Preparation method of porous graphite and application thereof

Abstract

This invention provides a method for preparing porous graphite, comprising the following steps: S1. Preparing CaC... 2 The powder is placed in a reaction vessel, and CO gas is introduced into the vessel. A gas-solid reaction is carried out at 800~1400 °C. After the reaction is completed, the mixture is cooled to room temperature to obtain a solid product. S2. The solid product is washed and dried to obtain porous graphite. The reaction temperature of this invention is much lower than that of traditional processes, and it can be combined with the process for preparing CaC2, eliminating CO emission problems and utilizing the waste heat of the reaction, which is beneficial to the comprehensive utilization of energy consumption.

Description

Technical Field

[0001] This invention belongs to the field of battery technology and relates to a method for preparing porous graphite and its application. Background Technology

[0002] Lithium-ion batteries (LIBs) dominate the modern secondary power supply field due to their excellent energy and power density, long cycle life, and reasonable cost, making them an indispensable core component for applications such as electric vehicles and energy storage power stations. Graphite, with its good electrical, mechanical, and chemical stability, as well as considerable specific capacity and mature application reliability, remains the mainstream anode material for lithium-ion batteries. With the continuous expansion of lithium-ion battery applications and the sustained growth in consumption, the global market demand for graphite anodes is rapidly increasing, leading to a tightening supply of both natural and synthetic graphite. Limited by resource endowment, natural graphite reserves are declining rapidly; while current synthetic graphite is mainly synthesized through the traditional Acheson process, which requires extreme high temperatures above 3000°C and expensive specialized production facilities, resulting in high energy consumption and high production costs.

[0003] Calcium carbide (CaC2) is a low-cost industrial chemical, typically produced industrially from lime (CaO) and coke / anthracite in an electric furnace at 2000 °C: CaO + 3C → CaC2 + CO. Graphitized carbon materials can be successfully synthesized by reacting calcium carbide with oxidants such as CO2, sulfur, and nitrogen in the intermediate temperature range, and the resulting graphite products have shown promise as anode materials for lithium-ion batteries. However, this type of reaction still has many limitations, such as low product yield, low degree of graphitization, and environmental emissions. The use of oxidants also increases costs, and the reaction itself still consumes a large amount of heat energy. Furthermore, previous research has rarely considered the source of calcium carbide. Industrially, calcium carbide is prepared by reacting calcium oxide with carbon at approximately 2200 °C (CC process), which generates a large amount of waste heat and leads to CO emissions.

[0004] Besides the high difficulty in preparation, commercial graphite (CG) also suffers from insufficient rate performance as a negative electrode for lithium-ion batteries. Current approaches to improve rate performance involve creating pores or modifying defects in graphite materials, which further increases the energy consumption and cost of negative electrode graphite production. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing porous graphite. Highly crystalline mesoporous graphite is prepared by reacting calcium carbide (CaC2) with CO at a temperature of around 1000℃. The reaction temperature is much lower than that of traditional processes, and it can be combined with the CC process for preparing CaC2 to eliminate CO emission problems and utilize the waste heat of the reaction, which is beneficial to the comprehensive utilization of energy consumption.

[0006] To achieve the above objectives, the present invention provides a method for preparing porous graphite, comprising the following steps: S1. Place CaC2 powder in a reaction vessel, introduce CO gas into the reaction vessel, and carry out a gas-solid reaction at 800~1400 ℃. After the reaction is completed, cool to room temperature to obtain a solid product. S2. Porous graphite can be obtained by washing and drying the solid product.

[0007] In step S1, the metal catalyst can also be mixed with CaC2 powder and placed in a reaction vessel.

[0008] The metal catalyst contains at least one or more elements including iron, cobalt, and nickel.

[0009] When the metal catalyst is mixed with CaC2 powder, the mass percentage of the metal catalyst is 6%-30%.

[0010] The pressure of CO gas inside the reactor is maintained above 0.1 MPa-8 MPa, and the reaction time is 4-6 hours.

[0011] During the washing process in step S2, multiple washes can be performed using dilute hydrochloric acid and distilled water.

[0012] A porous graphite, obtained by the aforementioned preparation method, wherein the porous graphite has a pore size of 2-50 nm and S BET / V Tot <400.

[0013] A lithium-ion battery includes a negative electrode, wherein the negative electrode material is the porous graphite described above.

[0014] Beneficial effects: The highly crystalline porous graphite prepared by this invention can not only be used as a lithium battery anode to improve rate performance, but also is expected to have important applications in adsorption, catalysis and other fields. It has a wide range of applications and can be combined with the CC process for preparing CaC2, which is conducive to the comprehensive utilization of energy consumption. The catalyst used is easy to wash and will not have the difficulty of removing catalyst particles that are encapsulated by products. Attached Figure Description

[0015] Figure 1 The XRD pattern of the final product prepared in Example 1 of this invention; Figure 2 This is a SEM image of the final product prepared in Example 1 of the present invention; Figure 3 The image shows the BET analysis chromatogram of the final product prepared in Example 1 of this invention. Figure 4 The image shows the Raman chromatogram of the final product prepared in Example 1 of this invention. Figure 5The XRD pattern of the final product prepared in Example 2 of this invention; Figure 6 This is a SEM image of the final product prepared in Example 2 of the present invention; Figure 7 The image shows the BET analysis chromatogram of the final product prepared in Example 2 of this invention. Figure 8 The image shows the Raman chromatogram of the final product prepared in Example 2 of this invention. Figure 9 The XRD pattern of the final product prepared in Example 3 of this invention; Figure 10 The XRD pattern of the final product prepared in Example 4 of this invention; Figure 11 This is a SEM image of the final product prepared in Example 4 of the present invention; Figure 12 The image shows the BET analysis chromatogram of the final product prepared in Example 4 of this invention. Figure 13 This is a Raman chromatogram of the final product prepared in Example 4 of the present invention. Detailed Implementation

[0016] The present invention will now be described in detail with reference to specific embodiments. These embodiments are based on the technical solution of the present invention and provide detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments. Unless otherwise specified, the equipment used in the following embodiments is conventional equipment in the art; unless otherwise specified, the reagents used are commercially available products or prepared using conventional methods in the art. Specific details not described in the following embodiments can be achieved using conventional experimental methods in the art.

[0017] In the preparation of negative electrode active materials for lithium-ion batteries, porous graphite, due to its tunable pore structure, can not only effectively accommodate the volume changes of silicon but also provide abundant lithium-ion transport pathways. The total pore volume V of porous graphite... Tot Specific surface area S BET The size of the aperture D has a significant impact on the initial coulombic efficiency and cycle performance of the battery, among which S BET / V Tot This represents the pore volume per unit specific surface area; the smaller the value, the higher the proportion of micropores. Microporous structures enhance the adsorption capacity of graphitized porous carbon materials for silicon sources during deposition, while ultraporous structures cannot effectively deposit silicon particles. A high proportion of ultraporous structures reduces the material's initial coulombic efficiency and stability.

[0018] Specifically, silicon particles preferentially fill the micropores of graphitized porous carbon materials. When the silicon particles expand, they do not compress the overall electrode structure, preventing electrode cracking. The micropores also limit the disordered aggregation of silicon particles, maintaining their uniform dispersion within the electrode. This improves the battery's cycle performance. The high-density cross-linked structure and appropriate pore volume distribution increase the material's mechanical strength, providing stable support for the silicon particles and reducing particle breakage and pulverization caused by volume expansion or contraction during charging and discharging. This helps maintain the integrity of the electrode material, thereby improving the initial coulombic efficiency and cycle performance. Simultaneously, a suitable pore structure and specific surface area contribute to the formation of a uniform and stable solid electrolyte interphase (SEI) film. The presence of ultrapores and micropores limits excessive reactions between the electrolyte and electrode materials, reducing side reactions and thus minimizing irreversible capacity loss and improving the initial coulombic efficiency. Furthermore, the stable SEI film prevents further decomposition of the electrolyte, protecting the electrode material and extending the battery's cycle life.

[0019] The porous graphite material prepared by this invention has a suitable pore structure and specific surface area, which can improve the first coulombic efficiency and cycle performance of the battery. The technical solution of this invention will be described below with reference to specific embodiments.

[0020] Example 1 The method for preparing porous graphite material in this embodiment includes the following steps: 1) Place 1.5 g of CaC2 powder in a ceramic crucible, then place the alumina ceramic crucible in an alumina reactor. Seal the reactor and evacuate it. Then, introduce CO gas at a certain pressure and heat the reactor to 1000 °C, maintaining the pressure inside the reactor at 0.2 MPa. After reacting for 5 h, allow the reactor temperature to naturally cool to room temperature. Remove the product from the crucible. 2) After washing with 0.1 M dilute hydrochloric acid and distilled water several times in sequence, the solid powder was separated by centrifugation and dried in an oven at 80 ℃ to obtain porous graphite material.

[0021] like Figure 1-2 As shown, porous graphite materials were tested, and XRD showed that the product had a graphite structure; SEM images showed that micron-sized bulk products were obtained.

[0022] Example 2 The preparation method of the porous graphite material in this embodiment is basically the same as that in Example 1, except that the reaction vessel temperature is 1200 ℃ and the pressure inside the reaction vessel is 0.1 MPa. Figure 5-8 As shown, the porous graphite material was tested and analyzed. XRD showed that the product was a graphite structure; SEM showed that the product was a micron-sized bulk product; BET analysis showed that the product was a mesoporous structure.

[0023] Example 3 The preparation method of the porous graphite material in this embodiment is basically the same as that in Example 1, except that the reaction vessel temperature is 850℃ and the pressure inside the reaction vessel is 8MPa. Figure 9 As shown, XRD reveals that the product has a graphite structure.

[0024] Example 4 The method for preparing porous graphite material in this embodiment includes the following steps: 1) Mix 1.5 g CaC2 and 0.1 g iron powder evenly in a mortar and pestle in a glove box, then place the mixture into an alumina crucible. Place the alumina ceramic crucible inside an alumina reactor, seal the reactor, evacuate it, and then introduce CO gas at a certain pressure. Heat the reactor to 1200 ℃ and maintain the pressure inside the reactor at 0.1 MPa. After reacting for 5 h, allow the reactor temperature to naturally cool to room temperature, and then remove the product from the crucible. 2) After washing repeatedly with 0.1 M dilute hydrochloric acid and distilled water, the mixture was centrifuged, and the resulting solid powder was dried in an oven at 80 ℃. Figure 10-13 As shown, XRD revealed that the product has a graphite structure, which is superior to the product obtained under the same conditions without an iron catalyst; SEM images showed that the product was obtained in micron-sized bulk form; BET analysis showed that the product has a porous structure; Raman analysis showed that highly crystalline graphite was obtained.

[0025] Example 5 The preparation method of the porous graphite material in this embodiment is basically the same as that in Example 4, except that the reaction vessel temperature is 1350℃. XRD shows that the product has a graphite structure; BET analysis shows that the product has a porous structure.

[0026] Example 6 The preparation method of the porous graphite material in this embodiment is basically the same as that in Example 4, except that 0.1 g of iron powder is replaced with 0.3 g of nickel powder, and the reaction vessel temperature is 1100 ℃. XRD shows that the product has a graphite structure.

[0027] Example 7 The preparation method of the porous graphite material in this embodiment is basically the same as that in Example 4, except that 0.1 g of iron powder is replaced with 0.6 g of cobalt powder, the temperature of the reactor is 900℃, the pressure inside the reactor is 5 MPa, and the XRD shows that the product has a graphite structure.

[0028] Example 8 The preparation method of the porous graphite material in this embodiment is basically the same as that in Example 4, except that 0.1 g of iron powder is replaced with 0.6 g of iron powder, the temperature of the reactor is 900℃, the pressure inside the reactor is 0.5 MPa, and the XRD shows that the product has a graphite structure.

[0029] Aperture: Tested using a laser particle size analyzer. Pore ​​structure: The specific surface area and pore volume of graphitized porous carbon materials were tested using the BET static method. First, the porous graphite material was placed in a sample tube of a specialized adsorption instrument and pretreated at high temperature (200℃, nitrogen blowing for 2 hours) to remove surface impurities and moisture. Subsequently, an inert gas (usually nitrogen or other adsorbent) was brought into contact with the porous carbon material under a series of known relative pressures until adsorption equilibrium was reached. The instrument measured the adsorption amount at different relative pressures, and based on these data, the specific surface area and pore volume were calculated using BET theory, as shown in Table 1.

[0030] Table 1 As can be seen from the XRD patterns of Examples 1, 2, and 3, the peak at approximately 26° in the XRD pattern of Example 1 typically corresponds to the (002) crystal plane diffraction peak of graphite, indicating the presence of a graphite structure. However, many obvious and sharp impurity peaks appear in the 35°-40° and 45°-50° ranges. This indicates that although the sample contains graphite, its purity is low, containing a large amount of other crystalline impurities (possibly unreacted raw materials or other minerals). Furthermore, the presence of numerous baseline noise points suggests that the amorphous portion or disorder of the sample is relatively high. In the XRD pattern of Example 2, the main peak at approximately 26° remains very strong and sharp, compared to... Figure 1 Narrower Figure 1 The obvious impurity peaks (in the 35°-50° range) have largely disappeared, and the baseline has become very smooth. This indicates that the sample has undergone purification or further high-temperature treatment. The crystalline structure of graphite is more complete, and a large number of impurities have been removed, resulting in a significant improvement in sample purity.

[0031] The main peak ratio around 26° in the XRD pattern of Example 3 Figure 5 The peaks are sharper (narrower half-width), indicating larger graphite crystallites, a more orderly and structured layered structure, and fewer defects. There are almost no other peaks across the entire scan range, and the baseline is extremely flat and clean. This represents a very high degree of graphitization.

[0032] This indicates that the crystallinity of graphite increases with increasing reaction temperature. (Based on the BET plot of Example 1...) Figure 3 ) and the BET diagram of Example 2 ( Figure 7 In contrast, as the reaction temperature increases, the mesopores increase in size.

[0033] Compared to Example 2, Example 4 involved the addition of a catalyst to the reaction, resulting in... Figure 6 and Figure 9 It can be seen that the crystallinity of graphite is increased and the mesopores are reduced, as shown in the Raman spectra of Examples 2 and 4 ( Figure 8 and Figure 13 )look, Figure 13In the figure, the height of the D peak is significantly lower than that of the G peak. A lower I_D / ​​I_G ratio usually indicates a higher degree of graphitization and a relatively lower defect density.

[0034] Compared to Example 1, Example 2, after increasing the reaction temperature, shows the Raman spectra of Examples 2 and 1 (…). Figure 8 and Figure 4 As you can see, a lower I_D / ​​I_G ratio usually means a higher degree of graphitization and a relatively lower defect density.

[0035] It should be understood that the above description of the preferred embodiments is quite detailed, but it should not be considered as a limitation on the scope of protection of this invention. Those skilled in the art, under the guidance of this invention, can make substitutions or modifications without departing from the scope of protection of the claims of this invention, and all such substitutions or modifications fall within the scope of protection of this invention. The scope of protection of this invention should be determined by the appended claims.

Claims

1. A method for preparing porous graphite, characterized in that, Includes the following steps: S1. Place CaC2 powder in a reaction vessel, introduce CO gas into the reaction vessel, and carry out a gas-solid reaction at 800~1400 ℃. After the reaction is completed, cool to room temperature to obtain a solid product. S2. Porous graphite can be obtained by washing and drying the solid product.

2. The method for preparing porous graphite according to claim 1, characterized in that, In step S1, the metal catalyst can also be mixed with CaC2 powder and placed in a reaction vessel.

3. The method for preparing porous graphite according to claim 2, characterized in that, The metal catalyst contains at least one or more elements including iron, cobalt, and nickel.

4. The method for preparing porous graphite according to claim 2, characterized in that, When the metal catalyst is mixed with CaC2 powder, the mass percentage of the metal catalyst is 6%-30%.

5. The method for preparing porous graphite according to claim 1, characterized in that, The pressure of CO gas inside the reactor is maintained above 0.1 MPa-8 MPa, and the reaction time is 4-6 hours.

6. The method for preparing porous graphite according to claim 1, characterized in that, During the washing process in step S2, multiple washes can be performed using dilute hydrochloric acid and distilled water.

7. A porous graphite, characterized in that, The porous graphite is obtained by the preparation method according to any one of claims 1-6, wherein the pore size is 2-50 nm, and S BET / V Tot <400.

8. A lithium-ion battery, characterized in that, Includes a negative electrode, wherein the negative electrode material is the porous graphite as described in claim 7.

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