A method for preparing a spherical porous carbon and silicon-carbon composite material

Abstract

This invention discloses a method for preparing spherical porous carbon and silicon-carbon composite materials. The method involves uniformly mixing a carbohydrate compound, an inorganic pore-forming agent, a fibrous pore-forming agent, and a crosslinking agent solution, followed by spray drying, carbonization, and activation pore formation to obtain secondary spherical porous carbon particles. The resulting material is then deposited with nano-silicon via silane pyrolysis to obtain the silicon-carbon composite material. The material obtained by this invention utilizes the fibrous and granular channels within the porous carbon to facilitate nano-silicon deposition and reduce expansion. Simultaneously, the secondary particle structure shortens the lithium-ion insertion / extraction path during charging and discharging, improving rate performance.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of material preparation, and particularly relates to a preparation method of a spherical porous carbon and a silicon-carbon composite material. BACKGROUND

[0002] As a key material for preparing a silicon-carbon material, the performance of the porous carbon determines the expansion, cycle and power performance of the silicon-carbon material. The porous carbon is divided into a granular structure, a spherical structure and a perfect spherical structure according to its material morphology. The granular porous carbon has low cost and high power, but has low compaction density and low compression resistance. The perfect spherical porous carbon has high compaction density, but has large particle size, resulting in poor adhesion and poor fast charging performance. The spherical porous carbon has a spherical structure, and under the condition of high compaction density, the contact between the materials is good and the impedance is low, thereby improving the rate performance of the material, and the compression resistance of the material is maintained, and the preparation is simple and the yield is high.

[0003] At present, there are few silicon-carbon materials prepared by using the spherical porous carbon on the market. For example, patent application No. CN202310250745.2 discloses a spherical silicon-carbon negative electrode material and a preparation method and application thereof. The preparation method comprises the following steps: after a mixed solution of a soluble ammonium salt and a carbon source is sprayed and granulated, the spherical porous carbon is obtained by sequentially performing sintering treatment and pore forming treatment, pyrolysis treatment with a silane compound and carbon coating treatment, thereby obtaining the spherical silicon-carbon negative electrode material. The carbon source is starch, and the starch includes one of millet starch and rice starch. Although the silicon-carbon material prepared by the method has a spherical morphology, the connectivity of the pores of the porous carbon is poor, the efficiency of depositing nano-silicon is low, the deposition is uneven, and the impedance is high. SUMMARY

[0004] In order to improve the power performance and compaction density of the porous carbon and reduce the cost, the present application uses a sugar compound, an inorganic pore forming agent, a fibrous pore forming agent and a crosslinking agent to prepare the spherical porous carbon with good pore connectivity, thereby improving the power performance and reducing the expansion, and the spherical porous carbon is applied to the silicon-carbon material to improve the rate charging and discharging performance and the cycle performance.

[0005] A preparation method of a spherical porous carbon composite material, characterized in that the method comprises the following steps:

[0006] A multi-hydroxyl sugar compound, an inorganic pore forming agent, a fibrous pore forming agent, a crosslinking agent and an ionic liquid are weighed according to a mass ratio of 100:1-5:1-5:1-5:100-500, mixed uniformly, spray dried, pre-carbonized at 500-800 DEG C for 1-6 hours, then heated to 900-1100 DEG C, and activated and pore-formed by introducing carbon dioxide gas at a flow rate of 100-500 SCCM for 1-6 hours, thereby obtaining the spherical porous carbon.

[0007] The polyhydroxy sugar compound is one of fructose, galactose, sucrose, maltose, and lactose.

[0008] The inorganic pore-forming agent is one of ammonium bicarbonate, ammonium carbonate, and ammonium chloride; the fibrous pore-forming agent is one of polyimide fiber, poly-p-phenylene isoxazole fiber, poly-p-phenylene benzobisoxazole fiber, poly-p-phenylene pyridine diimidazole fiber, and polyvinyl alcohol fiber.

[0009] The cross-linking agent is one of 2-dimethylimidazole, 2-ethylimidazole, 2-ethyl-4-methylimidazole, and isopropylimidazole; the ionic liquid is one of 1-butyl-3-methylimidazole dihydrogen phosphate, 1-butyl-3-methylimidazole tetrafluoroborate, 1-butyl-3-methylimidazole dicyanamide, 1-butyl-3-methylimidazole bistrifluoromethane phthalimide, 1-octyl-3-methylimidazole dihydrogen phosphate, 1-octyl-3-methylimidazole tetrafluoroborate, 1-octyl-3-methylimidazole dicyanamide, 1-allyl-3-butylimidazole dicyanamide, 1-cyanopropyl-3-methylimidazole dihydrogen phosphate, 1-cyanopropyl-3-methylimidazole tetrafluoroborate, or 1-cyanopropyl-3-methylimidazole bistrifluoromethane phthalimide.

[0010] A preparation method of a silicon-carbon composite material, characterized in that the method comprises the following steps:

[0011] The spheroidal porous carbon is transferred into a fluidized bed, air in the pipe is discharged by introducing inert gas, then heated to 450-550 DEG C, and chlorosilane mixed gas is introduced at a flow rate of 100-500 SCCM for 30-300 min, then the introduction of chlorosilane mixed gas is stopped, the temperature is raised to 650-750 DEG C, and heteroatom gas is introduced at a flow rate of 10-50 SCCM for 30-300 min, to obtain a silicon-carbon composite material.

[0012] The chlorosilane mixed gas is one of dichlorodihydrogen silicon, trichlorohydrogen silicon, or silicon tetrachloride mixed with cross-linking gas, and the volume ratio is 10:1-3; the cross-linking gas is one of vaporized dibenzoyl peroxide, dicumyl peroxide, or dicarbonate peroxide.

[0013] The heteroatom gas is one of borane, dihydrogen phosphide, or hydrogen sulfide.

[0014] Beneficial effects

[0015] 1. The inorganic pore-forming agent and the fibrous pore-forming agent are mixed with the porous carbon precursor (saccharide compound), carbonized and activated to generate the porous carbon with the round-hole structure and the fibrous structure, improve the connectivity of the holes, and improve the deposition efficiency and uniformity of the nanosilicon; at the same time, the saccharide compound is heated and polymerized to generate the small-particle-size spherical structure and improve the compaction density of the material.

[0016] 2. The porous carbon precursor is crosslinked by using the crosslinking agent, the crosslinking agent is crosslinked and combined with the carbon radicals of the saccharide compound through the oxygen radicals of the crosslinking agent to form the crosslinking structure of -C-O-C, form the secondary particle structure, and the secondary particle structure has the advantage of isotropy, so that the lithium ions can be embedded and extracted from multiple directions in the charging and discharging process, and the rate performance and kinetic performance are improved.

[0017] 3. The chlorosilane mixed gas is introduced, the chlorosilane is heated and decomposed into Si, Cl - , H + , the crosslinking agent gas containing O radicals is introduced at the same time, the oxygen radicals have strong electronegativity, are adsorbed on the surface of carbon, and facilitate the deposition of nanosilicon to improve the silicon deposition efficiency, at the same time, the element with higher electronegativity among the two elements (Cl - , O 2- ) will take electrons from the element with lower electronegativity, form cations and anions, and combine through electrostatic action to realize the Cl-doped porous carbon and improve the electronic conductivity. The chlorosilane is cracked to generate nanosilicon and deposit in the internal pores of the porous carbon to improve the specific capacity, and the chlorine is doped in the internal pores of the porous carbon to improve the electronic conductivity of the material, and the heteroatoms are coated and doped on the outside of the silicon-carbon material to improve the electronic conductivity of the material, improve the rate performance, and reduce the contact between the core nanosilicon and the electrolyte to avoid the reaction between the core nanosilicon and the electrolyte to generate gas and improve the first efficiency. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 SEM image of the silicon-carbon composite material prepared in Example 1. DETAILED DESCRIPTION

[0019] Example 1

[0020] A preparation method of a spherical silicon-carbon composite material, comprising the following steps:

[0021] Step S1:

[0022] 100g fructose, 3g ammonium bicarbonate, 3g polyimide fiber and 3g 2-dimethylimidazole were added to 300g 1-butyl-3-methylimidazole sodium dihydrogen phosphate and mixed evenly. After spray drying, the resulting material was carbonized at 650℃ for 3h, and then the temperature was raised to 1000℃. Carbon dioxide was introduced at a flow rate of 300SCCM to activate and create pores for 3h to obtain spherical porous carbon.

[0023] Step S2:

[0024] The spherical porous carbon was transferred to a fluidized bed, and nitrogen inert gas was introduced to purge the air from the tube. Then, it was heated to 500°C, and a dichlorosilane mixed gas with a volume ratio of dichlorosilane:benzoyl peroxide = 10:2 was introduced at a flow rate of 300 SCCM for 150 min. After that, the introduction of the dichlorosilane mixed gas was stopped, the temperature was raised to 700°C, and diborane gas was introduced at a flow rate of 30 SCCM for 150 min to obtain a silicon-carbon composite material.

[0025] Example 2

[0026] A method for preparing a spherical silicon-carbon composite material includes the following steps:

[0027] Step S1:

[0028] 100g of galactose, 1g of ammonium carbonate, 1g of poly(p-benzimidazole) fiber and 1g of 2-ethylimidazole were added to 100g of 1-butyl-3-methylimidazole sodium tetrafluoroborate and mixed evenly. After spray drying, the mixture was carbonized at 500℃ for 6h. Then, the temperature was raised to 900℃ and carbon dioxide gas was introduced at a flow rate of 100SCCM to activate and form pores for 6h, resulting in secondary particulate spherical porous carbon.

[0029] Step S2:

[0030] Secondary particulate spherical porous carbon was transferred to a fluidized bed, and nitrogen inert gas was introduced to purge the air from the tube. The mixture was then heated to 450°C, and a trichlorosilane mixture with a volume ratio of 10:1 (trichlorosilane:diisopropylbenzene peroxide) was introduced at a flow rate of 100 SCCM for 300 min. After that, the introduction of the diisopropylbenzene peroxide mixture was stopped, the temperature was raised to 650°C, and borane gas was introduced at a flow rate of 10 SCCM for 300 min to obtain a silicon-carbon composite material.

[0031] Example 3

[0032] A method for preparing a spherical silicon-carbon composite material includes the following steps:

[0033] Step S1:

[0034] 100g sucrose, 5g ammonium chloride, 5g poly(p-phenylenebenzobisoxazole) fiber and 5g 2-ethyl-4-methylimidazolium were added to 500g sodium 1-butyl-3-methylimidazolium dinitrile and mixed evenly. After spray drying, the mixture was carbonized at 800℃ for 1h. Then, the temperature was raised to 1100℃ and carbon dioxide gas was introduced at a flow rate of 500 SCCM to activate and form pores for 1h, thus obtaining secondary particulate spherical porous carbon.

[0035] Step S2:

[0036] Secondary particulate spherical porous carbon was transferred to a fluidized bed, and nitrogen inert gas was introduced to purge the air from the tube. The mixture was then heated to 550°C, and a silicon tetrachloride mixture with a volume ratio of silicon tetrachloride:dicarbonate peroxide = 10:3 was introduced at a flow rate of 500 SCCM for 30 min. After that, the introduction of the silicon tetrachloride mixture was stopped, the temperature was raised to 750°C, and phosphine gas was introduced at a flow rate of 50 SCCM for 30 min to obtain a silicon-carbon composite material.

[0037] Comparative Example 1:

[0038] Unlike Example 1, ammonium bicarbonate is not added in step S1, but everything else is the same as in Example 1.

[0039] Comparative Example 2:

[0040] Unlike Example 1, in step S2, benzoyl peroxide crosslinking gas is not added to the dichlorosilane mixed gas; otherwise, it is the same as in Example 1.

[0041] Comparative Example 3:

[0042] Unlike Example 1, no diborane heteroatom gas is introduced in step S3; otherwise, it is the same as Example 1.

[0043] Comparative Example 4:

[0044] Unlike Example 1, polyimide fibers are not added in step S1, but otherwise the process is the same as in Example 1.

[0045] 1. SEM testing:

[0046] Figure 1 The image shows a SEM image of the silicon-carbon composite material prepared in Example 1. As can be seen from the image, the material exhibits a spherical structure with a particle size between 3 and 5 μm and a uniform size distribution.

[0047] 2. Physicochemical properties of porous carbon and its coin cell testing:

[0048] 2.1 Physicochemical property testing:

[0049] The pore volume and pore size of the porous carbons obtained in Examples 1-3 and Comparative Examples 1 and 4 were tested according to the national standard GB / T-38949-2020 "Determination of Pore Size of Porous Membranes - Standard Particle Method". The specific surface area was tested according to the national standard GB / T38823-2020 "Silicon Carbon". The powder conductivity of each porous carbon material was tested using a four-probe tester. The diffusion coefficient of the material was tested by GITT. The test results are shown in Table 1.

[0050] 2.2 Button Cell Battery Performance Test:

[0051] The porous carbon corresponding to Examples 1-3 and Comparative Examples 1 and 4 was used as the negative electrode material for lithium-ion batteries to prepare coin cells according to the following method:

[0052] A binder, conductive agent, and solvent are added to the corresponding porous carbon, stirred to form a slurry, coated onto copper foil, and dried and rolled to obtain a negative electrode sheet. The binder used is LA136D, the conductive agent is SP (conductive carbon black), and the solvent is NMP. The ratio of porous carbon:SP:LA136D:NMP is 70g:15g:15g:300mL. The electrolyte is a solution with LiPF6 as the electrolyte and a concentration of 1mol / L. The solvent is a mixture of EC and DEC with a volume ratio of 1:1. The lithium metal sheet is used as the counter electrode, and the separator is a polypropylene (PP) membrane.

[0053] Each coin cell was assembled in an argon-filled glove box, and then the following performance tests were performed: Electrochemical performance test: Specifically, the electrochemical performance was performed on the Wuhan Landian CT2001A battery tester, with a charge / discharge voltage range of 0.005V to 1.5V and a charge / discharge rate of 0.1C. The discharge specific capacity and initial efficiency of the corresponding coin cell were tested, and the room temperature charge DCR (50% SOC) of the corresponding coin cell was also tested.

[0054] The test results are shown in Table 1.

[0055]

[0056] As can be seen from Table 1, Examples 1-3 have low powder resistivity and high first-pass efficiency. This is because the doping of ammonium bicarbonate and polyimide fibers in the examples creates pores, which improves the diffusion coefficient of the material, reduces material polarization, improves the first-pass efficiency of porous carbon, and reduces DCR.

[0057] 3. Physicochemical properties of silicon-carbon materials and their coin cell testing:

[0058] The tap density, specific surface area, and specific capacity of the silicon-carbon composite materials obtained in Examples 1-3 and Comparative Examples 1-4 were tested according to the methods in the national standard GB / T 38823-2020 "Silicon-Carbon". The powder resistivity was tested using a four-probe test. The test results are shown in Table 1 below.

[0059] 3.1 Button Cell Battery Test:

[0060] The silicon-carbon composite materials obtained in Examples 1-3 and Comparative Examples 1-4 were used as active materials for the negative electrode sheets of the batteries to prepare and assemble seven coin cells, which were labeled as A1, A2, A3, B1, B2, B3, and B4 in sequence.

[0061] The specific preparation process of each coin cell is as follows: Preparation of the negative electrode sheet: Add binder, conductive agent and solvent to the silicon-carbon composite materials (as the active material of the negative electrode sheet) corresponding to Examples 1-3 and Comparative Examples 1-4 respectively, stir and slurry, coat on copper foil, and obtain the negative electrode sheet of each battery after drying and rolling; wherein, the binder is LA136D binder, the conductive agent is SP (conductive carbon black), and the solvent is double-distilled water, and the ratio is: silicon-carbon composite material: SP: LA136D: double-distilled water = 95g: 1g: 4g: 220mL;

[0062] Coin cell fabrication: The electrolyte used was a LiPF6 solution with a concentration of 1.1 mol / L. The solvent used was a 1:1 weight ratio mixture of ethylene carbonate (EC) and diethyl carbonate (DMC). A lithium metal sheet was used as the counter electrode, and polyethylene (PE) was used as the separator. The simulated battery was assembled in an argon-filled glove box. Electrochemical performance was tested using a Wuhan Landian CT2001A battery tester under the following conditions: charge / discharge voltage range of 0.005V to 1.5V, and charge / discharge rate of 0.1C. The charge DCR (0.1C, 50% SOC) and cycle performance (test conditions: 0.2C / 0.2C, 100 cycles) of the coin cell were also tested, as well as the full-charge expansion of the negative electrode. The test results are shown in Table 2 below.

[0063]

[0064] As can be seen from Table 2 above, the silicon-carbon composite materials provided in Examples 1-3 of this application have high specific surface area, low DCR, high initial discharge specific capacity, and high initial efficiency. The reason for this is that the materials in the examples have a spherical structure and doped with fibrous materials to reduce expansion, and doped with heteroatoms in the outer layer to reduce powder resistivity, reduce polarization, and improve the initial efficiency of the material.

[0065] 3.2. Soft-pack battery test:

[0066] The silicon-carbon composite materials obtained in Examples 1-3 and Comparative Examples 1-4 were each doped with 90% artificial graphite as anode materials (i.e., anode sheets), with ternary material LiNi 0.8 Co 0.1 Mn 0.1 O2 was used as the positive electrode material, electrolyte, and separator to assemble a 5Ah soft-pack battery. The separator of the soft-pack battery was Celegard 2400, and the electrolyte was a LiPF6 solution. The solvent of the LiPF6 solution was a mixed solution of EC and DEC with a volume ratio of 1:1, and the concentration of LiPF6 was 1.1 mol / L. The soft-pack batteries made of silicon-carbon composite materials corresponding to Examples 1-3 and Comparative Examples 1-4 were labeled as C1, C2, C3, D1, D2, D3, D4 and their corresponding negative electrode sheets, respectively. The liquid absorption capacity and electrode resistivity of each negative electrode sheet were tested, and the test results are shown in Table 3 below.

[0067] The liquid absorption capacity test process is as follows: a 1mL burette is used to draw 1mL of electrolyte, which is then dropped onto the surface of the negative electrode. The time is recorded until the electrolyte is completely absorbed, and the resistivity of the electrode is measured using a film resistance tester.

[0068]

[0069] As can be seen from Table 3 above, the liquid absorption capacity and resistivity of the negative electrode sheets made using the silicon-carbon composite materials provided in Examples 1-3 of this application are significantly better than those of Comparative Examples 1-4. The main reason may be that the specific surface area of ​​the silicon-carbon composite material provided in this embodiment increases the liquid absorption capacity of the material and the powder resistivity is reduced by the doping of heteroatoms, thereby reducing the resistivity of the electrode sheet.

[0070] This application also tested the rate performance and cycle performance of each pouch cell, and the test results are shown in Table 4 below.

[0071] The conditions for the rate performance test are as follows:

[0072] The charging and discharging voltage range is 2.5-4.2V, and the temperature is 25±3.0℃. Each coin cell was charged at 1.0C and 3.0C respectively, and discharged at 1.0C. The constant current ratio of charging was tested.

[0073] The conditions for cyclic performance testing are:

[0074] The cycle retention rate was tested at a charge / discharge rate of 1C / 1C, a voltage range of 2.5-4.2V, a temperature of 25±3.0℃, and 500 cycles.

[0075]

[0076] As shown in Table 4 above, the rate charging performance of the soft-pack battery made using the silicon-carbon composite material provided in Examples 1-3 of this application is significantly better than that of Comparative Examples 1-4. In other words, the soft-pack battery made in the examples of this application has a shorter and faster charging time. The reason may be that the examples of this application have low powder conductivity and high specific surface area to improve the rate performance of the material; at the same time, carbon fiber material is doped in the examples to reduce expansion and improve cycle performance.

[0077] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

Claims

1. A method for preparing a spheroid-like porous carbon, characterized by, The method comprises the following steps: The polyhydroxyl sugar compound, the inorganic pore-forming agent, the fibrous pore-forming agent, the crosslinking agent and the ionic liquid are weighed according to the mass ratio of 100:1-5:1-5:1-5:100-500, mixed uniformly, spray-dried, pre-carbonized at 500-800 DEG C for 1-6h, then heated to 900-1100 DEG C, activated and pore-formed by flowing in carbon dioxide gas at a flow rate of 100-500 SCCM for 1-6h to obtain the spherical porous carbon. The inorganic pore-forming agent is one of ammonium bicarbonate, ammonium carbonate and ammonium chloride; the fibrous pore-forming agent is one of polyimide fiber, poly-p-phenylene isoxazole fiber, poly-p-phenylene benzobisoxazole fiber, poly-p-phenylene pyridine di-imidazole fiber and polyvinyl alcohol fiber. The crosslinking agent is one of 2-dimethyl imidazole, 2-ethyl imidazole, 2-ethyl-4-methyl imidazole and isopropyl imidazole; the ionic liquid is one of 1-butyl-3-methyl imidazole dihydrogen phosphate, 1-butyl-3-methyl imidazole tetrafluoroborate, 1-butyl-3-methyl imidazole dicyanamide, 1-butyl-3-methyl imidazole bistrifluoromethane yellow formamide, 1-octyl-3-methyl imidazole dihydrogen phosphate, 1-octyl-3-methyl imidazole tetrafluoroborate, 1-octyl-3-methyl imidazole dicyanamide, 1-allyl-3-butyl imidazole dicyanamide, 1-nitrile propyl-3-methyl imidazole dihydrogen phosphate, 1-nitrile propyl-3-methyl imidazole tetrafluoroborate or 1-nitrile propyl-3-methyl imidazole bistrifluoromethane yellow formamide.

2. The method for preparing spherical porous carbon according to claim 1, characterized in that, The polyhydroxyl sugar compound is one of fructose, galactose, sucrose, maltose and lactose.

3. A method for preparing a spheroid-like silicon-carbon composite material, characterized by, The method comprises the following steps: The spherical porous carbon prepared by the method of any one of claims 1-2 is transferred into a fluidized bed, air in the inner air exhaust pipe is flowed in, then heated to 450-550 DEG C, and a chlorosilane mixed gas is flowed in at a flow rate of 100-500 SCCM for 30-300 min, then the flowing in of the chlorosilane mixed gas is stopped, heated to 650-750 DEG C, and a heteroatomic gas is flowed in at a flow rate of 10-50 SCCM for 30-300 min to obtain a silicon-carbon composite material.

4. The method of claim 3, wherein the method further comprises the step of: The chlorosilane mixed gas is mixed by one of dichlorodihydrogen silicon, trichlorohydrogen silicon or silicon tetrachloride and a crosslinking gas at a volume ratio of 10:1-3; the crosslinking gas is one of gasified dibenzoyl peroxide, dicumyl peroxide and dicarbonate peroxide.

5. The method of claim 3, wherein the class spherical silicon-carbon composite material is prepared by the steps of: preparing a mixture of a carbon source and a silicon source; and heating the mixture to form the class spherical silicon-carbon composite material. The heteroatomic gas is one of borane, diborane, phosphine and hydrogen sulfide.

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