Preparation method of anthracite-based graphite negative electrode material

Abstract

The invention discloses a preparation method of an anthracite-based graphite negative electrode material, which comprises the following steps: placing anthracite in a reaction furnace, vacuumizing twice, introducing nitrogen, keeping the nitrogen atmosphere, heating to 350-450 DEG C, then switching to hydrogen, keeping the temperature for 4-12 hours in the hydrogen atmosphere, and finally switching to nitrogen for natural cooling to obtain pretreated anthracite; and mixing the pretreated anthracite with 1-3wt% of a catalyst, and carrying out a high-temperature catalytic graphitization reaction to obtain the anthracite-based graphite negative electrode material. The anthracite is pretreated, so that the crosslinking effect of oxygen and sulfur in the anthracite on a carbon layer is effectively avoided, and the breakage of a side chain in the anthracite is promoted, so that residual carbon is more likely to be represented as pure side-chain-free aromatic hydrocarbon, and the internal structure of the anthracite is more easily and directionally arranged under the action of a catalyst; pores are formed in the surfaces of anthracite particles, so that permeation of the catalyst in the anthracite is enhanced, the catalytic effect is enhanced, and the catalytic graphitization effect is improved while the dosage of the catalyst is reduced.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of battery materials, in particular to a preparation method of anthracite-based graphite negative electrode material. BACKGROUND

[0002] Anthracite is widely available and low in price, and has a high fixed carbon content, and can realize crystal directional arrangement under high-temperature heat treatment conditions, so as to form a graphite material. According to this characteristic, anthracite can be used as a raw material for a lithium ion battery negative electrode. In recent years, a plurality of colleges and universities and negative electrode enterprises have carried out research on anthracite-based graphite negative electrode materials for lithium ion batteries, and it has been found that anthracite generally has the problem of low capacity.

[0003] Catalytic graphitization is considered to be an efficient method for improving the capacity of coal-based negative electrodes, and the types of catalysts mainly include boron-based catalysts, silicon-based catalysts and metal-based catalysts.

[0004] For example, Chinese patent CN111232970A discloses a graphite negative electrode material and a preparation method, which comprises the following steps: subjecting a mixture of mesocarbon microbead green balls, anthracite powder and a catalyst to graphitization high-temperature treatment, wherein the mass ratio of the mesocarbon microbead green balls to the anthracite powder is 1:9 to 8:1, the particle size D50 of the anthracite powder is 10 to 20 microns, the catalyst is one or more of carbonides or oxides of silicon, iron, tin or boron, and the amount of the catalyst is 4% to 10% of the sum of the mass of the mesocarbon microbead green balls and the anthracite powder; the graphite negative electrode material prepared by the method has high compaction density, and the energy density of the battery is correspondingly improved, but the catalyst amount is high in the application, and mesocarbon microbead green balls are added.

[0005] For another example, Chinese patent CN116354334A discloses a graphite coated with amorphous carbon and a preparation method thereof, wherein 3 to 15 wt% of boron carbide powder is added to deashed anthracite, and then high-temperature graphitization is carried out to obtain boron-catalyzed graphite, and then a strong oxidizing agent and an intercalation agent are used to oxidize and intercalate the boron-catalyzed graphite, so as to expand the interlayer spacing of the graphite, and the intercalation reaction graphite is coated with carbon, so as to finally obtain modified graphite, improve the graphitization degree and conductivity of the graphite, and improve the reversible specific capacity and cycle performance of the graphite; similarly, the catalyst amount is high in the application.

[0006] According to the data reported in the literature, the catalyst ratio has a significant effect on the catalytic effect of anthracite-based materials. However, if the capacity of the anthracite-based graphite negative electrode is to be improved to the level of high-quality petroleum coke, a large amount of catalyst needs to be added, which will inevitably lead to a decrease in graphitization yield, difficulty in escaping impurities from the graphitized material, and high pollution during graphitization. More seriously, a large amount of catalyst will damage the surface of the graphite particles, resulting in low energy efficiency and poor cycle performance of the negative electrode material. If only a small amount of catalyst is added, the catalytic effect is limited, and the anthracite-based graphite negative electrode after catalysis cannot achieve a reasonable capacity value.

[0007] Therefore, providing a method for achieving a higher capacity of anthracite-based graphite negative electrode material with a low proportion of catalyst content is of great significance for the application of anthracite in the battery field. SUMMARY

[0008] In view of the above, the present application provides a method for preparing an anthracite-based graphite negative electrode material. The anthracite is pretreated to reduce the amount of catalyst and promote the catalytic graphitization effect of the anthracite powder, thereby improving the capacity of the anthracite-based graphite negative electrode material.

[0009] The present application provides a method for preparing an anthracite-based graphite negative electrode material, which comprises uniformly mixing anthracite and a catalyst, then performing a catalytic graphitization reaction in a reaction furnace under an inert atmosphere to obtain an anthracite-based graphite negative electrode material. The anthracite is pretreated by heating it in a reaction furnace under a hydrogen atmosphere at 350-450℃ for 4-12h.

[0010] The pretreatment of the anthracite serves to reduce the impurities contained in the anthracite, such as oxides, sulfides, oxygen-containing functional groups, and sulfur-containing functional groups, using hydrogen. This allows the catalytic graphitization effect of the catalyst on the anthracite to be maximized. The oxygen and sulfur elements contained in the impurities in the anthracite can easily cross-link the carbon layers, forming cross-linking bonds that fix the carbon layers in a three-dimensional network structure, making it difficult for the carbon layers to form parallel stacked graphite layers during catalytic graphitization, and hindering the free stacking of the carbon layers. At the same time, these elements can also consume the activity of the catalyst, weaken the promoting effect of the catalyst on the rearrangement of the carbon layers, and reduce the degree of graphitization. Therefore, heating the anthracite in a hydrogen atmosphere can effectively remove compounds or functional groups containing oxygen and sulfur elements, effectively avoid the cross-linking effect of oxygen and sulfur elements on the carbon layers, and thus promote the catalytic graphitization effect. At the same time, when hydrogen reacts with some easily reducible oxides in the ash of the anthracite (such as iron oxides), pores can be formed on the surface of the anthracite particles, enhancing the adhesion of the catalyst on the surface of the anthracite, facilitating the dispersion of the catalyst on the surface of the anthracite, and promoting the penetration of the catalyst into the interior during graphitization, thereby enhancing the catalytic effect and promoting the catalytic graphitization effect.

[0011] The temperature of the pretreatment is 350-450℃, and the time is 4-12h. Reasonable control of the temperature and time helps to better optimize the anthracite and improve the effect of catalytic graphitization. If the temperature is too low or the time is too short, the reaction of hydrogen and anthracite is not complete, the removal efficiency of the compounds or functional groups of oxygen, sulfur and the like is low, it is difficult to promote the side chain rupture in the anthracite, and it is not conducive to the formation of pores on the surface of the anthracite particles, so that the effect of improving the catalytic graphitization cannot be achieved. If the temperature is too high, the following side effects will occur: 1) the gasification product during the pretreatment is increased, and the utilization rate of raw materials is reduced; 2) safety accidents may occur under high temperature; 3) the energy consumption is increased and the cost is increased due to the too high temperature. If the time is too long, the production efficiency is reduced and the cost is increased.

[0012] In the pretreatment of the anthracite, the anthracite is placed in the reaction furnace, and before the hydrogen atmosphere is introduced for heat treatment, the vacuum degree is first extracted to ≤1*10 -4 Pa, then nitrogen is introduced to a pressure of 0-0.1KPa, the vacuum degree is extracted again to ≤1*10 -4 Pa, and then nitrogen is introduced to a pressure of 0-0.1KPa. The two vacuum extractions have the following effects: ①completely remove the active oxygen source and eliminate safety hazards. The residual air (O2) in the reaction furnace cavity is the biggest safety hazard and interference factor. Under the subsequent heating condition of 350-450℃, when hydrogen and oxygen are mixed to a certain concentration (the explosion limit of hydrogen is 4%-75%), it is easy to cause violent explosion. Through two high-vacuum extractions and inert gas replacement, the air (O2) in the furnace cavity, especially the air (O2) between the gaps of the anthracite particles, can be completely removed, so as to create an absolutely safe environment for the introduction of hydrogen. ②eliminate the competitive reaction and ensure the treatment effect. If there is a small amount of oxygen, it will preferentially react with the anthracite under the heating condition, not only consuming the carbon in the anthracite and reducing the final yield, but also forming an oxidation layer on the surface, which is not conducive to graphitization. The specific role of the two vacuum extractions and nitrogen introduction is to quickly remove the air. If only nitrogen is used to replace the air, due to the dead angle in the equipment and the adsorption of a part of the air by the coal, the replacement time will be too long, and the use of vacuum extraction will remove almost all the air in the equipment space and the air adsorbed by the coal in a short time. At this time, the nitrogen filling has a dilution effect on the residual air in the equipment and the coal, and the last vacuum extraction can ensure that the residual air in the hydrogenation equipment will not have a negative impact on the hydrogenation process.

[0013] In the pretreatment of anthracite, the anthracite is subjected to heat treatment, nitrogen is introduced and natural cooling is performed. The anthracite has a vitrinite content of ≥75%, an ash content of ≤5% and a sulfur content of ≤1%. Related researches show that the vitrinite in the coal maceral is easier to graphitize than the inertinite, and thus the higher the vitrinite content in the anthracite, the easier the graphitization. Although catalytic graphitization can reduce the difficulty of graphitization of the anthracite, selection of the anthracite raw material with a high vitrinite content (≥75%) is beneficial to obtaining the graphite negative electrode material with better performance. The ash mainly has a reduction reaction with carbon elements to generate CO in the graphitization process, and the ash itself also boils and gasifies at high temperature, and thus the higher the ash content, the more the gas volatilization generated in the graphitization process, thereby increasing the risk of a blowout accident of the graphitization furnace. Too high sulfur content generates hydrogen sulfide which is difficult to handle and consumes hydrogen, thereby increasing the cost. Therefore, the anthracite with a vitrinite content of ≥75%, an ash content of ≤5% and a sulfur content of ≤1% is selected.

[0014] The anthracite has a particle size of 5-30 μm. Selection of the particle size is crucial to the subsequent catalytic graphitization process. If the particle size is too small, the gas permeability of the graphitization furnace is easily deteriorated, and a blowout accident is easily induced. If the particle size is too large, the processing performance of the obtained graphite negative electrode material is poor. For example, the slurry uniformity and coating process in the preparation process of the graphite negative electrode material is affected. In addition, too large particle size also reduces the diffusion rate of the hydrogenation pretreatment reaction, which is not conducive to the reaction.

[0015] The heat treatment has a heating rate of 1-10 ℃ / min. If the heating rate is too high, the volatile in the coal is too fast to escape, the surface cracks of the particles are too many, and even the particles are broken, thereby greatly increasing the specific surface area, which is not conducive to the control of the specific surface area of the final graphite negative electrode material. In addition, too much powder in the coal also increases the probability of a blowout accident in the graphitization process. In addition, too fast heating also causes the volatile to be concentrated and rapidly released, thereby locally and greatly increasing the pressure in the graphitization furnace in a short time, and causing a burden on the exhaust system and increasing the safety risk.

[0016] The catalyst has a content of 1-3 wt% of the pretreated anthracite, and the catalyst includes one or more of boric acid, silicon dioxide, iron oxide, cobalt sesquioxide and nickel.

[0017] The catalytic graphitization has a temperature of 1800-3000 ℃.

[0018] The present application at least has the following beneficial effects:

[0019] (1) the present application carries out heat treatment on anthracite in a hydrogen atmosphere, reduces the oxygen and sulfur content in anthracite, effectively avoids the crosslinking effect of oxygen and sulfur on the carbon layer, promotes the catalytic graphitization effect; at the same time, the side chain of anthracite is broken, the content of aliphatic hydrocarbon in anthracite is reduced, the internal structure of anthracite is more easily arranged in a direction under the action of the catalyst, the catalytic graphitization effect is improved; and pores are formed on the surface of anthracite particles, the penetration of the catalyst in the anthracite is enhanced, the catalytic effect is enhanced, and the catalytic graphitization effect is further enhanced;

[0020] (2) the present application has a promoting effect on the catalytic graphitization effect of boron-based, silicon-based and metal-based catalysts, and the catalyst dosage is only 1-3wt% of the pretreated anthracite, which reduces the catalyst dosage and improves the capacity of the anthracite-based graphite negative electrode material;

[0021] (3) the present application pretreats anthracite, which can improve the catalytic graphitization effect and improve the capacity of the material, and also appropriately reduces the sulfur and oxygen content in anthracite, so that the desulfurization and deashing in the catalytic graphitization process is more thorough. DETAILED DESCRIPTION

[0022] The embodiments of the present application will be described in more detail below. The present application can be implemented in various forms, and should not be interpreted as being limited to the embodiments set forth herein, but rather, the embodiments are provided to make the present application more thorough and complete. It should be understood that the embodiments of the present application are only for exemplary purposes, and are not intended to limit the scope of protection of the present application.

[0023] The embodiments of the present application are implemented according to the following technical solutions, comprising the following steps:

[0024] The anthracite with a particle size of 5-30μm is used as raw material and is placed in a reduction furnace, vacuum is extracted to a vacuum degree of ≤1*10 -4 Pa, then nitrogen is introduced to a pressure of 0-0.1KPa, vacuum is extracted again to a vacuum degree of ≤1*10 -4 Pa, then nitrogen is introduced to a pressure of 0-0.1KPa; then the exhaust valve is opened and the nitrogen atmosphere is maintained, the air volume is adjusted to maintain the pressure in the furnace cavity within the range of 0-0.1KPa; the power of the reduction furnace is turned on, the temperature is raised to 350-450℃ at a temperature rising rate of 1-10℃ / min, then the hydrogen gas is switched, the gas pressure is still maintained within the range of 0-0.1KPa, the temperature is kept for 4-12h under the hydrogen atmosphere, finally the nitrogen is switched and the temperature is naturally lowered, to obtain the pretreated anthracite; the pretreated anthracite is mixed with 1-3wt% of the catalyst, and the catalytic graphitization reaction is carried out at 3000℃ to obtain the anthracite-based graphite negative electrode material.

[0025] Table 1 is the process conditions of the specific implementation of the examples and the comparative examples of the present application, and Table 2 is the capacity and the initial efficiency obtained after the 2032 button cell assembled by the anthracite-based graphite negative electrode material prepared in the examples and the comparative examples is detected for the electrochemical performance.

[0026] Table 1 is the process conditions of the specific implementation of the examples and the comparative examples of the present application, and Table 2 is the capacity and the initial efficiency obtained after the 2032 button cell assembled by the anthracite-based graphite negative electrode material prepared in the examples and the comparative examples is detected for the electrochemical performance.

[0027]

[0028] Table 2 is the electrochemical performance of the anthracite-based graphite negative electrode material cell prepared in the examples and the comparative examples of the present application.

[0029]

[0030]

[0031] As can be seen from the examples 1-5 and the comparative examples 1-5, under the condition of the same catalyst and the same amount, the capacity of the anthracite-based graphite negative electrode material obtained from the pretreated anthracite is better than that of the anthracite-based graphite negative electrode material obtained from the anthracite without pretreatment, and the initial efficiency is also better, which fully proves that the present application can significantly improve the effect of catalytic graphitization, and further improve the electrochemical performance of the anthracite-based graphite negative electrode material, and also shows that more catalyst is needed for the anthracite without pretreatment in the catalytic graphitization to achieve the effect of the pretreated anthracite in the catalytic graphitization.

[0032] As can be seen from the example 1 and the comparative examples 6-9, under the condition of the same catalyst and the same amount, the capacity and the initial efficiency of the anthracite-based graphite negative electrode material obtained from the anthracite with a particle size of 5 microns as the pretreatment raw material are better than those of the anthracite-based graphite negative electrode material obtained from the anthracite with a particle size of 3 microns and the anthracite with a particle size of 40 microns as the pretreatment raw material; the capacity and the initial efficiency of the anthracite-based graphite negative electrode material obtained at a pretreatment temperature of 350℃ are better than those of the anthracite-based graphite negative electrode material obtained at a pretreatment temperature of 300℃ and 500℃. The above fully proves that the particle size of the anthracite is too large or too small, and the pretreatment temperature is too high or too low, which will reduce the electrochemical performance of the anthracite-based graphite negative electrode material.

[0033] The above is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto, any person skilled in the art can easily think of changes or replacements within the technical scope disclosed in the present application, which should be covered in the protection scope of the present application, therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A method for preparing anthracite-based graphite anode material, comprising uniformly mixing anthracite and a catalyst, and then carrying out a catalytic graphitization reaction in a reactor under an inert atmosphere to obtain the anthracite-based graphite anode material; characterized in that: The anthracite is pretreated by heat-treating it in a reactor at 350°C to 450°C under a hydrogen atmosphere for 4 to 12 hours.

2. The method of claim 1, wherein the lignite-based graphite negative electrode material is prepared by the steps of: In the pretreatment of the anthracite, the anthracite is placed in a reaction furnace, vacuumized to a vacuum degree of ≤1*10 -4 Pa, then hydrogen gas is introduced to a pressure of 0-0.1 KPa, vacuumized again to a vacuum degree of ≤1*10 -4 Pa, and then nitrogen gas is introduced to a pressure of 0-0.1 KPa. ​ 3. The method of claim 1, wherein the lignite-based graphite negative electrode material is prepared by the steps of: In the pretreatment of anthracite, after the anthracite undergoes heat treatment, nitrogen gas is introduced and the coal is naturally cooled. ​ 4. The method for preparing anthracite-based graphite anode material according to any one of claims 1 to 3, characterized in that: The anthracite coal has a vitrinite content of ≥75%, ash content of ≤5%, and sulfur content of ≤1%.

5. The method for preparing anthracite-based graphite anode material according to claim 4, characterized in that: The anthracite has a particle size of 5–30 μm.

6. The method for preparing anthracite-based graphite anode material according to claim 1, characterized in that: The heating rate of the heat treatment is 1 to 10 °C / min.

7. The method for preparing anthracite-based graphite anode material according to claim 1, characterized in that: The amount of catalyst used is 1-3 wt% of the pretreated anthracite.

8. The method for preparing anthracite-based graphite anode material according to claim 7, characterized in that: The catalyst includes one or more of boric acid, silicon dioxide, iron oxide, cobalt trioxide, and nickel.

9. The method for preparing anthracite-based graphite anode material according to claim 1, characterized in that: The temperature for catalytic graphitization is 1800–3000 °C.

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