Method for acid washing and purifying porous carbon for silicon-carbon negative electrode material and product thereof

Abstract

The application provides a pickling purification method of porous carbon for silicon-carbon negative electrode materials and a product thereof, and belongs to the technical field of battery material preparation. The method overcomes the defects of poor purity and long process flow of the existing pickling method. The production method comprises the following steps: crushing carbonization raw materials to 20-50 meshes, and then performing physical activation. The method further comprises the steps of "blowing and stirring cleaning" and "belt rinsing while simultaneously performing vacuum exhaust and controlling the water content to be 60%". The porous carbon is deeply and efficiently purified, so that the iron content and ash content of the porous carbon are reduced to a very low level (Fe<30ppm, ash content<0.2%), and the high-pore structure (iodine value≥1600mg / g) of the porous carbon is maintained. The unique blowing and stirring method has smaller shearing force on the carbon skeleton, and better protects the microstructure of the porous carbon. The belt rinsing is continuously operated, and has high automation degree, and is suitable for large-scale industrial production. The porous carbon product prepared by the method has very high purity and high specific surface area, and meets the needs of high-end lithium ion batteries.

Description

Technical Field

[0001] This invention belongs to the field of battery material preparation technology, specifically relating to an acid washing and purification method for high-purity porous carbon used in silicon-carbon anodes of lithium-ion batteries, and the high-purity porous carbon product prepared by this method. Background Technology

[0002] Porous carbon, especially activated carbon with a high specific surface area, is used as a carrier or composite component in silicon-based anode materials due to its excellent conductivity and stable structure. It can effectively buffer the volume expansion of silicon during charge and discharge, improving the cycle stability of the battery. However, when used as an anode in high-end lithium-ion batteries, impurities in porous carbon, particularly metallic impurities such as iron (Fe), nickel (Ni), and chromium (Cr), as well as ash, can severely affect the battery's electrochemical performance, leading to increased self-discharge, shortened cycle life, and even safety hazards.

[0003] Currently, acid washing is commonly used in industry to reduce the impurity content in porous carbon. Traditional acid washing purification processes typically have the following problems:

[0004] Limited purification level: Conventional soaking or simple agitation and acid washing are insufficient to stably reduce the iron content to below 50 ppm, which cannot meet the requirements of high-performance silicon-carbon anodes.

[0005] The process is lengthy: it often requires multiple pickling and washing processes, which is time-consuming, inefficient, and generates a large amount of wastewater.

[0006] Pore ​​structure is easily damaged: Violent or improper stirring or cleaning processes may damage the fragile pore structure of activated carbon, leading to a decrease in its specific surface area (such as iodine adsorption value).

[0007] Poor uniformity: Insufficient or uneven pickling and rinsing may lead to unstable quality of batches of products.

[0008] Therefore, developing a purification method that can efficiently and deeply remove metal impurities and ash while maintaining or even optimizing the pore structure and high adsorption performance of porous carbon is crucial for improving the performance of silicon-carbon anode materials. Summary of the Invention

[0009] One objective of this invention is to overcome the shortcomings of existing technologies and provide an acid washing purification method for porous carbon used in silicon-carbon anode materials that offers high purification efficiency and effectiveness. This method can deeply remove metallic impurities such as iron and ash while maintaining the high specific surface area of ​​the porous carbon.

[0010] The second objective of this invention is to provide a porous carbon product with high purity and high specific surface area prepared by the above method, which is particularly suitable for high-performance silicon-carbon anode materials.

[0011] To achieve the above objectives, the present invention adopts the following technical solution:

[0012] In a first aspect, the present invention provides an acid washing and purification method for porous carbon used in silicon-carbon anode materials, comprising the following steps:

[0013] (1) Screen the carbonization raw materials to remove impurities;

[0014] (2) Crush the screened carbonized raw materials to 20-50 mesh;

[0015] (3) Physically activate the crushed carbonized raw materials to obtain activated carbon;

[0016] (4) The activated carbon is subjected to sieving and magnetic separation to remove fine powder and iron;

[0017] (5) Mix the activated carbon treated in step (4) with a hydrochloric acid solution of 30%-36% at a solid-liquid ratio of 0.3-0.5 kg / l and cook it for 4 ± 0.2 hours, stirring during the acid cooking process;

[0018] (6) After draining the acid, add purified water and perform agitation and cleaning with a blower for 0.5-1 hour. Repeat this cleaning process 4-6 times.

[0019] (7) The cleaned activated carbon is rinsed in a belt, and vacuum is drawn from the bottom of the rinsing belt to control the moisture content of the activated carbon after rinsing to be within the range of 60±3%.

[0020] (8) The rinsed activated carbon is dried to obtain the porous carbon precursor for silicon-carbon anode material.

[0021] In a second aspect, the present invention provides a porous carbon material for silicon-carbon anode materials prepared by the method described in the first aspect above.

[0022] Preferably, the silicon-carbon anode material is made of porous carbon with an iodine adsorption value of not less than 1600 mg / g, an iron content of less than 30 ppm, and an ash content of less than 0.2%.

[0023] The advantages and beneficial effects of this invention are as follows:

[0024] 1. Deep Purification: A synergistic effect is achieved through a combination of "hydrochloric acid cooking," "blown agitation cleaning," and "belt vacuum rinsing." Cooking allows the acid to fully react with impurities (especially iron trapped deep within the pores); blower agitation utilizes the vigorous movement of airflow to efficiently peel off and carry away reaction products; and belt vacuum rinsing enables continuous and highly efficient countercurrent cleaning, ultimately removing iron content to below 30 ppm and ash content to below 0.2%, far exceeding the level of conventional acid washing processes.

[0025] 2. Structural Protection and Performance Enhancement: By optimizing the process sequence and placing crushing before activation, the raw material particle size becomes uniform, activation is more complete, and the damage to the existing pores caused by crushing after activation is avoided. The unique forced-air stirring method (compared to mechanical stirring) exerts less shear force on the carbon skeleton, better protecting the microstructure of porous carbon and maintaining its iodine adsorption value at a high level of over 1600 mg / g.

[0026] 3. High efficiency and low cost: This method features a rationally designed process, significant purification effect, reduced number of repeated acid washings, and savings in time and reagent costs. The continuous belt rinsing operation is highly automated and suitable for large-scale industrial production.

[0027] 4. Excellent product performance: The porous carbon product prepared by this method has extremely high purity and high specific surface area. When applied to silicon-carbon anodes, it can significantly improve the first efficiency, cycle life and safety of the battery, meeting the needs of high-end lithium-ion batteries. Detailed Implementation

[0028] The present invention will now be described in detail with reference to specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0029] Example 1

[0030] Using coconut shell carbonized material as raw material (volatile matter 9%, moisture 12%, ash 4.2%, iron content 850ppm, bulk density 680g / l, activated iodine value 1600 mg / g), the following operations were performed:

[0031] (1) Screen the coconut shell carbonized material to remove large impurities and dust;

[0032] (2) Use a crusher to crush the screened carbonized material to about 30 mesh;

[0033] (3) The crushed carbonized material is fed into a multi-tube activation furnace and physical activation is carried out by passing water vapor at 900°C to obtain activated carbon.

[0034] (4) The activated carbon is sieved and magnetically separated to remove fine powder and magnetic iron.

[0035] (5) Add the above activated carbon and 33% hydrochloric acid solution into the reaction vessel at a solid-liquid ratio of 0.4 kg / l, heat to a gentle boiling state, maintain cooking for 4 hours, and continue to stir slowly.

[0036] (6) After the cooking is finished, drain the acid liquid, add pure water to the kettle, turn on the Roots blower to blow and stir for 45 minutes; after draining the sewage, repeat the above blowing and cleaning steps 5 times.

[0037] (7) The washed activated carbon is conveyed to a belt rinsing machine, where it is rinsed with clean water during the conveying process, while vacuum suction (wind speed 50m) is performed at the bottom of the rinsing belt. 3 (At a speed of 0.09 MPa, the vacuum degree was 0.09 MPa). The moisture content of the material was controlled at 60%. After rinsing, the pH value of the material was measured to be 7, the ash content was 0.18%, and the iron content was 45 ppm.

[0038] (8) The rinsed wet charcoal is fed into the dryer, the feed temperature is controlled at 420℃, the discharge temperature is 95℃, the material residence time is about 1.3 hours, and the moisture content of the dried product is 4%.

[0039] The final porous carbon product was tested:

[0040] Iodine adsorption value (GB / T 12496.8-1999): 1620 mg / g;

[0041] Iron content (GB / T 12496.19-2015): 42 ppm;

[0042] Ash content (GB / T 12496.3-1999): 0.16%;

[0043] Moisture content (GB / T 12496.4-1999): 4%;

[0044] pH value (GB / T 12496.7-1999): 7.2;

[0045] Bulk density (GB / T 12496.1-1999): 205 g / l.

[0046] Example 2

[0047] Using bamboo carbonized material as raw material (volatile matter 11%, moisture 14%, ash 4.5%, iron content 920ppm, bulk density 345g / l, activation iodine value 1450 mg / g), the following operations were performed:

[0048] (1) Screening the bamboo carbonized material;

[0049] (2) Crush the sieved carbonized material to about 40 mesh;

[0050] (3) Physically activate the crushed carbonized material to obtain activated carbon;

[0051] (4) The activated carbon is subjected to sieving and magnetic separation after activation;

[0052] (5) Mix activated carbon with a 35% hydrochloric acid solution at a solid-liquid ratio of 0.35 kg / l and cook for 3.9 hours;

[0053] (6) After the acid is drained, the mixture is stirred and cleaned with a blower for 1 hour, and this process is repeated 4 times.

[0054] (7) Perform belt rinsing and vacuum suction (wind speed 55m) 3 The vacuum rate was 0.092 MPa, and the moisture content was controlled at 62%. After rinsing, the material had a pH of 6.8, an ash content of 0.19%, and an iron content of 48 ppm.

[0055] (8) Drying is carried out with a feed temperature of 410℃, a discharge temperature of 92℃, a residence time of 1.5 hours, and a moisture content of 4.5% after drying.

[0056] Test the final product:

[0057] Iodine adsorption value: 1580 mg / g;

[0058] Iron content: 46 ppm;

[0059] Ash content: 0.17%.

[0060] Comparative Example

[0061] The traditional acid washing process was adopted: the activated and crushed coconut shell activated carbon of the same batch (the same material after step (4) of Example 1) was directly immersed in 33% hydrochloric acid for 12 hours, and mechanically stirred for 10 minutes every 2 hours. After that, it was washed with water in a normal filter until neutral, and then dried in a dryer.

[0062] Testing the final product:

[0063] Iodine adsorption value: 1480 mg / g (mechanical stirring caused partial pore collapse);

[0064] Iron content: 150ppm (static soaking cannot remove iron deeply);

[0065] Ash content: 0.35%.

[0066] Conclusion: Compared with the comparative example, the method of the present invention has significant improvements in key performance indicators (iodine value, iron content, and ash content), proving the superiority of the process of the present invention.

[0067] 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 scope of the technology disclosed 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 acid washing purification of porous carbon for silicon-carbon negative electrode material, characterized by, The method comprises the following steps: (1) screening the carbonized raw material to remove impurities; (2) crushing the screened carbonized raw material to 20-50 mesh; (3) physically activating the crushed carbonized raw material to obtain activated carbon; (4) screening and magnetically selecting the activated carbon to remove fine powder and iron; (5) mixing the activated carbon treated in step (4) with a hydrochloric acid solution with a concentration of 30%-36% at a solid-liquid ratio of 0.3-0.5 kg / l, and performing cooking treatment for 4±0.2 hours, and stirring during the acid cooking process; (6) after discharging the acid solution, adding pure water and performing air blowing and stirring cleaning for 0.5-1 hour, and repeating the cleaning process 4-6 times; (7) performing belt rinsing on the cleaned activated carbon, and performing vacuum air draft under the lower part of the rinsing belt, so that the water content of the rinsed activated carbon is controlled within 60±3%, the ash content of the rinsed activated carbon is less than 0.2%, the iron content is less than 30 ppm, and the pH value is 6-8; (8) drying the rinsed activated carbon to obtain the porous carbon precursor for the silicon-carbon negative electrode material.

2. The method of claim 1, wherein, The carbonized raw material in step (1) is coconut shell carbonized material, the volatile content is 9-13%, the water content is not more than 15%, the ash content is 3-5%, the iron content is not more than 1000 ppm, the bulk specific gravity is 650-700 g / ml, and the activated iodine value is 1550-1650 mg / g.

3. The method of claim 1, wherein, The carbonized raw material in step (1) is bamboo carbonized material, the volatile content is 10-15%, the water content is not more than 15%, the ash content is 3-5%, the iron content is not more than 1000 ppm, the bulk specific gravity is 330-360 g / ml, and the activated iodine value is 1400-1500 mg / g.

4. The method of claim 1, wherein: The activation in step (3) is performed in a multi-tube activation furnace.

5. The method of claim 1, wherein, The air draft speed in step (7) is ≤60 m³ / min, and the vacuum degree is ≤0.093 Mpa.

6. The method of claim 1, wherein: The water content of the activated carbon after drying in step (8) is within 5%, the feeding temperature of the dryer is not less than 400℃, the time from feeding to discharging is controlled to be 1.2-1.5 hours, and the discharging temperature is not less than 90℃.

7. The method of claim 1, wherein, The porous carbon precursor obtained after drying in step (8) has an ash content of less than 0.2% and an iron content of less than 30 ppm.

8. A porous carbon for a silicon-carbon negative electrode material, characterized by, It is prepared by the method of any one of claims 1-7.

9. The porous carbon for a silicon-carbon negative electrode material according to claim 8, characterized by, The iodine adsorption value is not less than 1600 mg / g, the iron content is less than 30 ppm, and the ash content is less than 0.2%.