A surface-porous graphite material and a method for producing the same

Abstract

This invention discloses a method for preparing a porous graphite material. The method involves uniformly mixing a foaming agent solution with graphite powder and a coating material, evaporating the solvent, and then simultaneously performing foaming and carbonization treatments. The resulting porous graphite material is then pulverized. This method is simple, and the prepared porous graphite material has a porous structure with controllable pore size. The graphite core in this porous graphite material has no pore structure, and the carbon layer covering the graphite core has uniformly distributed crater structures, which can be embedded in silicon-based materials to prepare silicon-carbon composite anodes for lithium-ion batteries.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery technology and relates to a porous graphite material and its preparation method. Background Technology

[0002] Lithium-ion batteries have become the mainstream development direction for rechargeable batteries due to their superior performance. Their anode materials are primarily graphite-based, offering advantages such as abundant resources, stable electrochemical performance, high tap density, and low irreversible capacity. However, the upper limit of the specific capacity of graphite materials can no longer meet the ever-increasing demands of power batteries. Therefore, in order to continuously improve the energy density of lithium-ion batteries, the development of novel anode materials with high specific capacity is imperative.

[0003] Silicon-based anode materials are a novel type of anode material, with a theoretical specific capacity of 4200 mAh / g, far exceeding the theoretical specific capacity of graphite (372 mAh / g). Their lithium intercalation potential is similar to that of graphite, and they possess advantages such as low operating voltage, abundant availability, and low cost, making them a preferred alternative to carbon-based anode materials. In recent years, they have gained considerable favor from both academia and industry. Despite these numerous advantages, silicon-based anode materials have yet to achieve large-scale commercial application due to significant drawbacks. During charge and discharge, silicon-based anode materials undergo 100–400% volume expansion and contraction, leading to electrode material fragmentation, loss of connection with the current collector and electrode conductive network, and the formation of a new solid electrolyte interface (SEI). This results in substantial electrolyte consumption and a significant reduction in the cycle stability of silicon-based anode materials.

[0004] To address this issue, the industry has attempted to combine physical or chemical methods, such as nano-sizing, inert buffering, and surface coating technologies. Another approach involves combining nano-silicon materials with carbon-based materials through surface coating and loading. By leveraging the advantages of multiple materials and mitigating their respective disadvantages, the conductivity of silicon-based materials can be improved while mitigating breakage during charging and discharging. Furthermore, direct contact between the electrolyte and silicon-based materials can be avoided, thereby reducing side reactions, improving cycle stability, and ultimately producing silicon-carbon composite anode materials with high capacity and long cycle life.

[0005] Therefore, it is of great significance to develop a graphite material with a simple process and a porous structure with controllable pore size for embedding in silicon-based materials to prepare high-performance silicon-carbon composite anode materials. Summary of the Invention

[0006] To address the aforementioned deficiencies in existing technologies, the present invention aims to provide a porous graphite material and its preparation method. The method involves uniformly mixing a foaming agent solution with graphite powder and a coating material, evaporating the solvent, and then simultaneously performing foaming and carbonization treatments. Following this, the material is pulverized to obtain a porous graphite material. This method is simple, and the prepared porous graphite material has a porous structure with controllable pore size. The graphite core in this porous graphite material has no pore structure, and the carbon layer covering the graphite core has uniformly distributed crater structures, which can be embedded in silicon-based materials to prepare silicon-carbon composite anodes for lithium-ion batteries.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] The first aspect of the present invention provides a method for preparing a porous graphite material, comprising the following steps:

[0009] S1, graphite powder and coating material are added to a foaming agent solution, stirred evenly, and the solution is heated to evaporate the solvent to obtain a mixture containing graphite powder, coating material and foaming agent;

[0010] S2, the mixture is simultaneously subjected to foaming and carbonization treatments to obtain a graphite / porous carbon composite material;

[0011] S3, the graphite / porous carbon composite material is ball-milled to obtain a porous graphite material.

[0012] Preferably, in step S1:

[0013] The graphite powder is one or more of natural graphite, artificial graphite, and mesophase carbon microspheres; and / or

[0014] The coating material is selected from one of low-temperature asphalt, phenolic resin, and epoxy resin; and / or

[0015] The foaming agent used in the foaming agent solution is selected from one or more of azo compounds, sulfonyl hydrazide compounds, nitroso compounds, carbonates, bicarbonates, ammonium salts, and urea.

[0016] Preferably, in step S1, the concentration of the foaming agent solution is 0.1–30 wt%.

[0017] Preferably, in step S1, the mass ratio of graphite powder, coating material and foaming agent is (30-85):(3-15):(5-70).

[0018] Preferably, in step S1, the stirring time is 0.1 to 6 hours and the stirring speed is 100 to 2000 rpm.

[0019] Preferably, in step S1, during the heating and evaporation process, stirring is maintained and the evaporation temperature is controlled at 60–120°C.

[0020] Preferably, in step S2, the temperature of the foaming treatment and carbonization treatment is 600-1200℃, and the treatment time is 0.5-5h.

[0021] Preferably, in step S3, the ball milling process takes 0.5 to 5 hours.

[0022] A second aspect of the present invention provides a porous graphite material obtained by the preparation method of the porous graphite material according to the first aspect of the present invention, comprising a graphite core and a carbon layer covering the surface of the graphite core.

[0023] The graphite core has no porous structure; the carbon layer has uniformly distributed crater structures.

[0024] Preferably, the size of the crater structure on the carbon layer is 1 nm to 30 μm.

[0025] The porous graphite material and its preparation method provided by this invention have the following beneficial effects:

[0026] 1. The present invention relates to a porous graphite material and its preparation method, wherein a foaming agent solution is mixed uniformly with graphite powder and a coating material, and the solvent is evaporated. Then, foaming and carbonization treatments are performed simultaneously, followed by pulverization to obtain a porous graphite material. The method is simple, and the prepared porous graphite material has a porous structure with controllable pore size. The graphite core in the porous graphite material has no pore structure, and the carbon layer covering the graphite core has a uniformly distributed crater structure, which can be embedded in silicon-based materials to prepare silicon-carbon composite anodes for lithium-ion batteries.

[0027] 2. The crater structure distributed on the carbon layer of the porous graphite material of the present invention is obtained by foaming treatment, and its average pore size is small, the pore size is porous, the pore size distribution is narrow, and the pore density is high.

[0028] 3. The carbon layer on the surface of the porous graphite material of the present invention is recarbonized and foamed at the same time, without adding extra operations and energy consumption, and is easy to mass-produce. Attached Figure Description

[0029] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings:

[0030] Figure 1 This is a schematic diagram of the structure of the porous graphite material of the present invention. Detailed Implementation

[0031] To better understand the above-mentioned technical solutions of the present invention, the technical solutions of the present invention will be further described below in conjunction with embodiments.

[0032] The present invention provides a method for preparing a porous graphite material, comprising the following steps:

[0033] S1, graphite powder and coating material are added to a foaming agent solution, stirred evenly, and the solution is heated to evaporate the solvent to obtain a mixture containing graphite powder, coating material and foaming agent;

[0034] Specifically, a foaming agent solution is first prepared. Then, graphite powder and coating material are added to the prepared foaming agent solution and stirred for a period of time. After the graphite powder and coating material are evenly dispersed in the foaming agent solution, stirring is continued, and the solution is heated to evaporate the solvent, resulting in a mixture containing graphite powder, coating material, and foaming agent. The foaming agent used in the foaming agent solution is selected from one or more of azo compounds, sulfonyl hydrazides, nitroso compounds, carbonates, bicarbonates, ammonium salts, and urea. The concentration of the prepared foaming agent solution is 0.1–30 wt%, that is, the concentration of the foaming agent in the foaming agent solution is 0.1–30 wt%. The graphite powder is one or more of natural graphite, artificial graphite, and mesophase carbon microspheres. The coating material is selected from one of low-temperature asphalt, phenolic resin, and epoxy resin. The mass ratio of the graphite powder, coating material, and foaming agent used above is (30–85):(3–15):(5–70). During the stirring process, the stirring time is controlled to be 0.1–6 h, and the stirring speed is 100–2000 rpm. During the heating and evaporation process, the evaporation temperature is controlled to be 60–120℃.

[0035] S2, the mixture is simultaneously subjected to foaming and carbonization treatments to obtain a graphite / porous carbon composite material;

[0036] Specifically, the mixture containing graphite powder, coating material, and foaming agent obtained above is simultaneously subjected to foaming and carbonization treatments at a certain temperature to obtain a graphite / porous carbon composite material. The temperature for both foaming and carbonization treatments is 600–1200℃, and the treatment time is 0.5–5 hours. During the foaming and carbonization processes, the graphite is unaffected by foaming, while the coating material becomes a porous structure after foaming and carbonization. The foaming and carbonization processes can be carried out in a rotary tube furnace under a nitrogen atmosphere.

[0037] S3, the graphite / porous carbon composite material is subjected to ball milling to obtain a porous graphite material. The ball milling process takes 0.5–5 hours. The particle size of the porous graphite material is 5–100 μm.

[0038] Combination Figure 1 As shown, the above-prepared porous graphite material includes a graphite core and a carbon layer covering the surface of the graphite core; wherein the graphite core is not affected by foaming and has no porous structure; a crater structure 1 is uniformly distributed on the carbon layer covering the surface of the graphite core. The crater structure 1 is obtained by foaming the carbon layer on the surface of the graphite particles. It has a small average pore size, controllable pore size, narrow pore size distribution, and high pore density. The size of the crater structure 1 is 1 nm to 30 μm, preferably 0.2 μm to 5 μm.

[0039] The following section provides a further description of the porous graphite material and its preparation method according to the present invention, using specific examples.

[0040] Example 1

[0041] The method for preparing the porous graphite material in this embodiment is as follows:

[0042] (1) Prepare 200 mL of 15 wt% ammonium carbonate aqueous solution (foaming agent solution), add 20 g of natural graphite and 2 g of low temperature asphalt, stir at high speed for 30 minutes at a stirring rate of 500 rpm, and then heat the solution to 50 °C while stirring to evaporate the solvent, and collect the mixture of natural graphite, low temperature asphalt and ammonium carbonate.

[0043] (2) The mixture obtained in step (1) is placed in a rotary tube furnace, nitrogen is introduced at high temperature, and foaming and carbonization are carried out at 800°C for 2 hours. After the reaction is completed, the temperature is lowered to room temperature to obtain graphite / porous carbon composite material.

[0044] (3) The graphite / porous carbon composite material obtained in step (2) is subjected to ball milling to obtain graphite powder material with a crater structure with a pore size of about 1 μm that is uniformly distributed on the surface.

[0045] Example 2

[0046] The method for preparing the porous graphite material in this embodiment is as follows:

[0047] (1) Prepare 300 mL of 2 wt% benzyl sulfonyl hydrazine ethanol solution (foaming agent solution), add 40 g of artificial graphite and 5 g of low temperature asphalt, stir at high speed for 40 minutes at a stirring rate of 350 rpm, and then heat the solution to 60 °C while stirring to evaporate the solvent, and collect the mixture of artificial graphite, low temperature asphalt and benzyl sulfonyl hydrazine.

[0048] (2) The mixture obtained in step (1) is placed in a rotary tube furnace, nitrogen is introduced at high temperature, and foaming and carbonization are carried out at 900°C for 3 hours. After the reaction is completed, the temperature is lowered to room temperature to obtain graphite / porous carbon composite material.

[0049] (3) The graphite / porous carbon composite material obtained in step (2) is subjected to ball milling to obtain graphite powder material with a crater structure with a pore size of about 0.8 μm that is uniformly distributed on the surface.

[0050] Example 3

[0051] The method for preparing the porous graphite material in this embodiment is as follows:

[0052] (1) Prepare 200 mL of 0.3 wt% azobisisobutyronitrile ethanol solution (foaming agent solution), add 10 g of natural graphite and 1 g of low temperature asphalt, stir at high speed for 120 minutes at a stirring rate of 300 rpm, and then heat the solution to 60 °C while stirring to evaporate the solvent, and collect the mixture of natural graphite, low temperature asphalt and azobisisobutyronitrile.

[0053] (2) The mixture obtained in step (1) is placed in a rotary tube furnace, nitrogen is introduced at high temperature, and foaming and carbonization are carried out at 850°C for 2 hours. After the reaction is completed, the temperature is lowered to room temperature to obtain graphite / porous carbon composite material.

[0054] (3) The graphite / porous carbon composite material obtained in step (2) is subjected to ball milling to obtain graphite powder material with a crater structure with a pore size of about 1.5 μm and a uniform surface distribution.

[0055] Example 4

[0056] The method for preparing the porous graphite material in this embodiment is as follows:

[0057] (1) Prepare 500 mL of aqueous solution of 15 wt% ammonium nitrate and 5 wt% ammonium carbonate (foaming agent solution), add 50 g of artificial graphite and 8 g of low temperature asphalt, stir at high speed for 90 minutes at a stirring rate of 400 rpm, and then heat the solution to 80°C while stirring to evaporate the solvent, and collect the mixture of natural graphite, low temperature asphalt, ammonium nitrate and ammonium carbonate.

[0058] (2) The mixture obtained in step (1) is placed in a rotary tube furnace, nitrogen is introduced at high temperature, and foaming and carbonization are carried out at 900°C for 1 hour. After the reaction is completed, the temperature is lowered to room temperature to obtain graphite / porous carbon composite material.

[0059] (3) The graphite / porous carbon composite material obtained in step (2) is subjected to ball milling to obtain graphite powder material with a crater structure with a pore size of about 2 μm that is uniformly distributed on the surface.

[0060] Example 5

[0061] The method for preparing the porous graphite material in this embodiment is as follows:

[0062] (1) Prepare 300 mL of ethanol solution of 1 wt% benzenesulfonyl hydrazine and 0.1 wt% azobisisobutyronitrile (foaming agent solution), add 20 g of natural graphite and 1 g of low-temperature asphalt, stir at high speed for 100 minutes at a stirring rate of 350 rpm, and then heat the solution to 60 °C while stirring to evaporate the solvent, and collect the mixture of natural graphite, low-temperature asphalt, benzenesulfonyl hydrazine and azobisisobutyronitrile.

[0063] (2) The mixture obtained in step (1) is placed in a rotary tube furnace, nitrogen is introduced at high temperature, and foaming and carbonization are carried out at 950°C for 1.5 hours. After the reaction is completed, the temperature is lowered to room temperature to obtain graphite / porous carbon composite material.

[0064] (3) The graphite / porous carbon composite material obtained in step (2) is subjected to ball milling to obtain graphite powder material with a crater structure with a pore size of about 2.5 μm that is uniformly distributed on the surface.

[0065] Those skilled in the art should recognize that the above embodiments are merely illustrative of the present invention and are not intended to limit the present invention. Any variations or modifications to the above embodiments that are within the spirit and essence of the present invention will fall within the scope of the claims of the present invention.

Claims

1. A method for preparing a porous graphite material, characterized in that, Includes the following steps: S1, graphite powder and coating material are added to a foaming agent solution, stirred evenly, and the solution is heated to evaporate the solvent to obtain a mixture containing graphite powder, coating material and foaming agent; S2, the mixture is simultaneously subjected to foaming and carbonization treatments to obtain a graphite / porous carbon composite material. The temperature for the foaming and carbonization processes is 600–1200°C, and the processing time is 0.5–5 hours. S3, the graphite / porous carbon composite material is ball-milled to obtain a graphite material with a porous surface. The porous graphite material comprises a graphite core and a carbon layer covering the surface of the graphite core; the graphite core has no porous structure; and the carbon layer has uniformly distributed crater structures.

2. The method for preparing a porous graphite material according to claim 1, characterized in that, In step S1: The graphite powder is one or more of natural graphite, artificial graphite, and mesophase carbon microspheres; and / or The coating material is selected from one of low-temperature asphalt, phenolic resin, and epoxy resin; and / or The foaming agent used in the foaming agent solution is selected from one or more of azo compounds, sulfonyl hydrazide compounds, nitroso compounds, carbonates, bicarbonates, ammonium salts, and urea.

3. The method for preparing a porous graphite material according to claim 2, characterized in that, In step S1, the concentration of the foaming agent solution is 0.1 to 30 wt%.

4. The method for preparing a porous graphite material according to claim 3, characterized in that, In step S1, the mass ratio of graphite powder, coating material and foaming agent is (30-85):(3-15):(5-70).

5. The method for preparing a porous graphite material according to claim 1, characterized in that, In step S1, the stirring time is 0.1 to 6 hours and the stirring speed is 100 to 2000 rpm.

6. The method for preparing a porous graphite material according to claim 1, characterized in that, In step S1, during the heating and evaporation process, stirring is maintained and the evaporation temperature is controlled at 60–120°C.

7. The method for preparing a porous graphite material according to claim 1, characterized in that, In step S3, the ball milling process takes 0.5 to 5 hours.

8. A porous graphite material obtained by the method for preparing a porous graphite material according to any one of claims 1 to 7, characterized in that, It includes a graphite core and a carbon layer covering the surface of the graphite core; The graphite core has no porous structure; the carbon layer has uniformly distributed crater structures.

9. The porous graphite material according to claim 8, characterized in that, The size of the crater structure on the carbon layer is 1 nm to 30 μm.

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