156] S3, the first intermediate product is mixed with 1.0 kg of asphalt (softening point 180℃) in a VC mixer for 25 min to obtain the first intermediate product;

[0157] S4. The first intermediate product is pressed in a hydraulic press at a pressure of 25 MPa for 0.5 min, and repeated 3 times to obtain the second intermediate product.

[0158] S5, the second intermediate product is subjected to high-temperature heat treatment and carbonized at 1250°C for 18 hours under a nitrogen protective atmosphere. After carbonization, it is dispersed, demagnetized and sieved to obtain the negative electrode material of this embodiment.

[0159] Example 9

[0160] S1. 20 kg of graphite raw material (D50 particle size of 16 μm) and 2.5 kg of asphalt (softening point of 180℃) were added to a VC mixer and mixed for 25 min. After uniform mixing, the mixture was subjected to low-temperature heat treatment at 350℃ for 4 h under a nitrogen protective atmosphere. After cooling to room temperature, the composite was obtained.

[0161] S2, the composite is subjected to isostatic pressing to densify it. The maximum isostatic pressing pressure is 50 MPa. After holding the pressure for 15 min, the material is crushed to about 16 μm to obtain the first intermediate product.

[0162] S3, the first intermediate product is mixed with 1.5 kg of asphalt (softening point 180℃) in a VC mixer for 25 min to obtain the first intermediate product;

[0163] S4. The first intermediate product is pressed in a hydraulic press at a pressure of 25 MPa for 0.5 min, and repeated 3 times to obtain the second intermediate product.

[0164] S5, the second intermediate product is subjected to high-temperature heat treatment and carbonized at 1250°C for 18 hours under a nitrogen protective atmosphere. After carbonization, it is dispersed, demagnetized and sieved to obtain the negative electrode material of this embodiment.

[0165] Comparative Example 1

[0166] The preparation method of the comparative example negative electrode material includes the following steps:

[0167] 20 kg of graphite raw material (D50 particle size of 16 μm) and 2.2 kg of asphalt (softening point of 250℃) were added to a VC mixer and mixed for 25 min. After mixing, the mixture was carbonized at 1250℃ for 16 h under a nitrogen protective atmosphere. After carbonization, the anode material of this comparative example was obtained by dispersing, demagnetizing and sieving.

[0168] Comparative Example 2

[0169] The preparation method of the comparative example negative electrode material includes the following steps:

[0170] 20 kg of graphite raw material (D50 particle size of 16 μm), 2.25 kg of asphalt (softening point of 250℃) and 40 g of graphene powder were mixed in a VC mixer for 25 min. Then, the mixture was heat-treated at 400℃ to make the asphalt and graphene powder adhere evenly and tightly to the surface of the graphite particles. After the heat treatment, the mixture was carbonized at 1250℃ for 16 h under a nitrogen protective atmosphere. After carbonization, the mixture was dispersed, demagnetized and sieved to obtain the negative electrode material of this comparative example.

[0171] Comparative Example 3

[0172] The preparation method of the comparative example negative electrode material includes the following steps:

[0173] S1. 20 kg of graphite raw material (D50 particle size of 16 μm) is subjected to isostatic pressing densification treatment. The maximum isostatic pressing pressure is 60 MPa, and the pressure is held for 15 min. After crushing the material, it is pressed in a hydraulic press. The hydraulic press pressure is 30 MPa, and the pressure is held for 0.5 min. After repeating 3 times, it is crushed to about 16 μm to obtain the densified product.

[0174] S2, the densification product and 2.2 kg of asphalt (softening point 250℃) were added to a VC mixer and mixed for 25 min. Then, under a nitrogen protective atmosphere, it was carbonized at 1250℃ for 16 h. After carbonization, it was dispersed, demagnetized and sieved to obtain the negative electrode material of this comparative example.

[0175] Test case

[0176] 1. Hole ratio test

[0177] The negative electrode material is ionized into argon ions (Ar) under high vacuum using an ion mill (HITACHI E3500) through an ion source. + Argon ions are then accelerated by a high-voltage electric field to bombard the sample surface with high energy, thereby removing the surface material and achieving the effects of grinding and polishing. The cross-section of the particles is observed under a high-magnification electron microscope (HITACHI S4800), with a magnification of 2.5kX to 9.0kX for each particle to ensure the cross-section shows a complete single particle.

[0178] Select at least 20 particle cross-sections; take the intersection of the transverse median and the longitudinal median of the cross-section of a single particle kernel as the center of the ellipse, the major axis of the ellipse is 1 / 2 the length of the transverse median, and the minor axis is 1 / 2 the length of the longitudinal median. Divide the kernel cross-section into a central region (a1) and an edge region (b1) with the outline of the ellipse as the boundary, as shown in Figure 3. The inner side of the outline of the ellipse is the central region (a1), and the outer side of the outline of the ellipse is the edge region (b1).

[0179] The aforementioned transverse median line is the longest horizontal diameter of the cut surface. The longitudinal median line is perpendicular to the transverse median line and passes through the midpoint of the transverse median line, intersecting with the edge of the material cut surface.

[0180] Software such as Image Pro Plus, Image J, and Aztec Feature were used to statistically analyze and calculate the pore area ratio of the core cross-section of a single particle. Pore ​​area ratio of the central region Pore ​​area ratio in the edge region and the ratio of the pore area of ​​the central region to that of the peripheral region (A j ),in,

[0181] The percentage of pore area in the entire core section of the anode material can be calculated using the following formula. And the mean (A) of the ratio of pore area to tangential area in the central and peripheral regions:

[0182] Where m≥20, 1≤j≤m, and j and m are positive integers.

[0183] Taking Image Pro Plus as an example, the statistical process is illustrated as follows: 1) After opening Image Pro Plus software, open the electron microscope cross-sectional morphology image of a single particle by pressing File (F), Open (O), or Ctrl+O; 2) Perform scale calibration in Measure (M), Calibration (C), and Spatial Calibration Wizard; 3) Click Irregular AOI and draw the outline of a single particle in Trace mode; 4) Click Measure (M) and Count / Size and select Colors..., click Histogram Based, select the range of 0-255, click Count to fill the selected area, and click View and Statistics to record the area of ​​a single particle at Sum; 5) In RGB mode, use the extractor to extract the RGB values ​​of the pores, and then click Count to identify them; then click Draw / Merge Objects in Edit to select the unfilled pores, click OK after selection, and click View and Statistics to record the area value at Sum, which is the pore area of ​​a single particle; 6) Click Measure (M), Measure... Draw a line parallel to the ruler using the distance tool, and move this line segment to the selected area of ​​the AOI to obtain the horizontal median line (the maximum value of the line segment). Click Measure distance to draw a line segment with a length of 1 / 2 the horizontal median line starting from the endpoint. At the midpoint of the horizontal median line, draw a vertical median line perpendicular to the horizontal median line and intersecting the particle outline. 7) Using the center of the horizontal median line as the center of an ellipse, with the major axis of the ellipse being 1 / 2 the length of the horizontal median line and the minor axis being 1 / 2 the length of the short side of the vertical median line, first use Measure distance to mark the length range, and then use Elliptical AOI to draw an ellipse at the marked location as the central region. 8) Repeat steps 4) and 5) to calculate the area of ​​the central region and the pore area. 9) Calculate the area of ​​the edge region and the pore area using the particle area, particle pore area, and the area of ​​the central region and the pore area. Also calculate the proportion of the pore area of ​​the core section of a single particle. Pore ​​area ratio of the central region Pore ​​area ratio in the edge region and the ratio of the pore area of ​​the central region to that of the peripheral region (A j ); 10) Perform the above steps 1)-9) on 20 particles, and calculate the A value of the negative electrode material using the above formula. value.

[0184] 2. I D / I G test

[0185] At least 15 cross-sections of particles were selected. On the core cross-section of each particle, a rectangle with a width of 1 μm–6 μm and a length of 5 μm–20 μm was selected, not exceeding the particle outline. The Raman scattering spectrum of the anode material cross-section was measured using an InVia microconfocal Raman spectrometer. A 532 nm laser wavelength was used to measure the selected rectangles, with the scanning direction being first transverse and then longitudinal. The material's D peak is located at 1350 cm⁻¹. -1 Nearby, peak G is located at 1580cm. -1 Nearby, I D / I G The value is the D / G peak intensity ratio. The Raman mapping region diagram and rectangular region selection diagram of a single particle cross section are shown in Figures 1 and 2.

[0186] The specific steps for selecting the rectangular area are as follows: 1) Select a cross-sectional particle whose longitudinal length is greater than its transverse length (if the particle does not meet the requirements, rotate the stage before selecting); 2) Within a single particle, select a rectangular frame containing the longest longitudinal diameter, with a width of 1μm to 6μm and a length approximately between 3 / 5 and 1 of the longest longitudinal diameter, and at least two points close to the particle's outline. The longest longitudinal diameter is the longest distance along the particle's cross-section relative to the test interface.

[0187] 3) When processing Raman data, first determine whether the rectangular region contains the longest longitudinal diameter. The steps are as follows: 3.1) Open Image Pro Plus software and open the electron microscope cross-sectional morphology image of a single particle using File (F), Open (O), or Ctrl+O; 3.2) Click Irregular AOI and draw the outline of a single particle in Trace mode; 3.4) Click Measure (M) and Measure distance to draw a line perpendicular to the scale, and move the line segment to the selected area of ​​AOI, intersecting the particle outline, thus obtaining the position of the longest longitudinal diameter (the maximum pixel value of the line segment, with the midpoint of the longest longitudinal diameter considered as the center of the cross-section). Determine whether the selected rectangle contains the longest longitudinal diameter. If not, remove the Raman data of that particle. Test and filter at least 15 Raman data of particle cross-sections that meet the criteria.

[0188] Raman mapping data processing was performed on the qualified rectangular regions. Based on data classification, the mapping regions were divided into inner rectangular region a and outer rectangular region b. When the scanning rule was that the horizontal scan should be performed first, followed by the vertical scan, the Raman mapping data were arranged in chronological order. The first and last quarters of the data were considered as Raman data for outer rectangular region b, and the middle portion was considered as Raman data for inner rectangular region a. Peak fitting was performed on the Raman scattering spectrum of each point to determine the characteristic peaks of the material. The D peak was located at 1350 cm⁻¹. -1 Nearby, peak G is located at 1580cm. -1 Nearby, calculate the intensity ratio (ID to GG) of the inner rectangular region a and outer rectangular region b of each particle. D / I G ) value, K ai I is the rectangular region within the i-th particle. D / I G K bi I is the outer rectangular region of the i-th particle. D / I G ;

[0189] The I of the inner region is calculated using the following formula. D / I G mean (K) a ), inner region and outer region I D / I G The mean (K) of the ratio: K i =K ai / K bi

[0190] Where n≥15, 1≤i≤n, and i and n are positive integers.

[0191] 3. Specific surface area SSA test

[0192] The specific surface area of ​​the negative electrode material was measured using a JW-DX dynamic specific surface area analyzer. Based on the relevant theories of physical adsorption, and using the continuous flow method proposed by Nelsen and Eggertsen as the structure, the specific surface area of ​​the solid was determined. A mixed gas of hydrogen as the carrier and nitrogen as the adsorbent gas was introduced into the sample tube. When the sample tube was immersed in liquid nitrogen to reach a low-temperature environment, the nitrogen in the mixed gas was physically adsorbed by the sample until adsorption saturation. At this point, the proportion of nitrogen in the mixed gas changed. During the adsorption process, a high-precision thermal conductivity detector performed the detection and calculation.

[0193] 4. D50 particle size test

[0194] The D50 particle size of the negative electrode material was tested using a Malvern 3000 laser particle size analyzer. The sample, a small amount of dispersant (a mixture of ethanol, pure water, and a low-foaming surfactant), and pure water were added to a 50 mL beaker. The mixture was stirred thoroughly with a glass rod to ensure uniform dispersion. The sample was then transferred to the sample cell of the Malvern 3000 laser particle size analyzer, and the pump speed was set to 2400–2500 r / min at a frequency of 19.5 Hz for particle size analysis. This application pertains to the cumulative volumetric particle size distribution statistics.

[0195] 5. Tap density test

[0196] The tap density of the anode material was tested using a Quanta Dual Autotap instrument. A 100 mL sample of the anode material was placed in a graduated cylinder and mechanically vibrated 1000 times. The sample mass and volume after tapping were then recorded. The tap density (g / cm³) was calculated accordingly. 3 The tapped density is calculated as (sample mass / tapped volume).

[0197] 6. Average aperture d test

[0198] The average pore size d of the anode material was tested using a BSD-660M A6M analyzer. A static volumetric method was employed, with degassing at 300℃ for 300 min. Nitrogen gas (77.3 K) was used as the adsorbate, and the amount of nitrogen adsorbed was measured at different pressures (P / P0 range of 0.1-0.99). The average pore size d of the anode material was determined by analyzing the adsorption isotherms.

[0199] 7. Electrochemical performance testing

[0200] The negative electrode materials, carboxymethyl cellulose, and styrene-butadiene rubber of the examples and comparative examples were dissolved in pure water at a mass ratio of 96.5:1.5:2, respectively, and the solid content was controlled at 50% to obtain a negative electrode slurry. The negative electrode slurry was coated on a copper foil current collector, and after vacuum drying at 95°C, rolling, and pressurizing, a negative electrode sheet was obtained. Using a lithium metal sheet as the counter electrode, a coin cell was assembled in a glove box filled with argon gas.

[0201] The coin cell was charged and discharged at a current density of 0.1C, within a charge-discharge range of 0.001 to 1.5V, to obtain the first reversible specific capacity, the first charge capacity, and the first discharge capacity. The first coulombic efficiency (first efficiency) was calculated according to the formula: first discharge capacity / first charge capacity.

[0202] The electrode expansion rate was tested using the battery electrode thickness change measuring device and system disclosed in patent document CN209991940U. The negative electrode material, carboxymethyl cellulose, and styrene-butadiene rubber were uniformly mixed at a mass percentage of 96.5:1.5:2, with the solid content controlled at 50%, to obtain the negative electrode slurry. The negative electrode slurry was coated onto a copper foil current collector, and after vacuum drying and rolling, a compacted density of 1.60 g / cm³ was obtained. 3 The negative electrode sheet was tested to determine its initial thickness. d 1. The positive electrode active material lithium cobalt oxide, conductive carbon black, and polyvinylidene fluoride are mixed evenly in a mass ratio of 96.5:2:1.5 and then coated onto aluminum foil (single-sided) to obtain a positive electrode sheet. The positive and negative electrode sheets prepared above are loaded into a self-made three-electrode testing device (using the battery disclosed in patent document CN209991940U) for testing. This three-electrode testing device can record the changes in electrode thickness in situ.

[0203] The following charge / discharge regime was used for testing: In the first week, the battery was charged at a constant rate of 0.01C for 30 minutes, then at a constant rate of 0.05C for 30 minutes, followed by a constant rate of 0.1C to 4.2V. Once the voltage reached the upper limit of 4.2V, constant voltage charging was implemented, with the current gradually decreasing to 0.01C to complete the charging process. The battery was then discharged at 0.1C to 3V. In the second week, the battery was charged at a constant rate of 0.2C to 4.2V; once the voltage reached 4.2V, the current gradually decreased to 0.01C. After the initial charge cycle, the battery was discharged at a constant rate of 0.2C to 3V. From cycle 3 to 20, it was charged at a constant rate of 0.5C to 4.2V. Once the voltage reached 4.2V, it was charged at a constant voltage until the current decreased to 0.01C, at which point the charging was complete. Then, it was discharged at a constant rate of 0.5C to 3V. In the final half-cycle, it was charged at a constant rate of 0.5C to 4.2V. Once the voltage reached 4.2V, it was charged at a constant voltage until the current decreased to 0.01C, at which point the charging was complete. The battery was then removed, and the thickness d2 of the negative electrode was measured after 20 cycles. The expansion rate was calculated using the formula: Electrode Expansion Rate = (d2 - d1) / d1 × 100%.

[0204] Table 1

[0205] In Table 1, d represents the average pore size of the negative electrode material.

[0206] As shown in Table 1, in the negative electrode materials of Examples 1 to 9, the graphite is filled with amorphous carbon, and the carbon content satisfies 0.4 ≤ K. a The values ​​are ≤0.7 and 0.5≤K<0.9, while Comparative Examples 1 and 3 do not satisfy 0.5≤K≤0.9 and 0.4≤K. a The negative electrode material in Comparative Example 2 only satisfies 0.5≤K≤0.9, but does not satisfy 0.4≤K. a≤0.7, the anode materials of Examples 1-9 have higher initial coulombic efficiency, lower expansion rate, and higher capacity compared to Comparative Examples 1-3. Therefore, this application achieves this by making the anode material satisfy 0.4≤K a ≤0.7, 0.5≤K<0.9, can reduce Li + The structural expansion caused by entering and exiting the graphite interlayer improves the structural stability of the material, and the initial coulombic efficiency, expansion performance and capacity are improved.

[0207] Furthermore, compared to Examples 7, 8, and 9, the negative electrode materials of Examples 1 to 6 satisfy 0.5 ≤ K ≤ 0.9 and 0.4 ≤ K. a While keeping the value ≤0.7, the percentage of pore area in the kernel is reduced. satisfy: Furthermore, ensuring that the average ratio A of the pore area percentage between the inner and outer layers satisfies 1.2 ≤ A ≤ 2.0 can further improve the initial coulombic efficiency, expansion performance, and capacity. The negative electrode material in Example 9 does not satisfy this requirement. The improvement in the electrochemical performance of the negative electrode material is limited, and the performance is worse than that of Examples 1-6. The negative electrode materials of Example 7 do not satisfy 1.2≤A≤2.0, and the negative electrode material of Example 8 does not satisfy... The improvement in the electrochemical performance of the negative electrode material is limited, and its performance is worse than that of Examples 1-6. The negative electrode materials in Example 9 do not meet the requirements. 1.2≤A≤2.0, which is worse than Examples 7-8.

[0208] Examples 1-6, through batch coating and the application of low-temperature heat treatment, molding, and high-temperature heat treatment, resulted in the filling of amorphous carbon within the particles, improving internal defects and filling pores in both the inner and outer layers, particularly the outer layer. This ensured the material met the properties 0.5 ≤ K ≤ 0.9 and 0.4 ≤ K. a ≤0.7, 1.2≤A≤2.0, This graphite anode material possesses advantages such as high density and low expansion, exhibiting excellent electrochemical performance when applied to secondary lithium-ion batteries. In Comparative Example 1, the amorphous carbon failed to fill the interior of the graphite, thus not satisfying 0.5≤K≤0.9 and 0.4≤K. a ≤0.7, and also does not satisfy 1.2≤A≤2.0, This results in poor initial coulombic efficiency, capacity, and expansion performance of the anode material; in Comparative Example 2, the introduction of a small amount of graphene satisfies 0.5≤K≤0.9, but does not satisfy 0.4≤K. a ≤0.7 and 1.2≤A≤2.0, The initial coulombic efficiency, capacity, and expansion performance were improved compared to Comparative Example 1, but the improvement was limited. Comparative Example 3 used a densification technique to reduce the internal porosity of graphite before coating with asphalt, but the amorphous carbon failed to fill the graphite interior to the maximum extent, resulting in the anode material satisfying 1.2≤A≤2.0. However, it does not satisfy 0.5≤K≤0.9, 0.4≤K a ≤0.7, the initial coulombic efficiency and expansion performance are improved compared to Comparative Example 1 and Comparative Example 2, but the capacity is reduced compared to Comparative Example 2, and the improvement is limited.

[0209] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A negative electrode material, characterized in that, The negative electrode material includes a core and a coating layer, the coating layer being located on the surface of the core, the core including natural graphite and a first amorphous carbon filling the pores of the natural graphite, and the coating layer including a second amorphous carbon. The Raman spectrum of the negative electrode material contains D peaks and G peaks, with an intensity ratio of ID to G peaks. D / I G ; The kernel includes an inner region and an outer region located outside the inner region, the outer region being adjacent to the covering layer; The inner layer region I D / I G The mean is K a The inner layer region and the outer layer region I D / I G The mean of the ratio is K; Satisfy: 0.4≤K a ≤0.7, 0.5≤K<0.

9.

2. The negative electrode material according to claim 1, characterized in that, The negative electrode material satisfies: 0.41≤K a ≤0.68; or, 0.4≤K a ≤0.6; or, 0.45≤K a ≤0.7; or, K a The range is 0.4, 0.41, 0.45, 0.5, 0.55, 0.6, 0.65, 0.68, 0.7 or any two of the aforementioned values.

3. The negative electrode material according to claim 1, characterized in that, The negative electrode material satisfies: 0.51≤K≤0.88; or, 0.5≤K≤0.89; or, 0.6≤K≤0.8; or, K is a range of values ​​consisting of 0.5, 0.51, 0.6, 0.7, 0.8, 0.88, 0.89, or any two of the aforementioned values.

4. The negative electrode material according to claim 1, characterized in that, The percentage of pore area in the kernel is The satisfy:

5. The negative electrode material according to claim 4, characterized in that, The negative electrode material satisfies: or, or, or, The range is 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, or any two of the aforementioned values.

6. The negative electrode material according to claim 4, characterized in that, The kernel includes a central region and an edge region located on the periphery of the central region. The mean ratio of the pore area percentage of the central region to that of the edge region is A, and A satisfies: 1.2≤A≤2.

0.

7. The negative electrode material according to claim 6, characterized in that, The negative electrode material satisfies: 1.2≤A≤1.8; or, 1.2≤A≤1.6; or, 1.4≤A≤1.9; or, A is a range of values ​​consisting of 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, or any two of the aforementioned values.

8. The negative electrode material according to any one of claims 1 to 7, characterized in that, The D50 particle size of the negative electrode material is 5μm to 20μm.

9. The negative electrode material according to any one of claims 1 to 7, characterized in that, The shape of the negative electrode material includes at least one of spherical, ellipsoidal, and near-spherical shapes.

10. The negative electrode material according to any one of claims 1 to 7, characterized in that, The specific surface area of ​​the negative electrode material is 2m². 2 / g~5m 2 / g.

11. The negative electrode material according to any one of claims 1 to 7, characterized in that, The tap density of the negative electrode material is 0.9 g / cm³. 3 ~1.4g / cm 3 .

12. The negative electrode material according to any one of claims 1 to 7, characterized in that, The average pore size of the negative electrode material is 10 nm to 20 nm.

13. The negative electrode material according to any one of claims 1 to 7, characterized in that, The thickness of the coating layer is 2nm to 100nm.

14. A negative electrode sheet, characterized in that, The negative electrode sheet comprises the negative electrode material according to any one of claims 1 to 13.

15. A secondary battery, characterized in that, The secondary battery includes the negative electrode sheet as described in claim 14.

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