Graphite negative electrode material, and preparation method therefor and use thereof

Abstract

The present application relates to the technical field of battery materials, and in particular relates to a graphite negative electrode material, and a preparation method therefor and the use thereof. The graphite negative electrode material comprises graphite particles of which the average length La in the a-axis direction of microcrystals is greater than or equal to 40 nm, the average thickness Lc in the c-axis direction of the microcrystals is greater than or equal to 25 nm, and the interlayer spacing d002 is 0.336-0.338 nm. The number parameters of the microcrystals comprised in a single graphite particle are defined as N = D503 / (La2*Lc), wherein D50 is the median particle size of the graphite particles, with the unit thereof being μm, and the numerical value of N satisfies 0＜N≤0.04. The graphite negative electrode material of the embodiments of the present application comprises graphite particles having a stable microcrystal structure, a large microcrystal size and a large interlayer spacing, thereby improving the expansion and stress distribution uniformity of the negative electrode material during the cycle process, facilitating the diffusion of ions in graphite particles, reducing the consumption of active lithium, and improving the dynamic and ultra-long cycle stability of the graphite negative electrode material.

Description

Graphite negative electrode material and its preparation method and application

[0001] This application claims priority to the Chinese patent application filed with the State Intellectual Property Office on June 30, 2023, with application number 202310802845.1 and application name “Graphite Negative Electrode Materials, Preparation Methods and Applications Thereof”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present application belongs to the technical field of battery materials, and in particular relates to a graphite negative electrode material and a preparation method and application thereof. Background Art

[0003] Against the backdrop of the "dual carbon" initiative, energy storage technology, as a key enabler for renewable energy and smart grids, is experiencing rapid growth. Lithium-ion batteries are the most popular energy storage medium in energy storage systems. To meet the long-life and low-cost requirements of large-scale energy storage systems, the cycling and storage characteristics of lithium batteries have become core competitive advantages. Currently, in the lithium iron phosphate-graphite battery system, which is widely used in energy storage scenarios, the high PO bond energy of the lithium iron phosphate (LiFePO) polyanion in the positive electrode allows for structural stability across the charge and discharge voltage range, with virtually no loss of active material. Therefore, the shortcoming in the cycle life of lithium iron phosphate-graphite battery systems is primarily attributed to the graphite in the negative electrode. During the charge and discharge process of a ion battery, the negative electrode polarizes, and the electrolyte solution components undergo reduction and decomposition on the negative electrode surface, forming new chemical products that deposit on the negative electrode surface, forming a dense passivation film called the solid electrolyte interface (SEI). The growth of the SEI film or lithium metal deposition on the graphite negative electrode surface can cause capacity fading or even a significant drop in capacity. The growth of the SEI film on the graphite anode surface comes from the expansion and contraction of the graphite anode during lithium insertion and extraction, resulting in the formation of newly exposed surfaces. This newly exposed surface reacts with the electrolyte and consumes active lithium. The structural stability of the graphite anode during cycling is one of the key factors affecting the cycle life of lithium-ion batteries.

[0004] Therefore, reducing the volume shrinkage and expansion of the graphite negative electrode during the cycle and improving the structural stability of the graphite negative electrode during the cycle are key factors in achieving long-term cycling of graphite negative electrode materials and lithium-ion batteries.

[0005] Summary of the Invention

[0006] The purpose of this application is to provide a graphite negative electrode material and its preparation method and application, aiming to solve the problem that the stability of existing graphite negative electrode materials needs to be improved during the cycle process.

[0007] To achieve the above application objectives, the technical solutions adopted in this application are as follows:

[0008] The first aspect of the present application provides a graphite negative electrode material, wherein the graphite negative electrode material comprises graphite particles having an average length La ≥ 40 nm along the a-axis direction of the crystallite, an average thickness Lc ≥ 25 nm along the c-axis direction of the crystallite, and an interlayer spacing d002 of 0.336 to 0.338 nm, and the number parameter of the crystallites contained in a single graphite particle is defined as N = D50 3 / (La 2 *Lc); wherein D50 is the median particle size of the graphite particles, in μm, and the numerical value of the crystallite number parameter N satisfies 0<N≤0.04.

[0009] The graphite negative electrode material provided in this application has the following advantages:

[0010] On the one hand, the graphite crystallite size La in the graphite particles of the graphite negative electrode material is ≥40nm, Lc ≥25nm, and the number parameter of the crystallites contained in a single graphite particle is defined as N=D50 3 / (La 2 *Lc), where D50 is the median particle size of the graphite particles, expressed in μm, and N satisfies the value 0<N≤0.04. This ensures that the graphite crystallites in the graphite anode material are large. When lithium ions are embedded in the hexagonal network of the graphite crystallites, the large graphite crystallites provide more sites for ion insertion and removal, facilitating ions to enter the intercalation and removal of ions from the edge embedding sites between the graphite crystal layers, improving ion insertion and removal efficiency and facilitating rapid ion transport. This in turn improves the kinetic performance of the graphite anode material during cyclic charge and discharge, and enhances the electrochemical properties of the battery, including rate capability and cycling performance. This reduces the risk of lithium plating and reduces the risk of safety failures such as battery capacity drop and thermal runaway.

[0011] On the other hand, the interlayer spacing d002 of the graphite crystallites along the c-axis in the graphite anode material is 0.336-0.338 nm. This large interlayer spacing reduces the degree of graphitization. When lithium ions are embedded in the hexagonal mesh of the graphite crystals, the interlayer spacing d(002) at the edge embedding sites (002 crystal planes) is large, and the crystallite size Lc along the c-axis and the crystallite size La along the 110 crystal plane are both large, ensuring uniform expansion between the crystallites when ions are embedded within the graphite particles. This improves the uniformity of expansion and stress distribution of the graphite anode material during cycling, resulting in small and uniform volume expansion and contraction during lithium insertion and deintercalation. This results in better kinetics and long-cycle stability, reducing the rate of active lithium consumption. This reduces the impact of the continuous rupture and regeneration of the SEI film on the graphite anode surface on the battery cycle life and safety performance.

[0012] As some possible implementations of the graphite anode material of this application, the crystallite number parameter 0 < N ≤ 0.02. In some implementations, the crystallite number parameter 0.001 ≤ N ≤ 0.01. In this case, the graphite anode material has better kinetics, reduces the risk of lithium plating, and reduces the risk of safety failures such as battery capacity drop and thermal runaway.

[0013] As some possible implementations of the graphite negative electrode material of this application, La ≤ 200nm and Lc ≤ 200nm. In this case, the uniformity of expansion between crystallites when ions are embedded in the graphite particles is ensured, the long-term cycling stability of the graphite negative electrode is improved, and the impact of continuous rupture and regeneration of the SEI film on the graphite negative electrode surface on the battery cycle life and safety performance is reduced.

[0014] As some possible implementations of the graphite anode material of the present application, the median particle size D50 of the graphite particles is 5 to 25 μm. In some implementations, the median particle size D50 of the graphite particles is 7 to 14 μm. In this case, the median particle size D50 of the graphite particles ensures the comprehensive electrochemical performance of the graphite anode material, such as cycle stability and rate performance.

[0015] As some possible implementations of the graphite negative electrode material of the present application, the median particle size D50 of the graphite particles, the particle size D10, and the particle size D90 satisfy (D90-D10) / D50≤1.7. In some implementations, the median particle size D50 of the graphite particles, the particle size D10, and the particle size D90 satisfy (D90-D10) / D50≤1.5. In this case, the ratio of (D90-D10) / D50 is relatively small, indicating that the particle size distribution uniformity of the graphite particles is relatively high, which is beneficial to improving the flatness and thickness uniformity of the film layer prepared by the graphite negative electrode material.

[0016] As some possible implementations of the graphite negative electrode material of the present application, the specific surface area of ​​the graphite negative electrode material is 0.8 to 2.0 m 2 In some implementations, the specific surface area of ​​the graphite negative electrode material is 0.9 to 1.5 m 2 / g. In this case, the size range of the specific surface area of ​​the graphite negative electrode material balances the relationship between the reaction rate, capacity and mechanical stability of the graphite negative electrode material to achieve the best electrochemical performance and safety performance.

[0017] As some possible implementation methods of the graphite negative electrode material of the present application, the graphite particles are single particles or secondary particles. In actual application, single-particle or secondary particle graphite negative electrode materials can be selected according to specific application requirements to ensure that the graphite negative electrode has the best electrochemical performance.

[0018] A second aspect of the present application provides a method for preparing a graphite negative electrode material, comprising the following steps:

[0019] forming a carbon precursor material into precursor particles;

[0020] After graphitizing the precursor particles, the graphite particles are screened to obtain a graphite negative electrode material; in the graphite particles, the average length La along the a-axis direction of the crystallite is ≥40nm, the average thickness Lc along the c-axis direction of the crystallite is ≥25nm, the interlayer spacing d002 is 0.336-0.338nm, and the number parameter of the crystallite contained in a single graphite particle is defined as N=D50 3 / (La 2 *Lc); wherein D50 is the median particle size of the graphite particles, in μm, and the numerical value of the crystallite number parameter N satisfies 0<N≤0.04.

[0021] The preparation method of the graphite negative electrode material provided by the present application is to prepare precursor particles from a carbon precursor material, perform graphitization treatment, and screen graphite particles whose microcrystal parameters meet the requirements to obtain a graphite negative electrode material. The preparation process is simple and suitable for industrial large-scale production and application. In addition, by screening the structure of the carbon source precursor material and regulating the graphitization process of the carbon precursor material, the microcrystalline structure of the graphite particles can be improved / optimized, the stability of the particle hierarchy and microcrystalline hierarchical structure of the graphite particles can be improved, and the rapid transmission of ions can be facilitated. In the prepared graphite negative electrode material, the number of graphite crystallites in the graphite particles is small, the relative size of the microcrystalline particles is large, and the distance between the graphite layers is large, which reduces the degree of graphitization. When lithium ions are embedded in the hexagonal mesh of graphite crystals, the interlayer spacing d(002) at the edge embedding sites (002 crystal plane) is large, and the crystallite size Lc in the c-axis direction and the crystallite size La of the 110 crystal plane are both large. This allows for better kinetics when ions are embedded in the graphite particles, improving ion deintercalation efficiency, facilitating rapid ion transport, and improving the rate performance of the applied battery. Furthermore, the crystallites have more uniform expansion properties, improving the uniformity of expansion and stress distribution of the graphite negative electrode material during the cycle, reducing the active lithium consumption rate, and improving the long-cycle stability and safety of the graphite negative electrode material.

[0022] As some possible implementations of the method for preparing the graphite negative electrode material of the present application, the fixed carbon content in the carbon precursor material is not less than 60%. In this case, a high fixed carbon content in the carbon precursor material means that the material has a high carbon content, which is conducive to the preparation of high-performance graphite negative electrode materials.

[0023] As some possible implementations of the method for preparing the graphite negative electrode material of the present application, the carbon precursor material includes at least one of calcined petroleum coke, calcined petroleum coke, coal tar coke, and anthracite. In this case, these carbon precursor materials all have a high fixed carbon content, and the carbon structure in these carbon precursor materials is conducive to obtaining large-sized microcrystalline particles and graphite particles with large interlayer spacing after subsequent graphitization.

[0024] As some possible implementations of the method for preparing the graphite negative electrode material of the present application, the step of preparing the precursor particles includes: crushing the carbon precursor material into a particle sample with an average particle size D50 of 1 to 20 μm, and then performing a shaping process to obtain the precursor particles with an average particle size D50 of 1 to 30 μm. In this case, after the carbon precursor material is crushed, the particle sample obtained by crushing is then subjected to a shaping process to remove particle edges and corners and improve particle sphericity. This not only helps to improve the processing performance of subsequent particles, but also helps to avoid problems such as too many edges and corners that are easy to break in subsequent application processes such as rolling.

[0025] As some possible implementations of the method for preparing the graphite negative electrode material of the present application, the step of preparing the precursor particles includes: after the carbon precursor material is made into particles by crushing and shaping, the particles are mixed with an organic carbon source and granulated, and the granulated product is carbonized to obtain the precursor particles. In this case, after the carbon precursor material is crushed and shaped into particles, it is mixed with an organic carbon source and granulated to obtain composite precursor particles, and then the composite precursor particles obtained by the mixed granulation are carbonized to convert the organic carbon source into carbon material through a chemical reaction. The precursor particles obtained at this time are secondary particles.

[0026] As some possible implementations of the method for preparing the graphite negative electrode material of the present application, the organic carbon source includes asphalt having a softening temperature of 100 to 500°C. In this case, the asphalt is solid at room temperature, which facilitates uniform mixing with the crushed precursor. After the organic carbon source softens during mixed granulation, it can stably bond the crushed particles together to obtain a mixed granulation product.

[0027] As some possible implementations of the method for preparing the graphite negative electrode material of the present application, the average particle size D50 of the organic carbon source is 0.5 to 5 μm; in this case, the particle size of the organic carbon source is small, which is conducive to mixing and granulating with the crushed particles of the precursor to form composite particles.

[0028] As some possible implementations of the method for preparing the graphite negative electrode material of the present application, the mass ratio of the particles to the organic carbon source is 100:(0.5-5). In this case, it is not only conducive to the mixed granulation to form composite particles of the precursor and the organic carbon source, but also avoids the excessive proportion of the organic carbon source in the composite particles of the granulated product, which leads to an excessively high amorphous carbon content in the secondary precursor particles and reduces the electrochemical performance of the subsequently prepared graphite negative electrode material.

[0029] As some possible implementations of the graphite anode material preparation method of the present application, the carbonization treatment conditions include: heating to 600-900°C at a rate of 2-10°C / min and holding for 1-10 hours in an inert atmosphere. Under these carbonization conditions, in the secondary precursor particles obtained by mixing and granulating the precursor material and the organic carbon source, the organic carbon source undergoes a high-temperature pyrolysis reaction, converting the carbon element in the organic carbon source into a structure that forms fixed carbon.

[0030] As some possible implementations of the graphite negative electrode material preparation method of the present application, the graphitization treatment conditions include: maintaining the temperature at 2400-3000°C for 24-72 hours. Under these graphitization treatment conditions, the precursor particles can be fully graphitized with high graphitization efficiency.

[0031] As some possible implementations of the method for preparing the graphite negative electrode material of the present application, the graphitization step includes: pre-carbonizing the precursor particles at a temperature of 700-1200°C for 2-7 days, and then maintaining the temperature at a temperature of 2400-3000°C for 24-72 hours. In this case, pre-carbonizing the precursor particles first to remove volatile matter from the precursor particles in advance before graphitizing them is beneficial for the sample to grow into more complete graphite crystals during subsequent high-temperature graphitization.

[0032] As some possible implementations of the method for preparing the graphite negative electrode material of the present application, the step of screening the graphite particles includes: screening and demagnetizing the product after the graphitization treatment in sequence, and screening the graphite particles whose microcrystal parameters meet the requirements. In this case, screening is used to remove larger particles and impurities, demagnetize, control magnetic foreign matter by electric current, further purify the product, and screen the microcrystal parameters of the product to obtain the graphite particles whose microcrystal parameters meet the requirements.

[0033] A third aspect of the present application provides a battery pole piece, wherein the battery pole piece contains the above-mentioned graphite negative electrode material or the graphite negative electrode material prepared by the above-mentioned method.

[0034] The battery electrode provided herein, incorporating the aforementioned graphite negative electrode material, has a stable microcrystalline structure. Application to the battery electrode improves the uniformity of expansion and stress distribution during cycling, reduces the rate of active lithium consumption, and thus achieves an ultra-long cycle life for the battery system. Furthermore, the graphite negative electrode material has a large crystallite size and large inter-graphite interlayer spacing, which facilitates the diffusion of lithium ions within the particles, improves the dynamics of the battery electrode, and facilitates rapid charging of the battery.

[0035] A fourth aspect of the present application provides a secondary battery, which includes the above-mentioned battery electrode.

[0036] The secondary battery provided in the present application includes the above-mentioned battery pole piece, which contains a graphite negative electrode material with a stable microcrystalline structure, large microcrystalline size and large graphite layer spacing, so that the battery pole piece has excellent kinetic performance and long-cycle stability, thereby improving the electrochemical properties of the secondary battery such as rate performance and cycle performance, reducing the risk of lithium plating, reducing the impact of continuous rupture and regeneration and repair of the SEI film on the electrode surface on the battery cycle life and safety performance, and reducing the risk of safety failures such as battery capacity diving and thermal runaway.

[0037] A fifth aspect of the present application provides an energy storage device, which includes the secondary battery mentioned above.

[0038] The energy storage device provided by this application, because it includes the aforementioned secondary battery with good long-cycle stability, good rate performance, and high safety performance, improves the overall performance of the energy storage device, such as stability and safety. As a result, the energy storage device provided by this application has good cycle performance and a long service life.

[0039] A sixth aspect of the present application provides an electrical device, which includes the above-mentioned secondary battery.

[0040] The electrical device provided in the present application includes a secondary battery having the above-mentioned characteristics of good long-cycle stability, good rate performance, and high safety performance, thereby improving the use stability and safety of the electrical device.

[0041] The above description is only an overview of the technical solution of the present application. In order to more clearly understand the technical means of the present application, it can be implemented in accordance with the contents of the specification. In order to make the above and other purposes, features and advantages of the present application more obvious and easy to understand, the specific implementation methods of the present application are listed below. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] FIG1 is a schematic diagram of the structure of graphite microcrystals in the graphite negative electrode material provided in an embodiment of the present application, wherein (a) is a schematic diagram of the unit cell structure of the graphite microcrystal, and (b) is a schematic diagram of the relationship between La, Lc, and d002 in the unit cell of the graphite microcrystal;

[0043] FIG2 is a schematic structural diagram of natural graphite and mosaic coke-based artificial graphite provided by the prior art;

[0044] FIG3 is a schematic diagram of the structure of graphite particles and graphite crystallites in the graphite negative electrode material provided in an embodiment of the present application;

[0045] FIG4 is a schematic flow chart of a method for preparing a graphite negative electrode material provided in an embodiment of the present application. DETAILED DESCRIPTION

[0046] In order to make the technical problems, technical solutions and beneficial effects to be solved by this application more clearly understood, the present application is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain this application and are not intended to limit this application.

[0047] In this application, the term "and / or" describes the relationship between associated objects, indicating that three possible relationships exist. For example, A and / or B can represent: A exists alone, A and B exist simultaneously, and B exists alone. A and B can be singular or plural. The character " / " generally indicates that the associated objects are in an "or" relationship.

[0048] In this application, "at least one" means one or more, and "more than one" means two or more. "At least one of the following" or similar expressions refers to any combination of these items, including any combination of single items or plural items. For example, "at least one of a, b, or c", or "at least one of a, b, and c" can all mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be single or multiple.

[0049] It should be understood that in the various embodiments of the present application, the size of the serial numbers of the above-mentioned processes does not mean the order of execution. Some or all of the steps can be executed in parallel or sequentially. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.

[0050] The terms used in the embodiments of the present application are for the purpose of describing specific embodiments only and are not intended to limit the present application. The singular forms "a", "an", "the" and "the" used in the embodiments of the present application and the appended claims are also intended to include plural forms unless the context clearly indicates otherwise.

[0051] The term "SEI" is the abbreviation of "Solid Electrolyte Interface", which means solid electrolyte interface membrane. During the charging and discharging process of the ion battery, the negative electrode of the battery is polarized, and the components of the electrolyte solution undergo reduction and decomposition on the surface of the negative electrode to form new chemical products, which are deposited on the surface of the negative electrode to form a dense passivation film. This passivation film is called solid electrolyte interface membrane, abbreviated as SEI membrane.

[0052] The term "LFP" is the abbreviation of "LiFePO4", which stands for "Lithium iron phosphate" in English. It means lithium iron phosphate, also known as lithium iron phosphate. It is a positive electrode material for lithium-ion batteries, also known as lithium iron phosphate batteries.

[0053] The term "La" refers to the length of a graphite crystal along the a-axis (diameter of the sheet). As shown in Figure 1, C=C double bonds form a hexagonal structure, forming a plane, i.e., a single graphite sheet. Multiple sheets stacked together form a graphite crystal, with the radial direction of a single graphite sheet being the a-axis (corresponding to the 110-degree crystal plane). La represents the length of the graphite crystal along the a-axis.

[0054] The term "Lc" refers to the thickness of a graphite crystal along the c-axis (perpendicular to the lamellar structure). As shown in Figure 1, C=C double bonds form a hexagonal structure, forming a plane, i.e., a single graphite lamella. Multiple lamellae stacked together form a graphite crystal, with the c-axis (corresponding to the 002 crystal plane) perpendicular to the lamellae. Lc represents the stacking thickness of a graphite crystal along the c-axis.

[0055] The term "d002" is the distance between two adjacent graphite sheets along the c-axis in a graphite crystal. As shown in Figure 1, C=C double bonds form a hexagonal structure, forming a plane, i.e., a single graphite sheet; multiple sheets stacked on top of each other form a graphite crystal. Along the c-axis, perpendicular to the sheet structure, the distance between adjacent graphite sheets is represented by d002. The ideal graphite crystal interlayer spacing is 0.3354 nm, which can also be expressed as ), the larger the interlayer spacing in the graphite crystal, the more the graphite tends to be amorphous carbon. The interlayer spacing of amorphous carbon is greater than or equal to 0.344nm and can be as high as 0.37nm (also expressed as ). Wherein, the relationship among La, Lc and d002 is shown in FIG1 (b).

[0056] The term "D10" refers to the particle size at which the cumulative particle size distribution of a sample (the percentage of all particle sizes preceding or following it) reaches 10%. Its physical meaning is that the particles with a diameter smaller than this account for 10%.

[0057] The term "D50" refers to the particle size at which the cumulative particle size distribution of a sample reaches 50%. Its physical meaning is that 50% of the particles are larger than this value, and 50% of the particles are smaller than this value. D50 is also called the median diameter or median particle size. D50 is often used to indicate the average particle size of a powder.

[0058] The term "D90" refers to the particle size at which the cumulative particle size distribution of a sample reaches 90%. Its physical meaning is that 90% of the particles have a particle size smaller than this.

[0059] The term "battery cell" refers to a single electrochemical cell containing positive and negative electrodes. It is the smallest unit of a power battery and the energy storage unit. A battery cell consists of three main parts: positive and negative electrode sheets, electrolyte, and separator.

[0060] The term "module" refers to when multiple battery cells are encapsulated together in the same shell frame and connected to the outside through a unified boundary, this forms a module.

[0061] The term "battery pack" refers to the unified whole of several modules that are jointly controlled or managed by the battery management system (BMS) and the thermal management system.

[0062] At present, judging from the development of the market situation, with the continuous expansion of the application field of power batteries, the market demand is also constantly increasing. In particular, lithium-ion batteries have been rapidly and widely popularized and applied in the fields of mobile terminals, energy storage devices, electric vehicles, etc. Therefore, higher and higher requirements are also placed on the performance of lithium-ion batteries such as initial efficiency, energy density, and cycle life. Lithium-ion batteries contain electrolytes. During the charge and discharge process of ion batteries, the negative electrode of the battery is polarized, and the components of the electrolyte solution undergo reduction and decomposition on the surface of the negative electrode to form new chemical products, which are deposited on the surface of the negative electrode to form a dense passivation film. This passivation film is called a solid electrolyte interface film, or SEI film for short.

[0063] Although the formation of the SEI film improves the cycle performance and service life of the electrode, some lithium ions are consumed during the formation of the SEI film, resulting in an increase in the irreversible capacity of the electrode material and a reduction in the initial coulombic efficiency of the electrode material. Furthermore, during the subsequent charge and discharge process of the battery, the graphite negative electrode will expand and contract in volume due to the deintercalation of lithium, resulting in the formation of a newly exposed surface. This newly exposed surface will react with the electrolyte and consume active lithium again. Therefore, during the charge and discharge process of the battery, the SEI film on the surface of the graphite negative electrode will continue to repair and grow, and during this repair and growth process, the lithium ions in the ion battery will continue to be consumed, thereby reducing the cycle performance of the battery.

[0064] The graphite crystals in the graphite negative electrode are in a lamellar structure, as shown in Figure 1. The carbon atoms form covalent bonds by sp2 hybridization, and are connected by C=C double bonds in the same plane to form a hexagonal ring extension, forming a planar lamellar layer (ink lamellar surface), such as lamellar A and lamellar B in (a) of Figure 1. The layers are stacked together through weak van der Waals forces and π-π delocalized orbital interactions to form graphite crystals. The radial direction of a single lamellar layer is the direction of the a-axis (corresponding to the 110 crystal plane), and the direction perpendicular to the lamellar structure is the c-axis direction (corresponding to the 002 crystal plane). The distance between adjacent lamellar layers in an ideal graphite crystal is 0.3354nm (can also be expressed as ), while the distance between adjacent sheets in amorphous graphite is as high as 0.37nm (also expressed as During the lithium ion embedding process, the graphite crystal gradually transitions from the original carbon structure to the fully lithiated LiC6 structure, and enters the graphite crystal sheets according to the embedding amount, accompanied by the interlayer spacing in the c-axis direction from the original ≈ becomes ≈ During lithium removal, the volume of the graphite anode shrinks in the opposite direction. Therefore, during the process of lithium ion insertion and extraction, the volume change of the graphite anode comes from the expansion and contraction of the graphite crystals in the c-axis direction. In micron-sized graphite particles, the expansion of the particle layer during lithium ion insertion and extraction is not only related to the initial interlayer spacing (d002) of the graphite crystals and their own expansion, but also to the orientation degree, size and bonding mode of the graphite crystals in the graphite particles. Therefore, factors that are not conducive to the structural stability of the graphite anode will exacerbate the volume change of the graphite anode during the cycle, thereby leading to the loss of active lithium in the lithium-ion battery and a reduction in the battery cycle life.

[0065] Therefore, in order to improve the cycle life of ion batteries, it is necessary to improve the structural stability of graphite negative electrode materials during the cycle. In some known solutions, as shown in Figure 2, natural graphite and coke-based artificial graphite are compounded, natural graphite and embedded coke-based artificial graphite are used as negative electrode materials together, although the electrical conductivity characteristics of natural graphite can be improved to a certain extent, it is still impossible to effectively solve the inherent characteristics of natural graphite such as multi-pores inside the natural graphite and large specific surface area, causing it to expand greatly during the cycle, active lithium loss is fast, and the problem of obvious disadvantage in the cycle. In addition, the Lc of coke-based artificial graphite is relatively small, and the d002 interlayer spacing is small, and the expansion after lithium insertion is large, which improves the effect of the cycle. In other known solutions, graphite particles are bonded into spherical secondary particles by additives to increase the sphericity of graphite. Although it is beneficial to improve the tap density and compaction density of the graphite negative electrode material, the expansion characteristics of the original particles of the graphite negative electrode material have not changed, and the stress accumulation caused by long-term cycling will cause the bonding to break, resulting in loss of active materials and increase in the side reaction area, thereby accelerating battery degradation.

[0066] Based on the above considerations, in order to solve the problem of long cycle life of ion batteries, after in-depth research, a graphite negative electrode material is proposed. The graphite particles contained in the graphite negative electrode material have larger crystallite sizes La and Lc, and the interlayer spacing d002 along the c-axis direction is also larger. The number parameter of crystallites contained in a single graphite particle is defined as N = D50 3 / (La 2 *Lc), by limiting the parameters of graphite particle size D50 and crystallite size La and Lc, the number of crystallites contained in the graphite particles is reduced, resulting in a larger graphite crystallite size in the graphite particles. At this time, when lithium ions are embedded in the hexagonal mesh layer of the graphite crystal, the interlayer spacing d(002) of the edge embedding site (002 crystal plane) is large, the crystallite size Lc in the c-axis direction and the crystallite size La of the 110 crystal plane are both large, ensuring the uniformity of expansion between crystallites when ions are embedded in the graphite particles. As a result, the volume expansion and contraction of the graphite negative electrode material during the lithium insertion and deinsertion process are small and uniform, and the graphite negative electrode material has better kinetics and long-cycle stability. This reduces the impact of the continuous repair and regeneration of the SEI film on the surface of the graphite negative electrode due to rupture on the battery cycle life and safety performance.

[0067] For the convenience of description, the following embodiments of the present application are described by taking graphite negative electrode materials and their preparation methods and applications as examples.

[0068] In the first aspect, the embodiment of the present application provides a graphite negative electrode material, wherein the graphite negative electrode material includes graphite particles having an average length La ≥ 40 nm along the a-axis direction of the crystallite, an average thickness Lc ≥ 25 nm along the c-axis direction of the crystallite, and an interlayer spacing d002 of 0.336 to 0.338 nm, and the number parameter of the crystallites contained in a single graphite particle is defined as N = D50 3 / (La 2 *Lc); wherein D50 is the median particle size of the graphite particles, in μm, and the value of the crystallite number parameter N satisfies 0<N≤0.04.

[0069] Thus, the graphite negative electrode material provided in the embodiments of the present application has the following advantages:

[0070] On the one hand, the graphite crystallite size La in the graphite particles of the graphite negative electrode material is ≥40nm, Lc ≥25nm, and the number of crystallites contained in a single graphite particle is defined as N=D50 3 / (La 2*Lc), where D50 is the median particle size of the graphite particles, expressed in μm, and N satisfies the condition 0 < N ≤ 0.04. This ensures that the graphite crystallites in the graphite anode material are large. When lithium ions embed within the hexagonal mesh of the graphite crystallites, the large crystallites provide more sites for ion insertion and removal, facilitating ion insertion and removal from the edge embedding sites between the graphite crystal layers. This improves ion insertion and removal efficiency and facilitates rapid ion transport. This in turn enhances the kinetic performance of the graphite anode material during cyclic charge and discharge, and improves the rate capability, cycling performance, and other electrochemical properties of the battery in which it is used. This reduces the risk of lithium plating and mitigates the risks of safety failures such as battery capacity drop and thermal runaway.

[0071] On the other hand, the interlayer spacing d002 of the graphite crystallites along the c-axis in the graphite anode material is 0.336-0.338 nm. This large interlayer spacing reduces the degree of graphitization. When lithium ions are embedded in the hexagonal mesh of the graphite crystals, the interlayer spacing d(002) at the edge embedding sites (002 crystal planes) is large, and the crystallite size Lc along the c-axis and the crystallite size La along the 110 crystal plane are both large, ensuring uniform expansion between the crystallites when ions are embedded within the graphite particles. This improves the uniformity of expansion and stress distribution of the graphite anode material during cycling, resulting in small and uniform volume expansion and contraction during lithium insertion and deintercalation. This results in better kinetics and long-cycle stability, reducing the rate of active lithium consumption. This reduces the impact of the continuous rupture and regeneration of the SEI film on the graphite anode surface on the battery cycle life and safety performance.

[0072] In some possible embodiments, in the graphite negative electrode material, the parameter N of the number of crystallites in a single graphite particle is D50. 3 / (La 2 *Lc), where the unit of D50 is μm, and the units of Lc and La are nm, so the unit of the crystallite number parameter can be expressed as μm / nm. In the calculation formula of the crystallite number parameter of the embodiment of the present application, when the units of D50, Lc and La are determined, the value of N is only related to the numerical value and is no longer affected by the parameter unit. The crystallite number parameter N represents the graphite crystallite number parameter contained in a single graphite particle. The numerical value of N satisfies 0<N≤0.04, which is the average value, indicating that the number of graphite crystallites in a single graphite particle is not higher than 0.04*10 9For example, 0<N≤0.039, 0<N≤0.038, 0<N≤0.037, 0<N≤0.035, 0<N≤0.033, 0<N≤0.031, 0<N≤0.03, 0<N≤0.028, 0<N≤0.026, 0<N≤0.025, 0<N≤0.023, 0<N≤0.021, 0<N≤0.02, 0<N≤0.01 8. 0<N≤0.016, 0<N≤0.015, 0<N≤0.014, 0<N≤0.012, 0<N≤0.01, 0<N≤0.009, 0<N≤0.008, 0<N≤0.007, 0<N≤0.006, 0<N≤0.005, 0<N≤0.004, 0<N≤0.003, 0<N≤0.002, 0<N≤0.001, etc.

[0073] In some specific embodiments, the graphite particles are approximated as a cube, the edge length of which is D50, and the volume of the graphite particles is expressed as D50. 3 The structural diagram of graphite particles and graphite microcrystals is shown in Figure 3. The microcrystal particles are approximately shaped like a cuboid. The size of a single graphite sheet is the bottom area of ​​the microcrystal particle, which is expressed as La*La. The height (thickness) of the microcrystal particle is Lc. At this time, the volume of the microcrystal particle is expressed as La 2 *Lc. Therefore, the number of crystallites contained in a single graphite particle can be calculated by the ratio of the volume of the graphite particle to the volume of the crystallite particle. The crystallite number parameter is approximately expressed as N = D50 3 / (La 2 *Lc). Since graphite particles and microcrystalline particles are not necessarily regular polyhedrons, the number of microcrystalline represents an approximate average parameter rather than an exact quantitative value.

[0074] In some specific embodiments, in the graphite negative electrode material, the crystallite number parameter in a single graphite particle is 0<N≤0.03. In a further embodiment, the crystallite number parameter is 0<N≤0.02. In a further embodiment, the crystallite number parameter is 0.001≤N≤0.01. The above embodiments of the present application further limit the crystallite number parameter in the graphite particles to ensure that the graphite crystallites in the graphite particles have a larger size. The large-sized graphite crystallites provide more deintercalation sites for the insertion and extraction of ions, which is more conducive to the ions entering between the sheets of graphite crystals from the edge embedding sites, improving the ion deintercalation efficiency, and facilitating the rapid transmission of ions. This makes the graphite negative electrode material have better kinetics, reduces the risk of lithium plating, and reduces the risk of safety failures such as battery capacity diving and thermal runaway.

[0075] For example, the parameter N of the number of crystallites in a single graphite particle can be typically but not limited to 0.0205, 0.0039, 0.0088, 0.0391, 0.04, 0.037, 0.035, 0.033, 0.03, 0.028, 0.025, 0.023, 0.02, 0.018, 0.015, 0.013, 0.01, 0.009, 0.006, 0.005, 0.003, 0.001, etc.

[0076] In some possible embodiments, the interlayer spacing d002 of the graphite crystallites along the c-axis in the graphite particles of the graphite negative electrode material may typically, but not limitedly, be in the range of 0.336-0.338 nm, 0.336-0.3363 nm, 0.3363-0.3364 nm, 0.3364-0.3368 nm, 0.3368-0.337 nm, 0.337-0.3373 nm, 0.3373-0.3375 nm, 0.3375-0.3378 nm, 0.3378-0.338 nm, etc. In this case, the interlayer spacing of the graphite crystallites along the c-axis is larger, which reduces the degree of graphitization, is more conducive to the insertion of lithium ions into the hexagonal network layer of the graphite crystal, and improves the expansion uniformity between the crystallites when ions are inserted into the graphite particles, thereby improving the kinetics and long-cycle stability of the graphite negative electrode material.

[0077] In some possible embodiments, the graphite crystallite parameters in the graphite particles are such that the average length La along the crystallite a-axis is ≥40 nm and La≤200 nm, and the average thickness Lc along the crystallite c-axis is ≥25 nm and Lc≤200 nm. In this case, the crystallite size La of the graphite crystallite in the 110 crystal plane of the graphite particles is large, and the crystallite thickness Lc in the c-axis direction is also large, thereby ensuring that the graphite crystallite has a large size. When lithium ions are embedded in the hexagonal mesh layer of the graphite crystal, the expansion uniformity between the crystallites when the ions are embedded in the graphite particles is ensured, thereby improving the long-term cycle stability of the graphite negative electrode and reducing the impact of the continuous rupture and regeneration and repair of the SEI film on the surface of the graphite negative electrode on the battery cycle life and safety performance.

[0078] For example, the average length La of the graphite crystallite parameter along the crystallite a-axis direction in the graphite particles may typically but not limitatively be 40 to 200 nm, 50 to 200 nm, 60 to 200 nm, 70 to 200 nm, 80 to 200 nm, 90 to 200 nm, 100 to 200 nm, 110 to 200 nm, 120 to 200 nm, 130 to 200 nm, 140 to 200 nm, 150 to 200 nm, 160 to 200 nm, 170 to 200 nm, 180 to 200 nm, 190 to 200 nm, 200 to 200 nm, 210 to 200 nm, 220 to 200 nm, 230 to 200 nm, 240 to 200 nm, 250 to 200 nm, 260 to 200 nm, 270 to 200 nm, 280 to 200 nm, 290 to 200 nm, 300 to 200 nm, 310 to 200 nm, 320 to 200 nm, 330 to 200 nm, 340 to 200 nm, 350 to 200 nm, 360 to 200 nm, 370 to 200 nm, 380 to 200 nm, 390 to 200 nm, 400 to 200 nm, 410 to 200 nm, 420 to 200 nm, 430 to 200 nm, 440 to 200 nm, 450 to 200 nm, 460 to 200 nm, 470 to 2 50~200nm, 160~200nm, 170~200nm, 180~200nm, 190~200nm, 50~190nm, 60~180nm, 70~170nm, 80~160nm, 90~150nm, 100~140nm, 110~130nm, 42.5~51nm, 51~55nm, 55~58nm, 58~60.5nm, etc.

[0079] The average thickness Lc of the graphite crystallite parameters along the crystallite c-axis in the exemplary graphite particles may typically, but not limited to, be in the range of 25 to 200 nm, 30 to 200 nm, 40 to 200 nm, 50 to 200 nm, 60 to 200 nm, 70 to 200 nm, 80 to 200 nm, 90 to 200 nm, 100 to 200 nm, 110 to 200 nm, 120 to 200 nm, 130 to 200 nm, 140 to 200 nm, 150 to 200 nm, 160 to 200 nm, 170 to 200 nm, 180 to 200 nm, 190 to 200 nm, 200 to 200 nm, 210 to 200 nm, 220 to 200 nm, 230 to 200 nm, 240 to 200 nm, 250 to 200 nm, 260 to 200 nm, 270 to 200 nm, 280 to 200 nm, 290 to 200 nm, 300 to 200 nm, 310 to 200 nm, 320 to 300 nm, 330 to 300 nm, 340 to 300 nm, 350 to 300 nm, 360 to 300 nm, 370 to 300 nm, 380 to 300 nm, 390 to 400 nm, 400 to 400 nm, 410 to 400 nm, 420 to 400 nm, 430 to 400 nm, 440 to 400 nm, 450 to 0nm, 180~200nm, 190~200nm, 30~190nm, 40~180nm, 50~170nm, 60~160nm, 70~150nm, 80~140nm, 90~130nm, 100~120nm, 25~30nm, 30~35nm, 35~38nm, 38~40.1nm, 40.1~42.6nm, 42.6~45nm, 45~50nm, 50~60nm, 60~70nm, 70~80nm, 80~90nm, etc.

[0080] In some possible embodiments, the median particle size D50 of the graphite particles is 5 to 25 μm. In this case, the particle size represents the median value of the particle size distribution of the graphite particles. Among all graphite particle samples, 50% of the particles have a diameter greater than this value and 50% of the particles have a diameter less than this value. The median particle size D50 of the graphite particles ensures the electrochemical comprehensive performance of the graphite negative electrode material, such as cycle stability and rate performance. Exemplarily, the median particle size D50 of the graphite particles can be typically but not limited to 5 to 24 μm, 5 to 22 μm, 5 to 20 μm, 5 to 18 μm, 5 to 16 μm, 5 to 14 μm, 5 to 12 μm, 5 to 10 μm, 5 to 8 μm, 5 to 6 μm, 5 to 7 μm, 7 to 9 μm, 9 to 11 μm, 11 to 14 μm, 14 to 16 μm, 16 to 18 μm, etc.

[0081] In some possible embodiments, the median particle size D50 of the graphite particles is 7 to 14 μm. In the case of this median particle size of the graphite particles, graphite particles with small particle size have a larger specific surface area, providing more active surface area for ion insertion and extraction, which is beneficial to improving the rate performance and cycle performance of the battery used in the graphite negative electrode material. Exemplarily, the median particle size D50 of the graphite particles can be 7 to 8.3 μm, 8.3 to 9 μm, 9 to 10 μm, 10 to 11 μm, 11 to 11.2 μm, 11.2 to 11.5 μm, 11.5 to 12 μm, 12 to 13 μm, 13 to 14 μm, etc.

[0082] In some possible embodiments, the median particle size D50 of the graphite particles satisfies the particle size D10 and the particle size D90 (D90-D10) / D50≤1.7. In this case, D90 means that 90% of the particles in the graphite particle sample have a particle size smaller than the particle size D90, and D10 means that 10% of the particles in the graphite particle sample have a particle size smaller than the particle size D10. (D90-D10) / D50 represents the particle size distribution width of large and small particles after all the particles in the graphite particles are combined together. The smaller the value of (D90-D10) / D50, the more uniform the particle size in the graphite particles. In the embodiment of the present application, (D90-D10) / D50≤1.7, the ratio is relatively small, indicating that the particle size distribution uniformity of the graphite particles is relatively high, which is beneficial to improving the flatness and thickness uniformity of the film layer prepared from the graphite negative electrode material. If the particle size distribution of graphite particles is too wide, on the one hand, it will affect the relationship between graphite particles and microcrystals. On the other hand, excessive content of fine powder in the graphite negative electrode material will affect the cycle performance of the negative electrode material, thereby affecting the cycle performance of the battery cell.

[0083] For example, the (D90-D10) / D50 of the graphite particles can be typically but not limited to (D90-D10) / D50≤1.7, (D90-D10) / D50≤1.6, (D90-D10) / D50≤1.5, (D90-D10) / D50≤1.4, (D90-D10) / D50≤1.3, (D90-D10) / D50≤1.2, (D90-D10) / D50≤1.1, etc.

[0084] In some possible embodiments, the median particle size D50, particle size D10, and particle size D90 of the graphite particles satisfy (D90-D10) / D50≤1.5. In this case, the particle size distribution of the graphite particles has a higher uniformity, which is more conducive to improving the flatness and thickness uniformity of the negative electrode film prepared from the graphite negative electrode material, thereby improving the structure and cycle stability of the negative electrode.

[0085] In some possible embodiments, the specific surface area of ​​the graphite negative electrode material is 0.8 to 2.0 m 2 / g. In this case, the size of the specific surface area of ​​the graphite negative electrode material will affect its electrochemical performance. Specifically, a larger specific surface area generally means more active surfaces available for electrochemical reactions to occur, thereby improving the electrochemical reaction rate and capacity of the graphite negative electrode material. However, a larger specific surface area may also cause the mechanical stability of the graphite negative electrode material to decrease, making it prone to falling off and damage, thereby affecting its cycle life and safety performance, and being detrimental to processing performance. Therefore, the size range of the specific surface area of ​​the graphite negative electrode material in the embodiment of the present application balances the relationship between the reaction rate, capacity and mechanical stability of the graphite negative electrode material to achieve optimal electrochemical performance and safety performance.

[0086] For example, the specific surface area of ​​the graphite negative electrode material may be typically but not limited to 0.8 to 2.0 m 2 / g, 0.9~1.9m 2 / g, 1.0~1.8m 2 / g, 1.1~1.7m 2 / g, 1.2~1.6m 2 / g, 1.3~1.5m 2 / g, 0.8~1.8m 2 / g, 0.8~1.4m 2 / g, 0.8~1.2m 2 / g, 0.8~1.0m 2 / g, 1.0~2.0m 2 / g, 1.2~2.0m 2 / g, 1.4~2.0m 2 / g, 1.6~2.0m 2 / g, 1.8~2.0m 2 / g, etc.

[0087] In some possible embodiments, the specific surface area of ​​the graphite negative electrode material is 0.9 to 1.5 m 2 / g. In this case, the specific surface area of ​​the graphite negative electrode material can better take into account the reaction rate, capacity and mechanical stability of the graphite negative electrode material, so that the graphite negative electrode material has better electrochemical stability and safety performance.

[0088] In some possible embodiments, the graphite particles are single particles or secondary particles. The single graphite particles in the embodiment of the present application refer to graphite particles obtained by directly graphitizing the graphite precursor material after it is crushed into a target size, that is, single particles. Secondary particles refer to graphite precursor materials that are crushed into a target size, the precursor particles are mixed and granulated with an organic carbon source such as asphalt to obtain composite precursor particles, and then the composite precursor particles obtained by the mixed granulation are subjected to carbonization, pre-carbonization, graphitization and other treatments, and the graphitized products are crushed again to obtain graphite particles of the target size, which are then obtained as secondary particles. Compared with single-particle graphite negative electrode materials, secondary particle graphite negative electrode materials have better thermal conductivity, which is beneficial to reducing the temperature rise of the material and improving its safety performance. Secondary particle graphite negative electrode materials have higher specific surface area and more microporous structures, which are beneficial to improving their electrochemical reaction rate and capacity on the one hand, and on the other hand, the high specific surface area and microporous structure may also cause structural changes and capacity decay in long-term use. Furthermore, secondary graphite anode materials lack the mechanical stability of single-particle graphite and are prone to shedding and damage, which impacts their cycle life and safety performance. Furthermore, the preparation process for secondary particles is complex and costly. Therefore, in practical applications, single-particle or secondary-particle graphite anode materials can be selected based on specific application requirements to ensure optimal electrochemical performance.

[0089] The graphite negative electrode material provided in the embodiments of the present application can be prepared by the following embodiment method.

[0090] In a second aspect, as shown in FIG4 , an embodiment of the present application provides a method for preparing a graphite negative electrode material, comprising the following steps:

[0091] S10. The carbon precursor material is made into precursor particles;

[0092] S20. After graphitizing the precursor particles, the graphite particles are screened to obtain a graphite negative electrode material; in the graphite particles, the average length La along the a-axis direction of the crystallite is ≥40 nm, the average thickness Lc along the c-axis direction of the crystallite is ≥25 nm, the interlayer spacing d002 is 0.336-0.338 nm, and the number parameter of the crystallites contained in a single graphite particle is defined as N=D503 / (La 2 *Lc); wherein D50 is the median particle size of the graphite particles, in μm, and the value of the crystallite number parameter N satisfies 0<N≤0.04.

[0093] The second aspect of the present invention provides a method for preparing a graphite negative electrode material, wherein a carbon precursor material is prepared into precursor particles, graphitized, and graphite particles having crystallite parameters that meet the requirements are screened to obtain a graphite negative electrode material. In the prepared graphite negative electrode material, the crystallite parameters of the graphite particles meet the following requirements: the average length La along the crystallite a-axis direction is ≥ 40 nm, the average thickness Lc along the crystallite c-axis direction is ≥ 25 nm, the interlayer spacing d002 is 0.336 to 0.338 nm, and the number of crystallites contained in a single graphite particle is defined as N = D50. 3 / (La 2 *Lc), where the unit of median particle size D50 is μm. It ensures that the number of graphite crystallites in the graphite particles is small, the relative size of the crystallite particles is large, and the graphite layer spacing is large, which reduces the degree of graphitization. When lithium ions are embedded in the hexagonal mesh layer of the graphite crystal, the layer spacing d(002) of the edge embedding site (002 crystal plane) is large, the crystallite size Lc in the c-axis direction and the crystallite size La of the 110 crystal plane are both large, so that when ions are embedded in the interior of the graphite particles, it not only has better dynamics, improves the ion deintercalation efficiency, is conducive to the rapid transmission of ions, and improves the rate performance of the applied battery; but also has more uniform expansion performance between the crystallites, improves the expansion and stress distribution uniformity of the graphite negative electrode material during the cycle, reduces the active lithium consumption rate, and improves the long-cycle stability and safety of the graphite negative electrode material. In addition, the preparation process of the embodiment of the present application is simple and suitable for industrial large-scale production and application. In addition, by screening the structure of the carbon source precursor material and regulating the graphitization process of the carbon precursor material, the microcrystalline structure of the graphite particles can be improved / optimized, and the stability of the particle level and microcrystalline level structure of the graphite particles can be improved, which is beneficial to the rapid transmission of ions.

[0094] In the above step S10, the carbon precursor material is made into precursor particles; by crushing the carbon precursor material, the carbon precursor material is processed into particles with appropriate and relatively uniform particle size, which is beneficial to improving the efficiency of subsequent graphitization treatment.

[0095] In some possible embodiments, the fixed carbon content in the carbon precursor material is not less than 60%; in this case, the high fixed carbon content in the carbon precursor material means that the carbon element content in the material is relatively high, which is conducive to the preparation of high-performance graphite negative electrode materials. Specifically, carbon precursor materials with high fixed carbon content can withstand high temperature environments, are not easy to decompose and burn, and have good thermal stability. At the same time, they have high mechanical strength and can provide better tensile, bending and compression properties. And it is conducive to the preparation of graphite negative electrode materials with better electrical and thermal conductivity. Exemplarily, the fixed carbon content in the carbon precursor material can be typically but not limitatively ≥60%, further ≥70%, further ≥80%, further ≥90%, etc.

[0096] In some possible embodiments, the carbon precursor material includes at least one of calcined petroleum coke, calcined petroleum coke, coal tar coke, and anthracite. All of these carbon precursor materials used in the examples of this application have a high fixed carbon content, and the carbon structure in these carbon precursor materials, after subsequent graphitization, is conducive to obtaining large-sized microcrystalline particles and graphite particles with large interlayer spacing. Calcined petroleum coke refers to raw petroleum coke obtained through the petroleum coking process without high-temperature treatment. It has a relatively loose structure, contains a large amount of volatile matter and impurities, and has a fixed carbon content below 80%. Calcined petroleum coke has relatively stable physical and chemical properties. Calcined petroleum coke refers to a material obtained by calcining calcined petroleum coke at high temperatures. Calcined petroleum coke has a higher fixed carbon content, a lower volatile content, and improved physical properties such as mechanical strength, electrical conductivity, and thermal conductivity. Coal tar coke refers to a material obtained by coking coal tar or asphaltene feedstock. Its structure is denser than calcined petroleum coke, and it has a higher fixed carbon content and mechanical properties. Anthracite is a type of coal with a high carbon content, exceeding 80%. Anthracite has a dense structure and contains small amounts of oxygen, hydrogen and other elements, but has a high ash content and good combustion properties and chemical stability.

[0097] In some possible embodiments, the step of preparing precursor particles includes: crushing the carbon precursor material into particle samples with an average particle size D50 of 1 to 20 μm, and then performing a shaping process to obtain precursor particles with an average particle size D50 of 1 to 30 μm. In the embodiment of the present application, the carbon precursor material is crushed into particle samples with an average particle size D50 of 1 to 20 μm by mechanical grinding, roller grinding or air flow grinding, and then the crushed particle samples are shaped to remove the particle edges and corners and improve the sphericity of the particles. This is not only beneficial to improving the processing performance of subsequent particles, but also to avoiding problems such as too many edges and corners that are easy to break in subsequent application processes such as rolling. In the crushing and shaping processes, air is used to remove fine powder, remove broken fine powder and angular fine powder, reduce the number of fine particles, and obtain precursor particles with an average particle size D50 of 1 to 30 μm. This particle size is conducive to subsequent uniform graphitization treatment to obtain graphite negative electrode materials of suitable particle size.

[0098] Exemplarily, the average particle size D50 of the precursor particles can typically but not limitatively be 1-30 μm, 2-29 μm, 3-28 μm, 4-27 μm, 5-26 μm, 6-25 μm, 7-24 μm, 8-23 μm, 9-22 μm, 10-21 μm, 11-20 μm, 12-19 μm, 13-18 μm, 14-17 μm, 15-16 μm, 3-10 μm, 5-15 μm, 10-20 μm, 15-25 μm, 20-30 μm, etc.

[0099] In other possible embodiments, the step of preparing precursor particles includes: after the carbon precursor material is made into particles by crushing and shaping, the particles are mixed with an organic carbon source for granulation, and the granulated product is carbonized to obtain precursor particles. In this case, after the carbon precursor material is crushed and shaped into particles, it is mixed with an organic carbon source for granulation to obtain composite precursor particles, and then the composite precursor particles obtained by the mixed granulation are carbonized to convert the organic carbon source into carbon material through a chemical reaction. The precursor particles obtained at this time are secondary particles. The secondary precursor particles obtained by this method can more flexibly and efficiently regulate the size and sphericity of the precursor particles during the granulation process, which is beneficial to improving the specific surface area and microporous structure of the precursor particles.

[0100] In some possible embodiments, the organic carbon source includes asphalt with a softening temperature of 100 to 500°C. The asphalt used in the embodiment of the present application is a dark brown complex mixture composed of hydrocarbons of different molecular weights and their non-metallic derivatives, and is a type of high-viscosity organic liquid carbon source. Using asphalt with this softening temperature as an organic carbon source is solid at room temperature, which is conducive to uniform mixing with the crushed precursor. After the mixed granulation organic carbon source is softened, the crushed particles can be stably bonded together to obtain a mixed granulation product. Exemplarily, the organic carbon source includes a softening temperature of 100 to 200°C, 200 to 300°C, 300 to 400°C, 400 to 500°C, etc.

[0101] In some possible embodiments, the average particle size D50 of the organic carbon source is 0.5-5 μm. In this case, the small particle size of the organic carbon source facilitates mixing with the crushed precursor particles to form composite particles. For example, the average particle size D50 of the organic carbon source can be 0.5-1 μm, 1-1.5 μm, 1.5-2 μm, 2-2.5 μm, 2.5-3 μm, 3-3.5 μm, 3.5-4 μm, 4-4.5 μm, 4.5-5 μm, etc.

[0102] In some possible embodiments, the mass ratio of particles to organic carbon sources is 100:(0.5-5). In this case, after the carbon precursor material is crushed and shaped into particles, it is mixed and granulated with the organic carbon source at a mass ratio of 100:(0.5-5). This mass ratio is conducive to the mixed granulation to form composite particles of the precursor and the organic carbon source, and avoids the excessive proportion of the organic carbon source in the composite particles of the granulated product, resulting in excessive amorphous carbon content in the secondary precursor particles, which reduces the electrochemical performance of the subsequently prepared graphite negative electrode material. Exemplarily, the mass ratio of particles to organic carbon sources can be 100:(0.5-1), 100:(1-2), 100:(2-3), 100:(3-4), 100:(4-5), etc.

[0103] In some possible embodiments, the carbonization treatment conditions include: heating to 600-900°C in an inert atmosphere at a rate of 2-10°C / min and maintaining the temperature for 1-10 hours. The inert atmosphere includes, but is not limited to, gases such as nitrogen, argon, and helium that do not participate in the conversion of the organic carbon source into a carbon material. Under these carbonization conditions, the organic carbon source undergoes a high-temperature pyrolysis reaction in the secondary precursor particles obtained by mixing and granulating the precursor material and the organic carbon source, converting the carbon elements in the organic carbon source into a structure that forms fixed carbon. Specifically, the organic carbon source undergoes cracking and polymerization reactions at high temperatures in the absence of oxygen, generating a series of intermediate products and ultimately forming a solid carbon material. During the carbonization process, the organic carbon source undergoes different stages, including: Initially, the volatile components in the organic carbon source are heated and evaporated, leaving a residue containing a high carbon concentration. As the temperature increases, the organic carbon source begins to crack, producing macromolecular compounds containing carbon skeletons, namely tar. When the temperature rises to a certain level, the carbon skeletons in the tar further polymerize to form compounds with even higher molecular weights, namely coke. Coke is a solid carbon material with high purity, high density, high strength and high conductivity. During the carbonization process of the organic carbon source, factors such as carbonization temperature, carbonization time, and raw material composition will affect the process of the carbonization reaction and the product structure. By controlling these factors, carbon materials with different properties and structures can be prepared. For example, the heating rate of the carbonization treatment can be 2-5°C / min, 5-8°C / min, 8-10°C / min, etc., the holding temperature can be 600-700°C, 700-800°C, 800-900°C, etc., and the holding time can be 1-3h, 3-5h, 5-8h, 8-10h, etc.

[0104] In the above step S20, after the precursor particles are graphitized, the graphite particles are screened to obtain a graphite negative electrode material. In the embodiment of the present application, the amorphous or partially ordered carbon material in the precursor particles is converted into a graphite structure with a highly ordered arrangement at high temperature by graphitizing the precursor particles. Graphitizing the precursor particles can, on the one hand, change the electronic structure in the carbon material of the precursor particles, thereby improving its electrical conductivity. The carbon material after graphitization has higher electrical conductivity and lower resistivity, which is beneficial to improving the application performance of the graphite negative electrode material in the battery. On the other hand, since the molecular structure in the carbon material after graphitization is more ordered, its thermal conductivity will also be improved. On the other hand, graphitization can make the structure in the carbon material more compact, thereby improving its mechanical strength and hardness. In addition, the surface of the carbon material after graphitization is smoother and the structure is more stable, which can improve its resistance to chemical corrosion. After graphitization treatment, screening and demagnetization are carried out, and the crystallite parameters are screened to meet the following requirements: the average length La along the a-axis of the crystallite is ≥ 40 nm, the average thickness Lc along the c-axis of the crystallite is ≥ 25 nm, and the interlayer spacing d002 is 0.336-0.338 nm. The number of crystallites contained in a single graphite particle is defined as N = D50. 3 / (La 2 *Lc); where D50 is the median particle size of the graphite particles, expressed in μm. Graphite particles with a crystallite number parameter, N, satisfying the condition 0 < N ≤ 0.04 exhibit a stable microcrystalline structure. As graphite anode materials, these particles can improve the uniformity of expansion and stress distribution during cycling, reduce the rate of active lithium consumption, and thus achieve ultra-long cycling in battery systems. Furthermore, these graphite particles possess a large crystallite size and large interlayer spacing, which facilitates lithium ion diffusion within the particles, improves the kinetics of the graphite anode material, and facilitates rapid charging of the battery.

[0105] In some possible embodiments, the conditions for the graphitization treatment include: keeping the temperature at 2400-3000°C for 24-72 hours. Under the graphitization treatment conditions, the precursor particles can be fully graphitized and the graphitization efficiency is high. Exemplarily, the temperature of the graphitization treatment can be 2400-2500°C, 2500-2600°C, 2600-2700°C, 2700-2800°C, 2800-2900°C, 2900-3000°C, etc., and the graphitization holding time can be 24-36 hours, 36-48 hours, 48-60 hours, 60-72 hours, etc.

[0106] In some possible embodiments, the graphitization step includes pre-carbonizing the precursor particles at a temperature of 700-1200°C for 2-7 days, followed by maintaining the temperature at 2400-3000°C for 24-72 hours. In the present embodiment, the graphitization process is performed by pre-carbonizing the precursor particles to remove volatiles from the precursor particles before graphitization. This facilitates the growth of more complete graphite crystals during subsequent high-temperature graphitization.

[0107] In some specific embodiments, the pre-carbonization step can include placing the shaped or granulated precursor particles into a crucible, placing the crucible into a tunnel kiln, and calcining the material in the crucible by igniting natural gas to generate heat. The temperature is in the range of 700-1200°C, and the calcination time is 2-7 days.

[0108] In some possible embodiments, the step of screening graphite particles includes: screening and demagnetizing the product after graphitization treatment in sequence, and screening graphite particles whose microcrystalline parameters meet the requirements. Among them, screening is used to remove particles and impurities with larger particle sizes. Specifically, vibration screening can be used to screen out particles and impurities with larger particle sizes, etc., to obtain qualified samples under the sieve. Demagnetization controls magnetic foreign matter by electric current to further purify the product. Specifically, the screened sample flows into the demagnetization equipment, and the excitation current is passed to control the content of magnetic foreign matter within 5ppm to obtain a demagnetized product. The microcrystalline parameters of the product are further screened to obtain graphite particles whose microcrystalline parameters meet the requirements.

[0109] In some embodiments, the carbon precursor material is crushed into particle samples with an average particle size D50 of 1 to 20 μm, and then subjected to shaping treatment to obtain precursor particles with an average particle size D50 of 1 to 30 μm. After the precursor particles are pre-carbonized at a temperature of 700 to 1200°C for 2 to 7 days, they are graphitized at a temperature of 2400 to 3000°C for 24 to 72 hours. The product after graphitization is vibrated and screened to remove larger particles and impurities to obtain qualified samples under the sieve. The screened sample flows into the demagnetization equipment, and the excitation current is passed to control the content of magnetic foreign matter within 5 ppm to obtain a demagnetized product. The microcrystalline parameters of the product are further screened to obtain graphite particles whose microcrystalline parameters meet the requirements. The graphite particles obtained at this time are single particles.

[0110] In other embodiments, after the carbon precursor material is made into particles by crushing and shaping, the particles are mixed with an organic carbon source including pitch with a softening temperature of 100-500°C for granulation, wherein the average particle size D50 of the organic carbon source is 0.5-5 μm, and the mass ratio of the particles to the organic carbon source is 100:(0.5-5). The granulated product is heated to 600-900°C at a rate of 2-10°C / min in an inert atmosphere and kept warm for 1-10 hours to obtain precursor particles. At this time, the precursor particles are secondary particles with an average particle size D50 of 1-30 μm. After the precursor particles are pre-carbonized at a temperature of 700-1200°C for 2-7 days, they are graphitized at a temperature of 2400-3000°C for 24-72 hours. The graphitized product is vibrated and screened to remove larger particles and impurities, obtaining a qualified sample. The screened sample is then fed into a demagnetization device, where an excitation current is applied to control the magnetic foreign matter content to less than 5 ppm, resulting in a demagnetized product. The product is then screened for crystallite parameters to obtain graphite particles that meet the required parameters. These graphite particles are considered secondary particles.

[0111] In some possible embodiments, the number parameter of crystallites contained in a single graphite particle is defined as N=D50 3 / (La 2 *Lc); where D50 is the median particle size of the graphite particles, expressed in μm, and the crystallite number parameter N satisfies the value of 0 < N ≤ 0.04. Furthermore, the crystallite number parameter 0 < N ≤ 0.02. Furthermore, the crystallite number parameter 0.001 ≤ N ≤ 0.01. In this case, the graphite crystallites in the graphite particles are ensured to be large. Large graphite crystallites provide more intercalation and deintercalation sites for ions, facilitating the entry of ions from edge intercalation sites into the intercalation and deintercalation layers of the graphite crystals, improving ion intercalation and deintercalation efficiency and facilitating rapid ion transport. This results in better kinetics for the graphite anode material, reducing the risk of lithium plating, and lowering the risk of safety failures such as battery capacity drop and thermal runaway.

[0112] In some possible embodiments, the graphite particles have a median particle size D50 of 5 to 25 μm. Exemplarily, the graphite particles have a median particle size D50 of 7 to 14 μm. This median particle size D50 of the graphite particles ensures the comprehensive electrochemical properties of the graphite negative electrode material, such as cycle stability and rate capability.

[0113] In some possible embodiments, the graphite particles have an average length along the crystallite a-axis of 40 ≤ La ≤ 200 nm, and an average thickness along the crystallite c-axis of 25 ≤ Lc ≤ 200 nm. The graphite crystallites in the graphite particles have a large crystallite size La along the 110 plane, and a large crystallite thickness Lc along the c-axis. This ensures that the graphite crystallites are large in size. When lithium ions are embedded in the hexagonal mesh layer of the graphite crystals, this ensures uniform expansion between the crystallites within the graphite particles during ion embedding, thereby improving the long-term cycling stability of the graphite negative electrode and reducing the impact of continuous rupture and regeneration of the SEI film on the surface of the graphite negative electrode on the battery cycle life and safety performance.

[0114] In some possible embodiments, the median particle size D50, particle size D10, and particle size D90 of the graphite particles satisfy (D90-D10) / D50≤1.7. Furthermore, (D90-D10) / D50≤1.5. This indicates that the particle size distribution of the graphite particles is relatively uniform, which is beneficial for improving the flatness and thickness uniformity of the film layer prepared from the graphite negative electrode material.

[0115] In some possible embodiments, the specific surface area of ​​the graphite negative electrode material is 0.8 to 2.0 m 2 / g. Furthermore, the specific surface area is 0.9 to 1.5 m 2 The range of the specific surface area of ​​the graphite negative electrode material in the embodiment of the present application balances the relationship between the reaction rate, capacity and mechanical stability of the graphite negative electrode material to achieve optimal electrochemical performance and safety performance.

[0116] In a third aspect, an embodiment of the present application provides a battery electrode sheet, which contains the above-mentioned graphite negative electrode material or the graphite negative electrode material prepared by the above-mentioned method.

[0117] The battery electrode provided in the third aspect of the embodiment of the present application comprises the above-mentioned graphite negative electrode material, wherein the graphite negative electrode material comprises graphite particles having an average length La ≥ 40 nm along the a-axis direction of the crystallite, an average thickness Lc ≥ 25 nm along the c-axis direction of the crystallite, and an interlayer spacing d002 of 0.336 to 0.338 nm, and the number parameter of the crystallites contained in a single graphite particle is defined as N = D50 3 / (La 2 *Lc)≤0.04. As a result, the graphite anode material has a stable microcrystalline structure. Its application in battery pole pieces can improve the uniformity of expansion and stress distribution during cycling, reduce the rate of active lithium consumption, and thus achieve ultra-long cycle life for the battery system. Furthermore, the large crystallite size and large inter-layer spacing of this graphite anode material facilitate the diffusion of lithium ions within the particles, improve the dynamics of the battery pole piece, and facilitate rapid charging of the battery.

[0118] In some possible implementations, the battery electrode is a negative electrode, which includes a negative electrode collector and a negative electrode material layer coated on the surface of the negative electrode collector. The negative electrode material layer includes the graphite negative electrode material of the above embodiment and may also include a certain amount of binder, conductive agent and other components.

[0119] In some possible implementations, the negative electrode active material may include, in addition to the aforementioned graphite negative electrode material, a silicon-based negative electrode material such as silicon, a compound of silicon and a non-metal, a compound of silicon and a metal, or lithium titanate. This is for illustrative purposes only and is not intended to be a specific limitation.

[0120] In some possible implementations, the negative electrode current collector may be a metal foil, such as copper foil, gold foil, platinum foil, etc. This is merely an example and is not specifically limited herein.

[0121] In some possible implementations, typical but non-limiting examples of the negative electrode binder include sodium carboxymethylcellulose (CMC-Na), styrene-butadiene rubber (SBR), polyacrylic acid (PAA), lithium polyacrylate (LiPAA), etc. These are merely exemplary and are not specifically limited herein.

[0122] In some possible implementations, the negative electrode conductive agent may be typically but not limited to amorphous carbon, carbon nanotubes, carbon fibers, graphene, etc. This is for illustrative purposes only and is not specifically limited herein.

[0123] In some possible implementations, the preparation of the negative electrode sheet includes the following steps: mixing the negative electrode active material with a conductive agent such as conductive carbon black, a binder such as carboxymethyl cellulose and styrene-butadiene rubber, and a solvent such as water in a mass ratio of (80-99):(1-5):(2-10):100 to form a negative electrode mixed slurry, vacuum degassing, discharging, coating on a coating machine, and obtaining a negative electrode sheet after rolling, slitting, and die-cutting.

[0124] In some possible implementations, the negative electrode sheet of the battery of the present application is combined with lithium metal to form a button battery, with an initial lithium insertion capacity of 355 to 74 mAh / g in the voltage range of 0.005 to 2 V, a reversible lithium removal capacity of 330 to 348 mAh / g, and an initial coulombic efficiency of 90% to 95%.

[0125] In a fourth aspect, an embodiment of the present application provides a secondary battery comprising the above-mentioned battery electrode.

[0126] The secondary battery provided in the fourth aspect of the embodiment of the present application includes the above-mentioned battery pole piece, which contains a graphite negative electrode material with a stable microcrystalline structure, large microcrystalline size and large graphite layer spacing, so that the battery pole piece has excellent kinetic performance and long-cycle stability, thereby improving the electrochemical properties of the secondary battery such as rate performance and cycle performance, reducing the risk of lithium plating, reducing the impact of continuous rupture and regeneration and repair of the SEI film on the electrode surface on the battery cycle life and safety performance, and reducing the risk of safety failures such as battery capacity diving and thermal runaway.

[0127] In some possible implementations, lithium-ion batteries are used as a typical system or scenario for secondary batteries. The core components of lithium-ion batteries are mainly positive electrodes, negative electrodes, separators, and electrolytes. The battery electrode contained in secondary batteries is the negative electrode. During charging, lithium ions are released from the lattice of the positive electrode material containing lithium, migrate through the separator in the electrolyte to the surface of the negative electrode graphite, and then desolvate. They then reach the graphite negative electrode through ion diffusion in the SEI on the negative electrode surface, complete the charge transfer reaction, and the electrons are reduced and embedded in the graphite layer. During discharge, the reverse process occurs, and lithium ions are re-embedded from the negative electrode through the electrolyte and separator into the lattice of the positive electrode material. During the charge and discharge cycle, the intrinsic expansion of the negative electrode not only causes the surface SEI to continue to grow, repair, and consume active lithium, but also causes uneven stress distribution inside the negative electrode particles, resulting in damage to the particle structure. Both of these will lead to battery capacity decay. The lithium battery using a graphite negative electrode material with long cycle stability and excellent kinetic performance used in the embodiment of the present application has the characteristics of a long cycle life. The system paired with a lithium iron phosphate positive electrode can achieve more than 10,000 cycles, which is suitable for various energy storage scenarios. It can also be used in fields such as electric vehicles.

[0128] This application does not specifically limit the positive electrode, electrolyte, separator, etc. in the secondary battery of the embodiment, and is applicable to any battery system.

[0129] In some possible implementations, the positive electrode in the secondary battery includes a positive electrode current collector and a positive electrode material layer coated on the surface of the positive electrode current collector. In addition to the positive electrode active material, the positive electrode material layer may also include a certain amount of binder, conductive agent and other components.

[0130] In some possible implementations, the positive electrode active materials in secondary batteries include metal oxides, such as lithium cobalt oxide, lithium nickel oxide, nickel-cobalt-manganese ternary materials, lithium nickel-cobalt-aluminum oxide, lithium-rich manganese-based materials, lithium manganate, lithium nickel-manganate, ferrosoferric oxide, and lithium vanadate. Polyanion salts such as phosphates, silicates, sulfates, borates, and titanates include lithium iron phosphate, lithium manganese phosphate, lithium iron manganese phosphate, lithium vanadium phosphate, lithium vanadium phosphate, lithium cobalt phosphate, lithium nickel phosphate, lithium iron silicate, lithium iron fluorosulfate, lithium iron borate, and lithium iron titanate. Fluors, sulfides, and selenides include iron trifluoride, cobalt trifluoride, nickel trifluoride (NiF3), titanium disulfide, iron disulfide, molybdenum disulfide, and niobium triselenide.

[0131] In some possible implementations, the positive electrode current collector may be a metal foil, such as aluminum foil, gold foil, platinum foil, etc. This is merely an example and is not specifically limited herein.

[0132] In some possible implementations, the positive electrode binder may be typically but not limited to polyvinylidene fluoride (PVDF), acrylonitrile multipolymer, polyacrylic acid, hydroxypropyl methylcellulose, etc. This is for illustrative purposes only and is not specifically limited herein.

[0133] In some possible implementations, the positive electrode conductive agent may be typically but not limited to amorphous carbon, carbon nanotubes, carbon fibers, graphene, etc. This is for illustrative purposes only and is not specifically limited herein.

[0134] In some possible implementations, the preparation of the positive electrode includes the following steps: preparing a positive electrode mixed slurry with a conductive agent such as conductive carbon black, a binder such as polyvinylidene fluoride, and a solvent such as N-methylpyrrolidone in a mass ratio of (80-99):(1-5):(2-10):100, vacuum degassing, discharging, coating on a coating machine, and obtaining a positive electrode 10 after rolling, slitting, and die-cutting.

[0135] In some possible implementations, a separator in a secondary battery can block the passage of electrons while allowing the passage of ions. Exemplary separators include, but are not limited to, single-layer polypropylene (PP), single-layer polyethylene (PE), double-layer PP / PE, double-layer PP / PP, triple-layer PP / PE / PP, and ceramic-coated PE.

[0136] In some possible implementations, the electrolyte in the secondary battery includes at least one soluble metal salt.

[0137] In some possible implementations, secondary battery types include lithium-ion batteries, as well as new batteries such as sodium-ion batteries and lithium-air batteries.

[0138] In some possible implementations, the secondary battery may be in the form of at least one of a battery cell, a battery module, and a battery pack.

[0139] In some possible implementations, the battery cell types include lithium-ion batteries, as well as new battery types such as sodium-ion batteries, lithium-air batteries, and lithium metal batteries. The embodiments of the present application have no particular restrictions on the shape of the battery cell, which can be cylindrical, square, or any other shape.

[0140] In some possible implementations, the battery cells according to the embodiments of the present application may be assembled into a battery module. The battery module may contain multiple battery cells, and the specific number may be adjusted according to the application and capacity of the battery module.

[0141] In a possible implementation, the battery cells and / or battery modules of the embodiments of the present application may also be assembled into a battery pack, and the number of battery cells or battery modules contained in the battery pack may be adjusted according to the application and capacity of the battery pack.

[0142] In a fifth aspect, an embodiment of the present application provides an energy storage device, which includes the secondary battery described above.

[0143] The energy storage device provided in the fifth aspect of the present application, because it includes a secondary battery with the aforementioned characteristics of good long-cycle stability, good rate performance, and high safety performance, improves the overall performance of the energy storage device, such as stability and safety. Therefore, the energy storage device provided in the present embodiment has good cycle performance and a long service life.

[0144] The energy storage device of the embodiment of the present application includes an energy storage unit, and of course may also include other auxiliary components or necessary components. Among them, the energy storage unit contains the secondary battery of the embodiment of the above text application. The secondary battery contained in the energy storage unit may be one or more. When there are multiple secondary batteries, multiple secondary batteries can form a battery module or battery pack. Since the energy storage device of the embodiment of the present application contains the above-mentioned secondary battery of the embodiment of the present application, the energy storage device has good cycle performance, long service life, and further high energy density.

[0145] In a sixth aspect, an embodiment of the present application provides an electrical device, which includes the aforementioned secondary battery.

[0146] The electric device provided in the sixth aspect of the embodiment of the present application includes a secondary battery with the above-mentioned characteristics of good long-cycle stability, good rate performance, and high safety performance, thereby improving the use stability and safety of the electric device.

[0147] In a possible implementation, the electrical equipment may select a secondary battery in the form of a battery cell, battery module, or battery pack according to its usage requirements.

[0148] In one possible embodiment, the electrical device may be, but is not limited to, a mobile device, such as a mobile phone, a laptop computer, etc., or an electric vehicle, such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc., or an electric train, a ship, a satellite, an energy storage system, etc.

[0149] In some specific embodiments, the electric device may be a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, etc. In order to meet the high power and high energy density requirements of such electric devices, the above-mentioned battery pack or battery module may be used.

[0150] In some specific embodiments, the electrical device may also be a tape recorder, a radio, an electronic learning machine, a mobile phone, a tablet computer, a laptop computer, etc. Such electrical devices are generally required to be lightweight and thin, and the battery cell in the above embodiment may be used as a power source.

[0151] Example

[0152] The following description will be made in conjunction with specific examples. The examples described below are exemplary and are intended only to explain the present application and are not to be construed as limiting the present application. Where specific techniques or conditions are not specified in the examples, the techniques or conditions described in the literature in this area or the product specifications are used. Reagents or instruments used without manufacturer's indication are conventional products that can be purchased commercially.

[0153] Example 1

[0154] The present invention provides a graphite negative electrode material, the preparation of which includes the following steps:

[0155] ① The calcined petroleum coke raw material C1 (fixed carbon content not less than 60%) was initially crushed by a coarse crusher and then sent to a mechanical mill for further pulverization to obtain a particle sample with an average particle size D50 of 11±0.5μm.

[0156] ② The crushed raw material particle sample is put into the particle shaping equipment, and the particle sample is subjected to shaping operations such as de-edging to obtain a shaped sample with an average particle size D50 of 11±1μm.

[0157] ③ The shaped sample was placed in a graphite crucible and placed in an Acheson graphitization furnace for high-temperature graphitization. The high-temperature graphitization temperature was 2800°C for 48 hours. The sample was then cooled to room temperature over 30 days to obtain a graphitized sample.

[0158] ④ Add the graphitized sample to the vibrating screen to screen out larger particles and impurities, take the sample under the screen for subsequent demagnetization operation, and screen the products whose microcrystalline parameters meet the requirements, as shown in Table 1 below, and finally obtain graphite negative electrode material 1.

[0159] Example 2

[0160] The present invention provides a graphite negative electrode material, the preparation of which includes the following steps:

[0161] ① The calcined petroleum coke raw material C2 (fixed carbon content not less than 60%) is initially crushed by a coarse crusher and then sent to a mechanical mill for further pulverization to obtain a particle sample with an average particle size D50 of 8±0.5μm.

[0162] ② The crushed raw material particle sample is put into the particle shaping equipment, and the particle sample is subjected to shaping operations such as de-edging to obtain a shaped sample with an average particle size D50 of 8±1μm.

[0163] ③ Place the shaped sample into a graphite crucible and place it in an internal furnace for high-temperature graphitization. The high-temperature graphitization temperature is 2850°C for 55 hours. The sample is then cooled to room temperature over 10 days to obtain a graphitized sample.

[0164] ④ Add the graphitized sample to the vibrating screen to screen out larger particles and impurities, take the sample under the screen for subsequent demagnetization operation, and screen the products whose microcrystalline parameters meet the requirements, as shown in Table 1 below, and finally obtain graphite negative electrode material 2.

[0165] Example 3

[0166] The present invention provides a graphite negative electrode material, the preparation of which includes the following steps:

[0167] ① The asphalt coke raw material C3 (fixed carbon content not less than 60%) is initially crushed by a coarse crusher and then sent to a mechanical mill for further pulverization to obtain a particle sample with an average particle size D50 of 11.0±0.5μm.

[0168] ② The crushed raw material particle sample is placed into the particle shaping equipment, and the particle sample is subjected to shaping operations such as de-edging to obtain a shaped sample with an average particle size D50 of 11.0±1μm.

[0169] ③ The shaped sample is placed in a stainless steel crucible and sent into a kiln for pre-carbonization. The sample is heated by igniting natural gas, maintained at 1000°C for 48 hours, and then cooled to obtain a pre-carbonized product.

[0170] ④ The pre-carbonized product was placed in a graphite crucible and subjected to high-temperature graphitization in an Acheson graphitization furnace. The high-temperature graphitization treatment temperature was 2800°C for 48 hours. The temperature was then cooled to room temperature over 30 days to obtain a graphitized sample.

[0171] ⑤ Add the graphitized sample to the vibrating screen to screen out larger particles and impurities, take the sample under the screen for subsequent demagnetization operation, and screen the products whose microcrystalline parameters meet the requirements, as shown in Table 1 below, and finally obtain graphite negative electrode material 3.

[0172] Example 4

[0173] The present invention provides a graphite negative electrode material, the preparation of which includes the following steps:

[0174] ① The asphalt coke raw material C4 (fixed carbon content not less than 60%) is initially crushed by a coarse crusher and then sent to a mechanical mill for further pulverization to obtain a particle sample with an average particle size D50 of 9.0±0.5μm.

[0175] ② The crushed raw material particle sample is put into the particle shaping equipment, and the particle sample is subjected to shaping operations such as de-edging to obtain a shaped sample with an average particle size D50 of 9.0±1μm.

[0176] ③ The shaped sample was mixed with asphalt material with a softening temperature of 250°C in a mass ratio of 100:1.5, and sent into a granulation reactor. Heating and granulation were carried out in an inert atmosphere under stirring. The reactor temperature was maintained at 700°C. After the reaction for 8 hours, it was cooled to obtain a granulated sample.

[0177] ④ The granulated samples were placed in a box furnace for high-temperature graphitization. The high-temperature graphitization temperature was 2700°C for 48 hours. The sample was then cooled to room temperature to obtain a graphitized sample.

[0178] ⑤ The graphitized sample was added to a blender to be broken up to prevent large pieces from agglomerating, and secondary particles of artificial graphite were obtained with a D50 of 16.5±1 μm.

[0179] ⑥ The broken up graphitized sample was added to a vibrating screen to screen out larger particles and debris, and the sample under the screen was taken for subsequent demagnetization operation to screen products whose microcrystalline parameters met the requirements, as shown in Table 1 below, and finally the graphite negative electrode material 4 was obtained.

[0180] Comparative Example 1

[0181] This comparative example provides a graphite material, the preparation of which includes the following steps:

[0182] ① After the petroleum coke raw material D1 is initially crushed by a coarse crusher, it is sent to a mechanical mill for further pulverization to obtain a particle sample with an average particle size D50 of 12±0.5μm.

[0183] ② The crushed graphite sample is placed in a particle shaping device to perform shaping operations such as de-edging the graphite particles to obtain a shaped sample with an average particle size D50 of 12±1 μm.

[0184] ③ The shaped sample was placed in a graphite crucible and placed in an Acheson graphitization furnace for high-temperature graphitization. The high-temperature graphitization temperature was 2900°C for 60 hours. The sample was then cooled to room temperature over 35 days to obtain a graphitized sample.

[0185] ④ The graphitized sample was added to a vibrating screen to screen out larger particles and impurities, and the sample under the screen was taken for subsequent demagnetization operation to obtain graphite material D1, whose crystallite parameters are shown in Table 1 below.

[0186] Comparative Example 2

[0187] This comparative example provides a graphite material, the preparation of which includes the following steps:

[0188] ① After the asphalt coke raw material D2 is initially crushed by a coarse crusher, it is sent to a mechanical mill for further pulverization to obtain a particle sample with an average particle size D50 of 8.0±0.5μm.

[0189] ② The crushed graphite sample is placed in a particle shaping device to perform shaping operations such as de-edging the graphite particles to obtain a shaped sample with an average particle size D50 of 8.0±1μm.

[0190] ③ The shaped sample was mixed with asphalt material with a softening temperature of 250°C in a mass ratio of 100:1.5, and sent into a granulation reactor. Heating and granulation were carried out in an inert atmosphere under stirring. The reactor temperature was maintained at 700°C. After the reaction for 8 hours, it was cooled to obtain a granulated sample.

[0191] ④ The granulated samples were placed in a box furnace for high-temperature graphitization. The high-temperature graphitization temperature was 2800°C for 48 hours. The sample was then cooled to room temperature to obtain a graphitized sample.

[0192] ⑤ The graphitized sample was added to a blender to be broken up to prevent large pieces from agglomerating, and secondary particles of artificial graphite were obtained with a D50 of 16.5±1 μm.

[0193] ⑥ The broken up graphitized sample was added to a vibrating screen to screen out larger particles and impurities, and the sample under the screen was taken for subsequent demagnetization operation to obtain graphite material D2, whose crystallite parameters are shown in Table 1 below.

[0194] In order to verify the progress of the embodiments of the present application, the following physicochemical properties and electrochemical tests were performed on the above embodiments and comparative examples respectively:

[0195] 1. XRD test to verify the crystallite parameters of the samples: The graphite negative electrode materials prepared in the above embodiments and the graphite material powder samples prepared in the comparative example were placed in a dedicated XRD sample stage, flattened with a cover glass, and loaded into the test instrument. The XRD test used Cu Kα radiation, with a test range of 2θ = 10-90° and a scan rate of 2° / min. After obtaining the XRD patterns of each sample, the average crystallite size La(110) in the single-sheet basal plane and the average crystallite size Lc(002) in the c-axis direction of the prepared graphite sample were calculated according to the Scherrer formula (D = kλ / βcosθ, where D is the grain size, i.e., La, k is the shape factor (generally 0.9-1.0), λ is the wavelength of the incident light, β is the peak width, and θ is the diffraction angle). The peak positions and half-peak widths of the 110 and 002 crystal planes were used for calculation, respectively, and the units were nm.

[0196] 2. XRD testing verifies the sample's degree of graphitization and d002: Refer to the national standard GB / T24533-2019 for the determination of interlayer spacing d002. During the XRD test, a high-purity single-crystal Si sample was mixed as an internal standard. The diffraction peak position of the graphite sample's (002) crystal plane was calculated (with half-peak width calibration required). The interlayer spacing d002 of the prepared graphite sample was then calculated using the Bragg equation (nλ = 2dsinθ, where n is the diffraction order, λ is the wavelength of the incident light, d is the interplanar spacing of the crystal, and θ is the angle between the incident light and the crystal plane). The unit of measurement is nm. The degree of graphitization is calculated as G = (0.3440 - d002) / 0.0086 * 100%.

[0197] 3. Particle size distribution test: Referring to the national standard GB / T 24533-2019 lithium-ion battery graphite negative electrode material - determination method of particle size distribution, the graphite samples prepared in each embodiment and comparative example were dispersed in a pure water solvent, and the graphite dispersed in the pure water solvent was subjected to laser particle size measurement using a Malvern MS-3000 instrument to obtain the Dv10, Dv50, and Dv90 information of each sample.

[0198] 4. Specific surface area test: A NOVA-Touch specific surface area tester was used to perform nitrogen adsorption and desorption tests (BET method) with high-purity N2 as the adsorbent to obtain the BET specific surface area of ​​each sample.

[0199] 5. Electrochemical test: The graphite materials prepared in each example and comparative example were mixed with CMC-SBR dispersant and binder to form an aqueous solution. The slurry was coated on a copper foil current collector to obtain a graphite negative electrode sheet, which was then roll-pressed. The sheet was punched into 16mm diameter discs. The coating weight of a single sheet was controlled to be ~20mg, and the compaction density was ~1.55g / cm 3The obtained negative electrode sheet was assembled with a lithium metal sheet into a CR2430 button cell. The battery was then discharged and charged at a low current between 0.005V and 2V on a charge-discharge device. The reversible capacity and initial efficiency of the graphite negative electrode material were obtained.

[0200] The test results of the above test items are shown in Table 1 below:

[0201] Table 1

[0202] From the test data in Table 1, it can be seen that the graphite negative electrode materials prepared in Examples 1 to 4 of the present application all meet the requirements of graphite crystallite size La ≥ 40nm, Lc ≥ 25nm. The interlayer spacing d002 in the c-axis direction is between 0.336 and 0.338nm, and the crystallite number parameter N = D50 3 / (La 2 *Lc) are all less than or equal to 0.04. This shows that the graphite negative electrode material prepared in the embodiment of the present application has a small number of crystallites per unit volume, a relatively large crystallite size, a large interlayer spacing, and a reduced degree of graphitization, which is beneficial to improving the long-cycle stability and kinetic performance of the graphite negative electrode material. Comparative Examples 1 and 2 use conventional petroleum coke raw materials as precursors to prepare single-particle or secondary-particle graphite negative electrode materials. The crystallite parameters of the graphite particles are not screened. The test shows that the crystallite parameters of the graphite particles are small, the degree of graphitization is high, and the crystallite number parameter is high, indicating that the number of crystallites per unit volume is large and the crystallite size is small, which is not conducive to providing long-cycle stability and kinetic performance of the graphite negative electrode material.

[0203] 6. Cycling performance test: The graphite negative electrode materials prepared in each example and the graphite materials prepared in the comparative example were assembled into lithium iron phosphate (LFP)-graphite soft-pack batteries, and subjected to 0.5C / 0.5C cycling at 25°C and 1C / 1C accelerated cycling at a high temperature of 55°C.

[0204] The preparation steps of lithium iron phosphate LFP-graphite soft pack battery are as follows:

[0205] ① Preparation of positive electrode sheet: Weigh 2% polyvinylidene fluoride (PVDF), 2% conductive agent Super P and 96% lithium iron phosphate positive electrode active material by weight, add them into N-methylpyrrolidone (NMP) in sequence, stir and mix thoroughly, apply the slurry on aluminum foil current collector, dry, cold press and cut to obtain positive electrode sheet.

[0206] ② Preparation of negative electrode sheet: Weigh 1.5% sodium carboxymethyl cellulose (CMC), 2.5% styrene-butadiene rubber (SBR), 1% Super P and 95% of the graphite negative electrode material prepared in each embodiment or comparative example as the negative electrode active material, add them to deionized water in sequence, stir and mix thoroughly, apply the slurry on a copper foil current collector, dry, cold press, and cut to produce the negative electrode sheet.

[0207] ③ Preparation of electrolyte: Ethylene carbonate (EC), ethyl methyl carbonate (EMC) and dimethyl carbonate (DMC) were mixed in a mass ratio of EC:EMC:DMC=30:30:40, and then lithium hexafluorophosphate (LiPF6) was added to the resulting mixture to a molar concentration of 1 mol / L to obtain an electrolyte.

[0208] ④ Battery assembly: The positive electrode sheet, negative electrode sheet and commercial PE separator prepared above are made into a battery cell, which is packaged with a polymer and perfused with the electrolyte prepared above. After infiltration, formation and volume separation, a 4Ah LFP-graphite soft-pack battery cell is obtained.

[0209] The capacity retention rates of the LFP-graphite soft-pack batteries prepared from the graphite materials of the above embodiments and comparative examples after 500 cycles of 0.5C / 0.5C cycling at 25°C and 1000 cycles of 1C / 1C accelerated cycling at high temperature of 55°C are shown in Table 2 below.

[0210] Table 2

[0211] It can be seen from the test data in Table 2 that compared with the lithium-ion batteries prepared in the comparative examples, the lithium-ion batteries prepared from the graphite negative electrode materials provided in the embodiments of the present application have a small number of crystallites per unit volume, a relatively large crystallite size, and a large interlayer spacing. In the process of lithium ions being embedded in the graphite hexagonal mesh layer, the kinetics can be faster, ensuring good expansion uniformity between crystallites when lithium is embedded in the particles, and a slow rate of active lithium consumption. Therefore, the lithium-ion batteries prepared from the single-particle graphite negative electrode materials of Examples 1 to 3 of the present application and the secondary particle graphite negative electrode materials of Example 4, whether 0.5C / 0.5C at 25°C or 1C / 1C at 55°C, have a capacity retention rate at the same number of cycles that is much higher than that of the lithium-ion batteries prepared from the graphite materials of Comparative Examples 1 and 2. In addition, the lithium-ion batteries prepared from the single-particle graphite negative electrode materials of Examples 1 to 3 of the present application exhibit better cycle stability.

[0212] 7. To verify the dynamics of the graphite negative electrode material of the present application, the graphite negative electrode materials prepared in each example and the graphite material prepared in the comparative example were assembled into lithium iron phosphate (LFP)-graphite soft-pack batteries. The batteries were then charged and disassembled at 1C, 1.5C, and 2C at 25°C to determine lithium deposition. The preparation method for the lithium iron phosphate (LFP)-graphite soft-pack batteries was the same as that used in Test 6.

[0213] The LFP-graphite soft-pack batteries prepared with the above examples and comparative examples were charged and disassembled at 1C, 1.5C, and 2C at 25°C to determine lithium deposition. The test results are shown in Table 3 below.

[0214] Table 3

[0215] It can be seen from the test data in Table 3 that the lithium-ion batteries prepared from the graphite negative electrode materials of Examples 1 to 4 of the present application meet the requirement of no lithium deposition during 2C charging and disassembly at room temperature, indicating that the graphite negative electrode materials prepared from the examples of the present application have good kinetic performance, reduce the risk of lithium deposition, and reduce the risk of safety failures such as battery capacity drop and thermal runaway. It is also beneficial to improve the electrochemical properties of the applied battery, such as rate performance and cycle performance. However, the lithium-ion battery prepared from the single-particle graphite material of Comparative Example 1 does not deposit lithium at 1C, but deposits lithium at 1.5C, and its kinetics are poor; the lithium-ion battery prepared from the secondary particle graphite material of Comparative Example 2 meets the requirement of no lithium deposition at 1.5C, but deposits lithium at 2C, and its kinetic performance is also significantly lower than that of the battery applied with the graphite negative electrode material of the examples of the present application.

[0216] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them; although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some or all of the technical features therein; and these modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present application, and they should all be included in the scope of the claims and specification of the present application. In particular, as long as there is no structural conflict, the various technical features mentioned in each embodiment can be combined in any way. The scope of protection of the present application is not limited to the specific embodiments disclosed herein, but includes all technical solutions that fall within the scope of the claims. Therefore, the scope of protection of the present application shall be based on the scope of protection of the claims.

Claims

1. A graphite negative electrode material, characterized in that: The graphite negative electrode material includes graphite particles with an average length La≥40nm along the a-axis direction of the microcrystal, an average thickness Lc≥25nm along the c-axis direction of the microcrystal, and an interlayer spacing d002 of 0.336-0.338nm. The number parameter of microcrystals contained in a single graphite particle is defined as N=D50. 3 / (La 2 *Lc); wherein D50 is the median particle size of the graphite particles, in μm, and the numerical value of the crystallite number parameter N satisfies 0<N≤0.

04.

2. The graphite negative electrode material according to claim 1, characterized in that The crystallite number parameter 0<N≤0.

02.

3. The graphite negative electrode material according to claim 2, characterized in that The crystallite number parameter is 0.001≤N≤0.

01.

4. The graphite negative electrode material according to claim 1, characterized in that The La is ≤ 200nm, and the Lc is ≤ 200nm.

5. The graphite negative electrode material according to claim 1, characterized in that The median particle size D50 of the graphite particles is 5 to 25 μm.

6. The graphite negative electrode material according to claim 5, characterized in that The median particle size D50 of the graphite particles is 7 to 14 μm.

7. The graphite negative electrode material according to any one of claims 1 to 6, characterized in that: The median particle size D50, the particle size D10 and the particle size D90 of the graphite particles satisfy (D90-D10) / D50≤1.

7.

8. The graphite negative electrode material according to claim 7, characterized in that The median particle size D50, the particle size D10 and the particle size D90 of the graphite particles satisfy (D90-D10) / D50≤1.

5.

9. The graphite negative electrode material according to claim 1 or 8, characterized in that: The specific surface area of ​​the graphite negative electrode material is 0.8 to 2.0 m 2 / g.

10. The graphite negative electrode material according to claim 9, characterized in that The specific surface area of ​​the graphite negative electrode material is 0.9 to 1.5 m 2 / g.

11. The graphite negative electrode material according to claim 1 or 10, characterized in that: The graphite particles are single particles or secondary particles.

12. A method for preparing a graphite negative electrode material, characterized in that: The following steps are involved: forming a carbon precursor material into precursor particles; After the precursor particles are graphitized, the graphite particles are screened to obtain a graphite negative electrode material; in the graphite particles, the average length La along the a-axis direction of the microcrystal is ≥40nm, the average thickness Lc along the c-axis direction of the microcrystal is ≥25nm, the interlayer spacing d002 is 0.336-0.338nm, and the number parameter of microcrystals contained in a single graphite particle is defined as N=D50 3 / (La 2 *Lc); wherein D50 is the median particle size of the graphite particles, in μm, and the numerical value of the crystallite number parameter N satisfies 0<N≤0.

04.

13. The method for preparing a graphite negative electrode material according to claim 12, characterized in that: The fixed carbon content in the carbon precursor material is not less than 60%; and / or, The carbon precursor material includes at least one of calcined petroleum coke, calcined petroleum coke, coal tar coke and anthracite.

14. The method for preparing a graphite negative electrode material according to claim 12, characterized in that: The step of preparing the precursor particles comprises: crushing the carbon precursor material into particle samples with an average particle size D50 of 1 to 20 μm, and then performing shaping treatment to obtain the precursor particles with an average particle size D50 of 1 to 30 μm.

15. The method for preparing a graphite negative electrode material according to claim 12, characterized in that: The step of preparing the precursor particles comprises: preparing the carbon precursor material into particles by crushing and shaping, mixing the particles with an organic carbon source for granulation, and carbonizing the granulated product to obtain the precursor particles.

16. The method for preparing a graphite negative electrode material according to claim 15, characterized in that: The organic carbon source includes asphalt having a softening temperature of 100 to 500° C.; and / or, The average particle size D50 of the organic carbon source is 0.5 to 5 μm; and / or, The mass ratio of the particles to the organic carbon source is 100:(0.5-5).

17. The method for preparing a graphite negative electrode material according to claim 15, characterized in that: The carbonization treatment conditions include: in an inert atmosphere, heating to 600-900° C. at a rate of 2-10° C. / min and keeping the temperature for 1-10 hours.

18. The method for preparing a graphite negative electrode material according to any one of claims 12 to 17, characterized in that: The graphitization treatment conditions include: keeping the temperature at 2400-3000° C. for 24-72 hours.

19. The method for preparing a graphite negative electrode material according to claim 18, characterized in that: The graphitization treatment step includes: pre-carbonizing the precursor particles at a temperature of 700-1200° C. for 2-7 days, and then maintaining the temperature at a temperature of 2400-3000° C. for 24-72 hours.

20. The method for preparing a graphite negative electrode material according to claim 12 or 19, characterized in that: The step of screening graphite particles comprises: sequentially screening and demagnetizing the product after the graphitization treatment, and screening the graphite particles whose microcrystalline parameters meet the requirements.

21. A battery pole piece, characterized in that: The battery pole piece contains the graphite negative electrode material as described in any one of claims 1 to 11 or the graphite negative electrode material prepared by the method as described in any one of claims 12 to 20.

22. A secondary battery, characterized in that: The secondary battery comprises the battery electrode as claimed in claim 21.

23. An energy storage device, characterized in that: The energy storage device includes the secondary battery as claimed in claim 22.

24. An electrical device, characterized in that: The electrical device comprises the secondary battery as claimed in claim 22.

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