A porous carbon material, its preparation method and application

Abstract

This invention provides a porous carbon material, its preparation method, and its applications, belonging to the technical field of lithium battery anode materials. This invention introduces a large number of oxygen-containing functional groups through oxidative crosslinking modification, controlling the formation of an ordered structure in the raw coal during carbonization. After carbonization, the material possesses a disordered structure. The colloidal process of the raw coal during carbonization can be controlled by precisely regulating the heating rate during the oxidative crosslinking process. The porous carbon samples prepared through further activation, pore formation, and purification show smaller particle size changes and higher mechanical strength after applying different pressures, enhancing the inhibitory effect of porous carbon on the volume expansion of silicon during long-term cycling after silicon deposition.

Description

Technical Field

[0001] This invention relates to the field of lithium battery anode material technology, and in particular to a porous carbon material, its preparation method and application. Background Technology

[0002] In existing technologies, coal-based porous carbon is produced by directly carbonizing coal of varying metamorphic degrees, uniformly mixing it with a pore-forming agent, and then further purifying and drying it to obtain the finished coal-based porous carbon product. During carbonization, raw coal of different metamorphic degrees undergoes a colloidal process, during which the carbon lattice grows in an ordered direction, ultimately forming a structure close to soft carbon. Subsequent compressive strength tests of the porous carbon show that the particles are easily pulverized, and during long-term cycling tests of silicon-carbon anode materials prepared by further silicon deposition, the ability to suppress silicon volume expansion is reduced.

[0003] Currently, most domestic and international literature reports on improving the strength of carbon frameworks focus on doping porous carbon with elements such as nitrogen, boron, and phosphorus. This alters the electronic structure and chemical bonding of the carbon framework, enhancing the interactions between carbon atoms and improving the strength and stability of porous carbon. For example, nitrogen doping can introduce lone pairs of electrons, forming covalent or coordinate bonds with carbon atoms, increasing the bonding strength of the carbon framework. Although heteroatom doping can improve the bonding strength of the carbon framework by forming covalent or coordinate bonds with carbon atoms, the chemical reagents containing nitrogen, boron, and phosphorus heteroatoms are expensive, significantly increasing the preparation cost of heteroatom-doped porous carbon.

[0004] Therefore, it is urgent to solve the problem of how to improve the mechanical strength of porous carbon products prepared from raw coal with different degrees of metamorphism and enhance the inhibitory effect of porous carbon on the volume expansion of silicon during long-term cycling after silicon precipitation. Summary of the Invention

[0005] The purpose of this invention is to provide a porous carbon material, its preparation method and application, which can improve the mechanical strength of porous carbon products prepared from raw coal with different degrees of metamorphism, and enhance the inhibitory effect of porous carbon on the volume expansion of silicon during long-term cycling after silicon precipitation.

[0006] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0007] This invention provides a method for preparing porous carbon materials, comprising the following steps:

[0008] After the raw coal is crushed to the target particle size, it is subjected to oxidative cross-linking under oxygen-containing gas conditions to obtain oxidized material;

[0009] The oxidized material is subjected to a first heat treatment to obtain a carbonized material;

[0010] The carbonized material is mixed with an activating pore-forming agent, subjected to a second heat treatment, and then purified to obtain porous carbon.

[0011] Preferably, the raw coal includes one or more of the following: long-flame coal, gas coal, fat coal, coking coal, lean coal, poor coal, and anthracite.

[0012] The target particle size D after the raw coal is crushed 50 The range is 1–100 μm.

[0013] Preferably, the oxygen-containing gas includes at least one of air and oxygen;

[0014] The oxidative crosslinking includes: heating at a first heating rate to perform a first oxidative crosslinking, and then heating at a second heating rate to perform a second oxidative crosslinking, wherein the temperature of the first oxidative crosslinking is 80–250°C and the time is 0.5–6 h; the temperature of the second oxidative crosslinking is 150–400°C and the time is 0.5–6 h; and the first heating rate is less than or equal to the second heating rate.

[0015] Preferably, the temperature of the first heat treatment is 400-900℃, the holding time is 1-6h, and the heating rate to the temperature of the first heat treatment is 1-10℃ / min.

[0016] Preferably, the particle size D of the carbonized material 50 The range is 1–20 μm.

[0017] Preferably, the activating pore-forming agent includes one or more of potassium hydroxide, sodium hydroxide, potassium carbonate, phosphoric acid, and zinc chloride; the mass ratio of the carbonized material to the activating pore-forming agent is 1:1 to 3.

[0018] Preferably, the temperature of the second heat treatment is 700-1000℃, the holding time is 1-6h, and the heating rate to the temperature of the second heat treatment is 1-10℃ / min.

[0019] Preferably, the reagents used for purification include acid reagents or base reagents, wherein the acid reagents include one or more of hydrochloric acid, hydrofluoric acid, phosphoric acid, sulfuric acid and nitric acid; and the base reagents include NaOH and / or KOH.

[0020] This invention provides porous carbon materials prepared by the preparation method described in the above technical solution.

[0021] This invention provides the application of the porous carbon material described in the above technical solution in the preparation of silicon-carbon anode materials for lithium batteries.

[0022] This invention provides a method for preparing porous carbon materials. By introducing a large number of oxygen-containing functional groups through oxidative crosslinking modification, the method controls the formation of an ordered structure in the raw coal during carbonization, resulting in a disordered structure after carbonization. The method also allows for precise control of the heating rate during oxidative crosslinking, reducing the formation of colloidal particles in the raw coal during carbonization. Compared to samples without oxidative crosslinking modification, the porous carbon samples prepared through further activation, pore-forming, and purification exhibit smaller particle size changes and higher mechanical strength after applying different pressures.

[0023] This invention modifies raw coal through gradient oxidation and crosslinking to prevent the decomposition of macromolecular side chains and the formation of a colloidal body. During further low-temperature carbonization, the original carbon skeleton is maintained, resulting in porous carbon produced via physical / chemical activation. By applying progressively increasing external pressure to the finished porous carbon powder, the particle size changes under different pressures are tested. The particle size change results show that the crosslinking modification of the raw material effectively improves the skeleton strength of the porous carbon. In contrast, existing technologies for preparing coal-based porous carbon, whether using physical activation methods (H2O, CO2, air, etc.) or chemical activation methods (KOH, NaOH, ZnCl2, H3PO4, etc.), cause further decomposition of the coal macromolecular side chains during low-temperature carbonization of raw coal with different metamorphic degrees. This produces a large amount of viscous liquid, and simultaneously, bubbles composed of coal gas appear, forming a three-phase colloidal body (gas, liquid, solid). This reduces the strength of the porous carbon and silicon-carbon particles, causing the silicon-carbon negative electrode sheet to expand, leading to silicon expansion and silicon-carbon pulverization during cycling, thus affecting battery cycle performance. Detailed Implementation

[0024] In this invention, unless otherwise specified, the raw materials or reagents required for preparation are all commercially available products well known to those skilled in the art.

[0025] This invention provides a method for preparing porous carbon materials, comprising the following steps:

[0026] After the raw coal is crushed to the target particle size, it is subjected to oxidative cross-linking under oxygen-containing gas conditions to obtain oxidized material;

[0027] The oxidized material is subjected to a first heat treatment to obtain a carbonized material;

[0028] The carbonized material is mixed with an activating pore-forming agent, subjected to a second heat treatment, and then purified to obtain porous carbon.

[0029] This invention involves pulverizing raw coal to the target particle size and then performing oxidative crosslinking under oxygen-containing gas conditions to obtain an oxidized material.

[0030] In this invention, the raw coal preferably includes one or more of the following: long-flame coal, gas coal, fat coal, coking coal, lean coal, poor coal, and anthracite. When the raw coal is two or more of the above, this invention does not have a special limitation on the proportion of different types of raw coal, and any proportion is acceptable. This invention uses coal raw materials with different degrees of metamorphism as carbon sources and prepares carbonization precursors through oxidative crosslinking modification. Coal-based carbon sources have the advantages of low cost and easy availability. Using coal as a carbon source can achieve high-value conversion of raw coal.

[0031] In this invention, the target particle size D of the crushed raw coal is... 50 Preferably, it is 1–100 μm, more preferably 50–80 μm.

[0032] In this invention, the oxygen-containing gas preferably includes at least one of air and oxygen; when the oxygen-containing gas is two or more of the above, this invention does not have a special limitation on the ratio of different types of oxygen-containing gases, and any ratio is acceptable.

[0033] In this invention, the oxidative crosslinking preferably includes: heating at a first heating rate to perform a first oxidative crosslinking, and then heating at a second heating rate to perform a second oxidative crosslinking, wherein the temperature of the first oxidative crosslinking is 80–250°C, more preferably 100–220°C, and even more preferably 200°C, and the time is 0.5–6 h, more preferably 2–5 h; the temperature of the second oxidative crosslinking is 150–400°C, more preferably 250–300°C, and the time is preferably 0.5–6 h, more preferably 2–5 h; and the first heating rate is less than or equal to the second heating rate.

[0034] In this invention, the first heating rate is preferably 2 to 3 °C / min, more preferably 5 to 6 °C / min.

[0035] After obtaining the oxidized material, the present invention performs a first heat treatment on the oxidized material to obtain carbonized material.

[0036] In this invention, the temperature of the first heat treatment is preferably 400–900°C, more preferably 600–700°C, the holding time is preferably 1–6 h, more preferably 2–5 h, and the atmosphere is nitrogen; the heating rate to the temperature of the first heat treatment is preferably 1–10°C / min, more preferably 5–8°C / min. This invention further carbonizes the modified oxidant through the first heat treatment, forming an initial porous structure.

[0037] In this invention, the particle size D of the carbonized material 50 Preferably, it is 1–20 μm, more preferably 8–15 μm.

[0038] After obtaining the carbonized material, the present invention mixes the carbonized material with an activating pore-forming agent, performs a second heat treatment, and then purifies it to obtain porous carbon.

[0039] In this invention, the activating pore-forming agent preferably includes one or more of potassium hydroxide, sodium hydroxide, potassium carbonate, phosphoric acid, and zinc chloride; when the activating pore-forming agent is two or more of the above, this invention does not have a special limitation on the ratio of different types of activating pore-forming agents, and any ratio is acceptable.

[0040] In this invention, the mass ratio of the carbonized material to the activating pore-forming agent is preferably 1:1 to 3, and more preferably 1:1 to 2.

[0041] In this invention, the temperature of the second heat treatment is preferably 700–1000°C, more preferably 750–850°C, the holding time is preferably 1–6 h, more preferably 2–5 h, and the atmosphere is nitrogen; the heating rate to the temperature of the second heat treatment is preferably 1–10°C / min, more preferably 3–8°C / min. This invention uses the second heat treatment to etch and create pores on the surface of the carbonized material, constructing a rich porous structure.

[0042] After a second heat treatment, a porous carbon crude product with a high specific surface area is obtained. After purification, the finished porous carbon product is obtained.

[0043] In this invention, the reagents used for purification preferably include acid reagents or base reagents. The acid reagents include one or more of hydrochloric acid (mass concentration 1-30%), hydrofluoric acid, phosphoric acid, sulfuric acid, and nitric acid. The base reagents preferably include NaOH and / or KOH.

[0044] In this invention, the acid or alkali reagent is preferably prepared into an aqueous solution, and the obtained porous carbon crude product is immersed in the aqueous solution of the acid or alkali reagent and purified under stirring.

[0045] The present invention does not have a special limitation on the concentration of the aqueous solution of the acid or base reagent, which can be adjusted according to actual needs; the purification time is preferably 1 to 24 hours, more preferably 6 to 12 hours.

[0046] This invention provides porous carbon materials prepared by the preparation method described in the above technical solution.

[0047] This invention provides the application of the porous carbon material described above in the preparation of silicon-carbon anode materials for lithium batteries. This invention does not specifically limit the method of application; any method well-known in the art can be used.

[0048] The specific embodiments of the present invention are described in detail below, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0049] Unless otherwise specified, the experimental methods described in the various embodiments of this invention are conventional methods; unless otherwise specified, the reagents and raw materials described below are all commercially available.

[0050] Example 1

[0051] 1) Crush low-rank long-flame coal to the target particle size D. 50 The sample was 100 μm thick, placed in a crucible, transferred to a muffle furnace, and air was introduced. The temperature was increased to 200 °C at a rate of 2 °C / min and held for 2 h. The temperature was then increased to 400 °C at a rate of 5 °C / min and held for 2 h. After the oxidation crosslinking was completed, the oxidized material was obtained.

[0052] 2) Transfer the oxidized material to a box furnace, heat it to 700℃ at a rate of 5℃ / min under a nitrogen atmosphere, hold it at that temperature for 2 hours, allow it to cool naturally to room temperature, and then pulverize it to D. 50 The carbonized material was obtained with a thickness of 8 μm.

[0053] 3) The carbonized material and the activating pore-forming agent (potassium hydroxide) are mixed at a mass ratio of 1:2 and then placed in a sagger. The temperature is raised to 850°C in a nitrogen atmosphere activation furnace at a heating rate of 3°C / min and held at the temperature for 2 hours. The mixture is then naturally cooled to room temperature to obtain porous crude carbon.

[0054] 4) The porous carbon crude product is immersed in a 5% hydrochloric acid solution, stirred for 6 hours, filtered, washed with water until neutral, and dried to obtain porous carbon.

[0055] Example 2

[0056] The only difference from Example 1 is that in step 1), the temperature is increased to 220°C at a rate of 2°C / min and held for 2 hours; and the temperature is increased to 300°C at a rate of 5°C / min and held for 2 hours. Everything else is the same as in Example 1.

[0057] Example 3

[0058] The only difference from Example 1 is that in step 1), the temperature is increased to 250°C at a rate of 2°C / min and held for 2 hours; and the temperature is increased to 300°C at a rate of 5°C / min and held for 2 hours. Everything else is the same as in Example 1.

[0059] Example 4

[0060] The only difference from Example 1 is that: in step 1), high-ranking anthracite is used as raw material.

[0061] Example 5

[0062] The only difference from Example 4 is that in step 1), the temperature is increased to 220°C at a rate of 2°C / min and held for 2 hours; and the temperature is increased to 300°C at a rate of 5°C / min and held for 2 hours. Everything else is the same as in Example 4.

[0063] Example 6

[0064] The only difference from Example 4 is that in step 1), the temperature is increased to 250°C at a rate of 2°C / min and held for 2 hours; and the temperature is increased to 300°C at a rate of 5°C / min and held for 2 hours. Everything else is the same as in Example 4.

[0065] Comparative Example 1

[0066] The only difference from Example 1 is that step 1) is omitted, and the long-flame coal is directly processed in steps 2) to 4), with the conditions being the same as in Example 1.

[0067] Comparative Example 2

[0068] The only difference from Comparative Example 1 is that high-ranking anthracite coal was used as the raw material.

[0069] Characterization and performance testing

[0070] XRD interlayer spacing was tested on the carbonized materials of Comparative Examples 1-2 and Examples 1-6. The data obtained from the XRD test results are shown in Table 1.

[0071] Table 1 shows the interlayer spacing measurement results of carbonized materials in different cases.

[0072] Experiment type Heating rate (°C / min) Target final temperature ℃ interlayer spacing (nm) Comparative Example 1 2 280 0.376 Comparative Example 2 2 280 0.377 Example 1 2 280 0.380 Example 2 5 280 0.382 Example 3 5 300 0.383 Example 4 2 280 0.381 Example 5 5 280 0.383 Example 6 5 300 0.384

[0073] The interlayer spacing results calculated from the XRD results of different experiments in Table 1 show that after oxidative crosslinking of coal raw materials, the interlayer spacing of the carbonized material is significantly increased compared with that of the carbonized material obtained by direct carbonization. This indicates that crosslinking (ester group-dominated) hinders the orderly stacking of aromatic rings and inhibits soft carbonization.

[0074] Mechanical strength tests were conducted on the porous carbon products prepared in Example 1 and Comparative Example 1. Different mechanical pressures, such as 0 MPa, 100 MPa, 200 MPa, and 300 MPa, were applied to the porous carbon samples prepared from raw coal with different degrees of metamorphism. The particle size of the samples after applying mechanical pressure was then tested, and the results are shown in Table 2.

[0075] Table 2 shows the particle size test results of porous carbon in Example 1 and Comparative Example 1 after being compressed under different mechanical pressures.

[0076] Experiment type Apply pressure D00 D10 D50 D97 D100 Comparative Example 1 0 2.12 3.06 5.04 13.65 30.39 Comparative Example 1 100 2.11 3.04 4.98 13.52 30.25 Comparative Example 1 200 2.08 3.00 4.89 13.42 30.11 Comparative Example 1 300 1.98 2.95 4.65 13.24 29.88 Example 1 0 2.32 3.21 5.23 14.23 31.21 Example 1 100 2.31 3.18 5.19 14.24 31.23 Example 1 200 2.33 3.23 5.18 14.18 31.25 Example 1 300 2.30 3.20 5.14 14.05 31.01

[0077] Table 2 shows the particle size distribution results after compression under different mechanical pressures. It can be seen that the porous carbon samples obtained after oxidative cross-linking modification of the raw coal, followed by a series of carbonization, activation, and purification processes, did not show significant changes in the overall particle size distribution (D10) after being subjected to increasing external pressures (0 MPa - 100 MPa - 200 MPa - 300 MPa). This indicates that even under 300 MPa of external pressure, the particles did not break and maintained their original particle size. However, the uncross-linked modified sample showed a decrease in overall particle size after being compressed under 300 MPa, indicating that the particles broke and smaller particles were produced.

[0078] Test case

[0079] The porous carbon prepared in Examples 1-6 was used to prepare silicon-carbon anode materials: Under argon protection, silane was deposited on the porous carbon at a deposition temperature of 550°C for 100 s, with a silane gas flow rate of 6 L / min and a protective gas to silane flow rate ratio of 1:8. Then, ethane gas was introduced for carbon coating at a deposition temperature of 800°C for 120 s and an ethane gas flow rate of 5 L / min. The protective gas to ethane flow rate ratio was 10:1, resulting in a silicon-carbon anode material with a silicon content of 50 wt%.

[0080] The expansion rate of the silicon-carbon anode material was tested using an in-situ expansion tester. The expansion rates of the silicon-carbon anode materials prepared with porous carbon in Examples 1 to 6 were 63%, 60%, 58%, 62%, 58%, and 55%, respectively.

[0081] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing porous carbon materials, characterized in that, Includes the following steps: After the raw coal is crushed to the target particle size, it is subjected to oxidative crosslinking under oxygen-containing gas conditions to obtain oxidized material; The oxidized material is subjected to a first heat treatment to obtain a carbonized material; The carbonized material is mixed with an activating pore-forming agent, subjected to a second heat treatment, and then purified to obtain porous carbon. The target particle size D after the raw coal is crushed 50 The range is 1~100μm; The oxidative crosslinking includes: heating at a first heating rate to perform a first oxidative crosslinking, and then heating at a second heating rate to perform a second oxidative crosslinking, wherein the temperature of the first oxidative crosslinking is 80~250℃ and the time is 0.5~6h; the temperature of the second oxidative crosslinking is 150~400℃ and the time is 0.5~6h; and the first heating rate is ≤ the second heating rate. The temperature of the first heat treatment is 400~900℃, and the holding time is 1~6h; The particle size D of the carbonized material 50 The range is 1~20μm; The mass ratio of the carbonized material to the activating pore-forming agent is 1:1~3; The temperature of the second heat treatment is 700~1000℃, and the holding time is 1~6h.

2. The preparation method according to claim 1, characterized in that, The raw coal includes one or more of the following: long-flame coal, gas coal, fat coal, coking coal, lean coal, poor coal, and anthracite.

3. The preparation method according to claim 1 or 2, characterized in that, The oxygen-containing gas includes at least one of air and oxygen.

4. The preparation method according to claim 1, characterized in that, The heating rate to the temperature of the first heat treatment is 1~10℃ / min.

5. The preparation method according to claim 1, characterized in that, The activating pore-forming agent includes one or more of potassium hydroxide, sodium hydroxide, potassium carbonate, phosphoric acid, and zinc chloride.

6. The preparation method according to claim 1, characterized in that, The heating rate to the temperature of the second heat treatment is 1~10℃ / min.

7. The preparation method according to claim 6, characterized in that, The reagents used for purification include acid reagents or base reagents. The acid reagents include one or more of hydrochloric acid, hydrofluoric acid, phosphoric acid, sulfuric acid, and nitric acid. The base reagents include NaOH and / or KOH.

8. The porous carbon material prepared by the preparation method according to any one of claims 1 to 7.

9. The application of the porous carbon material according to claim 8 in the preparation of silicon-carbon anode materials for lithium batteries.