Low-cost silicon-carbon negative electrode material and preparation method thereof

Abstract

The invention provides a low-cost silicon-carbon negative electrode material and a preparation method thereof, and belongs to the field of lithium ion battery negative electrode materials. The preparation method of the low-cost silicon-carbon negative electrode material provided by the invention comprises the following steps: introducing a gaseous silicon source and a first protective gas into a reactor, and carrying out silicon deposition on the pore wall surface of porous carbon to obtain a silicon-carbon composite material; and introducing a gaseous organic carbon source and a second protective gas into the reactor for carbon deposition to obtain the low-cost silicon-carbon negative electrode material, the staying time of the gaseous organic carbon source in the reactor is 20-95 seconds. The method comprises the following steps: introducing a gaseous silicon source and a first protective gas into a reactor, and carrying out silicon deposition on the surface of the porous carbon to obtain the silicon-modified porous carbon. By controlling the retention time of the organic carbon source in the reactor, the deposition rate of the organic carbon source is effectively improved, and the problems of low carbon deposition rate, poor coating effect and high production cost in the process of preparing the low-cost silicon-carbon negative electrode material by a vapor deposition method are solved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of lithium ion battery negative electrode materials, and in particular to a preparation method of a low-cost silicon-carbon negative electrode material. BACKGROUND

[0002] Currently, the rapid expansion of electric vehicles and 3C electronic products drives the demand for high-energy density and high-rate batteries to continue to rise, and how to effectively improve the energy density of electrode materials has become a key challenge.

[0003] Silicon-based negative electrodes have attracted widespread attention due to their high theoretical specific capacity and low cost. However, the energy storage mechanism of silicon-based negative electrodes in lithium ion batteries is alloying reaction, which is accompanied by significant volume change during the reaction process. The significant volume change will induce a large internal stress, leading to the structure rupture and pulverization of active materials, and accelerating the continuous growth of solid electrolyte interface (SEI), thereby causing rapid capacity decay, cycle stability deterioration and low first cycle efficiency. The combination of silicon-based negative electrodes with carbon matrix with stable structure and good ductility can effectively inhibit the volume change during charging and discharging.

[0004] Currently, the mainstream synthesis strategy of silicon-carbon negative electrodes in the industry focuses on gas deposition technology. This process uses a porous carbon matrix as a carrier to deposit silicon components by pyrolysis of an organic silicon source at a specific temperature, and then introduces an organic carbon source to coat a carbon layer. This design uses the pore structure of the matrix to constrain the expansion of silicon particles, and the surface carbon coating layer can improve the structural integrity and conductivity. Among them, the deposition efficiency of the organic silicon source is usually higher than 90%, while the deposition efficiency of the organic carbon source is generally less than 20%. To optimize the deposition effect, the conventional process is to increase the deposition temperature and extend the deposition time. However, as the deposition temperature increases, the organic carbon source is accelerated to generate pyrolytic carbon with low graphitization degree, which has limited improvement on the structural stability and conductivity of the material. Moreover, if the deposition temperature is too high, the deposition rate on the surface of the matrix is greater than that in the pores, which can easily cause excessive "sealing" phenomenon and affect subsequent deposition. Extending the carbon source deposition time has limited effect on improving the carbon layer coating effect. These two methods cannot effectively improve the carbon source deposition rate, and the industrial production equipment generally uses resistance wire heating method, which consumes a large amount of energy, thereby increasing the production cost. SUMMARY

[0005] The present application provides a low-cost silicon-carbon negative electrode material and a preparation method thereof. The preparation method of the present application is simple and feasible, effectively improves the carbon source deposition rate, improves the carbon layer coating effect, improves the electrochemical performance of the material, and reduces the production cost.

[0006] The present application provides a preparation method of a low-cost silicon-carbon negative electrode material, comprising the following steps: The gaseous silicon source and the first protective gas are introduced into the reactor to deposit silicon on the pore wall surface of the porous carbon, obtaining a silicon-carbon composite material; depositing carbon in the reactor by introducing a gaseous organic carbon source and a second protective gas to obtain the low-cost silicon-carbon negative electrode material; The gaseous organic carbon source stays in the reactor for 20-95 seconds.

[0007] Preferably, the method for filling the reactor with the third protective gas comprises: opening the tail gas valve of the reactor, then increasing the temperature of the reactor to the silicon deposition temperature, then placing the porous carbon in the reactor, and then introducing the third protective gas into the reactor to replace the air in the reactor.

[0008] Preferably, the gaseous silicon source comprises one or more of silane, silicon tetrachloride, and dichlorodihydrogen silicon. The silane comprises monosilane.

[0009] Preferably, the flow rate ratio of the gaseous silicon source to the first protective gas is 1:4, and the flow rate of the gaseous silicon source is 10-50 L / min.

[0010] Preferably, the silicon deposition temperature is 500-700℃, the pressure is 5-40 kPa, and the time is 30-350 min.

[0011] Preferably, the temperature increasing rate to the silicon deposition temperature is 2-5℃ / min.

[0012] Preferably, the gaseous organic carbon source comprises one or more of methane, ethylene, propylene, and acetylene.

[0013] Preferably, the flow rate ratio of the gaseous organic carbon source to the second protective gas is 1:3-4, and the flow rate of the gaseous organic carbon source is 10-50 L / min.

[0014] Preferably, the carbon deposition temperature is 500-700℃, the pressure is 5-40 kPa, the time is 30-350 min, and the tail gas valve opening is 20-75%.

[0015] Preferably, after the carbon deposition, the method further comprises: introducing a fourth protective gas for cooling.

[0016] The application also provides a low-cost silicon-carbon negative electrode material prepared by the preparation method.

[0017] The application solves the problems of low carbon deposition rate, poor coating effect and high production cost in the process of preparing low-cost silicon-carbon negative electrode material by gas deposition method by controlling the residence time of organic carbon source in the reactor and regulating the carbon deposition mechanism: if the residence time of organic carbon source in the reactor is too long, the deposited carbon layer is too thick, even carbon black is generated, which is not conducive to the shuttle of lithium ions, resulting in too low initial efficiency of the material; if the residence time is too short, the small molecule chains generated by the decomposition of organic carbon source cannot react further in time, and the deposited carbon layer has many defects and low graphitization degree, poor conductivity. By controlling the appropriate residence time of organic carbon source, a material with moderate thickness of deposited layer and high graphitization degree can be obtained, which is conducive to improving the electrochemical performance of the material.

[0018] Further, the application controls the residence time of organic carbon source in the reactor by adjusting the exhaust gas discharge degree. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 SEM image of the low-cost silicon-carbon negative electrode material prepared in Example 2. DETAILED DESCRIPTION

[0020] The application provides a preparation method of low-cost silicon-carbon negative electrode material, comprising the following steps: introducing gaseous silicon source and first protective gas into the reactor to deposit silicon on the pore wall surface of the porous carbon, and obtaining silicon-carbon composite material; introducing gaseous organic carbon source and second protective gas into the reactor to deposit carbon, and obtaining the low-cost silicon-carbon negative electrode material; The residence time of the gaseous organic carbon source in the reactor is 20-95s.

[0021] The reactor used in the application is preferably a fluidized bed, a tubular furnace or a muffle furnace, and more preferably a fluidized bed.

[0022] The method for filling the reactor with third protective gas comprises: opening the tail gas valve of the reactor, then increasing the temperature of the reactor to the silicon deposition temperature, then placing the porous carbon in the reactor, and then introducing third protective gas into the reactor to replace the air therein.

[0023] In the application, the flow rate of the third protective gas is preferably 100L / min, the third protective gas preferably comprises nitrogen, and the replacement time is preferably 30-120min, which can be 40min, 50min, 60min, 70min, 80min, 90min, 100min or 110min in specific embodiments of the application.

[0024] In the application, the specific surface area of the porous carbon is preferably 1800m 2The mass of the porous carbon is preferably 1-50 kg, and in specific embodiments of the application can be 5 kg, 10 kg, 20 kg, 30 kg or 40 kg.

[0025] In the present application, the flow rate ratio of the gaseous silicon source to the first protective gas is preferably 1:4, the flow rate of the gaseous silicon source is preferably 10-50 L / min, and in specific embodiments of the application can be 15 L / min, 20 L / min, 30 L / min or 40 L / min; the gaseous silicon source preferably comprises one or more of silane, silicon tetrachloride and dichlorodihydrogen silicon; the silane preferably comprises monosilane; and the first protective gas preferably comprises nitrogen.

[0026] In the present application, the temperature of the silicon deposition is preferably 500-700℃, the time is preferably 30-350 min, and the pressure is preferably 5-40 kPa, and in specific embodiments of the application the temperature of the silicon deposition can be 520℃, 550℃, 580℃, 600℃, 620℃, 650℃ or 680℃, the time can be 50 min, 80 min, 100 min, 120 min, 150 min, 180 min, 200 min, 250 min, 280 min, 300 min or 320 min, and the pressure can be 10 kPa, 15 kPa, 20 kPa, 25 kPa, 30 kPa or 35 kPa.

[0027] In the present application, the heating rate for heating to the silicon deposition temperature is preferably 2-5℃ / min.

[0028] After obtaining the silicon-modified porous carbon, the present application passes a gaseous organic carbon source and a second protective gas into the reactor to carry out carbon deposition, thereby obtaining the low-cost silicon-carbon negative electrode material.

[0029] In the present application, the flow rate ratio of the gaseous organic carbon source to the second protective gas is preferably 1:3-4, the flow rate of the gaseous organic carbon source is preferably 10-50 L / min, and in specific embodiments of the application can be 15 L / min, 20 L / min, 30 L / min or 40 L / min; the gaseous organic carbon source preferably comprises one or more of methane, ethylene, propylene and acetylene; and the second protective gas preferably comprises nitrogen.

[0030] In the present application, the temperature of carbon deposition is preferably 500-700℃, the time is preferably 30-350min, and the pressure is preferably 5-40kPa. In specific embodiments of the present application, the temperature of carbon deposition can be 520℃, 550℃, 580℃, 600℃, 620℃, 650℃ or 680℃, the time can be 50min, 80min, 100min, 120min, 150min, 180min, 200min, 250min, 280min, 300min or 320min, and the pressure can be 10kPa, 15kPa, 20kPa, 25kPa, 30kPa or 35kPa.

[0031] In the present application, the time for the gaseous organic carbon source to stay in the reactor is preferably 20-95s, and in specific embodiments of the present application, it can be 25s, 30s, 35s, 40s, 45s, 50s, 55s, 60s, 65s, 70s, 75s, 80s, 85s or 90s. If the residence time is too long, the carbon layer deposited is too thick, and even carbon black is generated, which is not conducive to the shuttling of lithium ions, resulting in too low first efficiency of the material; if the residence time is too short, the small molecule chains generated by the decomposition of the organic carbon source do not have enough time to further react, and the carbon layer deposited has more defects and a low degree of graphitization, resulting in poor electrical conductivity.

[0032] In the present application, the time for the gaseous organic carbon source to stay in the reactor is controlled by adjusting the degree of tail gas discharge. In the present application, the way to adjust the degree of tail gas discharge can be to control the tail gas valve opening degree and / or adjust the tail gas flow control meter flow. In the present application, the tail gas valve opening degree is preferably 25-70%, and in specific embodiments of the present application, it can be 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65% or 70%; the tail gas flow control meter flow is preferably 20-40L / min, and in specific embodiments of the present application, it can be 20L / min, 30L / min, 35L / min or 40L / min.

[0033] After carbon deposition, the present application preferably further comprises: introducing a fourth protective gas for cooling; and the fourth protective gas preferably comprises nitrogen.

[0034] The application solves the problems of low carbon deposition rate, poor coating effect and high production cost in the process of preparing low-cost silicon-carbon negative electrode material by gas deposition method by controlling the residence time of organic carbon source in the reactor and regulating the carbon source deposition mechanism: if the residence time of organic carbon source in the reactor is too long, the deposited carbon layer is too thick, even carbon black is generated, which is not conducive to the shuttle of lithium ions, resulting in too low first efficiency of the material; if the residence time is too short, the small molecule chains generated by the decomposition of organic carbon source cannot further react in time, and the deposited carbon layer has many defects and low graphitization degree, poor conductivity. By controlling the appropriate residence time of organic carbon source, a material with moderate thickness of deposited layer and high graphitization degree can be obtained, which is conducive to improving the electrochemical performance of the material.

[0035] The preparation method of the low-cost silicon-carbon negative electrode material provided by the application will be described in detail below in combination with examples, but they should not be understood as limiting the protection scope of the application.

[0036] Example 1 Start the fluidized bed reactor, open the exhaust valve, and heat to 500℃ at a rate of 2℃ / min. Add 5kg of porous carbon (specific surface area of 1800 m 2 / g), and replace it with nitrogen gas (gas flow rate of 100L / min) for 0.5h. Then, introduce silane, with a gas flow rate of 20L / min, and a volume ratio of silicon source to nitrogen gas of 1:4. The reactor pressure is 14 KPa. After 3h of deposition, stop introducing the silicon source, introduce acetylene, with a flow rate of 25L / min, and a volume ratio of carbon source to nitrogen gas of 1:3. Reduce the opening degree of the exhaust valve to 75%, and the residence time of the carbon source gas in the reactor is 22s. The reactor pressure is 15KPa. After 35min of deposition, stop introducing the carbon source, fully open the exhaust valve, and cool down the reactor.

[0037] Example 2 Start the fluidized bed reactor, open the exhaust valve, and heat to 500℃ at a rate of 2℃ / min. Add 5kg of porous carbon (specific surface area of 1800 m 2 / g), and replace it with nitrogen gas (gas flow rate of 100L / min) for 0.5h. Then, introduce silane, with a gas flow rate of 20L / min, and a volume ratio of silicon source to nitrogen gas of 1:4. The reactor pressure is 14 KPa. After 3h of deposition, stop introducing the silicon source, introduce acetylene, with a flow rate of 25L / min, and a volume ratio of carbon source to nitrogen gas of 1:3. Reduce the opening degree of the exhaust valve to 75%, and the residence time of the carbon source gas in the reactor is 22s. The reactor pressure is 15KPa. After 35min of deposition, stop introducing the carbon source, fully open the exhaust valve, and cool down the reactor.

[0038] Example 3 A fluidised bed reactor was started and the exhaust valve opened. The temperature was increased to 500°C at 2°C / min and 5kg of porous carbon (specific surface area 1800 m 2 / g) was added. Nitrogen was introduced at a flow rate of 100L / min for 0.5h. After this time, silane was introduced at a flow rate of 20L / min and the volume ratio of silicon source to nitrogen was 1 :4. The reactor pressure was 14 KPa. Deposition was stopped after 3h and acetylene was introduced at a flow rate of 25L / min and the volume ratio of carbon source to nitrogen was 1 :3. The exhaust valve was reduced to 20% and the carbon source gas residence time in the reactor was 59s and the reactor pressure was 40 KPa. Deposition was stopped after 35min and the exhaust valve was opened fully and the reactor was cooled.

[0039] Example 4 A fluidised bed reactor was started and the exhaust valve opened. The temperature was increased to 500°C at 2°C / min and 5kg of porous carbon (specific surface area 1800 m 2 / g) was added. Nitrogen was introduced at a flow rate of 100L / min for 0.5h. After this time, silane was introduced at a flow rate of 20L / min and the volume ratio of silicon source to nitrogen was 1 :4. The reactor pressure was 14 KPa. Deposition was stopped after 3h and acetylene was introduced at a flow rate of 25L / min and the volume ratio of carbon source to nitrogen was 1 :3. The exhaust valve was reduced to 20% and the carbon source gas residence time in the reactor was 59s and the reactor pressure was 40 KPa. Deposition was stopped after 35min and the exhaust valve was opened fully and the reactor was cooled.

[0040] Example 5 A fluidised bed reactor was started and the exhaust valve opened. The temperature was increased to 500°C at 2°C / min and 5kg of porous carbon (specific surface area 1800 m 2 / g) was added. Nitrogen was introduced at a flow rate of 100L / min for 0.5h. After this time, silane was introduced at a flow rate of 20L / min and the volume ratio of silicon source to nitrogen was 1 :4. The reactor pressure was 14 KPa. Deposition was stopped after 3h and acetylene was introduced at a flow rate of 25L / min and the volume ratio of carbon source to nitrogen was 1 :3. The exhaust valve was reduced to 20% and the carbon source gas residence time in the reactor was 59s and the reactor pressure was 40 KPa. Deposition was stopped after 35min and the exhaust valve was opened fully and the reactor was cooled.

[0041] Comparative Example 1 A fluidised bed reactor was started and the exhaust valve opened. The temperature was increased to 500°C at 2°C / min and 5kg of porous carbon (specific surface area 1800 m 2The reactor is purged with nitrogen (gas flow rate is 100 L / min) for 0.5 h, then silane is introduced, and the gas flow rate is 20 L / min, the volume ratio of the silicon source to nitrogen is 1:4. After deposition for 3 h, the introduction of the silicon source is stopped, and acetylene is introduced, and the flow rate is 25 L / min, the volume ratio of the carbon source to nitrogen is 1:3. The tail gas valve is fully opened, the residence time of the carbon source gas in the reactor is 6 s, the pressure in the reactor is 5 KPa, and the deposition is stopped after 35 min, the tail gas valve is fully opened, and the reactor is cooled.

[0042] The application can effectively improve the deposition rate of the organic carbon source by controlling the residence time of the organic carbon source in the reactor and regulating the cracking mechanism of the organic carbon source, thereby reducing the cost, reducing the specific surface area of the material, and improving the initial efficiency of the material.

[0043] Table 1: Si and C contents of low-cost silicon-carbon negative electrode materials obtained in Examples 1-5 and Comparative Example 1, and carbon source deposition rate and specific surface area

[0044] The carbon source deposition rate can be calculated according to the product yield and the silicon-carbon content of the product.

[0045] As can be seen from Table 1, by comparing the results from Example 1 to Example 4, it can be seen that by prolonging the residence time of the organic carbon source in the reactor, the carbon source deposition rate can be increased, the specific surface area of the material can be effectively reduced, and the carbon layer on the surface of the silicon layer can prevent the silicon layer from directly contacting the electrolyte and generating a side reaction. In a conventional deposition process, the propylene deposition rate is less than 20%, and as can be seen from Examples 1-3, by prolonging the residence time of propylene in the reactor, the carbon source deposition rate can be effectively improved, and in industrial production, by improving the carbon source deposition rate, the production cost can be effectively reduced.

[0046] The low-cost silicon-carbon negative electrode material prepared is assembled into a CR2025 type button cell for testing, lithium metal is used as the counter electrode, PP film (thickness 25 μm) is used as the separator, 1M lithium hexafluorophosphate solution is used as the electrolyte, the voltage window is 0.2-2.2V, and the current density is 0.1C, and the results are shown in Table 2.

[0047] Table 2: initial discharge specific capacity and initial efficiency of the low-cost silicon-carbon negative electrode material obtained in Examples 1-5 and Comparative Example 1

[0048] The discharge specific capacity is mainly affected by the silicon content, and the higher the silicon content, the greater the discharge specific capacity. As can be seen from the initial efficiency results, by prolonging the residence time of the organic carbon source in the reactor and generating a carbon layer with high graphitization degree, the initial efficiency can be improved. Example 3 may be because the carbon layer is deposited too thick, hindering the shuttling of lithium ions, and the surface has many defects, resulting in poor conductivity, thereby reducing the initial efficiency.

[0049] Figure 1 SEM image of the low-cost silicon-carbon negative electrode material prepared for Example 2.

[0050] From Figure 1 It can be seen that the surface deposition layer of the material is smooth and dense, indicating that the carbon deposition coating effect can be effectively improved by prolonging the residence time of the carbon source in the reactor, improving the deposition rate of the carbon source, and regulating the deposition mechanism of the carbon source.

[0051] The above only describes the preferred embodiments of the present application, and it should be noted that for those skilled in the art, without departing from the principles of the present application, a number of improvements and refinements can be made, which should also be considered as the protection scope of the present application.

Claims

1. A method for preparing a low-cost silicon-carbon negative electrode material, characterized in that, The method comprises the following steps: introducing a gaseous silicon source and a first protective gas into a reactor filled with a third protective gas to deposit silicon on the pore wall surface of the porous carbon to obtain a silicon-carbon composite material; introducing a gaseous organic carbon source and a second protective gas into the reactor to deposit carbon to obtain the low-cost silicon-carbon negative electrode material; The gaseous organic carbon source stays in the reactor for 20-95 seconds.

2. The method for preparing the low-cost silicon-carbon anode material according to claim 1, characterized in that, The method for filling the reactor with the third protective gas comprises the following steps: opening a tail gas valve of the reactor, then increasing the temperature of the reactor to the silicon deposition temperature, then placing the porous carbon in the reactor, and then introducing the third protective gas into the reactor to replace the air in the reactor.

3. The method for preparing the low-cost silicon-carbon anode material according to claim 1, characterized in that, The gaseous silicon source comprises one or more of silane, silicon tetrachloride and dichlorodihydrogen silicon. The silane comprises monosilane.

4. The method for preparing the low-cost silicon-carbon anode material according to claim 1 or 3, characterized in that, The flow rate ratio of the gaseous silicon source to the first protective gas is 1:4, and the flow rate of the gaseous silicon source is 10-50 L / min.

5. The method for preparing the low-cost silicon-carbon anode material according to claim 4, characterized in that, The silicon deposition temperature is 500-700℃, the pressure is 5-40 kPa, and the time is 30-350 min.

6. The method for preparing the low-cost silicon-carbon anode material according to claim 5, characterized in that, The heating rate for increasing the temperature to the silicon deposition temperature is 2-5℃ / min.

7. The method for preparing the low-cost silicon-carbon anode material according to claim 1, characterized in that, The gaseous organic carbon source comprises one or more of methane, ethylene, propylene and acetylene.

8. The method for preparing the low-cost silicon-carbon anode material according to claim 1 or 7, characterized in that, The flow rate ratio of the gaseous organic carbon source to the second protective gas is 1:3-4, and the flow rate of the gaseous organic carbon source is 10-50 L / min.

9. The method for preparing the low-cost silicon-carbon anode material according to claim 8, characterized in that, The carbon deposition temperature is 500-700℃, the pressure is 5-40 kPa, the time is 30-350 min, and the tail gas valve opening is 20-75%.

10. A low-cost silicon-carbon negative electrode material prepared by the method of any one of claims 1-9.

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