Graphite anode active materials and their preparation methods, anode sheets, secondary batteries and electrical devices

Abstract

This application provides a graphite anode active material, its preparation method, and an anode sheet, a secondary battery, and an electrical device containing the same. The graphite anode active material comprises an internal region and a surface region that at least partially surrounds the internal region. The surface region refers to the area extending 30 nm from the surface of the graphite anode active material particle into the particle. The mass percentage of crystalline carbon in the internal region is denoted as η1, and the mass percentage of crystalline carbon in the surface region is denoted as η2, with 10% ≤ η1 - η2 ≤ 35%. This graphite anode active material can improve battery cycle performance.

Description

Technical Field

[0001] This application belongs to the field of battery technology, specifically relating to a graphite negative electrode active material and its preparation method, a negative electrode sheet, a secondary battery, and an electrical device. Background Technology

[0002] In recent years, secondary batteries have been widely used in energy storage power systems such as hydropower, thermal power, wind power and solar power plants, as well as in many fields such as power tools, electric bicycles, electric motorcycles, electric cars, military equipment, and aerospace.

[0003] As the requirements for the endurance of electrical devices continue to increase, more stringent requirements are being placed on the cycle life of secondary batteries. How to further improve the cycle life of secondary batteries is a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0004] The purpose of this application is to provide a graphite anode active material, its preparation method, anode sheet, secondary battery, and power-consuming device. This graphite anode active material maintains good capacity while improving battery cycle performance.

[0005] The first aspect of this application provides a graphite anode active material, wherein the particle body of the graphite anode active material includes an internal region and a surface region that at least partially surrounds the internal region. The surface region refers to the region formed by extending 30 nm from the surface of the particle body of the graphite anode active material into the particle. The mass percentage of crystalline carbon in the internal region is denoted as η1, and the mass percentage of crystalline carbon in the surface region is denoted as η2, and 10% ≤ η1 - η2 ≤ 35%.

[0006] The relatively lower percentage of crystalline carbon in the surface region of graphite anode active materials compared to their interior regions means that the carbon atoms in the surface layer are arranged in a less regular pattern, resulting in more complex intermolecular interactions. This leads to higher strength and hardness compared to the interior region. On one hand, this allows the graphite anode active material to maintain higher particle integrity during cold pressing, reducing side reactions and improving battery cycle stability. On the other hand, during cycling, active ions easily intercalate and deintercalate in the low-crystallinity surface region of the graphite anode active material, reducing the expansion rate of the secondary battery during long cycles and further improving cycle stability. The relatively high crystallinity in the interior region of the graphite anode active material allows the material to balance high capacity and high voltage density while reducing cycle expansion and improving cycle performance, preventing a significant decrease in the battery's energy density.

[0007] In any implementation, 75% ≤ η1 ≤ 99%, and optionally 80% ≤ η1 ≤ 95%.

[0008] The fact that the mass percentage of crystalline carbon in the internal region of the graphite anode active material particles is within the above range is beneficial to maintaining the high capacity of the graphite anode active material; and the graphite anode active material will not cause lattice interlacing due to excessive internal defects, so that the graphite anode active material can maintain excellent electrochemical performance during long-term cycling, reducing the probability of battery performance "plummeting".

[0009] In any implementation, 55% ≤ η2 ≤ 75%, and optionally 60% ≤ η2 ≤ 70%.

[0010] The crystalline carbon mass percentage in the surface region of the graphite anode active material particles within the above-mentioned range is beneficial to reducing the physical rebound of the graphite anode active material after cold pressing, reducing the expansion rate of the electrode during cycling, and thus improving the cycle stability of the secondary battery.

[0011] In any embodiment, the graphitization degree of the graphite anode active material is 88%-95%, and optionally 90%-95%.

[0012] It is understandable that the degree of graphitization is an overall measure of the crystallinity of graphite anode active materials. By adjusting the different mass content of crystalline carbon in the internal and surface regions of graphite anode active materials, the graphite anode active materials can have a suitable degree of graphitization, taking into account both the capacity and cycle stability of the graphite anode active materials.

[0013] In any embodiment, the volume distribution particle size Dv50 of the graphite anode active material is 7.5 μm-14.5 μm, and can be optionally 8.5 μm-12.5 μm.

[0014] Graphite anode active materials with a volume distribution particle size Dv50 within the above range can provide a certain ion channel without causing too many side reactions due to excessively small particle size and excessively large specific surface area, thus simultaneously taking into account kinetic performance and cycle stability.

[0015] In any embodiment, the specific surface area of ​​the graphite anode active material is 1.25 m². 2 / g-1.95m 2 / g, can be selected as 1.35m 2 / g-1.75m 2 / g.

[0016] This graphite anode active material has a low specific surface area, which allows it to leverage the advantage of a relatively low crystalline carbon content in the surface region to reduce battery expansion, while also reducing the probability of side reactions and improving the cycle stability of the battery through its relatively low specific surface area.

[0017] In any embodiment, the particle size distribution (Dv90-Dv10) / Dv50 of the graphite anode active material is 1.0-1.6, and can be selected as 1.1-1.5.

[0018] Controlling the particle size distribution of graphite anode active materials within the aforementioned range is beneficial for improving the compactness of the graphite anode active materials and increasing the compaction density of the anode film. In other words, the cold pressing pressure required to achieve the same compaction density of the anode sheet is smaller, thereby reducing the probability of cracking of the graphite anode active materials during cold pressing and further improving the integrity of the graphite anode active materials during processing. Moreover, the low stress inside the graphite anode active material particles helps maintain the long-term pore structure of the electrode during cycling, maintaining the original pore structure of the electrode during cycling, keeping the lithium-ion intercalation path unobstructed, and reducing the re-forming of the graphite anode active material during charging, thus improving kinetic performance, cycle life, and storage stability. Furthermore, the particle size distribution within the aforementioned range can also improve the uniformity of lithium intercalation between graphite anode active material particles, reduce polarization, and avoid lithium plating caused by uneven current density, which is beneficial for achieving long-term cycle stability. In addition, the particle size distribution within the above range also helps to improve the processing performance of the electrode. It will not affect the uniformity of slurry mixing due to excessive small-diameter particles in the graphite negative electrode active material, which is conducive to improving the uniformity and stability of the electrode quality and helps to achieve long-cycle stability.

[0019] In any embodiment, the powder compaction density of the graphite anode active material under a pressure of 49000N is 1.75 g / cm³. 3 -1.88g / cm 3 The option is 1.78 g / cm³. 3 -1.84g / cm 3 .

[0020] Graphite anode active materials with a powder compaction density within the above range are more likely to maintain high particle integrity during cold pressing, which helps improve the cycle life of secondary batteries.

[0021] In any embodiment, the tap density of the graphite anode active material is 1.05 g / cm³. 3 -1.30g / cm 3 .

[0022] In any embodiment, the specific capacity of the graphite anode active material is 345mAh / g-355mAh / g, and can be selected as 347mAh / g-353mAh / g.

[0023] Graphite anode active materials with a specific capacity within the above-mentioned range will not experience significant lattice expansion due to excessive graphitization during charge and discharge, nor will they be difficult to compact due to excessive graphitization. To achieve the same electrode compaction density, higher cold pressing pressure is required, which may lead to cracking during cold pressing and excessive consumption of active lithium by creating new interfaces during cycling. This will comprehensively improve the cycle life of the secondary battery.

[0024] In any embodiment, the graphite anode active material I D / I G It is 0.05-0.10, where I D / I G I represents the ratio of the intensity of the D peak to the intensity of the G peak obtained from the Raman spectrum. D This indicates that the Raman spectrum is at 1350±100 cm⁻¹ -1 D peak intensity at I G This indicates that the Raman spectrum is at 1580±100 cm⁻¹ -1 The intensity of the G peak at that location.

[0025] I of graphite anode active material D / I G This method can be used to characterize the surface disorder of graphite anode active materials. Unlike graphite anode active materials that undergo post-coating treatment on the surface of graphite particles, the graphite anode active materials provided in this application have both amorphous carbon on the surface and low surface disorder. In active materials where amorphous carbon is post-coated on the surface of graphite particles, the amorphous carbon is usually derived from the coating organic resin, which generates amorphous carbon at low temperature carbonization, resulting in high surface disorder of the amorphous carbon in the coating layer. However, the surface and internal regions of the graphite anode active material provided in this application are both derived from the same precursor and undergo the same heat treatment process. Therefore, the amorphous carbon in this graphite anode active material is uniformly distributed in the surface region, resulting in a low surface disorder in the surface region of the graphite anode active material while having a low crystalline carbon content. This allows graphite anode active materials to leverage the advantages of amorphous carbon, improving battery kinetic performance and reducing electrode cycle expansion rate. It also prevents excessive side reactions and significant capacity reduction due to the high disorder on the surface of graphite anode active materials, thus comprehensively improving battery cycle stability.

[0026] In any embodiment, the interlayer spacing of the surface region of the graphite anode active material is denoted as d1, and the interlayer spacing of the internal region of the graphite anode active material is denoted as d2, wherein the graphite anode active material satisfies d1>d2; optionally, 0.3365nm≤d1≤0.3378nm; optionally, 0.3358nm≤d2≤0.3364nm.

[0027] In any embodiment, the graphite anode active material includes both primary particles and secondary particles; optionally, based on the total number of primary and secondary particles in the graphite anode active material, the proportion of secondary particles is less than or equal to 50%.

[0028] Graphite anode active materials with a low proportion of secondary particles are beneficial for maintaining the particle integrity of the graphite anode active material during battery fabrication, reducing the formation of new interfaces, decreasing the consumption of active lithium during cycling, and further improving the cycle stability of the secondary battery. Simultaneously, a certain number of secondary particles can reduce anode sheet expansion while maintaining the kinetic performance of the secondary battery, thus enabling the cell to have a full life-cycle kinetic window. This prevents lithium plating caused by uneven current distribution from leading to a sharp decline in battery capacity and lifespan, comprehensively improving the battery's cycle stability.

[0029] A second aspect of this application provides a method for preparing a graphite anode active material, comprising the following steps: providing raw materials; processing the raw materials to obtain an intermediate product; graphitizing the intermediate product to obtain a graphitized product; and sieving the graphitized product to obtain a graphite anode active material. The particle body of the graphite anode active material includes an internal region and a surface region that at least partially surrounds the internal region. The surface region refers to the region extending 30 nm from the surface of the particle body of the graphite anode active material into the particle. The mass percentage of crystalline carbon in the internal region is denoted as η1, and the mass percentage of crystalline carbon in the surface region is denoted as η2, and 10% ≤ η1 - η2 ≤ 35%.

[0030] In any embodiment, the maximum power of the graphitization process is 70%-90% of the rated power of the graphitization process equipment.

[0031] In any embodiment, the temperature of the graphitization treatment is 2600℃~3000℃.

[0032] In any embodiment, the graphitization process takes 10 to 50 hours.

[0033] In any embodiment, the raw material includes one or more of petroleum coke, needle coke, and pitch coke, and may be selected as needle coke.

[0034] In any embodiment, based on the total volume of the raw material, the volume percentage of the fibrous structure in the raw material is greater than or equal to 55%, and can be selected as 58%-70%.

[0035] Raw materials with a high proportion of fibrous structure are beneficial for improving the compaction density and specific capacity of graphite anode active materials, allowing the graphite anode active material to retain high integrity during compaction. This results in batteries with both high cycle life and good energy density. However, an excessively high proportion of fibrous structure increases the cost and expansion rate of graphite anode active materials, and deteriorates kinetic performance. Raw materials with a fibrous structure volume ratio within the aforementioned range offer both lower cost and good specific capacity, providing the cell with a full life cycle kinetic window, thereby comprehensively improving the battery's long-term cycle life and electrochemical performance.

[0036] In any embodiment, the processing of raw materials specifically includes the following steps: crushing, shaping and classifying the raw materials to obtain a first precursor; granulating the first precursor to obtain a second precursor; and carbonizing the first precursor and the second precursor at low temperature to obtain the intermediate product.

[0037] A third aspect of this application provides a negative electrode sheet, comprising a graphite negative electrode active material in any embodiment or a graphite negative electrode active material prepared by any embodiment.

[0038] In any embodiment, the compaction density of the negative electrode film is 1.5 g / cm³. 3 ~1.65g / cm 3 .

[0039] A fourth aspect of this application provides a secondary battery, including the negative electrode sheet of the third aspect of this application.

[0040] The fifth aspect of this application provides an electrical device including a secondary battery as described in the fourth aspect of this application. Attached Figure Description

[0041] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments of this application will be briefly described below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the drawings without creative effort.

[0042] Figure 1 This is a schematic diagram of a cross-sectional image of the graphite anode active material particles of this application;

[0043] Figure 2 This is a schematic diagram of one embodiment of the secondary battery of this application;

[0044] Figure 3 This is an exploded view of one embodiment of the secondary battery of this application;

[0045] Figure 4 This is a schematic diagram of one embodiment of the battery module of this application;

[0046] Figure 5 This is a schematic diagram of one embodiment of the battery pack of this application;

[0047] Figure 6 yes Figure 5 An exploded view of an embodiment of the battery pack shown;

[0048] Figure 7 This is a schematic diagram of one embodiment of an electrical device that uses a secondary battery as a power source, as described in this application.

[0049] In the accompanying drawings, the figures may not be drawn to scale. The reference numerals are explained as follows: 1 Battery pack, 2 Upper casing, 3 Lower casing, 4 Battery module, 5 Secondary battery, 51 Housing, 52 Electrode assembly, 53 Cover plate, 100 Graphite negative electrode active material, 101 Surface area, 102 Internal area. Detailed Implementation

[0050] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the graphite negative electrode active material, its preparation method, the negative electrode sheet, and secondary batteries and power devices containing the same. 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 a thorough understanding of this application by those skilled in the art and are not intended to limit the subject matter of the claims.

[0051] 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.

[0052] Unless otherwise specified, all embodiments and optional embodiments of this application may be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure of this application.

[0053] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions, and such technical solutions shall be deemed to be included in the disclosure of this application.

[0054] 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.

[0055] 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.

[0056] 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).

[0057] Unless otherwise specified, the terms used in this application have the common meanings as commonly understood by those skilled in the art.

[0058] Unless otherwise specified, the values ​​of the parameters mentioned in this application can be determined using various testing methods commonly used in the art, for example, according to the testing methods given in this application.

[0059] Unless otherwise specified, in this application, the term "active ion" refers to ions that can be inserted and extracted back and forth between the positive and negative electrodes of a secondary battery, including but not limited to lithium ions.

[0060] In this application, the terms "multiple" or "various" refer to two or more kinds.

[0061] The electrochemical performance of carbon materials is often related to the mass content of crystalline carbon. Carbon materials with high crystalline carbon mass content usually have high capacity. However, the low interlayer spacing of crystalline carbon means that during long cycles, the repeated insertion and extraction of active ions will cause large lattice expansion, resulting in high cycling expansion rate and poor cycling stability of the electrode.

[0062] Based on this, this application provides a graphite anode active material. The particle body of the graphite anode active material includes an internal region and a surface region that at least partially surrounds the internal region. The surface region refers to the region formed by extending 30 nm from the surface of the particle body of the graphite anode active material into the particle. The mass percentage of crystalline carbon in the internal region is denoted as η1, and the mass percentage of crystalline carbon in the surface region is denoted as η2, and 10% ≤ η1 - η2 ≤ 35%.

[0063] Figure 1 This is a schematic diagram of a cross-sectional image of the particles of the graphite anode active material 100 of this application. Figure 1 As shown, the region extending 30 nm from the surface of the graphite anode active material 100 particle body into the interior is the surface region 101, and the region inside the surface region 101 is the interior region 102.

[0064] In this application, the mass percentage of crystalline carbon can be tested using methods known in the art. As an example, a slice approximately 20 nm to 50 nm thick is cut from the middle of the graphite anode active material particle using focused ion beam (FIB), and then the slice is tested using transmission electron microscopy (TEM). The content of carbon elements with different bond types in graphite is determined using transmission electron microscopy-energy loss spectroscopy (TEM-EELS), with the resultant being sp... 2 As carbon is crystalline, the mass percentage of crystalline carbon in different regions of the graphite anode active material is determined by the integral area ratio. At least 10 points are selected in each region, and at least 5 samples are selected to calculate the average mass percentage of crystalline carbon in different regions.

[0065] In some implementations, η1-η2 is a numerical range of 10%, 13%, 15%, 16%, 20%, 22%, 24%, 25%, 26%, 28%, 30%, 31%, 35%, or any combination thereof. For example, η1-η2 can be 10%-31%, 10%-28%, 13%-35%, 13%-31%, 13%-28%, 15%-35%, 15%-31%, 15%-28%, 16%-35%, 16%-31%, 16%-28%, 20%-35%, 20%-31%, 20%-28%, 22%-35%, 22%-31%, 24%-35%, 24%-31%, 25%-35%, or 25%-31%.

[0066] The relatively lower percentage of crystalline carbon in the surface region of graphite anode active materials compared to their interior regions means that the carbon atoms in the surface layer are arranged in a less regular pattern, resulting in more complex intermolecular interactions. This leads to higher strength and hardness compared to the interior region. On one hand, this allows the graphite anode active material to maintain higher particle integrity during cold pressing, reducing side reactions and improving battery cycle stability. On the other hand, during cycling, active ions easily intercalate and deintercalate in the low-crystallinity surface region of the graphite anode active material, reducing the expansion rate of the secondary battery during long cycles and further improving cycle stability. The relatively high crystallinity in the interior region of the graphite anode active material allows the material to reduce cycle expansion and improve cycle performance while maintaining high voltage density, achieving high battery capacity.

[0067] In some implementations, 75% ≤ η1 < 99%, and optionally 80% ≤ η1 ≤ 95%.

[0068] In some implementations, η1 is a numerical range of 75%, 80%, 85%, 90%, 95%, 99%, or any two of these.

[0069] The fact that the mass percentage of crystalline carbon in the internal region of the graphite anode active material particles is within the above range is beneficial to maintaining the high capacity of the graphite anode active material; and the graphite anode active material will not cause lattice interlacing due to excessive internal defects, so that the graphite anode active material can maintain excellent electrochemical performance during long-term cycling, reducing the probability of battery performance "plummeting".

[0070] In some implementations, 55% ≤ η2 ≤ 75%, and optionally 60% ≤ η2 ≤ 70%.

[0071] In some implementations, η2 is a numerical range of 55%, 57%, 60%, 63%, 65%, 67%, 70%, 73%, 75%, or any two of these.

[0072] The crystalline carbon mass percentage in the surface region of the graphite anode active material particles within the above-mentioned range is beneficial to reducing the physical rebound of the graphite anode active material after cold pressing, reducing the expansion rate of the electrode during cycling, and thus improving the cycle stability of the secondary battery.

[0073] In some embodiments, the graphitization degree of the graphite anode active material is 88%-95%, and optionally 90%-95%.

[0074] In this paper, the term "graphitization degree" refers to an indicator that measures the degree to which carbon atoms form a close-packed hexagonal graphite crystal structure.

[0075] In this application, the graphitization degree of the graphite anode active material can be tested using methods known in the art. As an example, high-purity silicon powder (purity ≥ 99.99%) is used as an internal standard for calibration. The graphite anode active material and silicon are mixed at a weight ratio of 5:1, ground uniformly, and pressed into tablets. X-ray diffractometer (e.g., Bruker D8 Discover) is used for testing. Referring to JIS K 0131-1996 and JB / T 4220-2011, the average interlayer spacing d002 of the (002) crystal plane in the crystal structure of the graphite anode active material is obtained. Then, the graphitization degree is calculated using the formula g = (0.344 - d002) / (0.344 - 0.3354) × 100%. In the above formula, d002 is the average interlayer spacing of the (002) crystal plane in the crystal structure of the graphite anode active material, expressed in nanometers (nm).

[0076] In some embodiments, the degree of graphitization of the graphite anode active material is 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, or any value between the two.

[0077] It is understandable that the degree of graphitization is an overall measure of the crystallinity of graphite anode active materials. By adjusting the different mass content of crystalline carbon in the internal and surface regions of graphite anode active materials, the graphite anode active materials can have a suitable degree of graphitization, taking into account both the capacity and cycle stability of the graphite anode active materials.

[0078] In some embodiments, the volume distribution particle size Dv50 of the graphite anode active material is 7.5 μm-14.5 μm, and can be optionally 8.5 μm-12.5 μm.

[0079] In this paper, the term "volume distribution particle size Dv50" refers to the particle size at which the cumulative volume distribution number of particles reaches 50% in the particle size distribution curve.

[0080] In this application, the volume distribution particle size Dv50 of the active material can be tested using methods known in the art. As an example, referring to GB / T 19077-2016, it is determined using a laser particle size analyzer. The testing instrument can be a Mastersizer 3000 laser particle size analyzer from Malvern Instruments Ltd., UK.

[0081] In some embodiments, the volume distribution particle size Dv50 of the graphite anode active material is 7.5 μm, 8.5 μm, 9.5 μm, 10.5 μm, 11.5 μm, 12.5 μm, 13.5 μm, 14.5 μm or any value range between the two.

[0082] Graphite anode active materials with a volume distribution particle size Dv50 within the above range can provide a certain ion channel without causing too many side reactions due to excessively small particle size and excessively large specific surface area, thus simultaneously taking into account kinetic performance and cycle stability.

[0083] In some embodiments, the specific surface area of ​​the graphite anode active material is 1.25 m². 2 / g-1.95m 2 / g, can be selected as 1.35m 2 / g-1.75m 2 / g.

[0084] In this application, the specific surface area of ​​the graphite anode active material can be tested using methods known in the art. As an example, referring to GB / T 19587-2017, the nitrogen adsorption specific surface area analysis method is used, and the result is calculated using the BET (Brunauer Emmett Teller) method. The testing instrument can be a Tri-Star3020 specific surface area and pore size analyzer from Micromeritics, USA.

[0085] In some embodiments, the specific surface area of ​​the graphite anode active material may be selected as 1.25 m². 2 / g, 1.35m 2 / g, 1.45m 2 / g, 1.55m 2 / g, 1.65m 2 / g, 1.75m 2 / g, 1.85m 2 / g, 1.95m 2 / g or any value between the two.

[0086] This graphite anode active material has a low specific surface area, which allows it to leverage the advantage of a relatively low crystalline carbon content in the surface region to reduce battery expansion, while also reducing the probability of side reactions and improving the cycle stability of the battery through its relatively low specific surface area.

[0087] In some embodiments, the particle size distribution (Dv90-Dv10) / Dv50 of the graphite anode active material is 1.0-1.6, and can be optionally 1.1-1.45.

[0088] In this paper, the terms "Dv90" and "Dv10" refer to the particle sizes corresponding to the cumulative volume distribution number of particles reaching 90% and 10% respectively in the particle size distribution curve.

[0089] In this application, the volume distribution particle sizes Dv90 and Dv10 of the graphite anode active material can be tested using methods known in the art. As an example, referring to GB / T 19077-2016, a laser particle size analyzer is used for determination. The testing instrument can be a Mastersizer 3000 laser particle size analyzer from Malvern Instruments Ltd., UK.

[0090] In some embodiments, the particle size distribution (Dv90-Dv10) / Dv50 of the graphite anode active material is a range of 1.0, 1.05, 1.1, 1.15, 1.2, 1.25, 1.3, 1.35, 1.4, 1.45, 1.5, 1.55, 1.6 or any two of these values.

[0091] Controlling the particle size distribution of graphite anode active materials within the aforementioned range is beneficial for improving the compactness of the graphite anode active materials and increasing the compaction density of the anode film. In other words, the cold pressing pressure required to achieve the same compaction density of the anode sheet is smaller, thereby reducing the probability of cracking of the graphite anode active materials during cold pressing and further improving the integrity of the graphite anode active materials during processing. Moreover, the low stress inside the graphite anode active material particles helps maintain the long-term pore structure of the electrode during cycling, maintaining the original pore structure of the electrode during cycling, keeping the lithium-ion intercalation path unobstructed, and reducing the re-forming of the graphite anode active material during charging, thus improving kinetic performance, cycle life, and storage stability. Furthermore, the particle size distribution within the aforementioned range can also improve the uniformity of lithium intercalation between graphite anode active material particles, reduce polarization, and avoid lithium plating caused by uneven current density, which is beneficial for achieving long-term cycle stability. In addition, the particle size distribution within the above range also helps to improve the processing performance of the electrode. It will not affect the uniformity of slurry mixing due to excessive small-diameter particles in the graphite negative electrode active material, which is conducive to improving the uniformity and stability of the electrode quality and helps to achieve long-cycle stability.

[0092] In some embodiments, the powder compaction density of the graphite anode active material at a pressure of 49000N is 1.75 g / cm³. 3 -1.88g / cm 3 The option is 1.78 g / cm³. 3 -1.84g / cm 3 .

[0093] In this article, the term "powder compaction density" refers to the mass of powder particles per unit volume under a given pressure.

[0094] In this application, the compaction density of the graphite anode active material powder under a pressure of 49000N can be tested using methods known in the art. As an example, referring to GB / T 24533-2009, 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, the pressure is increased to 5000 kg (equivalent to 49000 N), held for 30 s, then depressurized and held for 10 s. The compaction density of the graphite negative electrode active material under 49000 N pressure is determined by an electronic pressure testing machine (such as UTM7305 electronic pressure testing machine).

[0095] In some embodiments, the powder compaction density of the graphite anode active material under a pressure of 49000N can be selected as 1.75 g / cm³. 3 1.78g / cm 3 1.82g / cm 31.84 g / cm 3 1.85g / cm 3 1.88g / cm 3 Or the range of values ​​between any two.

[0096] Graphite anode active materials with a powder compaction density within the above range are more likely to maintain high particle integrity during cold pressing, which helps improve the cycle life of secondary batteries.

[0097] In some embodiments, the tap density of the graphite anode active material is 1.05 g / cm³. 3 -1.30g / cm 3 .

[0098] In this paper, the term "tapered density" refers to the mass per unit volume of powder in a container after it has been tapped under specified conditions.

[0099] In this application, the tap density of the graphite anode active material can be tested using methods known in the art. As an example, it can be determined using a powder tap density tester according to GB / T 5162-2006. The testing instrument can be Dandong Baite BT-301, with the following test parameters: vibration frequency 250±15 times / minute, amplitude 3±0.2mm, number of vibrations 5000 times, and a 25mL graduated cylinder.

[0100] In some embodiments, the tap density of the graphite anode active material is 1.05 g / cm³. 3 1.10 g / cm 3 1.15g / cm 3 1.20g / cm 3 1.25g / cm 3 1.30g / cm 3 Or the range of values ​​between any two.

[0101] In some embodiments, the specific capacity of the graphite anode active material is 345mAh / g-355mAh / g, and can be selected as 347mAh / g-353mAh / g.

[0102] In this article, the term "specific capacity" refers to the ratio of the electrical capacity that an active material can release to the mass of the active material.

[0103] In this application, the specific capacity of the graphite anode active material can be tested using methods known in the art. As an example, a graphite anode active material sample is thoroughly mixed with conductive agent 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, a lithium metal sheet is used as the counter electrode, and a polypropylene (PP) film is used as the separator. An electrolyte is then 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.

[0104] In some embodiments, the specific capacity of the graphite anode active material is 345 mAh / g, 346 mAh / g, 347 mAh / g, 348 mAh / g, 349 mAh / g, 350 mAh / g, 351 mAh / g, 352 mAh / g, 353 mAh / g, 354 mAh / g, 355 mAh / g, or any value between the two.

[0105] Graphite anode active materials with a specific capacity within the above-mentioned range will not experience significant lattice expansion due to excessive graphitization during charge and discharge, nor will they be difficult to compact due to excessive graphitization. To achieve the same electrode compaction density, higher cold pressing pressure is required, which may lead to cracking during cold pressing and excessive consumption of active lithium by creating new interfaces during cycling. This will comprehensively improve the cycle life of the secondary battery.

[0106] In some embodiments, the graphite anode active material I D / I G It is 0.05-0.10, where I D / I G I represents the ratio of the intensity of the D peak to the intensity of the G peak obtained from the Raman spectrum. D This indicates that the Raman spectrum is at 1350±100 cm⁻¹ -1 D peak intensity at I GThis indicates that the Raman spectrum is at 1580±100 cm⁻¹ -1 The intensity of the G peak at that location.

[0107] In this application, the graphite anode active material I D / I G Any known mode of Raman spectroscopy can be used for testing. As an example, referring to GB / T 40219-2021, an InVia Qontor (Reflex) Raman spectrometer is used for testing; a 523nm solid-state laser is used as the light source, and 100 points are sampled in a 100μm × 100μm region. I0 D / I G The median, which is the median of the collected I values ​​arranged in ascending order. D / I G The number that is in the middle of the data.

[0108] In some embodiments, the graphite anode active material I D / I G The value is 0.05, 0.06, 0.07, 0.08, 0.09, 0.10, or any two of these values.

[0109] Unlike active materials that have amorphous carbon coated onto the surface of graphite particles, the graphite anode active material provided in this application has both amorphous carbon on its surface and low surface disorder. In active materials with amorphous carbon coated onto the surface of graphite particles, the amorphous carbon typically originates from the coated organic resin, which generates amorphous carbon under low-temperature carbonization, resulting in high surface disorder in the coating layer. However, the surface and internal regions of the graphite anode active material provided in this application are both derived from the same precursor and undergo the same heat treatment process. Therefore, the amorphous carbon in this graphite anode active material is uniformly distributed in the surface region, resulting in a low crystalline carbon content and low surface disorder in the surface region. This allows graphite anode active materials to leverage the advantages of amorphous carbon, improving battery kinetic performance and reducing electrode cycle expansion rate. It also prevents excessive side reactions and significant capacity reduction due to the high disorder on the surface of graphite anode active materials, thus comprehensively improving battery cycle stability.

[0110] In some embodiments, the interlayer spacing of the surface region of the graphite anode active material is denoted as d1, and the interlayer spacing of the internal region of the graphite anode active material is denoted as d2, wherein the graphite anode active material satisfies d1>d2; optionally, 0.3365nm≤d1≤0.3378nm; optionally, 0.3358nm≤d2≤0.3364nm.

[0111] In this paper, the term "interlayer spacing" refers to the shortest distance between two adjacent carbon atoms in the same carbon layer of graphite.

[0112] In this application, the interlayer spacing of different regions of the graphite anode active material can be tested using instruments and methods known in the art. For example, a high-resolution transmission electron microscope (HRTEM) can be used. The testing instrument can be a Thermo Fisher Scientific Spectra S / TEM scanning transmission electron microscope.

[0113] In some embodiments, the interlayer spacing d1 of the surface region of the graphite anode active material can be selected as 0.3365 nm, 0.3367 nm, 0.3369 nm, 0.3371 nm, 0.3372 nm, 0.3373 nm, 0.3375 nm, 0.3378 nm, or any value range between two values. In some embodiments, the interlayer spacing d2 of the internal region of the graphite anode active material can be selected as 0.3358 nm, 0.3359 nm, 0.3361 nm, 0.3363 nm, 0.3364 nm, or any value range between two values.

[0114] The interlayer spacing of the surface region is higher than that of the internal region of the graphite anode active material, which can act as a lithium intercalation buffer layer, improve the wettability of the electrolyte to the graphite anode active material, and enhance the fast charging performance of the battery.

[0115] In some embodiments, the graphite anode active material includes both primary and secondary particles; optionally, based on the total number of primary and secondary particles in the graphite anode active material, the proportion of secondary particles is less than or equal to 50%.

[0116] In this paper, the term "primary particle" refers to a non-agglomerated particle.

[0117] In this paper, the term "secondary particle" refers to an aggregated particle composed of two or more primary particles.

[0118] Primary and secondary particles can be distinguished by observing the cross-section of the graphite anode active material using a scanning electron microscope (SEM). In this application, the proportion of secondary particles in the graphite anode active material can be tested using methods known in the art. As an example, the cross-section of the anode sheet can be prepared using a cross-section polisher (e.g., the IB-09010CP argon ion cross-section polisher from JEOL, Japan); then, referring to JY / T010-1996, the cross-section of the anode sheet is scanned using a scanning electron microscope (e.g., the Sigma 300 scanning electron microscope from ZEISS, Germany). Multiple test areas are randomly selected in the test sample, and images of multiple test areas are obtained using a scanning electron microscope. The proportion of the number of graphite anode active materials with secondary particle morphology in each image is counted to the total number of graphite anode active material particles. The average of the multiple statistical results is the proportion of secondary particles in the graphite anode active material.

[0119] In some implementations, the percentage of secondary particles can be selected as 50%, 40%, 30%, 20%, 10%, or any value between the two, based on the total number of primary and secondary particles in the graphite anode active material.

[0120] Graphite anode active materials with a low proportion of secondary particles are beneficial for maintaining the particle integrity of the graphite anode active material during battery fabrication, reducing the formation of new interfaces, decreasing the consumption of active lithium during cycling, and further improving the cycle stability of the secondary battery. Simultaneously, a certain number of secondary particles can reduce anode sheet expansion while maintaining the kinetic performance of the secondary battery, thus enabling the cell to have a full life-cycle kinetic window. This prevents lithium plating caused by uneven current distribution from leading to a sharp decline in battery capacity and lifespan, comprehensively improving the battery's cycle stability.

[0121] A second aspect of this application provides a method for preparing a graphite anode active material, comprising the following steps: providing raw materials; processing the raw materials to obtain an intermediate product; graphitizing the intermediate product to obtain a graphitized product; and sieving the graphitized product to obtain a graphite anode active material. The particle body of the graphite anode active material includes an internal region and a surface region that at least partially surrounds the internal region. The surface region refers to the region extending 30 nm from the surface of the particle body of the graphite anode active material into the particle interior. The mass percentage of crystalline carbon in the internal region is denoted as η1, and the mass percentage of crystalline carbon in the surface region is denoted as η2, and 10% ≤ η1 - η2 ≤ 35%.

[0122] 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.

[0123] In some implementations, the maximum power of the graphitization process is 70%-90% of the rated power of the graphitization process equipment.

[0124] In some implementations, the power of the graphitization process can be selected as 70%, 75%, 80%, 85%, 90% of the rated power of the equipment or any range between the two.

[0125] It can be understood that graphitization equipment refers to any device capable of performing graphitization processes, including but not limited to Atchison furnaces, box furnaces, internal furnaces, continuous graphitization furnaces, electric forging furnaces, medium-frequency furnaces, and tube furnaces. The rated power of graphitization equipment produced by different manufacturers may vary; you can select the appropriate device based on your specific needs.

[0126] The graphitization power used in this application needs to be lower than the rated power of the graphitization equipment to achieve uniformity of the temperature field during the graphitization process. This ensures the consistency of the material's specific capacity, which is beneficial for improving the battery's cycle life.

[0127] In some implementations, the graphitization equipment is an internal furnace with a rated power of 25000W-32000W.

[0128] In some implementations, the graphitization equipment is an Atchison furnace with a rated power of 28,000W-30,000W.

[0129] In some embodiments, the graphitization temperature is 2600°C to 3000°C.

[0130] In some embodiments, the graphitization temperature is 2600°C, 2700°C, 2800°C, 2900°C, 3000°C, or any value between two of these.

[0131] In some implementations, the graphitization process takes 10 to 50 hours.

[0132] In some implementations, the graphitization time is 10h, 15h, 20h, 25h, 30h, 35h, 40h, 45h, 50h, or any range between the two.

[0133] In some implementations, the graphitization equipment is an internal furnace, and the graphitization process is carried out at maximum power for 10-30 hours.

[0134] In some implementations, the graphitization equipment is an Atchison furnace, and the graphitization process is carried out at maximum power for 30-50 hours.

[0135] In some embodiments, the raw material includes at least one of petroleum coke, needle coke, and pitch coke, and may be needle coke.

[0136] In this article, the term "petroleum coke" refers to the coke formed after petroleum residue or petroleum asphalt has undergone high-temperature carbonization.

[0137] 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.

[0138] In this article, the term "asphalt coke" refers to the solid material generated after coal tar pitch is carbonized at high temperature.

[0139] In some embodiments, the volume percentage of fibrous structures in the raw material is greater than or equal to 55%, and can be selected as 58%-70%.

[0140] In this article, "fibrous structure" also known as streamlined structure refers to the structure with obvious fibrous texture observed in the raw material under a microscope.

[0141] Based on the morphological characteristics and isochromatic area size of the coke under a polarizing microscope, its microstructure can generally be classified into mosaic, regional, and fibrous types. Typically, 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.

[0142] In this application, the volume ratio of fiber structure in the raw material can be tested using methods known in the art. As an example, the raw material is taken according to GB 1997-89, and the raw material crushed to 1mm is mixed evenly 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 measuring 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 intersection of the crosshairs is determined, and the volume content of the fibrous structure in the raw material is obtained by dividing the effective number of measurement points of the fibrous optical structure by the total number of measurement points.

[0143] In some embodiments, based on the total volume of the raw material structure, the volume percentage of the raw material fiber structure can be selected as 55%, 58%, 60%, 63%, 65%, 68%, 70%, or any value range between the two.

[0144] Raw materials with a high proportion of fibrous structure are beneficial for improving the compaction density and specific capacity of graphite anode active materials, allowing the graphite anode active material to retain high integrity during compaction. This results in batteries with both high cycle life and good energy density. However, an excessively high proportion of fibrous structure increases the cost and expansion rate of graphite anode active materials, and deteriorates kinetic performance. Raw materials with a fibrous structure volume ratio within the aforementioned range offer both lower cost and good specific capacity, providing the cell with a full life cycle kinetic window, thereby comprehensively improving the battery's long-term cycle life and electrochemical performance.

[0145] In some implementations, the maximum specific capacity achievable by the raw material is greater than that of the graphite anode active material.

[0146] By using high-grade raw materials and controlling the degree of graphitization, the maximum achievable capacity of the raw materials is not fully utilized. This results in the crystalline carbon mass percentage in the surface region of the graphite anode active material being lower than that in the internal region, thereby reducing the cyclic expansion of the graphite anode active material and improving its cyclic stability.

[0147] In some embodiments, the processing of raw materials specifically includes: crushing, shaping, and classifying the raw materials to obtain a first precursor; granulating the first precursor to obtain a second precursor; and low-temperature carbonizing a mixture of the first precursor and the second precursor to obtain the intermediate product.

[0148] Crushing is the process of reducing the particle size of raw materials, which can be done by any mechanical device such as a crusher or a mechanical mill.

[0149] Shaping and grading is a process of adjusting the particle size distribution of raw materials to obtain a first precursor that meets the particle size requirements. The particle size and particle size distribution of the first precursor can be controlled by adjusting the grading frequency and the air intake. In some embodiments, the grading frequency is 40Hz-50Hz and the damper opening is 20%-70%.

[0150] It is understood that obtaining an intermediate product by low-temperature carbonization of the first precursor and the second precursor includes obtaining an intermediate product by low-temperature carbonization of a mixture of the first precursor and the second precursor; it also includes obtaining the first intermediate product and the second intermediate product by low-temperature carbonization of the first precursor and the second precursor, respectively. In some embodiments, the Dv50 particle size of the first precursor is 6.0 μm to 10.0 μm.

[0151] In some embodiments, the Dv50 particle size of the first precursor is 6.0 μm, 7.0 μm, 8.0 μm, 9.0 μm, 10.0 μm or any value between two of these.

[0152] In some embodiments, the particle size distribution (Dv90-Dv10) / Dv50 of the first precursor is 1.05-1.75.

[0153] In some embodiments, the particle size distribution (Dv90-Dv10) / Dv50 of the first precursor is a range of 1.05, 1.15, 1.25, 1.35, 1.45, 1.55, 1.65, 1.75 or any two of these values.

[0154] In some embodiments, the tap density of the first precursor is 0.5 g / cm³. 3 ~0.7g / cm 3 .

[0155] In some embodiments, the tap density of the first precursor is 0.5 g / cm³. 3 0.55g / cm 3 0.6g / cm 3 0.65g / cm 3 0.7g / cm 3 Or the range of values ​​between any two.

[0156] In some embodiments, the Dv50 particle size of the second precursor is 11.0 μm to 15.0 μm.

[0157] In some embodiments, the Dv50 particle size of the second precursor is 11.0 μm, 12.0 μm, 13.0 μm, 14.0 μm, 15.0 μm or any value range between the two.

[0158] The second precursor is obtained by granulation of the first precursor. Therefore, the second precursor mainly forms secondary particles in the graphite anode active material.

[0159] Controlling the particle size of the first and second precursors helps to regulate the particle size and particle size distribution of graphite anode active materials, thereby improving the cycle stability of the battery.

[0160] In some embodiments, the low-temperature carbonization temperature is 900℃-1300℃, and the low-temperature carbonization time is 24h-240h.

[0161] In some embodiments, the temperature for low-temperature carbonization can be selected as 900°C, 1000°C, 1100°C, 1200°C, 1300°C, or any value range between the two.

[0162] In some implementations, the low-temperature carbonization time can be selected as 24h, 50h, 75h, 100h, 150h, 200h, 240h or any range between the two.

[0163] [Negative electrode plate]

[0164] In some embodiments, 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. For example, the negative current collector has two surfaces opposite each other in its thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative current collector.

[0165] In some embodiments, the negative electrode film layer includes the graphite negative electrode active material of the first aspect of the present application or the graphite negative electrode active material prepared by the method of the second aspect of the present application, thereby enabling the secondary battery to have high initial coulombic efficiency, high energy density and good cycle performance.

[0166] In some embodiments, the compaction density of the negative electrode film is 1.5 g / cm³. 3 ~1.65g / cm 3 .

[0167] In this application, the compaction density of the negative electrode film can be tested using methods known in the art. As an example, an electronic balance is used to weigh a negative electrode sample with an area of ​​S, the weight of which is recorded as W1, and the thickness T1 of the negative electrode is measured using a micrometer. Then, the weighed electrode film is wiped off, the weight of the negative current collector is measured, recorded as W2, and the thickness T2 of the negative current collector is measured using a micrometer. The compaction density of the negative electrode film is then calculated as PD = (W1 - W2) / [(T1 - T2) × S].

[0168] In some embodiments, the compaction density of the negative electrode film is 1.5 g / cm³. 3 1.55g / cm 3 1.6g / cm 3 1.65g / cm 3 Or the range of values ​​between any two.

[0169] 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, other 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.

[0170] In some embodiments, the negative electrode film layer may optionally include a negative electrode conductive agent. This application does not impose any particular limitation on the type of negative electrode conductive agent. As an example, the negative electrode conductive agent may include one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0171] In some embodiments, the negative electrode film layer may optionally include a negative electrode binder. This application does not impose any particular limitation on the type of negative electrode binder. As an example, the negative electrode binder may include one or more of the following: styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, waterborne acrylic resins (e.g., polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS).

[0172] In some embodiments, the negative electrode film may optionally include other additives. As an example, other additives may include thickeners, such as sodium carboxymethyl cellulose (CMC), PTC thermistor materials, etc.

[0173] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. As an example of a metal foil, copper foil may be used. The composite current collector may include a polymeric material substrate and a metal material layer formed on at least one surface of the polymeric material substrate. As an example, the metal material may include one or more of copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. As an example, the polymeric material substrate may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0174] The negative electrode film layer is typically formed by coating a negative electrode slurry onto a negative electrode current collector, followed by drying and cold pressing. The negative electrode slurry is typically formed by dispersing the negative electrode active material, optional conductive agent, optional binder, and other optional additives in a solvent and stirring until homogeneous. The solvent can be N-methylpyrrolidone (NMP) or deionized water, but is not limited to these.

[0175] The negative electrode sheet does not exclude other additional functional layers besides the negative electrode film layer. For example, in some embodiments, the negative electrode sheet of this application further includes a conductive undercoat layer (e.g., composed of a conductive agent and an adhesive) sandwiched between the negative electrode current collector and the negative electrode film layer and disposed on the surface of the negative electrode current collector; in some embodiments, the negative electrode sheet of this application further includes a protective layer covering the surface of the negative electrode film layer.

[0176] [Positive electrode plate]

[0177] In some embodiments, 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. For example, the positive current collector has two surfaces opposite each other in its thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0178] The positive electrode current collector can be a metal foil or a composite current collector. As an example of a metal foil, aluminum foil can be used. The composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material may include one or more of aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. As an example, the polymer material base layer may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0179] The positive electrode film layer generally includes a positive electrode active material, an optional binder, and an optional conductive agent. The positive electrode film layer is generally formed by coating a positive electrode slurry on the positive electrode current collector and then drying and cold pressing. The positive electrode slurry is generally formed by dispersing a positive electrode active material, an optional conductive agent, an optional binder, and any other components in a solvent and stirring evenly. The solvent can be N-methylpyrrolidone (NMP), but is not limited thereto. As an example, the binder used for the positive electrode film layer may include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin. As an example, the conductive agent used for the positive electrode film layer includes one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0180] The positive electrode active material can adopt the positive electrode active materials for secondary batteries well-known in the art.

[0181] When the secondary battery of the present application is a lithium-ion battery, the positive electrode active material may include, but is not limited to, one or more of lithium-containing transition metal oxides, lithium-containing phosphates, and their respective modified compounds. Examples of the lithium transition metal oxides may include, but are not limited to, one or more of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and their respective modified compounds. Examples of the lithium-containing phosphates may include, but are not limited to, lithium iron phosphate, a composite material of lithium iron phosphate and carbon, lithium manganese phosphate, a composite material of lithium manganese phosphate and carbon, lithium manganese iron phosphate, a composite material of lithium manganese iron phosphate and carbon, and their respective modified compounds.

[0182] In some embodiments, in order to further improve the energy density of the secondary battery, the positive electrode active material for the lithium-ion battery may include a lithium transition metal oxide having the general formula Li a Ni b Co c M d O e A f and its 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.

[0183] In some embodiments, as an example, the positive electrode active material for lithium-ion batteries may include 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 One or more of O2, LiFePO4 and LiMnPO4.

[0184] In this application, the modified compounds of the above-mentioned positive electrode active materials may be those that have undergone doping modification and / or surface coating modification of the positive electrode active materials.

[0185] [Electrolytes]

[0186] In some embodiments, the electrolyte is an electrolyte solution comprising an electrolyte salt and a solvent.

[0187] The type of electrolyte salt is not specifically limited and can be selected according to actual needs.

[0188] When the secondary battery of this application is a lithium-ion battery, as an example, the electrolyte salt may include one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalate borate (LiDFOB), lithium dioxalate borate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorodioxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP).

[0189] The type of solvent is not specifically limited and can be selected according to actual needs. In some embodiments, as an example, the solvent may include one or more of the following: ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butyl ester carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE).

[0190] In some embodiments, the electrolyte may optionally include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain performance characteristics of the secondary battery, such as additives that improve the overcharge performance of the secondary battery, additives that improve the high-temperature performance of the secondary battery, and additives that improve the low-temperature power performance of the secondary battery.

[0191] [Isolation membrane]

[0192] This application does not impose any particular restrictions on the type of separator membrane; any known porous separator membrane with good chemical and mechanical stability can be selected.

[0193] In some embodiments, the material of the separator may include one or more of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may be a single-layer film or a multi-layer composite film. When the separator is a multi-layer composite film, the materials of each layer may be the same or different.

[0194] In some embodiments, the positive electrode, the separator, and the negative electrode can be fabricated into an electrode assembly using a winding process or a stacking process.

[0195] Secondary batteries

[0196] The fourth aspect of this application provides a secondary battery.

[0197] This application does not impose any particular limitation on the type of secondary battery; for example, the secondary battery can be a lithium-ion battery. Typically, a secondary battery includes a positive electrode, a negative electrode, and an electrolyte. During the charging and discharging process of the secondary battery, active ions repeatedly insert and extract between the positive and negative electrode, and the electrolyte acts as a conductor for these active ions. This application does not impose any particular limitation 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). Secondary batteries using electrolyte solutions, and some secondary batteries using solid electrolytes, may also include a separator membrane disposed between the positive and negative electrode to provide isolation.

[0198] 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.

[0199] In some embodiments, the outer packaging may be a hard shell, such as a hard plastic shell, aluminum shell, steel shell, etc. The outer packaging may also be a flexible package, such as a pouch. The material of the flexible package may be plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0200] 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. Figure 2 This is an example of a square-structured secondary battery 5.

[0201] In some embodiments, such as Figure 3 As shown, 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 is used to cover the opening to close the receiving cavity. The positive electrode, negative electrode, and separator may be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated in 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 adjusted according to requirements.

[0202] The method for preparing the secondary battery described in this application is well known. In some embodiments, a positive electrode, a separator, a negative electrode, and an electrolyte can be assembled to form a secondary battery. As an example, the positive electrode, separator, and negative electrode can be formed into an electrode assembly through a winding or stacking process. The electrode assembly is then placed in an outer packaging, dried, and injected with an electrolyte. After vacuum sealing, settling, formation, and shaping, a secondary battery is obtained.

[0203] In some embodiments of this application, the secondary battery according to this application can be assembled into a battery module. The number of secondary batteries contained in the battery module can be multiple, and the specific number can be adjusted according to the application and capacity of the battery module.

[0204] Figure 4 This is a schematic diagram of battery module 4 as an example. Figure 4 As shown, 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.

[0205] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of secondary batteries 5 are received.

[0206] 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 adjusted according to the application and capacity of the battery pack.

[0207] Figure 5 and Figure 6 This is a schematic diagram of battery pack 1 as an example. Figure 5 and Figure 6 As shown, 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. The upper body 2 covers the lower body 3, forming a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0208] Electrical appliances

[0209] This application also provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack described 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 be, but is not limited to, mobile devices (e.g., mobile phones, tablets, 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.

[0210] The electrical device can be equipped with a secondary battery, battery module, or battery pack according to its usage requirements.

[0211] Figure 7This is a schematic diagram of an example electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the device's requirements for high power and high energy density, a battery pack or battery module can be used.

[0212] Another example of an electrical device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use rechargeable batteries as their power source.

[0213] Example

[0214] The following embodiments describe the disclosure of this application in more detail. These embodiments are merely illustrative, as various modifications and variations will be apparent to those skilled in the art within the scope of the disclosure of this application. Unless otherwise stated, all parts, percentages, and ratios reported in the following embodiments are based on mass, and all reagents used in the embodiments are commercially available or synthesized by conventional methods and can be used directly without further processing, and the instruments used in the embodiments are commercially available.

[0215] Example 1

[0216] (1) Preparation of graphite anode active material

[0217] Needle coke with a fiber structure accounting for 60.8% was crushed; the crushed material was shaped and fine powder was removed to obtain the first precursor. The first precursor had a Dv50 particle size of 9.1 μm, a particle size distribution (Dv90-Dv10) / Dv50 of 1.35, and a tap density of 0.67 g / cm³. 3 .

[0218] A portion of the first precursor was granulated and reformed in a reactor to obtain a second precursor with a particle size Dv50 of 14.4 μm.

[0219] The ungranulated first and second precursors were placed in a kiln for carbonization at a temperature of 1150℃ for 24 hours to obtain the first and second intermediate products, respectively.

[0220] The first and second intermediate products were placed in an inner furnace and graphitized at 2800°C. The rated power of the inner furnace was 28000W, and the maximum power of the graphitization process was 22400W, which was 80% of the rated power of the equipment. The maximum power was maintained for 25 hours to obtain primary and secondary particles, respectively.

[0221] The primary and secondary particles are mixed evenly at a mass ratio of 1:1, and then sieved to remove magnetism to obtain graphite anode active material.

[0222] The graphite anode active material has a crystalline carbon mass percentage (η1) of 87% in its internal region and 65% (η2) in its surface region, with η1-η2=22%. Its graphitization degree is 92.97%, and its specific surface area is 1.49 m². 2 The powder has a volumetric particle size distribution (Dv50) of 10.5 μm and a compacted density of 1.78 g / cm³ under a pressure of 49000 N. 3 The capacity is 350.2 mAh / g, I D / I G The interlayer spacing d1 in the surface region is 0.3373 nm, the interlayer spacing d2 in the inner region is 0.3360 nm, and the particle size distribution (Dv90-Dv10) / Dv50 is 1.36.

[0223] (2) Preparation of negative electrode sheet

[0224] The graphite anode active material, conductive agent Super P, thickener sodium carboxymethyl cellulose (CMC-Na), 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, yielding an anode slurry. This slurry was then uniformly coated onto a copper foil current collector, and after drying, cold pressing, and slitting, the anode sheet was obtained. The compaction density of the anode film was 1.60 g / cm³. 3 Its surface density is 9.48 mg / cm³. 2 .

[0225] (3) Preparation of positive electrode sheet

[0226] Lithium iron phosphate (LFP) as the positive electrode active material, Super P as the conductive agent, and polyvinylidene fluoride (PVDF) as the binder were mixed at a mass ratio of 97:1:2. N-methylpyrrolidone (NMP) 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 after drying, cold pressing, and slitting, positive electrode sheets were obtained. The compaction density of the positive electrode film was 2.50 g / cm³. 3 Its surface density is 19.48 mg / cm³. 2 .

[0227] (4) Preparation of electrolyte

[0228] In an argon atmosphere glove box with a water content of <10ppm, diethyl carbonate (DEC), methyl ethyl carbonate (EMC), and ethylene carbonate (EC) were mixed in a weight 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 1.0 mol / L. Ethylene carbonate (VC) was then added, with the VC content being 2% of the total mass of the electrolyte.

[0229] (5) Preparation of the separating membrane

[0230] Polypropylene film is used as the separator.

[0231] (6) Preparation of lithium-ion batteries

[0232] 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.

[0233] Examples 2-8

[0234] The preparation method is basically the same as in Example 1, except that the raw material structure or preparation process is adjusted, thereby adjusting the crystallinity of the internal and / or surface regions of the graphite anode active material. The specific preparation parameters are shown in Table 1.

[0235] Table 1

[0236]

[0237] Comparative Example 1

[0238] The preparation methods of Comparative Example 1 and Example 1 are basically the same, except that the maximum power of graphitization treatment is 28000W (rated power of the equipment) and the constant power duration at the maximum power is 35h. The surface region of the prepared graphite negative electrode active material particles does not have a disordered layer.

[0239] Comparative Example 2

[0240] The preparation method is basically the same as that of Comparative Example 1, except that carbon coating treatment is performed on the surface of the graphite negative electrode active material prepared in Comparative Example 1. Specifically, the material obtained in Comparative Example 1 is mixed with a coating agent (asphalt) at a ratio of 100%:3%, and the mixed product is subjected to carbonization treatment at a temperature of 1100℃ for 2 hours. After the material cools to room temperature, it is sieved and demagnetized to obtain the finished material.

[0241] Performance testing

[0242] (1) Cold-pressed rebound rate test of negative electrode sheet

[0243] The thickness of the negative electrode sheet after cold pressing is L0. After placing the cold-pressed negative electrode sheet in an environment of 25℃ and 10% humidity for 24 hours, the thickness of the negative electrode sheet is tested and it is L1. The cold pressing rebound rate V0 of the negative electrode sheet is calculated by the following formula: V0=(L1-L0) / L0.

[0244] (2) Cyclic expansion rate test of negative electrode sheet

[0245] The thickness of the cold-pressed negative electrode sheet in each embodiment and comparative example is denoted as L0. Secondary batteries prepared in each embodiment and comparative example are subjected to charge-discharge tests at 25°C. They are discharged at a constant current of 1.0C (the current value at which the theoretical capacity is completely discharged within 1 hour) to 2.5V. Then, they are charged at a constant current of 1.0C to 3.65V, and then charged at a constant voltage until the current is 0.05C. After the fully charged cell is left to stand for 5 minutes, it is discharged at a constant current of 1.0C to 2.5V. The discharge capacity at this point is denoted as C0. The secondary battery is charged to 3.65V at 25°C, the secondary battery is disassembled, and the thickness of the negative electrode sheet at this point is measured and denoted as L2. The cyclic expansion rate of the negative electrode sheet is then calculated as: (L2-L0) / L0×100%.

[0246] (3) Cyclic stability test

[0247] 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.

[0248] Test Results

[0249] As shown in Table 2, graphite anode active materials with a difference of 10%-35% in the mass percentage of crystalline carbon between the internal and surface regions can improve battery cycle performance.

[0250] Table 2

[0251]

[0252] As shown in Table 3, when 80% ≤ η1 < 95%, the battery can achieve both good specific capacity and long cycle life.

[0253] Table 3

[0254]

[0255] As shown in Table 4, when 60%≤η2≤70%, the battery achieves a balance between low cold-press rebound rate, cycle expansion rate, and excellent cycle life.

[0256] Table 4

[0257]

[0258] 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 particle body includes an internal region and a surface region that at least partially surrounds the internal region. The surface region refers to the region formed by extending 30 nm from the surface of the graphite anode active material particle body into the particle. The mass percentage of crystalline carbon in the internal region is denoted as η1, and the mass percentage of crystalline carbon in the surface region is denoted as η2, and 10%≤η1-η2≤35%.

2. The graphite anode active material according to claim 1, characterized in that, 75%≤η1≤99%.

3. The graphite anode active material according to claim 2, characterized in that, 80%≤η1≤95%.

4. The graphite anode active material according to claim 1, characterized in that, 55%≤η2≤75%.

5. The graphite anode active material according to claim 4, characterized in that, 60%≤η2≤70%.

6. The graphite anode active material according to any one of claims 1 to 5, characterized in that, The degree of graphitization of the graphite anode active material is 88%-95%.

7. The graphite anode active material according to claim 6, characterized in that, The graphitization degree of the graphite anode active material is 90%-95%.

8. The graphite anode active material according to any one of claims 1 to 5, characterized in that, The volume distribution particle size Dv50 of the graphite anode active material is 7.5 μm-14.5 μm.

9. The graphite anode active material according to claim 8, characterized in that, The volume distribution particle size Dv50 of the graphite anode active material is 8.5μm-12.5μm.

10. The graphite anode active material according to any one of claims 1 to 5, characterized in that, The graphite anode active material satisfies at least one of the following: (1) The specific surface area of ​​the graphite anode active material is 1.25 m². 2 / g-1.95m 2 / g; (2) The particle size distribution (Dv90-Dv10) / Dv50 of the graphite negative electrode active material is 1.0-1.6; (3) The compacted density of the graphite anode active material under a pressure of 49000N is 1.75 g / cm³. 3 -1.88g / cm 3 ; (4) The tap density of the graphite anode active material is 1.05 g / cm³. 3 -1.30g / cm 3 ; (5) The specific capacity of the graphite negative electrode active material is 345mAh / g-355mAh / g; (6) The graphite anode active material I D / I G It is 0.05-0.10, where I D / I G I represents the ratio of the intensity of the D peak to the intensity of the G peak obtained from the Raman spectrum. D This indicates that the Raman spectrum is at 1350±100 cm⁻¹ -1 The intensity of peak D at I G This indicates that the Raman spectrum is at 1580±100 cm⁻¹ -1 The intensity of the G peak at that location; (7) The interlayer spacing of the surface region of the graphite anode active material is denoted as d1, and the interlayer spacing of the internal region of the graphite anode active material is denoted as d2. The graphite anode active material satisfies d1>d2. (8) The graphite negative electrode active material includes both primary particles and secondary particles.

11. The graphite anode active material according to claim 10, characterized in that, The graphite anode active material satisfies at least one of the following: (1) The specific surface area of ​​the graphite anode active material is 1.35 m². 2 / g-1.75m 2 / g; (2) The particle size distribution (Dv90-Dv10) / Dv50 of the graphite negative electrode active material is 1.1-1.5; (3) The compacted density of the graphite anode active material under a pressure of 49000N is 1.78 g / cm³. 3 -1.84g / cm 3 ; (4) The specific capacity of the graphite negative electrode active material is 347mAh / g-353mAh / g; (5) The interlayer spacing of the surface region of the graphite anode active material is denoted as d1, and the interlayer spacing of the internal region of the graphite anode active material is denoted as d2. The graphite anode active material satisfies d1>d2 and 0.3365nm≤d1≤0.3378nm; (6) The interlayer spacing of the surface region of the graphite anode active material is denoted as d1, and the interlayer spacing of the internal region of the graphite anode active material is denoted as d2. The graphite anode active material satisfies d1>d2 and 0.3365nm≤d1≤0.3378nm; (7) The graphite anode active material includes both primary particles and secondary particles; based on the total number of primary and secondary particles in the graphite anode active material, the proportion of secondary particles is less than or equal to 50%.

12. 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 intermediate products; The intermediate product is subjected to graphitization treatment to obtain the graphitized product; The graphitized product is sieved to obtain a graphite anode active material; The graphite anode active material particle body includes an internal region and a surface region that at least partially surrounds the internal region. The surface region refers to the region formed by extending 30 nm from the surface of the graphite anode active material particle body into the particle. The mass percentage of crystalline carbon in the internal region is denoted as η1, and the mass percentage of crystalline carbon in the surface region is denoted as η2, and 10%≤η1-η2≤35%.

13. The preparation method according to claim 12, characterized in that, The graphitization process satisfies at least one of the following conditions: (1) The maximum power of the graphitization process is 70%-90% of the rated power of the graphitization process equipment; (2) The temperature of the graphitization treatment is 2600℃~3000℃; (3) The graphitization treatment time is 10h~50h.

14. The preparation method according to claim 12, characterized in that, The raw materials include one or more of petroleum coke, needle coke, and pitch coke.

15. The preparation method according to claim 14, characterized in that, The raw materials include needle coke.

16. The preparation method according to claim 14, characterized in that, Based on the total volume of the raw material, the volume percentage of the fibrous structure in the raw material is greater than or equal to 55%.

17. The preparation method according to claim 16, characterized in that, Based on the total volume of the raw material, the volume percentage of the fibrous structure in the raw material is 58%-70%.

18. The preparation method according to any one of claims 12 to 17, characterized in that, The processing of the raw materials specifically includes the following steps: The raw materials are crushed, shaped, and graded to obtain a first precursor. The precursor is granulated to obtain a second precursor; The first precursor and the second precursor are carbonized at low temperature to obtain the intermediate product.

19. A negative electrode sheet, characterized in that, The negative electrode sheet comprises the graphite negative electrode active material according to any one of claims 1 to 11 or the graphite negative electrode active material prepared by the preparation method according to any one of claims 12 to 18.

20. The negative electrode sheet according to claim 19, characterized in that, 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, wherein the compaction density of the negative electrode film layer is 1.5 g / cm³. 3 ~1.65g / cm 3 .

21. A secondary battery, characterized in that, Includes the negative electrode sheet as described in claim 19 or 20.

22. An electrical appliance, characterized in that, Includes the secondary battery as described in claim 21.

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