High-rate graphite negative electrode material and preparation method thereof

Abstract

The application relates to a high-rate graphite negative electrode material and a preparation method, and belongs to the technical field of lithium ion battery negative electrode materials, which comprises the following steps: performing first heat treatment on isotropic coke at a temperature of 600-1300 DEG C, and the treatment time is 30-80 h to generate heat-treated coke; crushing the heat-treated coke and modifying the particle morphology to obtain shaped materials; performing graphitization heat treatment on the shaped materials at a temperature of 2500-2900 DEG C, and the treatment time is 3-11 h to obtain graphite crystal materials; after the graphite crystal materials are cooled, magnetic separation and grading screening are sequentially performed, and finally, the high-rate graphite negative electrode material is obtained; the area ratio of mosaic structures of the isotropic coke under a polarizing microscope is greater than 60%; and the high-performance-price ratio negative electrode material with simple process and excellent lithium ion diffusion rate is provided.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery anode material technology, and specifically relates to a high-rate graphite anode material and its preparation method. Background Technology

[0002] The performance of lithium-ion batteries largely depends on their core component—the anode material. Currently, carbon-based anode materials dominate commercial applications due to their comprehensive advantages, including high reversible specific capacity, suitable operating potential, excellent coulombic efficiency, and long cycle life. Among various carbon materials, graphite is considered one of the most promising anode materials due to its theoretical specific capacity of up to 372 mAh / g, excellent electronic conductivity, and stable layered crystal structure. Graphite materials are mainly derived from natural mining and artificial synthesis. While natural graphite performs well in terms of specific capacity and initial efficiency, its crystalline integrity easily leads to the co-intercalation of electrolyte solvent molecules, causing graphite layer exfoliation and thus impairing cycle stability. Furthermore, as a non-renewable resource, its quality fluctuations and cost controllability are also bottlenecks in its application. In contrast, artificial graphite, prepared through designable processes, exhibits superior rate performance, good compatibility with electrolytes, and cycle stability, despite typically having a slightly lower degree of graphitization. Therefore, it has become a key focus of current research and industrialization.

[0003] Currently, artificial graphite anode materials face severe challenges in meeting the multiple market demands for high-speed charging, long cycle life, and low-cost manufacturing. Specifically, the high-crystallinity materials obtained by traditional high-temperature graphitization processes have intrinsic lithium-ion diffusion rates that are insufficient to meet fast-charging requirements. To address this issue, existing technologies often employ complex surface modification or pore-building processes, but these inevitably introduce new drawbacks: firstly, the processes are cumbersome, leading to high production costs; secondly, excessive modification can damage the material's density and conductive network, resulting in a decrease in energy density and cycle stability; and thirdly, the processing performance and consistency of the electrode sheets are difficult to guarantee.

[0004] Therefore, there is an urgent need for an innovative preparation method that can synergistically optimize ionic conductivity, electronic conductivity, and structural stability from the material source to solve the above-mentioned technical problems. Summary of the Invention

[0005] This invention provides a high-rate graphite anode material and its preparation method, which can solve the technical problems of high-temperature graphitization in the prior art to pursue high capacity, but which leads to poor rate performance, low initial efficiency and high cost.

[0006] To achieve the above objectives, the present invention is implemented through the following technical solution:

[0007] In a first aspect, this application provides a method for preparing a high-rate graphite anode material, comprising the following steps:

[0008] S1. The isotropic coke is subjected to a first heat treatment at a temperature of 600-1300℃ for 30-80 hours to produce heat-treated coke.

[0009] S2. The heat-treated coke is crushed and its particle morphology is modified to obtain shaped material;

[0010] S3. The shaped material is subjected to graphitization heat treatment at a temperature of 2500-2900℃ for 3-11 hours to obtain graphite crystal material.

[0011] S4. After the graphite crystal material is cooled, magnetic separation and grading sieving are performed in sequence to finally obtain high-ratio graphite anode material.

[0012] Furthermore, in step S1, the area ratio of the mosaic structure of the isotropic focal plane under a polarizing microscope is >60%.

[0013] Furthermore, in step S1, the true density of the heat-treated coke is ≥2.05 g / cm³. 3 The volatile matter content is ≤0.5%.

[0014] Furthermore, in step S2, the particle size Dv50 of the shaped material is 7–17 μm.

[0015] Furthermore, in step S4, the specific surface area of ​​the high-rate graphite anode material is ≤1.5 m² / g.

[0016] Furthermore, in step S4, the graphitization degree of the high-ratio graphite anode material is 88% to 96%.

[0017] In a second aspect, this application provides a high-rate graphite anode material prepared by any of the methods described in the first aspect, wherein the specific surface area of ​​the graphite anode material is ≤1.5 m² / g and the degree of graphitization is 88% to 96%.

[0018] Furthermore, the initial efficiency of the graphite anode material is ≥94%.

[0019] Thirdly, this application provides a high-rate graphite anode material comprising the one described in the second aspect, wherein, under conditions of 25±2℃, the 5C rate discharge capacity of the lithium-ion battery retains ≥80% of the 0.2C discharge capacity.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] 1. The high-rate graphite anode material preparation method provided by the present invention selects isotropic coke with a specific structure as raw material, and constructs a high-speed ion transport channel inside the material through a synergistic process of key processes such as crushing, shaping, first heat treatment, and low-temperature graphitization at 2500-2800℃, while maintaining low specific surface area characteristics and improving rate performance.

[0022] 2. The high-rate graphite anode material preparation method provided by the present invention is prepared by low-temperature graphitization process. This combination, through the synergy of the isotropic structure of the raw materials and the controllable crystallization at medium and low temperatures, constructs a high-speed ion transport channel inside the material while maintaining the low specific surface area characteristics.

[0023] 3. The high-rate graphite anode material provided by the present invention has the core characteristic of forming a dual continuous structure of "ion migration shortcut" and "stable conductive network" inside. This structure, through a moderate degree of graphitization, constructs abundant active interfaces on its crystal surface and inside that are conducive to lithium ion intercalation and deintercalation, significantly reducing the diffusion barrier of lithium ions. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 This is a scanning electron microscope image of the fast-charging graphite anode material provided in Embodiment 2 of the present invention;

[0026] Figure 2 The XRD pattern of the fast-charging graphite anode material provided in Embodiment 2 of the present invention;

[0027] Figure 3 This is the first charge-discharge curve provided in Embodiment 2 of the present invention. Detailed Implementation

[0028] The embodiments of this application will now be described in detail with reference to the accompanying drawings.

[0029] In the description of this application, it should be understood that the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, unless otherwise stated, "multiple" means two or more.

[0030] Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0031] Example 1:

[0032] This embodiment provides a method for preparing a high-rate graphite anode material, including the following steps:

[0033] S1. The isotropic coke is subjected to a first heat treatment at a temperature of 600-1300℃ for 30-80 hours to produce heat-treated coke.

[0034] S2. The heat-treated coke is crushed and its particle morphology is modified to obtain shaped material;

[0035] S3. The shaped material is subjected to graphitization heat treatment at a temperature of 2500-2900℃ for 3-11 hours to obtain graphite crystal material.

[0036] S4. After the graphite crystal material is cooled, magnetic separation and grading sieving are performed in sequence to finally obtain high-ratio graphite anode material.

[0037] In step S1, the isotropic focal plane has an area ratio of >60% for its mosaic structure under a polarizing microscope; the true density of the heat-treated focal plane is ≥2.05 g / cm³. 3 The volatile matter content is ≤0.5%.

[0038] In step S2, the generated shaping material is a near-spherical particle intermediate product with a particle size Dv50 of 7–17 μm.

[0039] In step S4, the specific surface area of ​​the high-rate graphite anode material is ≤1.5 m² / g, and the degree of graphitization is 88%~96%.

[0040] Rate capability measures a battery’s ability to maintain capacity under high current (fast charging and discharging), and improving it hinges on optimizing the transport dynamics of lithium ions within the electrode material.

[0041] In existing technologies, pursuing high capacity through high-temperature graphitization leads to poor ion diffusion kinetics; while complex surface modifications to improve rate performance sacrifice compaction density, increase side reactions, and drive up costs. This invention uses isotropic coke as a precursor and employs a low-temperature graphitization process. This combination, through the synergy of the intrinsic isotropic structure of the raw material and controllable crystallization at medium to low temperatures, constructs high-speed ion transport channels within the material while maintaining low specific surface area characteristics, thus improving the rate performance of the graphite anode material. The preparation process is simple, and excellent overall performance is achieved without the use of complex modification processes, providing a key material solution for the development of next-generation high-power lithium-ion batteries.

[0042] In step S3, the shaped material undergoes graphitization heat treatment by programming the temperature in a furnace to 2500-2900℃ at a rate not exceeding 10℃ / min, and then holding it at this temperature for 10 hours to complete the transformation from amorphous carbon to graphite crystals, i.e., crystal reconstruction.

[0043] Unlike traditional high-temperature graphitization (e.g., 3100℃) that pursues extreme crystallinity, this invention uses low-temperature graphitization (2500~2900℃) to control the degree of graphitization within an optimal range of 88%~96%. The advantages of this approach are: it ensures that the carbon layer forms sufficiently regular graphite crystals, establishing a good electronic conductivity network; and it avoids an overly dense structure caused by excessive crystallization. It retains appropriate grain boundaries and active interfaces, which become "highway ramps" or "migration shortcuts" for the rapid insertion and extraction of lithium ions, significantly reducing diffusion resistance.

[0044] Example 2:

[0045] This embodiment provides one implementation method for preparing high-rate graphite anode materials, and the specific implementation method includes the following steps:

[0046] Isotropic coke, whose mosaic structure area accounts for approximately 73% as analyzed by polarized light microscopy, was selected. The raw coke was placed in a crucible, pushed into a tunnel kiln, and subjected to a first heat treatment according to a preset specific temperature program. The total treatment time was 46 hours, with the high-temperature zone set at 900℃.

[0047] After heat treatment, the coke is pulverized by roller mill and continuously shaped to obtain a shaped material with a D50 of 10.72 μm. This shaped material is an intermediate product of spherical particles.

[0048] The pulverized and shaped material undergoes graphitization heat treatment: the temperature is programmed to rise to 2800℃ in a furnace at a rate not exceeding 10℃ / min, and held at this temperature for 10 hours to complete crystal reconstruction. Subsequently, the material is slowly cooled to room temperature in the furnace, and then purified by 325-mesh vibrating sieve and magnetic separation to obtain the final graphitized single-particle artificial graphite anode material.

[0049] refer to Figures 1-3 ,in, Figure 1 This is a scanning electron microscope image of the fast-charging graphite anode material in this embodiment. Figure 2 This is the XRD pattern of the fast-charging graphite anode material in this embodiment. Figure 3 The first charge-discharge curve shows that the graphite anode material prepared in this embodiment exhibits ideal reversible capacity and coulombic efficiency. This test result confirms that the material structure advantages constructed by the process of this invention have been successfully transformed into performance advantages, and it can be applied to high-performance fast-charging batteries.

[0050] Example 3:

[0051] Isotropic coke, whose mosaic structure area accounts for approximately 73% as analyzed by polarized light microscopy, was selected. The raw coke was placed in a crucible, pushed into a tunnel kiln, and subjected to a first heat treatment according to a preset specific temperature program, with a total treatment time of 46 hours, of which the high-temperature zone was set at 900℃.

[0052] After heat treatment, the coke is pulverized by roller mill and continuously shaped to obtain a shaped material with a D50 of 15.09 μm. This shaped material is an intermediate product of spherical particles.

[0053] The shaped material undergoes graphitization heat treatment: the temperature is programmed to rise to 2800℃ in a furnace at a rate not exceeding 10℃ / min, and held at this temperature for 10 hours to complete crystal reconstruction. Subsequently, the material is slowly cooled to room temperature in the furnace, and then purified by 325-mesh vibrating sieve and magnetic separation to obtain the final graphitized single-particle artificial graphite anode material.

[0054] Example 4:

[0055] Isotropic coke, whose mosaic structure accounts for approximately 75% of the total area as analyzed by polarized light microscopy, was selected. The raw coke was placed in a crucible, pushed into a tunnel kiln, and subjected to a first heat treatment according to a preset specific temperature program, with a total treatment time of 46 hours, of which the high-temperature zone was set at 900℃.

[0056] After heat treatment, the coke is pulverized by roller mill and continuously shaped to obtain a shaped material with a D50 of 10.83μm.

[0057] The shaped material undergoes graphitization heat treatment: the temperature is programmed to rise to 2600℃ in a furnace at a rate not exceeding 10℃ / min, and held at this temperature for 10 hours to complete crystal reconstruction. Subsequently, the material is slowly cooled to room temperature in the furnace, and then purified by 325-mesh vibrating sieve and magnetic separation to obtain the final graphitized single-particle artificial graphite anode material.

[0058] Comparative Example 1:

[0059] Isotropic coke, whose mosaic structure area accounts for approximately 73% as analyzed by polarized light microscopy, was selected. The raw coke was placed in a crucible, pushed into a tunnel kiln, and subjected to a first heat treatment according to a preset specific temperature program, with a total treatment time of 46 hours, of which the high-temperature zone was set at 900℃.

[0060] After heat treatment, the coke was roller-milled, pulverized, and continuously shaped to obtain a shaped material with a D50 of 11.01 μm.

[0061] The shaped material was subjected to high-temperature graphitization heat treatment: the graphitization temperature was 3100℃, and the graphitized material was purified by 325 mesh vibrating sieve and magnetic separation to obtain Comparative Example 1.

[0062] Comparative Example 2:

[0063] Needle coke, analyzed by polarized light microscopy, was selected, with its mosaic structure accounting for approximately 35% of the total area. The needle coke was placed in a crucible, pushed into a tunnel kiln, and subjected to a first heat treatment according to a preset specific temperature program, with a total treatment time of 46 hours, including a high-temperature zone set at 900℃.

[0064] After heat treatment, the coke is pulverized by roller mill and continuously shaped to obtain a shaped material with a D50 of 11.15μm.

[0065] The shaped material was subjected to graphitization heat treatment: the temperature was raised to 2800℃ and held for 10 hours. The material was then slowly cooled to room temperature in the furnace and then purified by 325 mesh vibrating sieve and magnetic separation to obtain Comparative Example 2.

[0066] Physicochemical properties and electrochemical performance testing:

[0067] Physicochemical properties and electrochemical performance were tested for Examples 2, 3, and 4, and Comparative Examples 1 and 2. The electrochemical performance testing method involved assembling the materials from the examples and comparative examples as working electrodes with lithium metal counter electrodes to form CR2032 coin cells. The working electrodes were made of active material, conductive agent, and binder in a mass ratio of 96:2:2, and were coated, dried, rolled, and then punched for use. The electrolyte was a carbonate solvent containing 1 mol / L LiPF6. All tests were conducted at 25±2°C. Rate performance was tested by charging at a constant current rate of 0.2C, followed by constant current discharge at different rates (2C / 3C / 5C). Capacity retention was calculated as the percentage of the discharge capacity at that rate to the discharge capacity at 0.2C in the same period. The experimental results for Examples 2-4 and Comparative Examples 1-2 were obtained, as detailed in Table 1. In Table 1, the particle size D50 is the particle size of the graphite anode material finally prepared after graphitization in each embodiment or comparative example. It is different from the particle size D50 after crushing and shaping because the material will shrink and volatiles will be discharged during the high-temperature graphitization process, so there will be size changes.

[0068] Table 1. Experimental Results and Test Data of Graphite Anode Materials

[0069]

[0070] The data in Table 1 show that Example 2 maintained a capacity of 82.5% at a 5C rate, significantly better than Comparative Example 1 (70.2%), which used the same raw materials but underwent high-temperature graphitization. This demonstrates the crucial role of low-temperature processing in constructing high-speed ion channels. Regarding initial efficiency, Comparative Example 2 (needle coke), under the same process, exhibited a higher specific surface area (2.1 m² / g) due to its anisotropic layered structure, which was more easily cleaved during processing. This was far higher than the examples (1.0-1.6 m² / g). The larger specific surface area triggered more severe initial electrolyte side reactions, directly resulting in its initial efficiency (88.9%) significantly lagging behind all examples (≥94.5%). This strongly demonstrates that using isotropic coke is a key prerequisite for achieving low specific surface area and high initial efficiency. Furthermore, the variations in specific surface area within the examples (e.g., Example 4 had a slightly higher specific surface area due to a slightly lower graphitization temperature) also confirms the controllability of the process.

[0071] Example 5:

[0072] This embodiment provides a high-rate graphite anode material prepared by the method described in Example 1. The specific surface area of ​​the graphite anode material is ≤1.5 m² / g, and the degree of graphitization is 88%–96%. The initial efficiency of the graphite anode material is ≥94%.

[0073] Therefore, the high-rate graphite anode material provided by this invention has a specific surface area ≤1.5 m² / g and exhibits excellent kinetic characteristics. This graphite anode material boasts a high initial efficiency of ≥94%, demonstrating low irreversible lithium loss. Most importantly, it exhibits outstanding rate performance, retaining over 82% of its capacity during 5C high-current discharge, while maintaining excellent structural stability even under these fast-charging conditions. Thus, this invention provides a key material solution for the development of next-generation high-power lithium-ion batteries and has significant practical implications.

[0074] Example 6:

[0075] This embodiment provides a high-rate graphite anode material as described in Embodiment 5, wherein the 5C rate discharge capacity of the lithium-ion battery retains ≥80% of the 0.2C discharge capacity under conditions of 25±2℃.

[0076] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope described in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for preparing a high-rate graphite anode material, characterized in that, Includes the following steps: S1. The isotropic coke is subjected to a first heat treatment at a temperature of 600-1300℃ for 30-80 hours to produce heat-treated coke. S2. The heat-treated coke is crushed and its particle morphology is modified to obtain shaped material; S3. The shaped material is subjected to graphitization heat treatment at a temperature of 2500-2900℃ for 3-11 hours to obtain graphite crystal material. S4. After the graphite crystal material is cooled, magnetic separation and grading sieving are performed in sequence to finally obtain high-ratio graphite anode material.

2. The method for preparing a high-rate graphite anode material according to claim 1, characterized in that, In step S1, the area of ​​the isotropic focal spot in the mosaic structure under a polarizing microscope is greater than 60%.

3. The method for preparing a high-rate graphite anode material according to claim 1, characterized in that, In step S1, the true density of the heat-treated coke is ≥2.05 g / cm³. 3 The volatile matter content is ≤0.5%.

4. The method for preparing a high-rate graphite anode material according to claim 1, characterized in that, In step S2, the particle size Dv50 of the shaped material is 7-17 μm.

5. The method for preparing a high-rate graphite anode material according to claim 1, characterized in that, In step S4, the specific surface area of ​​the high-rate graphite anode material is ≤1.5 m² / g.

6. The method for preparing a high-rate graphite anode material according to claim 1, characterized in that, In step S4, the graphitization degree of the high-ratio graphite anode material is 88% to 96%.

7. A high-rate graphite anode material, characterized in that, The graphite anode material is prepared by the method described in any one of claims 1-6, and the specific surface area of ​​the graphite anode material is ≤1.5 m² / g, and the degree of graphitization is 88% to 96%.

8. The high-rate graphite anode material according to claim 7, characterized in that, The first-efficiency of the graphite anode material is ≥94%.

9. A lithium-ion battery, characterized in that, The lithium-ion battery comprising a high-rate graphite anode material as described in claim 7 or 8, wherein, under conditions of 25±2℃, the retention rate of the 5C rate discharge capacity relative to the 0.2C discharge capacity is ≥80%.

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