A preparation method of modified porous carbon based on photocatalytic halogen atom transfer and silicon-carbon negative electrode

Abstract

The present invention relates to a preparation method of modified porous carbon based on photocatalytic halogen atom transfer and a silicon-carbon negative electrode. The preparation method comprises the following steps: (S1) immersing porous carbon in a C1-C5 halogenated hydrocarbon solution containing a photosensitizer to obtain halogenated hydrocarbon-loaded porous carbon; (S2) subjecting the halogenated hydrocarbon-loaded porous carbon to a photocatalytic reaction under an inert atmosphere, and obtaining a modified porous carbon precursor after washing and drying; (S3) heat-treating the modified porous carbon precursor under an inert atmosphere to obtain modified porous carbon based on photocatalytic halogen atom transfer. The present invention uses C1-C5 halogenated hydrocarbons to introduce carbon radicals into the pores of the porous carbon through a halogen atom transfer (XAT) reaction, and then forms amorphous carbon through heat treatment to fill the ultramicropores, thereby solving the problems of low effective silicon deposition rate caused by the inability to utilize ultramicropores and irreversible lithium insertion, thereby improving the electrochemical performance of the silicon-carbon negative electrode.

Description

Technical Field

[0001] The present invention belongs to the technical field of porous carbon, and in particular relates to a preparation method of modified porous carbon based on photocatalytic halogen atom transfer and a silicon-carbon negative electrode. Background Art

[0002] In recent years, with the continuous development of lithium-ion batteries, silicon-carbon composites (SiC composites) have gradually attracted widespread attention as a new type of anode material. Silicon materials have great application potential in lithium-ion batteries due to their high theoretical specific capacity (approximately 3579 mAh / g). However, silicon undergoes significant volume expansion (up to approximately 300%) during charge and discharge, leading to structural damage and capacity degradation in SiC composites, thus limiting their practical application in batteries. To address this issue, researchers have adopted various approaches, among which vapor deposition (VPD) has emerged as an effective solution for preparing SiC composites. In this preparation method, silane gas (such as monosilane SiH₄) is introduced into a reaction chamber of a porous carbon material. Under high temperature conditions (typically between 300°C and 600°C), the Si-H bonds of the silane molecules break, generating highly reactive silicon atoms and hydrogen. As the silicon atoms migrate and adsorb, these reactive silicon atoms deposit within the pores of the porous carbon material, forming amorphous nanosilicon.

[0003] However, the structure of the porous carbon skeleton has a significant impact on the performance of silicon-carbon composites made from vapor-deposited silicon. In particular, when ultramicropores (pore size less than 0.7 nm) in the porous carbon account for a large proportion, the following problems will arise: (1) Silane cannot be decomposed and deposited: Because the pore size of the ultramicropores is too small, silane molecules cannot enter and decompose and deposit inside them, resulting in the ultramicropores being unusable and reducing the effective deposition rate of silicon. (2) Irreversible lithium insertion: During the lithium insertion process, ultramicropores will capture lithium ions and form irreversible lithium insertion, resulting in battery capacity decay and decreased cycle performance.

[0004] Therefore, reducing the number of ultramicropores in porous carbon materials is the key to improving the performance of vapor-deposited silicon-carbon negative electrodes, while traditional methods (such as chemical activation and physical activation) are difficult to accurately control the proportion and pore volume of ultramicropores. Summary of the Invention

[0005] In view of the fact that the ultramicropores of porous carbon in the prior art cannot effectively deposit silicon and there is a problem of irreversible lithium insertion, and traditional methods are difficult to accurately control the proportion of ultramicropores, the present invention provides a preparation method of modified porous carbon based on photocatalytic halogen atom transfer, which utilizes halogen atom transfer (XAT) reaction to introduce carbon free radicals into the ultramicropores of porous carbon, and then forms amorphous carbon through heat treatment to fill the ultramicropores, thereby solving the problem that ultramicropores cannot effectively deposit silicon and irreversible lithium insertion, thereby improving the electrochemical performance of silicon-carbon negative electrode materials.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] A method for preparing modified porous carbon based on photocatalytic halogen atom transfer comprises the following steps:

[0008] (S1) impregnating the porous carbon into a C1-C5 halogenated hydrocarbon solution containing a photosensitizer, filtering, washing, and drying after the impregnation to obtain the halogenated hydrocarbon-loaded porous carbon;

[0009] (S2) subjecting the halogenated hydrocarbon-loaded porous carbon to a photocatalytic reaction under an inert atmosphere, and obtaining a modified porous carbon precursor after washing and drying;

[0010] (S3) The modified porous carbon precursor is heat-treated under an inert atmosphere to obtain modified porous carbon based on photocatalytic halogen atom transfer.

[0011] Furthermore, the particle size D50 of the porous carbon in step (S1) is 1~10μm, the specific surface area is 1000~3000m² / g, preferably 2000~3000m² / g, the total pore volume is 0.5~2.0cm³ / g, and the ultramicropores account for 15%~30%; preferably, the porous carbon is dried before impregnation, and the drying is vacuum drying at 130~160℃ for 5~8h.

[0012] Furthermore, the photosensitizer is at least one of tris(2-phenylpyridine)iridium (Ir(ppy)3), terpyridine ruthenium chloride (Ru(bpy)3Cl2), and 2,4,5,6-tetrakis(9-carbazolyl)-isophthalonitrile (4CzlPN), and its usage is 0.5~1.5wt% of the porous carbon.

[0013] Furthermore, in step (S1), the C1-C5 halogenated hydrocarbon is at least one of dichloromethane, chloroform, ethyl chloride, dichloroethane, propyl chloride, isopropyl chloride, n-butyl chloride, isobutyl chloride, n-pentane chloride, ethyl bromide, propyl bromide, isopropyl bromide, n-butyl bromide, ethyl iodide, and propyl iodide, preferably at least one of dichloromethane, ethyl chloride, propyl chloride, and ethyl bromide. The halogenated hydrocarbon in the present invention has a small molecular size that matches the kinetic diameter of the ultramicropores, allowing the halogenated hydrocarbon to penetrate into the pores during the impregnation process. Preferred halogenated hydrocarbons have smaller molecular sizes and better effects. Furthermore, the bond energy between the halogen and carbon is low, making them easily excited and broken to form carbon free radicals during the subsequent photocatalytic reaction.

[0014] Furthermore, in step (S1), the concentration of the C1-C5 halogenated hydrocarbon solution is 0.05-0.5 mol / L, and the solvent is at least one of ethanol, acetone, and tetrahydrofuran; the amount of the porous carbon and the C1-C5 halogenated hydrocarbon solution is 1 g: (10-20) mL; and the immersion conditions are: immersion at 20-30° C. for 12-48 hours, preferably, ultrasonic treatment is also applied during the immersion, with an ultrasonic frequency of 30-40 kHz, a power of 50-100 W, and a time of 10-30 minutes.

[0015] Furthermore, the washing in step (S1) is ethanol washing for 3 to 5 times to remove the halogenated hydrocarbons physically adsorbed on the surface of the porous carbon; and the drying is vacuum drying at 60 to 80° C. for 6 to 12 hours.

[0016] Furthermore, the photocatalytic reaction conditions in step (S2) are: irradiation with light of a wavelength of 200-800 nm and an intensity of 50-150 mW / cm² at 20-50°C for 1-5 hours; the wavelength is preferably 350-500 nm. Under light excitation, the C-X bonds of the halogenated hydrocarbon (RX) break to generate carbon radicals (R·) and halogen radicals (X·). The carbon radicals are fixed to the pore wall surface through physical adsorption or chemical bonding, forming a uniform coating.

[0017] Furthermore, in step (S2), the inert atmosphere is nitrogen and / or argon; the washing is performed by soaking in acetone or ethanol for 1 to 3 hours and then washing with water until neutrality is achieved, thereby removing unreacted halogen byproducts; and the drying is performed by vacuum drying at 80 to 120° C. for 4 to 12 hours.

[0018] Furthermore, the heat treatment conditions in step (S3) are: 400-600°C for 1-5 hours; the inert atmosphere is nitrogen and / or argon. During the heat treatment, carbon radicals are dehydrogenated and carbonized, forming amorphous carbon that fills the ultramicropores. The heat treatment temperature of 400-600°C is below the graphitization temperature of the porous carbon framework, effectively preventing damage to the main structure.

[0019] The principle diagram of the present invention is as follows Figure 1 shown.

[0020] In a second aspect, the present invention provides a modified porous carbon based on photocatalytic halogen atom transfer, which is prepared by the aforementioned preparation method.

[0021] In a third aspect, the present invention further provides a silicon-carbon negative electrode, which is prepared by vapor-depositing silicon and then carbon-coating the modified porous carbon obtained by the aforementioned preparation method. The processes of vapor-depositing silicon and carbon-coating are well known to those skilled in the art. For example, an organosilicon silicon source gas is used for vapor-depositing silicon, and the organosilicon source gas is selected from at least one of silane, dichlorosilane, trichlorosilane, silicon tetrachloride, silicon tetrafluoride, and disilane; and a carbon source gas is used for carbon coating, and the carbon source gas is selected from at least one of C1-4 alkanes, C2-4 alkenes, and C2-4 alkynes.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] 1. The halogen atom transfer (XAT) reaction is a widely used method for generating carbon radicals in photochemistry and photocatalysis. It involves transferring halogen atoms (such as Cl, Br, and I) from an organic halide (RX) to a radical initiator or catalyst via photoexcitation or photocatalysis, simultaneously generating a carbon-centered radical (R·). This invention uses C1-C5 halogenated hydrocarbons to introduce carbon radicals into the pores of porous carbon via the XAT reaction. The molecular size of the selected C1-C5 halogenated hydrocarbons matches the kinetic diameter of the ultramicropores. The carbon radicals formed after impregnation and photocatalytic reaction effectively adhere to the pore walls of the ultramicropores. Heat treatment then forms amorphous carbon that fills the ultramicropores. This solves the problems of low silicon deposition efficiency and irreversible lithium insertion caused by unused ultramicropores, thereby improving the electrochemical performance of silicon-carbon anodes, particularly the first coulombic efficiency and sequential performance.

[0024] 2. Compared to traditional chemical or physical activation methods, this invention provides a new technology for precisely controlling the number and volume of ultramicropores. This technology generates carbon free radicals under mild conditions and fills the ultramicropores through heat treatment, avoiding the unevenness and controllability issues of traditional methods. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a schematic diagram of the principle of the present invention;

[0026] Figure 2 The pore size distribution diagram of the porous carbon in the embodiment and the pore size distribution diagram of the modified porous carbon prepared in embodiment 1;

[0027] Figure 3 This is the first charge and discharge curve of the lithium battery of Application Example 1. DETAILED DESCRIPTION

[0028] In order to make the purpose, technical solutions and advantages of the present invention clearer, the technical solutions of the present invention will be described in detail below. The following examples are convenient for better understanding of the present invention, but are not intended to limit the present invention. In the following examples, unless otherwise specified, all parts are by weight.

[0029] The porous carbon was selected from Shandong Shengquan New Energy Technology Co., Ltd. with a particle size D50 of 2.0 μm, a specific surface area of ​​2056 m² / g, a total pore volume of 0.87 cm³ / g, a proportion of ultramicropores of 28.2%, and an average pore diameter of 1.7 nm.

[0030] Example 1

[0031] (S1) 0.5 g of a photosensitizer, Ru(bpy)3Cl2, was dissolved in 1000 mL of an ethanol solution of bromoethane (C2H5Br) (concentration 0.1 mol / L). 50 g of porous carbon, which had been dried (dried in a vacuum oven at 150°C for 6 h), was then added to the ethanol solution of bromoethane to form a mixture. The mixture was immersed in a constant temperature oscillator (25°C, 120 rpm) for 24 h. After the immersion, the mixture was filtered, washed with ethanol three times, and vacuum dried at 70°C for 6 h to obtain bromoethane-loaded porous carbon.

[0032] (S2) The bromoethane-loaded porous carbon was spread flat in a quartz reactor, nitrogen was introduced at a flow rate of 50 mL / min, and a 365 nm UV LED light source (intensity of 100 mW / cm²) was used to vertically irradiate the surface of the material for 2 hours at 30°C for a photocatalytic reaction (reaction process is as follows); the porous carbon after the reaction was soaked in acetone for 1 hour, washed with pure water until neutral, and vacuum dried at 80°C for 6 hours to obtain a modified porous carbon precursor;

[0033] (Carbon radicals adsorbed on the pore wall)

[0034] (S3) The modified porous carbon precursor was transferred to a tube furnace, heated to 550°C at a rate of 5°C / min in a nitrogen atmosphere (flow rate of 200 mL / min), kept at this temperature for 3 hours, and cooled to room temperature to obtain modified porous carbon based on photocatalytic halogen atom transfer.

[0035] Example 2

[0036] The rest is the same as in Example 1, except that chloropropane (C3H7Cl) is used instead of bromoethane in step (S1).

[0037] Example 3

[0038] The rest is the same as in Example 1, except that iodine propane (C3H7I) is used instead of bromoethane in step (S1).

[0039] Example 4

[0040] The rest is the same as in Example 1, except that chloropentane (C5H 11 Cl) to replace ethyl bromide, the concentration of chloropentane solution is 0.3 mol / L.

[0041] Example 5

[0042] The rest is the same as embodiment 1, except that, in step (S2): a visible light LED light source with a wavelength of 450 nm is used instead of an ultraviolet LED light source with a wavelength of 365 nm, and the irradiation time is 4 hours.

[0043] Comparative Example 1

[0044] The rest is the same as in Example 1, except that step (S2) is omitted, and in step (S3), porous carbon loaded with halogenated hydrocarbons is used instead of the modified porous carbon precursor.

[0045] Comparative Example 2

[0046] The rest is the same as in Example 1, except that bromodecane (C 10 H 21 Br) instead of ethyl bromide.

[0047] Application Example 1

[0048] 30 g of modified porous carbon obtained in Example 1 was placed in a tubular rotary kiln with a rotary kiln speed of 50 r / min. Nitrogen was introduced at a flow rate of 5 L / min. After heating to 460°C at a heating rate of 5°C / min under a nitrogen environment, the nitrogen flow rate was maintained and monosilane (SiH4) gas was introduced at a flow rate of 0.2 L / min for chemical vapor deposition for 1 hour. Silane was cracked to form nano-silicon deposited in the pores of the porous carbon. After the deposition was completed, the monosilane gas was stopped, and helium was continuously introduced at a flow rate of 5 L / min to remove excess monosilane gas. Acetylene gas was then introduced at a flow rate of 0.2 L / min and maintained at 500°C for vapor deposition for 1 hour. After the acetylene gas was cracked, a carbon coating layer was formed to obtain a silicon-carbon negative electrode material.

[0049] Application Example 2-5

[0050] Other conditions are the same as those in Application Example 1, except that the modified porous carbon is prepared according to Example 2-5.

[0051] Comparative Application Examples 1-2

[0052] Other conditions are the same as those in Application Example 1, except that the modified porous carbon is prepared according to Comparative Example 1-2.

[0053] Testing and Analysis

[0054] 1) Performance test of modified porous carbon

[0055] Particle size distribution and specific surface area test: According to the gas adsorption BET method of GB / T 19587-2017, the modified porous carbon prepared in the embodiment and the comparative example was subjected to a low-temperature nitrogen adsorption experiment using a Tristar II3020 fully automatic specific surface and pore size analyzer produced by Micromeritics Instrument Corporation of the United States to measure its specific surface area, pore size distribution, and pore volume. The test results are shown in Table 1. The pore size distribution diagram of the porous carbon in the embodiment and the pore size distribution diagram of the modified porous carbon prepared in Example 1 are shown in Table 1. Figure 2 shown.

[0056] Table 1 Pore size distribution, specific surface area and pore volume of modified porous carbon

[0057] .

[0058] As can be seen from Table 1, the proportion of ultramicropores in the modified porous carbon prepared by the preparation method of the present invention is significantly reduced, and the specific surface area and pore volume are slightly reduced accordingly; Figure 2 As can be seen from the pore size distribution diagram in , the significant reduction in ultramicropores has led to a corresponding increase in the proportion of micropores. The reduction in pore volume and specific area is mainly due to the significant reduction in the proportion of ultramicropores, which verifies the effect of ultramicropores being carbonized and filled by carbon free radicals. In Comparative Example 1, no photocatalytic halogen transfer reaction was carried out, and the reduction in the proportion of ultramicropores in the modified porous carbon obtained was limited. In Comparative Example 2, a halogenated hydrocarbon with a larger molecular ruler was used, and the reduction in the proportion of ultramicropores in the modified porous carbon obtained was also limited. The possible reason is that the halogenated hydrocarbon with a larger molecular ruler does not match the kinetic diameter of the ultramicropores and cannot effectively penetrate into the ultramicropores, and then the carbon free radicals formed after the photocatalytic reaction cannot effectively adhere to the pore wall.

[0059] 2) Performance testing of silicon-carbon anode materials prepared in application examples and comparative application examples

[0060] The silicon-carbon anode materials prepared in the above application examples and comparative application examples were used in the negative electrode of lithium-ion batteries, assembled into lithium batteries, and their electrochemical performance was tested. Specifically, the silicon-carbon composite anode material was mixed with polyacrylic acid (PAA) and conductive carbon black (Super P) in a mass ratio of 8:1:1, ground into a slurry using deionized water as a solvent, and then evenly coated on copper foil with a wet film thickness of 200 μm. The material was then vacuum-dried at 80°C for 12 hours. The dried material was punched into 12 mm electrode sheets. In an argon glove box, a metal lithium sheet was used as the counter electrode, Celgard 2600 was used as the separator, and a 1 M LiPF6 solution was selected as the electrolyte. The solvent was prepared in a volume ratio of ethylene carbonate (EC) to diethyl carbonate (DEC) = 1:1. 25% fluoroethylene carbonate (FEC) was added as an additive. Finally, CR2032 button cells were assembled. The charge and discharge test was carried out using the Blue Power CT2001A test system in the voltage range of 0.01~1.5 V and the current density of 100 mA / g. The test results are shown in Table 2. The first charge and discharge curve of the lithium battery in Application Example 1 is shown in Table 2. Figure 3 shown.

[0061] Table 2 Performance test

[0062] .

[0063] As can be seen from Table 2, when the silicon-carbon negative electrode material prepared by silicon deposition and carbon coating of the modified porous carbon based on photocatalytic halogen atom transfer prepared in the embodiment of the present invention is used as the negative electrode of a lithium battery, the first coulombic efficiency is significantly improved, and can reach more than 86% at a low voltage (0.8V), and the capacity retention rate after 100 cycles is as high as more than 95%.

[0064] The above detailed description is a specific description of one feasible embodiment of the present invention. This embodiment is not intended to limit the patent scope of the present invention. Any equivalent implementation or modification that does not depart from the present invention should be included in the scope of the technical solution of the present invention.

Claims

1. A method for preparing modified porous carbon based on photocatalytic halogen atom transfer, characterized in that: The following steps are involved: (S1) impregnating the porous carbon into a C1-C5 halogenated hydrocarbon solution containing a photosensitizer, filtering, washing, and drying after the impregnation to obtain the halogenated hydrocarbon-loaded porous carbon; the photosensitizer is at least one of tris(2-phenylpyridine)iridium, terpyridine ruthenium chloride, and 2,4,5,6-tetrakis(9-carbazolyl)-isophthalonitrile; (S2) subjecting the halogenated hydrocarbon-loaded porous carbon to a photocatalytic reaction under an inert atmosphere, and obtaining a modified porous carbon precursor after washing and drying; The conditions for the photocatalytic reaction are: irradiation at 20-50°C for 1-5 hours with a light source having a wavelength of 200-800 nm and a light intensity of 50-150 mW / cm²; (S3) heat-treating the modified porous carbon precursor under an inert atmosphere to obtain modified porous carbon based on photocatalytic halogen atom transfer; the heat treatment conditions are: keeping the temperature at 400-600° C. for 1-5 hours.

2. The preparation method according to claim 1, characterized in that The porous carbon in step (S1) has a particle size D50 of 1 to 10 μm, a specific surface area of ​​1000 to 3000 m² / g, a total pore volume of 0.5 to 2.0 cm³ / g, and a proportion of ultramicropores of 15% to 30%.

3. The preparation method according to claim 1, characterized in that The amount of the photosensitizer used in step (S1) is 0.5-1.5 wt % of the porous carbon.

4. The preparation method according to claim 1, characterized in that In step (S1), the C1-C5 halogenated hydrocarbon is at least one of dichloromethane, chloroform, ethyl chloride, dichloroethane, propyl chloride, isopropyl chloride, n-butyl chloride, isobutyl chloride, n-pentane chloride, ethyl bromide, propyl bromide, isopropyl bromide, n-butyl bromide, ethyl iodide, and propyl iodide.

5. The preparation method according to claim 4, characterized in that The C1-C5 halogenated hydrocarbon in step (S1) is at least one of dichloromethane, ethyl chloride, propyl chloride, and ethyl bromide.

6. The preparation method according to claim 1, characterized in that The concentration of the C1-C5 halogenated hydrocarbon solution in step (S1) is 0.05-0.5 mol / L, and the solvent is at least one of ethanol, acetone, and tetrahydrofuran; the amount of the porous carbon and the C1-C5 halogenated hydrocarbon solution is 1 g: (10-20) mL; the impregnation conditions are: 20-30° C., 12-48 h; and / or The washing is ethanol washing for 3 to 5 times; and the drying is vacuum drying at 60 to 80° C. for 6 to 12 hours.

7. The preparation method according to claim 1, characterized in that In step (S2), the inert atmosphere is nitrogen and / or argon; the washing is performed by soaking in acetone or ethanol for 1 to 3 hours and then washing with water until neutral; and the drying is performed by vacuum drying at 80 to 120° C. for 4 to 12 hours.

8. The preparation method according to claim 1, characterized in that The inert atmosphere in step (S3) is nitrogen and / or argon.

9. A silicon-carbon negative electrode, characterized in that The modified porous carbon is prepared by the preparation method according to any one of claims 1 to 8, and is prepared by vapor deposition of silicon and carbon coating.

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