A method for preparing a high-rate lithium battery composite silicon-carbon negative electrode material

Abstract

The present invention belongs to the field of battery technology, and specifically relates to a method for preparing a high-rate lithium battery composite silicon-carbon negative electrode material. The present invention uses low-cost carbon source materials, such as xylose and asphalt, and a simple preparation process, including the steps of mixing and dispersing silicon powder and xylose, melting and stirring asphalt, carbonization treatment, ball milling classification and CVD coating, to ensure the uniformity of the carbon layer and the performance of the material, so that the material has a low production cost and is suitable for large-scale industrial production, laying a foundation for the commercial application of high-performance lithium-ion batteries.

Description

Technical Field

[0001] The invention belongs to the technical field of batteries, and in particular relates to a method for preparing a high-rate lithium battery composite silicon-carbon negative electrode material. Background Art

[0002] As an innovative solution for the negative electrode of lithium-ion batteries, silicon-carbon composites not only make full use of the high theoretical specific capacity of silicon materials, but also cleverly overcome the fatal weakness of silicon materials, which is volume expansion during charging and discharging. When silicon reacts with lithium, its volume will expand to nearly four times its original volume, which will cause silicon particles to break, active material loss, and loss of contact with the current collector, thereby reducing the cycle stability and overall performance of the battery. However, by compounding with carbon materials, especially hard carbon, silicon-carbon composites can effectively alleviate this problem.

[0003] Hard carbon materials are known for their unique layered structure and rich pore network, which give them superior kinetics and electrolyte compatibility. Compared with graphite, hard carbon has a larger interlayer spacing and higher porosity, which means it can provide additional space buffer for silicon volume expansion, reduce silicon particle rupture and active material shedding. In addition, the pore structure of hard carbon is conducive to the rapid diffusion of lithium ions, thereby increasing the lithium ion transmission rate and enhancing the battery's rate performance.

[0004] At present, the hard carbon negative electrode materials on the market are mainly divided into several categories: biomass-based, resin-based, asphalt-based and anthracite-based. Biomass-based hard carbon materials, such as those converted from wood, rice husks, fruit shells, etc., have the advantages of abundant resources and low cost, but they contain more impurities, which may affect the electrochemical performance of the battery. Resin-based and asphalt-based hard carbon materials usually have higher purity and better electrochemical performance because they can finely control the pore structure and degree of graphitization through chemical modification and heat treatment processes. Although anthracite-based hard carbon is widely available, it may require more complex pretreatment steps during the preparation process to remove impurities and optimize its performance. Although hard carbon materials perform well in kinetics and structural stability, their specific capacity and first coulombic efficiency (first efficiency) are relatively low.

[0005] A Chinese patent application document (publication number: CN107394137A) discloses a method for preparing a high-performance silicon-carbon negative electrode material, which uses phenolic resin as a coating carbon source to provide a skeleton. However, its high price will increase the cost of raw materials for the product, and the preparation process is prone to agglomeration, which will lead to uneven distribution of the carbon layer, affecting the utilization rate and electrochemical performance of the active material. In addition, during the pyrolysis or carbonization process, the phenolic resin is prone to condensation, causing adhesion between materials, affecting the dispersibility and processing performance of the finished product. Furthermore, the pore structure of the phenolic resin after carbonization may not be ideal, which will have an adverse effect on the diffusion rate of lithium ions and the cycle performance of the electrode.

[0006] The Chinese patent application document (publication number: CN117038874A) discloses an asphalt-based lithium-ion battery silicon-carbon negative electrode material and its preparation method and application. The use of organic solvents to dissolve it will increase the cost of the product. One of its solvent components, ethylene glycol, is a flammable chemical, which poses a risk in terms of safety. In addition, asphalt itself is a dark brown complex mixture composed of hydrocarbons of different molecular weights and their non-metallic derivatives. When asphalt is diluted by organic solvents, its carbon content will be relatively reduced. The reduction in carbon content directly affects the conductivity of the silicon-carbon composite material, because the carbon layer is a key component that provides an electron transmission channel. The reduction in carbon content may cause the conductivity of the composite material to deteriorate, thereby affecting the charge and discharge efficiency and cycle life of the battery. Summary of the invention

[0007] The purpose of the present invention is to address the deficiencies in the prior art. The present invention provides a method for preparing a high-rate lithium battery composite silicon-carbon negative electrode material, which can not only effectively inhibit the volume expansion of silicon during the charge and discharge process, but also significantly improve the conductivity of the composite material, thereby significantly improving the cycle performance and rate characteristics of the silicon-based negative electrode material.

[0008] The above-mentioned object of the present invention is achieved by the following scheme: a method for preparing a high-rate lithium battery composite silicon-carbon negative electrode material, the method comprising the following steps:

[0009] S1, dispersing silicon powder in a xylose aqueous solution, then adding a surfactant to disperse, and then drying to obtain powder particles;

[0010] S2, adding the powder particles into the asphalt for dispersion, and then performing roller pressing;

[0011] S3, after roller pressing, carbonization treatment is performed, and then crushing is performed to obtain powder particles;

[0012] S4. The powder particles are coated by CVD to obtain a silicon-carbon negative electrode material.

[0013] In the above-mentioned method for preparing a high-rate lithium battery composite silicon-carbon negative electrode material, the mass ratio of silicon powder to xylose in step S1 is 1:0.5-1.5.

[0014] The present invention uses xylose as a precursor to improve the conductivity of the negative electrode material. Since the silicon powder used in the present invention is nano-spherical silicon with a particle size of 0.03-0.08 μm, it is difficult to disperse. Xylose can be well matched with the nano-spherical silicon to achieve uniform sugar coating and improve the dispersibility of nano-silicon. The powder provides capacity, and the mass ratio of silicon powder to xylose is controlled within the range of 1:0.5-1.5, so that the capacity and cycle of the negative electrode material can be maintained in a higher range. Because the ratio of xylose to silicon powder directly determines the comprehensive performance of the negative electrode material, if the xylose ratio is too low, it is not enough to form an effective conductive network, resulting in a decrease in the cycle performance of the negative electrode material; if the xylose ratio is too high, although the conductivity may be enhanced, the capacity of the battery will be sacrificed. At the same time, in the process of material preparation, a high proportion of xylose will cause the powder to become too viscous and easy to agglomerate, increasing the difficulty of processing. When the xylose ratio is too high, the material may become very viscous and easy to agglomerate during heat treatment or mixing, which not only affects the uniformity of the material, but also reduces its electrochemical properties, such as rate capability and cycle stability.

[0015] Preferably, the silicon powder has a particle size D50 of 0.05-0.06 μm and a particle size Dmax of <0.6 μm.

[0016] Preferably, the amount of surfactant added is 3-5% of the mass of the silicon powder.

[0017] In the above-mentioned method for preparing a high-rate lithium battery composite silicon-carbon negative electrode material, the surfactant in step S1 is at least one of hexadecyltrimethylammonium bromide and dodecyltrimethylammonium bromide.

[0018] In the above-mentioned method for preparing a high-rate lithium battery composite silicon-carbon negative electrode material, the asphalt temperature in step S2 is 400-450°C. The high-temperature molten asphalt of 400-450°C of the present invention has strong fluidity and can evenly wrap nano-silicon particles, which can not only effectively prevent the agglomeration of silicon particles and effectively alleviate volume expansion, but also improve the electrode conductivity and obtain a stable SEI film, providing a stable carbon coating layer. The asphalt-silicon / xylose powder in this temperature range is just in a molten state, easy to stir, and evenly dispersed. Preferably, the national standard No. 10 asphalt selected by the present invention is completely melted at 400-450°C, but if the temperature is too high, the asphalt / silicon / xylose mixed powder will have the risk of deflagration. If the temperature is too low, the asphalt will not melt, and the asphalt and powder in the solid state cannot be evenly dispersed.

[0019] As a preference, the density of asphalt is 1.00-1.10 g / cm 3 , softening point is 95-110℃;

[0020] Further preferably, the asphalt penetration test (25°C, 100g, 5s) shows that the 0.1mm penetration is 10.8mm.

[0021] Preferably, the mass ratio of the powder particles to the asphalt in step S2 is 1:0.8-1.2. In the present invention, the mass ratio of the powder particles to the asphalt is controlled to be 1:0.8-1.2 to obtain a negative electrode material with higher cycle performance and first efficiency.

[0022] In the above-mentioned method for preparing a high-rate lithium battery composite silicon-carbon negative electrode material, the carbonization treatment in step S3 is carried out in an Ar atmosphere at a temperature of 750-1000° C. for a time of 60-180 min.

[0023] Preferably, the carbonization treatment heating rate is 4-6°C / min, and the carbonization yield is 40-60%.

[0024] In the above-mentioned method for preparing a high-rate lithium battery composite silicon-carbon negative electrode material, after crushing in step S3, ball milling is performed and then sieving is performed; wherein the ball milling time is 1-5h, and the sieving mesh size is generally at least one of 425 mesh, 625 mesh, and 800 mesh.

[0025] In the above-mentioned method for preparing a high-rate lithium battery composite silicon-carbon negative electrode material, the median particle size of the precursor in step S3 is 8-12 μm. The present invention controls the precursor particle size within the range of 8-12 μm, which helps to ensure that the precursor is evenly dispersed in the molten asphalt and is completely wrapped by the asphalt. Too large a particle size may cause particle sedimentation, while too small a particle size may cause aggregation between particles, both of which will affect the uniformity of the material. Within this particle size range, each particle has enough surface area to contact the asphalt and is completely wrapped, which forms a uniform carbon layer, which can effectively alleviate the volume expansion of silicon during charging and discharging, improve the cycle stability and structural integrity of the material, and particles of appropriate size can also provide an ideal electrochemical reaction interface, which is conducive to the embedding and de-embedding of lithium ions, thereby improving the conductivity and rate performance of the material. In addition, the optimization of particle size also helps to form a more stable solid electrolyte interface (SEI) film, which is crucial to the long-term cycle performance of the battery.

[0026] In the above-mentioned method for preparing a high-rate lithium battery composite silicon-carbon negative electrode material, step S4 is to perform CVD coating using methane and acetylene as carbon source gases under an argon atmosphere, wherein the vacuum degree during the coating process is 300-1000Pa.

[0027] In the above-mentioned method for preparing a high-rate lithium battery composite silicon-carbon negative electrode material, the flow rate of methane is 40-60cm 3 / min, the flow rate of acetylene is 120-180cm 3 / min, the flow rate of argon is 120-180cm 3 / min.

[0028] Preferably, the purity of methane, acetylene and argon is at least 99.9%.

[0029] In the above-mentioned method for preparing a high-rate lithium battery composite silicon-carbon negative electrode material, the CVD coating temperature is 800-1100°C and the time is 80-240min. In the preparation process of the present invention, the temperature of CVD coating is set between 800-1100°C to ensure that xylose and asphalt can be completely converted into carbon during the pyrolysis process to form a uniform carbon coating layer while avoiding the generation of undesirable byproducts. If the CVD coating temperature exceeds 1100°C, the carbonization reaction will cause excessive generation of undesirable byproducts such as silicon carbide (SiC). Although silicon carbide has a certain conductivity, its combination with silicon-based materials will change the electrochemical properties of the material, which is not conducive to improving the conductivity and capacity of the powder, but may reduce the overall electrochemical performance of the material; when the CVD coating temperature is lower than 800°C, the carbonization reaction of xylose and asphalt is incomplete, resulting in residual non-carbonized substances in the material. Since xylose and asphalt are non-conductive and have no capacity contribution, their presence will reduce the conductivity and capacity of the sample, thereby affecting the cycle performance and energy density of the battery.

[0030] The present invention sets the CVD coating time at 80-240 minutes. This time window is to ensure that the carbonization reaction is fully carried out, so that xylose and asphalt are completely converted into carbon to form a stable carbon coating layer. If the coating time is too short, xylose and asphalt may not be completely converted, and the remaining non-carbonized substances will affect the performance of the material; if the coating time is too long, long-term high-temperature treatment may cause changes in the structure of the carbon coating layer, and even induce unnecessary side reactions, which may also have an adverse effect on the electrochemical properties of the material.

[0031] Preferably, the CVD coating is carried out in a CVD rotary furnace at a rotation speed of 1-5 r / min.

[0032] The present invention also provides a lithium ion battery, which comprises the silicon-carbon negative electrode material prepared by the above preparation method.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] 1. The present invention uses multi-layer carbon coating technology and chemical vapor deposition (CVD) on the surface of silicon powder to form a uniform and highly covered carbon layer, which effectively buffers the volume change of silicon material during charging and discharging, reduces structural damage, and improves the cycle stability and service life of the material;

[0035] 2. The silicon-carbon negative electrode material prepared by the present invention has an initial reversible capacity of up to 1500mAh / g and an initial coulombic efficiency of not less than 88% under 0.1C half-cell conditions, showing excellent electrochemical performance, especially high capacity and high initial coulombic efficiency;

[0036] 3. The present invention uses low-cost carbon source materials, such as xylose and asphalt, and a simple preparation process, including the steps of mixing and dispersing silicon powder and xylose, melting and stirring asphalt, carbonization treatment, ball milling classification and CVD coating, to ensure the uniformity of the carbon layer and the performance of the material, so that the material has a low production cost and is suitable for large-scale industrial production, laying the foundation for the commercial application of high-performance lithium-ion batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 This is a process flow chart for preparing silicon-carbon negative electrode material in Example 1.

[0038] Figure 2 These are the SEM images of xylose and nano-silicon coated with xylose in Example 1; a is the SEM image of xylose; b is the SEM image of nano-silicon coated with xylose.

[0039] Figure 3 This is a SEM image of the silicon-carbon negative electrode material prepared in Example 1.

[0040] Figure 4 These are rate test diagrams of the silicon-carbon negative electrode material prepared in Example 1; a, 0.3C rate current, b, 0.6C rate current. DETAILED DESCRIPTION

[0041] The following are specific embodiments of the present invention, which further describe the technical solutions of the present invention, but the present invention is not limited to these embodiments. Example 1

[0042] according to Figure 1 The preparation of silicon-carbon negative electrode material is shown in the figure, which specifically includes the following steps:

[0043] S1, take 250g xylose and dissolve it in 1200ml water, add 250g silicon powder with a median particle size of 50nm, then add 10g hexadecyltrimethylammonium bromide, heat in a water bath at 70°C, stir at 350rpm, blow dry for 24h, and pass the mixed powder through a 625-mesh sieve to obtain powder;

[0044] S2. Stir the powder and asphalt in a molten state at 400°C for 15 minutes at a mass ratio of 1:1, stir at high speed until uniform, and roll on a roller press for 3 times or more until a uniform and stable precursor is formed;

[0045] S3, the precursor at 200cm 3 / min argon atmosphere, carbonized at 900℃ for 60min, and sieved to obtain powder particles with a median particle size of 10μm;

[0046] S4, then at 50 cm 3 / minMethane, 150 cm 3 / min acetylene, 150 cm 3 / min argon gas condition, CVD positive pressure coating was carried out at 950°C in a rotary kiln with a rotation speed of 2r / min for 240min, and after cooling, the silicon-carbon negative electrode material was sieved through 625 mesh.

[0047] Figure 2 These are the SEM images of xylose and the SEM images of nano-silicon coated with xylose. It can be seen that the porous structure of xylose provides a good skeleton structure for silicon powder, which can better inhibit its expansion effect.

[0048] Figure 3 This is a SEM image of the silicon-carbon negative electrode material prepared in Example 1; it can be seen from the figure that the material has the appearance of smooth spherical nanoparticles, which can increase the specific surface area, shorten the ion transmission path, and improve the coulomb efficiency of the material; carbon nanotubes grow on the surface, have a complete conductive network, and improve electronic conductivity.

[0049] Figure 4 This is a rate test diagram of the silicon-carbon negative electrode material prepared in Example 1; it can be seen from the figure that at the rate current of 0.3C and 0.6C, the coulombic efficiency of the battery is maintained above 98%, and the capacity is at a relatively high value, indicating that the asphalt-xylose-silicon powder composite negative electrode material has a relatively high rate and cycle performance. Example 2

[0050] S1, take 125g xylose and dissolve it in 1200ml water, add 250g silicon powder with a median particle size of 50nm, then add 10g hexadecyltrimethylammonium bromide, heat in a water bath at 70°C, stir at 350rpm, blow dry for 24h, and pass the mixed powder through a 625-mesh sieve to obtain powder;

[0051] S2. Stir the powder and asphalt in a molten state at 400°C for 15 minutes at a mass ratio of 1:1.2, stir at high speed until uniform, and roll on a roller press for 3 times or more until a uniform and stable precursor is formed;

[0052] S3, the precursor at 200cm 3 / min argon atmosphere, carbonized at 900℃ for 60min, and sieved to obtain powder particles with a median particle size of 10μm;

[0053] S4, then at 50 cm 3 / minMethane, 150 cm 3 / min acetylene, 150 cm 3 / min argon gas condition, CVD positive pressure coating was carried out at 950°C in a rotary kiln with a rotation speed of 2r / min for 240min, and after cooling, the silicon-carbon negative electrode material was sieved through 625 mesh. Example 3

[0054] S1, take 375g xylose and dissolve it in 1200ml water, add 250g silicon powder with a median particle size of 50nm, then add 10g hexadecyltrimethylammonium bromide, heat in a water bath at 70℃, stir at 350rpm, blow dry for 24h, and pass the mixed powder through a 625-mesh sieve to obtain powder;

[0055] S2. Stir the powder and asphalt in a molten state at 450°C for 15 minutes at a mass ratio of 1:0.8, stir at high speed until uniform, and roll on a roller press for 3 times or more until a uniform and stable precursor is formed;

[0056] S3, the precursor at 200cm 3 / min argon atmosphere, carbonized at 900℃ for 60min, and sieved to obtain powder particles with a median particle size of 10μm;

[0057] S4, then at 50 cm 3 / minMethane, 150 cm 3 / min acetylene, 150 cm 3 / min argon gas condition, CVD positive pressure coating was carried out at 950°C in a rotary kiln with a rotation speed of 2r / min for 240min, and after cooling, the silicon-carbon negative electrode material was sieved through 625 mesh. Example 4

[0058] The only difference from Example 1 is that the amount of xylose added is 50 g. Example 5

[0059] The only difference from Example 1 is that the amount of silicon powder added is 50 g. Example 6

[0060] The only difference from Example 1 is that the mass ratio of the powder in step S2 to the asphalt in a molten state at 400° C. is 1:0.5. Example 7

[0061] The only difference from Example 1 is that the mass ratio of the powder in step S2 to the asphalt in a molten state at 400° C. is 1:1.5. Example 8

[0062] The only difference from Example 1 is that the asphalt temperature in step S2 is 300°C. Example 9

[0063] The only difference from Example 1 is that the asphalt temperature in step S2 is 550°C.

[0064] Comparative Example 1:

[0065] After the large piece of asphalt is crushed, it is frozen with liquid nitrogen and crushed further. After passing through a 40-mesh sieve, 150 g is taken out and mixed with 150 g of 50 nm silicon powder using a three-dimensional powder mixer for 40 min (20 min forward, 20 min reverse) / time, and the powder is mixed for 120 min. The mixture is then carbonized at 1100 °C for 90 min in a rotary kiln under an Ar atmosphere, cooled and taken out, and passed through a 625-mesh sieve to obtain the desired powder material.

[0066] Then at 50 cm 3 / minMethane, 50 cm 3 / min acetylene, 200 cm 3 Under the condition of argon gas / min, CVD positive pressure coating was carried out at 1050°C for 135 min in a rotary kiln with a rotation speed of 2r / min, and the silicon-carbon negative electrode material was obtained after cooling.

[0067] Comparative Example 2:

[0068] The only difference from Example 1 is that the silicon powder is directly and continuously stirred with the asphalt in a molten state at 400°C.

[0069] Comparative Example 3:

[0070] The only difference from Example 1 is that the surfactant hexadecyltrimethylammonium bromide is not added in step S1.

[0071] Comparative Example 4:

[0072] The only difference from Example 1 is that the powder in step S1 is directly subjected to the carbonization treatment in step S3, without being mixed with asphalt in step S2.

[0073] Comparative Example 5:

[0074] The only difference from Example 1 is that the precursor is not subjected to CVD coating treatment.

[0075] Table 1: Charge and discharge cycle test of silicon-carbon negative electrode materials prepared in Examples 1-9 and Comparative Examples 1-5

[0076]

[0077] In summary, the present invention uses low-cost carbon source materials, such as xylose and asphalt, and a simple preparation process, including the steps of mixing and dispersing silicon powder and xylose, melting and stirring asphalt, carbonization treatment, ball milling classification and CVD coating, to ensure the uniformity of the carbon layer and the performance of the material, so that the material has a low production cost and is suitable for large-scale industrial production, laying the foundation for the commercial application of high-performance lithium-ion batteries.

[0078] The specific embodiments described herein are merely examples of the spirit of the present invention. Those skilled in the art may make various modifications or additions to the specific embodiments described or replace them in similar ways, but they will not deviate from the spirit of the present invention or exceed the scope defined by the appended claims.

[0079] Although the present invention has been described in detail and some specific embodiments have been cited, it is obvious to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the present invention.

Claims

1. A method for preparing a high-rate lithium battery composite silicon-carbon negative electrode material, It is characterized in that The method comprises the following steps: S1, dispersing silicon powder in a xylose aqueous solution, then adding a surfactant to disperse, and then drying to obtain powder particles; S2, adding the powder particles into the asphalt for dispersion, and then performing roller pressing; S3, after roller pressing, carbonizing treatment is performed, and then crushing is performed to obtain a precursor; S4, coating the precursor by CVD to obtain a silicon-carbon negative electrode material; The mass ratio of silicon powder to xylose in step S1 is 1:0.5-1.5; The asphalt temperature in step S2 is 400-450°C; The mass ratio of powder particles to asphalt in step S2 is 1:0.8-1.2; The CVD coating temperature is 800-1100°C and the time is 80-240min.

2. The method for preparing a high-rate lithium battery composite silicon-carbon negative electrode material according to claim 1, It is characterized in that The surfactant in step S1 is at least one of hexadecyltrimethylammonium bromide and dodecyltrimethylammonium bromide.

3. The method for preparing a high-rate lithium battery composite silicon-carbon negative electrode material according to claim 1, It is characterized in that The carbonization treatment in step S3 is carried out in an Ar atmosphere at a temperature of 750-1000° C. for a time of 60-180 min.

4. The method for preparing a high-rate lithium battery composite silicon-carbon negative electrode material according to claim 1, It is characterized in that In step S4, CVD coating is performed under an argon atmosphere using methane and acetylene as carbon source gases, wherein the vacuum degree during the coating process is 300-1000 Pa.

5. The method for preparing a high-rate lithium battery composite silicon-carbon negative electrode material according to claim 4, It is characterized in that The flow rate of methane is 40-60cm 3 / min, the flow rate of acetylene is 120-180cm 3 / min, the flow rate of argon is 120-180cm 3 / min.

6. A lithium ion battery, It is characterized in that The lithium-ion battery comprises the silicon-carbon negative electrode material prepared by the preparation method according to claim 1.

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