Silicon-carbon negative electrode material and preparation method thereof

Abstract

The invention discloses a preparation method of a silicon-carbon negative electrode material, which is characterized by comprising the following steps: S1, injecting a mixed gas formed by silane, a gas carbon source and an inert gas into a plasma reactor through high-pressure injection for instant reaction to prepare a silicon-carbon in-situ composite nano material, and cooling the silicon-carbon in-situ composite nano material; s2, performing coating granulation on asphalt or resin and the silicon-carbon in-situ composite nanomaterial prepared in the step S1, and carbonizing in the carbonization furnace again; and S3, mixing the carbonized material in the step S2, sieving and removing iron to obtain the finished product silicon-carbon negative electrode material. According to the preparation method, abnormal growth of silicon in the deposition process can be avoided through in-situ compounding of silane and a gas carbon source, and the expansion problem in the later material use process and the carbon stripping problem occurring in the later material circulation period can be effectively inhibited and improved; the negative electrode material prepared by the preparation method has high discharge capacity and excellent rate capability.

Description

Technical Field

[0001] The invention belongs to the technical field of lithium battery negative electrode material preparation, and relates to a silicon-carbon negative electrode material and a preparation method thereof. Background Art

[0002] Silicon is abundant in reserves, cheap in price, and has a theoretical lithium storage capacity of up to 4200mAh / g, making it a promising new generation of negative electrode material for lithium-ion batteries. However, silicon expands greatly during the process of lithium insertion and extraction, causing the material to crack and pulverize, resulting in rapid capacity decay.

[0003] At present, the industry mostly prepares silicon-carbon materials by grinding silicon powder through ball milling process and compounding it with carbon. However, the size reduction of silicon in the materials prepared by ball milling process is limited, the energy consumption is high, the amount of silicon added is small, and the capacity improvement is limited. At present, some researchers also use CVD technology to deposit silane on porous carbon to improve the expansion of silicon. However, this method is to pass silane gas at a constant temperature and time to decompose it into Si on the carbon material. In this way, there may be excessive and uneven deposition of Si in some positions, causing the particles to become larger, thereby causing volume expansion during the charging and discharging process. At the same time, it is easy to peel off between carbon and Si. Therefore, the improvement effect is not good, and this method requires the use of excessive silane, and there will be unreacted silane gas, which poses an environmental risk and requires the treatment of excessive tail gas. Summary of the invention

[0004] Purpose of the invention: The purpose of the present invention is to provide a silicon-carbon negative electrode material and a preparation method thereof. The method can synthesize in-situ composited silicon-carbon nanomaterials, which can avoid the problem of carbon peeling in the later stage of material circulation. At the same time, the material prepared by this method has a small particle size, which avoids the expansion of the material.

[0005] Technical solution: A method for preparing a silicon-carbon negative electrode material of the present invention comprises the following steps:

[0006] S1, injecting a mixed gas formed by silane, a gaseous carbon source and an inert gas into a plasma reactor at a pressure of 0.2-0.6 MPa to react instantly to prepare a silicon-carbon in-situ composite nanomaterial, and cooling the silicon-carbon in-situ composite nanomaterial;

[0007] S2, coating and granulating the asphalt or resin with the silicon-carbon in-situ composite nanomaterial prepared in step S1, and carbonizing them again in a carbonization furnace;

[0008] S3, mixing and screening the carbonized materials in step S2 to remove iron to obtain a finished silicon-carbon negative electrode material.

[0009] Further, the silane in step S1 is a combination of one or more of monosilane, disilane, trisilane, monochlorosilane, dichlorosilane, trichlorosilane and tetrachlorosilane;

[0010] Furthermore, the gaseous carbon source in step S1 includes one or more combinations of methane, ethane, propane, acetylene, and ethylene.

[0011] Furthermore, in step S1, the volume ratio of silane to gaseous carbon source is (1-4):1.

[0012] Furthermore, the flow rate of the mixed gas in step S1 is 10 to 2000 L / h.

[0013] Furthermore, the plasma flame temperature in the plasma reactor in step S1 is 600-800° C., and the power of the plasma reactor is 50-120 kW.

[0014] Furthermore, the plasma excitation gas of the plasma reactor in step S1 is nitrogen or argon, and the flow rate of the excitation gas is 100-200 sccm.

[0015] Furthermore, the asphalt or resin in step S2 accounts for 5-20% of the mass ratio of the silicon-carbon in-situ composite nanomaterial.

[0016] Furthermore, the carbonization process in step S2 is to maintain the temperature of the carbonization furnace at 700-1000° C. and react at a constant temperature for 1-10 hours.

[0017] Furthermore, a silicon-carbon negative electrode material is provided, which is prepared by the above-mentioned method for preparing the silicon-carbon negative electrode material.

[0018] Reaction mechanism: The biggest problem of silicon used in negative electrodes is the volume expansion during the charge and discharge process. The volume expansion of silicon negative electrodes can reach 300% of the body, but when the structural size of silicon is smaller than the critical value, that is, when the diameter of nano-silicon particles is smaller than 150nm, there will be no rupture within the volume expansion range. The preparation method of the present invention uses a mixed gas to enter a plasma reactor through high-pressure injection and instantaneous reaction to prepare an in-situ composite silicon-carbon nanomaterial. Silane and carbon source are both gaseous raw materials and are in a mixed state before entering. At the same time, the reaction is completed instantaneously. Therefore, the primary particles of the prepared in-situ composite silicon-carbon nanomaterial are 5 to 50nm, without aggregation, in a monodisperse form, and the silicon and carbon are evenly mixed, and silicon agglomeration is not easy to occur.

[0019] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: 1. The in-situ compounding of silane and gaseous carbon source can avoid the abnormal growth of Si during the deposition process, and can effectively inhibit and improve the expansion problem during the later use of the material. The in-situ compounding can also avoid the carbon peeling problem that occurs in the later stage of the material cycle;

[0020] 2. The conventional method of using a rotary kiln or a fluidized bed to deposit silane on porous carbon requires the introduction of excessive silane gas, resulting in low utilization rate, and the need to treat the tail gas, resulting in large equipment investment. The present invention has high utilization rates of silane and gaseous carbon sources, and does not require post-treatment, thereby avoiding waste of materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a schematic flow chart of a method for preparing a silicon-carbon negative electrode material of the present invention;

[0022] Figure 2 is a SEM image of the silicon-carbon negative electrode material prepared at a mixed gas flow rate of 1500 L / h in Example 2 of the present invention;

[0023] Figure 3 This is a SEM image of the silicon-carbon negative electrode material prepared when the mixed gas flow rate is 2500 L / h in Example 2 of the present invention. DETAILED DESCRIPTION

[0024] The technical solution of the present invention is further described below in conjunction with the accompanying drawings.

[0025] Unless otherwise specified, the experimental methods used in the following examples are all conventional methods, and the materials, reagents, etc. used are all available from commercial sources unless otherwise specified.

[0026] Combination Figure 1 The schematic diagram of the process of preparing a silicon-carbon negative electrode material of the present invention is shown, and the following embodiments are set:

[0027] Example 1 (Effect of the ratio of monosilane to methane on the performance of silicon-carbon negative electrode materials)

[0028] S1, injecting monosilane, methane and nitrogen at a ratio of 1:1, 2:1, 3:1 and 4:1 at a flow rate of 800 L / h into a plasma reactor with a flame temperature of 600°C and a power of 50Kw to react instantly to prepare silicon and carbon in-situ composite nanomaterials, and cooling the materials;

[0029] S2, coating and granulating 5% asphalt and the above silicon and carbon in-situ composite nanomaterials in a mechanical fusion machine to obtain 5 μm microspheres, and then carbonizing the microspheres in a carbonization furnace to 700° C. and reacting at a constant temperature for 6 hours;

[0030] S3, mixing and screening the carbonized materials in step S2 to remove iron to obtain a finished silicon-carbon negative electrode.

[0031] In order to verify the progress of the embodiment of the present application, the following performance tests were conducted on the materials prepared in the above embodiment: the above materials were mixed with LA132 and Super P in a ratio of 80:10:10 to prepare a negative electrode sheet, and metal lithium was used as a counter electrode. A half-cell was assembled in a conventional manner, and the half-cell was tested using the Xinwei half-cell test system, with a charge and discharge test voltage of 0.01 to 2.0 V. The test results are shown in Table 1.

[0032] Table 1:

[0033]

[0034] It can be seen from Table 1 that when the silane content is higher, the capacity is higher, but when the silane content exceeds a certain ratio, the Si particles in the silicon-carbon material grow abnormally, resulting in a rapid deterioration of the material's capacity and cycle. Therefore, when the ratio of monosilane, methane and nitrogen is (1-4):1, the prepared negative electrode material has a high discharge capacity and excellent rate performance.

[0035] Example 2 (Effect of mixed gas flow rate on the performance of silicon-carbon negative electrode material)

[0036] S1. Disilane and acetylene are injected at a ratio of 2:1 at flow rates of 10 L / h, 150 L / h, 300 L / h, 800 L / h, 1500 L / h, 2000 L / h, and 2500 L / h, respectively, into a plasma reactor at 600°C and a power of 80 kW for instantaneous reaction to prepare silicon and carbon in-situ composite nanomaterials, and the materials are cooled;

[0037] S2, 13% asphalt and the above nanomaterials are coated and granulated in a mechanical fusion machine to obtain 8 μm microspheres, and the microspheres are again heated to 900° C. in a carbonization furnace for constant temperature reaction for 4 hours;

[0038] S3, mixing and screening the carbonized materials in step S2 to remove iron to obtain a finished silicon-carbon negative electrode.

[0039] In order to verify the progress of the embodiment of the present application, the following performance tests were conducted on the materials prepared in the above embodiment: the above materials were mixed with LA132 and Super P in a ratio of 80:10:10 to prepare a negative electrode sheet, and metal lithium was used as a counter electrode. A half-cell was assembled in a conventional manner, and the half-cell was tested using the Xinwei half-cell test system, with a charge and discharge test voltage of 0.01 to 2.0 V. The test results are shown in Table 2.

[0040] Table 2:

[0041]

[0042] It can be seen from Table 2 that with the change of the mixed gas flow rate, when the mixed gas flow rate is too large, the agglomeration phenomenon of the prepared product is more serious, and it is impossible to prepare a monodisperse product, such as Figure 2 The figure shows the SEM at a flow rate of 1500 L / h. Figure 3 For SEM with a flow rate of 2500L / h, Figure 3 The particles in the mixture agglomerate significantly. When the flow rate increases, the raw materials cannot be fully decomposed to form silicon-carbon composite materials, which will cause loss of electrical performance. Therefore, when the mixed gas flow rate is 10-2000L / h, the prepared negative electrode material has high discharge capacity and excellent rate performance.

[0043] Example 3 (Effect of flame flow temperature on the performance of silicon-carbon negative electrode material)

[0044] S1, injecting monosilane and acetylene at a ratio of 2:1 at a flow rate of 800L / h into a plasma reactor with flame flow temperatures of 400°C, 600°C, 800°C, 1000°C, and 1200°C and a power of 80Kw to react instantly to prepare silicon and carbon in-situ composite nanomaterials, and cooling the materials;

[0045] S2, coating and granulating 20% ​​resin and the above nanomaterials in a mechanical fusion machine to obtain 16 μm microspheres, and then carbonizing the microspheres in a carbonization furnace to 1000° C. and reacting at a constant temperature for 10 hours;

[0046] S3, mixing and screening the carbonized materials in step S2 to remove iron to obtain a finished silicon-carbon negative electrode.

[0047] In order to verify the progress of the embodiment of the present application, the following performance tests were conducted on the materials prepared in the above embodiment: the above materials were mixed with LA132 and Super P in a ratio of 80:10:10 to prepare a negative electrode sheet, and metal lithium was used as a counter electrode. A half-cell was assembled in a conventional manner, and the half-cell was tested using the Xinwei half-cell test system, with a charge and discharge test voltage of 0.01 to 2.0 V. The test results are shown in Table 3.

[0048] Table 3:

[0049]

[0050] It can be seen from Table 3 that when the flame temperature is too high, silicon carbide crystal phase appears in the material, affecting the electrical properties of the material. Therefore, when the flame temperature is 600-800°C, the negative electrode material prepared has high discharge capacity and excellent rate performance.

Claims

1. A method for preparing a silicon-carbon negative electrode material, characterized in that: The following steps are involved: S1, injecting a mixed gas formed by silane, a gaseous carbon source and an inert gas into a plasma reactor at a pressure of 0.2-0.6 MPa to react instantly to prepare a silicon-carbon in-situ composite nanomaterial, and cooling the silicon-carbon in-situ composite nanomaterial; S2, coating and granulating the asphalt or resin with the silicon-carbon in-situ composite nanomaterial prepared in step S1, and carbonizing them again in a carbonization furnace; S3, mixing and screening the carbonized materials in step S2 to remove iron to obtain a finished silicon-carbon negative electrode material.

2. The method for preparing the silicon-carbon negative electrode material according to claim 1, characterized in that: The silane in step S1 is a combination of one or more of monosilane, disilane, trisilane, monochlorosilane, dichlorosilane, trichlorosilane and tetrachlorosilane.

3. The method for preparing the silicon-carbon negative electrode material according to claim 1, characterized in that: The gaseous carbon source in step S1 includes one or more of methane, ethane, propane, acetylene and ethylene.

4. The method for preparing the silicon-carbon negative electrode material according to claim 1, characterized in that: In step S1, the volume ratio of silane to gaseous carbon source is (1-4):

1.

5. The method for preparing the silicon-carbon negative electrode material according to claim 1, characterized in that: The flow rate of the mixed gas in step S1 is 10 to 2000 L / h.

6. The method for preparing the silicon-carbon negative electrode material according to claim 1, characterized in that: The plasma flame temperature in the plasma reactor in step S1 is 600-800° C., and the power of the plasma reactor is 50-120 kW.

7. The method for preparing the silicon-carbon negative electrode material according to claim 1, characterized in that: The plasma excitation gas of the plasma reactor in step S1 is nitrogen or argon, and the flow rate of the plasma excitation gas is 100-200 sccm.

8. The method for preparing the silicon-carbon negative electrode material according to claim 1, characterized in that: The asphalt or resin in step S2 accounts for 5-20% of the mass ratio of the silicon-carbon in-situ composite nanomaterial.

9. The method for preparing the silicon-carbon negative electrode material according to claim 1, characterized in that: The carbonization process in step S2 is to maintain the temperature of the carbonization furnace at 700-1000° C. and react at a constant temperature for 1-10 hours.

10. A silicon-carbon negative electrode material, characterized in that: The silicon-carbon negative electrode material is prepared by the preparation method of any one of claims 1 to 9.

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