High-rate lithium ion battery graphite negative electrode material and preparation method thereof

Abstract

The invention discloses a high-rate lithium ion battery graphite negative electrode material and a preparation method thereof. The high-rate lithium ion battery graphite negative electrode material is prepared by the steps of crushing petroleum coke particles, calcining at low temperature, graphitizing at high temperature, cooling, demagnetizing and the like. Through the synergistic effect of multiple processes of raw material crushing, low-temperature calcination and high-temperature graphitization, a large number of micropores and defects are introduced into a carbon matrix, and a shorter diffusion path and an isotropic ion transmission channel are provided for lithium ions; and the lithium ion battery graphite negative electrode material with better rate capability, cycling stability and dynamic performance is prepared.

Description

Technical Field

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

[0002] Artificial graphite anode materials have been widely used in consumer electronics, electric vehicles, and energy storage systems due to their advantages such as high energy density, good cycle performance, wide availability, and low cost. However, with the increasingly urgent demand for fast charging and high-rate charging and discharging of electric vehicles, the inherent defects of traditional graphite anode materials in terms of rate performance have become increasingly prominent, becoming one of the technical bottlenecks restricting the development of lithium-ion batteries.

[0003] The lithium storage mechanism of graphite involves the insertion and extraction of lithium ions between graphite sheets. Graphite anode materials have an anisotropic sheet structure, which tends to align parallel to the current collector during charge and discharge. This results in the lithium ion diffusion path being perpendicular to the graphite sheets, hindering rapid ion / electron transport. Under high-rate charge and discharge conditions, lithium ions struggle to diffuse quickly and uniformly into the interior of the graphite particles, leading to poor rate performance.

[0004] To address the aforementioned problems, existing technologies disclose methods such as secondary granulation and small aggregate design to optimize the microstructure and shorten the transport path. For example, artificial graphite is mixed with asphalt, heated and melted to bind graphite particles together to form secondary particles, and then subjected to high-temperature graphitization. However, the improvement effect is limited and still cannot meet the requirements for high-rate performance artificial graphite materials. Therefore, this invention provides a high-rate lithium-ion battery graphite anode material and its preparation method. Through the synergistic effect of multiple processes including raw material crushing, low-temperature calcination, and high-temperature graphitization, a lithium-ion battery graphite anode material with better rate performance, improved cycle stability, and enhanced kinetic performance is obtained. Summary of the Invention

[0005] The purpose of this invention is to provide a high-rate lithium-ion battery graphite anode material.

[0006] Another objective of this invention is to provide a method for preparing graphite anode materials for high-rate lithium-ion batteries.

[0007] This invention is achieved through the following technical solution: The preparation method of the present invention includes the following steps: Step S1: Crush the petroleum coke particles to 8-14μm aggregate for later use; Step S2: The aggregate described in S1 is placed in a graphite crucible and calcined in a box furnace. Nitrogen gas is introduced to remove air. The temperature is raised to 650-950℃ at a rate of 5-8℃ / min and held for 1-12 hours. After natural cooling, the calcined material is obtained. Step S3: The calcined material described in S2 is subjected to high-temperature graphitization treatment. Specifically, the temperature is first raised to 1000-1400℃ at a rate of 3-7℃ / min for pre-carbonization, then raised to 3000℃ at a rate of 40-60℃ / min and held for 18-22 hours, then lowered to 2250-2750℃ at a rate of 3-7℃ / min, then lowered to 1000℃ at a rate of 1-4℃ / min, and finally naturally cooled from 1000℃ to room temperature to obtain graphitized material. Step S4: Demagnetize the graphitized material and pass it through a 325-mesh sieve to obtain the finished product.

[0008] Preferably, the particle size of the pulverized material in step S1 of the present invention is 11 μm.

[0009] Preferably, the heating rate in step S2 of the present invention is 8°C / min, and the temperature is raised to 700°C.

[0010] Preferably, the heat preservation time in step S2 of the present invention is 5 hours.

[0011] Preferably, the pre-carbonization heating rate in step S3 of the present invention is 5°C / min.

[0012] Preferably, the pre-carbonization temperature in step S3 of the present invention is raised to 1200°C.

[0013] Preferably, in step S3 of the present invention, the heating rate to 3000°C is 50°C / min, and the holding time is 20h.

[0014] Preferably, the cooling rate in step S3 of the present invention is 5°C / min, cooling down to 2500°C.

[0015] Preferably, the cooling rate in step S3 of the present invention is 2°C / min.

[0016] The high-rate lithium-ion battery graphite anode material of the present invention is prepared by the preparation method described above.

[0017] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention introduces a large number of micropores and defects into the carbon matrix through the synergistic effect of multiple processes, including raw material crushing, low-temperature calcination, and high-temperature graphitization. This provides lithium ions with a shorter diffusion path and isotropic ion transport channels, resulting in lithium-ion battery graphite anode materials with better rate performance, while also effectively improving cycle stability and kinetic performance.

[0018] 2. The preparation method of the present invention first crushes the raw materials and then performs low-temperature calcination. The resulting negative electrode material has a lower aspect ratio compared with the comparative example of calcination followed by crushing, which is beneficial to improving rate performance.

[0019] 3. The button cell assembled from the negative electrode material prepared in this invention still has a charge retention rate of 91% and 64% at charging rates of 0.5C and 1.0C, respectively, which is significantly improved compared with the comparative example. However, the OI value is lower than that of the comparative example, and the rate performance is significantly better than that of the comparative example. Attached Figure Description

[0020] Figure 1 A schematic diagram of the preparation process of graphite anode materials for high-rate lithium-ion batteries; Figure 2 SEM image of the high-rate lithium-ion battery graphite anode material prepared in Example 1; Figure 3 SEM image of the lithium-ion battery graphite anode material prepared in Comparative Example 3; Figure 4 Rate performance of coin cells of graphite anode materials prepared in the examples and comparative examples. Detailed Implementation

[0021] The technical solution of the present invention will be further described in detail below through specific embodiments. A schematic diagram of the preparation process of the high-rate lithium-ion battery graphite anode material of the present invention is shown below. Figure 1 .

[0022] Example 1 Step S1: Crush the petroleum coke particles to 11μm for use as aggregate.

[0023] Step S2: The aggregate described in S1 is placed in a graphite crucible and calcined in a box furnace. Nitrogen gas is introduced to remove air. The temperature is raised to 700°C at a rate of 8°C / min and held for 5 hours. After natural cooling, the calcined material is obtained.

[0024] Step S3: The calcined material described in S2 is subjected to high-temperature graphitization treatment. Specifically, the temperature is first raised to 1200℃ at 5℃ / min for pre-carbonization, then raised to 3000℃ at 50℃ / min and held for 20 hours, then lowered to 2500℃ at a cooling rate of 5℃ / min, then lowered to 1000℃ at a rate of 2℃ / min, and finally naturally cooled from 1000℃ to room temperature to obtain graphitized material.

[0025] Step S4: Demagnetize the graphitized material and pass it through a 325-mesh sieve to obtain the finished product.

[0026] Example 2 Unlike Example 1, Step S1: Crush the petroleum coke particles to 14μm for use as aggregate.

[0027] Step S2: Heat the temperature to 650℃ at a rate of 5℃ / min and hold for 5 hours. After natural cooling, the calcined material is obtained.

[0028] Example 3 Unlike Example 1, step S2 involves heating the material to 950°C at a rate of 5°C / min and holding it there for 1 hour. After natural cooling, the calcined material is obtained.

[0029] Example 4 Unlike Example 1, step S1 involves pulverizing oil-based needle coke particles to 8μm as aggregate for later use.

[0030] Example 5 Step S1: Crush the petroleum coke particles to 8μm aggregate for later use.

[0031] Step S2: The aggregate described in S1 is placed in a graphite crucible and calcined in a box furnace. Nitrogen gas is introduced to remove air, and the temperature is raised to 650°C at a rate of 5°C / min and held for 5 hours. After natural cooling, the calcined material is obtained.

[0032] Step S3: The calcined material described in S2 is subjected to high-temperature graphitization treatment. Specifically, the temperature is first raised to 1000℃ at 3℃ / min for pre-carbonization, then raised to 3000℃ at 40℃ / min and held for 18 hours, then lowered to 2250℃ at a cooling rate of 3℃ / min, then lowered to 1000℃ at a rate of 1℃ / min, and finally naturally cooled from 1000℃ to room temperature to obtain graphitized material.

[0033] Step S4: Demagnetize the graphitized material and pass it through a 325-mesh sieve to obtain the finished product.

[0034] Example 6 Step S1: Crush the petroleum coke particles to 14μm for use as aggregate.

[0035] Step S2: The aggregate described in S1 is placed in a graphite crucible and calcined in a box furnace. Nitrogen gas is introduced to remove air, and the temperature is raised to 950°C at a rate of 8°C / min and held for 12 hours. After natural cooling, the calcined material is obtained.

[0036] Step S3: The calcined material described in S2 is subjected to high-temperature graphitization treatment. Specifically, the temperature is first raised to 1400℃ at 7℃ / min for pre-carbonization, then raised to 3000℃ at 60℃ / min and held for 22 hours, then lowered to 2750℃ at a cooling rate of 7℃ / min, then lowered to 1000℃ at a rate of 4℃ / min, and finally naturally cooled from 1000℃ to room temperature to obtain graphitized material.

[0037] Step S4: Demagnetize the graphitized material and pass it through a 325-mesh sieve to obtain the finished product.

[0038] Comparative Example 1 Unlike Example 1, step S2 is omitted.

[0039] Comparative Example 2 Unlike Example 1, in step S1: the petroleum coke raw material is placed in a graphite crucible and placed in a box furnace for low-temperature calcination. Nitrogen gas is introduced to remove air, and the temperature is raised to 700°C at a rate of 8°C / min and held for 5 hours. After natural cooling, the calcined material is obtained.

[0040] Step S2: Crush the calcined material described in S1 to 11μm for later use.

[0041] Comparative Example 3 Unlike Example 1, in step S1: the petroleum coke raw material is placed in a graphite crucible and placed in a box furnace for low-temperature calcination. Nitrogen gas is introduced to remove air, and the temperature is raised to 950°C at a rate of 5°C / min and held for 5 hours. After natural cooling, the calcined material is obtained.

[0042] Step S2: Crush the calcined material described in S1 to 11μm for later use.

[0043] To verify the effectiveness of the invention, the inventive team conducted a series of experiments, as follows: (1) SEM test SEM tests were performed on the graphite anode materials prepared in Example 1 and Comparative Example 3, and the results are as follows: Figure 2 , Figure 3 As shown in the figure, the prepared graphite anode material is an irregular single-particle shape with a uniform size distribution.

[0044] (2) Physical and chemical tests and button cell tests The key technical parameters of Examples 1-4 and each comparative example were statistically analyzed, as shown in Table 1.

[0045] As shown in Table 1, the tap values ​​of Examples 1-4 and the comparative examples are all ≥1.0. The ratio is 1.6~1.9. 2T compaction is approximately 1.7. Examples 1-4 and the comparative examples showed no significant differences in particle size, vibration compaction, specific surface area, and compaction parameters. Combined with... Figure 2 and Figure 3 It can be seen that the aspect ratios of Examples 1-4, which were subjected to low-temperature calcination after pulverization, were not significantly different from those of Comparative Example 1 (which was directly graphitized after pulverization). However, Comparative Examples 2 and 3 were calcined before pulverization, which resulted in an increase in aspect ratios, which was not conducive to improving the rate performance.

[0046] The prepared graphite anode materials were assembled into coin cells according to the following methods: A slurry was prepared using PVDF as a binder, SP as a conductive agent, and NMP as a solvent, with an NMP:PVDF:SP ratio of 50:3.67:1. This slurry was then mixed evenly with graphite powder at a ratio of 1:1 to form a negative electrode slurry. The negative electrode slurry was coated onto the anode current collector (copper foil), dried, and rolled and cut to obtain the negative electrode sheet. A lithium sheet was used as the counter electrode, a polyethylene (PE) film as the separator, and lithium hexafluorophosphate as the electrolyte. The battery was assembled in a vacuum glove box.

[0047] The prepared button cells were installed on a Wuhan Landian CT3002A battery tester, with a charge / discharge voltage range of 0.005V to 2.0V, and were charged and discharged at rates of 0.1C, 0.3C, 0.5C, and 1.0C. The test results are shown in Table 2.

[0048] From Table 2 and Figure 4 It can be seen that after the pulverization and calcination treatment, the charge retention rate of Examples 1-4 was not significantly different from that of the comparative example at charge rates of 0.1C and 0.3C. However, at 0.5C and 1.0C, it was significantly improved compared with Comparative Example 1 (without low-temperature calcination treatment), and the OI value was also significantly reduced. Its rate performance was significantly better than that of the comparative example. This is because under low-temperature calcination, light hydrocarbons and hydrogen-containing functional groups in petroleum coke decompose or escape, generating a large number of mesopores and defects in the carbon matrix. These defects and pores are retained in the subsequent high-temperature treatment, forming a permanent, interconnected mesoporous system. This provides shorter diffusion paths and more diffusion channels for lithium ions, greatly improving the ion transport rate and significantly enhancing the rate performance. Comparative Examples 2 and 3, which employed a process of calcination followed by pulverization, showed a decrease in rate performance and an increase in OI value. This is because after the raw coke underwent low-temperature calcination, some graphite microcrystals had already grown, making the material more brittle. During subsequent pulverization, the particles would break along the growth direction of the graphite microcrystals, resulting in elongated materials (such as...). Figure 3 Lithium ions need to diffuse over long distances and anisotropically within a complete layered structure, which in turn leads to a decrease in their rate performance.

[0049] Although the present invention has been described in detail above with general descriptions, specific embodiments, and experiments, modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, all such modifications or improvements made without departing from the spirit of the present invention fall within the scope of protection claimed by the present invention.

Claims

1. A method for preparing a high-rate lithium-ion battery graphite anode material, characterized in that, The preparation method includes the following steps: Step S1: Crush the petroleum coke particles to 8-14μm aggregate for later use; Step S2: The aggregate described in S1 is placed in a graphite crucible and calcined in a box furnace. Nitrogen gas is introduced to remove air. The temperature is raised to 650-950℃ at a rate of 5-8℃ / min and held for 1-12 hours. After natural cooling, the calcined material is obtained. Step S3: The calcined material described in S2 is subjected to high-temperature graphitization treatment. Specifically, the temperature is first raised to 1000-1400℃ at a rate of 3-7℃ / min for pre-carbonization, then raised to 3000℃ at a rate of 40-60℃ / min and held for 18-22 hours, then lowered to 2250-2750℃ at a rate of 3-7℃ / min, then lowered to 1000℃ at a rate of 1-4℃ / min, and finally naturally cooled from 1000℃ to room temperature to obtain graphitized material. Step S4: Demagnetize the graphitized material and pass it through a 325-mesh sieve to obtain the finished product.

2. The method for preparing the high-rate lithium-ion battery graphite anode material according to claim 1, characterized in that, The particle size of the pulverized material in step S1 is 11 μm.

3. The method for preparing the high-rate lithium-ion battery graphite anode material according to claim 1, characterized in that, The heating rate in step S2 is 8°C / min, and the temperature is increased to 700°C.

4. The method for preparing the high-rate lithium-ion battery graphite anode material according to claim 1, characterized in that, The heat preservation time in step S2 is 5 hours.

5. The method for preparing the high-rate lithium-ion battery graphite anode material according to claim 1, characterized in that, The pre-carbonization heating rate in step S3 is 5℃ / min.

6. The method for preparing the high-rate lithium-ion battery graphite anode material according to claim 1, characterized in that, The pre-carbonization process in step S3 involves heating the temperature to 1200°C.

7. The method for preparing the high-rate lithium-ion battery graphite anode material according to claim 1, characterized in that, The heating rate to 3000℃ in step S3 is 50℃ / min, and the holding time is 20h.

8. The method for preparing the high-rate lithium-ion battery graphite anode material according to claim 1, characterized in that, The cooling rate in step S3 is 5℃ / min, cooling down to 2500℃.

9. The method for preparing the high-rate lithium-ion battery graphite anode material according to claim 1, characterized in that, The cooling rate in step S3, the second stage, is 2°C / min.

10. A high-rate lithium-ion battery graphite anode material, characterized in that, It is prepared by the preparation method described in claims 1-9.

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