Frost-resistant coal-based carbon material, method for preparing the same, and use thereof

Abstract

The application discloses a kind of antifreeze coal-based carbon materials and its preparation method and application, belong to lithium ion battery negative material technical field.The antifreeze coal-based carbon material is prepared by using coal powder crushing, acid-base coupling pretreatment, washing and drying, high-temperature carbonization, nano-mill refinement modification, ball milling, secondary carbonization heat treatment process;The material can be used in lithium ion battery negative, and the synergistic effect of multistage pore and continuous conductive network greatly accelerates the migration rate of lithium ion at low temperature;The low-temperature antifreeze performance of the material is outstanding: lithium ion transmission is smooth under the condition of-15 DEG C, low-temperature capacity retention is excellent, and low-temperature discharge capacity is greatly improved;And preparation route is economical and efficient, easy to industrialization promotion.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery anode material technology, specifically relating to an antifreeze coal-based carbon material, its preparation method, and its application. Background Technology

[0002] Coal-based carbon raw materials are abundant and inexpensive, making them a preferred material to replace graphite for lithium-ion battery anodes. However, conventional coal-based carbon has a simple pore structure and poor continuity of the conductive network. In low-temperature environments, the electrolyte viscosity increases, solid-phase lithium-ion diffusion is hindered, electrode interface impedance surges, the lithium insertion / extraction kinetics at the anode deteriorate, and low-temperature capacity decay is severe.

[0003] Currently, most technologies for improving the low-temperature performance of lithium batteries focus on electrolyte modification, with little research on regulating the bulk structure of carbon materials. This makes it difficult to optimize lithium-ion transport channels at their source and completely overcome the shortcomings of coal-based carbon anodes in low-temperature performance, thus restricting their application in the field of low-temperature energy storage batteries. Summary of the Invention

[0004] To address the issues of poor low-temperature kinetics, high interfacial impedance, and capacity decay in conventional coal-based carbon anodes, this invention provides an antifreeze coal-based carbon material, its preparation method, and its application. The coal-based carbon material, prepared from coal, achieves low-temperature antifreeze properties through molecular structure regulation of the carbon material, and is suitable for applications such as low-temperature power batteries and energy storage batteries.

[0005] This invention constructs an integrated structure that combines a flexible framework, uniform multi-level channels, and a continuous conductive network through the synergistic regulation of acid-base coupling activation, nano-grinding refinement, and conductive carbon composite. Acid-base coupling activation, through etching to create pores and grafting functional groups, introduces polar groups such as nitrate and sulfonate groups onto the carbon rings, forming a flexible framework that can buffer low-temperature thermal expansion and contraction stress and inhibit lithium dendrite growth, while simultaneously building a multi-level island-like channel foundation. Nano-wet grinding refinement further nanoscales the particles and optimizes the channel distribution, making the pore size more uniform and interconnected. When used as a lithium-ion battery anode, this shortens the lithium-ion solid-phase diffusion path and reduces low-temperature ion diffusion impedance. Conductive carbon composite constructs a continuous electron transport network, reducing interfacial impedance and avoiding lithium plating problems caused by excessive low-temperature polarization, while also enhancing structural strength and flexibility. These three elements work synergistically to solve the key problems of slow ion transport, hindered electron conduction, and structural fragility at low temperatures from an intrinsic material perspective, significantly improving the low-temperature cycle stability and safety of the battery.

[0006] This invention provides a method for preparing antifreeze coal-based carbon material, including coal powder crushing, acid-base coupling pretreatment, water washing and drying, high-temperature carbonization, nano-milling refinement modification, ball milling, and secondary carbonization heat treatment, to prepare antifreeze coal-based carbon material. Specifically, the method includes the following steps: Step 1: Preparation of Coal-Based Carbon Matrix (1) The coal powder is crushed to below 200 mesh, and then subjected to acid leaching (80-100℃, 1-6h) and alkali leaching (80-100℃, 1-6h) in sequence. It is then washed with water until neutral and dried to obtain activated coal powder. (2) The activated coal powder is carbonized at high temperature, with a carbonization temperature of 700-1200℃ and a carbonization time of 1-3h, to obtain a highly active coal-based carbon matrix; Step 2: Low-temperature antifreeze modification (1) Coal-based carbon matrix and deionized water are mixed at a solid-liquid ratio of 1:4-1:10 to form a slurry, which is then ultra-finely modified by a nano wet mill (50-80Hz, 0.5-4h) and dried until the moisture content is less than 10%; (2) The dried coal-based carbon was ball-milled (300-500 r / min) and subjected to secondary carbonization heat treatment (500-800℃, 1-4h) to construct a three-dimensional continuous conductive network on the surface of the coal-based carbon, while retaining the multi-level mesoporous structure to improve the low-temperature ion / electron transport capability; coal-based carbon materials were prepared.

[0007] Furthermore, the volatile matter content of the pulverized coal is 10-30%, and the ash content is <10%.

[0008] Furthermore, the acid is a mixed nitric acid and sulfuric acid, with a volume ratio of nitric acid to sulfuric acid of 3:7-5:5, and the base is a potassium hydroxide solution with a concentration of 1-10 mol / L.

[0009] Furthermore, the protective gas for carbonization is high-purity nitrogen or argon.

[0010] This invention provides an antifreeze coal-based carbon material prepared by the above-described method.

[0011] This invention provides the application of the aforementioned antifreeze coal-based carbon material in the negative electrode of a lithium-ion battery. The specific application process is as follows: the antifreeze coal-based carbon material is used as the negative electrode active material, and is prepared into a negative electrode sheet through pulping, coating, drying, and rolling for use in assembling lithium-ion batteries.

[0012] In the above applications, the slurry preparation method is as follows: Active material (antifreeze coal-based carbon material), conductive agent, thickener, and binder are mixed and dispersed using a ball mill according to the specified ratio. The resulting negative electrode slurry has the following proportions: active material 85%-98%, conductive agent 1%-10%, thickener 0.5%-3%, and binder 0.5%-3%. The coating is applied to a thickness of 100-200 μm, and the drying temperature is 70-90℃.

[0013] Test Method: 2032-type coin cells were assembled using the fabricated negative electrode sheet. Under normal temperature conditions, the reversible specific capacity, initial coulombic efficiency, long-cycle performance, and rate performance of the materials were tested according to fixed charge and discharge parameters. The coin cells under test were placed in a high and low temperature test chamber at -15℃ and an ultra-low temperature storage chamber at -80℃ for 24h, 48h, and 30d, respectively, and the low-temperature antifreeze capability under different low-temperature conditions was tested using the same charge and discharge parameters as at room temperature.

[0014] The beneficial effects of this invention are: (1) Excellent low-temperature antifreeze performance: The battery can maintain good capacity retention rate in environments of -15℃ and -80℃, with low capacity loss at low temperatures and good electrochemical stability.

[0015] (2) Interface performance optimization: By controlling the conductive network and surface characteristics, the surface characteristics of the material are optimized, the conductive network of the material is perfected, the interface properties are uniform, the low-temperature lithium intercalation kinetics are improved, the low-temperature lithium deposition is effectively suppressed, the low-temperature cycling stability is improved, the lithium intercalation process is stable, and the low-temperature metallic lithium deposition is effectively avoided.

[0016] (3) High product purity and structural stability: Deep deashing is achieved through acid-base coupling pretreatment, resulting in low impurity content and a more regular and stable structure.

[0017] (4) Significantly improved low-temperature dynamics: The synergistic effect of multi-level channels and continuous conductive network greatly accelerates the lithium-ion migration rate at low temperatures.

[0018] (5) The preparation route is economical and efficient with obvious industrial advantages: the special antifreeze battery anode material is prepared by using cheap coal as raw material. It is widely available and has low cost, which is far lower than traditional graphite and silicon carbon materials. Moreover, the preparation process of this invention is simple and industrializable: the preparation process is mild and controllable, highly compatible with existing coal-based carbon production lines, with few modification steps, and easy to scale up production and promotion. Attached Figure Description

[0019] Figure 1 This is a scanning electron microscope image of the antifreeze coal-based carbon material prepared in Example 1. Detailed Implementation

[0020] The present invention will be further illustrated by the following embodiments, but is not limited to the following embodiments.

[0021] Example 1: 200g of raw coal was ground to below 200 mesh, and 1000mL of a mixed nitric-sulfur acid solution (volume ratio of nitric acid:sulfuric acid = 3:7) was added. The mixture was stirred at 90℃ for 2 hours, washed with water until the pH reached 6-8, filtered, and then the coal powder was added to deionized water at a solid-liquid weight ratio of 1:4. Simultaneously, a 5mol / L potassium hydroxide solution (8% by weight of solids) was added, and the mixture was stirred at 100℃ for 2 hours. After drying, activated coal powder was obtained. The activated coal powder was then subjected to high-temperature carbonization in a high-temperature carbonization furnace at 1000℃ under a nitrogen atmosphere for 2 hours to obtain a highly active coal-based carbon matrix. The coal-based carbon matrix was mixed with deionized water at a solid-liquid ratio of 1:5 to form a slurry. This slurry was then ultra-finely modified by milling at 60Hz for 2 hours using a nanomill, and dried until the moisture content was less than 10%. The dried coal-based carbon was ball-milled (400r / min) and subjected to a secondary carbonization heat treatment in a carbonization furnace under a nitrogen atmosphere (600℃, 2 hours) to obtain an antifreeze coal-based carbon material.

[0022] Antifreeze-type coal-based carbon material was used as the negative electrode active material. The slurry preparation method was as follows: the active material (antifreeze-type coal-based carbon material), acetylene black, carboxymethyl cellulose (CMC) and LA133 water-based binder were mixed and dispersed in a ball mill according to the ratio. The ratio of the negative electrode slurry was 85:10:2:3. The slurry was coated to 100μm, dried at 80℃, and rolled into a negative electrode sheet.

[0023] Figure 1 The image shows a SEM image (×1500) of the antifreeze carbon-based anode material. This material has a rich hierarchical porous structure, which can provide a fast transport channel for lithium ions in low-temperature environments, reduce interfacial impedance, and improve low-temperature lithium storage performance.

[0024] Example 2: 200g of raw coal was ground to below 200 mesh, and 1000mL of nitric acid-sulfur mixed acid (volume ratio of nitric acid:sulfuric acid = 5:5) was added. The mixture was stirred at 100℃ for 3h, washed with water until the pH was 6-8, filtered, and then the coal powder was added to deionized water at a solid-liquid weight ratio of 1:4. At the same time, 9% by weight of 5mol / L potassium hydroxide solution was added, and the mixture was stirred at 100℃ for 3h. After drying, activated coal powder was obtained. The activated coal powder was then subjected to high-temperature carbonization in a high-temperature carbonization furnace at 700℃ under a nitrogen atmosphere for 2h to obtain a highly active coal-based carbon matrix. Coal-based carbon matrix and deionized water were mixed at a solid-liquid ratio of 1:4 to form a slurry. The slurry was then milled at 80 Hz for 0.5 h in a nanomill for ultrafine modification and dried until the moisture content was less than 10%. The dried coal-based carbon was ball-milled (390 r / min) and then subjected to a secondary carbonization heat treatment (500 ℃, 2 h) in a carbonization furnace under a nitrogen atmosphere to obtain an antifreeze coal-based carbon material.

[0025] Antifreeze-resistant coal-based carbon material was used as the negative electrode active material. The slurry preparation method was as follows: the active material (antifreeze-resistant coal-based carbon material), acetylene black, carboxymethyl cellulose (CMC) and LA133 water-based binder were mixed and dispersed in a ball mill according to the ratio. The ratio of the negative electrode slurry was 97.5:1:0.5:1. The slurry was coated to 200μm, dried at 85℃, and rolled to form a negative electrode sheet.

[0026] Example 3: 200g of raw coal was ground to below 200 mesh, and 1000mL of a mixed nitric-sulfur acid solution (volume ratio of nitric acid:sulfuric acid = 3:7) was added. The mixture was stirred at 100℃ for 2 hours, washed with water until the pH reached 6-8, filtered, and then the coal powder was added to deionized water at a solid-liquid weight ratio of 1:4. Simultaneously, a 5mol / L potassium hydroxide solution (8% by weight of solids) was added, and the mixture was stirred at 90℃ for 2 hours. After drying, activated coal powder was obtained. The activated coal powder was then subjected to high-temperature carbonization in a high-temperature carbonization furnace at 800℃ under a nitrogen atmosphere for 2 hours to obtain a highly active coal-based carbon matrix. The coal-based carbon matrix was mixed with deionized water at a solid-liquid ratio of 1:8 to form a slurry. This slurry was then ultra-finely modified by milling at 60Hz for 3 hours using a nanomill, and dried until the moisture content was less than 10%. The dried coal-based carbon was ball-milled (330r / min) and subjected to a secondary carbonization heat treatment (500℃, 2 hours) in a carbonization furnace under a nitrogen atmosphere to obtain an antifreeze coal-based carbon material.

[0027] Antifreeze-type coal-based carbon material was used as the negative electrode active material. The slurry preparation method was as follows: the active material (antifreeze-type coal-based carbon material), acetylene black, carboxymethyl cellulose (CMC) and LA133 water-based binder were mixed and dispersed in a ball mill according to the ratio. The ratio of the negative electrode slurry was 98:1:0.5:0.5. The slurry was coated to 200μm, dried at 85℃, and rolled to form a negative electrode sheet.

[0028] The negative electrode sheet made of the antifreeze coal-based carbon material obtained in Examples 1-3 above was used to assemble a battery with lithium metal as the counter electrode, and electrochemical tests were performed. The specific test method was as follows: a 1 mol / L LiPF6 / EC+DMC+EMC (volume ratio 1:1:1) electrolyte, a Celgard 2400 separator, and a 2032 specification coin cell casing were used to assemble a coin cell battery. The battery was tested at room temperature using the Landian Battery Testing System of Wuhan Landian Electronics Co., Ltd. Test conditions: room temperature and -15℃, initial charge / discharge I=0.1C, cycle I=0.1C, voltage range 0.1-3.5V. The test results are shown in Table 1. In addition, the negative electrode sheet prepared in Example 1 was subjected to a progressive freezing test at -80°C for 1 hour, 24 hours, 8.5 days, and 30 days. Before the test, it was left to stand at room temperature for 30 minutes. The first charge-discharge was I=0.1C, the cycle was I=0.1C, and the voltage range was 0.1-3.5V. The test results are shown in Table 2.

[0029] Table 1 Electrochemical performance tests of coal-based carbon materials at room temperature and -15℃

[0030] Table 2 Electrochemical performance test of coal-based carbon materials in Example 1 at -80℃

[0031] As shown in Table 1, the electrochemical specific capacity of the three groups of samples differs significantly under normal temperature and -15℃ low-temperature conditions. Example 2 exhibits the highest reversible specific capacity at room temperature and the highest specific capacity at -15℃ for different standing times among the three groups, demonstrating the best electrochemical capacity performance. Example 1 shows a steady decrease in specific capacity with increasing low-temperature standing time, indicating good structural and electrochemical stability under low-temperature conditions. Example 3 shows a gradual decrease in specific capacity with increasing low-temperature standing time, with overall performance falling between the other two groups, indicating suitability for low-temperature use.

[0032] Table 2 shows the electrochemical specific capacity test results of the sample from Example 1 under different freezing times at -80℃. The sample exhibited phased capacity changes under ultra-low temperature conditions. The capacity decay was significant in the first 1 hour of freezing; from 1 hour to 8.5 days, the specific capacity tended to stabilize with minimal decay; after 30 days of freezing, the specific capacity showed a slight decrease. This sample maintained a high reversible specific capacity even under long-term ultra-low temperature conditions, demonstrating excellent ultra-low temperature tolerance.

Claims

1. A method for preparing an antifreeze coal-based carbon material, characterized in that, The process includes coal powder crushing, acid-base coupling pretreatment, water washing and drying, high-temperature carbonization, nano-milling refinement and modification, ball milling, and secondary carbonization heat treatment to prepare antifreeze coal-based carbon materials. Specifically, the steps include: Step 1: Preparation of Coal-Based Carbon Matrix (1) The coal powder is crushed to below 200 mesh, then subjected to acid leaching and alkali leaching in sequence, washed with water until neutral, and dried to obtain activated coal powder; (2) The activated coal powder is carbonized at high temperature, with a carbonization temperature of 700-1200℃ and a carbonization time of 1-3h, to obtain a highly active coal-based carbon matrix; Step 2: Low-temperature antifreeze modification (1) Mix coal-based carbon matrix with deionized water at a solid-liquid ratio of 1:4-1:10 to prepare a slurry, and then modify it by ultrafine grinding in a nano wet mill at a power of 50-80 Hz for 1-4 hours; then dry it until the moisture content is less than 10%; (2) The dried coal-based carbon was ball-milled at a speed of 300-500 r / min; a secondary carbonization heat treatment was performed for 1-4 h at a temperature of 500-800℃ to construct a three-dimensional continuous conductive network on the surface of the coal-based carbon, while retaining the multi-level mesoporous structure to improve the low-temperature ion / electron transport capability; and coal-based carbon materials were prepared.

2. The method for preparing antifreeze coal-based carbon material according to claim 1, characterized in that, The pulverized coal is low-rank coal with volatile matter content of 10-30% and ash content of <10%.

3. The method for preparing antifreeze coal-based carbon material according to claim 1, characterized in that, The acid is a nitrate-sulfur mixture, and the base is a potassium hydroxide solution.

4. The method for preparing antifreeze coal-based carbon material according to claim 3, characterized in that, In the nitric acid-sulfuric acid mixture, the volume ratio of nitric acid to sulfuric acid is 3:7-5:5, and the concentration of potassium hydroxide solution is 1-10 mol / L.

5. The method for preparing antifreeze coal-based carbon material according to claim 1, characterized in that, The acid immersion time is 1-6 hours and the temperature is 80-100℃; the alkali immersion time is 1-6 hours and the temperature is 80-100℃.

6. The method for preparing antifreeze coal-based carbon material according to claim 1, characterized in that, The protective gas used in the carbonization process is high-purity nitrogen or argon.

7. A frost-resistant coal-based carbon material prepared by the preparation method according to any one of claims 1 to 6.

8. The application of the antifreeze coal-based carbon material as described in claim 7 in the negative electrode of a lithium-ion battery.

9. The application according to claim 8, characterized in that, The antifreeze coal-based carbon material is used as the negative electrode active material. The negative electrode sheet is obtained by pulping, coating, drying and rolling. The battery is assembled with lithium metal as the counter electrode.

10. The application according to claim 9, characterized in that, Slurry preparation method: The antifreeze coal-based carbon material, conductive agent, thickener and binder are mixed and dispersed in a ball mill. The negative electrode slurry has the following ratio: antifreeze coal-based carbon material 85%-98%, conductive agent 1%-10%, thickener 0.5%-3%, binder 0.5%-3%; coated to 100-200μm, and dried at 70-90℃.

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