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

Abstract

The application provides a graphite negative electrode active material, a preparation method of the graphite negative electrode active material, a secondary battery and an electric device. The graphitization degree of the graphite negative electrode active material is 88%-93%, and the oil absorption value of the graphite negative electrode active material is not more than 50ml / 100g. The graphite negative electrode active material can improve the cycle performance of the battery and prolong the service life of the battery.

Description

[0001] This application is a divisional application based on the invention with application number 202311676609.6, application date December 7, 2023, applicant CATL, and invention title "Graphite negative electrode active material and its preparation method, secondary battery and power device". Technical Field

[0002] This application relates to the field of secondary battery technology, and in particular to a graphite negative electrode active material and its preparation method, a secondary battery, and an electrical device. Background Technology

[0003] With the introduction of carbon neutrality targets and policies, the market for secondary batteries used in energy storage is experiencing explosive growth. For energy storage batteries, long cycle life is a key indicator, especially for energy storage batteries used in large-scale energy storage power stations. In order to extend service life and reduce replacement frequency, it is necessary to further develop energy storage batteries with longer cycle life. Summary of the Invention

[0004] This application addresses the aforementioned issues and aims to provide a graphite anode active material, its preparation method, a secondary battery, and an electrical device, which can effectively improve the cycle life of the battery and extend its service life. A first aspect of this application provides a graphite anode active material with a graphitization degree of 88%-93% and an oil absorption value not exceeding 50 ml / 100g.

[0005] On the one hand, controlling the oil absorption value of the graphite anode active material to no more than 50 ml / 100 g ensures good dispersion of the graphite anode active material in the anode slurry. This results in excellent anti-settling properties of the anode slurry, making it easier to control the coating weight during electrode coating and to prepare electrodes with uniform distribution and thickness of the graphite anode active material. This reduces the possibility of uneven local current density during charging and discharging, minimizes lithium plating caused by electrode polarization, improves battery cycle performance and storage performance, and extends battery life. On the other hand, controlling the graphitization degree of the graphite anode active material to 88%-93% results in a larger interlayer spacing, which is beneficial for the rapid intercalation and deintercalation of active ions. The graphite anode active material experiences less expansion when active ions intercalate into the anode, which is beneficial for long-term battery cycling. Simultaneously, a suitable graphitization degree helps improve the specific capacity of the graphite anode active material, providing a material basis for the preparation of high-energy-density batteries.

[0006] In summary, graphite anode active materials that meet the above requirements are beneficial for improving the cycle performance and storage performance of batteries, while also enabling batteries to have high energy density.

[0007] In any embodiment, the oil absorption value of the graphite negative electrode active material is 30ml / 100g-43ml / 100g.

[0008] As mentioned earlier, graphite anode active materials have a low oil absorption value, resulting in better dispersion in the anode slurry. This facilitates the preparation of anode sheets with uniform graphite distribution, thereby improving battery cycle performance. However, excessively low oil absorption values ​​place high demands on the particle regularity or particle size distribution of graphite anode active materials, leading to higher costs and hindering industrial-scale promotion.

[0009] By controlling the oil absorption value of graphite anode active materials within a suitable range, the cost of graphite anode active materials can be reduced while meeting the requirements of long-cycle performance, which is conducive to industrial production.

[0010] In any embodiment, the particle size distribution (Dv90-Dv10) / Dv50 of the graphite anode active material is 1.2-1.6.

[0011] When the particle size distribution (Dv90-Dv10) / Dv50 of the graphite anode active material is within the above range, the oil absorption value of graphite can be controlled to be at a lower value, which is beneficial to improve the uniformity of the anode slurry and the uniformity of the graphite anode active material in the anode sheet. At the same time, it can also reduce the negative impact of large-particle-size graphite anode active material on cycle performance and storage performance, thereby comprehensively improving the cycle performance and storage performance of the battery.

[0012] In any embodiment, based on the total number of particles in the graphite anode active material, the proportion of primary particles in the graphite anode active material is greater than or equal to 85%, and can be selected as 85%-100%.

[0013] Compared to secondary particles, primary particles have fewer gaps between them, smaller surface edges, and a smoother morphology. This results in lower oil absorption values ​​for the graphite anode active material, better slurry leveling properties, and facilitates the fabrication of anode sheets with uniformly distributed graphite active material, thus improving battery cycle performance. Furthermore, primary particles exhibit better structural stability than secondary particles, making them less prone to breakage during cycling and further enhancing battery cycle performance.

[0014] In any embodiment, the specific surface area of ​​the graphite anode active material is less than or equal to 1.4 m². 2 / g, optional 0.6m 2 / g-1.3m 2 / g.

[0015] Graphite anode active materials have a low specific surface area, which is beneficial for obtaining graphite anode active materials with low oil absorption value. At the same time, it also makes graphite anode active materials have low surface activity, thereby reducing the consumption of active ions by SEI film formation and improving the cycle performance and storage performance of the battery.

[0016] In any embodiment, the volume distribution particle size Dv50 of the graphite anode active material is 12μm-16μm, and can be selected as 13μm-15μm.

[0017] Graphite anode active material has a large volume distribution particle size Dv50 and a large pore size in the anode film layer, which is conducive to the electrolyte fully wetting the anode sheet, reducing the possibility of local polarization of the electrode sheet, and reducing the impact of black spots on the cycle life and storage performance of the battery.

[0018] In any embodiment, the graphite anode active material satisfies at least one of the following: (1) The compacted density of the graphite anode active material under a pressure of 49000N is less than or equal to 1.85 g / cm³. 3 The option is 1.70 g / cm³. 3 -1.85g / cm 3 ; (2) The tap density of the graphite anode active material is 1.2 g / cm³. 3 -1.4g / cm 3 ; (3) The specific capacity of the graphite negative electrode active material is greater than or equal to 340 mAh / g, and can be selected as 341 mAh / g-347 mAh / g.

[0019] When the powder compaction density of graphite anode active material is within a suitable range under a pressure of 49000N, the cycle performance of the battery can be further improved.

[0020] When the tap density of the graphite anode active material is within the above range, the tap density of the anode sheet can be increased, thereby improving the energy density of the secondary battery. It is also beneficial to form a reasonable pore structure between the particles of the anode film, which can improve the transport performance of active ions and electrons, and improve the cycle performance and storage performance of the secondary battery.

[0021] Graphite anode active materials possess high specific capacity, providing a material basis for high-energy-density batteries. Simultaneously, within the specified specific capacity range, graphite anode active materials exhibit relatively small lattice expansion during cycling, good crystal structure stability, and reduced irreversible consumption of active ions, thereby improving battery cycle performance and storage performance.

[0022] This application also provides a method for preparing a graphite anode active material, characterized by comprising the following steps: Provide raw materials; The raw materials are processed to obtain a precursor; The precursor is graphitized to obtain an intermediate product; The intermediate product is subjected to sieving to obtain a graphite anode active material; the graphitization degree of the graphite anode active material is 88%-93%, and the oil absorption value of the graphite anode active material does not exceed 50ml / 100g.

[0023] Using the above preparation method, graphite anode active materials with low oil absorption value and low graphitization degree can be prepared, which can improve the cycle performance of the battery and extend its service life.

[0024] In any embodiment, the raw material includes at least one of petroleum coke, needle coke, and pitch coke, and may be selected as petroleum coke.

[0025] Based on the total volume of the raw material structure, the volume ratio of the mosaic and regional structures is greater than or equal to 50%, and can be selected as 50%-65%.

[0026] In any embodiment, the adhesion index of the raw material is less than or equal to 10, and can be selected as 1-9.

[0027] In any embodiment, the precursor satisfies at least one of the following conditions: The precursor has a volumetric particle size distribution (Dv50) of 12 μm-18 μm; and / or, The particle size distribution (Dv90-Dv10) / Dv50 of the precursor is 1.2-1.8.

[0028] Controlling the volume distribution particle size Dv50 or particle size distribution (Dv90-Dv10) / Dv50 of the precursor within a suitable range is beneficial for controlling the particle size distribution (Dv90-Dv10) / Dv50 of the graphite anode active material within a suitable range, thereby regulating the oil absorption value of the graphite anode active material within a smaller range.

[0029] In any embodiment, the maximum power of the graphitization process is 70%-90% of the rated power of the graphitization equipment.

[0030] In any embodiment, the maximum power of the graphitization process is 23000W-25000W; and / or, the constant power time of the graphitization process at the maximum power is 10h-50h.

[0031] In any embodiment, the screening process of the intermediate product specifically includes the following steps: The intermediate product is sieved to remove particles with a maximum particle size Dmax greater than 100 μm, thus obtaining the graphite anode active material.

[0032] Removing large-diameter particles from intermediate products reduces the negative impact of large-particle materials on battery cycle performance and storage performance.

[0033] A third 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 formed on at least one surface of the negative current collector, the negative electrode film layer including the graphite negative electrode active material of the first aspect of this application or the graphite negative electrode active material prepared by the preparation method of the second aspect.

[0034] In any embodiment, the negative electrode film layer includes a conductive agent, and based on the mass of the negative electrode film layer, the mass content of the conductive agent is greater than or equal to 1.5%, optionally 1.8%-2.5%.

[0035] A fourth aspect of this application provides an electrical device including a secondary battery as described in the third aspect of this application. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of a secondary battery according to one embodiment of this application.

[0037] Figure 2 yes Figure 1 An exploded view of a secondary battery according to one embodiment of this application is shown.

[0038] Figure 3 This is a schematic diagram of a battery module according to one embodiment of this application.

[0039] Figure 4 This is a schematic diagram of a battery pack according to one embodiment of this application.

[0040] Figure 5 yes Figure 4 An exploded view of a battery pack according to one embodiment of this application is shown.

[0041] Figure 6 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.

[0042] Explanation of reference numerals in the attached figures: 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Secondary battery; 51 Housing; 52 Electrode assembly; 53 Top cover assembly. Detailed Implementation

[0043] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the graphite anode 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.

[0044] 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.

[0045] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0046] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0047] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates 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.

[0048] 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.

[0049] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0050] The negative electrode active material is the main material of a battery. It stores energy by storing lithium during charging, and its performance significantly impacts the battery's cycle life. Current technologies typically control parameters such as the graphitization degree of the negative electrode active material or the compaction density of the negative electrode sheet to achieve long cycle life. However, another factor influencing capacity decay is the uniformity of the active material within the negative electrode sheet. If the negative electrode active material is not mixed uniformly with conductive agents and binders during the preparation of the negative electrode slurry, sedimentation or agglomeration may occur. This results in uneven distribution of active material or inconsistent electrode thickness in the coated negative electrode sheet, easily leading to uneven local current during cycling. Differences in the diffusion concentration of active ions can cause lithium plating, resulting in capacity decay and affecting the battery's cycle and storage performance.

[0051] [Graphite Anode Active Material] Based on this, this application proposes a graphite anode active material, wherein the graphitization degree of the graphite anode active material is 88%-93%, and the oil absorption value of the graphite anode active material does not exceed 50ml / 100g.

[0052] In some embodiments, the degree of graphitization of the graphite anode active material can be selected as any value from 88%, 89%, 90%, 91%, 92%, 93%, or a range of any two of these values.

[0053] In this paper, the term "degree of graphitization" macroscopically characterizes the proportion of a material that achieves a complete graphite crystal structure; microscopically, it refers to the degree to which the carbon structure in different transition states approaches an ideal graphite crystal.

[0054] The degree of graphitization in graphite anode active materials reflects the integrity of the graphite crystal structure, that is, the regularity of the carbon atom arrangement in the graphite structure. High graphitization indicates small interlayer spacing, smaller lattice rotation, less random stacking of layers, and more orderly arrangement, resulting in high specific capacity, which is beneficial for obtaining high-energy-density rechargeable batteries. Low graphitization indicates large interlayer spacing, which facilitates rapid insertion and extraction of active ions, minimizes material expansion during lithium insertion, and provides a shallow charge-discharge effect, which is beneficial for long cycle life and long storage.

[0055] In this application, the degree of graphitization of the graphite anode active material has a meaning known in the art and can be tested 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 test can be performed with reference to JISK 0131-1996 and JB / T 4220-2011 to obtain the average interlayer spacing d002 of the C(002) crystal plane in the material's crystal structure. Then, the degree of graphitization is calculated according to the formula g=(0.344-d002) / (0.344-0.3354)×100%. In the above formula, d002 is the average interlayer spacing of the C(002) crystal plane in the material's crystal structure, expressed in nanometers (nm).

[0056] In some embodiments, the oil absorption value of the graphite negative electrode active material can be selected as any one of 30ml / 100g, 35ml / 100g, 40ml / 100g, 45ml / 100g, or 50ml / 100g.

[0057] In this article, the term "oil absorption value" refers to the volume of linseed oil that 100g of graphite anode active material can absorb. For example, an oil absorption value of 40ml / 100g for graphite anode active material means that 100g of graphite anode active material can absorb 40ml of linseed oil.

[0058] The oil absorption value of graphite anode active materials can be tested using methods and equipment known in the art, as illustrated below: Test oil and graphite anode active material samples are obtained separately, and the torque threshold of the oil absorption value tester is set. Oil is added at a constant rate to the sample in the mixing chamber of the oil absorption value tester. As the amount of oil absorbed by the sample increases, the viscosity of the sample-oil mixture continuously increases. When the viscosity of the mixture reaches the preset torque threshold of the oil absorption value tester, the test is stopped, and the volume of oil absorbed per unit mass of sample is calculated. This value is the oil absorption value QI of the sample. The test oil is linseed oil (DBP), and the torque threshold is 1 N.

[0059] The oil absorption value of graphite anode active materials is mainly related to the material's specific surface area, surface properties, particle shape, and particle size distribution. It reflects the material's dispersibility in the anode slurry. A low oil absorption value indicates excellent dispersibility in the anode slurry, which in turn provides excellent resistance to sedimentation and dispersion. This facilitates control over the coating weight during electrode coating, resulting in anodes with uniform distribution and thickness of graphite active material. This reduces the likelihood of uneven local current density during charging and discharging, minimizes lithium plating caused by electrode polarization, improves battery cycle performance, and extends battery life and storage life.

[0060] In summary, graphite anode active materials have a suitable range of graphitization degree and oil absorption value, which is beneficial to improving the cycle performance and storage performance of batteries, while the batteries have high energy density.

[0061] In some embodiments, the oil absorption value of the graphite anode active material is 30 ml / 100g-43 ml / 100g. In some embodiments, the oil absorption value of the graphite anode active material can be selected as any value or a range of any two of the following: 30 ml / 100g, 32 ml / 100g, 34 ml / 100g, 36 ml / 100g, 38 ml / 100g, 40 ml / 100g, 42 ml / 100g, and 43 ml / 100g.

[0062] As mentioned earlier, graphite anode active materials have a low oil absorption value, resulting in better dispersion in the anode slurry. This facilitates the preparation of anode sheets with uniform graphite distribution, thereby improving battery cycle performance. However, excessively low oil absorption values ​​place high demands on the particle regularity or particle size distribution of graphite anode active materials, leading to higher costs and hindering industrial-scale promotion.

[0063] By controlling the oil absorption value of graphite anode active materials within a suitable range, the cost of graphite anode active materials can be reduced while meeting the requirements of long-cycle performance, which is conducive to industrial production.

[0064] In some embodiments, the particle size distribution (Dv90-Dv10) / Dv50 of the graphite anode active material is 1.2-1.6. In some embodiments, the particle size distribution (Dv90-Dv10) / Dv50 of the graphite anode active material can be selected as any value from 1.2, 1.3, 1.4, 1.5, 1.6 or a range consisting of any two values ​​therein.

[0065] The volume distribution particle sizes Dv10, Dv50, and Dv90 of graphite anode active materials are well-known in the art, representing the particle sizes corresponding to a cumulative volume distribution percentage of 10%, 50%, and 90%, respectively. These sizes can be determined using instruments and methods known in the art. For example, they can be conveniently determined using a laser particle size analyzer, referring to GB / T 19077-2016 Particle Size Distribution Laser Diffraction Method. The testing instrument can be the Mastersizer 3000 laser particle size analyzer from Malvern Instruments Ltd., UK.

[0066] The particle size distribution (Dv90-Dv10) / Dv50 of graphite anode active materials affects their oil absorption value. When the particle size distribution (Dv90-Dv10) / Dv50 is too large, the oil absorption value of the graphite anode active material is high. Small and large particles in the graphite anode active material hinder the dispersion of the graphite anode active material in the anode slurry, adversely affecting the uniformity and thickness of the electrode and deteriorating the cycle performance of the battery. When the particle size distribution (Dv90-Dv10) / Dv50 is too small, the preparation process of the graphite anode active material becomes relatively complex, the yield of the graphite anode active material decreases significantly, and the cost increases significantly.

[0067] In summary, when the particle size distribution (Dv90-Dv10) / Dv50 of the graphite anode active material is within a suitable range, the oil absorption value of the graphite anode active material is low, the cycle performance of the battery is excellent, and the cost of the graphite anode active material can be reduced, which is conducive to industrial application.

[0068] In some embodiments, based on the total number of particles in the graphite anode active material, the proportion of primary particles in the graphite anode active material is greater than or equal to 85%.

[0069] In some embodiments, the proportion of primary particles in the graphite anode active material is 85%-100% based on the total number of particles. In some embodiments, the proportion of primary particles in the graphite anode active material can be selected as any value from 85%, 90%, 95%, 100%, or a range of any two of these values.

[0070] In some embodiments, the particles in the graphite anode active material include primary particles and secondary particles. Hereinafter, primary particles and secondary particles have meanings known in the art. "Secondary particles" refers to aggregated particles formed from the aggregation of multiple primary particles. The agglomeration force between particles can be facilitated by another substance (e.g., a viscous chemical substance).

[0071] The proportion of primary particles can be determined using instruments and methods known in the art. For example, a graphite anode active material is laid and adhered to conductive adhesive to form a sample with dimensions of 6 cm × 1.1 cm. The morphology of the particles in the sample is tested using a scanning electron microscope (SEM) or energy dispersive spectroscopy (EDS) instrument (e.g., ZEISS SEM (Sigma 300)). The testing method can be referenced in JY / T010-1996. To ensure the accuracy of the test results, multiple (e.g., 10 or 20) different regions can be randomly selected from the sample for scanning. At a certain magnification (e.g., 500x or 1000x), the number of secondary particles and the total number of particles in the test regions are counted. The ratio of the number of primary particles to the total number of particles in any test region is the proportion of primary particles in that region. The average of the test results from 10 test regions is taken as the proportion of primary particles. To ensure the accuracy of the results, multiple test samples (e.g., 5 or 10) can be prepared and the above test can be repeated. The average value of the test results of each test sample can be taken as the proportion of the number of particles in the graphite anode active material.

[0072] Compared to secondary particles, primary particles have fewer gaps between them, smaller surface edges, and a smoother morphology. This results in lower oil absorption values ​​for the graphite anode active material, better slurry leveling properties, and facilitates the fabrication of anode sheets with uniformly distributed graphite active material, thus improving battery cycle performance. Furthermore, primary particles exhibit better structural stability than secondary particles, making them less prone to breakage during cycling and further enhancing battery cycle performance.

[0073] In some embodiments, the specific surface area of ​​the graphite anode active material is less than or equal to 1.4 m². 2 / g.

[0074] In some embodiments, the specific surface area of ​​the graphite anode active material may be selected as 0.4 m². 2 / g, 0.5m 2 / g, 0.6m 2 / g, 0.7m 2 / g, 0.75m 2 / g, 0.85m 2 / g, 0.85m 2 / g, 1.05m 2 / g, 1.15m 2 / g, 1.25m 2 / g, 1.3m 2 / g, 1.4m 2 Any value in / g or a range consisting of any two of its values.

[0075] In this paper, the term "specific surface area" refers to the sum of the total external surface areas of all particles in one gram of material.

[0076] The specific surface area of ​​graphite anode active materials can be determined using instruments and methods known in the art. For example, it can be measured using the nitrogen adsorption specific surface area analysis method according to GB / T 19587-2017, and calculated using the BET (Brunauer-Emmett-Teller) method. The nitrogen adsorption specific surface area analysis can be performed using a Tri-Star 3020 specific surface area and pore size analyzer from Micromeritics, Inc.

[0077] The specific surface area of ​​graphite anode active material affects the oil absorption value of the material. A lower specific surface area results in a lower oil absorption value. Improving the uniformity of the distribution of graphite anode active material and the uniformity of electrode thickness in the anode sheet improves the cycle performance and storage performance of the battery. At the same time, the low specific surface area of ​​graphite anode active material results in low surface activity, which can reduce the consumption of active ions by SEI film formation and improve the cycle performance and storage performance of the battery.

[0078] In some embodiments, the specific surface area of ​​the graphite anode active material is 0.6 m². 2 / g-1.3m 2 / g.

[0079] In some embodiments, the specific surface area of ​​the graphite anode active material may be selected as 0.6 m². 2 / g, 0.7m 2 / g, 0.75m 2 / g, 0.85m 2 / g, 0.85m 2 / g, 1.05m 2 / g, 1.15m 2 / g, 1.25m 2 / g, 1.3m 2 Any value in / g or a range consisting of any two of its values.

[0080] As mentioned earlier, graphite anode active materials have a small specific surface area and a low oil absorption value, which is beneficial to the cycle life of the battery. However, if the specific surface area is too small, it will affect the wettability of the electrolyte to the electrode, affect the kinetic performance of the electrode, and easily lead to lithium plating, thus affecting the cycle life and storage life of the battery. A suitable specific surface area can further improve the cycle life and storage life of the battery.

[0081] In some embodiments, the volume distribution particle size Dv50 of the graphite anode active material is 12μm-16μm.

[0082] In some embodiments, the volume distribution particle size Dv50 of the graphite anode active material can be selected as any value or a range of any two of the following: 12 μm, 12.5 μm, 13 μm, 13.5 μm, 14 μm, 14.5 μm, 15 μm, 15.5 μm, and 16 μm.

[0083] Graphite anode active material has a large volume distribution particle size Dv50 and a large pore size in the anode film layer, which is conducive to the electrolyte fully wetting the anode sheet, reducing the possibility of local polarization of the electrode sheet, and reducing the impact of black spots on the cycle life and storage performance of the battery.

[0084] In some embodiments, the volume distribution particle size Dv50 of the graphite anode active material is 13μm-15μm.

[0085] In some embodiments, the volume distribution particle size Dv50 of the graphite anode active material can be selected as any value or a range of any two of the following: 13 μm, 13.5 μm, 14 μm, 14.5 μm, and 15 μm.

[0086] Graphite anode active materials possess a suitable volume distribution particle size (Dv50), and the anode film layer has appropriate pore size, which facilitates the full wetting of the anode sheet by the electrolyte, reduces the possibility of local polarization, and minimizes the impact of black spots on the battery's cycle life and storage performance. Simultaneously, it enhances the transport performance of active ions and electrons, resulting in excellent kinetic performance of the electrode and reducing the impact of lithium plating on battery life.

[0087] In some embodiments, the powder compaction density of the graphite anode active material at a pressure of 49000N is less than or equal to 1.85 g / cm³. 3 .

[0088] In this paper, the term "powder compaction density" refers to the density of the powder to be tested under a preset pressure.

[0089] The method for measuring the compacted density of powder can be any method known in the art. For example, referring to GB / T24533-2009, 1g of graphite anode active material powder is weighed and added to a container with a bottom area of ​​1.327cm². 2 In the mold, pressure is applied to a specific pressure, such as 49000N, held for 30s, then depressurized and held for 10s. The compaction density of the graphite anode active material under the selected pressure is determined by an electronic pressure testing machine (such as UTM7305 electronic pressure testing machine).

[0090] When the compacted density of the graphite powder in the graphite anode active material is greater than 1.85 g / cm³ under a pressure of 49000 N. 3 The particle strength of graphite anode active material is insufficient. During cycling, it is constantly squeezed and it is difficult to maintain the original pore structure of the electrode. This will change the tortuosity of the electrode, increase the lithium-ion intercalation path, affect the dynamic performance of the battery, and is not conducive to achieving long-term cycle stability.

[0091] In some embodiments, the powder compaction density of the graphite anode active material at a pressure of 49000N is 1.70 g / cm³. 3 -1.85g / cm 3 In some embodiments, the powder compaction density of the graphite anode active material under a pressure of 49000N can be selected as 1.70 g / cm³. 3 1.72g / cm 3 1.74 g / cm 3 1.76 g / cm 3 1.78g / cm 3 1.80g / cm 3 182g / cm 3 1.84 g / cm 3 1.85g / cm 3 Any value in or a range consisting of any two values ​​in it.

[0092] As mentioned earlier, the compacted density of graphite anode active material powder under a pressure of 49000N is less than or equal to 1.85 g / cm³. 3 This is beneficial for improving the cycle performance of the battery. At the same time, the powder compaction density of the graphite anode active material under a pressure of 49000N also affects the energy density of the battery. The higher the powder compaction density, the greater the compaction density of the anode film, which is more conducive to increasing the energy density of the secondary battery.

[0093] By controlling the powder compaction density of graphite anode active material within a suitable range under a pressure of 49000N, the cycle life of the battery can be improved while also ensuring the high energy density of the battery.

[0094] In some embodiments, the tap density of the graphite anode active material is 1.2 g / cm³. 3 -1.4g / cm 3 In some embodiments, the tap density of the graphite anode active material may be selected as 1.2 g / cm³. 3 1.25g / cm 3 1.30g / cm 3 1.35g / cm 3 1.4g / cm 3 Any value in or a range consisting of any two values ​​in it.

[0095] In this paper, the term "taper density" refers to the density of a powder material after it has been vibrated and compressed under certain conditions.

[0096] The tap density can be measured using any method known in the art; for example, it can be determined using a powder tap density tester, referring to GB / T5162-2006. The testing instrument can be the Dandong Baite BT-301.

[0097] When the tap density of the graphite anode active material is within the above range, the tap density of the anode sheet can be increased, thereby improving the energy density of the secondary battery. It is also beneficial to form a reasonable pore structure between the particles of the anode film, which can improve the transport performance of active ions and electrons, and improve the cycle performance and storage performance of the secondary battery.

[0098] In some embodiments, the specific capacity of the graphite anode active material is greater than or equal to 340 mAh / g. In some embodiments, the specific capacity of the graphite anode active material can be selected as any value or a range of any two of the following: 340 mAh / g, 341 mAh / g, 342 mAh / g, 343 mAh / g, 344 mAh / g, 345 mAh / g, 346 mAh / g, 347 mAh / g, 349 mAh / g, 350 mAh / g, 351 mAh / g, and 352 mAh / g.

[0099] The specific capacity can be measured using any method known in the art. For example, a graphite anode active material sample can be thoroughly mixed with conductive carbon black and polyvinylidene fluoride (PVDF) in a mass ratio of 91.6:1.8:6.6 in an appropriate amount of NMP solvent to form a uniform anode slurry. The anode slurry is then uniformly coated onto the surface of the copper foil anode current collector and dried and cold-pressed. Subsequently, using a lithium metal sheet as the counter electrode and a polypropylene (PP) film as the separator, an electrolyte is injected. The electrolyte formulation is as follows: dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and ethylene carbonate (EC) are mixed in a weight ratio of 1:1:1 to obtain an organic solvent. LiPF6 is then dissolved in the organic solvent to prepare an electrolyte with a concentration of 1.0 mol / L. A CR2430 coin cell is assembled in an argon-protected glove box. At 25°C, the prepared coin cell was first discharged at a constant current of 0.05C to 0.005V, then discharged at a constant current of 10μA to 0.005V, and allowed to stand for 5 minutes. The first discharge capacity of the coin cell was recorded. Subsequently, it was charged at a constant current of 0.1C to 2.0V, and the charging capacity of the coin cell was recorded. The ratio of the charging capacity of the coin cell to the mass of the graphite anode active material sample is the specific capacity of the graphite anode active material.

[0100] Graphite anode active materials have excellent specific capacity, which can improve the energy density of secondary batteries.

[0101] In some embodiments, the specific capacity of the graphite anode active material is 341 mAh / g to 347 mAh / g. In some embodiments, the specific capacity of the graphite anode active material can be selected from any value or a range of any two of the following: 341 mAh / g, 342 mAh / g, 343 mAh / g, 344 mAh / g, 345 mAh / g, 346 mAh / g, and 347 mAh / g.

[0102] The specific capacity of the graphite anode active material is within the specified range. The lattice expansion during material cycling is relatively small, the crystal structure is stable, the irreversible consumption of active ions is reduced, and the cycle performance and storage performance of the battery are improved.

[0103] The embodiments of this application also provide a method for preparing a graphite anode active material, characterized by comprising the following steps: Provide raw materials; The raw materials are processed to obtain a precursor; The precursor is graphitized to obtain an intermediate product; The intermediate product is subjected to sieving to obtain a graphite anode active material; the graphitization degree of the graphite anode active material is 88%-93%, and the oil absorption value of the graphite anode active material does not exceed 50ml / 100g.

[0104] Using the above preparation method, graphite anode active materials with low oil absorption value and low graphitization degree can be prepared, which can further improve the cycle performance of the battery and extend the battery's service life.

[0105] In some embodiments, the raw material includes at least one of petroleum coke, needle coke, and pitch coke.

[0106] In this article, the term "petroleum coke" refers to the coke formed after petroleum residue or petroleum asphalt has undergone high-temperature carbonization.

[0107] In this article, the term "needle coke" refers to coke with needle-like textures that can be generated from coal tar pitch or petroleum pitch after liquid-phase carbonization to produce anisotropic mesophases and then undergoing high-temperature carbonization and other processes.

[0108] In this article, the term "asphalt coke" refers to the solid material generated after coal tar pitch is carbonized at high temperature.

[0109] In some embodiments, the raw material includes petroleum coke.

[0110] Petroleum coke has excellent anisotropy, which is beneficial for preparing graphite anode active materials with low graphitization and low expansion, thus contributing to the long cycle life of batteries. At the same time, petroleum coke has high compaction density and high specific capacity, which is beneficial for improving the energy density of batteries. In addition, petroleum coke has a wider range of sources, which is conducive to industrial production.

[0111] Based on the total volume of the raw material structure, the volume ratio of the mosaic and regional structures is greater than or equal to 50%.

[0112] Based on the morphological characteristics and isochromatic area size of the coke under a polarizing microscope, its microstructure can be classified into mosaic, regional, and fibrous types. Generally, isochromatic microstructures with a size less than 30 μm are classified as mosaic; isochromatic microstructures with a size greater than 30 μm are classified as regional; and anisotropic strip-shaped isochromatic areas are classified as fibrous structures.

[0113] In this application, the volume ratio of mosaic and regional structures in the raw materials can be tested using methods known in the art. As an example, raw materials are taken according to GB 1997-89, and raw materials crushed to 1mm are mixed and reduced to 40g~50g. 4g~5g of 0.07mm~1.0mm grade samples are taken using a square-hole sieve for slide preparation. Powdered coke and block coke films are prepared according to MT 116.1-86. The diameter of the powdered coke film should not be less than 22mm, and the volume occupied by the cementing material should be less than 1 / 3. The sample is placed on a slide with clay, flattened, and then placed on the stage for focusing. After calibrating the microscope, the polarizer and analyzer are adjusted to make them orthogonal. A lapis lazuli test plate (1λ) is inserted to make the field of view show the interference color of first-order red. The step length of the moving scale is determined to ensure that more than 400 effective measurement points are evenly distributed, with a point spacing of 0.3~0.5mm and a row spacing of 0.5~0.8mm. Starting from one end of the sample, the type of microstructure under the crosshair intersection is determined. The volume ratio of mosaic and regional structures in the raw material is calculated by dividing the effective number of measurement points of the optical structure of mosaic and regional structures by the total number of measurement points.

[0114] In some embodiments, the volume ratio of the mosaic and regional structures is 50%-65% based on the total volume of the raw material structure. In some embodiments, the volume ratio of the mosaic and regional structures can be selected as any value from 50%, 55%, 60%, 65%, or a range of any two of these values, based on the total volume of the raw material structure.

[0115] As mentioned earlier, a high volume ratio of embedded and regional structures is beneficial for obtaining graphite anode active materials with low oil absorption values. However, an excessively high volume ratio of embedded and regional structures will affect the specific capacity of graphite anode active materials and thus the energy density of the battery.

[0116] In some embodiments, the adhesion index of the raw material is less than or equal to 10. In some embodiments, the adhesion index of the raw material can be selected as any value from 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, or a range of any two values ​​therein.

[0117] In some embodiments, the adhesion index of the raw material is less than or equal to 1-9. In some embodiments, the adhesion index of the raw material can be selected as any value from 1, 2, 3, 4, 5, 6, 7, 8, 9 or a range of any two values ​​therein.

[0118] In this paper, the term "adhesion index" is used to characterize the adhesiveness of raw materials. It refers to the property of raw materials forming a plastic gel-like body during high-temperature heating, which binds itself or added inert substances and possesses a certain strength. It is a manifestation of the combined effect of surface bonding and internal forces (adhesive force and cohesive force) of gel-like substances.

[0119] In this application, the caking index of the raw material can be tested using methods known in the art. As an example, the caking index is tested using TX-600 according to GB / T5447-2014 / ISO 15585:2006. First, take 200g of sample and dry it in a 100℃ drying oven for 1 hour. Then, pass the dried sample through a sieve with a pore size of 200μm+100μm, and take the sample that passes through the 200μm sieve and the sample that passes through the 100μm sieve. Next, weigh 3.00±0.001g of special anthracite and another 3.00±0.001g of test sample and place them in a crucible, stirring and mixing them evenly. Use tweezers to hold the pressure block in the center of the crucible, then place it under a pressure device, gently lower the pressure rod, and apply pressure for 30s. Quickly place the crucible into a preheated muffle. Heat in a furnace (850℃) for 15 minutes; the temperature of the muffle furnace is maintained at 850℃±10℃ throughout the heating process; after the crucible is removed from the furnace and cooled, the total weight of the sample is measured as m, and then the sample is placed in a rotary drum device for rotary drum experiment; after rotary drum, the sample is sieved through a 1mm round hole sieve, and the weight of the material on the sieve is recorded as m1; the material on the sieve is placed in a rotary drum for a second rotary drum experiment, and then sieved and weighed again, and the material on the sieve m2 is measured; the adhesion index G is calculated according to the formula G=(30×m1+70×m2) / (5×m).

[0120] If the adhesion index of the raw material is too high, the material is prone to adhesion during heat treatment, which can easily form secondary particles. This results in a relatively irregular morphology of the graphite anode active material, which has a large oil absorption value. This is not conducive to the dispersion of the anode slurry and affects the cycle performance and storage performance of the battery.

[0121] In some embodiments, the processing of raw materials specifically includes the following steps: The raw materials are crushed, shaped, and graded to obtain secondary raw materials; Remove some of the fine powder from the secondary raw materials to obtain the precursor.

[0122] In some embodiments, the step of crushing the raw materials can be performed using a crusher, such as a jaw crusher. For example, the raw materials can be crushed to a set particle size before being sieved.

[0123] In some embodiments, during the step of shaping the raw materials, a shaping machine can be used to shape the crushed raw materials. Shaping can reduce burrs on the surface of the crushed raw materials, facilitating the acquisition of rounded graphite anode active materials and graphite anode active materials with low oil absorption values.

[0124] In some embodiments, the step of classifying the raw materials can be performed using an air classifier. Optionally, the draft frequency can be greater than or equal to 20 Hz, and the classification frequency can be greater than or equal to 65 Hz. Classification can reduce the content of large and small particles in the precursor.

[0125] In some embodiments, the volumetric particle size distribution Dv50 of the precursor is 12 μm-18 μm. In some embodiments, the volumetric particle size distribution Dv50 of the precursor can be selected as any value or a range of any two values ​​from 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, and 18 μm.

[0126] In some embodiments, the particle size distribution (Dv90-Dv10) / Dv50 of the precursor is 1.2-1.8. In some embodiments, the particle size distribution (Dv90-Dv10) / Dv50 of the precursor can be selected as any value from 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8 or a range consisting of any two values ​​therein.

[0127] Controlling the volume distribution particle size Dv50 or particle size distribution (Dv90-Dv10) / Dv50 of the precursor within a suitable range is beneficial for controlling the particle size distribution (Dv90-Dv10) / Dv50 of the graphite anode active material within a suitable range, thereby regulating the oil absorption value of the graphite anode active material within a smaller range.

[0128] In this article, the term "graphitization treatment" refers to the heat treatment process of carbon materials, in which carbon materials undergo "microcrystal" growth to transform from a two-dimensional carbon network structure to a three-dimensional ordered structure.

[0129] In some implementations, the maximum power of the graphitization process is 70%-90% of the rated power of the graphitization process equipment.

[0130] In some implementations, the maximum power for graphitization processing can be selected as 70%, 75%, 80%, 85%, 90%, or any range between two of the rated power of the graphitization processing equipment. It is understood that graphitization processing equipment refers to any device capable of performing graphitization processing, including but not limited to Atchison furnaces, box furnaces, internal furnaces, continuous graphitization, electric forging furnaces, medium-frequency furnaces, and tube furnaces. The rated power of graphitization processing equipment produced by different manufacturers may vary; the appropriate device can be selected based on the specific circumstances.

[0131] The maximum power used in this application for graphitization needs to be lower than the rated power of the graphitization equipment to ensure uniformity of the temperature field during the graphitization process. Ensuring consistency in the specific capacity of the material is beneficial for improving the cycle life of the battery.

[0132] In some implementations, the graphitization equipment is an internal furnace with a rated power of 25000W-32000W.

[0133] In some implementations, the graphitization equipment is an Atchison furnace with a rated power of 28,000W-30,000W.

[0134] In some embodiments, the graphitization process has a maximum power of 23000W-25000W.

[0135] For example, the maximum power for graphitization can be selected as 23000W, 23500W, 24000W, 24500W, 25000W or any value range between the two.

[0136] By controlling the maximum power of graphitization treatment, the degree of graphitization of graphite anode active materials during heat treatment can be effectively controlled, which is beneficial to improving the cycle life of the battery.

[0137] In some implementations, the graphitization process is carried out at a constant power of 10-50 hours at maximum power.

[0138] In some implementations, the graphitization process is carried out at constant power for a period of 10h, 13h, 16h, 19h, 22h, 25h, 28h, 31h, 33h, 36h, 39h, 42h, 45h, 48h, 50h or any range between the two.

[0139] In some implementations, the graphitization equipment is an internal furnace, and the graphitization process is carried out at a constant power of maximum power for 10-30 hours.

[0140] In some implementations, the graphitization equipment is an Atchison furnace, and the graphitization process is carried out at a constant power of maximum power for 30-50 hours.

[0141] A suitable constant power time at maximum power is not likely to cause excessive rearrangement of the precursor, which can effectively reduce the specific surface area of ​​the graphite anode active material and thus improve the cycle performance of the battery; it can also effectively increase the specific capacity of the graphite anode active material, which is beneficial to the energy density of the secondary battery.

[0142] In some embodiments, the screening process of the intermediate product specifically includes the following steps: The intermediate product is sieved to remove particles with a maximum particle size Dmax greater than 100 μm, thus obtaining the graphite anode active material.

[0143] Removing large-diameter particles from intermediate products reduces the negative impact of large-particle materials on battery cycle performance and storage performance.

[0144] 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.

[0145] [Negative electrode plate] The negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector. The negative electrode film layer includes a graphite negative electrode active material according to the first aspect of the present application or a graphite negative electrode active material prepared by the method according to the second aspect of the present application.

[0146] In some embodiments, the negative electrode film layer includes a conductive agent, and the mass content of the conductive agent is greater than or equal to 1.5% based on the mass of the negative electrode film layer.

[0147] In some embodiments, based on the total mass of the negative electrode film, the mass percentage of the conductive agent is 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 3.0%, 3.1%, 3.2%, 3.2%, 3.3%, or any value between the two.

[0148] During battery cycling, active ions continuously insert and extract within the lattice of the graphite anode active material. This leads to particle "isolation," resulting in loss of electrochemical activity, uneven local current, polarization, accelerated capacity decay, and a significant drop in battery performance. To address these issues, a relatively high content of conductive agent is typically added to the anode film to effectively enhance the electrical contact between graphite anode active materials and improve battery cycle stability. However, adding a high content of conductive agent to the anode slurry can negatively impact its dispersibility. The low oil absorption value graphite anode active material of this application exhibits excellent dispersibility in the anode slurry, thus compensating for the negative impact of a high conductive agent content on the slurry's dispersibility.

[0149] The combination of high-conductivity agent and low-oil-absorption graphite anode active material results in good spreadability of the anode slurry, excellent uniformity of the electrode sheet, and good electrical contact of the graphite anode active material, thus comprehensively improving the cycle performance of the battery.

[0150] In some embodiments, based on the mass of the negative electrode film, the mass content of the conductive agent is 1.8%-2.5%. In some embodiments, based on the total mass of the negative electrode film, the mass percentage of the conductive agent is 1.8%, 1.9%, 2%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, or any value between two of these.

[0151] When the mass ratio of the conductive agent is within a suitable range, it can enhance the electrical contact between the graphite anode active materials without causing a loss in the battery's energy density due to excessive active conductive agent in the anode film.

[0152] 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.

[0153] 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 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 (copper, copper 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.).

[0154] In some embodiments, the negative electrode film layer may further include other negative electrode active materials besides the graphite negative electrode active material described above. In some embodiments, the other negative electrode active materials include, but are not limited to, one or more of conventional natural graphite, artificial graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate. The silicon-based materials may include one or more of elemental silicon, silicon oxide, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based materials may include one or more of elemental tin, tin oxide, and tin alloys.

[0155] In some embodiments, 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.

[0156] In some embodiments, the negative electrode film layer may optionally include an adhesive. The adhesive 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).

[0157] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0158] In some embodiments, the negative electrode sheet can be prepared by dispersing the above-mentioned components for preparing the negative electrode sheet, such as 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 obtaining the negative electrode sheet after drying, cold pressing and other processes.

[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 the positive electrode active material of the first aspect of this application.

[0160] 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.

[0161] 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.).

[0162] In some embodiments, the positive electrode active material may be a known battery positive electrode active material. As an example, the positive electrode active material may include 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 / 3 Co 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 Co0.25 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) 0.85 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.

[0163] 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), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0164] In some embodiments, the positive electrode film 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.

[0165] 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.

[0166] [Electrolytes] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific restrictions on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel, or entirely solid.

[0167] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0168] 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.

[0169] 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.

[0170] 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.

[0171] [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.

[0172] 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.

[0173] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0174] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above.

[0175] 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.

[0176] 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 1 This is an example of a square-structured secondary battery 5.

[0177] In some implementations, refer to Figure 2 The outer packaging may include a housing 51 and a cover 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 cover 53 can be placed over the opening to close the receiving cavity. A positive electrode, a negative electrode, and a separator can be formed into an electrode assembly 52 using a winding or stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The secondary battery 5 may contain one or more electrode assemblies 52, which can be selected by those skilled in the art according to specific practical needs.

[0178] In some implementations, the secondary batteries can be assembled into a battery module, and the number of secondary batteries contained in the battery module 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 module.

[0179] Figure 3 This is battery module 4, used as an example. (See reference...) Figure 3 In battery module 4, multiple secondary batteries 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 secondary batteries 5 can be fixed in place using fasteners.

[0180] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of secondary batteries 5 are received.

[0181] 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.

[0182] Figure 4 and Figure 5 This is battery pack 1 as an example. (See reference...) Figure 4 and Figure 5 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.

[0183] 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 a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., 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.

[0184] As the electrical device, a secondary battery, battery module, or battery pack can be selected according to its usage requirements.

[0185] Figure 6 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.

[0186] 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.

[0187] Example 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.

[0188] Example 1 (1) Preparation of graphite anode active material Petroleum coke with a volume ratio of 57.3% for both mosaic and regional structures and a bonding index of 6.2 was coarsely crushed. The coarsely crushed material was then crushed and sieved. The sieved material was shaped and classified. During the classification process, a certain amount of fine powder was removed to obtain the precursor. The fine powder refers to particles with a volume distribution particle size Dv50 of 3-7 μm and a particle size distribution (Dv90-Dv10) / Dv50 > 1.6. The precursor had a volume distribution particle size Dv50 of 16.2 μm and a particle size distribution (Dv90-Dv10) / Dv50 of 1.78. The precursor was graphitized in an Atchison furnace at a temperature of 2800℃. The maximum power used for graphitization was 23000W (this refers to the actual power used by the Atchison furnace, which is about 85% of the rated power of the Atchison furnace). After maintaining this power for 40 hours, the surface temperature of the graphite crucible in the Atchison furnace was cooled to 200℃ to obtain the intermediate product. The obtained intermediate product was sieved and demagnetized to obtain the graphite anode active material. The graphite anode active material has a graphitization degree of 88%, an oil absorption value of 43 ml / 100 g, and a specific surface area of ​​0.92 m². 2 / g, Dv50 is 14.8μm.

[0189] (2) Preparation of negative electrode sheet The graphite anode active material, conductive agent Super P, thickener carboxymethyl cellulose (CMC), and binder styrene-butadiene rubber (SBR) prepared above were mixed at a dry mass ratio of 96:1:1.2:1.8. Deionized water was added as a solvent, and the mixture was stirred under vacuum until homogeneous to obtain an anode slurry. The anode slurry was uniformly coated onto a copper foil anode current collector, and then dried, cold-pressed, and slit to obtain the anode sheet. The compacted density of the anode sheet was 1.50 g / cm³. 3 The areal density is 9.6 mg / cm³. 2 .

[0190] (3) Preparation of positive electrode sheet Lithium iron phosphate (LFP) as the positive electrode active material, Super P as the conductive agent, and polyvinylidene fluoride as the binder were mixed at a mass ratio of 97:1:2. N-methylpyrrolidone as the solvent was added, and the mixture was stirred under vacuum until homogeneous to obtain a positive electrode slurry. The positive electrode slurry was uniformly coated onto an aluminum foil current collector, and then dried, cold-pressed, and slit to obtain the positive electrode sheet. The compacted density of the positive electrode sheet was 2.50 g / cm³. 3 Its surface density is 19.7 mg / cm³. 2 .

[0191] (4) Preparation of electrolyte In an argon atmosphere glove box with a water content of <10ppm, ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) are mixed in a volume ratio of 1:1:1 to obtain an organic solvent. Then, fully dried lithium salt LiPF6 is dissolved in the mixed organic solvent to prepare an electrolyte with a concentration of 1mol / L. Ethylene carbonate is added to the above solution, with the mass content of ethylene carbonate being 2% of the total mass of the electrolyte.

[0192] (5) Preparation of the separating membrane Polypropylene film is used as the separator.

[0193] (6) Preparation of lithium-ion batteries The positive electrode, separator, and negative electrode are stacked in sequence, with the separator acting as a separator between the positive and negative electrodes. The electrode assembly is then wound up to obtain the electrode assembly. The electrode assembly is placed in an outer packaging, dried, and then injected with electrolyte. After vacuum sealing, settling, formation, and shaping, a lithium-ion battery is obtained.

[0194] Examples 2-3 are basically the same as Example 1, except that the bonding index of the raw materials, the maximum power of graphitization treatment, and the particle size distribution (Dv90-Dv10) / Dv50 of the precursor are adjusted, as shown in Table 1.

[0195] Comparative Examples 1-3 are basically the same as Example 1, except that the volume ratio of embedded and regional structures in the raw materials, the bonding index of the raw materials, the maximum power of graphitization treatment, and the particle size distribution (Dv90-Dv10) / Dv50 of the precursor are adjusted, as shown in Table 1.

[0196] Table 1

[0197] Performance testing 1. Filtration time of negative electrode slurry First, determine that the filter screen is 200 mesh. Cut the filter screen into 25cm x 25cm pieces using scissors. Find a clean 500ml beaker and ensure it is clean. Fold the 150 mesh filter screen into a triangle. Pour 500ml of slurry onto the top of the filter screen all at once. Start recording the time when the slurry begins to flow into the beaker from the tip of the filter screen. Record the filtration time for 300ml of slurry.

[0198] 2. Cyclic performance test of secondary batteries at 60℃ At 60°C, the batteries of the above embodiments and comparative examples were charged at a constant current of 1C to a voltage of 3.65V, then charged at a constant voltage of 3.65V until the current was ≤0.05C. The batteries were then discharged at a constant current of 1C to a voltage of 2.5V. This constitutes one charge-discharge cycle, and the discharge capacity C1 of the first cycle was recorded. This charge-discharge cycle was repeated until the battery capacity decreased to 80% of the initial capacity C1. The test was then stopped, and the number of test cycles was recorded.

[0199] 3. Room temperature storage performance of secondary batteries In a 25℃ environment, charge-discharge tests were conducted. The battery was charged at a constant current of 1C until the voltage reached 3.65V, then charged at a constant voltage of 3.65V until the current ≤0.05C. The battery was then discharged at a constant current of 1C until the voltage reached 2.5V. This constituted one charge-discharge cycle, and the discharge capacity of the first cycle was recorded as the initial discharge capacity, denoted as C0. The battery cells were then fully charged and placed in a 60℃ environment for varying durations. Every 30 days, the cells were removed and tested at 25℃ for the remaining capacity C1. This constituted one storage cycle, and the discharge capacity recorded during this cycle was the discharge capacity after the first storage. Subsequently, the first storage test procedure was repeated, recording the discharge capacity values ​​during storage and the 120-day cycle capacity retention rate.

[0200] III. Results As shown in Table 2, the graphitization degree of the graphite anode active materials provided in Examples 1-3 of this application is 88%-93%, and the oil absorption value of the graphite anode active materials does not exceed 50 ml / 100g. A comparison of Examples 1-3 with Comparative Example 1 shows that controlling the oil absorption value of the graphite anode active material to not exceed 50 ml / 100g can improve the dispersibility and filterability of the anode slurry, thereby improving the cycle life and storage performance of the battery. A comparison of Examples 1-3 with Comparative Examples 2-3 shows that controlling the graphitization degree of the graphite anode active material to 88%-93% can balance the specific capacity and cycle performance of the graphite anode active material, resulting in a battery that balances high energy density and long cycle life, while also improving the battery's storage performance.

[0201] As shown in Examples 1-3, the specific surface area of ​​the graphite anode active material is less than or equal to 1.4 m². 2 / g, the negative electrode slurry has excellent dispersibility and filterability, the graphite negative electrode active material has high specific capacity, and the secondary battery has excellent cycle stability and storage stability.

[0202] As can be seen from Examples 1-3, the volume distribution particle size Dv50 of the graphite anode active material is 12-16 μm, the anode slurry has excellent dispersibility and filterability, the graphite anode active material has high specific capacity, and the secondary battery has excellent cycle stability and storage stability.

[0203] Table 2

[0204] 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 graphite anode active material, characterized in that, The graphite anode active material has a graphitization degree of 88%-93%, and its oil absorption value does not exceed 50ml / 100g. The volume distribution particle size Dv50 of the graphite anode active material is 12-16 μm and the particle size distribution (Dv90-Dv10) / Dv50 of the graphite anode active material is 1.3-1.

6.

2. The graphite anode active material according to claim 1, characterized in that, The oil absorption value of the graphite negative electrode active material is 30ml / 100g-43ml / 100g.

3. The graphite anode active material according to claim 1, characterized in that, Based on the total number of particles in the graphite anode active material, the proportion of primary particles in the graphite anode active material is greater than or equal to 85%.

4. The graphite anode active material according to claim 1, characterized in that, Based on the total number of particles in the graphite anode active material, the proportion of primary particles in the graphite anode active material is 85%-100%.

5. The graphite anode active material according to claim 1, characterized in that, The specific surface area of ​​the graphite anode active material is less than or equal to 1.4 m². 2 / g.

6. The graphite anode active material according to claim 1, characterized in that, The specific surface area of ​​the graphite anode active material is 0.6 m². 2 / g-1.3m 2 / g.

7. The graphite anode active material according to claim 1, characterized in that, The volume distribution particle size Dv50 of the graphite anode active material is 13-15 μm.

8. The graphite anode active material according to any one of claims 1 to 7, characterized in that, The graphite anode active material satisfies at least one of the following: (1) The compacted density of the graphite anode active material under a pressure of 49000N is less than or equal to 1.85 g / cm³. 3 ; (2) The compacted density of the graphite anode active material under a pressure of 49000N is 1.70 g / cm³. 3 -1.85g / cm 3 ; (3) The tap density of the graphite anode active material is 1.2 g / cm³. 3 -1.4g / cm 3 ; (4) The specific capacity of the graphite negative electrode active material is greater than or equal to 340 mAh / g; (5) The specific capacity of the graphite negative electrode active material is 341mAh / g-347mAh / g.

9. A method for preparing a graphite anode active material, characterized in that, Includes the following steps: Provide raw materials; The raw materials are processed to obtain a precursor; The precursor is graphitized to obtain an intermediate product; The intermediate product is subjected to sieving to obtain a graphite anode active material; the graphitization degree of the graphite anode active material is 88%-93%, and the oil absorption value of the graphite anode active material does not exceed 50ml / 100g. The volume distribution particle size Dv50 of the graphite anode active material is 12-16 μm; The particle size distribution (Dv90-Dv10) / Dv50 of the graphite anode active material is 1.3-1.

6.

10. The preparation method according to claim 9, characterized in that, The raw materials include at least one of petroleum coke, needle coke, and pitch coke.

11. The preparation method according to claim 9, characterized in that, The raw materials include petroleum coke.

12. The preparation method according to claim 9, characterized in that, Based on the total volume of the raw material structure, the volume ratio of the mosaic and regional structures is greater than or equal to 50%.

13. The preparation method according to claim 9, characterized in that, Based on the total volume of the raw material structure, the volume ratio of the mosaic and regional structures is 50%-65%.

14. The preparation method according to claim 9, characterized in that, The adhesiveness index of the raw material is less than or equal to 10.

15. The preparation method according to claim 9, characterized in that, The adhesiveness index of the raw material is 1-9.

16. The preparation method according to claim 9, characterized in that, The precursor satisfies at least one of the following conditions: The precursor has a volumetric particle size distribution (Dv50) of 12 μm-18 μm; and / or, The particle size distribution (Dv90-Dv10) / Dv50 of the precursor is 1.2-1.

8.

17. The preparation method according to claim 9, characterized in that, The maximum power of the graphitization process is 70%-90% of the rated power of the graphitization equipment.

18. The preparation method according to claim 9, characterized in that, The maximum power of the graphitization treatment is 23000W-25000W; and / or, the constant power time of the graphitization treatment at the maximum power is 10h-50h.

19. The preparation method according to any one of claims 9 to 18, characterized in that, The screening process for the intermediate product specifically includes the following steps: The intermediate product is sieved to remove particles with a maximum particle size Dmax greater than 100 μm, thus obtaining the graphite anode active material.

20. A secondary battery, comprising a negative electrode, characterized in that, The negative electrode sheet includes a negative current collector and a negative electrode film layer formed on at least one surface of the negative current collector, wherein the negative electrode film layer includes the graphite negative electrode active material according to any one of claims 1 to 8 or the graphite negative electrode active material prepared by the preparation method according to any one of claims 9 to 19.

21. The secondary battery according to claim 20, characterized in that, The negative electrode film layer includes a conductive agent, and based on the mass of the negative electrode film layer, the mass content of the conductive agent is greater than or equal to 1.5%.

22. The secondary battery according to claim 20, characterized in that, The negative electrode film layer includes a conductive agent, and the mass content of the conductive agent is 1.8%-2.5% based on the mass of the negative electrode film layer.

23. An electrical appliance, characterized in that, The secondary battery includes any one of claims 20 to 22.

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