Negative active material, method for preparing the same, secondary battery, and electric device

Abstract

This application provides a negative electrode active material and its preparation method, a secondary battery, and an electrical device, relating to the field of lithium battery technology. The secondary battery includes a negative electrode sheet, which includes a negative electrode current collector and a negative electrode film layer located on at least one side of the negative electrode current collector. The negative electrode film layer includes a negative electrode active material, which includes graphite particles. The average sphericity of the graphite particles is 0.65-0.95, and the average concavity T of the graphite particles is... n The OI value of the graphite particles is 0.5-8, ranging from 0.05 to 0.45. These settings effectively reduce the expansion of the secondary battery during cycling.

Description

Technical Field

[0001] This application relates to the field of lithium battery technology, and in particular to a negative electrode active material and its preparation method, a secondary battery, and an electrical device. Background Technology

[0002] The development of electric vehicles has placed higher demands on battery range. As battery energy density increases, battery expansion also increases, leading to safety issues such as battery electrode breakage. In addition, as battery life requirements increase, the reliability requirements for batteries are also constantly rising.

[0003] Currently, for graphite-containing secondary batteries, the actual expansion during charging and discharging needs to be further reduced. Summary of the Invention

[0004] This application is made in view of the above-mentioned issues, and its purpose is to provide a negative electrode active material and its preparation method, a secondary battery and an electrical device, so as to alleviate the expansion of graphite-containing negative electrode sheets and batteries during cycling.

[0005] The first aspect of this application provides a secondary battery including a negative electrode sheet, the negative electrode sheet including a negative current collector and a negative electrode film layer located on at least one side of the negative current collector, the negative electrode film layer including a negative electrode active material.

[0006] The negative electrode active material includes graphite particles with an average sphericity of 0.65-0.95 and an average concavity T. n The OI value is 0.05-0.45, and the OI value of graphite particles is 0.5-8.

[0007] Wherein, the concavity T of the graphite particle is 1 - the actual volume of the graphite particle / the convex hull volume of the graphite particle. The actual volume of the graphite particle is obtained directly from the dataset obtained by computed tomography with micron-level resolution, and the convex hull volume of the graphite particle is calculated from the dataset.

[0008] Therefore, in the secondary battery provided in this application, by controlling the average sphericity of the graphite particles to be 0.65-0.95, the high sphericity of the graphite particles can optimize particle stacking and, to a certain extent, convert the volume expansion caused by lithium intercalation into spatial position adjustment and pore filling of the graphite particles inside the electrode, which is beneficial to reducing the macroscopic thickness expansion rate of the electrode. However, if the T value is too small (T<0.05), the particle surface is closer to a convex geometry, or even a perfect sphere, which leads to: (1) lack of buffer space, and the volume change of lithium intercalation has nowhere to be released; (2) expansion Forced to be transmitted outward, the thickness of the electrode increases rapidly; (3) Internal stress accumulation may cause the electrode to crack; (4) The surface is smooth, the adhesive is not anchored enough, and when the T value is too large (T>0.25), the particle surface is severely concave and the protrusions are sharp, resulting in: (1) Protrusion-protrusion point contact, the radius of curvature of the contact point is small, and the Hertz contact stress increases significantly; (2) High stress directly transmits displacement, generating mechanical disturbance to adjacent particles; (3) The risk of protrusion breakage increases, and the rearrangement of fragments intensifies the expansion; (4) Continuous rearrangement and breakage in the cycle, and the expansion rate continues to increase. Therefore, this application controls the average concavity T to be 0.05-0.25 based on the average sphericity of graphite particles of 0.65-0.95. Within this range, the degree of concavity of graphite particles is moderate, which retains the low friction characteristics of high sphericity particles to facilitate particle rearrangement during lithium intercalation expansion, while avoiding excessive stress point contact and breakage risk. At the same time, it provides appropriate physical anchoring points to ensure stable adhesion of the binder, so that lithium intercalation expansion can be effectively buffered through particle rearrangement and pore filling, thereby suppressing the irreversible expansion of the negative electrode sheet. Meanwhile, the OI value of graphite particles is controlled to be 0.5-8, and the graphite particle orientation is small, which disperses stress after lithium intercalation and helps to reduce expansion.

[0009] In any embodiment, the average sphericity of the graphite particles is 0.71-0.85. Sphericity determines the macroscopic arrangement of graphite particles. When the sphericity is within the above range, the shape of the graphite particles deviates slightly from a sphere, which can promote the orderly arrangement of particles during cold pressing while maintaining sufficient contact area. This is beneficial for good bonding between particles and between particles and binder, improving the cohesion of the negative electrode sheet, thereby effectively reducing the expansion of the negative electrode sheet during cycling.

[0010] In any embodiment, the average concavity T of the graphite particles n The average concavity is 0.12-0.36. Based on controlling the average sphericity of graphite particles to be 0.71-0.85, the average concavity is optimized within the above range. This retains the low-friction characteristics of high-sphericity particles to facilitate particle rearrangement during lithium intercalation expansion, while avoiding excessive stress point contact and breakage risks. Simultaneously, it provides appropriate physical anchoring points to ensure stable adhesion of the binder, allowing lithium intercalation expansion to be effectively buffered through particle rearrangement and pore filling, thereby suppressing irreversible expansion of the negative electrode sheet.

[0011] In any embodiment, at least 50% of the graphite particles have a concavity T ≤ 0.40. Controlling the concavity of most or all of the graphite particles within the above range, that is, controlling the surface concavity of most or all of the graphite particles within a suitable range, is more conducive to both preserving the low-friction surface characteristics to facilitate particle rearrangement during lithium intercalation expansion, and avoiding excessive stress point contact and breakage risks. At the same time, it provides appropriate physical anchoring points to ensure stable adhesion of the binder, so that lithium intercalation expansion can be effectively buffered through particle rearrangement and pore filling, thereby suppressing the irreversible expansion of the negative electrode sheet.

[0012] In any embodiment, at least 50% of the graphite particles have a sphericity ≥ 0.65. Controlling the sphericity of most or all graphite particles within the above range, i.e., controlling the sphericity of most or all graphite particles to be high, utilizes the isotropic expansion characteristics of most or all graphite particles and the point contact between particles, which is beneficial to improving the cohesion of the negative electrode sheet, thereby effectively reducing expansion.

[0013] In any embodiment, the graphite particles include secondary particles with a carbon coating layer on their surface. This secondary particle structure effectively reduces material volume expansion during lithium intercalation, thereby improving the maximum expansion force. Furthermore, the carbon coating on the secondary particle surface acts as a protective layer, firmly binding the primary particles together, increasing the overall mechanical strength of the particles, effectively buffering volume change stress, suppressing particle breakage, and enhancing structural and interfacial stability.

[0014] In any embodiment, the tap density of the secondary particles is 1.25 g / cc to 1.45 g / cc. A tap density within this relatively high and suitable range is beneficial for the close arrangement of graphite particles and increases the contact area. Each particle is supported by surrounding particles, thus reducing local stress concentration and maintaining a confined pressure state during cold pressing. This helps suppress lateral slippage and cracking of the particles, ensuring the graphite particles maintain mechanical integrity and structural stability after cold pressing. This allows for more effective resistance and dispersion of internal stress during battery cycling. Simultaneously, this dense structure also helps suppress electrode expansion during cycling, thereby improving the trend of increasing expansion force.

[0015] In any embodiment, the graphite particles include secondary particles with an OI value of 0.5-5. Controlling the OI value of the secondary particles within the aforementioned low range indicates that the orientation of the primary particles tends to be random, and the secondary particles as a whole possess good isotropic characteristics. After lithium intercalation, stress is dispersed, which helps to reduce expansion. In addition, combined with the aforementioned sphericity and average concavity, the secondary particles are easy to rotate and slide during cold pressing, which can promote the orderly arrangement of particles during cold pressing, reduce the stress accumulation during cold pressing, and also ensure good contact between graphite particles and between graphite particles and binder, thereby improving the cohesion of the negative electrode sheet and effectively reducing the expansion of the negative electrode sheet during cycling.

[0016] In any embodiment, the graphite particles comprise single particles with a tap density of 1.30 g / cc to 1.50 g / cc. Controlling the tap density of the single particles to within this relatively high and suitable range facilitates a tighter arrangement of the graphite particles and increases the contact area. Each particle is supported by surrounding particles, thus reducing local stress concentration during cold pressing and maintaining a confined pressure state. This helps suppress lateral slippage and cracking of the particles, ensuring the graphite particles maintain mechanical integrity and structural stability after cold pressing. Consequently, they more effectively resist and disperse internal stress during battery cycling. Simultaneously, this dense structure also helps suppress electrode expansion during cycling, thereby improving the trend of increasing expansion force.

[0017] In any embodiment, the graphite particles include single particles with an OI value of 2-8. By controlling the OI value of the single particles within the above range, the single particles exhibit good isotropy, and stress is dispersed after lithium intercalation, which helps reduce expansion. Combined with the aforementioned sphericity and concavity, the particle structure remains stable during cold pressing, facilitating rotation and sliding. This promotes the orderly arrangement of particles during cold pressing, reduces stress accumulation during cold pressing, and ensures good contact between graphite particles and between graphite particles and the binder, thereby enhancing the cohesion of the negative electrode sheet and effectively reducing expansion.

[0018] In any embodiment, the volumetric particle size distribution Dv50 of the graphite particles is 4μm-20μm. Within this range, the particles are less prone to breakage during rolling, thus suppressing the risk of accelerated electrode expansion due to breakage.

[0019] In any embodiment, the ratio of (Dv90-Dv10) to Dv50 of the graphite particles is 1.1-1.5. The relatively concentrated particle size distribution and similar particle size of the graphite particles reduce the absolute expansion, which is beneficial for reducing battery expansion.

[0020] In any embodiment, the liquid absorption rate of the negative electrode sheet with a compaction density of 1.60 g / cc is ≥1.8 mg / s. 0.5Controlling the liquid absorption rate within the above range indicates that during the initial formation, the electrolyte can rapidly and synchronously wet the surface of all negative electrode active materials, forming a uniform and stable SEI film. This can suppress the expansion of the negative electrode caused by uneven volume changes due to excessively rapid local lithium intercalation or excessive stress concentration. It also indicates that the negative electrode has a suitable pore structure and wettability, which can provide a buffer space for the volume expansion of the negative electrode material during charging and discharging, absorb some mechanical stress, and reduce electrode expansion.

[0021] A second aspect of this application also provides a negative electrode active material comprising graphite particles, wherein the average sphericity of the graphite particles is 0.65-0.95, and the average concavity T of the graphite particles is... n The OI value is 0.05-0.45, and the OI value of graphite particles is 0.5-8.

[0022] Wherein, the concavity T of the graphite particle is 1 - the actual volume of the graphite particle / the convex hull volume of the graphite particle. The actual volume of the graphite particle is obtained directly from the dataset obtained by computed tomography with micron-level resolution, and the convex hull volume of the graphite particle is calculated from the dataset.

[0023] The negative electrode active material provided in this application controls the average sphericity of graphite particles to be 0.65-0.95. The high sphericity of graphite particles can optimize particle stacking and can, to a certain extent, convert the volume expansion caused by lithium intercalation into spatial position adjustment and pore filling of graphite particles inside the electrode, which is beneficial to reduce the macroscopic thickness expansion rate of the electrode. However, if the T value is too small (T<0.05), the surface of the particles is closer to a convex geometry, or even close to a perfect sphere, lacking depressions, resulting in: (1) lack of buffer space, and the volume change of lithium intercalation has nowhere to be released; (2) expansion is forced to be transmitted outward, and the thickness of the electrode increases rapidly; (3) internal stress accumulation may cause the electrode to crack; (4) the surface is smooth, and the binder anchoring is insufficient. When the T value is too large (T>0.25), the particle surface is severely concave and the protrusions are sharp, resulting in: (1) protrusion-protrusion point contact, small contact point curvature radius, and significantly increased Hertzian contact stress; (2) high stress directly transmits displacement, generating mechanical disturbance to adjacent particles; (3) the risk of protrusion breakage increases, and fragment rearrangement intensifies expansion; (4) continuous rearrangement and breakage during the cycle, and the expansion rate continues to increase. Therefore, this application controls the average concavity T to be 0.05-0.25 based on the average sphericity of graphite particles of 0.65-0.95. Within this range, the degree of concavity of graphite particles is moderate, which not only retains the low friction characteristics of high sphericity particles to facilitate particle rearrangement during lithium intercalation expansion, but also avoids excessive stress point contact and breakage risk, while providing appropriate physical anchoring points to ensure stable adhesion of the binder, so that lithium intercalation expansion can be effectively buffered through particle rearrangement and pore filling, thereby suppressing the irreversible expansion of the negative electrode sheet. Simultaneously controlling the OI value of graphite particles to 0.5-8 results in low orientation of the graphite particles, which disperses stress after lithium intercalation and helps reduce expansion.

[0024] In any embodiment, the graphite particles include secondary particles, the surface of which has a carbon coating layer; And / or, the graphite particles include secondary particles with a tap density of 1.25 g / cc to 1.45 g / cc; And / or, the graphite particles include secondary particles with an OI value of 0.5-5; And / or, the graphite particles include single particles with a tap density of 1.30 g / cc to 1.50 g / cc; And / or, the OI value of a single particle is 2-8; And / or, of the plurality of graphite particles, at least 50% of the graphite particles have a sphericity of ≥0.65; And / or, of the multiple graphite particles, at least 50% of the graphite particles have a concavity T ≤ 0.40. By controlling the graphite particles to meet any of the above conditions, when applied to secondary batteries, it can simultaneously reduce the volume expansion of the electrode during the lithium intercalation process and the expansion throughout the battery's entire life cycle.

[0025] A third aspect of this application provides a method for preparing a negative electrode active material, comprising: The first raw material is shaped to obtain the second raw material. The first raw material includes a first aggregate and / or granulated material. The first aggregate is obtained by crushing and shaping the raw coke. The granulated material is obtained by crushing and shaping the raw coke. The second aggregate is mixed with a binder and granulated. The Dv50 of the second raw material is D1, the Dv50 of the first raw material is D2, and the D2 / D1 ratio is 0.68-0.90. The second raw material is pre-carbonized, the obtained carbide is mixed with an antioxidant, and graphitized to obtain graphite particles as a negative electrode active material. The antioxidant includes boron compounds, and the mass ratio of antioxidant to carbide is 0.5-1.5:100. The average sphericity of the graphite particles is 0.65-0.95, and the average concavity T of the graphite particles is... n The OI value of graphite particles is 0.5-8, ranging from 0.05 to 0.45. The concavity of graphite particles is T = 1 - actual volume of graphite particles / convex hull volume of graphite particles. The actual volume of graphite particles is obtained directly from a dataset obtained by computed tomography with micron-level resolution, and the convex hull volume of graphite particles is calculated from the dataset.

[0026] The preparation method provided in this application, during the preparation of the negative electrode active material, achieves deep shaping of the first raw material by controlling D2 / D1 to 0.68-0.90, thereby achieving rounding and spheroidization of the first raw material. This is beneficial for improving the sphericity of the second raw material particles and reducing the concavity, and is conducive to obtaining particles with an average sphericity of 0.65-0.95 and an average concavity T. n Graphite particles with a diameter of 0.05-0.45 mm and an OI value of 0.5-8 were obtained. By introducing boron-based compounds as antioxidants during the pre-carbonization process, and controlling the mass ratio of antioxidant to carbide at 0.5-1.5:100, the increase in concavity during pre-carbonization can be suppressed, maintaining the original low concavity of the graphite particles. This is beneficial for obtaining graphite particles with an average sphericity of 0.65-0.95 and an average concavity T0. n The graphite particles are 0.05-0.45 mm in size. Within this range, the graphite particles have a moderate degree of indentation, which retains the low friction characteristics of highly spherical particles to facilitate particle rearrangement during lithium intercalation expansion, while avoiding excessive stress point contact and breakage risks. At the same time, it provides appropriate physical anchoring points to ensure stable adhesion of the binder, so that lithium intercalation expansion can be effectively buffered through particle rearrangement and pore filling, thereby suppressing the irreversible expansion of the negative electrode sheet.

[0027] In any embodiment, granulation includes: heating to 290℃-310℃, maintaining the temperature for 50 min-70 min while stirring, and then heating to 690℃-710℃ while maintaining the temperature for 100 min-140 min while stirring. Through the above process improvement, the granulation strength is improved, which is beneficial to improving the density of the first raw material obtained after granulation, which is beneficial to improving the tap density of the final high sphericity and concavity negative electrode active material, reducing the particle rearrangement caused by repeated particle expansion of the negative electrode active material, slowing down stress release, and thus improving the expansion force growth trend.

[0028] And / or, the amount of binder added is 12%-20% of the aggregate mass. Controlling the amount of binder added within the above-mentioned higher range is beneficial to improving the density of the first raw material obtained after granulation. This not only helps to increase the tap density of the negative electrode active material, reduce particle rearrangement caused by repeated particle expansion, and slow down stress release, thereby improving the trend of expansion force growth, but also enhances the structural stability of the secondary particles.

[0029] In any embodiment, the volatile matter content of the raw coke is 10 wt%-18 wt%, and the Hayek grindability coefficient is 60-150. Controlling the raw coke to meet the above parameters is beneficial for better rounding and spheroidization in the subsequent deep shaping process, and also helps to reduce the expansion performance of the prepared graphite particles.

[0030] The fourth aspect of this application provides an electrical device, including a secondary battery of the first aspect of this application, a negative electrode active material of the second aspect, or a negative electrode active material prepared by the preparation method of the third aspect of this application. Attached Figure Description

[0031] Figure 1 This is a schematic diagram illustrating an example of calculating the concavity of graphite particles.

[0032] Figure 2 This is a schematic diagram of a secondary battery according to one embodiment of this application.

[0033] Figure 3 yes Figure 2 An exploded view of a secondary battery according to one embodiment of this application is shown.

[0034] Figure 4 This is a schematic diagram of a battery module according to one embodiment of this application.

[0035] Figure 5 This is a schematic diagram of a battery pack according to one embodiment of this application.

[0036] Figure 6 yes Figure 5 An exploded view of a battery pack according to one embodiment of this application is shown.

[0037] Figure 7 This is a schematic diagram of an electrical device that uses a secondary battery as a power source according to one embodiment of this application.

[0038] Explanation of reference numerals in the attached figures: 1-Battery pack; 2-Upper housing; 3-Lower housing; 4-Battery module; 5-Battery cell; 51-Housing; 52-Electrode assembly; 53-Top cover assembly. Detailed Implementation

[0039] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the negative electrode active material, its preparation method, secondary battery, and power application device of this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for the purpose of enabling those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0040] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0041] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0042] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0043] Unless otherwise specified, all steps of this application may be performed sequentially or randomly, preferably sequentially. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, if the method may also include step (c), it means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0044] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0045] The development of electric vehicles has placed higher demands on battery range. As battery energy density increases, battery expansion also increases, leading to safety issues such as battery electrode breakage. In addition, as battery life requirements increase, battery reliability requirements are also constantly rising. Therefore, graphite is usually used as the negative electrode. However, for high energy density batteries, the problem of large expansion still exists.

[0046] Currently, to reduce expansion, the orientation of graphite particles is usually reduced to make the volume expansion of graphite particles anisotropic, thereby achieving the expansion of the electrode, and / or the particle size of graphite particles is reduced, thereby reducing the expansion by reducing the absolute amount of particle expansion.

[0047] Analysis of the causes of battery expansion revealed that the increase in cell expansion force primarily originates from the expansion of the negative electrode. Further analysis of the negative electrode expansion showed that its sustained rebound is due to the continuous irreversible expansion of the electrode, while the reversible expansion of the cell changes relatively little during cycling. In other words, reducing material orientation, decreasing material expansion, and improving the intrinsic physical properties of the active material can only reduce the volume expansion of the electrode during lithium intercalation; however, it has no significant effect on improving expansion throughout the battery's entire lifespan.

[0048] Experiments and simulations revealed that the irreversible thickness increase of the electrode sheet is mainly due to stress release during cycling. After the rolling process, the negative electrode active material particles in the electrode sheet undergo orientational arrangement, resulting in residual stress inside the electrode sheet. This stress is gradually released during cycling, altering the arrangement of the negative electrode active material particles and eventually reverting to the arrangement before rolling. This leads to an irreversible increase in the electrode sheet thickness. Furthermore, poor adhesion of the binder at this point directly weakens the mechanical integrity of the entire electrode structure, significantly reducing its ability to resist and restrain this rebound, thus amplifying the magnitude and speed of thickness increase. Simultaneously, the change in the arrangement of the negative electrode active material particles is strongly correlated with the surface characteristics of the particles; the smoothness of the particle surface significantly affects particle accumulation.

[0049] Based on this, the first aspect of the present application provides a secondary battery, which includes a negative electrode sheet, the negative electrode sheet including a negative current collector and a negative electrode film layer located on at least one side of the negative current collector, the negative electrode film layer including a negative electrode active material.

[0050] The negative electrode active material includes graphite particles, with an average sphericity of 0.65-0.95 and an average concavity T of 0.65. n The OI value is 0.05-0.45, and the OI value of graphite particles is 0.5-8.

[0051] Wherein, the concavity T of the graphite particle is 1 - actual volume of the graphite particle / convex volume of the graphite particle. The actual volume of the graphite particle is directly obtained from a dataset obtained by computed tomography scan with micron-level resolution, and the convex volume of the graphite particle is calculated from the dataset. "At least one side of the negative electrode film layer" means that the negative electrode current collector has two opposite sides in its own thickness direction. A negative electrode film layer can be formed on one side of the negative electrode current collector, or a negative electrode film layer can be formed on both sides of the negative electrode current collector. In the same electrode assembly, a negative electrode film layer can be formed on one side of some negative electrode current collectors, and a negative electrode film layer can be formed on both sides of some negative electrode current collectors; or a negative electrode film layer can be formed on one side of all negative electrode current collectors in the same electrode assembly; or a negative electrode film layer can be formed on both sides of all negative electrode current collectors in the same electrode assembly. This application does not limit this.

[0052] "Sphericity" refers to the macroscopic sphericity of graphite particles. Sphericity can be defined as the value obtained by dividing the circumference of a circle having the same area as the projected image of the graphite particles for secondary batteries by the circumference of the projected image of the graphite particles for secondary batteries. Specifically, sphericity = (circumference of a circle having the same area as the projected image of the graphite particles for secondary batteries) / (circumference of the projected image of the graphite particles for secondary batteries). The closer the sphericity is to 1, the closer the graphite particles are to being spherical.

[0053] "Average sphericity" can be defined as the number-average of the sphericity of arbitrarily selected 50 graphite particles.

[0054] Sphericity can be measured using a particle shape analyzer such as the Sysmex FPIA3000 (manufactured by Mavern).

[0055] A "convex hull" refers to the smallest convex geometry that contains all points of a particle. That is, in three-dimensional geometry, for a given set of points, the convex hull is the smallest convex polyhedron containing all of these points. In this application, based on all points extracted from the particle surface using CT, the three-dimensional convex hull of these points is calculated, resulting in a convex polyhedron that completely encloses the particle and does not enter any depressions. For ease of explanation, this is referred to as... Figure 1 The explanation is based on two-dimensional projection, such as... Figure 1 As shown, the outer contour indicated by the dashed line is the convex hull.

[0056] The concavity T of graphite particles is calculated as 1 - actual volume of graphite particles / convex hull volume of graphite particles. The actual volume of graphite particles / total convex hull volume of graphite particles represents the proportion of actual volume to convex hull volume. 1 - actual volume of graphite particles / convex hull volume of graphite particles gives the proportion of actual volume missing. Therefore, in this application, "concavity" reflects the microscopic characteristics of the material surface and the degree of concavity on the particle surface.

[0057] The concavity testing method includes: fully dispersing graphite particles (hundreds of particles) using capillary tubes, and constructing a three-dimensional morphological characterization of the graphite particles through micron-level resolution X-ray computed tomography (i.e., micron-level CT) testing. The actual volume of the graphite particles is directly obtained from the dataset obtained by micron-level resolution computed tomography, and the convex hull volume of the graphite particles is calculated from the dataset using a three-dimensional convex hull algorithm. It can be understood that for the same graphite particle, both the actual volume of the graphite particle and the convex hull volume of the graphite particle are obtained based on the same CT dataset.

[0058] Mean concavity T n " is the number average of the concavity T of n graphite particles, where n is, for example, 50.

[0059] Concavity T = 1 - actual particle volume / particle convexity volume. The larger the T value, the more the actual volume is missing relative to the convexity volume, and the greater the degree of concavity on the particle surface. Based on the average sphericity of graphite particles of 0.65-0.95, when the T value is too small (T<0.05), the particle surface is closer to the convex geometry, or even close to a perfect sphere, lacking concavity, which leads to: (1) lack of buffer space, and the volume change of lithium intercalation has nowhere to be released; (2) expansion is forced to be transmitted outward, and the electrode thickness increases rapidly; (3) internal stress accumulation may cause electrode cracking; (4) the surface is smooth, and the binder anchoring is insufficient. When the T value is too large (T>0.25), the particle surface is severely concave, resulting in sharp protrusions, which leads to: (1) protrusion-protrusion point contact, small contact point curvature radius, and significantly increased Hertzian contact stress; (2) high stress directly transmits displacement, generating mechanical disturbance to adjacent particles; (3) the risk of protrusion breakage increases, and fragment rearrangement intensifies expansion; (4) continuous rearrangement and breakage during the cycle, and the expansion rate continues to increase. Therefore, this application controls the average concavity T to be 0.05-0.25 based on the average sphericity of graphite particles of 0.65-0.95. Within this range, the degree of concavity of graphite particles is moderate, which not only retains the low friction characteristics of high sphericity particles to facilitate particle rearrangement during lithium intercalation expansion, but also avoids excessive stress point contact and breakage risk. At the same time, it provides appropriate physical anchoring points to ensure stable adhesion of the binder, so that lithium intercalation expansion can be effectively buffered through particle rearrangement and pore filling, thereby suppressing the irreversible expansion of the negative electrode sheet.

[0060] "OI value" refers to the orientation degree of graphite particles, describing the uniformity of crystal orientation within the graphite particle material. The OI value is the ratio of the peak area of ​​plane (004) to the peak area of ​​plane (110) obtained by X-ray diffraction (XRD). In this application, the powder OI value of the material can be determined using instruments and methods known in the art. For example, an X-ray diffractometer (such as a Bruker D8 Discover) can be used for testing, and the testing can be performed with reference to JIS K0131-1996 and JB / T4220-2011. The X-ray diffraction pattern of the powder sample is obtained, and the powder OI value is calculated according to OI value = I004 / I110. I004 is the integrated area of ​​the diffraction peak of the 004 crystal plane of crystalline carbon in the powder sample, and I110 is the integrated area of ​​the diffraction peak of the 110 crystal plane of crystalline carbon in the powder sample. In the X-ray diffraction analysis test of this application, a copper target can be used as the anode target, CuKα rays can be used as the radiation source, the ray wavelength scanning 2θ angle range is 20°-80°, and the scanning rate is 4° / min.

[0061] The lower the OI value, the smaller the orientation of the graphite particles. Controlling the OI value of the graphite particles to 0.5-8 results in a smaller orientation of the graphite particles, which disperses stress after lithium intercalation and helps reduce expansion.

[0062] It should be noted that when performing tests on the sphericity, concavity and below tap density and OI of the graphite particles in the negative electrode sheet of the secondary battery provided in the first aspect of this application, the corresponding method of obtaining the graphite particles includes: disassembling the secondary battery after full discharge, cleaning the negative electrode sheet three times with DMC for 2 hours each time to remove residual electrolyte on the surface, drying it, cleaning the negative electrode sheet with a hot solution of 2M HCl to separate the graphite particles from the negative electrode current collector, cleaning it with deionized water and drying it to obtain black powder, and then carbonizing the black powder at high temperature to obtain the final reduced graphite particle powder.

[0063] In this application, the average sphericity of the graphite particles is controlled to be 0.65-0.95. The high sphericity of the graphite particles can optimize the particle stacking and can, to a certain extent, convert the volume expansion caused by lithium intercalation into the spatial position adjustment and pore filling of the graphite particles inside the electrode, which is beneficial to reduce the macroscopic thickness expansion rate of the electrode. However, if the T value is too small (T<0.05), the particle surface is closer to a convex geometry, or even close to a perfect sphere, which leads to: (1) lack of buffer space, and the volume change of lithium intercalation has nowhere to be released; (2) expansion is forced to be transmitted outward, and the electrode thickness increases rapidly; (3) internal stress accumulation may cause the electrode to crack; (4) the surface is smooth and the binder anchoring is insufficient. When the T value is too large (T>0.25), the particle surface is severely concave and the protrusions are sharp, resulting in: (1) the protrusion-protrusion point contact, the radius of curvature of the contact point is small, and the Hertzian contact stress is significantly increased; (2) the high stress directly transmits displacement, generating mechanical disturbance to adjacent particles; (3) the risk of protrusion breakage increases, and the rearrangement of fragments intensifies expansion; (4) continuous rearrangement and breakage in the cycle, and the expansion rate continues to increase. Therefore, this application controls the average concavity T to be 0.05-0.25 based on the average sphericity of graphite particles of 0.65-0.95. Within this range, the degree of concavity of graphite particles is moderate, which retains the low friction characteristics of high sphericity particles to facilitate particle rearrangement during lithium intercalation expansion, while avoiding excessive stress point contact and breakage risk. At the same time, it provides appropriate physical anchoring points to ensure stable adhesion of the binder, so that lithium intercalation expansion can be effectively buffered through particle rearrangement and pore filling, thereby suppressing the irreversible expansion of the negative electrode sheet. Meanwhile, the OI value of graphite particles is controlled to be 0.5-8, and the graphite particle orientation is small, which disperses stress after lithium intercalation and helps to reduce expansion.

[0064] For example, the average sphericity of the graphite particles is any one of 0.65, 0.70, 0.71, 0.75, 0.80, 0.85, 0.90, 0.95, 0.83, 0.87, 0.78, 0.86, 0.82 or between any two values.

[0065] For example, the average concavity T of the graphite particles nIt is any value among 0.05, 0.08, 0.10, 0.12, 0.13, 0.15, 0.16, 0.17, 0.20, 0.22, 0.25, 0.27, 0.30, 0.33, 0.34, 0.35, 0.36, 0.38, 0.40, 0.42, 0.43, and 0.45, or between any two values.

[0066] For example, the OI value of the graphite particles is any one of 0.5, 2, 3, 4, 5, 6, 7, 8, 1.0, 1.5, 2.0, 2.5, 3.5, 4.5, 1.2, 1.3, 4.7, 0.8 or between any two values.

[0067] In some embodiments, the average sphericity of the graphite particles is 0.71-0.85. Sphericity determines the macroscopic arrangement of graphite particles. When the sphericity is within the above range, the shape of the graphite particles deviates slightly from a sphere, which can promote the orderly arrangement of particles during cold pressing while maintaining sufficient contact area. This is beneficial for good bonding between particles and between particles and binder, improving the cohesion of the negative electrode sheet, thereby effectively reducing battery expansion.

[0068] For example, the average sphericity of the graphite particles is any one of 0.71, 0.72, 0.73, 0.74, 0.75, 0.78, 0.79, 0.80, 0.82, 0.83, 0.84, 0.85 or between any two values.

[0069] In some embodiments, the average concavity of the graphite particles is 0.12-0.36. By controlling the average sphericity of the graphite particles to be 0.8-0.93, optimizing the average concavity within this range retains the low-friction characteristics of high-sphericity particles to facilitate particle rearrangement during lithium intercalation expansion, while avoiding excessive stress point contact and breakage risks. Simultaneously, it provides adequate physical anchoring points to ensure stable adhesion of the binder, allowing lithium intercalation expansion to be effectively buffered through particle rearrangement and pore filling, thereby suppressing irreversible expansion of the negative electrode sheet.

[0070] For example, the average concavity of the graphite particles is any one of 0.12, 0.15, 0.18, 0.20, 0.22, 0.25, 0.27, 0.30, 0.33, 0.35, 0.36 or between any two values.

[0071] In some embodiments, at least 50% of the graphite particles have a concavity T ≤ 0.40. Controlling the concavity of most or all of the graphite particles within the above range, that is, controlling the surface depression of most or all of the graphite particles within a suitable range, is more conducive to both preserving the low-friction surface characteristics to facilitate particle rearrangement during lithium intercalation expansion, and avoiding excessive stress point contact and breakage risks. At the same time, it provides appropriate physical anchoring points to ensure stable adhesion of the binder, so that lithium intercalation expansion can be effectively buffered through particle rearrangement and pore filling, thereby suppressing the irreversible expansion of the negative electrode sheet.

[0072] For example, in the case of multiple graphite particles, at least 50% of the graphite particles have a concavity T ≤ 0.40, which means: when imaging graphite particles for secondary batteries, as fluid flows through the sample cell, a high-speed camera captures the projection of the particles and transmits it to the software. Then, image processing technology is used to determine the particle size and perform quantitative analysis of the morphology of the graphite particles. In this case, 100 graphite particles are randomly selected, and the number of particles with a concavity T ≤ 0.40 is calculated as A. The percentage of graphite particles with a concavity T ≤ 0.40 is calculated by A / 100*100%.

[0073] For example, the proportion of graphite particles with concavity T ≤ 0.40 in a plurality of graphite particles is any one of 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 100% or between any two values.

[0074] In some embodiments, at least 50% of the graphite particles have a sphericity ≥ 0.65. Controlling the sphericity of most or all graphite particles within the above range, i.e., controlling the sphericity of most or all graphite particles to be high, utilizes the isotropic expansion characteristics of most or all graphite particles and the point contact between particles, which is beneficial to improving the cohesion of the negative electrode sheet, thereby effectively reducing expansion.

[0075] For example, in the multiple graphite particles mentioned here, at least 50% of the graphite particles are graphite particles that meet the following criteria: when 100 graphite particles are randomly selected, 50 or more of them meet the requirement that the sphericity of the graphite particles is ≥0.65.

[0076] For example, in a plurality of graphite particles, at least 60% of the graphite particles have a sphericity ≥ 0.65.

[0077] In some embodiments, the graphite particles include secondary particles with a carbon coating on their surface. This secondary particle structure effectively reduces material volume expansion during lithium intercalation, thereby improving the maximum expansion force. Furthermore, the carbon coating on the secondary particles acts as a protective layer, firmly binding the primary particles together, increasing the overall mechanical strength of the particles, effectively buffering volume change stress, suppressing particle breakage, and enhancing structural and interfacial stability.

[0078] "Secondary particles" refer to larger particles formed by the aggregation of multiple primary particles. Primary particles refer to individual fine grains, which are the most basic units in negative electrode active materials and the initial fine particles formed during the crystallization process. Under an electron microscope, they appear as individual particles with complete boundaries. Defects may exist inside the particles, but there are no complete boundaries within the particles sufficient to divide them into two or more particles. Secondary particles typically have relatively regular shapes, such as spherical or near-spherical.

[0079] The graphite particles and carbon coating can be distinguished by: ultrasonically dispersing the graphite particles in ethanol, dropping them onto a copper mesh carbon support film, drying them, and then testing them. TEM is then turned on, and high-resolution TEM (HRTEM) mode is selected. The highly crystalline graphite particle region will show clear parallel lattice fringes (corresponding to the (002) crystal plane of the graphite particles, with a spacing of approximately 0.335 nm), while the outer carbon coating layer will not show long-range ordered lattice fringes.

[0080] It should be noted that the surface of the secondary particles has a carbon coating layer. In this case, the carbon coating layer is actually part of the secondary particles. That is, the secondary particles include a core composed of primary graphite particles and a carbon coating layer covering the core.

[0081] The thickness of the carbon coating layer can be determined with reference to relevant technologies. For example, the thickness of the carbon coating layer can be, but is not limited to, 0.5 nm-4 nm, and for example, the thickness of the carbon coating layer is 0.5 nm-3 nm.

[0082] In some embodiments, the tap density of the secondary particles is 1.25 g / cc to 1.45 g / cc. A tap density within this relatively high and suitable range is beneficial for the close arrangement of graphite particles and increases the contact area. Each particle is supported by surrounding particles, thus reducing local stress concentration and maintaining a confined pressure state during cold pressing. This helps suppress lateral slippage and cracking of the particles, allowing the graphite particles to maintain mechanical integrity and structural stability after cold pressing. This results in more effectively resisting and dispersing internal stress during battery cycling. Simultaneously, this dense structure also helps suppress electrode expansion during cycling, thereby improving the trend of increasing expansion force.

[0083] Tap density can be measured by filling a container with the negative electrode active material of a secondary battery, measuring the final volume obtained by vibrating the container a specific number of times, and calculating the apparent density based on the final volume.

[0084] It should be noted that the tap density of secondary particles here refers to the tap density of secondary particles with a carbon coating on the surface.

[0085] For example, the tap density of the secondary particles is any one of 1.25 g / cc, 1.28 g / cc, 1.29 g / cc, 1.30 g / cc, 1.31 g / cc, 1.32 g / cc, 1.33 g / cc, 1.34 g / cc, 1.35 g / cc, 1.36 g / cc, 1.37 g / cc, 1.38 g / cc, 1.39 g / cc, 1.40 g / cc, 1.41 g / cc, 1.42 g / cc, 1.43 g / cc, 1.44 g / cc, or 1.45 g / cc, or between any two of these values.

[0086] In some embodiments, the graphite particles include secondary particles with an OI value of 0.5-5. Controlling the OI value of the secondary particles within this low range indicates that the orientation of the primary particles tends to be random, and the secondary particles as a whole possess good isotropic characteristics. After lithium intercalation, stress is dispersed, which helps to reduce expansion. Combined with the aforementioned sphericity and concavity, the secondary particles are easy to rotate and slide during cold pressing, which can promote the orderly arrangement of particles during cold pressing, reduce the stress accumulation during cold pressing, and at the same time ensure good contact between graphite particles and between graphite particles and binder, improve the cohesion of the negative electrode sheet, and thus effectively reduce the expansion of the negative electrode sheet during cycling. It is understandable that the OI value for secondary particles referred to here includes both secondary particles without a carbon coating on their surface and those with a carbon coating on their surface.

[0087] For example, the OI value of the secondary particles is any one of 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5, 1.2, 1.3, 4.7, 0.8 or between any two values.

[0088] In some embodiments, the graphite particles comprise single particles with a tap density of 1.30 g / cc to 1.50 g / cc. Controlling the tap density of the single particles to within this relatively high and suitable range facilitates a tighter arrangement of the graphite particles and increases the contact area. Each particle is supported by surrounding particles, thus reducing local stress concentration during cold pressing and maintaining a confined pressure state. This helps suppress lateral slippage and cracking of the particles, allowing the graphite particles to maintain mechanical integrity and structural stability after cold pressing. Consequently, it more effectively resists and disperses internal stress during battery cycling. Simultaneously, this dense structure also helps suppress electrode expansion during cycling, thereby improving the trend of increasing expansion force.

[0089] A "single particle" refers to a particle consisting of a single primary particle. Single particles typically have an irregular shape.

[0090] The determination of "single particles" and "secondary particles" can be achieved by: ultrasonically dispersing graphite particles in ethanol, dropping the mixture onto a copper mesh carbon support film, and drying it before analysis. Then, using TEM (High Resolution Transformer) in high-resolution mode (HRTEM), images are acquired at, for example, 3000x magnification. The particles in the electron microscope images are then analyzed using ImageJ software (1.46r, Win64 version) to determine whether they are single or secondary particles.

[0091] For example, the tap density of a single particle is any one of 1.30 g / cc, 1.31 g / cc, 1.32 g / cc, 1.33 g / cc, 1.34 g / cc, 1.35 g / cc, 1.36 g / cc, 1.37 g / cc, 1.38 g / cc, 1.39 g / cc, 1.40 g / cc, 1.41 g / cc, 1.42 g / cc, 1.43 g / cc, 1.44 g / cc, 1.45 g / cc, 1.46 g / cc, 1.47 g / cc, 1.48 g / cc, 1.49 g / cc, or 1.50 g / cc, or between any two of these values.

[0092] In some embodiments, the graphite particles include single particles with an OI value of 2-8. By controlling the OI value of the single particles within the above range, the single particles exhibit good isotropy, and stress is dispersed after lithium intercalation, which helps reduce expansion. Combined with the aforementioned sphericity and concavity, the particle structure remains stable during cold pressing, facilitating rotation and sliding. This promotes the orderly arrangement of particles during cold pressing, reduces stress accumulation during cold pressing, and ensures good contact between graphite particles and between graphite particles and the binder, thereby enhancing the cohesion of the negative electrode sheet and effectively reducing expansion.

[0093] For example, the OI value of a single particle is any one of 2, 3, 4, 5, 6, 7, 8 or between any two values.

[0094] It should be noted that in this application, the graphite particles in the negative electrode film layer that serve as the negative electrode active material can be single particles, secondary particles, or a combination of single and secondary particles.

[0095] In some embodiments, the volumetric particle size distribution Dv50 of the graphite particles is 4 μm - 20 μm. Within this range, the particles are less prone to breakage during rolling, suppressing the risk of accelerated electrode expansion due to breakage.

[0096] Volumetric particle size distribution (Dv50) refers to the particle size at which the cumulative volumetric particle size distribution reaches 50%. Dv50 represents the median particle size of the powder. The test method for Dv50 is laser particle size analysis, referring to GB / T 19077-2016, using a laser particle size analyzer. The testing instrument can be the Mastersizer 3000 laser particle size analyzer from Malvern Instruments Ltd., UK.

[0097] For example, the Dv50 of the graphite particles is any value of 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, 16μm, 17μm, 18μm, 19μm, 20μm or between any two values.

[0098] In some embodiments, the ratio of (Dv90-Dv10) / Dv50 of the graphite particles is 1.1-1.5. Controlling the ratio of (Dv90-Dv10) / Dv50 of the graphite particles within the above range results in a more concentrated particle size distribution and similar particle sizes, which reduces the absolute expansion and is beneficial for reducing battery expansion.

[0099] The volumetric particle size distribution Dv10 refers to the particle size when the cumulative volumetric particle size distribution reaches 10%, and the volumetric particle size distribution Dv90 refers to the particle size when the cumulative volumetric particle size distribution reaches 90%.

[0100] For example, the (Dv90-Dv10) / Dv50 of the graphite particles is any value of 1.1, 1.2, 1.3, 1.4, 1.5 or between any two values.

[0101] In some embodiments, the liquid absorption rate of the negative electrode sheet with a compaction density of 1.60 g / cc is ≥1.8 mg / s. 0.5Controlling the liquid absorption rate within the above range indicates that during the initial formation, the electrolyte can rapidly and synchronously wet the surface of all negative electrode active materials, forming a uniform and stable SEI film. This can suppress the expansion of the negative electrode caused by uneven volume changes due to excessively rapid local lithium intercalation or excessive stress concentration. It also indicates that the negative electrode has a suitable pore structure and wettability, which can provide a buffer space for the volume expansion of the negative electrode material during charging and discharging, absorb some mechanical stress, and reduce electrode expansion.

[0102] The electrolyte absorption rate refers to the speed at which the electrolyte wets and fills the pores inside the dry negative electrode sheet.

[0103] The aspiration rate is derived from the Washburn equation / Lucas-Washburn equation, and is used here to illustrate that the Washburn equation / Lucas-Washburn equation is simplified as follows: m = k t 0.5 Where m is the mass of liquid absorbed, t is time, and k is the absorption rate constant, with units of mg / s. 0.5 .

[0104] In some embodiments, this application also provides a secondary battery comprising a negative electrode sheet, the negative electrode sheet including a negative current collector and a negative electrode film layer located on at least one side of the negative current collector, the negative electrode film layer including a negative electrode active material. The negative electrode active material includes graphite particles, the graphite particles having an average sphericity of 0.65-0.95 and an average concavity T of the graphite particles. n The value is 0.05-0.45. The concavity T of the graphite particle is calculated as 1 - actual volume of the graphite particle / convex hull volume of the graphite particle. The actual volume of the graphite particle is obtained directly from a dataset obtained using a computed tomography scan with micrometer-level resolution, while the convex hull volume is calculated from the dataset.

[0105] Therefore, in the secondary battery provided in this application, by controlling the average sphericity of the graphite particles to be 0.65-0.95, the high sphericity of the graphite particles can optimize particle stacking and, to a certain extent, convert the volume expansion caused by lithium intercalation into spatial position adjustment and pore filling of the graphite particles inside the electrode, which is beneficial to reducing the macroscopic thickness expansion rate of the electrode. However, if the T value is too small (T<0.05), the particle surface is closer to a convex geometry, or even a perfect sphere, which leads to: (1) lack of buffer space, and the volume change of lithium intercalation has nowhere to be released; (2) expansion Forced to be transmitted outward, the thickness of the electrode increases rapidly; (3) Internal stress accumulation may cause the electrode to crack; (4) The surface is smooth, the adhesive is not anchored enough, and when the T value is too large (T>0.25), the particle surface is severely concave and the protrusions are sharp, resulting in: (1) Protrusion-protrusion point contact, the radius of curvature of the contact point is small, and the Hertz contact stress increases significantly; (2) High stress directly transmits displacement, generating mechanical disturbance to adjacent particles; (3) The risk of protrusion breakage increases, and the rearrangement of fragments intensifies the expansion; (4) Continuous rearrangement and breakage in the cycle, and the expansion rate continues to increase. Therefore, this application controls the average concavity T to be 0.05-0.25 based on the average sphericity of graphite particles of 0.65-0.95. Within this range, the degree of concavity of graphite particles is moderate, which not only retains the low friction characteristics of high sphericity particles to facilitate particle rearrangement during lithium intercalation expansion, but also avoids excessive stress point contact and breakage risk. At the same time, it provides appropriate physical anchoring points to ensure stable adhesion of the binder, so that lithium intercalation expansion can be effectively buffered through particle rearrangement and pore filling, thereby suppressing the irreversible expansion of the negative electrode sheet.

[0106] A second aspect of this application provides a negative electrode active material comprising graphite particles, wherein the average sphericity of the graphite particles is 0.65-0.95, and the average concavity T of the graphite particles is... n The OI value is 0.05-0.45, and the OI value of graphite particles is 0.5-8.

[0107] Wherein, the concavity T of the graphite particle is 1 - the actual volume of the graphite particle / the convex hull volume of the graphite particle. The actual volume of the graphite particle is obtained directly from the dataset obtained by computed tomography with micron-level resolution, and the convex hull volume of the graphite particle is calculated from the dataset.

[0108] The testing methods for average sphericity, average concavity, and OI value of graphite particles can refer to the testing methods provided in the first aspect of this application, and will not be repeated here. It is understood that the testing method provided in the second aspect of this application is for directly prepared negative electrode active materials.

[0109] The negative electrode active material provided in this application controls the average sphericity of graphite particles to be 0.65-0.95. The high sphericity of graphite particles can optimize particle stacking and can, to a certain extent, convert the volume expansion caused by lithium intercalation into spatial position adjustment and pore filling of graphite particles inside the electrode, which is beneficial to reduce the macroscopic thickness expansion rate of the electrode. However, if the T value is too small (T<0.05), the surface of the particles is closer to a convex geometry, or even close to a perfect sphere, lacking depressions, resulting in: (1) lack of buffer space, and the volume change of lithium intercalation has nowhere to be released; (2) expansion is forced to be transmitted outward, and the thickness of the electrode increases rapidly; (3) internal stress accumulation may cause the electrode to crack; (4) the surface is smooth, and the binder anchoring is insufficient. When the T value is too large (T>0.25), the particle surface is severely concave and the protrusions are sharp, resulting in: (1) the protrusion-protrusion point contact, the radius of curvature of the contact point is small, and the Hertzian contact stress is significantly increased; (2) the high stress directly transmits displacement, generating mechanical disturbance to adjacent particles; (3) the risk of protrusion breakage increases, and the rearrangement of fragments intensifies expansion; (4) continuous rearrangement and breakage in the cycle, and the expansion rate continues to increase. Therefore, this application controls the average concavity T to be 0.05-0.25 based on the average sphericity of graphite particles of 0.65-0.95. Within this range, the degree of concavity of graphite particles is moderate, which retains the low friction characteristics of high sphericity particles to facilitate particle rearrangement during lithium intercalation expansion, while avoiding excessive stress point contact and breakage risk. At the same time, it provides appropriate physical anchoring points to ensure stable adhesion of the binder, so that lithium intercalation expansion can be effectively buffered through particle rearrangement and pore filling, thereby suppressing the irreversible expansion of the negative electrode sheet. Meanwhile, the OI value of graphite particles is controlled to be 0.5-8, and the graphite particle orientation is small, which disperses stress after lithium intercalation and helps to reduce expansion.

[0110] For example, the average sphericity of the graphite particles is any one of 0.65, 0.70, 0.75, 0.80, 0.85, 0.90, 0.95 or between any two values.

[0111] For example, the average concavity T of the graphite particles n It is any value among 0.05, 0.08, 0.10, 0.13, 0.15, 0.17, 0.20, 0.22, 0.25, 0.27, 0.30, 0.33, 0.35, 0.38, 0.40, 0.43, and 0.45, or between any two values.

[0112] For example, the OI value of the graphite particles is any one of 0.5, 2, 3, 4, 5, 6, 7, 8, 1.0, 1.5, 2.0, 2.5, 3.5, 4.5, 1.2, 1.3, 4.7, or 0.8, or between any two values. In some embodiments, the graphite particles include secondary particles, the surface of which has a carbon coating layer. The carbon coating layer, as a protective layer, can firmly bind the primary particles within the secondary particles together, improving the overall mechanical strength of the particles, effectively buffering volume change stress, suppressing particle breakage, and enhancing structural and interfacial stability.

[0113] In some embodiments, the tap density of the secondary particles is 1.25 g / cc to 1.45 g / cc. The tap density of the secondary particles is within the above-mentioned relatively high and suitable range, which is conducive to the close arrangement of graphite particles and the increase of contact area. Each particle is supported by the surrounding particles, so local stress concentration can be reduced during cold pressing and the particles are under confined pressure. This helps to suppress the lateral slippage and cracking of the particles, and allows the graphite particles to maintain mechanical integrity and structural stability after cold pressing. This enables them to more effectively resist and disperse internal stress during battery cycling. At the same time, this dense structure also helps to suppress electrode expansion during cycling, thereby improving the trend of expansion force growth.

[0114] In some embodiments, the graphite particles include secondary particles with an OI value of 0.5-5. Controlling the OI value of the secondary particles within this low range indicates that the orientation of the primary particles tends to be random, and the secondary particles as a whole possess good isotropic characteristics. After lithium intercalation, stress is dispersed, which helps to reduce expansion. Combined with the aforementioned sphericity and average roundness, the secondary particles are easy to rotate and slide during cold pressing, which can promote the orderly arrangement of particles during cold pressing, reduce the stress accumulation during cold pressing, and at the same time ensure good contact between graphite particles and between graphite particles and binder, improve the cohesion of the negative electrode sheet, and thus effectively reduce the expansion of the negative electrode sheet during cycling.

[0115] In some embodiments, the graphite particles include single particles with a tap density of 1.30 g / cc to 1.50 g / cc. Controlling the tap density of the single particles to reach the above-mentioned high and suitable range is beneficial for the graphite particles to be closely arranged and increase the contact area. Each particle is supported by the surrounding particles, so local stress concentration can be reduced during cold pressing and the particles are under confined pressure. This helps to suppress the lateral slippage and cracking of the particles, and allows the graphite particles to maintain mechanical integrity and structural stability after cold pressing. This enables them to more effectively resist and disperse internal stress during battery cycling. At the same time, this dense structure also helps to suppress electrode expansion during cycling, thereby improving the trend of expansion force growth.

[0116] In some embodiments, the graphite particles include single particles with an OI value of 2-8. By controlling the OI value of the single particles within the above range, the single particles exhibit good isotropy, and stress is dispersed after lithium intercalation, which helps reduce expansion. Combined with the aforementioned sphericity and concavity, the particle structure remains stable during cold pressing, facilitating rotation and sliding. This promotes the orderly arrangement of particles during cold pressing, reduces stress accumulation during cold pressing, and ensures good contact between graphite particles and between graphite particles and the binder, thereby enhancing the cohesion of the negative electrode sheet and effectively reducing expansion.

[0117] In some embodiments, at least 50% of the graphite particles have a concavity T ≤ 0.40. Controlling the concavity of most or all of the graphite particles within the above range, that is, controlling the surface depression of most or all of the graphite particles within a suitable range, is more conducive to both preserving the low-friction surface characteristics to facilitate particle rearrangement during lithium intercalation expansion, and avoiding excessive stress point contact and breakage risks. At the same time, it provides appropriate physical anchoring points to ensure stable adhesion of the binder, so that lithium intercalation expansion can be effectively buffered through particle rearrangement and pore filling, thereby suppressing the irreversible expansion of the negative electrode sheet.

[0118] In some embodiments, at least 50% of the graphite particles have a sphericity of ≥0.65. Controlling the sphericity of most or all graphite particles within the above range, i.e., controlling the sphericity of most or all graphite particles to be high, utilizes the isotropic expansion characteristics of most or all graphite particles and the point contact between particles, which is beneficial to improving the cohesion of the negative electrode sheet, thereby effectively reducing expansion. In some embodiments, the negative electrode active material provided in the second aspect of this application serves as the negative electrode active material in the negative electrode sheet of the first aspect of this application.

[0119] In some embodiments, a negative electrode active material is provided, comprising graphite particles with an average sphericity of 0.65-0.95 and an average concavity T of _____. n The value is 0.05-0.45. The concavity T of the graphite particle is calculated as 1 - actual volume of the graphite particle / convex hull volume of the graphite particle. The actual volume of the graphite particle is obtained directly from a dataset obtained using a computed tomography scan with micrometer-level resolution, while the convex hull volume is calculated from the dataset.

[0120] The negative electrode active material provided in this application controls the average sphericity of graphite particles to be 0.65-0.95. The high sphericity of graphite particles can optimize particle stacking and can, to a certain extent, convert the volume expansion caused by lithium intercalation into spatial position adjustment and pore filling of graphite particles inside the electrode, which is beneficial to reduce the macroscopic thickness expansion rate of the electrode. However, if the T value is too small (T<0.05), the surface of the particles is closer to a convex geometry, or even close to a perfect sphere, lacking depressions, resulting in: (1) lack of buffer space, and the volume change of lithium intercalation has nowhere to be released; (2) expansion is forced to be transmitted outward, and the thickness of the electrode increases rapidly; (3) internal stress accumulation may cause the electrode to crack; (4) the surface is smooth, and the binder anchoring is insufficient. When the T value is too large (T>0.25), the particle surface is severely concave and the protrusions are sharp, resulting in: (1) protrusion-protrusion point contact, small contact point curvature radius, and significantly increased Hertzian contact stress; (2) high stress directly transmits displacement, generating mechanical disturbance to adjacent particles; (3) the risk of protrusion breakage increases, and fragment rearrangement intensifies expansion; (4) continuous rearrangement and breakage during the cycle, and the expansion rate continues to increase. Therefore, this application controls the average concavity T to be 0.05-0.25 based on the average sphericity of graphite particles of 0.65-0.95. Within this range, the degree of concavity of graphite particles is moderate, which not only retains the low friction characteristics of high sphericity particles to facilitate particle rearrangement during lithium intercalation expansion, but also avoids excessive stress point contact and breakage risk, while providing appropriate physical anchoring points to ensure stable adhesion of the binder, so that lithium intercalation expansion can be effectively buffered through particle rearrangement and pore filling, thereby suppressing the irreversible expansion of the negative electrode sheet.

[0121] A third aspect of this application provides a method for preparing a negative electrode active material, comprising: The first raw material is shaped to obtain the second raw material. The first raw material includes a first aggregate and / or granulated material. The first aggregate is obtained by crushing and shaping the raw coke. The granulated material is obtained by crushing and shaping the raw coke. The second aggregate is mixed with a binder and granulated. The Dv50 of the second raw material is D1, the Dv50 of the first raw material is D2, and the D2 / D1 ratio is 0.68-0.90. The second raw material is pre-carbonized, the obtained carbide is mixed with an antioxidant, and graphitized to obtain graphite particles as a negative electrode active material. The antioxidant includes boron compounds, and the mass ratio of antioxidant to carbide is 0.5-1.5:100. The average sphericity of the graphite particles is 0.65-0.95, and the average concavity T of the graphite particles is... n The OI value of graphite particles is 0.05-0.45; the concavity of graphite particles is 0.5-8; the concavity T of graphite particles is 1-actual volume of graphite particles / convex hull volume of graphite particles. The actual volume of graphite particles is obtained directly from the dataset obtained by computed tomography with micron-level resolution, and the convex hull volume of graphite particles is calculated from the dataset.

[0122] It is understandable that when the first raw material is the first aggregate, the corresponding negative electrode active material is a single-particle graphite particle, and when the first raw material is a granulated material, the corresponding negative electrode active material is a secondary particle.

[0123] The deep shaping of the first raw material results in a more rounded shape, more uniform particle size, and less fine powder, which is beneficial for improving the sphericity and concavity of the final graphite particles. Furthermore, this application employs a process sequence of granulation followed by deep shaping for the secondary particles, which, compared to deep shaping followed by granulation, results in a more rounded second raw material.

[0124] Granulation is the process of agglomerating primary particles into secondary particles. The secondary aggregate before granulation is a primary particle. The first material obtained by granulating these secondary aggregates includes the secondary particles formed by the agglomeration of the secondary aggregate.

[0125] It is understandable that the preparation of the first raw material involves the crushing and preliminary shaping of the raw coke. The preliminary shaping here can refer to relevant processes.

[0126] The raw material coke includes, but is not limited to, at least one of petroleum coke, pitch coke, and needle coke.

[0127] Boron compounds include, but are not limited to, boron carbide or boron.

[0128] By introducing boron-based compounds as antioxidants during the pre-carbonization process, oxidative ablation can be inhibited. At the same time, controlling the mass ratio of antioxidant to carbide to be 0.5-1.5:100 can not only maintain the integrity of the particles and avoid the formation of surface depressions and pores, but also promote the graphite particles to obtain an ordered structure and improve the density of the structure. The combined effect can inhibit the increase of the concavity T value during the pre-carbonization process and keep the particles with a low degree of concavity.

[0129] The preparation method provided in this application, during the preparation of the negative electrode active material, achieves deep shaping of the first raw material by controlling D2 / D1 to 0.68-0.90, thereby achieving rounding and spheroidization of the first raw material. This is beneficial for improving the sphericity of the second raw material particles and reducing the concavity, and is conducive to obtaining particles with an average sphericity of 0.65-0.95 and an average concavity T. n The graphite particles have an average sphericity of 0.05-0.45 and an OI value of 0.5-8. By introducing boron-based compounds as antioxidants during the pre-carbonization process, the increase in concavity during pre-carbonization can be suppressed, maintaining the original low concavity of the graphite particles. This is beneficial for obtaining graphite particles with an average sphericity of 0.65-0.95 and an average concavity T... nThe graphite particles are 0.05-0.45 mm in size. Within this range, the graphite particles have a moderate degree of indentation, which retains the low friction characteristics of highly spherical particles to facilitate particle rearrangement during lithium intercalation expansion, while avoiding excessive stress point contact and breakage risks. At the same time, it provides appropriate physical anchoring points to ensure stable adhesion of the binder, so that lithium intercalation expansion can be effectively buffered through particle rearrangement and pore filling, thereby suppressing the irreversible expansion of the negative electrode sheet.

[0130] For example, the mass ratio of antioxidant to carbide is any one of 0.5:100, 0.6:100, 0.7:100, 0.8:100, 0.9:100, 1.0:100, 1.1:100, 1.2:100, 1.3:100, 1.4:100, or 1.5:100, or between any two values. In some embodiments, the Dv50 of the first aggregate and the second aggregate are 6.0 μm to 9.0 μm, respectively. Single-particle and secondary-particle graphite products with high mechanical strength and good structural integrity are readily obtained.

[0131] For example, D2 / D1 is any value among 0.68, 0.70, 0.75, 0.80, 0.85, 0.90, 0.773, 0.739, 0.850, 0.895, 0.895, 0.850, 0.789, 0.824, and 0.708, or between any two values.

[0132] In some embodiments, the Dv50 of the first aggregate and the second aggregate are 6.0 μm-10 μm, respectively. This readily yields single-particle and secondary-particle graphite products with high mechanical strength and good structural integrity.

[0133] For example, the Dv50 of the first aggregate and the second aggregate are any value of 6.0μm, 7μm, 8μm, 9.0μm, 9.5μm, 10μm or between any two values.

[0134] In some embodiments, when the first raw material is obtained by crushing and pre-shaping raw coke to obtain the second aggregate, and then mixing the second aggregate with a binder and granulating it, the Dv50 (D1) of the first raw material is 14μm-25μm. Controlling the Dv50 of the granulated first raw material within the above range helps to ensure that the obtained secondary particles have good structural stability and particle size, so as to cooperate with subsequent shaping to obtain a suitable second raw material.

[0135] For example, the Dv50 of the first raw material obtained by granulation is any value of 14μm, 15μm, 16μm, 17μm, 18μm, 19μm, 20μm, 21μm, 22μm, 23μm, 24μm, 25μm or between any two values.

[0136] In some embodiments, granulation includes: heating to 290℃-310℃, holding at this temperature for 50-70 minutes while stirring, and then further heating to 690℃-710℃ and holding at this temperature for 100-140 minutes while stirring. This process improvement enhances granulation strength, which in turn improves the density of the first raw material obtained after granulation, resulting in a high tap density with an average sphericity of 0.65-0.95 and an average concavity T. n Graphite particles with a size of 0.42-0.65 not only improve the tap density of the negative electrode active material and reduce particle rearrangement caused by repeated particle expansion, thus slowing down stress release and improving the trend of expansion force growth, but also enhance the structural stability of secondary particles. This is beneficial for obtaining graphite particles with high tap density, an average sphericity of 0.65-0.95, and an average concavity T. n Graphite particles with a size of 0.42-0.65 mm can promote the orderly arrangement of particles during the cold pressing process. This not only slows down the rate of stress release and reduces the stress accumulation during cold pressing, but also facilitates good contact between graphite particles and between graphite particles and binder, thereby improving the cohesion of the negative electrode sheet and effectively reducing the expansion during the entire battery life cycle.

[0137] In some embodiments, the amount of binder added is 12%-20% of the mass of the second aggregate. Controlling the amount of binder added within the above-mentioned higher range is beneficial to improving the density of the first raw material obtained after granulation. This not only helps to increase the tap density of the negative electrode active material, reduce particle rearrangement caused by repeated particle expansion, and slow down stress release, thereby improving the trend of expansion force growth, but also enhances the structural stability of the secondary particles.

[0138] For example, the amount of binder added is any one of 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, or 20% of the mass of the second aggregate, or between any two values.

[0139] In some embodiments, the softening point of the binder is 150°C-250°C. Selecting a binder with a suitable softening point facilitates the formation of a uniform, continuous, and robust carbonaceous binder phase between and on the surface of the primary particles, thereby improving the structural stability of the secondary particles and enhancing their density.

[0140] For the testing of softening point, refer to GB / T 4507 and use the ring and ball method to determine the softening point of the adhesive.

[0141] For example, the softening point of the adhesive is any value of 150°C, 160°C, 170°C, 180°C, 190°C, 200°C, 210°C, 220°C, 230°C, 240°C, 250°C, or between any two values.

[0142] The binder includes, but is not limited to, asphalt. Optionally, the asphalt has a softening point of 150℃-250℃ and a coking value of 50%-67%.

[0143] In some embodiments, the volatile matter content of the raw coke is 10 wt%-18 wt%, and the Hay Group grindability is 60-150. Controlling the raw coke to meet these parameters is beneficial for better rounding and spheroidization during subsequent deep shaping processes, and also helps to reduce the expansion properties of the prepared graphite particles.

[0144] The volatile matter was determined according to SH / T0026-1990, the method for determining volatile matter in petroleum coke.

[0145] The Hardy Grindability Index (HGA) is a relative indicator that measures the ease with which coal can be ground into powder. It can be tested using a Hardy Grindability Index tester. Controlling the HGA to be ≥80 is beneficial for obtaining aggregates with concentrated particle size distribution and good sphericity or near-sphericity. Controlling the raw coke to meet the above requirements is also beneficial for preparing low-expansion graphite particles, which helps to improve the expansion of graphite particles.

[0146] For example, the volatile matter content of the raw coke is any one of 10 wt%, 11 wt%, 12 wt%, 13 wt%, 14 wt%, 15 wt%, 16 wt%, 17 wt%, 18 wt%, or between any two of these values.

[0147] For example, the Hay Group grindability coefficient of the raw coke is any value of 60, 70, 80, 90, 100, 110, 120, 130, 140, 150, 105, 145, 106, 136, 85, 105, 115, 145 or between any two values.

[0148] In some embodiments, carbonization includes heat treatment at a temperature of 700°C-1500°C for 8-36 hours under an inert atmosphere. The carbonization temperature and time can be selected according to the type of raw coke and the type of the second raw material.

[0149] In some embodiments, graphitization includes holding at 2000℃-3000℃ for 24h-72h. The graphitization temperature and time can be selected according to the type of raw coke and the type of the second raw material.

[0150] Alternatively, graphitization can be carried out in an inert atmosphere.

[0151] In some embodiments, the product may also be shaped.

[0152] In some embodiments, this application provides a method for preparing a negative electrode active material, comprising: The first raw material is shaped to obtain the second raw material. The first raw material includes a first aggregate and / or granulated material. The first aggregate is obtained by crushing and shaping the raw coke. The granulated material is obtained by crushing and shaping the raw coke. The second aggregate is mixed with a binder and granulated. The Dv50 of the second raw material is D1, the Dv50 of the first raw material is D2, and the D2 / D1 ratio is 0.68-0.90. The second raw material is pre-carbonized, and the obtained carbide is mixed with an antioxidant and graphitized to obtain graphite particles as a negative electrode active material. The antioxidant includes boron compounds, and the mass ratio of antioxidant to carbide is 0.5-1.5:100. The average sphericity of the graphite particles is 0.65-0.95, and the average concavity T of the graphite particles is... n The value is 0.05-0.45. The concavity T of the graphite particle is 1 - the actual volume of the graphite particle / the convex hull volume of the graphite particle. The actual volume of the graphite particle is obtained directly from the dataset obtained by computed tomography with micron-level resolution, and the convex hull volume of the graphite particle is calculated from the dataset.

[0153] The preparation method provided in this application, during the preparation of the negative electrode active material, achieves deep shaping of the first raw material by controlling D2 / D1 to 0.68-0.90, thereby achieving rounding and spheroidization of the first raw material. This is beneficial for improving the sphericity of the second raw material particles and reducing the concavity, and is conducive to obtaining particles with an average sphericity of 0.65-0.95 and an average concavity T. n The graphite particles have a diameter of 0.05-0.45. By introducing boron-based compounds as antioxidants during the pre-carbonization process, the increase in concavity during pre-carbonization can be suppressed, maintaining the original low concavity of the graphite particles. This is beneficial for obtaining graphite particles with an average sphericity of 0.65-0.95 and an average concavity T. n The graphite particles are 0.05-0.45 mm in size. Within this range, the graphite particles have a moderate degree of indentation, which retains the low friction characteristics of highly spherical particles to facilitate particle rearrangement during lithium intercalation expansion, while avoiding excessive stress point contact and breakage risks. At the same time, it provides appropriate physical anchoring points to ensure stable adhesion of the binder, so that lithium intercalation expansion can be effectively buffered through particle rearrangement and pore filling, thereby suppressing the irreversible expansion of the negative electrode sheet.

[0154] The fourth aspect of this application provides an electrical device, including secondary particles provided in the first aspect of this application, negative electrode active material provided in the second aspect, or negative electrode active material prepared by the preparation method provided in the third aspect.

[0155] In addition, the secondary battery, battery module, battery pack and power device of this application will be described below with appropriate reference to the accompanying drawings.

[0156] [Rechargeable Battery] The second aspect of this application provides a secondary battery. This application does not particularly limit the type of secondary battery; for example, the secondary battery can be a lithium-ion battery, etc.

[0157] Typically, a secondary battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. During charging and discharging, active ions move back and forth between the positive and negative electrodes, inserting and releasing. The electrolyte acts as a conductor between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits while allowing ions to pass through.

[0158] This application does not impose any particular restriction on the type of electrolyte, which can be selected according to actual needs. For example, the electrolyte can be selected from at least one of solid electrolytes and liquid electrolytes (i.e., electrolyte solutions). This applies to secondary batteries using electrolyte solutions, as well as some secondary batteries using solid electrolytes.

[0159] [Positive electrode plate] The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector, the positive electrode film layer including a positive active material. As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0160] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0161] In some embodiments, when the secondary battery is a lithium-ion battery, the positive electrode active material may be a positive electrode active material known in the art for lithium-ion batteries. As an example, the positive electrode active material may include, but is not limited to, at least one of the following materials: lithium phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as battery positive electrode active materials may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides include, but are not limited to, lithium cobalt oxides (such as LiCoO2), lithium nickel oxides (such as LiNiO2), lithium manganese oxides (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, and lithium nickel cobalt manganese oxides (such as LiNi). 1 / 3Co 1 / 3 Mn 1 / 3 O2 (also known as NCM) 333 LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM) 523 LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM) 211 LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM) 622 LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM) 811 ), lithium nickel cobalt aluminum oxide (such as LiNi) 0.8 Co 0.15 Al 0.05 At least one of O2 and its modified compounds. Examples of lithium phosphates with an olivine structure include, but are not limited to, lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composites.

[0162] In some embodiments, to further improve the energy density of secondary batteries, the positive electrode active material for lithium-ion batteries may include materials with the general formula Li. a Ni b Co c M d O e A fOne or more of lithium transition metal oxides and their modified compounds. 0.8 ≤ a ≤ 1.2, 0.5 ≤ b < 1, 0 < c < 1, 0 < d < 1, 1 ≤ e ≤ 2, 0 ≤ f ≤ 1, M is selected from one or more of Mn, Al, Zr, Zn, Cu, Cr, Mg, Fe, V, Ti, and B, and A is selected from one or more of N, F, S, and Cl.

[0163] In some embodiments, by way of example, the positive electrode active material for a lithium ion battery may include one or more of LiCoO2, LiNiO2, LiMnO2, LiMn2O4, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O2 (NCM523), LiNi 0.6 Co 0.2 Mn 0.2 O2 (NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2 (NCM811), LiNi 0.85 Co 0.15 Al 0.05 O2, LiFePO4, and LiMnPO4.

[0164] In the present application, the modified compounds of the above positive electrode active materials may be doping modification and / or surface coating modification of the positive electrode active materials.

[0165] It should be noted that during the charge and discharge process of the battery, the insertion and extraction of Li and its consumption will occur, and the molar content of Li is different when the battery is discharged to different states. In the listing of the above positive electrode active materials in the present application, the molar content of Li is the initial state of the material, that is, the state before feeding. When the positive electrode material is applied to the battery system, after charge and discharge cycles, the molar content of Li will change. In the listing of the above positive electrode active materials in the present application, the molar content of O is only the theoretical state value, and the release of oxygen from the lattice will cause the molar content of oxygen to change, and the actual molar content of O will show fluctuations.

[0166] Non-limitingly, the weight percentage of the positive electrode active material in the positive electrode active material layer may be greater than or equal to 80 wt%, and further may be greater than or equal to 90 wt%. In the present application, unless otherwise specified, "wt%" represents weight percentage.

[0167] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a terpolymer of PVDF-tetrafluoroethylene-propylene, a terpolymer of PVDF-hexafluoropropylene-tetrafluoroethylene, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorinated acrylate resin. Non-limitingly, the weight percentage of the binder in the positive electrode active material layer may be 0.5wt%-15wt%, more further 0.5wt%-10wt%, even further 0.5-5wt%, even further 1wt%-5wt%, and even more preferably 1wt%-3wt%.

[0168] In some embodiments, the positive electrode film layer may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. Without limitation, based on the total weight of the positive electrode active material layer, the weight percentage of the conductive agent in the positive electrode active material layer may be 0-10 wt%, more further 0-8 wt%, and even more further 0-5 wt%.

[0169] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0170] [Negative electrode plate] In some embodiments, the negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one side of the negative current collector. The negative electrode film layer includes a negative electrode active material. The negative electrode active material includes graphite particles with an average sphericity of 0.65-0.95 and an average concavity T of 0.65. n The value is 0.05-0.45; where the concavity of the graphite particle T = 1 - actual volume of the graphite particle / convex hull volume of the graphite particle. The actual volume of the graphite particle is obtained directly from the dataset obtained by computed tomography with micron-level resolution, and the convex hull volume of the graphite particle is calculated from the dataset.

[0171] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0172] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0173] In some embodiments, the negative electrode active material may be solely the negative electrode active material shown in the second aspect of this application or the negative electrode active material prepared by the preparation method provided in the third aspect of this application, or it may be used in combination with negative electrode active materials for batteries known in the art. As an example, negative electrode active materials for batteries known in the art include at least one of the following materials: soft carbon, hard carbon, silicon-based materials, graphite whose parameters do not meet the relevant requirements of this application, etc. The silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys.

[0174] In some embodiments, the negative electrode film layer may optionally include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS). Non-limitingly, the weight percentage of the binder in the negative electrode active layer may be 0 wt%-20 wt%, more further 0 wt%-10 wt%, even further 0-5 wt%, even further 1 wt%-5 wt%, and even more preferably 1 wt%-3 wt%.

[0175] In some embodiments, the negative electrode film layer may optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. Non-limitingly, the weight percentage of the conductive agent in the negative electrode active layer may be 0wt%-15wt%, more preferably 0wt%-10wt%, and even more preferably 0wt%-5wt%.

[0176] In some embodiments, the negative electrode active material layer may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)). Non-limitingly, the weight percentage of other additives in the negative electrode active layer may be 0wt%-15wt%, further preferably 0wt%-10wt%, even more preferably 0wt%-5wt%, even more preferably 0wt%-3wt%, and even more preferably 0wt%-2wt%. In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as the negative electrode active material, conductive agent, binder, and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto a negative electrode current collector, and then performing processes such as drying and cold pressing to obtain the negative electrode sheet.

[0177] In other embodiments, the negative electrode sheet further includes a base coating layer disposed on the negative current collector. The base coating layer is located between the negative current collector and the negative electrode film layer. The base coating layer basically does not contain negative electrode active material, but may contain a small amount of carbon material. However, the carbon material forms a thin coating and cannot function as a negative electrode active material. In some embodiments, the base coating layer may also include a binder. The type of binder is not particularly limited, and those skilled in the art can choose flexibly according to actual needs.

[0178] [Electrolytes] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not specify any particular type of electrolyte; it can be selected according to requirements.

[0179] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0180] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0181] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0182] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0183] For example, the additive may include, but is not limited to, at least one of vinylene carbonate (VC), vinyl ethylene carbonate (VEC), vinyl sulfate (DTD), propylene sulfate, vinyl sulfite (ES), 1,3-propanesulfonate lactone (PS), 1,3-propenesulfonate lactone (PST), sulfonate cyclic quaternary ammonium salts, succinic anhydride, succinic anhydride (SN), adiponitrile (AND), tris(trimethylsilane) phosphate (TMSP), or tris(trimethylsilane) borate (TMSB).

[0184] [Isolation membrane] In some embodiments, the secondary battery also includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0185] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0186] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0187] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the aforementioned electrode assembly and electrolyte.

[0188] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the secondary battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0189] A secondary battery is a battery cell that can be recharged after it has been discharged, allowing the active materials to be activated and the battery to continue to be used.

[0190] This application does not impose any particular limitation on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 2 The example shown is a square-structured battery cell 5.

[0191] In some implementations, refer to Figure 3 The outer packaging may include a housing 51 and a top cover assembly 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the top cover assembly 53 can be placed over the opening to close the receiving cavity. The positive electrode sheet, negative electrode sheet, and separator may be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the battery cell 5 may be one or more, which can be selected by those skilled in the art according to specific practical needs.

[0192] In some implementations, individual battery cells can be assembled into a battery module. The number of individual battery cells contained in a battery module can be one or more, and the specific number can be selected by those skilled in the art based on the application and capacity of the battery module.

[0193] Figure 4 This is battery module 4, used as an example. (See reference...) Figure 4 In battery module 4, multiple battery cells 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple battery cells 5 can be fixed in place using fasteners.

[0194] Optionally, the battery module 4 may also include a housing with a receiving space in which multiple battery cells 5 are received.

[0195] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0196] Figure 5 and Figure 6 This is battery pack 1 as an example. (See reference...) Figure 5 and Figure 6 The battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3, with the upper body 2 covering the lower body 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0197] In addition, this application also provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack provided in this application. The secondary battery, battery module, or battery pack can be used as the power source of the electrical device or as the energy storage unit of the electrical device. The electrical device may include, but is not limited to, mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0198] As an electrical device, a secondary battery, battery module, or battery pack can be selected according to its usage requirements.

[0199] Figure 7 This is an example of an electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the secondary battery for this device, a battery pack or battery module can be used.

[0200] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a rechargeable battery as their power source.

[0201] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0202] Example 1 1. Petroleum coke with volatile matter of 12 wt% and a grindability coefficient of 105 is crushed, shaped and classified to obtain aggregate with Dv50=9.5μm.

[0203] 2. Mix aggregate and asphalt (softening point 195℃-200℃, coking value 54%-56%) at a mass ratio of 100:14, and granulate using a horizontal granulation reactor. The granulation reactor is heated from room temperature to 300℃ in a nitrogen atmosphere and kept at this temperature for 1 hour while stirring. The temperature is then increased to 700℃ and kept at this temperature for 2 hours while stirring. After granulation, the first raw material is obtained, and the Dv50 of the first raw material is D1, where D1=22μm.

[0204] The first raw material is subjected to deep shaping to obtain the second raw material. The Dv50 of the second raw material is D2, D2=17μm, and the ratio of D2 / D1 is 0.773.

[0205] 3. The second raw material is carbonized in a carbonization kiln at 1150℃ for 8 hours under a nitrogen atmosphere to obtain carbonized material.

[0206] 4. Mechanically mix the antioxidant, boron carbide, and carbide material at a mass ratio of 1:100. Perform high-temperature graphitization treatment at 3000℃ for 48 hours using an Atchison furnace. Shape, sieve, and demagnetize the resulting material to obtain the graphite material. The graphite material has a Dv50 of 16μm.

[0207] Preparation of the negative electrode sheet The above-mentioned graphite material, conductive carbon black (Super P), thickener sodium carboxymethyl cellulose, and binder styrene-butadiene rubber were thoroughly mixed in an appropriate amount of deionized water at a weight ratio of 96.4:1:1.2:1.4 to form a negative electrode slurry. The negative electrode slurry was coated onto a copper foil negative electrode current collector using an extrusion coating method. After drying, cold pressing, edge trimming, cutting, and slitting, a negative electrode sheet was obtained. The negative electrode film layer includes the negative electrode current collector and negative electrode film layers disposed on both sides of the negative electrode current collector along its thickness direction. The compaction density of a single-sided negative electrode film layer is 1.60 g / cc.

[0208] Preparation of Electrolyte The electrolyte was prepared in an argon atmosphere glove box with a water content of <10ppm. Ethyl carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a volume ratio of 1:1:1 to obtain an organic solvent. LiPF6 was then dissolved in the organic solvent to prepare an electrolyte with a concentration of 1mol / L.

[0209]

Isolation Film

[0210] Button cell batteries Using a lithium metal sheet as the counter electrode, the aforementioned negative electrode, separator, counter electrode, and electrolyte are assembled into a CR2430 coin cell in an argon-protected glove box.

[0211] The following tests were performed on Example 1: 1. Negative electrode active material: The battery was fully discharged and disassembled. After disassembly, the negative electrode sheet was cleaned three times with DMC for 2 hours each time to remove residual electrolyte on the surface. After drying, the negative electrode sheet was cleaned with a hot solution of 2M HCl to separate the graphite particles from the negative electrode current collector. The graphite was then cleaned with deionized water and dried to obtain black powder. The black powder was then carbonized at high temperature to obtain the final reduced graphite powder for relevant testing.

[0212] (1) The methods for testing concavity include: Graphite particles (hundreds of particles) were fully dispersed using capillary tubes. A three-dimensional morphological characterization of the graphite particles was constructed using micron-resolution X-ray computed tomography (XCT). The actual volume of the graphite particles was directly obtained from the dataset acquired via the micron-resolution X-ray computed tomography. The convex hull volume of the graphite particles was calculated using a three-dimensional convex hull algorithm based on the dataset. The concavity T of a single graphite particle was obtained according to the formula: concavity T = 1 - actual volume of graphite particle / convex hull volume of graphite particle. Then, the number-average T of the concavity was obtained from arbitrarily selected 50 graphite particles. n It is understandable that, for the same graphite particle, both the actual volume and the convex hull volume are obtained from the same CT dataset. Additionally, 100 graphite particles were randomly selected, and the number of particles with concavity T ≤ 0.40 was counted.

[0213] Test results: Average concavity T of graphite particles n The value is 0.15, and among 100 randomly selected graphite particles, the number of graphite particles with concavity T≤0.40 is 86. That is, among multiple graphite particles, 86% of the graphite particles have a concavity T≤0.40.

[0214] (2) Sphericity test: The sphericity of graphite particles was measured using a particle shape analyzer such as the Sysmex FPIA3000 (manufactured by Mavern). Sphericity was calculated as: (circumference of a circle with the same area as the projected image of the graphite particle) / (circumference of the projected image of the graphite particle). The mean sphericity was calculated as the numerical average of the sphericity of 50 randomly selected graphite particles. Simultaneously, 100 graphite particles were randomly selected, and the number of particles with a sphericity ≥ 0.65 was counted.

[0215] Test results: The average sphericity of the graphite particles is 0.83. When 100 graphite particles are randomly selected, 88 of them have a sphericity ≥ 0.65. That is, among multiple graphite particles, 88% of the graphite particles have a sphericity ≥ 0.65.

[0216] (3) Testing of powder OI value: Following the testing method in JIS K0131-1996, a Bruker D8 Discover X-ray diffractometer was used for testing. A copper target was used as the anode target, and CuKα rays were used as the radiation source. The X-ray wavelength scan ranged from 20° to 80° at a scanning rate of 4° / min to obtain the X-ray diffraction pattern of the powder sample. Based on the X-ray diffraction pattern, I004 and I110 were calculated, where I004 is the integrated area of ​​the diffraction peak of the 004 crystal plane of crystalline carbon in the powder sample, and I110 is the integrated area of ​​the diffraction peak of the 110 crystal plane of crystalline carbon in the powder sample. The OI value of the powder sample was calculated according to OI value = I004 / I110.

[0217] Test results: The OI value of the graphite particles is 1.5.

[0218] (4) Volumetric particle size distribution: Referring to GB / T19077-2016, the graphite particles were tested using a laser particle size distribution diffraction instrument (Mastersizer 3000 laser particle size analyzer from Malvern Instruments Ltd.), and the values ​​of Dv10, Dv50, and Dv90 were obtained, and the value of (Dv90-Dv10) / Dv50 was calculated.

[0219] Test results: The graphite particles have a Dv10 of 5.8 μm, a Dv50 of 16.0 μm, and a Dv90 of 24.3 μm. The calculated value of (Dv90-Dv10) / Dv50 is 1.17.

[0220] (5) Tap density: The density of the powder was determined using a powder tap density tester in accordance with GB / T5162-2006. The testing instrument can be Dandong Baite BT-301, with the following parameters: vibration frequency 250±15 times / minute, amplitude 3±0.2mm, number of vibrations 5000, and a 25mL graduated cylinder.

[0221] Test results: The tap density of the graphite particles is 1.35 g / cc.

[0222] 2. Negative electrode plate: Cut a negative electrode sheet to obtain a test sample with a dry weight of W1. Place the test sample horizontally and drop 50 μL of electrolyte onto the surface of the test sample using a dropper. Record the time it takes for the liquid to be completely absorbed. (When the liquid mirror disappears visually), obtain the weight W2 of the test sample. Calculate the liquid absorption rate using the Washburn equation with W2 and W1. The specific electrolyte formulation can be found in Example 1.

[0223] Test results: The liquid absorption rate of the negative electrode sheet with a compaction density of 1.60 g / cc was 1.84 mg / s.0.5 .

[0224] 3. Rebound rate of negative electrode sheet: The design thickness of the negative electrode sheet after cold pressing is denoted as h1. The electrode sheet thickness after the battery is fully charged (100% SOC) is denoted as h2. The rebound rate of the negative electrode sheet after full charge is denoted as (h2-h1) / h1. The electrode sheet thickness after the battery is fully charged after 600 cycles at 25℃ in the mode of 0.33C charging / 0.5C discharging is denoted as h3. The rebound rate of the negative electrode sheet after 600 cycles of full charge is denoted as (h3-h1) / h1.

[0225] Test results: The rebound rate of the negative electrode sheet after 600 cycles was 20%.

[0226] Comparative Example 1 The differences between Comparative Example 1 and Example 1 are shown in Table 1, except that in the preparation of the negative electrode active material, the volatile matter content of petroleum coke is 10 wt%, and the Hay Group grindability coefficient is 65. Aggregate and asphalt were mixed at a mass ratio of 100:10 and granulated using a horizontal granulation reactor. The granulation reactor was heated from room temperature to 300°C in a nitrogen atmosphere and held at this temperature for 1 hour while stirring. The temperature was then further increased to 700°C and held at this temperature for 2 hours while stirring. The granulated material yielded the first raw material, with a Dv50 of D1 and a Dv50 of 18 μm. The first raw material was then shaped to obtain the second raw material, with a Dv50 of D2 and a Dv50 of 17 μm. The D2 / D1 ratio was 0.944.

[0227] Comparative Example 2 The differences between Comparative Example 2 and Example 1 are shown in Table 1, except that in the preparation of the negative electrode active material, the volatile matter content of petroleum coke is 10 wt%, and the Hay Group grindability coefficient is 57. Aggregate and asphalt were mixed at a mass ratio of 100:8 and granulated using a horizontal granulation reactor. The reactor was heated from room temperature to 300°C in a nitrogen atmosphere and held at this temperature for 1 hour while stirring. The temperature was then further increased to 700°C and held at this temperature for 2 hours while stirring. The granulated material yielded the first raw material, with a Dv50 of D1 and a Dv50 of 19 μm. The first raw material was then shaped to obtain the second raw material, with a Dv50 of D2 and a Dv50 of 17 μm. The D2 / D1 ratio was 0.895.

[0228] Comparative Examples 1 and 2 were tested as shown in Example 1, and the results are shown in Table 2.

[0229] Table 1

[0230] Table 2

[0231] As can be seen from Tables 1 and 2 above, Example 1 can effectively reduce the rebound rate of the negative electrode sheet after 600 cycles compared to Comparative Examples 1-2.

[0232] In Comparative Examples 1 and 2, the average concavity was too large, resulting in a significantly larger rebound rate of the negative electrode sheet after 600 cycles compared to Example 1. This indicates that only the average sphericity meets the requirements of this application, while the average concavity does not, and therefore the rebound rate of the negative electrode sheet after 600 cycles cannot be effectively reduced.

[0233] According to Comparative Examples 1 and 2, the average sphericity of Comparative Example 1 is less than that of Comparative Example 2. Although better sphericity results in better suppression of expansion, the average concavity of Comparative Example 1 is less than that of Comparative Example 2, which leads to a greater rebound rate in Comparative Example 2 than in Comparative Example 1. This indicates that the average concavity has a greater impact on the rebound rate of the electrode.

[0234] Example 2-11 The differences between each embodiment and Embodiment 1 are shown in Table 3. Table 3

[0235] Table 4

[0236] As can be seen from Examples 1-12, the average sphericity of the graphite particles is 0.65-0.95, and the average concavity T of the graphite particles is... n With an average sphericity of 0.05-0.45, the expansion throughout the battery's lifespan can be reduced, and the rebound rate of the negative electrode sheet after 600 cycles can be decreased. Optionally, the average sphericity of the graphite particles is 0.71-0.85, and the average concavity T of the graphite particles is... n The value is 0.12-0.36, which can further reduce the expansion.

[0237] As can be seen from Examples 1-4, 7 and 10-11, even with very small differences in average sphericity, average concavity significantly affects the rebound rate of the negative electrode sheet after 600 cycles.

[0238] As can be seen from Examples 1 and 10-11, regardless of whether the graphite particles are secondary or single particles, as long as the average sphericity of the graphite particles is 0.65-0.95, the average concavity T of the graphite particles... n With a value of 0.05-0.45, the thickness change rate of the negative electrode sheet can be effectively reduced after 600 cycles, thus reducing the expansion during the battery cycle. As can be seen from Examples 1 and 12, the OI values ​​are the same. However, since the average sphericity of Example 12 is lower than that of Example 1, and the average concavity is higher than that of Example 1, the rebound rate is increased.

[0239] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A secondary battery, characterized in that, It includes a negative electrode sheet, the negative electrode sheet including a negative current collector and a negative electrode film layer located on at least one side of the negative current collector, the negative electrode film layer including a negative electrode active material; The negative active material includes graphite particles having an average sphericity of 0.65 to 0.95, an average concavity T of 0.05 to 0.45, and an OI value of 0.5 to 8. n 0.05 to 0.45, and an OI value of 0.5 to 8. Wherein, the concavity T of the graphite particle is 1 - the actual volume of the graphite particle / the convex hull volume of the graphite particle. The actual volume of the graphite particle is directly obtained from a dataset obtained by a computed tomography scan with micron-level resolution, and the convex hull volume of the graphite particle is calculated from the dataset.

2. The secondary battery according to claim 1, characterized in that, The average sphericity of the graphite particles is 0.71-0.

85.

3. The secondary battery according to claim 2, characterized in that, The average concavity T of the graphite particles n It ranges from 0.12 to 0.

36.

4. The secondary battery according to claim 1, characterized in that, Of the plurality of graphite particles, at least 50% of the graphite particles have a concavity T ≤ 0.40; And / or, of the plurality of graphite particles, at least 50% of the graphite particles have a sphericity ≥ 0.

65.

5. The secondary battery according to claim 1, characterized in that, The graphite particles include secondary particles; The surface of the secondary particles has a carbon coating layer; And / or, the tap density of the secondary particles is 1.25 g / cc - 1.45 g / cc.

6. The secondary battery according to claim 1, characterized in that, The graphite particles include secondary particles, and the OI value of the secondary particles is 0.5-5.

7. The secondary battery according to claim 1, characterized in that, The graphite particles include single particles, and the tap density of the single particles is 1.30 g / cc to 1.50 g / cc.

8. The secondary battery according to claim 1, characterized in that, The graphite particles include single particles, and the OI value of the single particles is 2-8.

9. The secondary battery according to any one of claims 1-8, characterized in that, The volumetric particle size distribution Dv50 of the graphite particles is 4μm-20μm; And / or, the (Dv90-Dv10) / Dv50 of the graphite particles is 1.1-1.

5.

10. The secondary battery according to claim 1, characterized in that, The negative electrode sheet with a compacted density of 1.60 g / cc has a liquid absorption rate ≥ 1.8 mg / s. 0.5 .

11. A negative electrode active material, characterized in that, The negative electrode active material includes graphite particles, the graphite particles having an average sphericity of 0.65-0.95, an average concavity of 0.05-0.45, and an OI value of 0.5-8. Wherein, the concavity T of the graphite particle is 1 - actual volume of graphite particle / volume of pits in graphite particle, the actual volume of graphite particle is measured by computed tomography, and the total volume of pits in graphite particle is calculated by the convex hull difference method after computed tomography.

12. The negative electrode active material according to claim 11, characterized in that, The graphite particles include secondary particles, and the surface of the secondary particles has a carbon coating layer; And / or, the graphite particles include secondary particles, the tap density of which is 1.25 g / cc to 1.45 g / cc; And / or, the graphite particles include secondary particles, the OI value of which is 0.5-5; And / or, the graphite particles include single particles, the tap density of which is 1.30 g / cc to 1.50 g / cc; And / or, the graphite particles include single particles, the single particles having an OI value of 2-8; And / or, of the plurality of graphite particles, at least 50% of the graphite particles have a sphericity of ≥0.65; And / or, of the plurality of graphite particles, at least 50% of the graphite particles have a concavity T ≤ 0.

40.

13. A method for preparing a negative electrode active material, characterized in that, include: The first raw material is shaped to obtain the second raw material. The first raw material includes a first aggregate and / or granulated material. The first aggregate is obtained by crushing and shaping the raw coke. The granulated material is obtained by crushing and shaping the raw coke. The second aggregate is mixed with a binder and granulated. The Dv50 of the second raw material is D1, the Dv50 of the first raw material is D2, and the D2 / D1 ratio is 0.68-0.

90. The second raw material is pre-carbonized, the obtained carbide is mixed with an antioxidant, and graphitized to obtain graphite particles as the negative electrode active material. The antioxidant includes boron compounds, and the mass ratio of the antioxidant to the carbide is 0.5-1.5:

100. The graphite particles have an average sphericity of 0.65-0.95 and an average concavity T. n The OI value of the graphite particles is 0.5-8, ranging from 0.05 to 0.

45. The concavity T of the graphite particles is 1 - actual volume of the graphite particles / convex hull volume of the graphite particles. The actual volume of the graphite particles is directly obtained from a dataset obtained by computed tomography with micron-level resolution, and the convex hull volume of the graphite particles is calculated from the dataset.

14. The preparation method according to claim 13, characterized in that, The granulation process includes: heating to 290℃-310℃, maintaining the temperature for 50 min-70 min while stirring, and then heating to 690℃-710℃ while stirring for 100 min-140 min. And / or, the amount of binder added is 12%-20% of the mass of the second aggregate.

15. The preparation method according to claim 13 or 14, characterized in that, The volatile matter content of the raw coke is 10wt%-18wt%, and the Haas grindability coefficient is 60-150.

16. An electrical appliance, characterized in that, It includes the secondary battery according to any one of claims 1-10, the negative electrode active material according to any one of claims 11-12, or the negative electrode active material prepared by the preparation method according to any one of claims 13-15.

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