Carbon-based negative active material, method of preparation, secondary battery, and electric device

Abstract

The application provides a carbon-based negative electrode active material, a preparation method, a secondary battery and an electric device, the carbon-based negative electrode active material has a specific capacity of 345 mAh / g-355 mAh / g, and a powder compaction density under a pressure of 20000 N is 1.55 g / cm 3 and less than 1.65 g / cm 3 . The secondary battery prepared from the carbon-based negative electrode active material has good cycle performance and high energy density.

Description

Technical Field

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

[0002] In recent years, secondary batteries have been increasingly 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, and aerospace. The market has also put forward higher requirements for the service life and energy storage performance of secondary batteries.

[0003] Negative electrode active materials are one of the important raw materials for secondary batteries and have a significant impact on their electrical performance. To meet increasingly demanding market requirements, it is necessary to provide a new type of negative electrode active material to improve the cycle performance of secondary batteries. Summary of the Invention

[0004] This application provides a carbon-based anode active material, wherein the specific capacity of the carbon-based anode active material is 345 mAh / g to 355 mAh / g, and the powder compaction density under 20000 N pressure is 1.55 g / cm³. 3 Above and less than 1.65 g / cm 3 The secondary battery prepared from the carbon-based anode active material exhibits both good cycle performance and high energy density.

[0005] In any embodiment, the powder compaction density of the carbon-based negative electrode active material under a pressure of 20000N is 1.57 g / cm³. 3 ~1.62g / cm 3 .

[0006] In any embodiment, the powder compaction density of the carbon-based anode active material at a pressure of 49000N is 1.73 g / cm³. 3 Above and less than 1.84 g / cm 3 Carbon-based anode active materials within the aforementioned range are beneficial for improving the cycle performance of secondary batteries.

[0007] In any embodiment, the specific capacity of the carbon-based anode active material is 346 mAh / g to 353 mAh / g. The specific capacity of the carbon-based anode active material within this range helps to improve the stability of the anode active material during cycling, thereby improving the cycle performance of the secondary battery.

[0008] In any embodiment, the carbon-based anode active material includes primary particles and secondary particles. Optionally, the proportion of primary particles in the carbon-based anode active material is greater than or equal to the proportion of secondary particles in the carbon-based anode active material. This helps to reduce the structural breakage of the active material caused by expansion and contraction during cycling, improves the structural stability of the carbon-based anode active material, and thus improves the cycle performance of the secondary battery.

[0009] In any embodiment, the carbon-based anode active material satisfies at least one of the following conditions:

[0010] a) The particle size distribution K is 1.0 to 1.6, and can be selected as 1.1 to 1.50, K = (Dv90 - Dv10) / Dv50;

[0011] b) The volumetric particle size Dv50 is 8μm to 13μm, and can be selected as 9μm to 12μm;

[0012] c) The degree of graphitization is 88%–95%, and can be selected as 90%–95%.

[0013] Controlling the particle size and particle size distribution within the specified range helps reduce side reactions of the carbon-based anode active material during cycling and the irreversible consumption of active ions (e.g., lithium ions), thereby improving the cycle performance of the secondary battery. The degree of graphitization of the carbon-based anode active material within the specified range helps increase the energy density of the anode active material, further improving the cycle performance of the secondary battery.

[0014] In any embodiment, the specific surface area of ​​the carbon-based anode active material is 1.25 m². 2 / g~1.95m 2 / g, can be selected as 1.25m 2 / g~1.85m 2 / g; tap density is 1.07g / cm³ 3 ~1.27g / cm 3 The specific surface area and / or tap density of the carbon-based anode active material meeting the specified range help reduce side reactions of the anode active material during cycling and improve the cycle performance of the secondary battery.

[0015] In any embodiment, the carbon-based negative electrode active material is artificial graphite. The negative electrode active material is widely available and inexpensive, which helps control the production cost of secondary batteries.

[0016] A second aspect of this application provides a method for preparing a carbon-based negative electrode active material, comprising the following steps:

[0017] Provide raw materials;

[0018] The raw materials are processed to obtain intermediates;

[0019] The intermediate is graphitized to obtain the graphitized product;

[0020] The graphitized product is sieved to obtain a carbon-based negative electrode active material;

[0021] The specific capacity of the carbon-based anode active material is 345 mAh / g to 355 mAh / g, and the powder compaction density under 20000 N pressure is 1.55 g / cm³. 3 Above and less than 1.65 g / cm 3 .

[0022] The carbon-based anode active material prepared by the method has a suitable energy density and good cycle stability, and the secondary battery prepared using the material has good cycle performance.

[0023] In any embodiment, the maximum power of the graphitization process is 70%-90% of the rated power of the graphitization process equipment.

[0024] In any embodiment, the temperature of the graphitization treatment is 2600℃~3000℃.

[0025] In any embodiment, the graphitization process takes 10 to 50 hours.

[0026] 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.

[0027] 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%.

[0028] 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 materials 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.

[0029] 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.

[0030] In any implementation, the first precursor satisfies at least one of the following conditions:

[0031] (1) The Dv50 particle size of the first precursor is 6.5 μm to 10.5 μm;

[0032] (2) The particle size distribution (Dv90-Dv10) / Dv50 of the first precursor is 1.05 to 1.75;

[0033] (3) The tap density of the first precursor is 0.55 g / cm³. 3 ~0.75g / cm 3 .

[0034] In any embodiment, the volumetric particle size Dv50 of the second precursor is 11 μm to 15 μm.

[0035] Controlling the particle size and particle size distribution of raw materials or intermediate materials for negative electrode active materials can yield negative electrode active materials with good specific surface area and particle size distribution. This helps to obtain negative electrode active materials with suitable powder compaction density, improves the wettability of negative electrode active materials, and enhances the cycle performance of secondary batteries prepared from carbon-based negative electrode active materials.

[0036] In any embodiment, the graphitized form of the first precursor and the second precursor are mixed in a mass ratio of (1:1) to (6:4), which can improve the structural stability of the negative electrode active material during cycling and help improve the cycle performance of the secondary battery.

[0037] A third aspect of this application provides a secondary battery including a negative electrode sheet, the negative electrode sheet including a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector, the negative electrode film layer including the carbon-based negative electrode active material described in the first aspect of this application or the carbon-based negative electrode active material prepared by the method described in the second aspect of this application.

[0038] In any implementation, the negative electrode sheet satisfies at least one of the following conditions:

[0039] (1) The compaction density of the negative electrode film is 1.5 g / cm³. 3 ~1.65g / cm 3 1.55g / cm³ is an optional value. 3 ~1.65g / cm 3 ;

[0040] (2) The specific surface area of ​​the negative electrode film is 0.7 m². 2 / g~2m 2 / g, optional 1.0m 2 / g~1.6m2 / g;

[0041] (3) The porosity of the negative electrode film is 0.22 to 0.42, and can be selected as 0.27 to 0.37.

[0042] Meeting the above conditions for the negative electrode helps the secondary battery achieve good energy density, reduces side reactions of the negative electrode active material during cycling, and / or the migration resistance of active ions (such as lithium ions), thereby improving the cycle performance of the secondary battery.

[0043] The fourth aspect of this application provides an electrical device including the secondary battery described in the third aspect. Attached Figure Description

[0044] Figure 1 This is a schematic diagram of a secondary battery according to one embodiment of this application.

[0045] Figure 2 yes Figure 1 An exploded view of a secondary battery according to an embodiment of this application is shown.

[0046] Figure 3 This is a schematic diagram of a battery module according to one embodiment of this application.

[0047] Figure 4 This is a schematic diagram of a battery pack according to one embodiment of this application.

[0048] Figure 5 yes Figure 4 An exploded view of a battery pack according to one embodiment of this application is shown.

[0049] Figure 6 This is a schematic diagram of an electrical device that uses a secondary battery as a power source according to one embodiment of this application.

[0050] Explanation of reference numerals in the attached figures:

[0051] 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Secondary battery; 51 Housing; 52 Electrode assembly; 53 Cover plate. Detailed Implementation

[0052] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the positive electrode active material, its manufacturing method, positive electrode sheet, secondary battery, battery module, battery pack, and electrical device of this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for the purpose of enabling those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0053] 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 understood that ranges of 60–110 and 80–120 are also expected. 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 "a–b" 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.

[0054] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0055] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0056] 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.

[0057] 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.

[0058] 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).

[0059] Carbon-based anode active materials are one of the key raw materials for rechargeable batteries, significantly impacting their electrical performance. During battery cycling, active ions (such as lithium and sodium ions) insert and deintercalate within the carbon-based anode active material, causing it to continuously expand and contract. Graphitization of the anode active material improves the orderliness of its crystal structure, which helps increase its energy density. However, increased graphitization narrows the interlayer spacing of the crystal structure. During battery cycling, this interlayer spacing widens, reducing the stability of the crystal structure and leading to cracking and breakage, thus reducing the battery's cycle performance. Furthermore, as the interlayer spacing narrows, the powder compaction density of the anode active material also increases. While increased compaction density improves the energy density, it reduces the wettability of the anode active material or electrode to the electrolyte, increasing electron migration resistance and polarization loss, further affecting the battery's cycle performance.

[0060] Based on this, this application provides a carbon-based anode active material that can improve the cycle performance of secondary batteries.

[0061] [Negative Electrode Active Materials]

[0062] This application provides a carbon-based anode active material, wherein the specific capacity of the carbon-based anode active material is 345 mAh / g to 355 mAh / g, and the powder compaction density under 20000 N pressure is 1.55 g / cm³. 3 Above and less than 1.65 g / cm 3 .

[0063] In this article, the term "specific capacity" refers to the ratio of the electrical capacity that a carbon-based anode active material can release to the mass of the carbon material. Generally speaking, the higher the specific capacity, the better it is for improving the energy density of secondary batteries.

[0064] The specific capacity of the carbon-based anode active material is in the range of 345 mAh / g to 355 mAh / g. The lattice expansion during the material cycling process is relatively small, the crystal structure is stable, and the irreversible consumption of active ions is reduced. At the same time, the carbon-based anode active material has excellent capacity, which can improve the energy density of the secondary battery and thus improve the cycle performance of the secondary battery.

[0065] In some embodiments, the specific capacity of the carbon-based anode active material is 346 mAh / g to 353 mAh / g. In some embodiments, the specific capacity of the carbon-based anode active material is 347 mAh / g to 353 mAh / g. In some embodiments, the specific capacity of the carbon-based 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, or 355 mAh / g, or a range between any two of the above values.

[0066] When the specific capacity is within the specified range, carbon-based anode active materials exhibit excellent crystal structure stability and capacity, significantly improving the cycle performance of secondary batteries.

[0067] The specific capacity can be measured using any method known in the art. For example, a negative electrode active material sample can be thoroughly mixed with conductive carbon black and polyvinylidene fluoride (PVDF) in a mass ratio of 91.6:1.8:6.6 in an appropriate amount of NMP solvent to form a uniform negative electrode slurry. The negative electrode slurry is then uniformly coated onto the surface of the negative electrode current collector copper foil and dried and cold-pressed. Subsequently, using a lithium metal sheet as the counter electrode and a polypropylene (PP) film as the separator, an electrolyte is injected. The electrolyte formulation is as follows: dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and ethylene carbonate (EC) are mixed in a weight ratio of 1:1:1 to obtain an organic solvent. LiPF6 is then dissolved in the organic solvent to prepare an electrolyte with a concentration of 1.0 mol / L. A CR2430 coin cell is assembled in an argon-protected glove box. At 25°C, the prepared coin cell was first discharged at a constant current of 0.05C to 0.005V, then discharged at a constant current of 10μA to 0.005V, and allowed to stand for 5 minutes. The first discharge capacity of the coin cell was recorded. Subsequently, it was charged at a constant current of 0.1C to 2.0V, and the charging capacity of the coin cell was recorded. The ratio of the charging capacity of the coin cell to the mass of the negative electrode active material sample is the specific capacity of the negative electrode active material.

[0068] In this article, the "compacted density" of powder refers to the density of the powder under a preset pressure. A higher compacted density indicates a higher mass of powder material per unit volume. For anode active materials, a higher compacted density results in a higher capacitance, which is beneficial for increasing the energy density of the secondary battery. However, increasing the compacted density also reduces the interlayer spacing of the anode active material, leading to increased lattice expansion, which is detrimental to the structural stability of the anode active material.

[0069] In addition, as the compaction density of the negative electrode active material powder increases, the porosity of the negative electrode active material decreases accordingly. This affects the wettability of the negative electrode active material in the battery electrode sheet with the secondary battery electrolyte, which is not conducive to the insertion and deinsertion of active ions in the negative electrode active material and the free migration of electrons, and also affects the cycle performance of the secondary battery.

[0070] The method for measuring the compacted density of powder can be any method known in the art. For example, referring to GB / T24533-2009, 1g of negative electrode active material powder is weighed and added to a container with a bottom area of ​​1.327cm². 2 In the mold, pressure is applied to a specific pressure, such as 20000N or 49000N, held for 30s, then depressurized and held for 10s. The compaction density of the negative electrode active material under the selected pressure is determined by an electronic pressure testing machine (such as UTM7305 electronic pressure testing machine).

[0071] In existing technologies, when the specific capacity of the negative electrode active material is in the range of 345 mAh / g to 355 mAh / g, it exhibits a strength of not less than 1.65 g / cm³ under a pressure of 20000 N. 3 The compaction density of the material is too low to simultaneously achieve both structural stability and cycle performance of the secondary battery. The carbon-based anode active material provided in this application has a reduced powder compaction density within the specified capacity range. This not only gives the carbon-based anode active material an ideal energy density but also results in a lower volume expansion rate during cycling, improving the structural stability of the anode active material and enhancing the cycle life of the secondary battery.

[0072] In some embodiments, the powder compaction density of the carbon-based anode active material under a pressure of 20,000 N is 1.55 g / cm³. 3 1.56g / cm 3 1.57g / cm 3 1.58g / cm 3 1.59g / cm 3 1.60g / cm 3 1.61 g / cm 3 1.62g / cm 3 1.63g / cm 3 1.64 g / cm 3 1.65g / cm 3 Or a range between any two of the above values. In some embodiments, the powder compaction density of the carbon-based negative electrode active material at a pressure of 20000N is 1.57 g / cm³. 3 ~1.62g / cm 3 This can further improve the capacitance and structural stability of the negative electrode active material, and enhance the cycle performance of the secondary battery.

[0073] In some embodiments, the powder compaction density of the carbon-based anode active material at a pressure of 49000N is 1.73 g / cm³. 3 Above and less than or equal to 1.84 g / cm 3 .

[0074] In some embodiments, the powder compaction density of the carbon-based anode active material at a pressure of 49000N is 1.75 g / cm³. 3 1.76 g / cm 3 1.77g / cm 3 1.78g / cm 3 1.79g / cm 3 1.80g / cm 3 1.81 g / cm 3 1.82g / cm 3 1.83g / cm 3 1.84 g / cm 3 Alternatively, the range between any two of the above values ​​can help to better improve the capacitance and structural stability of the negative electrode active material and improve the cycle performance of the secondary battery.

[0075] In some embodiments, the carbon-based negative electrode active material includes primary particles and secondary particles. Optionally, the proportion of primary particles in the carbon-based negative electrode active material is greater than or equal to the proportion of secondary particles in the carbon-based negative electrode active material. This helps to reduce the breakage of negative electrode active material particles caused by expansion and contraction during cycling, improve the chemical and mechanical stability of the carbon-based negative electrode active material, reduce the irreversible consumption of active ions, and improve the cycle performance of the secondary battery.

[0076] In this document, primary particles and secondary particles have meanings known in the art. In this document, "primary particle" refers to a non-agglomerated particle. In this document, "secondary particle" refers to an aggregated particle formed by the aggregation of two or more primary particles.

[0077] 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.

[0078] In some implementations, the percentage of primary particles can be selected as 50%, 52%, 54%, 56%, 58%, 60%, or any value between the two, based on the total number of primary and secondary particles in the graphite anode active material.

[0079] During cycling, the negative electrode active material undergoes repeated expansion and contraction deformation, leading to particle breakage. This severely reduces the mechanical integrity of both primary and secondary particles. Simultaneously, broken particles increase electrolyte penetration and side reactions, exacerbating the irreversible consumption of active ions. Graphite negative electrode active materials with a low proportion of secondary particles are beneficial for maintaining particle integrity during battery fabrication, reducing the formation of new interfaces, decreasing active lithium consumption during cycling, and further improving the cycle stability of the secondary battery. Furthermore, a certain number of secondary particles can reduce negative electrode expansion while maintaining the kinetic performance of the secondary battery, thus providing the cell with a full lifespan 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.

[0080] In some embodiments, the particle size distribution K of the carbon-based negative electrode active material is 1.0 to 1.6, where K = (Dv90 - Dv10) / Dv50, and can be selected as 1.1 to 1.5. In some embodiments, the particle size distribution K of the carbon-based negative electrode active material is 1.05, 1.1, 1.15, 1.2, 1.25, 1.3, 1.35, 1.4, 1.45, 1.5, 1.6, or any two of the above values. This helps to improve the concentration of the negative electrode active material particle size, reduce the uneven distribution of active ions in the negative electrode active material caused by large particle size differences, reduce side reactions between smaller particle size negative electrode active materials and electrolytes, and improve the cycle performance of secondary batteries.

[0081] In some embodiments, the volumetric particle size distribution (Dv50) of the carbon-based anode active material is 8 μm to 13 μm, optionally 9 to 12 μm. In some embodiments, the volumetric particle size distribution (Dv50) of the carbon-based anode active material is 8.0 μm, 8.5 μm, 9.0 μm, 9.5 μm, 10.0 μm, 10.5 μm, 11.0 μm, 11.5 μm, 12.0 μm, 12.5 μm, 13.0 μm, or any two of the above values. This results in shorter paths for active ion insertion and extraction, which is beneficial for improving the transport performance of active ions and electrons. It also facilitates the formation of a reasonable pore structure between the particles of the anode film, thereby further improving the cycle performance and / or rate performance of the secondary battery.

[0082] In this application, the volumetric particle size distribution (Dv50) of the carbon-based anode material has a well-known meaning in the art, representing the particle size corresponding to a cumulative volumetric distribution percentage of 50%, which can be determined using instruments and methods known in the art. For example, it can be determined using a laser particle size analyzer, referring to GB / T 19077-2016. The testing instrument can be the Mastersizer 3000 laser particle size analyzer from Malvern Instruments Ltd., UK.

[0083] In some embodiments, the degree of graphitization of the carbon-based anode active material is 88% to 95%. In some embodiments, the degree of graphitization of the carbon-based anode active material is 90.4%, 91.1%, 92.3%, 93.5%, 94.1%, 94.7%, or any two of the above values. This is beneficial for the anode active material to have excellent specific capacity and good active ion transport performance, thereby helping the secondary battery to achieve both high energy density and good kinetic performance.

[0084] In this application, the degree of graphitization of the carbon-based anode active material has a meaning known in the art and can be tested using instruments and methods known in the art. For example, it can be tested using an X-ray diffractometer (such as a Bruker D8 Discover), and the testing can be performed with reference to JISK 0131-1996 and JB / T 4220-2011. The average interlayer spacing d002 of the C(002) crystal plane in the material's crystal structure can be obtained, and then the degree of graphitization can be calculated according to the formula g = (0.344 - d002) / (0.344 - 0.3354) × 100%. In the above formula, d002 is the average interlayer spacing of the C(002) crystal plane in the material's crystal structure, expressed in nanometers (nm).

[0085] Graphitization degree reflects the integrity of the graphite crystal structure in a material, that is, the regularity of the arrangement of carbon atoms in the graphite structure. High graphitization degree indicates small interlayer spacing, smaller lattice rotation, less random stacking of layers, and a more ordered arrangement, resulting in high specific capacity. Low graphitization degree indicates large interlayer spacing, which is beneficial for rapid insertion and extraction of active ions, improving the rate performance of the battery. Furthermore, large interlayer spacing results in less material expansion during lithium insertion, leading to shallow charge and discharge effects. Additionally, low graphitization also results in higher specific energy density (SP) in the graphite material. 3 The presence of numerous bonds in graphite materials creates mutual restraint between the layers, resulting in a more stable structure and excellent stability during cycling, which is beneficial for long-term cycling.

[0086] In some embodiments, the specific surface area of ​​the carbon-based anode active material is 1.25 m². 2 / g~1.95m 2 / g, can be selected as 1.25m 2 / g~1.85m 2 / g. In some embodiments, the specific surface area of ​​the carbon-based anode active material is 1.3m². 2 / g, 1.35m 2 / g, 1.45m 2 / g, 1.5m 2 / g, 1.55m 2 / g, 1.6m 2 / g, 1.65m 2 / g, 1.7m 2 / g, 1.75m 2 / g, 1.8m 2 / g, 1.9m 2 / g, 1.95m 2 / g or any two of the above values ​​help reduce side reactions between the negative electrode active material and the electrolyte, reduce irreversible active consumption of metal ions, and improve the cycle performance of the secondary battery.

[0087] In some embodiments, the tap density of the carbon-based anode active material is 1.07 g / cm³. 3 ~1.27g / cm 3 In some embodiments, the tap density of the carbon-based anode active material is 1.1 g / cm³. 3 1.15g / cm 3 1.18 g / cm 3 1.2g / cm 3 1.23g / cm 3 Alternatively, the range between any two of the above values ​​can help improve the transport performance of active ions and electrons, thereby improving the kinetic performance of secondary batteries.

[0088] In some implementations, the carbon-based anode active material is artificial graphite.

[0089] [Preparation Method of Negative Electrode Active Material]

[0090] This application also provides a method for preparing a carbon-based anode active material, the method comprising the following steps: providing raw materials; processing the raw materials to obtain an intermediate product; and graphitizing the intermediate product to obtain the carbon-based anode active material; wherein the specific capacity of the carbon-based anode active material is 345 mAh / g to 355 mAh / g, and the powder compaction density under 20000 N pressure is 1.55 g / cm³. 3 Above and less than 1.65 g / cm 3 The secondary battery prepared from the carbon-based anode active material exhibits both good cycle performance and high energy density.

[0091] In this article, the term "graphitization treatment" refers to the high-temperature heat treatment process of carbon materials. Under high temperature, carbon materials undergo a transformation from a two-dimensional carbon network structure to a three-dimensional ordered structure through "microcrystalline" growth.

[0092] In some implementations, the maximum power of the graphitization process is 70%-90% of the rated power of the graphitization process equipment.

[0093] 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.

[0094] 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.

[0095] 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.

[0096] In some implementations, the graphitization equipment is an internal furnace with a rated power of 25000W-32000W.

[0097] In some implementations, the graphitization equipment is an Atchison furnace with a rated power of 28,000W-30,000W.

[0098] In some embodiments, the graphitization temperature is 2600°C to 3000°C.

[0099] In some embodiments, the graphitization temperature is 2600°C, 2700°C, 2800°C, 2900°C, 3000°C, or any value between two of these.

[0100] In some implementations, the graphitization process takes 10 to 50 hours.

[0101] In some implementations, the graphitization time is 10h, 15h, 20h, 25h, 30h, 35h, 40h, 45h, 50h, or any range between the two.

[0102] In some implementations, the graphitization equipment is an internal furnace, and the graphitization process is carried out at maximum power for 10-30 hours.

[0103] In some implementations, the graphitization equipment is an Atchison furnace, and the graphitization process is carried out at maximum power for 30-50 hours.

[0104] In some embodiments, the raw material includes at least one of petroleum coke, needle coke, and pitch coke, and may be needle coke.

[0105] In this article, the term "petroleum coke" refers to the coke formed after petroleum residue or petroleum asphalt has undergone high-temperature carbonization.

[0106] 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.

[0107] In this article, the term "asphalt coke" refers to the solid material generated after coal tar pitch is carbonized at high temperature.

[0108] 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%.

[0109] Needle coke possesses a series of advantages, including a low coefficient of thermal expansion, low porosity, low sulfur content, low ash content, low metal content, high electrical conductivity, and ease of graphitization. Graphitized needle coke can achieve high ultimate compaction density and exhibits low cyclic expansion rate.

[0110] Coke raw materials typically include at least one of the following structures: mosaic, regional, and fibrous. Generally, based on the morphological characteristics and isochromatic area size of the coke raw material under a polarizing microscope, 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.

[0111] 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.

[0112] In this application, the volume percentage of fibrous structure in the raw material can be tested using methods known in the art. As an example, raw materials are taken according to GB 1997-89, and raw materials crushed to 1mm are mixed and reduced to 40g-50g. 4g-5g of 0.07mm-1.0mm grade samples are taken using a square-hole sieve for slide preparation. Powdered coke and block coke films are prepared according to MT 116.1-86. The diameter of the powdered coke film should not be less than 22mm, and the volume occupied by the cementing material should be less than 1 / 3. The sample is placed on a slide with clay, flattened, and then placed on the stage for focusing. After calibrating the microscope, the polarizer and analyzer are adjusted to make them orthogonal. A lapis lazuli test plate (1λ) is inserted to make the field of view show the interference color of first-order red. The step length of the moving scale is determined to ensure that more than 400 effective measuring points are evenly distributed, with a point spacing of 0.3-0.5mm and a row spacing of 0.5-0.8mm being generally appropriate. Starting from one end of the sample, the type of microstructure under the intersection of the crosshairs is determined, and the volume ratio of the fibrous structure in the raw material is calculated by dividing the effective number of measurement points of the fibrous optical structure by the total number of measurement points.

[0113] In some implementations, based on the total volume of the raw material structure, the proportion of fibrous structure in the coke raw material can be selected as 55%, 58%, 60%, 63%, 65%, 68%, 70%, or any value between two ranges. Raw materials with a higher proportion of fibrous structure are beneficial for improving the compaction density and specific capacity of the graphite anode active material, allowing the graphite anode active material to retain high integrity during compaction, resulting in a battery with both high cycle life and good energy density. However, an excessively high proportion of fibrous structure increases the cost and expansion rate of the graphite anode active material, and deteriorates kinetic performance. Raw materials with a volume proportion of fibrous structure within the above-mentioned range offer both lower cost and good specific capacity of graphite, providing the cell with a full life-cycle kinetic window, thereby comprehensively improving the long-term cycle life and electrochemical performance of the battery.

[0114] By selecting coke raw materials with a fibrous structure volume ratio of ≥55% and ≤70%, under the same graphitization treatment conditions, the interlayer spacing of the crystal structure of the anode active material is larger, exhibiting both good capacitance and excellent structural stability; simultaneously, the carbon-based anode active material has a lower powder compaction density (below 1.65 g / cm³). 3 This approach is beneficial for balancing the structural stability and capacitance of carbon-based anode active materials.

[0115] In some implementations, the maximum specific capacity achievable by the raw material is greater than that of the graphite anode active material.

[0116] By using high-grade raw materials and controlling the degree of graphitization, the maximum specific capacity achievable by the raw materials is not fully utilized, thereby reducing the cyclic expansion of the graphite anode active material and improving its cyclic stability.

[0117] 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 the mixture of the first precursor and the second precursor to obtain the intermediate product.

[0118] 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.

[0119] 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%.

[0120] Granulation involves adding a binder to a predetermined amount of the first precursor for granulation. The binder can be any substance known in the art that can be used to prepare anode active materials, such as one or more of coal tar pitch, petroleum pitch, polymers, and resins. When heated and melted, the binder has low viscosity and maintains good flowability, reducing the agglomeration of raw material particles during subsequent preparation. This also reduces problems such as increased surface defects and surface active sites in carbon-based anode active material particles due to the need for additional deagglomeration processes.

[0121] The intermediate product is obtained by low-temperature carbonization of the first precursor and the second precursor. This includes obtaining the intermediate product by low-temperature carbonization of a mixture of the first precursor and the second precursor; and 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.

[0122] In some embodiments, the volumetric particle size Dv50 of the first precursor is 6.5 μm to 10.5 μm. In some embodiments, the Dv50 particle size of the first precursor is 6.5 μm, 7.0 μm, 8.0 μm, 9.0 μm, 10.0 μm, 10.5 μm, or any value between two of these.

[0123] In some embodiments, the particle size distribution (Dv90-Dv10) / Dv50 (or K) of the first precursor is 1.05 to 1.75. In some embodiments, the particle size distribution of the first precursor is 1.05, 1.15, 1.25, 1.35, 1.45, 1.55, 1.65, 1.75 or any value range between the two.

[0124] In some embodiments, the tap density of the first precursor is 0.55 g / cm³. 3 ~0.75g / cm 3 .

[0125] In some embodiments, the tap density of the first precursor is 0.55 g / cm³. 3 0.6g / cm 3 0.65g / cm 3 0.7g / cm 3 0.75g / cm 3 Or the range of values ​​between any two.

[0126] In some embodiments, the Dv50 particle size of the second precursor is 11.0 μm to 15.0 μm.

[0127] 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.

[0128] 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.

[0129] Controlling the particle sizes of the first and second precursors within the aforementioned range helps to regulate the particle size and particle size distribution of the graphite anode active material, thereby improving the cycle stability of the battery.

[0130] In some embodiments, the low-temperature carbonization temperature is 900℃-1300℃, and the low-temperature carbonization time is 24h-240h.

[0131] 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.

[0132] 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.

[0133] In some embodiments, graphitized derivatives of the first and second precursors are mixed in a mass ratio of (1:1) to (6:4) to obtain a carbon-based negative electrode active material. This improves the chemimechanical properties of the negative electrode active material during cycling, and also allows the negative electrode film to have a suitable pore structure, reducing the irreversible consumption of active ions and improving the transport performance of active ions, thereby improving the cycle performance of the secondary battery.

[0134] In some embodiments, the precursor is graphitized and then further screened and demagnetized.

[0135] In some embodiments, the primary particulate graphitization product and the secondary particulate graphitization product after screening and demagnetization are mixed in a mass ratio of (1:1) to (6:4), for example, 50:50, 55:45 or 60:40.

[0136] In addition, the secondary battery, battery module, battery pack and power device of this application will be described below with appropriate reference to the accompanying drawings.

[0137] In one embodiment of this application, a secondary battery is provided.

[0138] Typically, a secondary battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. During charging and discharging, active ions move back and forth between the positive and negative electrodes, inserting and releasing. The electrolyte acts as a conductor between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits while allowing ions to pass through.

[0139] [Positive electrode plate]

[0140] The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector, the positive electrode film layer including a positive electrode active material.

[0141] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0142] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0143] In some embodiments, the positive electrode active material may be a known battery positive electrode active material. As an example, the positive electrode active material may include at least one of the following materials: lithium phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as battery positive electrode active materials may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides include, but are not limited to, lithium cobalt oxides (such as LiCoO2), lithium nickel oxides (such as LiNiO2), lithium manganese oxides (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, and lithium nickel cobalt manganese oxides (such as LiNi). 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also known as NCM) 333 LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM) 523 LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM) 211 LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM) 622LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM) 811 ), lithium nickel cobalt aluminum oxide (such as LiNi) 0.85 Co 0.15 Al 0.05 At least one of O2 and its modified compounds. Examples of lithium phosphates with an olivine structure include, but are not limited to, lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composites.

[0144] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0145] In some embodiments, the positive electrode film may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0146] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0147] [Negative electrode plate]

[0148] The negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector, the negative electrode film layer including the aforementioned carbon-based negative electrode active material.

[0149] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0150] In some embodiments, the negative electrode film layer may further include other negative electrode active materials besides the carbon-based negative electrode active materials 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.

[0151] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0152] In some embodiments, the negative electrode film layer may optionally include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0153] In some embodiments, the negative electrode film may optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0154] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0155] In some embodiments, the negative electrode sheet can be prepared by dispersing the above-mentioned components for preparing the negative electrode sheet, such as negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto a negative electrode current collector, and after drying, cold pressing and other processes, a negative electrode sheet including a negative electrode film layer can be obtained.

[0156] In some embodiments, the compaction density of the negative electrode film is 1.5 g / cm³. 3 ~1.65g / cm 3In some embodiments, the compaction density of the negative electrode film is 1.55 g / cm³. 3 ~1.65g / cm 3 The compaction density of the negative electrode film within the specified range helps control the energy density of the secondary battery, thereby improving its cycle performance.

[0157] In some embodiments, the specific surface area of ​​the negative electrode film is 0.7 m². 2 / g~2m 2 / g, optional 1.0m 2 / g~1.6m 2 / g. The specific surface area of ​​the negative electrode film within the specified range helps to control its contact area with the electrolyte, reduce side reactions of the carbon-based negative electrode active material in the negative electrode sheet, reduce irreversible consumption of active ions, and thus improve the cycle performance of the secondary battery.

[0158] In some embodiments, the porosity of the negative electrode film is 0.22–0.42, optionally 0.27–0.37. A porosity within this range helps reduce the migration resistance of active ions and electrons, thereby improving the kinetic performance of the secondary battery.

[0159] The compaction density of the negative electrode film can be tested using methods known in the art. As an example, a negative electrode sample with an area of ​​S is weighed using an electronic balance, and the weight is recorded as W1. The thickness T1 of the negative electrode is then measured using a micrometer. The weighed electrode film is then wiped off, and the weight of the negative current collector is measured, recorded as W2. The thickness T2 of the negative current collector is then measured using a micrometer. The compaction density of the negative electrode film is then calculated as PD = (W1 - W2) / [(T1 - T2) × S].

[0160] The specific surface area of ​​the negative electrode film can be tested using methods known in the art. As an example, the specific surface area of ​​the negative electrode film can be measured by nitrogen adsorption / desorption using a specific surface area analyzer (e.g., the TriStar 3020 from the USA) in accordance with GB / T 19587-2017, following the method for determination of specific surface area: the negative electrode film is dried in a vacuum drying oven and then placed in a sample tube for measurement in the analyzer.

[0161] The porosity P of the negative electrode film can be tested using methods known in the art. As an example, referring to GB / T21650.2-2008, the porosity P of the negative electrode sheet is determined using the nitrogen adsorption method, which is the percentage of the pore volume in the negative electrode sheet to the total volume of the negative electrode sheet: the calculation formula is P = (V1 - V2) / V1 × 100%, where V1 is the apparent volume of the electrode sample and V2 is the actual volume of the electrode sample. The apparent volume V1 of the electrode sample is calculated using the formula V1 = S × H × A, where S is the area of ​​the negative electrode sheet (unit: cm2); H is the thickness of the negative electrode sheet (unit: cm); and A is the number of samples (unit: ea). The specific testing steps are as follows: In a normal laboratory environment, use tweezers to select no fewer than 20 electrode discs with good appearance and no powder falling off the edges and place them into a sample cup. Record the number of discs and calculate the apparent volume V1. After placing the sample electrode discs into a 3.5 cm3 sample cup, place it in a true density tester, seal the test system, and introduce ammonia gas according to the procedure. By detecting the pressure of the gas in the sample chamber and the expansion chamber, calculate the true volume V2 according to Bohr's law (PV = nRT), thereby obtaining the porosity of the negative electrode film layer to be tested.

[0162] [Electrolytes]

[0163] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific restrictions on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel, or entirely solid.

[0164] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0165] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0166] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0167] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0168] [Isolation membrane]

[0169] In some embodiments, the secondary battery also includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0170] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0171] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0172] 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.

[0173] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the secondary battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0174] This application does not impose any particular limitation on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 1 This is an example of a square-structured secondary battery 5.

[0175] In some implementations, refer to Figure 2 The outer packaging may include a housing 51 and a cover 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover 53 can be placed over the opening to close the receiving cavity. A positive electrode, a negative electrode, and a separator can be formed into an electrode assembly 52 using a winding or stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The secondary battery 5 may contain one or more electrode assemblies 52, which can be selected by those skilled in the art according to specific practical needs.

[0176] In some implementations, the secondary batteries can be assembled into a battery module, and the number of secondary batteries contained in the battery module can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery module.

[0177] Figure 3 This is battery module 4, used as an example. (See reference...) Figure 3 In battery module 4, multiple secondary batteries 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple secondary batteries 5 can be fixed in place using fasteners.

[0178] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of secondary batteries 5 are received.

[0179] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0180] Figure 4 and Figure 5 This is battery pack 1 as an example. (See reference...) Figure 4 and Figure 5 The battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3, with the upper body 2 covering the lower body 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0181] In addition, this application also provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack provided in this application. The secondary battery, battery module, or battery pack can be used as a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0182] As the electrical device, a secondary battery, battery module, or battery pack can be selected according to its usage requirements.

[0183] Figure 6This is an example of an electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the secondary battery for this device, a battery pack or battery module can be used.

[0184] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a rechargeable battery as their power source.

[0185] Example

[0186] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0187] I. Performance Testing of Negative Electrode Active Materials and Secondary Batteries

[0188] 1. Powder compaction density test

[0189] Referring to GB / T 24533-2009, weigh 1g of negative electrode active material powder and add it to a container with a bottom area of ​​1.327cm². 2 In the mold, pressure is applied to 20000N, held for 30s, then depressurized and held for 10s. The compaction density of the negative electrode active material under 20000N pressure is determined by an electronic pressure testing machine (such as UTM7305 electronic pressure testing machine).

[0190] Referring to GB / T 24533-2009, weigh 1g of negative electrode active material powder and add it to a container with a bottom area of ​​1.327cm². 2 In the mold, pressure is applied to 49000N, held for 30s, then depressurized and held for 10s. The compaction density of the carbon material powder under 49000N pressure is determined by an electronic pressure testing machine (such as UTM7305 electronic pressure testing machine).

[0191] 2. Particle size testing and particle size distribution testing of powders

[0192] Measurement method: Particle size distribution was measured using a laser particle size analyzer such as the Mastersizer 2000E from Malvern Instruments Ltd., in accordance with GB / T 19077-2016 standard. The volume distribution particle sizes Dv10, Dv50, and Dv90, as well as the particle size distribution, were obtained.

[0193] 3. Specific capacity testing of negative electrode active materials

[0194] The negative electrode active material sample, conductive agent carbon black, and polyvinylidene fluoride (PVDF) were thoroughly mixed in an appropriate amount of NMP solvent at a mass ratio of 91.6:1.8:6.6 to form a uniform negative electrode slurry. The negative electrode slurry was uniformly coated onto the surface of the negative electrode current collector copper foil and dried and cold-pressed. Then, using a lithium metal sheet as the counter electrode and a polypropylene (PP) film as the separator, an electrolyte was injected. The electrolyte formulation used was as follows: dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and ethylene carbonate (EC) were mixed in a weight ratio of 1:1:1 to obtain an organic solvent, and then LiPF6 was dissolved in the above organic solvent to prepare an electrolyte with a concentration of 1.0 mol / L. CR2430 coin cells were 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 negative electrode active material sample is the specific capacity of the negative electrode active material.

[0195] 4. Cycle performance test of secondary batteries

[0196] The prepared secondary battery was charged at 60℃ with a constant current of 1C until the voltage reached 3.65V, then charged at a constant voltage of 3.65V until the current ≤0.05C. The battery was then discharged at a constant current of 1C until the voltage reached 2.5V. This constituted one charge-discharge cycle, and the discharge capacity 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.

[0197] 5. Volume percentage test of fibrous structure in coke raw materials

[0198] Raw materials are taken according to GB 1997-89. Raw materials crushed to 1mm are mixed and reduced to 40g-50g. 4g-5g of 0.07mm-1.0mm grade samples are taken using a square-hole sieve for slide preparation. Powdered coke and block coke films are prepared according to MT 116.1-86. The diameter of the powdered coke film should not be less than 22mm, and the volume occupied by the cementing material should be less than 1 / 3. The sample is placed on a slide with cement, flattened, and then placed on the stage for focusing. After calibrating the microscope, the polarizer and analyzer are adjusted to ensure orthogonality. A lapis lazuli test plate (1λ) is inserted to produce a first-order red interference color in the field of view. 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 ratio of the fibrous structure in the raw material is calculated by dividing the effective number of measurement points of the fibrous optical structure by the total number of measurement points.

[0199] II. Preparation of Secondary Batteries

[0200] Example 1

[0201] 1) Preparation of carbon-based anode active materials

[0202] Needle coke, comprising 61.0% of the volumetric fiber structure, was crushed; the crushed material was then shaped and fine powder removed to obtain the first precursor. The first precursor had a Dv50 particle size of 9.4 μm, a particle size distribution (Dv90-Dv10) / Dv50 of 1.19, and a tap density of 0.68 g / cm³. 3 .

[0203] The first precursor was granulated and reformed in a reactor to obtain a second precursor with a particle size Dv50 of 14.1 μm;

[0204] The first and second precursors were placed in a kiln for carbonization at a temperature of 1100℃ for 24 hours, respectively, to obtain a first intermediate product and a second intermediate product. The tap density of the first intermediate product was 0.96 g / cm³. 3 The tap density of the second intermediate product is 0.92 g / cm³. 3 ;

[0205] The first and second intermediates were graphitized at 2800°C. The graphitization device was an internal furnace with a rated power of 28000W and a maximum power of 22400W. The maximum power was maintained at a constant power for 24 hours to obtain primary and secondary particles, respectively.

[0206] The primary and secondary particles are mixed evenly at a mass ratio of 50:50, and then sieved to remove magnetism to obtain the final product, graphite anode active material.

[0207] The compaction density of this graphite anode active material is 1.61 g / cm³ at 20000 N. 3 The degree of graphitization is 92.48%, and the specific surface area is 1.47 m². 2 The particle size distribution (Dv50) is 10.3 μm, and the compacted density of the powder under a pressure of 49000 N is 1.82 g / cm³. 3 The specific capacity is 350 mAh / g, the ID / IG ratio is 0.075, the interlayer spacing d1 of the surface region is 0.3373 nm, the interlayer spacing d2 of the internal region is 0.3360 nm, and the particle size distribution (Dv90-Dv10) / Dv50 is 1.36.

[0208] 2) Preparation of positive electrode sheet

[0209] Lithium iron phosphate (LFP) as the positive electrode active material, Super P as the conductive agent, and PVDF as the binder are mixed at a mass ratio of 97:1:2. N-methylpyrrolidone as the solvent is added, and the mixture is stirred until homogeneous to obtain a positive electrode slurry. The positive electrode slurry is then uniformly coated onto an aluminum foil current collector, and after drying, cold pressing, and slitting, a positive electrode sheet is obtained. The compacted density of the positive electrode sheet is 2.5 g / cm³. 3 .

[0210] 3) Preparation of negative electrode sheet

[0211] The prepared carbon-based negative electrode active material, conductive agent Super P, thickener sodium carboxymethyl cellulose, and binder styrene-butadiene rubber were mixed at a mass ratio of 96:1:1.2:1.8, and deionized water was added as a solvent. The mixture was stirred until homogeneous to obtain a negative electrode slurry. The negative electrode slurry was uniformly coated onto a copper foil current collector, dried, cold-pressed, and slit to obtain a negative electrode sheet. The compaction density of the negative electrode film was 1.6 g / cm³. 3 Its surface density is 9.48 mg / cm³. 2 .

[0212] 4) Preparation of electrolyte

[0213] 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.

[0214] 5) Separating membrane

[0215] Polypropylene film was selected as the separator.

[0216] 6) Preparation of secondary batteries

[0217] 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.

[0218] Examples 2-7 and Comparative Examples 1-4

[0219] Examples 2-7 and Comparative Examples 1-4 are similar to the preparation steps in Example 1, but the preparation parameters of the negative electrode active material have been adjusted. See Tables 1-1 and 1-2 for details.

[0220] Table 1-1: Preparation parameters of negative electrode active materials in Examples 1-7 and Comparative Examples 1-4

[0221]

[0222] Table 1-2: Preparation parameters of negative electrode active materials in Examples 1-7 and Comparative Examples 1-4

[0223]

[0224] The negative electrode active materials and secondary batteries prepared in Examples 1-7 and Comparative Examples 1-4 were tested using the above test methods. The results are shown in Table 2 below:

[0225] Table 2: Parameter and performance test results of Examples 1-7 and Comparative Examples 1-4

[0226]

[0227] As can be seen from Examples 1-7 and Comparative Examples 1-4, when the specific capacity of the negative electrode active material is in the range of 345 mAh / g to 355 mAh / g, the powder compaction density of the negative electrode active material under a pressure of 20000 N is 1.55 g / cm³. 3 ~1.65g / cm 3 The secondary battery prepared using this negative electrode active material exhibits a high number of cycles at 60℃, indicating that the secondary battery has good cycle performance.

[0228] In Comparative Example 1, the specific capacity of the negative electrode active material was 358.1 mAh / g, and the powder compaction density of the negative electrode active material under 20000 N pressure increased to 1.72 g / cm³. 3 However, the secondary battery only achieved 1573 cycles, indicating that the powder compaction density of the negative electrode active material under 20000N pressure exceeded 1.65 g / cm³. 3Once the capacity exceeds 355mAh / g, it is not conducive to improving the cycle performance of the secondary battery.

[0229] In Comparative Example 2, the specific capacity of the negative electrode active material was 348.5 mAh / g. When all the negative electrode active material was in the form of primary particles, the powder compaction density of the negative electrode active material under 20000 N pressure increased to 1.67 g / cm³. 3 However, the secondary battery only achieved 1650 cycles, indicating that the powder compaction density of the negative electrode active material under 20000N pressure exceeded 1.65 g / cm³. 3 Afterwards, it can affect the cycle performance of the secondary battery.

[0230] In Comparative Example 3, when the specific capacity of the negative electrode active material was 353.7 mAh / g, the powder compaction density of the negative electrode active material under 20000 N pressure increased to 1.69 g / cm³. 3 However, the secondary battery only achieved 1621 cycles, indicating that the powder compaction density of the negative electrode active material under 20000N pressure exceeded 1.65 g / cm³. 3 Afterwards, it can affect the cycle performance of the secondary battery.

[0231] In Comparative Example 4, when the specific capacity of the negative electrode active material was 350.3 mAh / g, the powder compaction density of the negative electrode active material under 20000 N pressure decreased to 1.54 g / cm³. 3 The secondary battery only completed 1605 cycles, indicating that the powder compaction density of the negative electrode active material under 20000N pressure is less than 1.55 g / cm³. 3 After that, the cycle performance of the secondary battery is poor.

[0232] 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 carbon-based anode active material, characterized in that, The carbon-based anode active material is artificial graphite, and its specific capacity is 345 mAh / g to 355 mAh / g, with a powder compaction density of 1.55 g / cm³ under 20000 N pressure. 3 Above and less than 1.65 g / cm 3 ; The carbon-based anode active material includes primary particles and secondary particles, wherein the proportion of primary particles in the carbon-based anode active material is greater than or equal to the proportion of secondary particles in the carbon-based anode active material. The particle size distribution K of the carbon-based negative electrode active material is 1.0~1.6, K=(Dv90-Dv10) / Dv50.

2. The carbon-based anode active material according to claim 1, characterized in that, The compacted density of the carbon-based anode active material under 20,000 N pressure is 1.57 g / cm³. 3 ~1.62g / cm 3 Alternatively, the compacted density of the carbon-based anode active material at a pressure of 49000N is 1.73 g / cm³. 3 Above and less than 1.84 g / cm 3 .

3. The carbon-based anode active material according to claim 1, characterized in that, The specific capacity of the carbon-based anode active material is 346 mAh / g to 353 mAh / g.

4. The carbon-based negative electrode active material according to any one of claims 1 to 3, characterized in that, The carbon-based anode active material satisfies at least one of the following conditions: a) Particle size distribution K is 1.1~1.5; b) The volumetric particle size Dv50 is 8μm~13μm; c) The degree of graphitization is 88%~95%.

5. The carbon-based negative electrode active material according to any one of claims 1 to 3, characterized in that, The carbon-based anode active material satisfies at least one of the following conditions: (1) The volumetric particle size Dv50 is 9μm~12μm; (2) The degree of graphitization is 90%~95%.

6. The carbon-based negative electrode active material according to any one of claims 1 to 3, characterized in that, The specific surface area of ​​the carbon-based anode active material is 1.25 m². 2 / g~1.95m 2 / g.

7. The carbon-based negative electrode active material according to any one of claims 1 to 3, characterized in that, The specific surface area of ​​the carbon-based anode active material is 1.25 m². 2 / g~1.85m 2 / g.

8. The carbon-based negative electrode active material according to any one of claims 1 to 3, characterized in that, The tap density of the carbon-based anode active material is 1.07 g / cm³. 3 ~1.27g / cm 3 .

9. A method for preparing a carbon-based negative electrode active material, characterized in that, Includes the following steps: Provide raw materials; The raw materials are processed to obtain intermediates. The processing of the raw materials includes the following specific steps: crushing, shaping and classifying the raw materials to obtain a first precursor, and granulating the precursor to obtain a second precursor. The intermediate is graphitized to obtain the graphitized product; The graphitized products are screened, and the graphitized products of the first precursor and the second precursor are mixed in a mass ratio of (1:1) to (6:4) to obtain a carbon-based negative electrode active material. The specific capacity of the carbon-based anode active material is 345 mAh / g to 355 mAh / g, and the powder compaction density under 20000 N pressure is 1.55 g / cm³. 3 Above and less than 1.65 g / cm 3 The particle size distribution K of the carbon-based negative electrode active material is 1.0~1.6, K=(Dv90-Dv10) / Dv50.

10. The preparation method according to claim 9, 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.

11. The preparation method according to claim 9, characterized in that, The raw materials include one or more of petroleum coke, needle coke, and pitch coke.

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

13. The preparation method according to any one of claims 9 to 12, 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%.

14. The preparation method according to any one of claims 9 to 12, 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%.

15. The preparation method according to any one of claims 9 to 12, characterized in that, The first precursor satisfies at least one of the following conditions: (1) The Dv50 particle size of the first precursor is 6.5 μm to 10.5 μm; (2) The particle size distribution (Dv90-Dv10) / Dv50 of the first precursor is 1.05~1.75; (3) The tap density of the first precursor is 0.55 g / cm³. 3 ~0.75g / cm 3 .

16. The preparation method according to any one of claims 9 to 12, characterized in that, The volumetric particle size distribution (Dv50) of the second precursor is 11 μm to 15 μm.

17. A secondary battery, comprising a negative electrode, characterized in that, The negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector, wherein the negative electrode film layer includes a carbon-based negative electrode active material according to any one of claims 1 to 8 or a carbon-based negative electrode active material prepared by the method according to any one of claims 9 to 16.

18. The secondary battery according to claim 17, characterized in that, The negative electrode sheet satisfies at least one of the following conditions: (1) The compaction density of the negative electrode film is 1.5 g / cm³. 3 ~1.65g / cm 3 ; (2) The specific surface area of ​​the negative electrode film is 0.7 m². 2 / g~2m 2 / g; (3) The porosity of the negative electrode film is 0.22~0.

42.

19. The secondary battery according to claim 17, characterized in that, The negative electrode sheet satisfies at least one of the following conditions: (1) The compaction density of the negative electrode film is 1.55 g / cm³. 3 ~1.65g / cm 3 ; (2) The specific surface area of ​​the negative electrode film is 1.0 m². 2 / g~1.6m 2 / g; (3) The porosity of the negative electrode film is 0.27~0.

37.

20. An electrical appliance, characterized in that, The secondary battery includes any one of claims 17 to 19.

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