Preparation method and application of silicon-carbon negative electrode material

Abstract

The application relates to a preparation method of a silicon-carbon negative electrode material and application thereof. The preparation method comprises the following steps: placing a silicon nanowire cluster dispersion liquid, a silane coupling agent and an acid solution in a first solvent to carry out first mixing, standing, filtering and drying to obtain surface-modified silicon nanowires; placing the surface-modified silicon nanowires and a first carbon source in a second solvent to carry out second mixing, filtering and drying, and then carrying out first sintering to obtain a first sintering product; grinding the first sintering product to a particle size of 1-20 mu m, carrying out ball milling with a second carbon source, and then carrying out second sintering to obtain a second sintering product; and grinding the second sintering product to obtain a silicon-carbon negative electrode material with a particle size of 0.5-5 mu m. The application solves the problems of uneven coating in the silicon nanowire coating process and separation of the carbon layer and the silicon wire during grinding, and a silicon-carbon negative electrode material with high cycle performance and high specific capacity is prepared.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion batteries, and specifically to a method for preparing and applying a silicon-carbon anode material. Background Technology

[0002] Lithium-ion batteries, as a new generation of rechargeable batteries, are lighter, have higher energy density, are more environmentally friendly, and have a longer lifespan compared to traditional lead-acid batteries, leading to their widespread use in energy storage devices, consumer electronics, and many other fields. Currently, commercially available lithium-ion batteries generally use graphite as the anode material, but graphite's theoretical specific capacity is only 372 mAh / g, which cannot meet the needs of applications requiring higher energy density. Silicon, with its high theoretical capacity (4200 mAh / g), moderate lithium insertion / extraction potential (below 0.5V), abundant reserves in the Earth's crust, and low price, is the next-generation anode material for lithium-ion batteries after graphite. However, silicon itself has poor conductivity, and there is a significant volume change (200–400%) during the electrochemical lithium insertion / extraction process. The resulting internal stress easily causes the anode to crack, pulverize, and peel off, leading to loss of conductive contact and battery failure, severely affecting its cycle performance.

[0003] CN106941153B proposes a cotton-like elemental silicon nanowire / carbon composite anode material, its preparation method, and its applications. The method involves preparing a polymer solution, uniformly mixing the polymer solution with the cotton-like elemental silicon nanowires, and then filtering, drying, carbonizing, pulverizing, and sieving to obtain the cotton-like elemental silicon nanowire / carbon composite anode material. However, the polymer solution cannot uniformly penetrate the interior of the silicon nanowires, and pulverization easily causes the carbon layer to detach from the silicon nanowires.

[0004] Rui Huang, Xing Fan, Wanci Shen, and Jing Zhu. Carbon-coated silicon nanowire array films for high-performance lithium-ion battery nanowires. Appl. Phys. Lett. 95, 133119 (2009) disclosed a method of coating silicon nanowires by forming a typical carbon gel by mixing resorcinol and formaldehyde, dispersing the carbon aerogel, and then pyrolyzing it. However, the raw materials are difficult to synthesize, cause pollution, and are too expensive, which is not conducive to industrial production.

[0005] CN 111995418 A discloses a method for preparing a high-strength, high-toughness silicon carbide nanowire-reinforced silicon carbide ceramic composite material. The method utilizes silane coupling agent-modified silicon nanowires and phenolic resin-coated silicon carbide nanowires. However, it does not address the issue of silicon nanowire breakage during subsequent grinding; therefore, the cycling performance of the prepared silicon nanowires cannot be guaranteed.

[0006] How to prepare a silicon-carbon anode material with uniform coating that does not cause separation of the carbon layer and silicon wire during grinding and can be mass-produced is an important research direction in this field. Summary of the Invention

[0007] The purpose of this invention is to provide a method and application for preparing silicon-carbon anode materials that have uniform coating, do not cause separation of the carbon layer and silicon wires during grinding, and can be mass-produced.

[0008] To achieve this objective, the present invention adopts the following technical solution:

[0009] One objective of this invention is to provide a method for preparing a silicon-carbon anode material, the method comprising the following steps:

[0010] (1) The silicon nanowire dispersion, silane coupling agent and acid solution were placed in the first solvent for the first mixing and then allowed to stand. After filtration and drying, surface-modified silicon nanowires were obtained.

[0011] (2) The surface-modified silicon nanowires described in step (1) and the first carbon source are placed in the second solvent for a second mixing, filtered and dried, and then subjected to a first sintering to obtain the first sintered product;

[0012] (3) Grind the first sintered product in step (2) to a particle size of 1 to 20 μm, ball mill it with the second carbon source, and then perform a second sintering to obtain a second sintered product. Grind the second sintered product to obtain a silicon-carbon anode material with a particle size of 0.5 to 5 μm.

[0013] Step (1) of this invention involves surface treatment of silicon nanowires to improve the bonding ability between silicon nanowires and organic carbon sources, preventing silicon / carbon separation during the grinding process after the first coating. Due to the relatively long length of silicon nanowires, they are typically mechanically ground, which can cause breakage, reducing their aspect ratio and deteriorating their electrochemical performance. After carbon coating, the material needs to be ground to the desired particle size, but during grinding, the coated silicon nanowires, due to their large aspect ratio, can separate from the carbon under mechanical force, resulting in a poor coating effect. Through two mixing and dispersion processes, aminosilanization is applied to the surface of the silicon nanowires, effectively improving their mechanical strength. Even after carbon coating, they retain a relatively long aspect ratio, thus effectively improving their capacity and cycle performance.

[0014] This invention employs a process of coating in step (2) followed by grinding, granulation, and spheroidization in step (3). This allows the silicon nanowires to be coated while maintaining a relatively intact state. The exposed silicon nanowires during grinding are then coated again, thus achieving carbon coating while ensuring the integrity of the silicon nanowires, forming a capsule-like structure. This invention improves the uniformity of the coating through two sintering processes, avoiding a series of side reactions caused by direct contact between the electrolyte and silicon.

[0015] As a preferred technical solution of the present invention, the dispersant in the silicon nanoparticle dispersion in step (1) includes any one or a combination of at least two of POIZ, PVP (polyvinylpyrrolidone) or DARVAN, wherein typical but non-limiting examples of the combination include: a combination of POIZ and PVP (polyvinylpyrrolidone), a combination of PVP (polyvinylpyrrolidone) and DARVAN, or a combination of POIZ and DARVAN, etc.

[0016] Preferably, the silane coupling agent in step (1) includes KH560 and / or KH570.

[0017] Preferably, the acid solution in step (1) includes glacial acetic acid.

[0018] Preferably, in step (1), the first solvent includes deionized water and / or ethanol.

[0019] As a preferred technical solution of the present invention, the mass fraction of silicon nanowires in the silicon nanowire dispersion in step (1) in the first solvent is 1 to 5%, wherein the mass fraction can be 1%, 2%, 3%, 4% or 5%, etc., but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0020] Preferably, the mass fraction of the dispersant in the silicon nanowire dispersion in step (1) in the first solvent is 0.1% to 0.5%, wherein the mass fraction can be 0.1%, 0.2%, 0.3%, 0.4% or 0.5%, etc., but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0021] Preferably, the mass fraction of the silane coupling agent in the first solvent in step (1) is 0.5% to 2%, wherein the mass fraction can be 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, or 2%, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0022] Preferably, the acid solution in step (1) is used to adjust the pH of the solution in the first mixture to 3.5 to 4.5, wherein the pH can be 3.5, 3.6, 3.7, 3.8, 3.9, 4.0, 4.1, 4.2, 4.3, 4.4 or 4.5, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0023] As a preferred technical solution of the present invention, the mixing rate of the first mixing in step (1) is 300 to 500 rpm, wherein the mixing rate can be 300 rpm, 320 rpm, 340 rpm, 360 rpm, 380 rpm, 400 rpm, 420 rpm, 440 rpm, 460 rpm, 480 rpm or 500 rpm, etc., but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0024] Preferably, the mixing time of the first mixing in step (1) is 2 to 4 hours, wherein the mixing time can be 2 hours, 2.2 hours, 2.4 hours, 2.6 hours, 2.8 hours, 3 hours, 3.2 hours, 3.4 hours, 3.6 hours, 3.8 hours or 4 hours, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0025] Preferably, the mixing temperature of the first mixture in step (1) is 20 to 30°C, wherein the mixing temperature can be 20°C, 21°C, 22°C, 23°C, 24°C, 25°C, 26°C, 27°C, 28°C, 29°C or 30°C, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0026] Preferably, the settling time in step (1) is 6 to 12 hours, wherein the time can be 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours or 12 hours, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0027] Preferably, the settling temperature in step (1) is 20 to 30°C, wherein the mixing temperature can be 20°C, 21°C, 22°C, 23°C, 24°C, 25°C, 26°C, 27°C, 28°C, 29°C or 30°C, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0028] Preferably, the drying in step (1) is spray drying.

[0029] Preferably, the inlet air temperature of the spray dryer is 80-160°C, wherein the inlet air temperature can be 80°C, 90°C, 100°C, 110°C, 120°C, 130°C, 140°C, 150°C or 160°C, etc., but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0030] Preferably, the outlet air temperature of the spray dryer is 60-100°C, wherein the outlet air temperature can be 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, 95°C or 100°C, etc., but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0031] As a preferred technical solution of the present invention, the first carbon source in step (2) includes any one or a combination of at least two of asphalt, tannic acid, phenolic resin, starch or polyacrylonitrile, wherein typical but non-limiting examples of the combination include: a combination of asphalt and tannic acid, a combination of tannic acid and phenolic resin, a combination of phenolic resin and starch, or a combination of starch and polyacrylonitrile, etc.

[0032] Preferably, in step (2), the second solvent includes any one of tetrahydrofuran, cyclohexane, deionized water, or anhydrous ethanol.

[0033] Preferably, the second solvent includes deionized water or anhydrous ethanol.

[0034] Preferably, in step (2), the mass fraction of the first carbon source in the second solvent is 20% to 50%, wherein the mass fraction can be 20%, 25%, 30%, 35%, 40%, 45%, or 50%, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0035] Preferably, the silicon-to-carbon ratio of the surface-modified silicon nanowires and the first carbon source in step (2) is 1:(0.5-2), wherein the silicon-to-carbon ratio can be 1:0.5, 1:0.6, 1:0.7, 1:0.8, 1:0.9, 1:1, 1:1.1, 1:1.2, 1:1.3, 1:1.4, 1:1.5, 1:1.6, 1:1.7, 1:1.8, 1:1.9 or 1:2, etc., but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0036] Preferably, in step (2), the solid content of the solution in the second mixture is 5-10%, wherein the solid content can be 5%, 6%, 7%, 8%, 9% or 10%, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0037] As a preferred technical solution of the present invention, the mixing time in step (2) is 2 to 8 hours, wherein the time can be 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours or 8 hours, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0038] Preferably, the mixing rate in step (2) is 100 to 600 rpm, wherein the rate can be 100 rpm, 150 rpm, 200 rpm, 250 rpm, 300 rpm, 350 rpm, 400 rpm, 450 rpm, 500 rpm, 550 rpm or 600 rpm, etc., but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0039] Preferably, the mixing time in step (2) is 2 to 8 hours, wherein the time can be 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours or 8 hours, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0040] Preferably, the sintering atmosphere of the first sintering in step (2) is an argon atmosphere.

[0041] Preferably, step (2) the first sintering includes a first sintering stage and a second sintering stage.

[0042] Preferably, the sintering temperature of the first sintering stage is 400-600℃, wherein the sintering temperature can be 400℃, 420℃, 440℃, 460℃, 480℃, 500℃, 520℃, 540℃, 560℃, 580℃ or 600℃, etc., but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0043] Preferably, the holding time for the first sintering stage is 1 to 4 hours, wherein the holding time can be 1 hour, 2 hours, 3 hours or 4 hours, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0044] Preferably, the sintering temperature of the second sintering stage is 800-1000℃, wherein the sintering temperature can be 800℃, 820℃, 840℃, 860℃, 880℃, 900℃, 920℃, 940℃, 960℃, 980℃ or 1000℃, etc., but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0045] Preferably, the holding time for the second sintering stage is 4 to 8 hours, wherein the holding time can be 4 hours, 5 hours, 6 hours, 7 hours or 8 hours, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0046] Preferably, the heating rate of the first sintering is 1 to 5 °C / min, wherein the heating rate can be 1 °C / min, 2 °C / min, 3 °C / min, 4 °C / min or 5 °C / min, etc., but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0047] As a preferred technical solution of the present invention, the second carbon source in step (3) includes any one or a combination of at least two of asphalt, tannic acid, phenolic resin, starch or polyacrylonitrile, wherein typical but non-limiting examples of the combination include: a combination of asphalt and tannic acid, a combination of tannic acid and phenolic resin, a combination of phenolic resin and starch, or a combination of starch and polyacrylonitrile, etc.

[0048] Preferably, in step (3), the mass ratio of the second carbon source to the first sintered product is 1:(0.5 to 9), wherein the mass ratio can be 1:0.5, 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8 or 1:9, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0049] As a preferred technical solution of the present invention, the grinding in step (3) is airflow vortex pulverization grinding.

[0050] Preferably, the main stage rotation speed of the airflow vortex pulverizer is 4000-6000 rpm, wherein the main stage rotation speed can be 4000 rpm, 4200 rpm, 4400 rpm, 4600 rpm, 4800 rpm, 5000 rpm, 5200 rpm, 5400 rpm, 5600 rpm, 5800 rpm, or 6000 rpm, etc., but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0051] Preferably, the grading speed of the airflow vortex pulverizing and grinding is 3000-4000 rpm, wherein the grading speed can be 3000 rpm, 3100 rpm, 3200 rpm, 3300 rpm, 3400 rpm, 3500 rpm, 3600 rpm, 3700 rpm, 3800 rpm, 3900 rpm, or 4000 rpm, etc., but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0052] Preferably, the time for airflow vortex grinding is 60 to 120 minutes, wherein the time can be 60 minutes, 65 minutes, 70 minutes, 75 minutes, 80 minutes, 85 minutes, 90 minutes, 95 minutes, 100 minutes, 105 minutes, 110 minutes, 115 minutes, or 120 minutes, etc., but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0053] This invention uses airflow vortex pulverization to spheroidize particles, resulting in a concentrated particle size distribution. This reduces the specific surface area and increases the tap density. Compared to irregular spheres, spherical shapes can maximize the filling of gaps between particles, facilitating uniform mixing of particles and carbon source during the second sintering coating. This increases the silicon nanowire content in the particles after the second sintering coating, which helps improve conductivity and cycle performance.

[0054] Preferably, the ball milling in step (3) is dry ball milling.

[0055] Preferably, the rotational speed of the ball mill in step (3) is 300 to 600 rpm, wherein the rotational speed can be 300 rpm, 330 rpm, 360 rpm, 390 rpm, 420 rpm, 450 rpm, 480 rpm, 510 rpm, 540 rpm, 570 rpm or 600 rpm, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0056] Preferably, the ball milling time in step (3) is 4 to 8 hours, wherein the time can be 4 hours, 5 hours, 6 hours, 7 hours or 8 hours, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0057] Preferably, the sintering atmosphere of the second sintering in step (3) is an argon atmosphere.

[0058] Preferably, step (3) the second sintering includes a third sintering stage and a fourth sintering stage.

[0059] Preferably, the sintering temperature of the third sintering stage in step (3) is 300-600℃, wherein the sintering temperature can be 300℃, 330℃, 360℃, 390℃, 420℃, 450℃, 480℃, 510℃, 540℃, 570℃ or 600℃, etc., but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0060] Preferably, the holding time for the third sintering stage in step (3) is 1 to 4 hours, wherein the holding time can be 1 hour, 2 hours, 3 hours or 4 hours, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0061] Preferably, the sintering temperature of the fourth sintering stage in step (3) is 800-1000℃, wherein the sintering temperature can be 800℃, 820℃, 840℃, 860℃, 880℃, 900℃, 920℃, 940℃, 960℃, 980℃ or 1000℃, etc., but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0062] Preferably, the holding time for the fourth sintering stage in step (3) is 4 to 8 hours. The holding time can be 4 hours, 5 hours, 6 hours, 7 hours or 8 hours, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0063] Preferably, the heating rate of the second sintering is 1 to 5 °C / min, wherein the heating rate can be 1 °C / min, 2 °C / min, 3 °C / min, 4 °C / min or 5 °C / min, etc., but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0064] As a preferred technical solution of the present invention, the preparation method includes the following steps:

[0065] (1) The silicon nanowire dispersion, silane coupling agent and acid solution are placed in the first solvent and mixed at a rate of 300-500 rpm for 2-4 hours. After the first mixing, the mixture is allowed to stand for 6-12 hours, filtered and dried to obtain surface-modified silicon nanowires.

[0066] (2) The surface-modified silicon nanowires described in step (1) and the first carbon source are placed in a second solvent and mixed at a rate of 100-600 rpm for 2-8 hours. After filtration and drying, a first sintering is performed at a heating rate of 1-5 °C / min. The first sintering includes a first stage sintering at a sintering temperature of 400-600 °C and a holding time of 1-4 hours, and a second stage sintering at a sintering temperature of 800-1000 °C and a holding time of 4-8 hours to obtain a first sintered product.

[0067] (3) Grind the first sintered product from step (2) to a particle size of 1-20 μm, ball mill it with the second carbon source, and then perform a second sintering at a heating rate of 1-5 °C / min. The second sintering includes a third sintering at a sintering temperature of 300-600 °C and a holding time of 1-4 h, and a fourth sintering at a sintering temperature of 800-1000 °C and a holding time of 4-8 h, to obtain a second sintered product. Grind the second sintered product to obtain a silicon-carbon anode material with a particle size of 0.5-5 μm.

[0068] The second objective of this invention is to provide an application of a method for preparing a silicon-carbon anode material as described in the first objective, wherein the preparation method is applied in the field of lithium-ion batteries.

[0069] Compared with the prior art, the present invention has the following beneficial effects:

[0070] The silicon-carbon anode material prepared by this invention has the advantages of high capacity and good cycle performance, with a capacity of over 776 mAh / g and a cycle performance of over 98%. Attached Figure Description

[0071] Figure 1 This is an electron microscope image of silicon nanowires, the silicon-carbon anode material, in Embodiment 1 of the present invention.

[0072] Figure 2 This is an electron microscope image of silicon nanowires, the silicon-carbon anode material in Comparative Example 1 of this invention.

[0073] Figure 3 These are battery cycle performance test diagrams from Embodiments 1, 4-5, and Comparative Examples 1-2 of the present invention. Detailed Implementation

[0074] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0075] Example 1

[0076] This embodiment provides a method for preparing a silicon-carbon anode material, including the following steps:

[0077] (1) 100 mL of silicon nanowire dispersion, the mass fraction of silicon nanowires in the dispersion is 2.5%, the solvent of the dispersion is deionized water, the dispersant is POIZ accounting for 0.25% of the mass fraction of the first solution, 0.5 g of KH560 silane coupling agent is added, glacial acetic acid is added to adjust the pH to 3.0, the mixture is stirred for 1 h and then allowed to stand for 10 h, the supernatant is removed, the mixture is filtered, and the mixture is spray-dried at 80 °C for 12 h to obtain surface-modified silicon nanowires;

[0078] (2) Prepare the asphalt into a solution and mix it with the surface-modified silicon nanowires obtained in step (1) at a silicon-to-carbon ratio of 1:1 for 2 hours. After spray drying, place it in an atmosphere sintering furnace, protect it with argon gas, keep it at 500℃ for 3 hours, and sinter at 900℃ for 6 hours. The heating rate is 5℃ / min.

[0079] (3) The first sintered product from step (2) was subjected to airflow vortex milling and grinding to a particle size of 10 μm. After drying at 80°C for 12 h, it was ball-milled with tannic acid at a mass ratio of 1:1 and placed in an atmosphere sintering furnace. Under argon protection, it was held at 500°C for 3 h and sintered at 900°C for 6 h, with a heating rate of 5°C / min. After the product was removed, it was further pulverized by grinding to obtain silicon-carbon anode material with a particle size of 2.5 μm. In this embodiment, the electron microscope image of the silicon nanowires when ground to 20 μm is shown below. Figure 1 As shown, no silicon wires have detached.

[0080] Example 2

[0081] This embodiment provides a method for preparing a silicon-carbon anode material, including the following steps:

[0082] (1) 100 mL of silicon nanowire dispersion, the mass fraction of silicon nanowire in the dispersion is 1%, the solvent of the dispersion is ethanol, the dispersant is PVP accounting for 0.1% of the mass fraction of the first solution, 0.5 g of KH560 silane coupling agent is added, glacial acetic acid is added to adjust the pH to 3.5, the mixture is stirred for 1 h and then allowed to stand for 12 h, the supernatant is removed, the mixture is filtered, and the mixture is spray-dried at 80 °C for 12 h to obtain surface-modified silicon nanowires;

[0083] (2) Phenolic resin was prepared into a solution and mixed with the surface-modified silicon nanowires obtained in step (1) at a silicon-to-carbon ratio of 1:2 for 2 hours. After spray drying, it was placed in an atmosphere sintering furnace, protected by argon, and kept at 400℃ for 4 hours and sintered at 800℃ for 8 hours. The heating rate was 3℃ / min.

[0084] (3) The first sintered product from step (2) was subjected to airflow vortex pulverization and grinding to a particle size of 20 μm. After drying at 80°C for 12 h, it was ball-milled with starch at a mass ratio of 1:9 and placed in an atmosphere sintering furnace. Under argon protection, it was held at 300°C for 4 h and sintered at 800°C for 8 h at a heating rate of 5°C / min. After the product was removed, it was pulverized by grinding to obtain silicon-carbon anode material with a particle size of 0.5 μm.

[0085] Example 3

[0086] This embodiment provides a method for preparing a silicon-carbon anode material, including the following steps:

[0087] (1) 100 mL of silicon nanowire dispersion, the mass fraction of silicon nanowire in the dispersion is 5%, the solvent of the dispersion is ethanol, the dispersant is PVP accounting for 0.5% of the mass fraction of the first solution, 0.5 g of KH570 silane coupling agent is added, glacial acetic acid is added to adjust the pH to 4.5, the mixture is stirred for 1 h and then allowed to stand for 6 h, the supernatant is removed, the mixture is filtered, and the mixture is spray-dried at 100 °C for 12 h to obtain surface-modified silicon nanowires;

[0088] (2) Prepare a solution of polyacrylonitrile and mix it with the surface-modified silicon nanowires obtained in step (1) at a silicon-to-carbon ratio of 1:0.5 for 2 hours. After spray drying, place it in an atmosphere sintering furnace, protect it with argon gas, keep it at 600℃ for 1 hour, and sinter at 1000℃ for 4 hours. The heating rate is 1℃ / min.

[0089] (3) The first sintered product from step (2) was subjected to airflow vortex pulverization and grinding to a particle size of 2 μm. After drying at 80°C for 12 h, it was mixed with asphalt at a mass ratio of 1:0.5 and placed in an atmosphere sintering furnace. Under argon protection, it was held at 600°C for 1 h and sintered at 1000°C for 4 h, with a heating rate of 5°C / min. After the product was removed, it was pulverized by grinding to obtain silicon-carbon anode material with a particle size of 5 μm.

[0090] Example 4

[0091] In this embodiment, the only difference is that step (1) of adding glacial acetic acid to adjust the pH to 3.0, stirring for 1 hour and then letting it stand for 10 hours is replaced with adding glacial acetic acid to adjust the pH to 3.5, stirring for 1 hour and then letting it stand for 10 hours. All other conditions are the same as in Example 1.

[0092] Example 5

[0093] In this embodiment, the only difference is that step (1) of adding glacial acetic acid to adjust the pH to 3.0, stirring for 1 hour and then letting it stand for 10 hours is replaced with adding glacial acetic acid to adjust the pH to 4.0, stirring for 1 hour and then letting it stand for 10 hours. All other conditions are the same as in Example 1.

[0094] Example 6

[0095] In this embodiment, the only difference is that the steps of adding glacial acetic acid to adjust the pH to 4.0, stirring for 1 hour and then letting it stand for 10 hours in step (1) are replaced with the steps of adding glacial acetic acid to adjust the pH to 5.0, stirring for 1 hour and then letting it stand for 10 hours in step (1). All other conditions are the same as in Example 1.

[0096] Example 7

[0097] In this embodiment, the only difference is that the first sintering product in step (2) is ground to a particle size of 25 μm instead of being subjected to airflow vortex pulverization and grinding to a particle size of 10 μm. All other conditions are the same as in Example 1.

[0098] Example 8

[0099] In this embodiment, the only difference is that the surface-modified silicon nanowires obtained by spray drying at 80°C for 12 hours in step (1) are replaced with surface-modified silicon nanowires obtained by ordinary evaporation drying at 80°C for 12 hours. All other conditions are the same as in Example 1.

[0100] Example 9

[0101] In this embodiment, except that step (3) of grinding the product to obtain a silicon-carbon anode material with a particle size of 2.5 μm is replaced by grinding the product to obtain a silicon-carbon anode material with a particle size of 5.5 μm, all other conditions are the same as in Example 1.

[0102] Example 10

[0103] In this embodiment, except that step (3) of grinding the product to obtain silicon-carbon anode material with a particle size of 2.5 μm is replaced by grinding the product to obtain silicon-carbon anode material with a particle size of 0.1 μm, all other conditions are the same as in Example 1.

[0104] Comparative Example 1

[0105] This comparative example provides a method for preparing a silicon-carbon anode:

[0106] (1) Take 100ml of silicon nanowire dispersion, add 0.5g of silane coupling agent, add glacial acetic acid to adjust the pH to 3.0, stir for 1h, let stand for 12h, remove the supernatant, filter, and dry at 80℃ for 12h to obtain surface modified silicon nanowires.

[0107] (2) The carbon source was prepared into a solution and mixed with the surface-modified silicon nanowires obtained in step (1) at a silicon-to-carbon ratio of 1:1. After stirring for 2 hours, the mixture was spray-dried and placed in an atmosphere sintering furnace. Under argon protection, the mixture was held at 500°C for 3 hours and then sintered at 900°C for 6 hours at a heating rate of 5°C / min. After the product was removed, it was ground to the required particle size to obtain the silicon-carbon anode material.

[0108] The electron microscope image of the silicon-carbon anode material ground to 20 μm in this comparative example is shown below. Figure 2 As shown, silicon nanowires detach.

[0109] Comparative Example 2

[0110] This comparative example provides a method for preparing a silicon-carbon anode material:

[0111] The carbon source was prepared into a solution and mixed with dispersed silicon nanowires at a silicon-to-carbon ratio of 1:1. The mixture was stirred for 2 hours, spray-dried, and then placed in an atmosphere sintering furnace under argon protection. The furnace was held at 500°C for 3 hours and then sintered at 900°C for 6 hours at a heating rate of 5°C / min. After removal, the product was ground to the desired particle size to obtain the silicon-carbon anode material. The cycle performance test results of the batteries assembled from the silicon-carbon anode materials in Examples 1, 4-5, and Comparative Examples 1-2 are as follows: Figure 3 As shown.

[0112] The silicon-carbon anode materials from Examples 1-10 and Comparative Examples 1-2 were assembled into batteries, and the battery cycle performance and battery capacity were tested. The test results are shown in Table 1.

[0113] The battery cycle performance refers to the efficiency at 20℃ / 1C on the 50th cycle.

[0114] Table 1

[0115]

[0116]

[0117] As can be seen from the table above, Example 1 showed the best results. After appropriate pH modification, the silicon nanowires could be well combined with the carbon source, preventing a large amount of silicon nanowires from falling off during subsequent grinding. Spray drying granulation controlled the particle morphology and reduced silicon wire agglomeration during ordinary drying. After the first sintering, airflow pulverization and spheroidization controlled the silicon wires to a suitable aspect ratio, ensuring the performance of the silicon nanowires while reducing the specific surface area of ​​the particles, increasing the tap density, and improving capacity and cycle performance. The second coating effectively re-coated the silicon nanowires that had partially fallen off after the first coating, reducing direct contact between the silicon nanowires and the electrolyte and improving cycle performance.

[0118] All parameters in Examples 1-5 are within the protection scope of this invention, and the battery performance is good. In Example 6, the pH value was changed to 5.0. After the pH increased, the battery capacity decreased and the battery cycle performance decreased. In Example 7, the particle size of the first sintered product was increased. Compared with Example 1, the battery capacity decreased and the battery cycle performance deteriorated. In Example 8, during normal drying, the particles agglomerated together, resulting in uneven subsequent drying, which reduced the battery capacity and deteriorated the cycle performance. It can be seen from Examples 8-9 that when the particle size of the silicon-carbon anode material is too large or too small, if it is too small, it will cause silicon nanowires to break and detach from carbon. If the particle size is too large, it will not be conducive to secondary coating. Therefore, the battery capacity of Examples 8-9 is lower than that of Example 1, and the cycle performance is poor.

[0119] In Comparative Example 1, only one sintering process was performed, resulting in a decrease in the battery's cycle performance. In Comparative Example 2, no further surface modification of the silicon nanowires was performed, leading to a further decrease in the battery's capacity and cycle performance.

[0120] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for preparing a silicon-carbon anode material, characterized in that, The preparation method includes the following steps: (1) The silicon nanowire dispersion, silane coupling agent and acid solution are placed in a first solvent for a first mixing and then allowed to stand. After filtration and drying, surface-modified silicon nanowires are obtained. The silane coupling agent includes KH560 and / or KH570. (2) The surface-modified silicon nanowires described in step (1) are mixed with the first carbon source in the second solvent, filtered and spray-dried, and then sintered to obtain the first sintered product. (3) The first sintered product in step (2) is subjected to airflow vortex pulverization and grinding to a particle size of 1~20µm, ball milled with the second carbon source, and then subjected to a second sintering to obtain a second sintered product. The second sintered product is then ground to obtain a silicon-carbon anode material with a particle size of 0.5~5µm.

2. The preparation method according to claim 1, characterized in that, The dispersant in the silicon nanoparticle dispersion in step (1) includes any one or a combination of at least two of POIZ, PVP or DARVAN.

3. The preparation method according to claim 1, characterized in that, The acid solution in step (1) includes glacial acetic acid.

4. The preparation method according to claim 1, characterized in that, Step (1) The first solvent includes deionized water and / or ethanol.

5. The preparation method according to claim 1, characterized in that, In step (1), the mass fraction of silicon nanowires in the silicon nanowire dispersion in the first solvent is 1-5%.

6. The preparation method according to claim 1, characterized in that, The mass fraction of the dispersant in the silicon nanowire dispersion in step (1) is 0.1~0.5% in the first solvent.

7. The preparation method according to claim 1, characterized in that, The mass fraction of the silane coupling agent in the first solvent in step (1) is 0.5~2%.

8. The preparation method according to claim 1, characterized in that, The acid solution in step (1) is used to adjust the pH of the solution in the first mixture to 3.5~4.

5.

9. The preparation method according to claim 1, characterized in that, Step (1) The mixing rate of the first mixture is 300~500 rpm.

10. The preparation method according to claim 1, characterized in that, Step (1) The mixing time of the first mixture is 2~4h.

11. The preparation method according to claim 1, characterized in that, Step (1) The mixing temperature of the first mixture is 20~30℃.

12. The preparation method according to claim 1, characterized in that, The settling time in step (1) is 6~12h.

13. The preparation method according to claim 1, characterized in that, The temperature for standing in step (1) is 20~30℃.

14. The preparation method according to claim 1, characterized in that, The inlet air temperature for the spray dryer is 80~160℃.

15. The preparation method according to claim 1, characterized in that, The outlet air temperature of the spray dryer is 60~100℃.

16. The preparation method according to claim 1, characterized in that, Step (2) The first carbon source includes any one or a combination of at least two of the following: asphalt, tannic acid, phenolic resin, starch or polyacrylonitrile.

17. The preparation method according to claim 1, characterized in that, Step (2) The second solvent includes any one of tetrahydrofuran, cyclohexane, deionized water or anhydrous ethanol.

18. The preparation method according to claim 17, characterized in that, The second solvent includes deionized water or anhydrous ethanol.

19. The preparation method according to claim 1, characterized in that, In step (2), the mass fraction of the first carbon source in the second solvent is 20-50%.

20. The preparation method according to claim 1, characterized in that, In step (2), the silicon-to-carbon ratio of the surface-modified silicon nanowires and the first carbon source is 1:(0.5~2).

21. The preparation method according to claim 1, characterized in that, In step (2), the solid content of the solution in the second mixture is 5-10%.

22. The preparation method according to claim 1, characterized in that, Step (2) The second mixing time is 2~8h.

23. The preparation method according to claim 1, characterized in that, In step (2), the second mixing rate is 100~600 rpm.

24. The preparation method according to claim 1, characterized in that, Step (2) The sintering atmosphere of the first sintering is an argon atmosphere.

25. The preparation method according to claim 1, characterized in that, Step (2) The first sintering includes a first sintering stage and a second sintering stage.

26. The preparation method according to claim 25, characterized in that, The sintering temperature of the first sintering stage is 400~600℃.

27. The preparation method according to claim 25, characterized in that, The holding time for the first sintering stage is 1 to 4 hours.

28. The preparation method according to claim 25, characterized in that, The sintering temperature for the second stage of sintering is 800~1000℃.

29. The preparation method according to claim 25, characterized in that, The holding time for the second sintering stage is 4 to 8 hours.

30. The preparation method according to claim 1, characterized in that, The heating rate of the first sintering is 1~5℃ / min.

31. The preparation method according to claim 1, characterized in that, Step (3) The second carbon source includes any one or a combination of at least two of the following: asphalt, tannic acid, phenolic resin, starch, or polyacrylonitrile.

32. The preparation method according to claim 1, characterized in that, In step (3), the mass ratio of the second carbon source to the first sintered product is 1:(0.5~9).

33. The preparation method according to claim 1, characterized in that, The main stage of the airflow vortex pulverizing and grinding process rotates at 4000~6000 rpm.

34. The preparation method according to claim 1, characterized in that, The grading speed of the airflow vortex pulverizer is 3000~4000 rpm.

35. The preparation method according to claim 1, characterized in that, The time for the airflow vortex pulverization and grinding is 60~120 minutes.

36. The preparation method according to claim 1, characterized in that, The ball milling in step (3) is a dry ball milling process.

37. The preparation method according to claim 1, characterized in that, The rotation speed of the ball mill in step (3) is 300~600 rpm.

38. The preparation method according to claim 1, characterized in that, The ball milling time in step (3) is 4 to 8 hours.

39. The preparation method according to claim 1, characterized in that, Step (3) The sintering atmosphere for the second sintering is an argon atmosphere.

40. The preparation method according to claim 1, characterized in that, Step (3) The second sintering includes a third sintering stage and a fourth sintering stage.

41. The preparation method according to claim 40, characterized in that, The sintering temperature of the third sintering stage in step (3) is 300~600℃.

42. The preparation method according to claim 40, characterized in that, The heat preservation time for the third sintering stage in step (3) is 1~4h.

43. The preparation method according to claim 40, characterized in that, The sintering temperature of the fourth sintering stage in step (3) is 800~1000℃.

44. The preparation method according to claim 40, characterized in that, The heat preservation time for the fourth sintering stage in step (3) is 4~8h.

45. The preparation method according to claim 1, characterized in that, The heating rate for the second sintering is 1~5℃ / min.

46. ​​The preparation method according to claim 1, characterized in that, The preparation method includes the following steps: (1) The silicon nanowire dispersion, silane coupling agent and acid solution are placed in the first solvent and mixed at a rate of 300-500 rpm for 2-4 hours. After the first mixing, the mixture is allowed to stand for 6-12 hours, filtered and dried to obtain surface-modified silicon nanowires. (2) The surface-modified silicon nanowires described in step (1) and the first carbon source are placed in a second solvent and mixed at a rate of 100-600 rpm for 2-8 hours. After filtration and drying, a first sintering is performed at a heating rate of 1-5℃ / min. The first sintering includes a first stage sintering at a sintering temperature of 400-600℃ and a holding time of 1-4 hours, and a second stage sintering at a sintering temperature of 800-1000℃ and a holding time of 4-8 hours to obtain a first sintered product. (3) Grind the first sintered product from step (2) to a particle size of 1~20µm, ball mill it with the second carbon source, and then perform a second sintering at a heating rate of 1-5℃ / min. The second sintering includes a third sintering at a sintering temperature of 300~600℃ and a holding time of 1~4h and a fourth sintering at a sintering temperature of 800~1000℃ and a holding time of 4~8h to obtain a second sintered product. Grind the second sintered product to obtain a silicon-carbon anode material with a particle size of 0.5~5µm.

47. The application of a method for preparing a silicon-carbon anode material as described in any one of claims 1-46 in the preparation of lithium-ion batteries.

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