Method for preparing silicon negative electrode material by taking SiF4 as raw material

Abstract

The invention provides a method for preparing a silicon negative electrode material by taking SiF4 as a raw material, and belongs to the field of battery negative electrode materials. According to the method for preparing the silicon negative electrode material by taking SiF4 as the raw material, silicon tetrafluoride is adopted as a silicon source, and microcrystalline silicon and amorphous silicon can be obtained at the same time by controlling the placement position of the substrate, sensing the radio frequency power of the radio frequency coil and the temperature of the reaction region; by controlling the proportion of the silicon tetrafluoride, the hydrogen and the argon, the silicon material which can be used for the negative electrode of the lithium ion battery can be further obtained. According to the method provided by the invention, the microcrystalline silicon and the amorphous silicon can be simultaneously obtained, and the lithium ion battery prepared from the microcrystalline silicon and the amorphous silicon has relatively good cycle life and coulombic efficiency and can be used as a negative electrode material.

Description

Technical Field

[0001] The present invention relates to the field of battery anode materials, and particularly to a method for preparing silicon anode materials using SiF4 as a raw material. Background Art

[0002] In recent years, the rapid growth in the number of new energy vehicles has continuously increased the demand for positive and negative electrode materials. In the development of consumer and power batteries, the demand for high-energy density batteries has also been increasing. As an important component of lithium batteries, the initial Coulombic efficiency and cycle stability of the anode material are important factors affecting the cycle life of the battery system, and the energy density of the anode material is an important factor determining the energy density and power density of the battery system.

[0003] Silicon-based anode materials have high energy density (the theoretical specific capacity at room temperature is as high as 3590 mAh / g), a lower discharge platform (0.4V vs. Li), and are rich in reserves and low in price. They are one of the most promising next-generation lithium-ion battery anode materials. There are various existing methods for preparing nano-silicon powder. Among them, the products prepared by chemical vapor deposition have the advantages of high initial charge-discharge efficiency, good cycle stability, low equipment requirements, and suitability for industrial production. Therefore, chemical vapor deposition is widely used. Currently, chemical vapor deposition mainly uses silane gas as a raw material. Electronic-grade silane gas is mainly used in fields such as solar cell panels and liquid crystal display panels. However, due to its high price and inconvenient transportation, its application is limited to a certain extent.

[0004] The tail gas in the wet-process phosphoric acid production process contains a large amount of silicon tetrafluoride gas. Industrially, water is usually directly used to absorb silicon tetrafluoride to produce a 10-15 wt% fluosilicic acid solution. If silicon tetrafluoride gas can be used as a raw material to prepare silicon anode materials, it is expected to reduce the production cost of silicon-based anode materials. Silicon anode materials include microcrystalline silicon and amorphous silicon. In the existing technology, the preparation of silicon anodes usually can only prepare microcrystalline silicon or amorphous silicon separately. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for preparing silicon anode materials using SiF4 as a raw material. The method provided by the present invention can use SiF4 gas as a silicon source to simultaneously prepare microcrystalline silicon and amorphous silicon.

[0006] To achieve the above invention purpose, the present invention provides the following technical solutions:

[0007] The present invention provides a method for preparing silicon anode materials using SiF4 as a raw material, including:

[0008] Performing plasma-enhanced chemical vapor deposition on a substrate in a mixed gas of silicon tetrafluoride, hydrogen, and argon to obtain a silicon anode material;

[0009] The plasma enhanced chemical vapor deposition is carried out in an inductively coupled plasma reaction chamber; the inductively coupled plasma reaction chamber includes a reaction cavity body and an inductive radio frequency coil; both ends of the reaction cavity body are an air inlet and an air outlet respectively; the reaction cavity body includes a first reaction zone and a second reaction zone which are arranged in sequence along the direction of the air inlet; the inductive radio frequency coil is arranged outside the first reaction zone;

[0010] The plasma enhanced chemical vapor deposition is as follows: after placing a first substrate in the first reaction zone and a second substrate in the second reaction zone, introducing silicon tetrafluoride, hydrogen and argon into the reaction cavity body from the air inlet, controlling the radio frequency power of the inductive radio frequency coil to be 180 - 220 W, the temperature of the first reaction zone to be 150 - 250 °C, and the temperature of the second reaction zone to be 300 - 500 °C, microcrystalline silicon is obtained on the surface of the first substrate, and amorphous silicon is obtained on the surface of the second substrate;

[0011] The flow rate ratio of the silicon tetrafluoride, hydrogen and argon is 1:(1.01 - 2):(1.01 - 2).

[0012] Preferably, the silicon tetrafluoride is obtained by recycling industrial waste gas.

[0013] Preferably, the flow rate ratio of the silicon tetrafluoride, hydrogen and argon is 1:(1.5 - 2):(1.5 - 2).

[0014] Preferably, the flow rate of the silicon tetrafluoride is 5 - 8 sccm.

[0015] Preferably, the substrate includes a single crystal silicon substrate, a stainless steel mesh substrate or a silicon carbide substrate.

[0016] Preferably, the reaction cavity body is evacuated before the plasma enhanced chemical vapor deposition.

[0017] Preferably, the degree of vacuum for evacuation is 10 - 300 Pa.

[0018] Preferably, the time for the plasma enhanced chemical vapor deposition is 1 - 2 h.

[0019] Preferably, after the plasma enhanced chemical vapor deposition is completed, the obtained product is cooled in argon and then peeled off from the substrate.

[0020] Preferably, the flow rate of the argon is 10 - 40 sccm.

[0021] The present invention provides a method for preparing a silicon negative electrode material using SiF4 as a raw material, comprising: performing plasma-enhanced chemical vapor deposition on a substrate in a mixed gas of silicon tetrafluoride, hydrogen, and argon to obtain the silicon negative electrode material; the plasma-enhanced chemical vapor deposition is carried out in an inductively coupled plasma reaction chamber; the inductively coupled plasma reaction chamber includes a reaction cavity and an inductive radio frequency coil; both ends of the reaction cavity are respectively an air inlet and an air outlet; the reaction cavity includes a first reaction zone and a second reaction zone sequentially arranged along the air inlet direction; the inductive radio frequency coil is arranged outside the first reaction zone; the plasma-enhanced chemical vapor deposition is as follows: after placing a first substrate in the first reaction zone and a second substrate in the second reaction zone, introducing silicon tetrafluoride, hydrogen, and argon into the reaction cavity through the air inlet, controlling the radio frequency power of the inductive radio frequency coil to be 180-220 W, the temperature of the first reaction zone to be 150-250 °C, and the temperature of the second reaction zone to be 300-500 °C, obtaining microcrystalline silicon on the surface of the first substrate and amorphous silicon on the surface of the second substrate; the flow rate ratio of silicon tetrafluoride, hydrogen, and argon is 1:(1.01-2):(1.01-2). By using silicon tetrafluoride as a silicon source, controlling the placement position of the substrate, the radio frequency power of the inductive radio frequency coil, and the temperature of the reaction zone, the crystal form of the silicon single crystal film on the first substrate can gradually change from amorphous to microcrystalline at a temperature of 150-250 °C, enhancing the surface migration ability of silicon atoms, promoting grain growth, and obtaining microcrystalline silicon; enabling the silicon single crystal film on the second substrate to be deposited to form amorphous silicon at a temperature of 300-500 °C; by controlling the ratio of silicon tetrafluoride, hydrogen, and argon, controlling the plasma density and deposition rate, thereby affecting the particle size and refining the particle size distribution, which helps to form micron-sized crystalline silicon on the first substrate and makes the crystal form of the crystalline silicon complete, and can also help to form amorphous silicon on the second substrate. The results of the examples show that the method provided by the present invention can obtain microcrystalline silicon and amorphous silicon simultaneously; the lithium-ion battery prepared from the microcrystalline silicon negative electrode material can reach an initial discharge specific capacity of 3185.95 mAh / g, a first Coulomb efficiency of 70.09%, a first charge specific capacity of 2232.90 mAh / g, and a charge specific capacity of 748.36 mAh / g after 100 cycles at a current density of 0.1 A / g, having good cycle life and Coulomb efficiency; the lithium-ion battery prepared from the amorphous silicon negative electrode material can reach an initial discharge specific capacity of 2161.98 mAh / g, a first Coulomb efficiency of 35.37%, a first charge specific capacity of 764.72 mAh / g, and a charge specific capacity of 588.49 mAh / g after 100 cycles at a current density of 0.1 A / g. The lithium-ion batteries prepared from microcrystalline silicon and amorphous silicon have good cycle life and Coulomb efficiency and can be used as negative electrode materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1The flowchart of the preparation method of the silicon negative electrode material in the embodiment of the present invention. Among them, 1 is a hydrogen generator, 2 is a one-way valve, 3 is a gas mass flow controller, 4 is a radio frequency power supply, 5 is an induction radio frequency coil, 6 is a tube furnace, 7 is a vacuum pump, and 8 is a tail gas absorption device;

[0023] Figure 2 The XRD pattern of the silicon negative electrode material (microcrystalline silicon) prepared in Example 3 of the present invention;

[0024] Figure 3 The XRD pattern of the silicon negative electrode material (amorphous silicon) prepared in Example 3 of the present invention;

[0025] Figure 4 The SEM image of the silicon negative electrode material (microcrystalline silicon) prepared in Example 3 of the present invention. Among them, the magnification of the left figure is 1000 times, and the magnification of the right figure is 10000 times;

[0026] Figure 5 The SEM image of the silicon negative electrode material (amorphous silicon) prepared in Example 3 of the present invention. Among them, the magnification of the left figure is 10000 times, and the magnification of the right figure is 20000 times;

[0027] Figure 6 The cycle performance diagram of the lithium-ion battery prepared from the microcrystalline silicon negative electrode material in Application Examples 1-3 of the present invention;

[0028] Figure 7 The cycle performance diagram of the lithium-ion battery prepared from the amorphous silicon negative electrode material in Application Examples 1-3 of the present invention;

[0029] Figure 8 The cycle performance diagram of the lithium-ion battery prepared from the microcrystalline silicon negative electrode material in Comparative Application Examples 1-2 of the present invention;

[0030] Figure 9 The cycle performance diagram of the lithium-ion battery prepared from the amorphous silicon negative electrode material in Comparative Application Examples 1-2 of the present invention. Detailed implementation manners

[0031] The present invention provides a method for preparing a silicon negative electrode material using SiF4 as a raw material, including:

[0032] Performing plasma-enhanced chemical vapor deposition on a substrate in a mixed gas of silicon tetrafluoride, hydrogen, and argon to obtain a silicon negative electrode material.

[0033] In the present invention, the silicon tetrafluoride is preferably recovered from industrial waste gas, more preferably silicon tetrafluoride recovered from tail gas generated during the production of wet phosphoric acid; the purity of the silicon tetrafluoride is preferably 99.999%. The present invention limits the purity of silicon tetrafluoride to the above range to improve the purity of the obtained silicon negative electrode. The present invention has no special restrictions on the separation and recovery operation of silicon tetrafluoride in the tail gas, and the separation and recovery operation commonly used in the industry in the field of silicon tetrafluoride in tail gas can be used.

[0034] As an embodiment of the present invention, the hydrogen is provided by a hydrogen generator. The present invention has no special limitation on the equipment and model of the hydrogen generator, and the equipment and model commonly used by those skilled in the art can be used.

[0035] In the present invention, the purity of the argon gas is preferably 99.99%.

[0036] In the present invention, the flow ratio of silicon tetrafluoride, hydrogen and argon is 1: (1.01-2): (1.01-2), preferably 1: (1.5-2): (1.5-2), and more preferably 1: (1.8-2): (1.8-2). In the present invention, limiting the flow ratio of silicon tetrafluoride, hydrogen and argon to the above range can facilitate the reduction reaction during the deposition process and obtain a silicon element (silicon negative electrode) with higher purity. In the present invention, the chemical equation of the reduction reaction is: SiF4+2H2=Si+4HF.

[0037] As an embodiment of the present invention, the flow rates of silicon tetrafluoride, hydrogen and argon can be controlled by a gas mass flow controller (MFC).

[0038] As an embodiment of the present invention, the flow rate of silicon tetrafluoride can be 5 to 8 sccm, or 6 to 7 sccm. The present invention limits the flow rate of silicon tetrafluoride to the above range, which is beneficial to the preparation of silicon negative electrode.

[0039] In the present invention, the substrate preferably includes a single crystal silicon substrate, a stainless steel mesh substrate or a silicon carbide substrate. The present invention limits the type of substrate to the above range, which is more conducive to the deposition of silicon on the substrate.

[0040] In the present invention, the substrate is preferably pretreated before use. As an embodiment of the present invention, the pretreatment may be cleaning. The present invention has no special limitation on the cleaning operation, and the conventional substrate cleaning operation in the art may be used to clean the substrate.

[0041] The plasma enhanced chemical vapor deposition is carried out in an inductively coupled plasma reaction chamber; the inductively coupled plasma reaction chamber includes a reaction cavity and an inductive radio frequency coil; two ends of the reaction cavity are respectively an air inlet and an air outlet; the reaction cavity includes a first reaction zone and a second reaction zone which are arranged in sequence along the air inlet direction; the inductive radio frequency coil is arranged outside the first reaction zone.

[0042] In the present invention, it is preferable to perform a vacuum pumping treatment on the inductively coupled plasma reaction chamber before the plasma enhanced chemical vapor deposition. As an embodiment of the present invention, the degree of vacuum for the vacuum pumping can be 10 - 300 Pa, can also be 20 - 200 Pa, and can also be 150 Pa; the equipment used for the vacuum pumping can be a vacuum pump; the pumping speed of the vacuum pump for the vacuum pumping can be 4 L / s. Performing a vacuum pumping treatment on the inductively coupled plasma reaction chamber before the plasma enhanced chemical vapor deposition in the present invention can avoid introducing impurities into the silicon negative electrode material. Limiting the pumping speed of the vacuum pump for the vacuum pumping to the above range in the present invention can avoid the reaction gases (silicon tetrafluoride, hydrogen, and argon) being pumped away, thereby affecting the deposition.

[0043] The plasma enhanced chemical vapor deposition is as follows: after placing a first substrate in the first reaction zone and a second substrate in the second reaction zone, silicon tetrafluoride, hydrogen, and argon are introduced into the reaction cavity through the air inlet, the radio frequency power of the inductive radio frequency coil is controlled to be 180 - 220 W, the temperature of the first reaction zone is 150 - 250 °C, and the temperature of the second reaction zone is 300 - 500 °C, and microcrystalline silicon is obtained on the surface of the first substrate, and amorphous silicon is obtained on the surface of the second substrate.

[0044] As an embodiment of the present invention, the radio frequency power of the inductive radio frequency coil can be 180 - 220 W, and can also be 200 W. Limiting the radio frequency power of the inductive radio frequency coil to the above range in the present invention can ensure that the deposited silicon negative electrode has better quality.

[0045] As an embodiment of the present invention, the temperature of the first reaction zone can be 150 - 250 °C, can also be 175 - 250 °C, can also be 200 - 250 °C, and can also be 225 - 250 °C. Limiting the temperature of the first reaction zone to the above range in the present invention can ensure the smooth progress of the reduction reaction and deposit microcrystalline silicon (silicon negative electrode material) with higher purity.

[0046] As an embodiment of the present invention, the temperature of the second reaction zone can be 300 - 500°C, or 350 - 500°C, or 400 - 500°C, or 450 - 500°C. By limiting the temperature of the second reaction zone within the above range, the present invention can ensure the smooth progress of the reduction reaction and deposit amorphous silicon (silicon anode material) with better quality.

[0047] As an embodiment of the present invention, part or all of the second reaction zone can be inside the tube furnace. In the embodiments of the present invention, the entire second reaction zone is inside the tube furnace. Defining the second reaction zone of the present invention to be entirely inside the tube furnace can better control the temperature of the second reaction zone.

[0048] As an embodiment of the present invention, the time of plasma enhanced chemical vapor deposition can be 1 - 2 h, or 1.5 h. By limiting the time of plasma enhanced chemical vapor deposition within the above range, the present invention can ensure the full progress of the reduction reaction, and thus the silicon in the silicon anode has a higher purity.

[0049] As an embodiment of the present invention, in the plasma enhanced chemical vapor deposition, the radio frequency power is controlled by a radio frequency power supply, and radio frequency signals are emitted and received through an induction radio frequency coil.

[0050] As an embodiment of the present invention, the temperatures of the first reaction zone and the second reaction zone in the plasma enhanced chemical vapor deposition can be controlled by a tube furnace; the tube furnace is arranged behind the induction radio frequency coil to heat the reaction chamber.

[0051] As an embodiment of the present invention, after the plasma enhanced chemical vapor deposition, the obtained product is cooled in argon and then peeled off from the substrate; the flow rate of the argon can be 10 - 40 sccm, or 30 sccm. By cooling in argon and limiting the flow rate of argon during the cooling process within the above range, the present invention can avoid the formation of other impurities in the obtained silicon anode and reduce the purity of the silicon in the silicon anode. The present invention has no special limitation on the peeling operation, as long as the product deposited on the substrate can be collected.

[0052] As an embodiment of the present invention, the tail gas generated during the plasma enhanced chemical vapor deposition process can be treated by a tail gas absorption device; the tail gas treatment liquid used in the tail gas absorption device can be sodium hydroxide solution; the concentration of the sodium hydroxide solution can be 0.05 - 1 wt%.

[0053] In the present invention, by using silicon tetrafluoride as the silicon source, controlling the placement position of the substrate, the radio frequency power of the inductive radio frequency coil, and the temperature of the reaction zone, the crystal form of the silicon elemental film on the first substrate can gradually change from amorphous to microcrystalline at a temperature of 150-250 °C, enhancing the surface migration ability of silicon atoms, promoting grain growth, and obtaining microcrystalline silicon; the silicon elemental film on the second substrate is deposited to form amorphous silicon at a temperature of 300-500 °C; by controlling the ratio of silicon tetrafluoride, hydrogen, and argon, the plasma density and deposition rate are controlled, thereby affecting the particle size and refining the particle size distribution, which helps the formation of micron-sized crystalline silicon on the first substrate and makes the crystal form of the crystalline silicon complete, and also helps the formation of amorphous silicon on the second substrate.

[0054] In a specific embodiment of the present invention, the flow chart of the preparation method of the silicon negative electrode material is as Figure 1 shown, where 1 is a hydrogen generator, 2 is a one-way valve, 3 is a gas mass flow controller, 4 is a radio frequency power supply, 5 is an inductive radio frequency coil, 6 is a tube furnace, 7 is a vacuum pump, and 8 is a tail gas absorption device.

[0055] In an embodiment of the present invention, the first substrate is placed in the area corresponding to the inductive radio frequency coil 5 (the first reaction zone), and the second substrate is placed in the area corresponding to the tube furnace 6 (the second reaction zone). First, the vacuum pump 7 is turned on to evacuate, and then the tube furnace 6 is turned on. The areas corresponding to the inductive radio frequency coil 5 (the first reaction zone) and the tube furnace 6 (the second reaction zone) are heated. Then, the switch of the radio frequency power supply 4 is turned on. When the area corresponding to the inductive radio frequency coil 5 (the first reaction zone) reaches 150-250 °C and the area corresponding to the tube furnace 6 (the second reaction zone) reaches 300-500 °C, the one-way valve 2 is opened to introduce argon, hydrogen, and silicon tetrafluoride respectively. After controlling the gas flow through the gas mass flow controller (MFC) 3 for plasma-enhanced chemical vapor deposition, the switch of the radio frequency power supply 4 is turned off, the switch of the one-way valve 2 is controlled, hydrogen and silicon tetrafluoride are turned off, and argon is retained to be introduced to cool the plasma-enhanced chemical vapor deposition product. After the cooling is completed, the vacuum pump 7 is turned off, and the plasma-enhanced chemical vapor deposition product is peeled off from the substrate (the first substrate and the second substrate) to obtain the silicon negative electrode material (microcrystalline silicon and amorphous silicon). The tail gas generated during the plasma-enhanced chemical vapor deposition process is absorbed by the tail gas absorption device 8.

[0056] The present invention also provides a silicon negative electrode material prepared by the preparation method described in the above technical solution, and the silicon negative electrode material is microcrystalline silicon and amorphous silicon.

[0057] As an implementation manner of the present invention, the particle size of the microcrystalline silicon can be 2-10 μm, and the particle size of the amorphous silicon can be 1-5 μm.

[0058] The present invention also provides the application of the silicon negative electrode material described in the above technical solution in the negative electrode of a lithium-ion battery.

[0059] The present invention also provides a negative electrode for a lithium-ion battery, which includes a current collector and a negative electrode material coated on the surface of the current collector, and the negative electrode material includes the silicon negative electrode material described in the above technical solution.

[0060] As an embodiment of the present invention, the current collector may be a copper foil.

[0061] As an embodiment of the present invention, the preparation method of the negative electrode for a lithium-ion battery may be:

[0062] Mix the silicon negative electrode material, conductive carbon black and sodium alginate described in the above technical solution and make a slurry to obtain a slurry.

[0063] Coat the slurry on a copper foil and dry it to obtain a negative electrode sheet for a lithium-ion battery.

[0064] The present invention can mix the silicon negative electrode material, conductive carbon black and sodium alginate described in the above technical solution and make a slurry to obtain a slurry.

[0065] As an embodiment of the present invention, the mass ratio of the silicon negative electrode material, conductive carbon black and sodium alginate may be 8:1:1.

[0066] As an embodiment of the present invention, the solid content of the slurry may be 45-60%. Limiting the solid content of the slurry within the above range in the present invention is beneficial to subsequent coating.

[0067] After obtaining the slurry, the present invention can coat the slurry on a copper foil and dry it to obtain a negative electrode for a lithium-ion battery.

[0068] The present invention has no special limitation on the coating amount and coating method of the coating, and can make the amount of the active substance (silicon negative electrode material) on the copper foil be 0.4-0.6 mg / cm 2 That's all.

[0069] As an embodiment of the present invention, the drying can be carried out in a vacuum drying oven; the drying temperature can be 60°C; the drying time can be 12 h.

[0070] As an embodiment of the present invention, after drying, the copper foil coated with the slurry can be cut, and the copper foil coated with the slurry can be cut into circular electrode sheets with a diameter of 10 mm.

[0071] The present invention also provides a lithium-ion battery, which includes the negative electrode for a lithium-ion battery, a positive electrode, a positive electrode case, a negative electrode case, a gasket, a spring piece, a separator and an electrolyte described in the above technical solution.

[0072] As an embodiment of the present invention, the method for preparing the lithium-ion battery may include assembling the negative electrode, positive electrode, separator, and electrolyte of the lithium-ion battery described in the above technical solution to obtain a lithium-ion battery.

[0073] As an embodiment of the present invention, the positive electrode may be a lithium sheet; the separator may be polypropylene (PP); the concentration of the lithium salt in the electrolyte may be 1 M; the lithium salt may be LiPF6; the organic solvent in the electrolyte may be ethylene carbonate (EC) and dimethyl carbonate (DMC); the volume ratio of ethylene carbonate (EC) to dimethyl carbonate (DMC) may be 1:1; the additive in the electrolyte may be fluoroethylene carbonate (FEC); the addition amount of fluoroethylene carbonate (FEC) may be 10% of the total volume of the electrolyte.

[0074] As an embodiment of the present invention, the assembly may be carried out in a glove box. The present invention has no special limitation on the operation of the assembly, and the operations commonly used by those skilled in the art can be adopted.

[0075] Next, the technical solutions in the present invention will be clearly and completely described in conjunction with the embodiments in the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present invention without making creative efforts shall fall within the protection scope of the present invention.

[0076] Example 1

[0077] A method for preparing a silicon negative electrode material using SiF4 as a raw material:

[0078] Performing plasma-enhanced chemical vapor deposition on a substrate in a mixed gas of silicon tetrafluoride, hydrogen, and argon to obtain a silicon negative electrode material;

[0079] The plasma-enhanced chemical vapor deposition is carried out in an inductively coupled plasma reaction chamber; the inductively coupled plasma reaction chamber includes a reaction cavity and an inductive radio frequency coil; both ends of the reaction cavity are an air inlet and an air outlet respectively; the reaction cavity includes a first reaction zone and a second reaction zone arranged in sequence along the air inlet direction; an inductive radio frequency coil is arranged outside the first reaction zone;

[0080] The plasma-enhanced chemical vapor deposition process is as follows: Place the first substrate (stainless steel mesh substrate) in the first reaction zone and the second substrate (stainless steel mesh substrate) in the second reaction zone (the entire second reaction zone is inside the tube furnace). Then, turn on the vacuum pump (pumping speed 4L / s) to evacuate the inductively coupled plasma reaction chamber to (50 Pa). Next, pass silicon tetrafluoride, hydrogen, and argon from the gas supply system through the gas supply pipeline and into the reaction chamber through the inlet. Then, turn on the tube furnace to heat the reaction chamber. Control the temperature of the first reaction zone to be 150°C and the temperature of the second reaction zone to be 300°C. Turn on the RF power switch and control the RF power of the induction RF coil to be 200 W. After that, open the one-way valve to pass silicon tetrafluoride (the silicon tetrafluoride generated from the tail gas during the production of wet-process phosphoric acid; the purity of the silicon tetrafluoride is 99.999%, and the pressure is stabilized to 260 Pa), hydrogen, and argon (purity 99.99%) respectively. Control the gas flow through the mass flow controller (MFC). The flow ratio of silicon tetrafluoride, hydrogen, and argon is 1:2:2 (the flow rate of the silicon tetrafluoride gas is 6 sccm). After performing plasma-enhanced chemical vapor deposition on the first and second substrates for 1 h, turn off the RF power switch, control the switch of the one-way valve, close hydrogen and silicon tetrafluoride, and keep argon flowing in (the flow rate of argon is 30 sccm) for cooling. After cooling, turn off the vacuum pump, peel the plasma-enhanced chemical vapor deposition product from the substrates (the first and second substrates) to obtain the silicon anode material (microcrystalline silicon and amorphous silicon). The tail gas generated during the plasma-enhanced chemical vapor deposition process is absorbed by sodium hydroxide solution;

[0081] Microcrystalline silicon is obtained on the first substrate, and amorphous silicon is obtained on the second substrate.

[0082] Example 2

[0083] The difference between Example 2 and Example 1 is only that the temperature at the position of the first substrate is 200°C, and the temperature range at the position of the second substrate is 400°C, and the others are the same as in Example 1.

[0084] Example 3

[0085] The difference between Example 3 and Example 1 is only that the temperature at the position of the first substrate is 250°C, and the temperature at the position of the second substrate is 500°C, and the others are the same as in Example 1.

[0086] The silicon anode material (microcrystalline silicon and amorphous silicon) obtained in Example 3 was analyzed using an X-ray diffractometer, and the XRD pattern obtained is as Figure 2 and Figure 3 shown. From Figure 2It can be seen that the silicon negative electrode material (microcrystalline silicon) obtained on the first substrate in Example 3 belongs to crystalline silicon, and the diffraction peaks are sharp, indicating that the crystal form of the crystal is good, the internal structure is neat and orderly, and it has a good crystal structure; from Figure 3 It can be seen that the silicon negative electrode material (amorphous silicon) obtained on the second substrate in Example 3 is a broadened "bun-shaped peak" (or diffuse scattering peak).

[0087] The silicon negative electrode materials (microcrystalline silicon and amorphous silicon) obtained in Example 3 were observed by scanning electron microscopy. The SEM image of the obtained silicon negative electrode material (microcrystalline silicon) is as Figure 4 shown, where the magnification of the left figure is 1000 times and the magnification of the right figure is 10000 times. From Figure 4 it can be seen that the particle size of the prepared silicon negative electrode material (microcrystalline silicon) is in the micron level; the SEM image of the obtained silicon negative electrode material (amorphous silicon) is as Figure 5 (amorphous silicon) shown, where the magnification of the left figure is 10000 times and the magnification of the right figure is 20000 times. From Figure 5 it can be seen that the surface of the prepared amorphous silicon shows a rough and loose structure.

[0088] Comparative Example 1

[0089] The difference between Comparative Example 1 and Example 1 is only that the flow rate ratio of silicon tetrafluoride, hydrogen and argon is 1:1:2, and the others are the same as in Example 1.

[0090] Comparative Example 2

[0091] The difference between Comparative Example 2 and Example 1 is only that the flow rate ratio of silicon tetrafluoride, hydrogen and argon is 1:1:1, and the others are the same as in Example 1.

[0092] Application Example 1

[0093] A method for preparing a lithium-ion battery:

[0094] The silicon negative electrode materials (microcrystalline silicon and amorphous silicon) prepared in Example 1 were respectively mixed with conductive carbon black and sodium alginate at a mass ratio of 8:1:1 and then slurried to obtain a slurry with a solid content of 60%;

[0095] The two slurries were respectively coated on the copper foil so that the amount of the active substance (silicon negative electrode material) on the copper foil was 0.6 mg / cm 2 and then dried (60 °C, 12 h), and then cut into circular electrodes with a diameter of 10 mm to obtain two lithium-ion battery negative electrodes;

[0096] Assemble the two types of lithium-ion battery anodes with a positive electrode (lithium sheet), a separator (polypropylene), and an electrolyte (the concentration of the lithium salt in the electrolyte can be 1 M; the lithium salt can be LiPF6; the organic solvent in the electrolyte can be ethylene carbonate (EC) and dimethyl carbonate (DMC); the volume ratio of ethylene carbonate (EC) and dimethyl carbonate (DMC) can be 1:1; the additive in the electrolyte can be fluoroethylene carbonate (FEC); the addition amount of fluoroethylene carbonate (FEC) can be 10% of the total volume of the electrolyte) in a glove box to obtain a lithium-ion battery.

[0097] Use Neware test software to test the electrochemical performance (charge-discharge specific capacity, cycle life, and Coulomb efficiency) of the two types of lithium-ion batteries in Application Example 1 (lithium-ion batteries prepared with microcrystalline silicon anode materials and lithium-ion batteries prepared with amorphous silicon anode materials).

[0098] For the lithium-ion battery prepared with the microcrystalline silicon anode material in Application Example 1 at a current density of 0.1 A / g, the initial discharge specific capacity is 1925.92 mAh / g, the first Coulomb efficiency is 56.77%, the first charge specific capacity is 1093.25 mAh / g, and the charge specific capacity after 100 cycles is 723.38 mAh / g; for the lithium-ion battery prepared with the amorphous silicon anode material at a current density of 0.1 A / g, the initial discharge specific capacity is 2074.28 mAh / g, the first Coulomb efficiency is 21.17%, the first charge specific capacity is 439.05 mAh / g, and the charge specific capacity after 100 cycles is 594.26 mAh / g.

[0099] Application Example 2

[0100] The difference between Application Example 2 and Application Example 1 is only that the silicon anode material prepared in Example 2 is used, and the others are the same as Application Example 1.

[0101] For the lithium-ion battery prepared with the microcrystalline silicon anode material in Application Example 2 at a current density of 0.1 A / g, the initial discharge specific capacity is 2801.83 mAh / g, the first Coulomb efficiency is 67.61%, the first charge specific capacity is 1894.44 mAh / g, and the charge specific capacity after 100 cycles is 740.04 mAh / g; for the lithium-ion battery prepared with the amorphous silicon anode material at a current density of 0.1 A / g, the initial discharge specific capacity is 1732.37 mAh / g, the first Coulomb efficiency is 25.24%, the first charge specific capacity is 437.16 mAh / g, and the charge specific capacity after 100 cycles is 434.09 mAh / g.

[0102] Application Example 3

[0103] The difference between Application Example 3 and Application Example 1 is only that the silicon anode material prepared in Example 3 is used, and the others are the same as Application Example 1.

[0104] For the lithium-ion battery prepared with the microcrystalline silicon anode material in Application Example 3, at a current density of 0.1 A / g, the initial discharge specific capacity is 3185.95 mAh / g, the first Coulombic efficiency is 70.09%, the first charge specific capacity is 2232.90 mAh / g, and the charge specific capacity after 100 cycles is 748.36 mAh / g; for the lithium-ion battery prepared with the amorphous silicon anode material, at a current density of 0.1 A / g, the initial discharge specific capacity is 2161.98 mAh / g and the first Coulombic efficiency is 35.37%, the first charge specific capacity is 764.72 mAh / g, and the charge specific capacity after 100 cycles is 588.49 mAh / g.

[0105] Comparative Application Example 1

[0106] The difference between Comparative Application Example 1 and Application Example 1 is only that the silicon anode material prepared in Comparative Example 1 is used, and the others are the same as in Application Example 1.

[0107] For the lithium-ion battery prepared with the microcrystalline silicon anode material in Comparative Application Example 1, at a current density of 0.1 A / g, the initial discharge specific capacity is 1592.95 mAh / g, the first Coulombic efficiency is 45.31%, the first charge specific capacity is 721.80 mAh / g, and the charge specific capacity after 100 cycles is 266.47 mAh / g; for the lithium-ion battery prepared with the amorphous silicon anode material, at a current density of 0.1 A / g, the initial discharge specific capacity is 1871.41 mAh / g and the first Coulombic efficiency is 19.94%, the first charge specific capacity is 373.19 mAh / g, and the charge specific capacity after 100 cycles is 463.87 mAh / g.

[0108] Comparative Application Example 2

[0109] The difference between Comparative Application Example 2 and Application Example 1 is only that the silicon anode material prepared in Comparative Example 2 is used, and the others are the same as in Application Example 1.

[0110] For the lithium-ion battery prepared with the microcrystalline silicon anode material in Comparative Application Example 2, at a current density of 0.1 A / g, the initial discharge specific capacity is 1497.44 mAh / g, the first Coulombic efficiency is 60.45%, the first charge specific capacity is 905.17 mAh / g, and the charge specific capacity after 100 cycles is 627.38 mAh / g; for the lithium-ion battery prepared with the amorphous silicon anode material, at a current density of 0.1 A / g, the initial discharge specific capacity is 1396.80 mAh / g and the first Coulombic efficiency is 30.87%, the first charge specific capacity is 431.16 mAh / g, and the charge specific capacity after 100 cycles is 240.64 mAh / g.

[0111] The cycle performance diagrams of the lithium-ion batteries prepared in Application Examples 1 to 3 are as Figure 6 and7 as shown, where Figure 6 is the cycle performance graph of a lithium-ion battery prepared with a microcrystalline silicon negative electrode material. As can be seen from Figure 6 it, after 40 charge-discharge cycles, the specific capacity of the lithium-ion battery prepared with the microcrystalline silicon negative electrode material under three temperature conditions shows a stable downward trend, indicating good cycle stability; Figure 7 is the cycle performance graph of a lithium-ion battery prepared with an amorphous silicon negative electrode material. As can be seen from Figure 7 it, the lithium-ion batteries prepared with the amorphous silicon negative electrode material under three temperature conditions exhibit excellent cycle stability.

[0112] The cycle performance graphs of the lithium-ion batteries prepared in Comparative Application Examples 1-2 are as shown in Figure 8 and Figure 9 as shown, where Figure 8 is the cycle performance graph of a lithium-ion battery prepared with a microcrystalline silicon negative electrode material. As can be seen from Figure 8 it, after 40 charge-discharge cycles, the specific capacity of the lithium-ion battery prepared with the microcrystalline silicon negative electrode material under two gas flow ratios shows a stable downward trend, indicating good cycle stability. However, the lithium-ion batteries under these two gas flow ratios have a relatively low specific capacity; Figure 9 is the cycle performance graph of a lithium-ion battery prepared with an amorphous silicon negative electrode material. As can be seen from Figure 9 it, during the charge-discharge process, the lithium-ion batteries under these two gas flow ratios have a relatively low specific capacity, and the cycle stability of Comparative Application Example 2 is relatively poor.

[0113] From the XRD patterns and SEM images of Example 1, as well as the data of Application Examples 1-3 and Comparative Application Examples 1-2, it can be seen that the method provided by the present invention can simultaneously prepare microcrystalline silicon and amorphous silicon. Moreover, for the lithium-ion battery prepared with the microcrystalline silicon negative electrode material, at a current density of 0.1 A / g, the initial discharge specific capacity can reach 3185.95 mAh / g, the first Coulombic efficiency can reach 70.09%, the first charge specific capacity can reach 2232.90 mAh / g, and the charge specific capacity after 100 cycles can reach 748.36 mAh / g. For the lithium-ion battery prepared with the amorphous silicon negative electrode material, at a current density of 0.1 A / g, the initial discharge specific capacity can reach 2161.98 mAh / g, the first Coulombic efficiency can reach 35.37%, the first charge specific capacity can reach 764.72 mAh / g, and the charge specific capacity after 100 cycles can reach 588.49 mAh / g. The lithium-ion batteries prepared from microcrystalline silicon and amorphous silicon have good cycle life and Coulombic efficiency and can be used as negative electrode materials.

[0114] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A method for preparing a silicon anode material using SiF4 as a raw material, comprising: Performing plasma-enhanced chemical vapor deposition on a substrate in a mixed gas of silicon tetrafluoride, hydrogen, and argon to obtain a silicon anode material; The plasma-enhanced chemical vapor deposition is carried out in an inductively coupled plasma reaction chamber; the inductively coupled plasma reaction chamber includes a reaction cavity and an induction radio frequency coil; both ends of the reaction cavity are an air inlet and an air outlet respectively; the reaction cavity includes a first reaction zone and a second reaction zone arranged in sequence along the air inlet direction; the induction radio frequency coil is arranged outside the first reaction zone; The plasma-enhanced chemical vapor deposition is as follows: after placing a first substrate in the first reaction zone and a second substrate in the second reaction zone, introducing silicon tetrafluoride, hydrogen, and argon into the reaction cavity through the air inlet, controlling the radio frequency power of the induction radio frequency coil to be 180-220 W, the temperature of the first reaction zone to be 150-250 °C, and the temperature of the second reaction zone to be 300-500 °C, obtaining microcrystalline silicon on the surface of the first substrate and amorphous silicon on the surface of the second substrate; The flow rate ratio of the silicon tetrafluoride, hydrogen, and argon is 1:(1.01-2):(1.01-2).

2. The method according to claim 1, wherein The silicon tetrafluoride is obtained by recycling industrial waste gas.

3. The method according to claim 1, wherein The flow rate ratio of the silicon tetrafluoride, hydrogen, and argon is 1:(1.5-2):(1.5-2).

4. The method according to claim 1, wherein The flow rate of the silicon tetrafluoride is 5-8 sccm.

5. The method according to claim 1, wherein The substrate includes a single crystal silicon substrate, a stainless steel mesh substrate, or a silicon carbide substrate.

6. The method according to claim 1, wherein Before the plasma-enhanced chemical vapor deposition, the reaction cavity is evacuated.

7. The method according to claim 6, wherein The vacuum degree of the evacuation is 10-300 Pa.

8. The method according to claim 1, wherein The time of the plasma-enhanced chemical vapor deposition is 1-2 h.

9. The method according to any one of claims 1 to 8, characterized in that After the plasma-enhanced chemical vapor deposition is completed, the obtained product is cooled in argon and then peeled off from the substrate.

10. The method according to claim 9, wherein The flow rate of the argon is 10-40 sccm.

Images