Preparation Method of Silicon-Carbon Anode Material

Abstract

The present invention discloses a method for preparing a silicon-carbon anode material, which specifically comprises the following steps: Step 1, mixing a carbon source and a pore-forming agent, and calcining the mixture in a tubular furnace into which a mixed gas is introduced; Step 2, performing pickling on the product obtained in Step 1, followed by washing with water until neutral and then drying; Step 3, placing the product obtained in Step 2 in a tubular furnace for calcination to obtain a porous carbon matrix; Step 4, placing the product obtained in Step 3 in a rotary furnace, and introducing a mixed gas of a protective gas and a silicon source gas to deposit nano-silicon inside the porous carbon matrix to obtain a porous carbon matrix with nano-silicon grown thereon; Step 5, placing the product obtained in Step 4 in a rotary furnace, and performing chemical vapor deposition in a mixed atmosphere of a protective gas and an organic gas source to perform soft carbon coating on the porous carbon matrix with nano-silicon grown thereon to obtain a silicon-based anode material. In the present invention, porous carbon is used as a raw material, solving the problem of the Li 15 Si4 phase in the existing silicon-carbon materials during charge and discharge cycles.

Description

Technical Field

[0001] The present invention belongs to the technical field of anode active material for lithium-ion batteries, and relates to a preparation method of a silicon-carbon anode material. Background Art

[0002] Carbon is one of the most abundant elements in nature. After being porous, carbon materials are widely used in various fields due to their large specific surface area, pore volume, adjustable pore structure, excellent physical, chemical and mechanical properties. In recent years, porous carbon materials have gradually been applied to the preparation of silicon-carbon anode materials. The porous framework structure can effectively inhibit the size of silicon particles and provide a fast channel for electron transport. Compared with the silicon-carbon materials prepared by the traditional sanding method, this new type of silicon-carbon material can effectively inhibit the generation of Li + during the Li 15 Si 4 phase formation during the deintercalation / insertion process, and thus has better electrochemical performance and lower expansion rate. Summary of the Invention

[0003] The purpose of the present invention is to provide a preparation method of a silicon-carbon anode material, which uses porous carbon as a raw material to solve the problem of Li 15 Si 4 phase in the existing silicon-carbon materials during charge and discharge cycles.

[0004] The technical solution adopted by the present invention is a preparation method of a silicon-carbon anode material, which specifically includes the following steps:

[0005] Step 1: Mix a carbon source and a pore-forming agent, and place them in a tube furnace with a mixed gas introduced for calcination;

[0006] Step 2: Pickle the product obtained in Step 1, then wash it with water until neutral and dry it;

[0007] Step 3: Place the product obtained in Step 2 in a tube furnace for calcination to obtain a porous carbon matrix;

[0008] Step 4: Place the product obtained in Step 3 in a rotary furnace, and introduce a mixed gas of a protective gas and a silicon source gas to deposit nano-silicon inside the porous carbon matrix to obtain a porous carbon matrix with nano-silicon grown;

[0009] Step 5: Place the product obtained in Step 4 in a rotary furnace, and carry out chemical vapor deposition in a mixed atmosphere of a protective gas and an organic gas source to perform soft carbon coating on the porous carbon matrix with nano-silicon grown to obtain a silicon-based anode material.

[0010] The characteristics of the present invention also lie in:

[0011] In Step 1, the carbon source is one of pitch-based, coal-based, resin-based, and biomass-based; the pore-forming agent is one of sodium hydroxide and potassium hydroxide; the mixing mass ratio of the carbon source to the pore-forming agent is 1:1 - 1:4.

[0012] In Step 1, the mixed gas is a mixture of hydrogen and nitrogen, or a mixture of hydrogen and argon. The volume ratio of the two gases in the mixed gas is 1:1 - 1:9, and the flow rate of the mixed gas is 30 L / min - 120 L / min.

[0013] In Step 1, the calcination temperature is 700°C - 1100°C, and the calcination time is 0.5 h - 5 h.

[0014] In Step 3, the calcination temperature is 200°C - 1000°C, and the calcination time is 0.5 h - 5 h.

[0015] In Step 4, the mixed volume ratio of the protective gas to the silicon source gas is 1:1 - 9:1, the flow rate of the mixed gas is 10 L / h - 50 L / h, the heating temperature is 500°C - 900°C, and the heat preservation time is 4 h - 10 h.

[0016] In Step 4, the protective gas is one of hydrogen, nitrogen, and argon; the silicon source gas is one of silane, disilane, trisilane, tetrasilane, chlorosilane, and hexachlorosilane.

[0017] In Step 5, the mixed volume ratio of the protective gas to the organic gas source is 1:1 - 9:1, the flow rate of the mixed gas is 10 L / h - 50 L / h, the heating temperature is 500°C - 900°C, and the heat preservation time is 2 h - 6 h.

[0018] In Step 5, the protective gas is one of nitrogen and argon, and the organic gas source is one of acetylene, propane, cyclohexane, methane, and benzene.

[0019] The beneficial effects of the present invention are as follows: During the alkali activation pore-forming process of the present invention, a certain amount of hydrogen is introduced. By reasonably controlling the gas flow rate and ratio of hydrogen, the etching rate of the carbon source during the activation process can be effectively slowed down, and the prepared porous carbon material has smaller pore sizes, and the pore size distribution shows a narrow single-peak shape. Compared with commercial activated carbon materials, the porous carbon material prepared by the present invention has small pore sizes, concentrated pore size distribution, and a smooth and flat particle surface. During the preparation of the silicon-carbon material, using hydrogen as the carrier gas for silane can effectively introduce silane into small pore diameters. The finally prepared silicon-carbon material generates less Li 15 Si 4 phase during the cycle test, has lower volume expansion during the electrochemical cycle test, and is more conducive to the safety and stability during the battery use process. Description of the Drawings

[0020] Figure 1It is the flow chart of the preparation method of the silicon-carbon anode material of the present invention;

[0021] Figure 2 It is the scanning electron microscope (SEM) images of the porous carbon in Example 1 and Comparative Examples 1-3 of the preparation method of the silicon-carbon anode material of the present invention;

[0022] Figure 3 It is the pore size distribution diagram of the porous carbon in Example 1 of the preparation method of the silicon-carbon anode material of the present invention;

[0023] Figure 4 It is the voltage-dQ / dV curve diagram of Example 1 of the preparation method of the silicon-carbon anode material of the present invention;

[0024] Figure 5 It is the voltage-dQ / dV curve diagram of Comparative Example 2 of the preparation method of the silicon-carbon anode material of the present invention;

[0025] Figure 6 (a)-(c) are the cross-sectional energy dispersive spectroscopy (EDS) images of Example 1 of the preparation method of the silicon-carbon anode material of the present invention. Detailed implementation manners

[0026] The present invention will be described in detail below with reference to the accompanying drawings and specific implementation manners.

[0027] The preparation method of the silicon-carbon anode material of the present invention, as Figure 1 shown, specifically includes the following steps:

[0028] Step 1, pulverize the carbon source and mix it with the pore-forming agent in a certain proportion, and place it in a tubular furnace with a mixed gas introduced for calcination;

[0029] The specific steps include: first crush and screen the carbon source, then place it in a mortar and grind it with the pore-forming agent until evenly mixed, and place it in a boat for calcination in a mixed gas atmosphere.

[0030] Among them, the carbon source is one of pitch-based, coal-based, resin-based, and biomass-based, the pore-forming agent is one of sodium hydroxide and potassium hydroxide, preferably potassium hydroxide, the mixed gas is hydrogen and nitrogen or hydrogen and argon, preferably hydrogen and nitrogen, the volume ratio of hydrogen and nitrogen is 1:1-1:9, the flow rate is 30L / min-120L / min, the mixing mass ratio of carbon and the pore-forming agent is 1:1-1:4, the calcination temperature is 700°C-1100°C, and the calcination time is 0.5h-5h.

[0031] Step 2, pickling the calcined material in Step 1, then washing it with water until neutral and drying it;

[0032] The specific steps include: dissolving the material that has completed calcination in Step 1 in a dilute hydrochloric acid solution and stirring, and after there are no obvious bubbles in the solution, washing the material with water until neutral, then filtering by suction, and putting it in an oven for drying.

[0033] Among them, the concentration of hydrochloric acid used for pickling is 1 M.

[0034] Step 3: Place the dried material in Step 2 into a tubular furnace for calcination to obtain a porous carbon material.

[0035] Among them, the calcination temperature is 200 - 1000 °C, and the calcination time is 0.5 - 5 h.

[0036] Step 4: Place the porous carbon matrix in Step 3 into a rotary furnace, and introduce a mixed gas of a protective gas and a silicon source gas to deposit nano-silicon inside the porous carbon matrix to obtain a porous carbon matrix with nano-silicon grown thereon;

[0037] Among them, the volume ratio of the protective gas to the silicon source gas is 1:1 - 9:1, the flow rate of the mixed gas is 10 L / h - 50 L / h, the heating temperature is 500 °C - 900 °C, the heat preservation time is 4 h - 10 h, the protective gas is one of hydrogen, nitrogen, and argon, preferably hydrogen, and the silicon source gas is one of silane, disilane, trisilane, tetrasilane, chlorosilane, and hexachlorosilane, preferably silane.

[0038] Step 5: Place the porous carbon matrix with nano-silicon grown in Step 4 into a rotary furnace, and perform chemical vapor deposition in a mixed atmosphere of a protective gas and an organic gas source to perform soft carbon coating on the porous carbon matrix with nano-silicon grown thereon to obtain a silicon-based anode material.

[0039] Among them, the mixing ratio of the protective gas to the organic gas source is 1:1 - 9:1, the flow rate of the mixed gas is 10 L / h - 50 L / h, the heating temperature is 500 °C - 900 °C, the heat preservation time is 2 h - 6 h, the protective gas is one of nitrogen and argon, and the organic gas source is one of acetylene, propane, cyclohexane, methane, and benzene.

[0040] In the embodiment of the present invention, the active material is used to prepare the anode material of a lithium-ion battery, and then a button-type lithium-ion battery is assembled. The raw materials used for assembling the lithium-ion battery are all the same. Among them, the positive electrode is a lithium sheet, and the current collector is a copper foil.

[0041] Test method for the surface morphology of porous carbon particles: Use a SEM scanning electron microscope.

[0042] Test method for the pore volume, specific surface area, and pore size distribution of porous carbon: Use a BET specific surface area tester.

[0043] Li 15 Si 4 Phase test method: Use the voltage - dQ / dV curve of Wuhan Blue Electric for testing, I 0.45 (peak intensity at 0.45 V during charging) / I 0.3 (peak intensity at 0.3 V during charging).

[0044] Testing method for expansion rate of silicon-based anode materials: Prepare CR2032 coin cells by the above method, perform charge and discharge tests on the cells using a Blue Power test system, disassemble the coin cells in a glove box after the second full charge cycle, and measure the thickness of the electrode sheet. Calculation method for expansion rate: (electrode sheet thickness after cycling - electrode sheet thickness before cycling) / electrode sheet thickness before cycling × 100%.

[0045] The silicon-carbon material is prepared by depositing silicon and coating with soft carbon on different porous carbon substrates of the porous carbon provided in the embodiments of the present invention by chemical vapor deposition. Among them, parameters such as the atmosphere environment, gas flow rate, deposition time, and temperature in the chemical vapor deposition process are the same.

[0046] Example 1

[0047] Crush and screen 50 g of petroleum asphalt, take 20 g of the powder, add 3 times the mass of KOH, and grind until the materials are evenly mixed. Place the ground materials in a tubular furnace and heat to 1100 °C under a mixed gas of 30% H 2 / 70% N 2 , keep warm for 2 h, the flow rate of the mixed gas is 60 L / min. After calcination and discharging, perform pickling with 1 M hydrochloric acid and water washing until neutral and then drying. Finally, place the dried materials in a tubular furnace and heat to 500 °C under an inert atmosphere, keep warm for 2 h to obtain porous carbon.

[0048] Put the porous carbon obtained in the above step into a rotary furnace, heat to 600 °C under a nitrogen atmosphere, introduce a mixed gas of 25% silane / 75% hydrogen for 6 h, the flow rate of the mixed gas is 20 L / h. After stopping the introduction of silane gas, further heat to 750 °C, introduce a mixed gas of 20% acetylene / 80% nitrogen for 3 h, the introduction amount of the mixed gas is 30 L / h. After cooling to room temperature, obtain the final silicon-based anode material.

[0049] Example 2

[0050] Compared with Example 1, the first calcination temperature is 700 °C, keep warm for 0.5 h, the grinding ratio of asphalt powder to KOH is 1:1, the mixed gas ratio is 10% H 2 / 90% N 2 , the flow rate of the mixed gas is 30 L / min, the second calcination temperature is 200 °C, keep warm for 0.5 h, and other steps are the same.

[0051] Example 3

[0052] Compared with Example 1, the first calcination temperature is 1100 °C, keep warm for 5 h, the grinding ratio of asphalt powder to KOH is 1:4, the mixed gas ratio is 50% H 2 / 50% N 2, the flow rate of the mixed gas is 120 L / min, the second calcination temperature is 1000 °C, and the heat preservation time is 5 h. Other steps are the same.

[0053] Example 4

[0054] Compared with Example 1, during the chemical vapor deposition process, a mixed gas of 50% silane / 50% hydrogen is introduced for 4 h and a mixed gas of 50% acetylene / 50% nitrogen is introduced for 2 h. Other steps are the same.

[0055] Example 5

[0056] Compared with Example 1, during the chemical vapor deposition process, a mixed gas of 10% silane / 90% hydrogen is introduced for 10 h and a mixed gas of 10% acetylene / 90% nitrogen is introduced for 6 h. Other steps are the same.

[0057] Comparative Example 1

[0058] Compared with Example 1, the mixed gas is 100% N 2 , and other steps are the same.

[0059] Comparative Example 2

[0060] Compared with Example 1, 50 g of commercial activated carbon from Company A is placed in 1 M HCl solution, stirred for 6 h, washed with water until neutral, and dried in an oven. The obtained porous carbon is used, and other steps are the same.

[0061] Comparative Example 3

[0062] Compared with Comparative Example 2, the carbon source uses commercial activated carbon from Company B, and other steps are the same.

[0063] Figure 2 are the scanning electron microscope (SEM) images of Example 1 and Comparative Examples 1-3; the test results show that the surface of the porous carbon particles prepared by the present invention is smoother and flatter, without obvious macropores and pits, proving that the introduction of hydrogen can effectively inhibit the pore formation rate and thus finely regulate the surface morphology of the material.

[0064] The pore volume, specific surface area, and pore size distribution of the porous carbon provided in Examples 1-3 and Comparative Examples 1-3 are tested respectively.

[0065] Table 1 Test Results of Porous Carbon Parameters

[0066]

[0067] The silicon-carbon anode materials are prepared by chemical vapor deposition of silicon on the porous carbon provided in Examples 1-3 and Comparative Examples 1-3 respectively, and voltage-dQ / dV tests are carried out.

[0068] Table 2 Li of Silicon-Carbon Anode Material 15 Si4 Phase and swelling rate test results

[0069]

[0070] Figure 3 The results show that the porous carbon prepared by introducing a certain amount of hydrogen during the pore-forming process of the present invention has smaller pore diameters and a higher proportion of micropores. Figure 4 and 5 The Li 15 Si 4 phase test results of silicon-carbon materials prepared from porous carbons with different pore diameters. Combining Tables 1 and 2, compared with commercial porous carbons with larger pore diameters, using the porous carbon of the present invention as a precursor and hydrogen as a carrier gas, it is easier to introduce silane gas into the interior of the carbon matrix with small pore diameters. The prepared silicon-carbon material can effectively inhibit the generation of the Li 15 Si 4 phase during the cycle test and has a lower swelling rate.

[0071] Figure 6 (a)-(c) are the energy dispersive spectroscopy (EDS) diagrams of the cross-section of the silicon-carbon material prepared in Example 1; the test results show that silicon is uniformly distributed inside the porous carbon, without obvious local aggregation or silicon-free regions, proving that the pore structure of the porous carbon itself is uniformly distributed and the silicon is uniformly distributed, which is beneficial to alleviating the volume expansion of the material. Figure 6 (a), Figure 6 (b), Figure 6 (c) are respectively the SEM diagram of the cross-section of the particle of the silicon-carbon material prepared in Example 1, the silicon element distribution diagram and the carbon element distribution diagram.

[0072] The preparation method of the silicon-carbon negative electrode material of the present invention is based on the mechanism of alkali activation pore formation (6KOH + 2C → 2K + 3H 2 + 2K 2 CO 3 ). During the pore-forming process, a certain amount of hydrogen is introduced, and the Gibbs free energy of the activation reaction is increased by reasonable control of the gas flow rate and ratio of hydrogen, so as to slow down the etching rate of potassium vapor on the carbon source during the activation process. The prepared porous carbon material has smaller pore diameters, and the pore size distribution shows a narrow single-peak shape, and the particle surface is smooth and flat, which is more conducive to the uniformity of vapor deposition of silicon.

[0073] The silicon-carbon material prepared by the gas-phase deposition method using the porous carbon material prepared by the present invention as a precursor has fewer Li + generated during the deintercalation / insertion process of 15 Si 4 and Si compared with commercial activated carbon materials, has a lower volume expansion during the electrochemical cycle test, and is more conducive to the safety and stability during the use of the battery.

Claims

1. Preparation method of silicon-carbon anode material, Characterized in that: Specifically includes the following steps: Step 1, mix the carbon source and the pore-forming agent, and place them in a tubular furnace with a mixed gas introduced for calcination; In the said Step 1, the carbon source is one of pitch-based, coal-based, resin-based, and biomass-based; the pore-forming agent is one of sodium hydroxide and potassium hydroxide; the mixing mass ratio of the carbon source to the pore-forming agent is 1:1 - 1:4; In the said Step 1, the mixed gas is a mixture of hydrogen and nitrogen, or a mixture of hydrogen and argon, the volume ratio of the two gases in the mixed gas is 1:1 - 1:9, and the flow rate of the mixed gas is 30L / min - 120L / min; In the said Step 1, the calcination temperature is 700°C - 1100°C, and the calcination time is 0.5h - 5h; Step 2, perform pickling on the product obtained in Step 1, then wash it with water until neutral and dry it; Step 3, place the product obtained in Step 2 in a tubular furnace for calcination to obtain a porous carbon matrix; in the said Step 3, the calcination temperature is 200°C - 1000°C, and the calcination time is 0.5h - 5h; Step 4, place the product obtained in Step 3 in a rotary furnace, introduce a mixed gas of a protective gas and a silicon source gas to deposit nano-silicon inside the porous carbon matrix, and obtain a porous carbon matrix with nano-silicon grown; in the said Step 4, the mixed volume ratio of the protective gas to the silicon source gas is 1:1 - 9:1, the flow rate of the mixed gas is 10L / h - 50L / h, the heating temperature is 500°C - 900°C, and the holding time is 4h - 10h; Step 5, place the product obtained in Step 4 in a rotary furnace, and perform chemical vapor deposition in a mixed atmosphere of a protective gas and an organic gas source to perform soft carbon coating on the porous carbon matrix with nano-silicon grown, and obtain a silicon-based anode material.

2. The preparation method of the silicon-carbon anode material according to claim 1, Characterized in that: In the said Step 4, the protective gas is one of hydrogen, nitrogen, and argon; the silicon source gas is one of silane, disilane, trisilane, tetrasilane, chlorosilane, and hexachlorosilane.

3. The preparation method of the silicon-carbon anode material according to claim 1, Characterized in that: In the said Step 5, the mixed volume ratio of the protective gas to the organic gas source is 1:1 - 9:1, the flow rate of the mixed gas is 10L / h - 50L / h, the heating temperature is 500°C - 900°C, and the holding time is 2h - 6h.

4. The preparation method of the silicon-carbon anode material according to claim 3, Characterized in that: In the said Step 5, the protective gas is one of nitrogen and argon, and the organic gas source is one of acetylene, propane, cyclohexane, methane, and benzene.

Images