Lithium-ion battery silicon carbon anode material, preparation method and use

Abstract

The present application provides a lithium-ion battery silicon carbon anode material and its preparation method and use. [Means] The preparation method includes the steps of: (1) fixing a porous carbon-based film material in a reactor, and then introducing an inert gas to replace the air in the reactor, thereby making the reactor an oxygen-free environment; (2) sequentially heating and keeping the reactor in an oxygen-free environment described in step (1), and then introducing silane gas to carry out a chemical vapor deposition reaction to obtain a precursor of silicon-carbon anode material; and (3) treating the precursor of carbon anode material obtained in step (2) to obtain the lithium-ion battery silicon-carbon anode material. The preparation method uses a porous carbon-based film material to realize uniform vapor deposition of nanosilicon particles, effectively alleviating the problem of volume expansion during silicon cycling, while effectively improving the polarization state of the material through carbon deposition, thereby effectively improving the electrochemical performance of the silicon-carbon anode material.

Description

[Technical Field]

[0001] The present application relates to the field of lithium ion battery anode materials, and in particular to lithium ion battery silicon carbon anode materials and their preparation methods and uses. [Background technology]

[0002] Lithium-ion batteries have great potential and widespread applications in the fields of portable electronic devices, electric vehicles, and large-scale energy storage. The anode materials selected in conventional lithium-ion battery systems are primarily graphite-based materials. Graphite-based materials have a low theoretical specific capacity of 372 mAh g -1 Therefore, it is crucial to develop new high-capacity anode materials for lithium-ion batteries.

[0003] Silicon has an extremely high theoretical capacity (4200 mAh / g) and a suitable lithium desorption potential, and is considered a new generation of lithium-ion battery anode material, attracting considerable attention and research interest. However, silicon's extremely large volume change rate (>300%) during the charge / discharge process results in low initial coulombic efficiency and poor cycling performance, which are obstacles that limit the commercial use of silicon-based lithium-ion battery anode materials.

[0004] In the conventional method of preparing nanosilicon by chemical vapor deposition, the silicon source is easily agglomerated on the carbon base material after decomposition, forming micron-order particulate or linear products, which results in the loss of the unique advantages of nanosilicon. Furthermore, when using nanosilicon-made silicon-carbon anode materials as they are, the nanosilicon is difficult to disperse uniformly throughout the entire system, which results in excessive expansion of the electrode pieces during charging and discharging, further deteriorating the performance of the material.

[0005] CN104103821A discloses a method for preparing silicon-carbon anode materials. The method includes the following steps: (1) introducing a catalyst into a chemical vapor deposition (CVD) reactor; (2) heating the CVD reactor and introducing a reactant gas source and a carrier gas into the CVD reactor; (3) passing the Si-SiOx generated during the CVD reaction through a dynamically rotating carboxylated carbon substrate to prepare a precursor for the silicon-carbon anode material; and (4) coating the precursor with organic pyrolytic carbon and then calcining it in a non-oxidizing atmosphere to obtain the silicon-carbon anode material. While this method can produce nanosilicon with a high specific capacity, it is difficult to ensure that silicon is distributed uniformly over the entire surface of the carbon substrate, resulting in poor cycling performance and a high volume expansion rate.

[0006] CN1903793 discloses a carbon-silicon composite material, its preparation method, and its use. The silicon-carbon composite material includes a silicon substrate and carbon nanotubes or nanocarbon fibers grown thereon. The carbon nanotubes or nanocarbon fibers can have a straight, bent, or spiral geometric appearance. There are several methods for preparing the carbon-silicon composite material. After adding a catalyst to a silicon substrate, or mixing a catalyst with silicon particles or preparing an alloy, the carbon nanotubes or nanocarbon fibers can be deposited by chemical vapor deposition. The carbon nanotubes or nanocarbon fibers grown on the surface by this method have a large specific surface area and large porosity, but the silicon particles are not uniformly distributed on the surface, which does not solve the problem of volume expansion of the silicon particles during cycling.

[0007] CN109449388A discloses a method for preparing a carbon-silicon anode material for lithium-ion batteries. The preparation method includes the following steps: (1) homogeneously mixing starch and a catalyst, carbonizing the mixture under vacuum conditions, and then washing, drying, grinding, and sieving to obtain porous carbon; (2) mixing an aqueous graphite solution with an aqueous nanosilicon solution, adding the mixture to the porous carbon prepared in (1), and drying, grinding, and sieving; and (3) dissolving an organic carbon source in water, sequentially adding the product from (2) and concentrated sulfuric acid, stirring the mixture, keeping it warm, washing, drying, and then vacuum carbonizing to obtain a carbon-silicon anode material for lithium-ion batteries. This method uses graphite as a buffer for the volume expansion of silicon particles, but the low theoretical specific capacity of graphite-based materials makes it difficult to meet the high energy density requirements of new lithium-ion batteries. Furthermore, the preparation method is complicated and unfavorable for industrial production.

[0008] Therefore, providing a method for preparing industrial silicon-carbon composite materials using silicon that can alleviate the problem of volume expansion during silicon cycling and reduce production difficulties has become one of the problems urgently needed to be solved in this field. Summary of the Invention [Problem to be solved by the invention]

[0009] The following is a general summary of the subject matter described further herein, which is not intended to limit the scope of the claims.

[0010] In response to the deficiencies of the prior art, the present application aims to provide a silicon-carbon anode material for lithium-ion batteries, and a preparation method and use thereof. The preparation method utilizes a porous carbon-based film material to achieve uniform vapor deposition of nano-silicon particles, effectively alleviating the problem of volume expansion during silicon cycling, while effectively improving the polarization state of the material through carbon deposition, thereby effectively improving the electrochemical performance of the silicon-carbon anode material. [Means for solving the problem]

[0011] To achieve this objective, the present application provides the following technical solutions.

[0012] In a first aspect, the present application provides a method for preparing a lithium-ion battery silicon carbon anode material, the method comprising: Step (1) of fixing a porous carbon-based film material inside a reactor, and then introducing an inert gas to replace the air inside the reactor, thereby creating an oxygen-free environment inside the reactor; Step (2) of sequentially heating and maintaining the temperature of the reactor in the oxygen-free environment described in step (1), and then introducing silane gas to carry out a chemical vapor deposition reaction to obtain a precursor of a silicon carbon anode material; and (3) sequentially subjecting the precursor of the silicon-carbon anode material obtained in step (2) to carbon coating, crushing, secondary coating and carbonization, and then obtaining the silicon-carbon anode material for lithium-ion batteries.

[0013] The method for preparing a silicon-carbon anode material for lithium-ion batteries according to the present invention uses a porous carbon-based film material as a base to achieve uniform vapor deposition of nano-silicon particles, effectively solving the problem of volume expansion during silicon cycling.

[0014] Normally, silane gas is difficult to deposit, but in this application, the pressure difference created before and after the silane gas is introduced into the porous carbon-based film material causes the silane gas to deposit in the voids of the porous carbon-based film material, and the porous carbon-based film material controls the flow direction of the gas, thereby directing the deposition and adsorption of silane molecules inside the voids, so that the silane gas can be effectively partially adsorbed inside the voids as it passes through the voids of the porous carbon-based film material.

[0015] In the present application, the reactor is not specifically limited, and may be any device that can ensure that gas passes through in a directional manner and that can be heated.

[0016] Preferably, the porous carbon-based film material described in step (1) comprises any one of carbon paper, carbon nanotube film, or graphene film.

[0017] Preferably, the thickness of the porous carbon-based film material described in step (1) is 100 to 500 μm, and may be, for example, 100 μm, 150 μm, 200 μm, 250 μm, 300 μm, 350 μm, 400 μm, 450 μm, or 500 μm, but is not limited to the listed values, and other unlisted values ​​within the range of values ​​also apply.

[0018] If the thickness of the porous carbon-based film material of the present application is too thick, there will be a large difference in the amount of silane deposited on both the front and back surfaces of the porous carbon-based film material, resulting in uneven deposition. If the thickness is too thin, the silane gas may penetrate the porous carbon-based film material when passing through at a certain flow rate, preventing the silane gas from being deposited within the porous carbon-based film, resulting in waste of material.

[0019] Preferably, the tortuosity of the porous carbon-based film material described in step (1) is 1.5 to 5, for example, 1.5, 2, 2.5, 3, 3.5, 4, 4.5 or 5, but is not limited to the listed values, and other unlisted values ​​within the range of values ​​also apply.

[0020] Preferably, the end point of the heating described in step (2) is 600 to 800°C, and may be, for example, 600°C, 620°C, 640°C, 660°C, 680°C, 700°C, 720°C, 740°C, 760°C, 780°C, or 800°C, but is not limited to the listed values, and other unlisted values ​​within the range of values ​​also apply.

[0021] Preferably, the incubation time described in step (2) is 0.5 to 2 hours, and may be, for example, 0.5 hours, 0.8 hours, 1 hour, 1.2 hours, 1.4 hours, 1.6 hours, 1.8 hours, or 2 hours, but is not limited to the listed values, and other values ​​not listed within the range of values ​​also apply.

[0022] Preferably, the angle between the placement position of the porous carbon-based film material described in step (1) and the flow direction of the silane gas described in step (2) is 60 to 120°, and may be, for example, 60°, 70°, 80°, 90°, 100°, 110° or 120°, but is not limited to the listed values, and other unlisted values ​​within the numerical range also apply.

[0023] Preferably, the angle between the position where the porous carbon-based film material is arranged in step (1) and the direction of flow of the silane gas in step (2) is 90°.

[0024] By arranging the position of the porous carbon base film material of the present application at a certain angle to the flow direction of the silane gas, the silane gas can pass through the porous carbon base film material, making it easier for the silane to accumulate inside the pores of the porous carbon base film material.

[0025] Preferably, the gas flow rate of the silane gas described in step (2) is 0.1 to 2 L / min, and may be, for example, 0.1 L / min, 0.5 L / min, 1 L / min, 1.5 L / min, or 2 L / min, but is not limited to the listed values, and other values ​​not listed within the range of values ​​also apply.

[0026] If the gas flow rate of the silane gas in the present invention is too fast, the silane gas will not remain inside the film material for long enough to effectively adsorb. If the gas flow rate is too high, the film material will not be strong enough to withstand the force, resulting in rupture. Furthermore, the film material has a certain tortuosity, which has a certain obstructive effect on the gas. If the gas flow rate is too slow, the silane gas will not pass through the film and will remain only on the surface of the film material.

[0027] Preferably, the flow time of the silane gas described in step (2) is 2 to 5 hours, and may be, for example, 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours, 4.5 hours, or 5 hours, but is not limited to the listed values, and other values ​​not listed within the range of values ​​also apply.

[0028] Preferably, the carbon coating described in step (3) is carried out in an inert gas atmosphere.

[0029] Preferably, the inert gas includes helium gas and / or argon gas.

[0030] Preferably, the temperature of the carbon coating described in step (3) is 800 to 1200°C, and may be, for example, 800°C, 850°C, 900°C, 950°C, 1000°C, 1050°C, 1100°C, 1150°C, or 1200°C, but is not limited to the listed values, and other values ​​not listed within the numerical range also apply.

[0031] Preferably, the coating time of the carbon coating described in step (3) is 2 to 6 hours, and may be, for example, 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours, 4.5 hours, 5 hours, 5.5 hours, or 6 hours, but is not limited to the listed values, and other values ​​not listed within the range of values ​​also apply.

[0032] Preferably, the carbon-containing gas source in the carbon coating process described in step (3) comprises any one or a combination of at least two of methane, ethane, propane, ethylene, propylene, or acetylene. Exemplary combinations include, but are not limited to, a combination of methane and ethane, a combination of methane and propane, a combination of methane and ethylene, a combination of methane and propylene, a combination of methane and acetylene, a combination of methane, ethane, and acetylene, or a combination of methane, ethane, propane, ethylene, and acetylene.

[0033] Preferably, the average particle size D50 of the crushed particles described in step (3) is 5 to 20 μm, and may be, for example, 5 μm, 8 μm, 10 μm, 12 μm, 14 μm, 16 μm, 18 μm, or 20 μm, but is not limited to the listed values, and other unlisted values ​​within the range of values ​​also apply.

[0034] Preferably, the coating material of the secondary coating described in step (3) comprises an organic carbon source.

[0035] Preferably, the organic carbon source comprises a combination of at least one of asphalt, tar, and phenolic resin. Typical combinations include, but are not limited to, a combination of asphalt and tar, a combination of asphalt and phenolic resin, a combination of tar and phenolic resin, or a combination of asphalt, tar, and phenolic resin.

[0036] Preferably, the coverage ratio of the secondary coating described in step (3) is 5 to 20%, and may be, for example, 5%, 8%, 10%, 12%, 14%, 16%, 18%, or 20%, but is not limited to the listed values, and other unlisted values ​​within the range of values ​​also apply.

[0037] Preferably, the carbonization temperature described in step (3) is 800 to 1200°C, and may be, for example, 800°C, 850°C, 900°C, 950°C, 1000°C, 1050°C, 1100°C, 1150°C, or 1200°C, but is not limited to the listed values, and other unlisted values ​​within the range of values ​​also apply.

[0038] Preferably, the carbonization time described in step (3) is 3 to 10 hours, for example, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, or 10 hours, but is not limited to the listed values, and other unlisted values ​​within the range of values ​​also apply.

[0039] As a preferred technical solution of the preparation method according to the first aspect of the present application, the preparation method comprises: Step (1) of fixing a porous carbon-based film material inside a reactor, and then introducing an inert gas to replace the air inside the reactor, thereby creating an oxygen-free environment inside the reactor, wherein the porous carbon-based film material has a thickness of 100-500 μm and a tortuosity of 1.5-5; Step (2) is to heat the reactor to 600 to 800°C to be in an oxygen-free environment as described in step (1), and keep the temperature for 0.5 to 2 hours. Then, silane gas is introduced at a gas flow rate of 0.1 to 2 L / min for 2 to 5 hours, so that the silane gas undergoes a chemical vapor deposition reaction in the porous carbon-based material to form nanosilicon particles, thereby obtaining a precursor of a silicon-carbon negative electrode material, wherein the angle between the flow direction of the silane gas and the position of the porous carbon-based film material described in step (1) is 60 to 120°; and (3) performing carbon coating on the precursor of the silicon-carbon anode material obtained in step (2) in an inert gas atmosphere at a temperature of 800-1200°C for 2-6 hours using a carbon-containing gas source, followed by crushing to obtain crushed particles with an average particle size D50 of 5-20 μm, which are then subjected to secondary coating using a coating material, and carbonized at 800-1200°C for 3-10 hours to obtain the lithium-ion battery silicon-carbon anode material, in which the coating ratio of the secondary coating is 5-20%.

[0040] In a second aspect, the present application provides a lithium-ion battery silicon carbon anode material obtainable by the preparation method according to the first aspect.

[0041] In a third aspect, the present application provides a use of a lithium ion battery silicon carbon anode material prepared by the preparation method according to the first aspect, wherein the lithium ion battery silicon carbon anode material is used as an anode material for a lithium ion battery.

[0042] The numerical ranges set forth herein include not only the recited point values ​​but also any point values ​​between the recited numerical ranges that are not recited, and for reasons of space and clarity, the present application does not exhaustively recite the specific point values ​​included in the ranges. [Effects of the Invention]

[0043] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0044] The method for preparing a silicon-carbon anode material for a lithium-ion battery according to the present invention utilizes a porous carbon-based film material to achieve vapor deposition of uniform nano-silicon particles, effectively alleviating the problem of volume expansion during silicon cycling, while effectively improving the polarization state of the material through carbon deposition, thereby effectively improving the electrochemical performance of the silicon-carbon anode material.

[0045] Other aspects may be understood after reading and understanding the detailed description. DETAILED DESCRIPTION OF THE INVENTION

[0046] The technical solution of the present application will be further described below through specific embodiments, which are merely intended to help those skilled in the art understand the present application and should not be construed as limiting the present application in any way.

[0047] Example 1 This embodiment provides a lithium ion battery silicon carbon anode material, and the preparation method of the lithium ion battery silicon carbon anode material includes the following steps:

[0048] (1) After carbon paper was fixed inside the reactor, helium gas was introduced to replace the air inside the reactor, creating an oxygen-free environment inside the reactor. The porous carbon-based film material had a thickness of 250 μm and a tortuosity of 3.

[0049] (2) The reactor, which was prepared in the oxygen-free environment described in step (1), was heated to 700°C and maintained at this temperature for 1.2 hours. Silane gas was then introduced at a flow rate of 0.5 L / min for 3.5 hours to carry out a chemical vapor deposition reaction, thereby obtaining a precursor of a silicon-carbon anode material. The angle between the flow direction of the silane gas and the position of the porous carbon-based film material described in step (1) was 90°.

[0050] (3) The precursor of the silicon-carbon anode material obtained in step (2) was coated with carbon using methane in a helium gas atmosphere at 1000°C for 4 hours, and then crushed to obtain crushed particles with an average particle size D50 = 10 μm. The secondary coating was performed using asphalt, and the particles were carbonized at 1000°C to obtain the lithium-ion battery silicon-carbon anode material. The secondary coating coverage was 10%.

[0051] Example 2 This embodiment provides a lithium ion battery silicon carbon anode material, and the preparation method of the lithium ion battery silicon carbon anode material includes the following steps:

[0052] (1) After carbon paper was fixed inside the reactor, helium gas was introduced to replace the air inside the reactor, creating an oxygen-free environment inside the reactor. The porous carbon-based film material had a thickness of 100 μm and a tortuosity of 1.5.

[0053] (2) The reactor, which was set to the oxygen-free environment described in step (1), was heated to 600°C and maintained at that temperature for 2 hours. Silane gas was then introduced at a flow rate of 0.1 L / min for 5 hours to carry out a chemical vapor deposition reaction, thereby obtaining a precursor of a silicon-carbon anode material. The angle between the flow direction of the silane gas and the position of the carbon paper described in step (1) was 60°.

[0054] (3) The precursor of the silicon-carbon anode material obtained in step (2) was coated with carbon using acetylene in a helium gas atmosphere at 1200°C for 2 hours, then crushed to obtain crushed particles with an average particle size D50 = 20 μm. The secondary coating was then applied using tar, and the resulting material was carbonized at 1200°C for 3 hours to obtain the lithium-ion battery silicon-carbon anode material. The secondary coating coverage was 8%.

[0055] Example 3 This embodiment provides a lithium ion battery silicon carbon anode material, and the preparation method of the lithium ion battery silicon carbon anode material includes the following steps:

[0056] (1) After carbon paper was fixed inside the reactor, helium gas was introduced to replace the air inside the reactor, creating an oxygen-free environment inside the reactor. The porous carbon-based film material had a thickness of 500 μm and a tortuosity of 5.

[0057] (2) The reactor, which was set to the oxygen-free environment described in step (1), was heated to 800°C and maintained at that temperature for 0.5 hours. Silane gas was then introduced at a gas flow rate of 2 L / min for 2 hours to carry out a chemical vapor deposition reaction, thereby obtaining a precursor of a silicon-carbon anode material. The angle between the flow direction of the silane gas and the position of the carbon paper described in step (1) was 120°.

[0058] (3) The precursor of the silicon-carbon anode material obtained in step (2) was carbon-coated in a helium gas atmosphere using a mixed gas of ethane and propane at 800°C for 6 hours, then crushed to obtain crushed particles with an average particle size D50 = 5 μm. Secondary coating was performed using phenolic resin, and the resulting material was carbonized at 800°C for 10 hours to obtain the lithium-ion battery silicon-carbon anode material. The secondary coating coverage was 12%.

[0059] Example 4 This embodiment provides a lithium ion battery silicon carbon anode material, and the preparation method of the lithium ion battery silicon carbon anode material includes the following steps:

[0060] (1) After carbon paper was fixed inside the reactor, helium gas was introduced to replace the air inside the reactor, creating an oxygen-free environment inside the reactor. The porous carbon-based film material had a thickness of 300 μm and a tortuosity of 2.7.

[0061] (2) The reactor was heated to 680°C and maintained at this temperature for 1.6 hours, after which silane gas was introduced at a flow rate of 0.8 L / min for 4 hours to carry out a chemical vapor deposition reaction, yielding a precursor for a silicon-carbon anode material. The angle between the flow direction of the silane gas and the position of the carbon paper described in step (1) was 85°.

[0062] (3) The silicon-carbon anode precursor obtained in step (2) was coated with carbon using a methane and acetylene mixture at 1050°C for 3.5 hours in a helium gas atmosphere, crushed to obtain crushed particles with an average particle size D50 of 15 μm, and then coated with asphalt as a secondary coating. After carbonization at 1050°C for 8 hours, the lithium-ion battery silicon-carbon anode material was obtained. The secondary coating had a coverage of 16%.

[0063] Example 5 This example provides a lithium-ion battery silicon carbon anode material, which is prepared in the same manner as in Example 1, except that the carbon paper in step (1) is replaced with a carbon nanotube film.

[0064] Example 6 This example provides a lithium-ion battery silicon-carbon anode material, which is prepared in the same manner as in Example 1, except that the carbon paper in step (1) is replaced with a graphene film.

[0065] Example 7 This example provides a lithium-ion battery silicon carbon anode material, which is prepared in the same manner as in Example 1, except that the thickness of the carbon paper in step (1) is changed to 80 μm.

[0066] Example 8 This example provides a lithium-ion battery silicon carbon anode material, which is prepared in the same manner as in Example 1, except that the thickness of the carbon paper in step (1) is changed to 600 μm.

[0067] Example 9 This example provides a silicon-carbon anode material for lithium-ion batteries, which is prepared in the same manner as in Example 1, except that the angle between the flow direction of silane gas in step (2) and the position of carbon paper in step (1) is changed to 20°.

[0068] Example 10 This example provides a silicon-carbon anode material for lithium-ion batteries, which is prepared in the same manner as in Example 1, except that the angle between the flow direction of silane gas in step (2) and the position of carbon paper in step (1) is changed to 0°.

[0069] Example 11 This example provides a lithium-ion battery silicon carbon anode material, which is prepared in the same manner as in Example 1, except that the end point of heating in step (2) is changed to 500°C.

[0070] Example 12 This example provides a lithium-ion battery silicon carbon anode material, which is prepared in the same manner as in Example 1, except that the end point of heating in step (2) is changed to 900°C.

[0071] Comparative Example 1 This comparative example provides a lithium ion battery silicon carbon negative electrode material, and the preparation method of the lithium ion battery silicon carbon negative electrode material includes the following steps:

[0072] The chemical vapor deposition apparatus was evacuated, and a mixture of silane and argon gas was introduced into the apparatus and heated at 800°C for 7 hours to prepare silicon particles. Next, a mixture of acetylene and argon gas was introduced into the chemical vapor deposition apparatus and heated at 800°C for 1 hour to prepare a carbon coating layer on the surface of the silicon particles, producing a silicon-carbon anode material.

[0073] Comparative Example 2 This comparative example provides a lithium ion battery silicon carbon negative electrode material, and the preparation method of the lithium ion battery silicon carbon negative electrode material includes the following steps:

[0074] (a) After mixing the nanosilicon dispersion, conductive additive, and coating material, the mixture was dispersed and stirred for 2 hours, and then spray-dried to obtain a powder material.

[0075] (b) The temperature was raised to 1000°C at a rate of 3°C / min, and the powder material obtained in step (a) was carbonized for 6 hours, after which it was pulverized to obtain a precursor of the silicon carbon anode material.

[0076] (c) Compounding the graphite material and the precursor of the silicon carbon anode material obtained in step (b) to obtain the silicon carbon anode material for lithium ion batteries.

[0077] The lithium-ion battery silicon carbon anode materials prepared in Examples 1 to 12 and Comparative Examples 1 and 2 were used in lithium-ion batteries to perform electrochemical performance testing. Tests were performed using a Wuhan Blue-Electron CT2001A battery testing device with a voltage range of 0.005 to 1.5 V, a capacity test rate of 0.05 C / 0.05 C, and a cycle test rate of 0.5 C / 0.5 C. The specific test configuration is shown in Table 1.

[0078] The battery cycle test was carried out by mixing the material with a commercial graphite material to prepare a 420mAh / g anode material, which was then combined with a ternary cathode material to produce a full cell. 1 / 3 Co 1 / 3 Mn 1 / 3 A soft pack battery was manufactured using O2) as the positive electrode, LiPF6 (solvent: EC+DEC, volume ratio 1:1, concentration 1.3 mol / l) as the electrolyte, and Celegard 2400 as the separator.

[0079] Full charge rebound test: First, the capacity was measured, and then the soft pack battery was disassembled to measure the thickness D1 of the negative electrode piece. Then, after fully charging the soft pack battery through 100 cycles, the soft pack battery was disassembled to measure the thickness D2 of the negative electrode piece. Then, the full charge rebound rate = (D2 - D1) / D1 was calculated. [Table 1]

[0080] As can be seen from Table 1, the silicon-carbon anode material of the present invention achieves a high capacity of over 1530 mAh / g, a high initial efficiency, and excellent cycle performance. Different carbon nanofilm substrates can effectively achieve nanosilicon deposition, ensuring improved battery cycle performance. It can be seen from the comparison that if the film material is too thin, the film material will be damaged during the reaction process, preventing the formation of an effective silane gas adsorption film, resulting in a decrease in the capacity of the material. However, if the film thickness is too thick, the gas permeability will be low, resulting in uneven silane gas deposition (too much at the front and too little at the rear). Furthermore, if the deposition at the front is too heavy, silicon nanoparticles will aggregate, reducing the cycle performance of the battery. It can also be seen from the comparison that if the film angle is small, silane gas will selectively bypass the film material, resulting in less deposition in the film material. As a result, nanosilicon particles will not be formed in the film material, and the function of preparing a high-capacity silicon-carbon anode material will not be achieved. High or low temperatures of the pyrolysis reaction were unfavorable to the deposition of nanosilicon in the material, and the capacity of the material decreased.

[0081] In summary, the method for preparing a silicon-carbon anode material for a lithium-ion battery according to the present invention utilizes a porous carbon-based film material to achieve uniform vapor deposition of nano-silicon particles, effectively alleviating the problem of volume expansion during silicon cycling, while effectively improving the polarization state of the material through carbon deposition, thereby effectively improving the electrochemical performance of the silicon-carbon anode material.

[0082] The above specific examples have been used to further illustrate the objectives, technical solutions and beneficial effects of the present application, but the applicant declares that these are merely specific embodiments of the present application and are not intended to limit the present application. Those skilled in the art should understand that any modifications, equivalent replacements, improvements, etc. made within the concept and principles of the present application are all within the scope of protection of the present application.

Claims

1. A method for preparing a lithium ion battery silicon carbon anode material, comprising: Step (1) of fixing a porous carbon-based film material inside a reactor, and then introducing an inert gas to replace the air inside the reactor, thereby creating an oxygen-free environment inside the reactor; Step (2) of sequentially heating and maintaining the temperature of the reactor in the oxygen-free environment described in step (1), and then introducing silane gas to carry out a chemical vapor deposition reaction to obtain a precursor of a silicon-carbon anode material; and step (3) sequentially subjecting the precursor of the silicon-carbon negative electrode material obtained in step (2) to carbon coating, crushing, secondary coating and carbonization, thereby obtaining the silicon-carbon negative electrode material for lithium ion batteries; The method for preparing the secondary coating in step (3) comprises a coating material containing an organic carbon source.

2. The porous carbon-based film material described in step (1) includes any one of carbon paper, carbon nanotube film, and graphene film; Preferably, the thickness of the porous carbon-based film material described in step (1) is 100-500 μm; The preparation method according to claim 1, wherein the tortuosity of the porous carbon-based film material in step (1) is preferably 1.5-5.

3. The end point of the heating described in step (2) is 600 to 800°C; The method according to claim 1, wherein the incubation time in step (2) is preferably 0.5 to 2 hours.

4. the angle between the position of the porous carbon-based film material described in step (1) and the flow direction of the silane gas described in step (2) is 60 to 120°; Preferably, the angle between the position of the porous carbon-based film material described in step (1) and the flow direction of the silane gas described in step (2) is 90°; Preferably, the gas flow rate of the silane gas described in step (2) is 0.1 to 2 L / min; The method according to claim 1, wherein the flow time of the silane gas in step (2) is preferably 2 to 5 hours.

5. The carbon coating described in step (3) is carried out in an inert gas atmosphere, Preferably, the inert gas comprises helium gas and / or argon gas; Preferably, the temperature of the carbon coating described in step (3) is 800 to 1200°C; Preferably, the coating time of the carbon coating described in step (3) is 2 to 6 hours; 2. The method of claim 1, wherein the carbon-containing gas source in the carbon coating process in step (3) comprises any one or a combination of at least two of methane, ethane, propane, ethylene, propylene, or acetylene.

6. The preparation method according to claim 1, wherein the average particle size D50 of the crushed particles described in step (3) is 5 to 20 μm.

7. The organic carbon source comprises any one or a combination of at least two of asphalt, tar, and phenolic resin; Preferably, the coverage of the secondary coating described in step (3) is 5-20%; Preferably, the temperature of the carbonization described in step (3) is 800 to 1200°C; The preparation method according to claim 1, wherein the carbonization time in step (3) is preferably 3-10 h.

8. Step (1) of fixing a porous carbon-based film material in a reactor, and then introducing an inert gas to replace the air in the reactor, thereby creating an oxygen-free environment in the reactor, wherein the porous carbon-based film material has a thickness of 100-500 μm and a tortuosity of 1.5-5; Step (2) is a step in which the reactor in the oxygen-free environment described in step (1) is heated to 600 to 800°C and kept at this temperature for 0.5 to 2 hours, and then silane gas is introduced at a gas flow rate of 0.1 to 2 L / min for 2 to 5 hours to carry out a chemical vapor deposition reaction, thereby obtaining a precursor of a silicon carbon anode material, wherein the angle between the flow direction of the silane gas and the arrangement position of the porous carbon base film material described in step (1) is 60 to 120°; and step (3) in an inert gas atmosphere, the precursor of the silicon-carbon anode material obtained in step (2) is carbon-coated using a carbon-containing gas source at a temperature of 800-1200°C for 2-6 hours, and then crushed to obtain crushed particles with an average particle size D50 of 5-20 μm, which are then secondary-coated using a coating material, and carbonized at 800-1200°C for 3-10 hours to obtain the lithium-ion battery silicon-carbon anode material, in which the coating ratio of the secondary coating is 5-20%. The preparation method according to claim 1.

Images