A silicon-carbon negative electrode composite material and its preparation method and application in lithium-ion batteries

Abstract

The present invention discloses a silicon-carbon negative electrode composite material, a preparation method thereof, and an application thereof in lithium-ion batteries. The preparation method comprises: using silicon powder as a raw material to generate silicon vapor in a high-temperature negative pressure environment by physical vapor deposition, and then depositing the silicon vapor on a carbon material substrate in a low-temperature zone under the purge of a carrier gas flow; finally, using hydrocarbon gas as a raw material, a carbon coating layer is formed on the surface of the material by chemical vapor deposition, and finally a silicon-carbon negative electrode composite material is obtained. The silicon-carbon interface inside the silicon-carbon negative electrode composite material is a face-to-face combination connected by Si-C chemical bonds. The strong chemical bond can suppress the volume expansion of silicon during the lithium insertion process, and can also enhance the transfer of electrons / ions at the silicon-carbon interface, effectively enhancing the lithium storage performance of the material as a negative electrode material.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-ion batteries, and in particular relates to a silicon-carbon negative electrode composite material, a preparation method thereof, and an application thereof in lithium-ion batteries. Background Art

[0002] With the rapid development of science and technology, portable electronic devices and electric vehicles are becoming increasingly popular, and the demand for high-performance lithium-ion batteries is constantly rising. Silicon-based negative electrode materials have attracted much attention due to their high specific capacity. However, their poor conductivity and huge volume effect during charging and discharging have become technical bottlenecks. The emergence of silicon-carbon composite materials provides a solution to this problem. It combines the high specific capacity of silicon with the stability of carbon materials, effectively alleviating the volume expansion problem of silicon and improving the cycle stability and rate performance of the battery. At present, although there has been some research on silicon-carbon composite materials, how to further develop safer and lower-cost nano-silicon preparation technology and improve the bonding strength between silicon and carbon are still urgent problems to be solved. Summary of the Invention

[0003] The purpose of the present invention is to provide a silicon-carbon negative electrode composite material, its preparation method and application in lithium-ion batteries, wherein the silicon vapor generated by silicon powder in a high-temperature negative pressure environment is transferred to a lower temperature zone by physical vapor deposition, and then condensed into nano-silicon on a carbon material substrate, and finally a complete carbon coating layer is formed on the surface of the silicon-carbon composite material by chemical vapor deposition. The efficient conductive network synergistically formed by the carbon material and the carbon coating greatly enhances the electron transmission rate. The face-to-face bonding of silicon and the carbon material substrate connected by Si-C bonds can enhance the conduction of electrons / ions at the silicon-carbon interface. At the same time, the strong bonding between silicon and carbon is also conducive to suppressing the volume expansion of silicon. Based on the optimized design of the structure and interface, the material provided by the present invention has excellent lithium storage performance.

[0004] To achieve the above object, the present invention provides the following technical solutions:

[0005] The method for preparing the silicon-carbon negative electrode composite material provided by the present invention comprises the following steps:

[0006] Step S1: placing silicon powder in a high-temperature evaporation zone of a physical vapor deposition furnace, and placing a carbon material substrate in a low-temperature deposition zone of the physical vapor deposition furnace;

[0007] Then the high temperature evaporation area and the low temperature deposition area are vacuumed.

[0008] The high-temperature evaporation zone and the low-temperature deposition zone are then heated to their respective target temperatures. Inert gas is then introduced while pressure is controlled to deposit silicon onto the surface of the carbon material substrate. During this deposition process, the silicon and the carbon material substrate are bonded face-to-face via Si-C chemical bonds, yielding a carbon material / nano-silicon composite powder containing a Si-C chemical bond layer.

[0009] Step S2: Place the carbon material / nano-silicon composite powder obtained in step S1 in a chemical vapor deposition furnace, evacuate the furnace, raise the temperature in the furnace to the target temperature, introduce a hydrocarbon gas / inert gas mixture for chemical vapor deposition, and form a carbon coating layer on the outer surface of the carbon material / nano-silicon composite powder to finally obtain a silicon-carbon negative electrode composite material.

[0010] Preferably, in step S1, the particle size of the silicon powder includes nanometer level, micrometer level and centimeter level, and the purity is above 90%.

[0011] Preferably, in step S1, the mass ratio of the silicon powder to the carbon material substrate is 1:0.15-0.35.

[0012] Preferably, in step S1, the carbon material substrate is graphite, graphene, etc., and its shape can be flake, spherical, square, etc. The surface of the carbon material substrate includes an open outer surface and an internal pore structure such as open pores and through holes.

[0013] Further preferably, the carbon material substrate is a graphite sheet with a sheet diameter of less than 50 μm and a purity of more than 99%.

[0014] In some specific embodiments, when the carbon material substrate is a graphite sheet, in step S1:

[0015] The vacuum in the high-temperature evaporation zone and low-temperature deposition zone of the physical vapor deposition furnace is ≤0.01Mpa;

[0016] The temperature of the high temperature evaporation zone is above 1400°C, preferably 1450°C to 2000°C;

[0017] The temperature of the low-temperature deposition zone is 800-1200°C;

[0018] The inert gas flow rate during the deposition process is 250-750 mL / min; the inert gas is argon, and the purity of argon is above 99.99%;

[0019] The pressure in the high-temperature evaporation zone and the low-temperature deposition zone is controlled at 100-200 Pa;

[0020] The deposition time is 1 to 2 hours.

[0021] Preferably, the vacuum during the heating process of the chemical vapor deposition furnace in step S2 is ≤0.01 MPa;

[0022] Preferably, the temperature of the chemical vapor deposition process in step S2 is 1000-1100° C.;

[0023] Preferably, in the hydrocarbon gas / inert gas mixture introduced into the chemical vapor deposition process in step S2, the flow ratio of hydrocarbon gas to inert gas is 1:8-10; the hydrocarbon gas includes any one of methane, ethane, propane, ethylene, propylene, and acetylene, with a purity of more than 99.99%; and the inert gas is argon.

[0024] Preferably, the chemical vapor deposition time in step S2 is 5 to 20 minutes.

[0025] The silicon-carbon negative electrode composite material is prepared according to the above preparation method.

[0026] The silicon-carbon negative electrode composite material comprises a carbon material / nano-silicon composite powder and a carbon coating layer; the carbon coating layer is wrapped around the outer surface of the carbon material / nano-silicon composite powder; the carbon material / nano-silicon composite powder is formed by nano-silicon deposited on the surface of a carbon material substrate, wherein a Si-C bond layer is present at the interface between the nano-silicon and the carbon material substrate, formed by face-to-face bonding via Si-C chemical bonds.

[0027] Preferably, in the carbon material / nano-silicon composite powder, the nano-silicon exists in the form of discontinuous islands on the surface of the carbon material substrate.

[0028] In the silicon-carbon negative electrode composite material, the mass proportion of nano-silicon is ≤70%.

[0029] Application of the silicon-carbon negative electrode composite material in lithium-ion batteries.

[0030] Specifically, the silicon-carbon negative electrode composite material is mixed with a conductive agent and a binder to form a slurry, which is then coated on a copper foil to form a negative electrode sheet for a lithium-ion battery.

[0031] In some specific implementation cases, in order to test the electrochemical performance of the silicon-carbon negative electrode composite material, a lithium-ion battery testing system consisting of two electrodes was constructed. The system uses the silicon-carbon negative electrode composite material as the working electrode and a high-purity lithium sheet as the counter electrode. For the electrolyte, 1M LiPF6 was used. LiPF6 was dissolved in a solvent mixed with ethylene carbonate (EC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) in a volume ratio of 1:1:1, and an additional 5% of the total weight of fluoroethylene carbonate (FEC) was added to improve battery performance. The battery assembly process was carried out precisely in an argon-filled glove box to ensure the stability and consistency of the assembly environment. Finally, the charge and discharge experiments of the lithium-ion battery were carried out on the blue battery test system to ensure the accuracy and reliability of the test results.

[0032] Principles and beneficial effects of the present invention:

[0033] (1) The silicon-carbon negative electrode composite material described in the present invention uses silicon powder as raw material and grows nano-silicon on the surface of the carbon material substrate from bottom to top through physical vapor deposition. This method involves stable raw materials and no risk of explosion. At the same time, no toxic or harmful by-products are produced during the entire preparation process.

[0034] (2) During the preparation of silicon-carbon anode composite materials, the negative pressure deposition environment is conducive to the diffusion and mixing of the reaction gases, thereby improving the reaction rate and deposition efficiency. In addition, the negative pressure environment can reduce the mean free path of gas molecules, making it easier for the reaction gases to evenly reach any open surface of the substrate (including pore structures such as openings and through-holes), thereby generating a more evenly distributed deposit. The reaction gases here include silicon vapor involved in the physical vapor deposition process and hydrocarbon gases in the chemical vapor deposition process.

[0035] (3) The silicon-carbon negative electrode composite material of the present invention utilizes silicon vapor to form silicon droplets during the condensation process on the surface of the carbon material substrate. These silicon droplets are combined with the carbon material substrate in a face-to-face manner driven by surface tension.

[0036] (4) The Si-C bond formed at the interface of the silicon and carbon material substrate in the silicon-carbon negative electrode composite material of the present invention is a strong bond composed of chemical bonds, which can ensure that the silicon maintains electrical contact with the carbon material substrate during the continuous lithium insertion / delithiation process.

[0037] (5) In the silicon-carbon anode composite material of the present invention, the nano-silicon deposited on the surface is optimally distributed as discontinuous islands, which facilitates the release of internal stress in the lithium-intercalated silicon, thereby maintaining structural stability. The formation of discontinuous islands of deposited silicon on the surface of the deposition substrate is primarily achieved by controlling parameters such as deposition temperature, deposition gas flow, and deposition time.

[0038] (6) The silicon-carbon negative electrode composite material described in the present invention uses hydrocarbon gas as raw material, and forms a uniform high-conductivity carbon coating layer on the surface of the material through chemical vapor deposition. Such a structure is conducive to improving the conductivity and stability of the electrode.

[0039] (7) The silicon-carbon negative electrode composite material described in the present invention has excellent cycle stability, high reversible specific capacity and rate performance when applied to lithium-ion batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 Schematic diagram of the structure of the silicon-carbon negative electrode composite material of Examples 1 to 3.

[0041] Among them, 1 is a graphite sheet; 2 is a bonding layer connected by Si-C bonds; 3 is nano-silicon; and 4 is a carbon coating layer.

[0042] Figure 2 1 and 2 are XRD patterns of the silicon-carbon negative electrode composite materials prepared in Example 1 and Comparative Example 1 of the present invention.

[0043] Figure 3 This is an SEM image of the silicon-carbon negative electrode composite material prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0044] The technical solutions provided by the present invention are described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0045] Example 1

[0046] The method comprises placing silicon powder in a high-temperature evaporation zone of a physical vapor deposition furnace, and placing a graphite sheet in a low-temperature deposition zone of the physical vapor deposition furnace, wherein the mass ratio of silicon powder to graphite sheet is 1:0.15; then evacuating the high-temperature evaporation zone and the low-temperature deposition zone to a vacuum of ≤0.01 MPa; then raising the temperature in the high-temperature evaporation zone to 1450° C. and the temperature in the low-temperature deposition zone to 800° C., introducing argon gas at a flow rate of 250 mL / min, and controlling the pressure in the high-temperature evaporation zone and the low-temperature deposition zone to 100 Pa for silicon deposition for 1 hour, so that silicon is deposited on the surface of the graphite sheet, and obtaining a graphite sheet / nano-silicon composite powder containing a Si-C chemical bond layer;

[0047] The graphite sheet / nano-silicon composite powder was placed in a chemical vapor deposition furnace, the chemical vapor deposition furnace was evacuated, the temperature of the deposition furnace was raised to 1000°C, and a methane / argon mixed gas with a flow ratio of 1:8 was introduced for deposition for 5 minutes to obtain a silicon-carbon negative electrode composite material.

[0048] The XRD pattern of the silicon-carbon negative electrode composite material prepared in this embodiment is shown in Figure 2 As shown. Figure 2 It can be seen that trace SiC crystals are formed in the silicon-carbon negative electrode composite material, indicating that Si-C bond connections are formed during the deposition of silicon on the graphite sheet substrate by physical vapor deposition.

[0049] The SEM image of the silicon-carbon negative electrode composite material prepared in this embodiment is shown in Figure 3 As shown, from Figure 3 It can be seen that nano-silicon exists in the form of discontinuous islands on the graphite substrate.

[0050] Example 2

[0051] The method comprises placing silicon powder in a high-temperature evaporation zone of a physical vapor deposition furnace, and placing a graphite sheet in a low-temperature deposition zone of the physical vapor deposition furnace, wherein the mass ratio of silicon powder to graphite sheet is 1:0.25; then evacuating the high-temperature evaporation zone and the low-temperature deposition zone to a vacuum of ≤0.01 MPa; then raising the temperature in the high-temperature evaporation zone to 1525° C., and the temperature in the low-temperature deposition zone to 1000° C., introducing argon gas at a flow rate of 500 mL / min, and controlling the pressure in the high-temperature evaporation zone and the low-temperature deposition zone to 150 Pa to deposit silicon for 1.5 hours, so that silicon is deposited on the surface of the graphite sheet, and obtaining a graphite sheet / nano-silicon composite powder containing a Si-C chemical bond layer;

[0052] The graphite sheet / nano-silicon composite powder was placed in a chemical vapor deposition furnace, the chemical vapor deposition furnace was evacuated, the temperature of the deposition furnace was raised to 1050°C, and a methane / argon mixed gas with a flow ratio of 1:9 was introduced for deposition for 10 minutes to obtain a silicon-carbon negative electrode composite material.

[0053] Example 3

[0054] The method comprises placing silicon powder in a high-temperature evaporation zone of a physical vapor deposition furnace, and placing a graphite sheet in a low-temperature deposition zone of the physical vapor deposition furnace, wherein the mass ratio of silicon powder to graphite sheet is 1:0.35; then evacuating the high-temperature evaporation zone and the low-temperature deposition zone to a vacuum pressure of ≤0.01 MPa; then raising the temperature in the high-temperature evaporation zone to 1600° C. and the temperature in the low-temperature deposition zone to 1200° C., introducing argon gas at a flow rate of 750 mL / min, and controlling the pressure in the high-temperature evaporation zone and the low-temperature deposition zone to 200 Pa for silicon deposition for 2 hours, so that silicon is deposited on the surface of the graphite sheet, and obtaining a graphite sheet / nano-silicon composite powder containing a Si-C chemical bond layer;

[0055] The graphite sheet / nano-silicon composite powder was placed in a chemical vapor deposition furnace, the chemical vapor deposition furnace was evacuated, the temperature of the deposition furnace was raised to 1100° C., and a methane / argon mixed gas with a flow ratio of 1:10 was introduced for deposition for 20 min to obtain a silicon-carbon negative electrode composite material.

[0056] Comparative Example 1

[0057] Nano-silicon powder (particle size of 100 nm) and graphite flakes were ground and mixed in a mass ratio of 0.65:0.35 for 30 min to obtain a graphite flake-nano-silicon mixed powder.

[0058] The graphite sheet-nanosilicon mixed powder was placed in a chemical vapor deposition furnace, the chemical vapor deposition furnace was evacuated, the temperature of the deposition furnace was raised to 1100°C, and a methane / argon mixed gas with a flow ratio of 1:10 was introduced for deposition for 20 minutes to obtain a silicon-carbon negative electrode composite material (graphite sheet-nanosilicon-carbon coating powder).

[0059] The XRD pattern of the silicon-carbon negative electrode composite material prepared in this comparative example is shown in FIG. Figure 2 As shown. Figure 2 It can be seen that no SiC crystals are produced in the silicon-carbon negative electrode composite material, indicating that no Si-C bond connection is formed during the ordinary grinding and mixing process.

[0060] In a specific embodiment of the present invention, in order to test the electrochemical performance of the silicon-carbon negative electrode composite material, the silicon-carbon negative electrode composite materials prepared in Examples 1 to 3 and Comparative Example 1 were respectively assembled into half-cells. The present invention constructs a lithium-ion battery testing system consisting of two electrodes. The system specifically selects the silicon-carbon negative electrode composite material as the working electrode and uses a high-purity lithium sheet as the counter electrode. As for the electrolyte, 1M LiPF6 was used. LiPF6 was dissolved in a solvent composed of ethylene carbonate (EC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) in a volume ratio of 1:1:1, and 5% of the total weight of fluoroethylene carbonate (FEC) was additionally added to improve battery performance. The battery assembly process was carried out precisely in an argon-filled glove box to ensure the stability and consistency of the assembly environment. Finally, the charge and discharge experiments of the lithium-ion battery were carried out on a blue battery testing system to ensure the accuracy and reliability of the test results. The results are shown in Table 1.

[0061] Table 1 Electrochemical performance test results of silicon-carbon negative electrode composite materials

[0062]

[0063] From the data in Table 1, it can be seen that the capacity of the silicon-carbon negative electrode composite material of the present invention reaches 1035.1~1304.3mAh / g, the first coulombic efficiency is 83.1~85.7%, and the capacity retention rate after 100 cycles is as high as 92.4%; while the coulombic efficiency of the silicon-carbon negative electrode composite material prepared in Comparative Example 1 is 80.6%, and the capacity retention rate after 100 cycles is 75.61%, which is lower than that of Examples 1 to 3. This is because the silicon-carbon negative electrode composite material prepared in Comparative Example 1 by simple mechanical mixing does not contain a bonding interface formed by Si-C bonds.

Claims

1. A method for preparing a silicon-carbon negative electrode composite material, comprising the following steps: Step S1: placing silicon powder in a high-temperature evaporation zone of a physical vapor deposition furnace, and placing a carbon material substrate in a low-temperature deposition zone of the physical vapor deposition furnace; Then the high temperature evaporation area and the low temperature deposition area are vacuumed. The high-temperature evaporation zone and the low-temperature deposition zone are then heated to their respective target temperatures. Inert gas is then introduced while pressure is controlled to deposit silicon onto the surface of the carbon material substrate. During this deposition process, the silicon and the carbon material substrate are bonded face-to-face via Si-C chemical bonds, yielding a carbon material / nano-silicon composite powder containing a Si-C chemical bond layer. Step S2: Place the carbon material / nano-silicon composite powder obtained in step S1 in a chemical vapor deposition furnace, evacuate the furnace, raise the temperature in the furnace to the target temperature, introduce a hydrocarbon gas / inert gas mixture for chemical vapor deposition, and form a carbon coating layer on the outer surface of the carbon material / nano-silicon composite powder to finally obtain a silicon-carbon negative electrode composite material.

2. The preparation method according to claim 1, characterized in that In step S1, the particle size of the silicon powder includes nanometer level, micrometer level and centimeter level, and the purity is above 90%.

3. The preparation method according to claim 1, characterized in that In step S1, the mass ratio of the silicon powder to the carbon material substrate is 1:0.15-0.

35.

4. The preparation method according to claim 1, characterized in that In step S1, the carbon material substrate includes any one of graphite and graphene, and its shape includes any one of flake, spherical, and square; the surface of the carbon material substrate includes an open outer surface, and an internal open hole and through hole structure.

5. The preparation method according to claim 4, characterized in that When the carbon material substrate is a graphite sheet, the sheet diameter of the graphite sheet is less than 50 μm and the purity is more than 99%; when the carbon material substrate is a graphite sheet, in step S1: The vacuum in the high-temperature evaporation zone and low-temperature deposition zone of the physical vapor deposition furnace is ≤0.01MPa; The temperature of the high-temperature evaporation zone is above 1400°C, and the temperature of the low-temperature deposition zone is 800-1200°C; The inert gas flow rate during the deposition process is 250-750 mL / min; the inert gas is argon, and the purity of argon is above 99.99%; The pressure in the high-temperature evaporation zone and the low-temperature deposition zone is controlled at 100-200 Pa; The deposition time is 1 to 2 hours.

6. The preparation method according to claim 1, characterized in that In step S2: the vacuum during the heating process of the chemical vapor deposition furnace is ≤0.01 MPa; The temperature of the chemical vapor deposition process is 1000-1100°C; In the hydrocarbon gas / inert gas mixture introduced during the chemical vapor deposition process, the flow ratio of hydrocarbon gas to inert gas is 1:8-10; the hydrocarbon gas includes any one of methane, ethane, propane, ethylene, propylene, and acetylene, with a purity of more than 99.99%; the inert gas is argon; The chemical vapor deposition time is 5 to 20 minutes.

7. A silicon-carbon negative electrode composite material prepared according to the preparation method according to any one of claims 1 to 6.

8. The silicon-carbon negative electrode composite material according to claim 7, characterized in that The silicon-carbon negative electrode composite material comprises a carbon material / nano-silicon composite powder and a carbon coating layer; the carbon coating layer is wrapped around the outer surface of the carbon material / nano-silicon composite powder; the carbon material / nano-silicon composite powder is formed by nano-silicon deposited on the surface of a carbon material substrate, wherein a Si-C bond layer is present at the interface between the nano-silicon and the carbon material substrate, formed by face-to-face bonding via Si-C chemical bonds.

9. The silicon-carbon negative electrode composite material according to claim 7, characterized in that In the silicon-carbon negative electrode composite material, the mass proportion of nano-silicon is ≤70%.

10. Use of the silicon-carbon negative electrode composite material prepared by the preparation method according to any one of claims 1 to 6 or the silicon-carbon negative electrode composite material according to any one of claims 7 to 9 in a lithium-ion battery.

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