A method for preparing a silicon negative electrode material using SiF4 as a raw material

Abstract

The application provides a method for preparing a silicon negative electrode material by using SiF4 as a raw material, and belongs to the field of battery negative electrode materials. The method for preparing the silicon negative electrode material by using SiF4 as the raw material can simultaneously obtain microcrystalline silicon and amorphous silicon by using silicon tetrafluoride as a silicon source, controlling the placement position of a substrate, the radio frequency power of an inductive radio frequency coil and the temperature of a reaction zone; and the silicon material capable of meeting the use of a lithium ion battery negative electrode can be further obtained by controlling the proportion of silicon tetrafluoride, hydrogen and argon. The method provided by the application can simultaneously obtain microcrystalline silicon and amorphous silicon, and the lithium ion battery prepared from the microcrystalline silicon and the amorphous silicon has good cycle life and coulomb efficiency, and can be used as a negative electrode material.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of battery negative electrode materials, and particularly relates to a method for preparing silicon negative electrode material by using SiF4 as raw material. BACKGROUND

[0002] In recent years, the rapid growth of 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 is also increasing. As an important component of lithium batteries, the first coulomb efficiency and cycle stability of the negative electrode material are important factors affecting the cycle life of the battery system, and the energy density of the negative electrode material is an important factor determining the energy density and power density of the battery system.

[0003] Silicon-based negative electrode materials have high energy density (the theoretical specific capacity at room temperature is as high as 3590 mAh / g), a low discharge platform (0.4 V vs. Li), and are abundant in reserves and low in price, so they are one of the most potential next-generation lithium-ion battery negative electrode materials. There are various methods for preparing existing nano-silicon powder, among which the products prepared by chemical vapor deposition have the advantages of high first charge-discharge efficiency, good cycle stability, low equipment requirements, and suitability for industrial production, so chemical vapor deposition method is widely used. At present, chemical vapor deposition method mainly uses silane gas as raw material, and electronic grade silane gas is mainly used in the fields of solar cell panels and liquid crystal display panels. However, due to the high price and inconvenience of transportation, its application is limited to a certain extent.

[0004] The tail gas in the production process of wet-process phosphoric acid contains a large amount of silicon tetrafluoride gas. In industry, water is usually used to directly absorb silicon tetrafluoride to generate a 10-15wt% fluorosilicic acid solution. If silicon tetrafluoride gas can be used as raw material to prepare silicon negative electrode material, it is expected to reduce the production cost of silicon-based negative electrode material. Silicon negative electrode material includes microcrystalline silicon and amorphous silicon, and in the prior art, silicon negative electrode is usually prepared to only produce microcrystalline silicon or amorphous silicon. SUMMARY

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

[0006] In order to achieve the above-mentioned purpose of the application, the present application provides the following technical solutions:

[0007] The present application provides a method for preparing silicon negative electrode material by using SiF4 as raw material, comprising:

[0008] Plasma-enhanced chemical vapor deposition is performed on the substrate in a mixed gas of silicon tetrafluoride, hydrogen and argon to obtain a silicon negative electrode material;

[0009] The plasma enhanced chemical vapor deposition is performed in an inductively coupled plasma reaction chamber; the inductively coupled plasma reaction chamber comprises a reaction chamber body and an inductive radio frequency coil; the reaction chamber body has a gas inlet and a gas outlet at two ends thereof; the reaction chamber body comprises a first reaction zone and a second reaction zone arranged in sequence along the direction of the gas inlet; the first reaction zone is externally provided with the inductive radio frequency coil;

[0010] The plasma enhanced chemical vapor deposition is performed by placing a first substrate in the first reaction zone and a second substrate in the second reaction zone, and then introducing silicon tetrafluoride, hydrogen and argon into the reaction chamber body through the gas 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℃, and the temperature of the second reaction zone to be 300-500℃, so as to obtain microcrystalline silicon on the surface of the first substrate and amorphous silicon 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 recovered from 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 comprises a single crystal silicon substrate, a stainless steel mesh substrate or a silicon carbide substrate.

[0016] Preferably, the reaction chamber body is subjected to vacuumizing treatment before the plasma enhanced chemical vapor deposition.

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

[0018] Preferably, the time of 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 application provides a method for preparing a silicon negative electrode material by using SiF4 as a raw material, and comprises the following steps: 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; the plasma enhanced chemical vapor deposition is performed in an inductively coupled plasma reaction chamber; the inductively coupled plasma reaction chamber comprises a reaction chamber body and an inductive radio frequency coil; the reaction chamber body is respectively provided with a gas inlet and a gas outlet at two ends thereof; the reaction chamber body comprises a first reaction zone and a second reaction zone which are sequentially arranged along the direction of the gas inlet; the first reaction zone is externally provided with an inductive radio frequency coil; the plasma enhanced chemical vapor deposition is performed by placing a first substrate in the first reaction zone and a second substrate in the second reaction zone, then introducing the silicon tetrafluoride, hydrogen and argon into the reaction chamber body from the gas 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 DEG C, and the temperature of the second reaction zone to be 300-500 DEG C, so that microcrystalline silicon is obtained on the surface of the first substrate and amorphous silicon is obtained on the surface of the second substrate; and the flow rate ratio of the 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 element thin film on the first substrate can be gradually changed from amorphous state to microcrystalline at a temperature of 150-250 DEG C, the surface migration ability of silicon atoms is enhanced, the crystal grain growth is promoted, and microcrystalline silicon is obtained; the silicon element thin film on the second substrate is deposited to form amorphous silicon at a temperature of 300-500 DEG C; by controlling the ratio of the silicon tetrafluoride, hydrogen and argon, the plasma density and the deposition rate are controlled, so that the particle size and the particle size distribution are affected, the micron-level crystalline silicon on the first substrate is formed, the crystal form of the crystalline silicon is complete, the formation of the amorphous silicon on the second substrate is also facilitated. The results of the examples show that the method provided by the application can obtain microcrystalline silicon and amorphous silicon at the same time; the lithium ion battery prepared by using the microcrystalline silicon negative electrode material has an initial discharge specific capacity of 3185.95 mAh / g, a first coulombic 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, and has good cycle life and coulombic efficiency; the lithium ion battery prepared by using the amorphous silicon negative electrode material has an initial discharge specific capacity of 2161.98 mAh / g, a first coulombic 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, and the lithium ion batteries prepared by using the microcrystalline silicon and the amorphous silicon have good cycle life and coulombic efficiency and can be used as negative electrode materials. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1Flow chart of the preparation method of silicon negative electrode material in an embodiment of the present invention, wherein 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 tubular furnace, 7 is a vacuum pump, and 8 is a tail gas absorption device;

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

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

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

[0026] Figure 5 This is an SEM image of the silicon negative electrode material (amorphous silicon) prepared in Example 3 of the present invention, wherein the magnification of the left image is 10,000 times, and the magnification of the right image is 20,000 times;

[0027] Figure 6 This is a graph showing the cycle performance of lithium-ion batteries prepared using microcrystalline silicon negative electrode materials from Application Examples 1 to 3 of the present invention;

[0028] Figure 7 This is a cycle performance diagram of lithium-ion batteries prepared using amorphous silicon negative electrode materials of Application Examples 1 to 3 of the present invention;

[0029] Figure 8 This is a cycle performance diagram of a lithium-ion battery prepared using microcrystalline silicon negative electrode materials of comparative application examples 1 and 2 of the present invention;

[0030] Figure 9 This is a cycle performance diagram of lithium-ion batteries prepared with amorphous silicon negative electrode materials according to comparative application examples 1 and 2 of the present invention. DETAILED DESCRIPTION

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

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

[0033] In the present application, the silicon tetrafluoride is preferably recovered from industrial waste gas, and more preferably recovered from tail gas generated in a wet-process phosphoric acid production process; the purity of the silicon tetrafluoride is preferably 99.999%. The present application limits the purity of the silicon tetrafluoride to the above range, which can improve the purity of the obtained silicon negative electrode. The present application does not have a special limitation on the separation and recovery operation of the silicon tetrafluoride in the tail gas, and a separation and recovery operation commonly used in the industry for the silicon tetrafluoride in the tail gas can be used.

[0034] As an embodiment of the present application, the hydrogen gas is provided by a hydrogen gas generator. The present application does not have a special limitation on the equipment and model of the hydrogen gas generator, and an equipment and model commonly used by those skilled in the art can be used.

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

[0036] In the present application, the flow rate ratio of the silicon tetrafluoride, hydrogen gas and argon gas 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). The present application limits the flow rate ratio of the silicon tetrafluoride, hydrogen gas and argon gas to the above range, which can be beneficial to the reduction reaction in the deposition process, and obtain a higher-purity silicon element (silicon negative electrode). In the present application, the chemical equation of the reduction reaction is: SiF4+2H2=Si+4HF.

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

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

[0039] In the present application, the substrate preferably includes a single-crystal silicon substrate, a stainless steel mesh substrate or a silicon carbide substrate. The present application limits the type of the substrate to the above range, which can be more beneficial to the deposition of the silicon element on the substrate.

[0040] In the present application, the substrate is preferably pretreated before use. As an embodiment of the present application, the pretreatment can be cleaning. The present application does not have a special limitation on the operation of the cleaning, and a conventional substrate cleaning operation in the art can be used, which can clean the substrate.

[0041] The plasma enhanced chemical vapor deposition is performed in an inductively coupled plasma reaction chamber; the inductively coupled plasma reaction chamber comprises a reaction chamber body and an inductive radio frequency coil; the reaction chamber body has a gas inlet and a gas outlet at two ends thereof; the reaction chamber body comprises a first reaction zone and a second reaction zone arranged in sequence along the direction of the gas inlet; and the first reaction zone is externally provided with the inductive radio frequency coil.

[0042] In the present application, the inductively coupled plasma reaction chamber is preferably subjected to vacuumizing treatment before the plasma enhanced chemical vapor deposition. As an embodiment of the present application, the vacuum degree of the vacuumizing can be 10-300 Pa, 20-200 Pa or 150 Pa; the equipment used for the vacuumizing can be a vacuum pump; and the pumping speed of the vacuum pump can be 4 L / s. The vacuumizing of the inductively coupled plasma reaction chamber before the plasma enhanced chemical vapor deposition can avoid the introduction of impurities into the silicon negative electrode material. The limitation of the pumping speed of the vacuum pump to the above range can avoid the excessive pumping speed from causing the reaction gases (silicon tetrafluoride, hydrogen and argon) to be pumped away and thus affect the deposition.

[0043] The plasma enhanced chemical vapor deposition is performed by placing the first substrate in the first reaction zone and the second substrate in the second reaction zone, and then introducing silicon tetrafluoride, hydrogen and argon into the reaction chamber body from the gas 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 ℃ and the temperature of the second reaction zone to be 300-500 ℃, so as to obtain microcrystalline silicon on the surface of the first substrate and amorphous silicon on the surface of the second substrate.

[0044] As an embodiment of the present application, the radio frequency power of the inductive radio frequency coil can be 180-220 W or 200 W. The limitation of the radio frequency power of the inductive radio frequency coil to the above range can ensure the silicon negative electrode obtained by the deposition to have better quality.

[0045] As an embodiment of the present application, the temperature of the first reaction zone can be 150-250 ℃, 175-250 ℃, 200-250 ℃ or 225-250 ℃. The limitation of the temperature of the first reaction zone to the above range can ensure the smooth progress of the reduction reaction and the deposition of microcrystalline silicon (silicon negative electrode material) with higher purity.

[0046] As an embodiment of the present application, the temperature of the second reaction zone can be 300-500°C, 350-500°C, 400-500°C, or 450-500°C. The present application limits the temperature of the second reaction zone to the above range to ensure the smooth progress of the reduction reaction and the deposition of amorphous silicon (silicon negative electrode material) with better quality.

[0047] As an embodiment of the present application, the second reaction zone can be partially or entirely in a tube furnace. In the embodiment of the present application, the second reaction zone is entirely in a tube furnace. The present application limits the second reaction zone to be entirely in a tube furnace to better control the temperature of the second reaction zone.

[0048] As an embodiment of the present application, the time of the plasma enhanced chemical vapor deposition can be 1-2h, or 1.5h. The present application limits the time of the plasma enhanced chemical vapor deposition to the above range to ensure the sufficient progress of the reduction reaction and the high purity of the silicon element in the silicon negative electrode.

[0049] As an embodiment of the present application, the plasma enhanced chemical vapor deposition controls the radio frequency power by a radio frequency power source and transmits and receives radio frequency signals by an inductive radio frequency coil.

[0050] As an embodiment of the present application, the temperature 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 inductive radio frequency coil to heat the reaction cavity.

[0051] As an embodiment of the present application, after the plasma enhanced chemical vapor deposition, the obtained product is cooled in argon and peeled off from the substrate; the flow rate of the argon can be 10-40sccm, or 30sccm. The present application cools in argon and limits the flow rate of the argon during the cooling process to the above range to avoid the generation of other impurities in the obtained silicon negative electrode and reduce the purity of the silicon element in the silicon negative electrode. The present application does not have special limitation on the peeling operation, which can collect the product deposited on the substrate.

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

[0053] The present application can make the crystal form of the silicon element thin film on the first substrate gradually change from amorphous state to microcrystalline at the temperature of 150-250 DEG C by using silicon tetrafluoride as silicon source, controlling the placing position of the substrate, the radio frequency power of the inductive radio frequency coil and the temperature of the reaction zone, enhancing the surface migration ability of silicon atom, promoting the grain growth and obtaining microcrystalline silicon; can make the silicon element thin film on the second substrate deposit to form amorphous silicon at the temperature of 300-500 DEG C; can control the plasma density and the deposition rate by controlling the proportion of silicon tetrafluoride, hydrogen and argon, thereby affecting the particle size and refining the particle size distribution, which is helpful to the formation of micron-level crystalline silicon on the first substrate and the formation of amorphous silicon on the second substrate.

[0054] In the embodiment of the present application, the preparation method of the silicon negative electrode material is shown in the flow chart as Figure 1 The flow chart is shown in the figure, wherein 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 the embodiment of the present application, the first substrate is placed in the area corresponding to the inductive radio frequency coil 5 (first reaction zone), the second substrate is placed in the area corresponding to the tube furnace 6 (second reaction zone), the vacuum pump 7 is first started to vacuumize, then the tube furnace 6 is started, the areas corresponding to the inductive radio frequency coil 5 (first reaction zone) and the tube furnace 6 (second reaction zone) are heated, then the radio frequency power supply 4 switch is started, when the area corresponding to the inductive radio frequency coil 5 (first reaction zone) reaches 150-250 DEG C and the area corresponding to the tube furnace 6 (second reaction zone) reaches 300-500 DEG C, the one-way valve 2 is opened to respectively introduce argon, hydrogen and silicon tetrafluoride, the plasma enhanced chemical vapor deposition is carried out by controlling the gas flow through the gas mass flow controller (MFC) 3, then the radio frequency power supply 4 switch is closed, the one-way valve 2 is controlled to open and close, the hydrogen and silicon tetrafluoride are closed and the argon is kept to introduce, the plasma enhanced chemical vapor deposition product is cooled, the vacuum pump 7 is closed after the cooling is finished, the plasma enhanced chemical vapor deposition product is stripped from the substrate (first substrate and second substrate) to obtain the silicon negative electrode material (microcrystalline silicon and amorphous silicon), the tail gas produced in the plasma enhanced chemical vapor deposition process is absorbed by the tail gas absorption device 8.

[0056] The present application also provides the silicon negative electrode material prepared by the preparation method.

[0057] As an embodiment of the present application, 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 application also provides the application of the silicon negative electrode material in the negative electrode of lithium ion battery.

[0059] The application further provides a lithium ion battery negative electrode, comprising a current collector and a negative electrode material coated on the surface of the current collector, wherein the negative electrode material comprises the silicon negative electrode material according to the technical solution.

[0060] As an embodiment of the application, the current collector can be a copper foil.

[0061] As an embodiment of the application, the preparation method of the lithium ion battery negative electrode can be:

[0062] The silicon negative electrode material, conductive carbon black and sodium alginate are mixed to obtain a slurry.

[0063] The slurry is coated on a copper foil and dried to obtain a lithium ion battery negative electrode sheet.

[0064] The silicon negative electrode material, conductive carbon black and sodium alginate are mixed to obtain a slurry.

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

[0066] As an embodiment of the application, the solid content of the slurry can be 45-60%. Limiting the solid content of the slurry to the above range can be beneficial for subsequent coating.

[0067] After obtaining the slurry, the slurry can be coated on a copper foil and dried to obtain a lithium ion battery negative electrode.

[0068] The application does not have special limitations on the coating amount and coating method of the coating, and the amount of active material (silicon negative electrode material) on the copper foil can be 0.4-0.6 mg / cm 2 That's it.

[0069] As an embodiment of the application, the drying can be performed in a vacuum drying oven; the temperature of the drying can be 60℃; and the time of the drying can be 12h.

[0070] As an embodiment of the application, after the drying is completed, the copper foil coated with the slurry can be cut to cut the copper foil coated with the slurry into a circular electrode sheet with a diameter of 10mm.

[0071] The application further provides a lithium ion battery, comprising the lithium ion battery negative electrode, the positive electrode, the positive electrode shell, the negative electrode shell, the gasket, the spring, the separator and the electrolyte according to the technical solution.

[0072] As an embodiment of the present application, the preparation method of the lithium ion battery can comprise assembling the negative electrode, the positive electrode, the separator and the electrolyte as described in the technical solution to obtain the lithium ion battery.

[0073] As an embodiment of the present application, the positive electrode can be a lithium sheet; the separator can be polypropylene (PP); the concentration of lithium salt in the electrolyte can be 1M; 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.

[0074] As an embodiment of the present application, the assembling can be carried out in a glove box. The present application does not have special limitations on the operation of the assembling, and the operation commonly used by those skilled in the art can be adopted.

[0075] The technical solutions in the present application will be described clearly and completely in combination with the embodiments in the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all the other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0076] Embodiment 1

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

[0078] Plasma enhanced chemical vapor deposition is carried out on a substrate in a mixture 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 comprises a reaction chamber body and an inductive radio frequency coil; the reaction chamber body has a gas inlet and a gas outlet at two ends respectively; the reaction chamber body comprises a first reaction zone and a second reaction zone arranged in sequence along the direction of the gas inlet; the first reaction zone is externally provided with an inductive radio frequency coil;

[0080] The plasma enhanced chemical vapor deposition is as follows: after the first substrate (stainless steel mesh substrate) is placed in the first reaction zone and the second substrate (stainless steel mesh substrate) is placed in the second reaction zone (the second reaction zone is entirely in the tube furnace), a vacuum pump (pumping speed 4 L / s) is started to vacuum the inductively coupled plasma reaction cavity to 50 Pa, then silicon tetrafluoride, hydrogen and argon are introduced into the reaction cavity from the gas supply system through the gas supply pipeline from the gas inlet, then the tube furnace is started to heat the reaction cavity, the temperature of the first reaction zone is controlled to be 150 DEG C, the temperature of the second reaction zone is controlled to be 300 DEG C, the radio frequency power of the inductive radio frequency coil is controlled to be 200 W, then the one-way valve is opened to introduce silicon tetrafluoride (silicon tetrafluoride in tail gas produced in the production process of wet phosphoric acid; the purity of the silicon tetrafluoride is 99.999%, the pressure is stabilized to 260 Pa), hydrogen and argon (the purity is 99.99%) at a flow ratio of 1:2:2 (the flow rate of the silicon tetrafluoride gas is 6 sccm), plasma enhanced chemical vapor deposition is carried out on the first substrate and the second substrate for 1 h, then the radio frequency power switch is turned off, the one-way valve is controlled to be opened and closed, the hydrogen and the silicon tetrafluoride are turned off, the argon is kept to be introduced (the flow rate of the introduced argon is 30 sccm) to cool, after the cooling is completed, the vacuum pump is turned off, the plasma enhanced chemical vapor deposition product is stripped from the substrate (the first substrate and the second substrate), the silicon negative electrode material (microcrystalline silicon and amorphous silicon) is obtained, and the tail gas produced in the plasma enhanced chemical vapor deposition process is absorbed by a sodium hydroxide solution.

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

[0082] Example 2

[0083] Example 2 is different from example 1 only in that the temperature of the first substrate position is 200 DEG C, the temperature of the second substrate position is 400 DEG C, and the others are the same as example 1.

[0084] Example 3

[0085] Example 3 is different from example 1 only in that the temperature of the first substrate position is 250 DEG C, the temperature of the second substrate position is 500 DEG C, and the others are the same as example 1.

[0086] The silicon negative electrode material (microcrystalline silicon and amorphous silicon) obtained in example 3 is analyzed by an x-ray diffractometer, and the obtained XRD graph is as shown in Figure 2 and Figure 3 Figure 2 ​As can be seen from Figure 3, the silicon negative electrode material (microcrystalline silicon) obtained on the first substrate in Example 3 is crystalline silicon, the diffraction peak is sharp, indicating that the crystal form is good, the internal structure is orderly and the crystal structure is good. Figure 3 As can be seen from Figure 4, the silicon negative electrode material (amorphous silicon) obtained on the second substrate in Example 3 is a widened "steamed bun 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, and the SEM image of the silicon negative electrode material (microcrystalline silicon) is shown in Figure 5. Figure 4 As can be seen from Figure 5, the magnification of the left image is 1000 times, and the magnification of the right image is 10000 times. Figure 4 As can be seen from Figure 5, the silicon negative electrode material (microcrystalline silicon) has a particle size of microns. Figure 5 The SEM image of the silicon negative electrode material (amorphous silicon) is shown in Figure 6. Figure 5 As can be seen from Figure 6, the magnification of the left image is 10000 times, and the magnification of the right image is 20000 times. As can be seen from Figure 6, the amorphous silicon prepared has a rough and loose structure.

[0088] Comparative Example 1

[0089] Comparative Example 1 differs from Example 1 only in that the flow 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] Comparative Example 2 differs from Example 1 only in that the flow 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 preparation method of a lithium ion battery:

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

[0095] The two slurries were respectively coated on copper foils to make the amount of active material (silicon negative electrode material) on the copper foils 0.6 mg / cm 2 After drying (60°C, 12h), the copper foils were cut into circular electrode pieces with a diameter of 10mm to obtain two kinds of lithium ion battery negative electrodes.

[0096] The two lithium ion batteries were assembled in a glove box, and the lithium ion batteries were obtained by using the two lithium ion battery negative electrodes, positive electrodes (lithium sheets), separators (polypropylene), and electrolytes (the concentration of lithium salt in the electrolyte can be 1M; 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 the ethylene carbonate (EC) and dimethyl carbonate (DMC) can be 1:1; the additive in the electrolyte can be fluoroethylene carbonate (FEC); and the addition amount of the fluoroethylene carbonate (FEC) can be 10% of the total volume of the electrolyte).

[0097] The two lithium ion batteries (lithium ion batteries prepared from the microcrystalline silicon negative electrode material and the lithium ion batteries prepared from the amorphous silicon negative electrode material) in Application Example 1 were tested for electrochemical performance (charge-discharge specific capacity, cycle life, and coulombic efficiency) by using a new Wei test software.

[0098] The lithium ion battery prepared from the microcrystalline silicon negative electrode material in Application Example 1 had an initial discharge specific capacity of 1925.92 mAh / g, a first coulombic efficiency of 56.77%, a first charge specific capacity of 1093.25 mAh / g, and a charge specific capacity of 723.38 mAh / g after 100 cycles at a current density of 0.1 A / g; and the lithium ion battery prepared from the amorphous silicon negative electrode material had an initial discharge specific capacity of 2074.28 mAh / g, a first coulombic efficiency of 21.17%, a first charge specific capacity of 439.05 mAh / g, and a charge specific capacity of 594.26 mAh / g after 100 cycles at a current density of 0.1 A / g.

[0099] Application Example 2

[0100] Application Example 2 is different from Application Example 1 only in that the silicon negative electrode material prepared in Example 2 is used, and the other conditions are the same as in Application Example 1.

[0101] The lithium ion battery prepared from the microcrystalline silicon negative electrode material in Application Example 2 had an initial discharge specific capacity of 2801.83 mAh / g, a first coulombic efficiency of 67.61%, a first charge specific capacity of 1894.44 mAh / g, and a charge specific capacity of 740.04 mAh / g after 100 cycles at a current density of 0.1 A / g; and the lithium ion battery prepared from the amorphous silicon negative electrode material had an initial discharge specific capacity of 1732.37 mAh / g, a first coulombic efficiency of 25.24%, a first charge specific capacity of 437.16 mAh / g, and a charge specific capacity of 434.09 mAh / g after 100 cycles at a current density of 0.1 A / g.

[0102] Application Example 3

[0103] Application Example 3 is different from Application Example 1 only in that the silicon negative electrode material prepared in Example 3 is used, and the other conditions are the same as in Application Example 1.

[0104] The lithium ion battery prepared by the microcrystalline silicon negative electrode material in Application Example 3 has an initial discharge specific capacity of 3185.95 mAh / g, a first coulombic 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; the lithium ion battery prepared by the amorphous silicon negative electrode material has an initial discharge specific capacity of 2161.98 mAh / g, a first coulombic 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.

[0105] Comparative Application Example 1

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

[0107] The lithium ion battery prepared by the microcrystalline silicon negative electrode material in Comparative Application Example 1 has an initial discharge specific capacity of 1592.95 mAh / g, a first coulombic efficiency of 45.31%, a first charge specific capacity of 721.80 mAh / g, and a charge specific capacity of 266.47 mAh / g after 100 cycles at a current density of 0.1 A / g; the lithium ion battery prepared by the amorphous silicon negative electrode material has an initial discharge specific capacity of 1871.41 mAh / g, a first coulombic efficiency of 19.94%, a first charge specific capacity of 373.19 mAh / g, and a charge specific capacity of 463.87 mAh / g after 100 cycles at a current density of 0.1 A / g.

[0108] Comparative Application Example 2

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

[0110] The lithium ion battery prepared by the microcrystalline silicon negative electrode material in Comparative Application Example 2 has an initial discharge specific capacity of 1497.44 mAh / g, a first coulombic efficiency of 60.45%, a first charge specific capacity of 905.17 mAh / g, and a charge specific capacity of 627.38 mAh / g after 100 cycles at a current density of 0.1 A / g; the lithium ion battery prepared by the amorphous silicon negative electrode material has an initial discharge specific capacity of 1396.80 mAh / g, a first coulombic efficiency of 30.87%, a first charge specific capacity of 431.16 mAh / g, and a charge specific capacity of 240.64 mAh / g after 100 cycles at a current density of 0.1 A / g.

[0111] The cycle performance diagrams of the lithium ion batteries prepared in Application Examples 1-3 are as follows: Figure 6 and7 Figure 2 is a cycle performance graph of the lithium ion battery prepared by the microcrystalline silicon negative electrode material, and Figure 3 is a cycle performance graph of the lithium ion battery prepared by the amorphous silicon negative electrode material. Figure 6 As can be seen from Figure 2, the specific capacity of the lithium ion battery prepared by the microcrystalline silicon negative electrode material under the three temperature conditions has a stable downward trend after 40 cycles of charging and discharging, and has good cycle stability. Figure 6 As can be seen from Figure 2, the specific capacity of the lithium ion battery prepared by the microcrystalline silicon negative electrode material under the three temperature conditions has a stable downward trend after 40 cycles of charging and discharging, and has good cycle stability. Figure 7 Figure 4 is a cycle performance graph of the lithium ion battery prepared by the amorphous silicon negative electrode material, and Figure 5 is a cycle performance graph of the lithium ion battery prepared by the amorphous silicon negative electrode material. Figure 7 As can be seen from Figure 4, the lithium ion battery prepared by the amorphous silicon negative electrode material has excellent cycle stability under the three temperature conditions.

[0112] Figure 6 is a cycle performance graph of the lithium ion battery prepared by the microcrystalline silicon negative electrode material, and Figure 7 is a cycle performance graph of the lithium ion battery prepared by the amorphous silicon negative electrode material. Figure 8 As can be seen from Figure 6, the specific capacity of the lithium ion battery prepared by the microcrystalline silicon negative electrode material under the two gas flow ratios has a stable downward trend after 40 cycles of charging and discharging, and has good cycle stability, but the lithium ion battery has a lower specific capacity under the two gas flow ratios. Figure 9 As can be seen from Figure 7, the lithium ion battery prepared by the amorphous silicon negative electrode material has a lower specific capacity under the two gas flow ratios during the charging and discharging process, and the cycle stability of Comparative Application Example 2 is poor. Figure 8 Figure 8 As can be seen from the XRD and SEM graphs of Example 1 and the data of Application Examples 1-3 and Comparative Application Examples 1-2, the method provided by the present application can simultaneously prepare microcrystalline silicon and amorphous silicon; the lithium ion battery prepared by the microcrystalline silicon negative electrode material has an initial discharge specific capacity of 3185.95 mAh / g, a first coulombic 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 under a current density of 0.1 A / g; the lithium ion battery prepared by the amorphous silicon negative electrode material has an initial discharge specific capacity of 2161.98 mAh / g, a first coulombic 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 under a current density of 0.1 A / g; the lithium ion batteries prepared by the microcrystalline silicon and the amorphous silicon have good cycle life and coulombic efficiency, and can be used as negative electrode materials. Figure 9 Figure 9

[0113]

[0114] ​​​​The above merely describes the preferred embodiments of the present application, and it should be pointed out that, for those skilled in the art, several improvements and refinements can be made without departing from the principles of the present application, and these improvements and refinements should also be considered as falling within the protection scope of the present application.

Claims

1. A method for preparing a silicon negative electrode material using SiF4 as a raw material, comprising: Plasma-enhanced chemical vapor deposition is performed on the substrate in a mixture of silicon tetrafluoride, hydrogen and argon to obtain a 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 chamber and an inductive radio frequency coil; the reaction chamber has an air inlet and an air outlet at both ends; the reaction chamber includes a first reaction zone and a second reaction zone arranged in sequence along the direction of the air inlet; an inductive radio frequency coil is arranged outside the first reaction zone; The plasma enhanced chemical vapor deposition method comprises the following steps: placing a first substrate in a first reaction zone and a second substrate in a second reaction zone, introducing silicon tetrafluoride, hydrogen, and argon into a reaction chamber through an 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., thereby obtaining microcrystalline silicon on the surface of the first substrate and amorphous silicon on the surface of the second substrate; The flow ratio of the silicon tetrafluoride, hydrogen and argon is 1:(1.01-2):(1.01-2).

2. The method according to claim 1, characterized in that The silicon tetrafluoride is recovered from industrial waste gas.

3. The method according to claim 1, characterized in that The flow 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 to 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, characterized in that The reaction chamber is vacuumed before the plasma enhanced chemical vapor deposition.

7. The method according to claim 6, characterized in that The vacuum degree of the vacuum pumping is 10-300 Pa.

8. The method according to claim 1, characterized in that The plasma enhanced chemical vapor deposition time is 1 to 2 hours.

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, characterized in that The flow rate of the argon gas is 10-40 sccm.

Images