Modified artificial graphite anode active materials and their preparation and application

Abstract

This invention belongs to the field of graphite materials, specifically relating to a modified graphite and its preparation and application. The method involves pre-heat-treating coke raw materials at temperature T1, followed by graphitization to obtain graphite materials. The graphite materials are then mixed with biomass oil and pre-calcined at temperature T2, followed by a second calcination at temperature T3 to obtain the final product. The temperatures T1, T2, and T3 are 500-800℃, 500-800℃, and 1000-1500℃, respectively. The biomass oil is at least one of acidified oil, swill oil, palm oil, rapeseed oil, and soybean oil, and / or a fraction collected from the carbonization of the biomass raw materials. The biomass raw materials include at least one of bamboo, straw, and bagasse. This method optimizes the electrical conductivity and ion diffusion properties of graphite, thereby improving the capacity and fast-charging performance of the prepared material.

Description

Technical Field

[0001] This invention belongs to the field of batteries, specifically relating to the field of graphite. Background Technology

[0002] Since the invention of the first BLC-2 battery in the 1990s, graphite carbon and its derived composites have been the mainstream anode material for lithium-ion batteries for the past three decades. In traditional lithium-ion battery configurations based on graphite anodes, the cathode material is generally considered the key factor affecting energy density, while the anode material is usually related to the battery's rate performance or power density. Existing modification methods using pitch-mixed graphite typically only achieve 2C charging capabilities. Improving the fast-charging performance of commercial graphite anodes is crucial for the commercialization of lithium-ion batteries.

[0003] To improve battery performance, the main existing technology involves carbon coating of graphite materials. For example, Chinese patent document CN107814382A discloses a modified natural graphite anode material, its preparation method, and its uses. Specifically, it involves impregnating natural graphite powder and pitch using a hot isostatic press. This ensures that the pitch completely fills the pores inside the graphite particles under high temperature and pressure, while simultaneously forming a pitch coating layer on the surface. After graphitization, a modified natural graphite anode material with a core-shell structure, in which artificial graphite is in situ embedded inside and on the surface of natural graphite, is obtained. The filling rate of artificial graphite in the pores of natural graphite is ≥94%, the particle surface is smooth, and the sphericity is high. The modified natural graphite anode material obtained by this invention has an initial coulombic efficiency of ≥96% and a capacity retention of ≥80% after 1500 cycles at room temperature (1C).

[0004] For example, Chinese patent document CN106486653A discloses a liquid-phase coated modified graphite anode material and its preparation method. It is prepared from 800-1200 parts of fine graphite powder and a liquid coating agent. The fine graphite powder and the liquid coating agent are mixed at high speed in a high-speed mixer under heating, and then added to a continuous coating machine for coating to obtain a precursor. This precursor is then subjected to high-temperature heat treatment in a tube furnace under inert gas protection, held at that temperature, and cooled to room temperature to obtain the liquid-phase coated modified graphite anode material. This technology uses pitch to coat the graphite anode; however, tests show that the rate capability of this patent is only 2-3C, which cannot meet the market demand of 4-6C.

[0005] In summary, existing conventional graphite composite materials are difficult to meet the requirements of high-rate fast charging applications. Furthermore, it is difficult to simultaneously meet the requirements of high fast charging and capacity performance. Summary of the Invention

[0006] To address the problem that existing graphite-coated materials struggle to achieve both high-speed charging and high capacity, the primary objective of this invention is to provide a method for preparing modified graphite, aiming to obtain a graphite-modified material that balances excellent fast charging and capacity.

[0007] The second objective of this invention is to provide modified graphite prepared by the aforementioned method and its applications.

[0008] A third objective of this invention is to provide a secondary battery comprising the modified graphite.

[0009] A method for preparing modified graphite involves pre-heat-treating coke raw material at temperature T1, followed by graphitization treatment to obtain graphite material; then mixing the graphite material with biomass oil, and pre-calcining it at temperature T2 in the first stage, followed by calcining it at temperature T3 in the second stage, to obtain the final product.

[0010] The temperature T1 is 500~800℃;

[0011] The temperature T2 is 500~800℃;

[0012] The temperature T3 is 1000~1500℃;

[0013] The biomass oil is at least one of acidified oil, swill oil, palm oil, rapeseed oil, and soybean oil, and / or a fraction collected from the carbonization of biomass raw materials; the biomass raw materials include at least one of bamboo, straw, and sugarcane bagasse.

[0014] This invention innovatively involves graphitizing the coke raw material after heat treatment at temperature T1, followed by a two-stage roasting process with the assistance of a special biomass oil. This synergistic approach allows for the deep utilization of the biomass oil's composition and physical characteristics, optimizes the physicochemical structure of graphite, improves the storage capacity of active ions, and constructs a highly efficient ion and electron conduction network, thereby improving conduction efficiency. As a result, graphite materials with excellent capacity, fast charging, and high-temperature stability can be prepared.

[0015] In this invention, the coking raw material includes at least one of petroleum coke, isoprismatic coke, needle coke, pellet coke, and sponge coke.

[0016] In this invention, the particle size of the coke raw material is controlled to be 7~10μm (particle size after pulverization).

[0017] In this invention, the atmosphere for heat treatment is a protective atmosphere;

[0018] Preferably, the heat preservation time at temperature T1 is 3~10 h.

[0019] Preferably, the material after heat treatment is graphitized after the particle size is controlled to be 5~15μm.

[0020] In this invention, the graphitization temperature is above 2600℃, preferably 2800~3300℃;

[0021] Preferably, the graphitization time is 10~30 h.

[0022] In this invention, the combination of components in the biomass oil from the special source can optimize the physicochemical structure of the material and further optimize the fast-charging and other electrochemical properties of the prepared modified graphite material.

[0023] In this invention, the biomass oil is a fraction (biomass oil) collected from the carbonization of bamboo and / or sugarcane bagasse; preferably, it is bamboo-based biomass oil and sugarcane-based biomass oil in a weight ratio of 1:0.5~2. Studies have shown that the preferred biomass oil can further benefit its physicochemical characteristics and further optimize the fast-charging and high-temperature performance of modified graphite.

[0024] The carbonization temperature is 400~600℃.

[0025] Preferably, the preparation steps of biomass oil are as follows: the biomass raw material is carbonized to obtain crude biomass oil, and the crude biomass oil is fractionated, hydrogenated, treated with alkali, treated with acid, washed with water and dehydrated.

[0026] In this invention, the method for collecting biomass oil can be conventional. For example, the carbonized exhaust gas can be passed into a condensation device to collect the biomass oil.

[0027] In this invention, the weight ratio of the graphite material to the biomass oil is 100:3~8.

[0028] Temperature T2 is 600~700℃.

[0029] In this invention, the first stage of roasting takes 0.5 to 2 hours, and can be further taken as 1 to 1.5 hours.

[0030] Temperature T3 is 1200~1400℃.

[0031] Preferably, the second stage of roasting takes 2 to 6 hours.

[0032] The present invention also provides modified graphite prepared by the aforementioned preparation method.

[0033] The preparation method described in this invention can endow the prepared material with special physicochemical properties, and the material with these physicochemical properties can take into account excellent capacity, fast charging and high temperature performance.

[0034] The present invention also provides an application of the modified graphite obtained by the preparation method described above, which is used as a negative electrode active material for the preparation of secondary batteries.

[0035] In this invention, the modified graphite described herein can be used as a negative electrode active material based on existing principles and methods to prepare the required secondary battery.

[0036] The secondary battery described in this invention can be an alkali metal ion battery, such as a sodium ion battery or a lithium ion battery.

[0037] The present invention also provides a secondary battery, characterized in that it comprises modified graphite prepared by the preparation method described in the present invention.

[0038] The secondary battery described in this invention, apart from containing the modified graphite described in this invention, may have other conventional components and features.

[0039] Beneficial effects

[0040] This invention innovatively involves graphitizing coke raw material after heat treatment at temperature T1, followed by a two-stage roasting process in combination with biomass oil. This optimizes the microstructure of graphite, controls parameters such as lattice structure, defects, and pore structure, and improves its electrical conductivity and ion diffusion performance, thereby enhancing the capacity, fast charging, and high-temperature performance of the prepared material. Attached Figure Description

[0041] Figure 1 This is a SEM image of the modified graphite material finally obtained in Example 1.

[0042] Figure 2 The specific volume diagram shows the final modified graphite material of Example 1;

[0043] Figure 3 High magnification images of Example 1, Comparative Example 1, and Comparative Example 3. Detailed Implementation

[0044] To address the current market demand for 4-6C fast charging of graphite anode materials in lithium-ion batteries, a method for preparing biomass oil-coated modified artificial graphite anode materials is proposed. The process steps and conditions are as follows: ① Petroleum coke is coarsely crushed to micron level. ② Raw materials are treated at high temperature (500-800℃). ③ Powdering is performed to a particle size of 5-15μm. ④ Graphitization is carried out at 3000℃ to obtain a precursor. ⑤ The graphite powder obtained from the precursor and biomass oil are mixed in one of a kneading / blending / fusion apparatus for 5-20 minutes. ⑥ After thorough mixing, the mixture is placed in a high-temperature heating coating kettle for coating at 500-800℃. ⑦ Carbonization is carried out in a tubular furnace at 1200℃ to obtain the product.

[0045] The petroleum coke selected is a coke product produced by separating light and heavy oils from crude oil through distillation, and then converting the heavy oils through thermal cracking. Its specifications are: moisture ≤10%, sulfur content 0.5~4.0%, and volatile matter 1.0~11.0%.

[0046] Biomass oil is produced by the pyrolysis of plants under airless conditions, resulting in biochar and a mixed liquid. After settling, the clear liquid on top is acetic acid, while the black, viscous liquid at the bottom is biomass oil. The unique molecular structure and carbonization characteristics of this biomass oil allow for microstructural regulation during the preparation of carbon materials. By controlling parameters such as the lattice structure, defects, and pore structure of carbon materials, their conductivity and ion diffusion performance can be optimized, thereby improving the fast-charging performance of graphite anode materials. Its specifications include a coking value of 10-20% and an ash content of <0.1%.

[0047] In the following examples, the biomass oil is prepared through the following steps:

[0048] Step 1. Raw material preparation and pretreatment

[0049] Raw material selection: Biomass (wood, agricultural residues) is placed in a carbonization furnace and carbonized at a temperature of 500±20℃ under nitrogen. The gas phase fractions of the carbonization stage are collected and cooled to obtain crude biomass oil.

[0050] Step 2. Fractionation and separation

[0051] Heating fractionation: The crude biomass oil is heated for fractionation, and the fractions in the temperature range of 250~300℃ are collected.

[0052] Step 3. Catalytic hydrogenation treatment

[0053] The fraction from step 2 is hydrogenated using a hydrogenation catalyst, which may be nickel-based, molybdenum-based, or Pd-based. The hydrogenation process involves introducing hydrogen gas at 300–450°C and 1–5 MPa for 1–2 hours.

[0054] 4. Acid-base neutralization

[0055] The components after hydrogenation in step 3 are pretreated with an alkaline solution (0.5-1M sodium hydroxide), then treated with an acid solution (0.5-1M dilute sulfuric acid), and then washed with water.

[0056] 5. Dehydration and impurity removal

[0057] The bio-oil from step 4 is dehydrated and filtered to obtain biomass oil.

[0058] Example 1

[0059] Step 1:

[0060] Petroleum coke is coarsely crushed using a jaw crusher and then placed in a nitrogen atmosphere. It is then heat-treated in a muffle furnace at 600℃ (carbonization temperature) for 5-6 hours to obtain the processed raw material. The processed raw material is then pulverized and classified into particles of 7-10 μm. Finally, it is graphitized at 3000℃ (graphitization temperature) for 20±0.5 hours to obtain graphite carbon.

[0061] Step 2:

[0062] Graphite carbon and biomass oil (biomass oil from bamboo, prepared as described above, with a weight ratio of 100:5 for graphite carbon and biomass oil) are added to a kneading / mixing / fusion apparatus for 10-15 minutes. Then, the first stage of calcination is carried out at 600°C under a nitrogen atmosphere (for 1 hour). The temperature is then raised to 1200°C for a second stage of calcination (for 4 hours) to obtain the desired modified graphite material.

[0063] Example 2

[0064] Compared to Example 1, the only difference is that the biomass oil was changed; the experimental groups were as follows:

[0065] Group A: Biomass oil is acidified oil;

[0066] Group B: Biomass oil is biomass oil collected by carbonizing sugarcane bagasse (the preparation method is the same as above, the difference is that the biomass is sugarcane bagasse).

[0067] All other operations and parameters are the same as in Example 1.

[0068] Example 3

[0069] Compared with Example 1, the only difference is that the processing atmosphere in step 1 is replaced with Ar. In step 1, the carbonization temperature is 750℃ and the graphitization temperature is 3100℃. In step 2, the weight ratio of graphite carbon to biomass oil is 100:7. The temperature of the first stage of roasting is 700℃ and the roasting time is 1.5h. The temperature of the second stage of roasting is 1400℃ and the roasting time is 2.5h. All other operations and parameters are the same as in Example 1.

[0070] Example 4

[0071] The only difference from Example 1 is that the biomass oil is the biomass oil of Example 1 and the biomass oil of Example 2B in a weight ratio of 1:1. All other operations and parameters are the same as in Example 1.

[0072] Comparative Example 1

[0073] Compared with Example 1, the only difference is that the biomass oil is biomass oil collected by carbonizing wood chips; other operations and parameters are the same as in Example 1.

[0074] Comparative Example 2

[0075] Compared with Example 1, the only difference is that no biomass oil was added in step 2; all other operations and parameters are the same as in Example 1.

[0076] Comparative Example 3

[0077] Compared with Example 1, the only difference is that step 2 is not performed, while all other operations and parameters are the same as in Example 1.

[0078] Capacity: Button cell preparation method: A binder, conductive agent, and solvent are added to a graphite composite material, stirred and mixed evenly to form a slurry, the resulting slurry is coated on copper foil, dried, and rolled to obtain a button cell. The binder is LA132 binder, the conductive agent is conductive agent SP, and the solvent is double-distilled water; and the weight ratio of graphite composite material, conductive agent SP, LA132 binder, and double-distilled water is 98:1:4:220.

[0079] Using lithium metal sheets as electrodes, a composite membrane of polyethylene (PE), polypropylene (PP), and polyethylene propylene (PEP) as the separator, and LiPF6 / EC+DEC (1:1) as the electrolyte, a simulated battery assembly was performed in an argon-filled glove box. The prepared coin cells were installed on a Wuhan Bluepoint CT2001A battery tester and charged at a 0.1C rate, with a charge / discharge voltage range of 0.005V to 2.0V. The initial discharge capacity was measured and is shown in Table 1.

[0080] The graphitization degree, specific surface area, and powder OI value of the above-mentioned anode materials were tested according to the national standard GB / T-24533-2019 "Graphite Anode Materials for Lithium-ion Batteries". The test results are shown in Table 1.

[0081] Cyclic expansion test: Anode formulation C (active material, materials prepared in each case): SP:CMC:SBR = 95.8:1:1.2:2. Cathode formulation LFP (lithium iron phosphate): SP:PVDF = 96:2:2. After 50 cycles of constant current and constant voltage charging (cutoff voltage 3.65V) and constant current discharging (cutoff voltage 2.5V) at 25±2℃, the battery thickness change was measured, and the expansion rate was calculated to evaluate its structural stability.

[0082] 60℃ Cycle Life Test: Anode formulation C (active material, materials prepared in each case): SP:CMC:SBR=95.8:1:1.2:2; Cathode formulation LFP:SP:PVDF=96:2:2. After 50 cycles of 0.5C constant current and constant voltage charging (cutoff voltage 3.65V) and 1C constant current discharging (cutoff voltage 2.5V) at 60±2℃, the capacity retention rate was tested.

[0083] 60℃ Storage (7d) Retention Rate (%) / Recovery Rate (%): Negative electrode formulation C (active material, materials prepared in each case): SP:CMC:SBR = 95.8:1:1.2:2 Positive electrode formulation LFP:SP:PVDF = 96:2:2 Under 25±2℃ environment, the capacity before storage C0 (cutoff voltage 2.5V) was recorded by constant current and constant voltage charging at 0.5C (cutoff voltage 3.65V) and constant current discharge at 0.5C. After full charge at constant current and constant voltage, the capacity was stored at 60℃ for 7d. The capacity was recorded as C1 (cutoff voltage 2.5V) by constant current discharge at 0.5C. Then, the capacity was fully charged by constant current and constant voltage, and then the capacity was restored to C2 (cutoff voltage 2.5V) by constant current discharge at 0.5C. Retention rate: C1 / C0; Recovery rate: C2 / C0.

[0084] In the full-cell system for cycle testing, the model can be CR2025; the separator is Celgard 2320; and the electrolyte is 1M LiPF6 in EC / DEC / DMC (1:1:1).

[0085]

[0086] See rate performance data Figure 3 .

[0087] As demonstrated in Example 1, the unique combination of biomass oils allows for the introduction of microstructure regulation during the preparation of carbon materials. By controlling parameters such as the lattice structure, defects, and pore structure of the carbon materials, their ion diffusion performance can be optimized. Examples 2A and 2B maintain the same improved performance as Example 1. In Example 3, the OI value of the sample was further reduced to 3.54, and the fast-charging performance was improved. A more uniform coating layer helps to form a thin coating layer, thereby improving the fast-charging performance. The capacity is comparable to that of Example 1, as the uniform and thin carbon layer encapsulates the porous structure of the graphite surface, thereby reducing the specific surface area. In Example 4, the use of a mixture of biomass oil and the biomass oil from Example 2B resulted in better material and electrochemical performance. This is because the decomposition process of the two biomass oils may produce complementary carbon sources, which can form a more uniform and dense carbon coating on the graphite surface. This not only improves the conductivity of graphite but also provides better structural stability during charge and discharge.

Claims

1. A method for preparing modified graphite, characterized in that, The coke raw material is preheated at temperature T1, followed by graphitization to obtain graphite material; then the graphite material is mixed with biomass oil and pre-calcined at temperature T2 in the first stage, followed by calcination at temperature T3 in the second stage to obtain the final product. The temperature T1 is 500~800℃; The temperature for graphitization is above 2600℃; The temperature T2 is 500~800℃; The temperature T3 is 1000~1500℃; The biomass oil is at least one of acidified oil, swill oil, palm oil, rapeseed oil, and soybean oil, and / or a fraction collected from the carbonization of biomass raw materials; the biomass raw materials include at least one of bamboo, straw, and sugarcane bagasse. The weight ratio of the graphite material to the biomass oil is 100:3~8.

2. The method for preparing modified graphite as described in claim 1, characterized in that, The coke raw materials include at least one of petroleum coke, isopriate coke, needle coke, pellet coke, and sponge coke.

3. The method for preparing modified graphite as described in claim 1, characterized in that, The particle size of the coke raw material is controlled to be 7~10μm.

4. The method for preparing modified graphite as described in claim 1, characterized in that, The atmosphere used for the heat treatment is a protective atmosphere.

5. The method for preparing modified graphite as described in claim 1, characterized in that, The heat preservation time at temperature T1 is 3~10h.

6. The method for preparing modified graphite as described in claim 1, characterized in that, The material is graphitized after heat treatment if the particle size is controlled to be 5~15μm.

7. The method for preparing modified graphite as described in claim 1, characterized in that, The graphitization temperature is 2800~3300℃.

8. The method for preparing modified graphite as described in claim 1, characterized in that, The graphitization time is 10~30 h.

9. The method for preparing modified graphite as described in claim 1, characterized in that, The biomass oil is a fraction collected from the carbonization of bamboo and / or sugarcane bagasse.

10. The method for preparing modified graphite as described in claim 1, characterized in that, The biomass oil is bamboo-based biomass oil and sugarcane-based biomass oil in a weight ratio of 1:0.5~2.

11. The method for preparing modified graphite as described in claim 9, characterized in that, The carbonization temperature is 400~600℃.

12. The method for preparing modified graphite as described in claim 1, characterized in that, The preparation steps of biomass oil are as follows: the biomass raw material is carbonized to obtain crude biomass oil, and the crude biomass oil is fractionated, hydrogenated, treated with alkali, treated with acid, washed with water and dehydrated.

13. The method for preparing modified graphite as described in claim 1, characterized in that, The first roasting time is 0.5~2 hours.

14. The method for preparing modified graphite as described in claim 1, characterized in that, The second roasting time is 2-6 hours.

15. A modified graphite prepared by the preparation method according to any one of claims 1 to 14.

16. The application of modified graphite prepared by the method according to any one of claims 1 to 14, characterized in that, It is used as a negative electrode active material in the preparation of secondary batteries.

17. A secondary battery, characterized in that, The modified graphite is prepared by the method according to any one of claims 1 to 14.

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