A nanocellulose-based silicon-carbon negative electrode material and a preparation method and application thereof

Abstract

The application belongs to the field of electrochemistry, and discloses a kind of silicon-carbon negative electrode material based on nanocellulose and its preparation method and application.Cellulose is dispersed in deionized water, and a cellulose colloid solution is obtained by physical peeling and ionic liquid assisted acidolysis;The conductive agent and carbon source are dispersed into the colloid solution, and after adding the coupling agent and silicon source, it is prepared by spray drying and sintering.The application combines the preparation of nanocellulose and the preparation of silicon-carbon, reduces the intermediate separation process, and simplifies the process.At the same time, during the silicon-carbon ball forming process, the ionic liquid and coupling agent in the slurry can induce and promote the surface combination of carbon source and silicon source;Nanocellulose promotes the nanometer formation of silicon, carbon and other components, and couples with the conductive agent to form an internal conductive network and a coating layer during the carbonization process;The metal ion of the hydrolysis catalyst plays a catalytic role in the carbonization process, and the stable carbon layer is formed by the deposition of the gas source.

Description

Technical Field

[0001] This invention belongs to the field of electrochemistry, and particularly relates to a method for preparing silicon-carbon anode materials. Background Technology

[0002] Cellulose is the most widely distributed and abundant polysaccharide in nature, accounting for more than 50% of the carbon content in the plant kingdom. It is one of the main sources of renewable materials and has wide applications in many fields, including energy storage. Nanocellulose is a nanoscale cellulose material with excellent mechanical strength, high crystallinity, high aspect ratio, large specific surface area, and modifiability, making it suitable for preparing high-performance nanocomposites. However, the highly ordered hydrogen bond network structure of cellulose makes it difficult to dissolve in conventional solvents, thus limiting further development and large-scale application. Existing cellulose dissolution systems suffer from problems such as excessive degradation, non-recyclability, and difficulty in depolymerization, necessitating the development of novel nanocellulose hydrolysis processes.

[0003] With the widespread application of lithium-ion batteries in new energy vehicles, low-altitude economy, portable electronics, and large-scale energy storage, high energy density and high rate capability have become the future development trend of batteries. The performance of the anode material directly determines the performance of lithium batteries. Currently, traditional graphite is the main anode material for lithium-ion batteries, and its specific capacity is approaching its theoretical limit, making it difficult to meet the performance requirements of high-energy-density batteries for high-specific-capacity anode materials. Silicon-based materials have advantages such as high capacity and suitable lithium insertion / extraction potential, showing good prospects for replacing graphite. However, their large volume expansion and poor conductivity remain key technical challenges restricting their large-scale application. The preparation of high-performance silicon-carbon materials by combining nanocellulose with silicon-based materials, utilizing its high mechanical strength, modifiability, high aspect ratio, and high carbonization conductivity, has attracted widespread attention.

[0004] Our team's previously published patent CN117525366A discloses a novel silicon-based anode material and its preparation method. The method involves preparing a solution of organic carbon source, carbon nanotubes, and binder, spray drying, and sintering to obtain a porous carbon material. The porous carbon material and nano-silicon powder are then added to a lithium fluoride conductive solution, and vacuum rotary sintering is performed to obtain a silicon-carbon precursor with nano-silicon deposited inside the porous carbon. This silicon-carbon precursor is then added to a nano-cellulose / ionic liquid solution, stirred, dried, and calcined to obtain a novel silicon-based anode material with a multi-layered composite coating structure. This patent employs a three-step sintering route, which is lengthy and energy-intensive. During the rotary evaporation process after stirring the porous carbon and nano-silicon in the solution, effective deposition inside the nano-silicon cannot be guaranteed, resulting in surface deposition and agglomeration. The high-temperature forced-air drying process after mixing the nano-cellulose and silicon-carbon precursor carries the risk of nano-silicon oxidation, and the carbonization process cannot guarantee the deposition of pyrolyzed carbon from the nano-cellulose on the surface of the silicon-carbon precursor to form a uniformly coated carbon layer. Patent CN114824234A discloses a silicon-carbon composite material, its preparation method, and its application. The method involves mixing a nanocellulose solution, a silicon source, and a coupling agent. The coupling agent binds the nanocellulose and silicon source together, allowing the nanocellulose to tightly coat the silicon source surface. After centrifugation, sintering is performed, forming a carbon fiber layer on the silicon source surface, which buffers volume expansion. While this patented process is simple, simply coating and carbonizing with nanocellulose cannot form a completely uniform carbon coating layer, limiting its effectiveness in buffering the volume expansion of the silicon source and failing to effectively suppress side reactions between the electrolyte and the silicon source surface. Summary of the Invention

[0005] To address the technical challenges of designing complex nanostructures, low initial efficiency, and poor cycle stability in silicon-based materials, this invention proposes a silicon-carbon anode material based on nanocellulose, its preparation method, and its applications. This preparation method utilizes a short-process flow to obtain nanocellulose and a one-pot process to granulate the silicon-carbon material. The resulting silicon-carbon anode exhibits advantages such as a well-formed, spherical structure, high porosity and density, and excellent electrochemical performance. The process is simple, easily scaled up, and shows promise for industrialization, providing a technical reference for the technological improvement and product upgrading of novel silicon-carbon anode materials for lithium-ion batteries.

[0006] To achieve the above objectives, the technical solution of the present invention is implemented as follows:

[0007] Nanocellulose is first prepared by physical milling and exfoliation followed by ionic liquid-assisted acid hydrolysis of cellulose, offering advantages such as a short process and low cost. A carbon source, conductive agent, coupling agent, and silicon source are sequentially added to the obtained nanocellulose colloidal solution to form a homogeneous mixture. This mixture is then spray-granulated to form a uniform nano-microstructured silicon-carbon precursor, which is carbonized to form a uniform surface coating layer. The prepared material possesses a multi-level coating structure and a pervasive conductive network, ensuring structural stability and fast carrier transport performance.

[0008] The preparation method of silicon-carbon anode material based on nanocellulose includes the following steps:

[0009] (1) Cellulose was added to deionized water, and after stirring and high-energy ultrasonic treatment, it was milled to obtain dispersion A. High-energy ultrasonic treatment promoted the separation of its lamellae and achieved preliminary separation; the milling process physically separated the cellulose lamellae and promoted the breaking of cellulose glycosidic bonds.

[0010] (2) Add the hydrolysis catalyst and ionic liquid to dispersion A, adjust the pH to 1.0-2.0 with acid solution, and obtain dispersion B after heating and stirring. The catalyst is a transition metal salt that can selectively degrade cellulose to generate an amorphous structure with microcrystalline size. The ionic liquid can destroy the complex structure of cellulose through swelling, weaken the hydrogen bond force, and promote the glycosidic bond breakage.

[0011] (3) After adjusting the pH of dispersion B to 3.0-4.0, a carbon source and a conductive agent are added; then a coupling agent and a silicon source are added, and dispersion C is obtained after dispersion. By adjusting the pH of the solution, the protonation of the coated carbon source can be promoted, and the bonding between the carbon source and the nano-silicon can be promoted to form a stable carbon layer. The introduction of the coupling agent can promote the cross-linking of nanocellulose, coated carbon source and silicon source, and promote the bonding between nanocellulose and coated carbon source and silicon source surface.

[0012] (4) The dispersion C is spray-dried to obtain silicon-carbon precursor D. The spray-drying process promotes the formation of nano- and micro-structures by granulation of silicon source, carbon source, and nanocellulose, so that the carbon source forms a stable carbon layer on the silicon surface, and the nanocellulose is uniformly distributed from the inside to the outside of the nano- and micro-structure, forming a uniform conductive network structure.

[0013] (5) Silicon-carbon precursor D is sintered in nitrogen and carbonized by vapor deposition to obtain silicon-carbon product E; then, after washing and drying, silicon-carbon anode material based on nanocellulose is obtained. High-temperature carbonization sintering can be performed using a plasma-enhanced vapor deposition furnace, first using nitrogen for sintering, and then introducing a deposition gas source to obtain spherical silicon-carbon product E. The carbonization process forms a stable amorphous carbon coating layer. Nanocellulose forms a microcrystalline carbon layer to achieve carbon coating on the one hand, and a conductive network is formed by coupling with conductive materials on the other hand. Finally, the transition metal catalytic sites in the catalyst are used to promote the formation of a deposited carbon film on the surface of the nano-microstructure, which improves the material's anti-expansion ability while inhibiting the side reactions between the electrolyte and the material surface, reducing irreversible lithium loss. In addition, washing removes impurities such as heteroatom salts remaining on the surface and inside the material, further improving the electrochemical activity of the material.

[0014] In step (1) above, the cellulose is any one of cotton cellulose, wheat straw cellulose and corn straw cellulose, with a purity of 90-95% and a particle size D50 of 30-65μm; the high-energy ultrasonic treatment time is 1-4h.

[0015] Furthermore, the grinding time in step (1) is 1-4 hours, and the zirconium oxide beads used for grinding have a particle size of 0.1 mm, 0.2 mm, or 0.3 mm.

[0016] In step (2) above, the hydrolysis catalyst is any one of zinc chloride, ferric chloride, nickel chloride, cobalt chloride, zinc nitrate, nickel nitrate, cobalt acetate, and nickel acetate; the ionic liquid is any one of 1-ethyl-3-methylimidazolium acetate, 1-allyl-3-methylimidazolium chloride, 1-butyl-3-methylimidazolium chloride, 1-ethyl-3-methylimidazolium hydrogen sulfate, and 3-ethoxymethyl-1-methylimine hydrogen sulfate.

[0017] Furthermore, the mass ratio of the hydrolysis catalyst to the ionic liquid is (2-5):(2-3); the acid solution is any one of oxalic acid, acetic acid, citric acid, sulfuric acid, hydrochloric acid, and nitric acid.

[0018] The heating and stirring process in step (2) above is carried out at a temperature of 60-90℃ for 2-8 hours.

[0019] In step (3) above, the mass ratio of cellulose, carbon source, conductive agent, coupling agent and silicon source in dispersion C is 5:(6-8):(0.1-0.25):(0.15-0.5):(7.5-15); the concentration of carbon source is 30-40 g / L.

[0020] Furthermore, in step (3) above, the carbon source is any one of chitosan, citric acid, phytic acid, sucrose, polyethylene glycol, phenolic resin, polydopamine, and fructose; the conductive agent is any one of single-walled or multi-walled carbon nanotubes, hydroxyl carbon nanotubes, carboxyl carbon nanotubes, graphene oxide, graphene, conductive carbon black, and acetylene black; the coupling agent is any one of γ-aminopropyltriethoxysilane, 3-glycidyl etheroxypropylmethyldiethoxysilane, N1-(3-(trimethoxysilyl)propyl)ethane-1,2-diamine, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, and hexadecyltrimethylammonium bromide; and the silicon source is at least one of silicon suboxide, nano-silicon, and micron-silicon, wherein the silicon suboxide particle size D50 is 3-5 μm, the nano-silicon particle size D50 is 50-150 nm, and the micron-silicon particle size D50 is 0.5-2 μm.

[0021] In step (4) above, the spray drying spray pressure is 0.15-0.25 MPa and the inlet temperature is 160-200℃.

[0022] In step (5) above, nitrogen sintering involves heating to 700-1000℃ at a rate of 3-15℃ / min and holding for 2-6 hours. In vapor deposition carbonization sintering, the deposition gas source is a mixture of at least one of acetylene, ethylene, methane, and ethane with nitrogen. The temperature of vapor deposition carbonization sintering is 500-800℃ and the time is 0.5-2 hours.

[0023] Furthermore, in step (5), the solid content of product E during the washing process is 10-20%, the washing time is 0.5-1h, and the number of washing cycles is 2-4.

[0024] The silicon-carbon anode material prepared using the above-described method has a pore structure from the inside out.

[0025] A lithium-ion battery comprising the aforementioned silicon-carbon anode material.

[0026] The beneficial effects of this invention are:

[0027] (1) This invention prepares nanocellulose and its colloidal solution in a low-cost and short-process manner. Cellulose is dispersed in deionized water, and the cellulose layers are peeled off and glycosidic bonds are broken through a physical pulverization process of high-energy ultrasound and sand milling. By adding acid, ionic liquid and hydrolysis catalyst, the strong hydrogen bond force between cellulose is weakened by the swelling effect of ionic liquid, and the dissociation and glycosidic bond breaking process under acidic conditions is strengthened, further realizing the depolymerization and bond breaking of cellulose, forming a uniform and stable nanocellulose suspension. Then the suspension is diluted and the pH is adjusted, and a coating carbon source, conductive agent, coupling agent and silicon source are added in sequence. By protonating part of the carbon source and under the induction of the coupling agent, the carbon source, nanocellulose and silicon source surfaces are organically combined to form a coated carbon layer. Spray drying is used to achieve nano-spherical formation of silicon and other materials, promoting stable coating of carbon source on silicon surface and between particles, and forming a conductive network from the inside out. During the carbonization process, nanocellulose is pyrolyzed to form cellulose microcrystalline carbon layer or conductive fiber, which plays a coating role and forms a mixed conductive channel with conductive agent components. The catalyst transition metal sites contained on the material surface and inside can induce the deposition of carbon source to form carbon film, carbon tube or mixed coating layer on the material surface, further improving the material structure and performance stability.

[0028] (2) The silicon-carbon anode material based on nanocellulose prepared in this invention has a multi-level coating structure and a hybrid conductive network, as well as a pore structure from the inside out. The multi-level coating structure mainly includes dissolved carbon source connected to the silicon surface, an amorphous carbon layer formed by the pyrolysis of nanocellulose during the carbonization process, and a deposited carbon layer formed by the plasma-enhanced vapor deposition process. The hybrid conductive network includes conductive agents, conductive fibers formed by the carbonization of nanocellulose, etc. The conductive agents are adsorbed on the surface of individual silicon source particles and form a conductive framework network structure from the inside out during the spray drying and spherical formation process. Finally, some carbon nanotubes are also grown in situ in the deposited carbon layer, further improving conductivity. In addition, certain pores are formed inside during the spray drying and nano-spherical formation process, and the pyrolysis process of carbonized nanocellulose releases certain space, further forming a porous structure. The multi-level coating and pore structure can effectively alleviate the volume change of the silicon source during the lithium insertion and extraction process and improve structural stability; the multi-level conductive network improves the electron transport efficiency and high electrochemical activity of the material, thereby improving the charging specific capacitance and first-time efficiency of the material and ensuring its good cycle stability.

[0029] (3) The process of the present invention is simple and easy to scale up in batches, and has industrialization prospects. It provides technical reference for the technical improvement and product upgrading of new silicon-carbon anode materials for lithium-ion batteries. Attached Figure Description

[0030] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0031] Figure 1 This is a flowchart of the preparation method of nanocellulose and silicon-carbon anode materials of the present invention.

[0032] Figure 2 This is a scanning electron microscope image of the silicon-carbon anode material based on nanocellulose obtained in Example 1.

[0033] Figure 3 This is a scanning electron microscope image of the silicon-carbon anode material based on nanocellulose obtained in Comparative Example 1.

[0034] Figure 4 This is a comparison diagram of the first charge and discharge of the silicon-carbon anode materials obtained in Example 1 and Comparative Examples 1 and 2.

[0035] Figure 5 This is a comparison chart of the cycle stability of the silicon-carbon anode materials obtained in Example 1 and Comparative Examples 1 and 2. Detailed Implementation

[0036] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0037] Example 1

[0038] The preparation method of silicon-carbon anode material based on nanocellulose in this embodiment is shown in the flowchart below. Figure 1 As shown, the steps are as follows:

[0039] (1) Add 5g of cotton cellulose (purity 95%, particle size D50 is 30μm) to 200mL of deionized water, stir and treat with high-energy ultrasound for 1h, and then treat in a sand mill with 0.3mm zirconia beads for 2h to obtain dispersion A.

[0040] (2) Add 0.2g zinc chloride and 0.2g 1-ethyl-3-methylimidazolium acetate to dispersion A, add oxalic acid solution to adjust the pH to 1.0, and stir at 60℃ for 2h to obtain dispersion B;

[0041] (3) Add ammonia water to adjust the pH to 3.0, then add 6g chitosan and 0.1g single-walled carbon nanotubes and ultrasonically disperse them evenly; then add 0.15g γ-aminopropyltriethoxysilane and 15g nano-silicon (particle size D50: 50-150nm) and ultrasonically disperse them evenly. Stir at room temperature for 2h to obtain dispersion C.

[0042] (4) Spray dry the dispersion C, adjust the spray drying pressure to 0.2 MPa and the inlet temperature to 180℃ to obtain silicon-carbon precursor D;

[0043] (5) The silicon-carbon precursor D was carbonized and sintered at high temperature using a plasma-enhanced vapor deposition furnace at a heating rate of 5℃ / min. The carbonization was carried out at 800℃ for 2h, and then 5% acetylene / nitrogen mixed gas was introduced. The deposition was carried out at 500℃ for 0.5h to obtain spherical silicon-carbon product E. Then it was dispersed in deionized water, the solid content was adjusted to 10%, and it was washed 3 times for 0.5h each time. The product was then filtered and dried to obtain silicon-carbon anode material.

[0044] The microstructure of the prepared samples was determined using a JEOL JSM-7900F scanning electron microscope (Japan). Figure 2 It can be seen that the prepared silicon-carbon material has a good nano-micro spherical structure and is rich in porous structure, which can ensure good wetting of electrolyte and greatly promote ion transport. Moreover, the lithium insertion and extraction process has the function of buffering silicon volume change.

[0045] Example 2

[0046] The preparation method of silicon-carbon anode material based on nanocellulose in this embodiment includes the following steps:

[0047] (1) Add 5g of wheat straw cellulose (purity 90%, particle size D50 is 65μm) to 200mL of deionized water, stir and treat with high-energy ultrasound for 2h, and then treat in a sand mill with 0.2mm zirconia beads for 1h to obtain dispersion A.

[0048] (2) Add 0.2g of ferric chloride and 0.25g of 3-ethoxymethyl-1-methylimine hydrogen sulfate to dispersion A, add acetic acid solution to adjust the pH to 2.0, and stir at 70℃ for 3h to obtain dispersion B;

[0049] (3) Add ammonia water to adjust the pH to 4.0, then add 6g of citric acid and 0.15g of multi-walled carbon nanotubes and ultrasonically disperse them evenly; then add 0.2g of 3-glycidyl etheroxypropylmethyldiethoxysilane and 15g of silica (particle size D50: 3-5μm) and ultrasonically disperse them evenly. Stir at room temperature for 6h to obtain dispersion C.

[0050] (4) Spray dry the dispersion C, adjust the spray drying pressure to 0.15 MPa and the inlet temperature to 160℃ to obtain silicon-carbon precursor D;

[0051] (5) The silicon-carbon precursor D was carbonized and sintered at high temperature using a plasma-enhanced vapor deposition furnace at a heating rate of 10℃ / min. It was carbonized at 700℃ for 4h, and then 5% ethylene / nitrogen mixed gas was introduced. It was deposited at 600℃ for 1h to obtain spherical silicon-carbon product E. Then it was dispersed in deionized water, the solid content was adjusted to 15%, and it was washed twice for 1h each time. Then it was filtered and dried to obtain silicon-carbon anode material.

[0052] Example 3

[0053] The preparation method of silicon-carbon anode material based on nanocellulose in this embodiment includes the following steps:

[0054] (1) Add 5g of corn stalk cellulose (purity 92.5%, particle size D50 of 40μm) to 200mL of deionized water, stir and treat with high-energy ultrasound for 2h, and then treat in a sand mill with 0.1mm zirconia beads for 3h to obtain dispersion A.

[0055] (2) Add 0.5g of nickel chloride and 0.3g of 1-allyl-3-methylimidazolium chloride to dispersion A, add citric acid solution to adjust the pH to 1.0, and stir at 80℃ for 5h to obtain dispersion B;

[0056] (3) Adjust the pH to 3.5 by adding ammonia water dropwise, then add 8g of phytic acid and 0.2g of hydroxyl carbon nanotubes and disperse them evenly by ultrasonication; then add 0.25g of N1-(3-(trimethoxysilyl)propyl)ethane-1,2-diamine and 15g of micron-sized silicon (particle size D50: 0.5-2μm) and disperse them evenly by ultrasonication. Stir at room temperature for 8h to obtain dispersion C.

[0057] (4) Spray dry the dispersion C, adjust the spray drying pressure to 0.25 MPa and the inlet temperature to 170 °C to obtain silicon-carbon precursor D;

[0058] (5) The silicon-carbon precursor D was carbonized and sintered at high temperature using a plasma-enhanced vapor deposition furnace at a heating rate of 3℃ / min. The carbonization was carried out at 750℃ for 4h, and then 5% methane / nitrogen mixed gas was introduced. The deposition was carried out at 700℃ for 1.5h to obtain spherical silicon-carbon product E. Then it was dispersed in deionized water, the solid content was adjusted to 20%, and it was washed 4 times, each time for 0.5h. Then it was filtered and dried to obtain silicon-carbon anode material.

[0059] Example 4

[0060] The preparation method of silicon-carbon anode material based on nanocellulose in this embodiment includes the following steps:

[0061] (1) Add 5g of corn stalk cellulose (purity 90%, particle size D50 is 50μm) to 200mL of deionized water, stir and treat with high-energy ultrasound for 3h, and then treat in a sand mill with 0.2mm zirconia beads for 4h to obtain dispersion A.

[0062] (2) Add 0.2g cobalt chloride and 0.2g 1-butyl-3-methylimidazolium chloride to dispersion A, add sulfuric acid solution to adjust the pH to 2.0, and stir at 90℃ for 6h to obtain dispersion B;

[0063] (3) Add ammonia water to adjust the pH to 3.0, then add 8g of sucrose and 0.15g of carboxylated carbon nanotubes and disperse them evenly by ultrasonication; then add 0.5g of 3-aminopropyltrimethoxysilane and 15g of silica (particle size D50: 3-5μm) and disperse them evenly by ultrasonication. Stir at room temperature for 2h to obtain dispersion C.

[0064] (4) Spray dry the dispersion C, adjust the spray drying pressure to 0.2 MPa and the inlet temperature to 190℃ to obtain silicon-carbon precursor D;

[0065] (5) The silicon-carbon precursor D was carbonized and sintered at high temperature using a plasma-enhanced vapor deposition furnace at a heating rate of 15℃ / min. It was carbonized at 900℃ for 2h, and then 5% ethane / nitrogen mixed gas was introduced. It was deposited at 800℃ for 2h to obtain spherical silicon-carbon product E. Then it was dispersed in deionized water, the solid content was adjusted to 20%, and it was washed twice, each time for 1h. Then it was filtered and dried to obtain silicon-carbon anode material.

[0066] Example 5

[0067] The preparation method of silicon-carbon anode material based on nanocellulose in this embodiment includes the following steps:

[0068] (1) Add 5g of cotton cellulose (purity 95%, particle size D50 is 65μm) to 200mL of deionized water, stir and treat with high-energy ultrasound for 4h, and then treat in a sand mill with 0.2mm zirconia beads for 4h to obtain dispersion A.

[0069] (2) Add 0.2g cobalt chloride and 0.2g 1-butyl-3-methylimidazolium chloride to dispersion A, add sulfuric acid solution to adjust the pH to 2.0, and stir at 90℃ for 6h to obtain dispersion B;

[0070] (3) Add ammonia water to adjust the pH to 3.0, then add 8g of polyethylene glycol and 0.15g of graphene oxide and disperse evenly by ultrasonication; then add 0.3g of 3-aminopropyltriethoxysilane and 15g of nano-silicon (particle size D50: 50-150nm) and disperse evenly by ultrasonication. Stir at room temperature for 3h to obtain dispersion C.

[0071] (4) Spray dry the dispersion C, adjust the spray drying pressure to 0.15 MPa and the inlet temperature to 200 ℃ to obtain silicon-carbon precursor D;

[0072] (5) The silicon-carbon precursor D was carbonized and sintered at high temperature using a plasma-enhanced vapor deposition furnace at a heating rate of 12℃ / min. It was carbonized at 1000℃ for 3h, and then 5% acetylene / nitrogen mixed gas was introduced. It was deposited at 600℃ for 1h to obtain spherical silicon-carbon product E. Then it was dispersed in deionized water, the solid content was adjusted to 15%, and it was washed 3 times, each time for 0.5h. Then it was filtered and dried to obtain silicon-carbon anode material.

[0073] Example 6

[0074] The preparation method of silicon-carbon anode material based on nanocellulose in this embodiment includes the following steps:

[0075] (1) Add 5g of corn stalk cellulose (purity 90%, particle size D50 is 30μm) to 200mL of deionized water, stir and treat with high-energy ultrasound for 4h, and then treat in a sand mill with 0.3mm zirconia beads for 2h to obtain dispersion A.

[0076] (2) Add 0.2g nickel nitrate and 0.25g 3-ethoxymethyl-1-methylimine hydrogen sulfate to dispersion A, add nitric acid solution to adjust the pH to 1.0, and stir at 80℃ for 4h to obtain dispersion B;

[0077] (3) Adjust the pH to 3.0 by adding ammonia dropwise, then add 6g of phenolic resin and 0.2g of graphene and disperse evenly by ultrasonication; then add 0.2g of cetyltrimethylammonium bromide, 7.5g of silicon suboxide (particle size D50: 3-5μm) and 7.5g of nano-silicon (particle size D50: 50-150nm) and disperse evenly by ultrasonication. Stir at room temperature for 4h to obtain dispersion C.

[0078] (4) Spray dry the dispersion C, adjust the spray drying pressure to 0.2 MPa and the inlet temperature to 180℃ to obtain silicon-carbon precursor D;

[0079] (5) The silicon-carbon precursor D was carbonized and sintered at high temperature using a plasma-enhanced vapor deposition furnace at a heating rate of 6℃ / min. The carbonization was carried out at 800℃ for 5h, and then 5% acetylene / nitrogen mixed gas was introduced. The deposition was carried out at 600℃ for 1.5h to obtain spherical silicon-carbon product E. Then it was dispersed in deionized water, the solid content was adjusted to 10%, and it was washed 3 times, each time for 1h. Then it was filtered and dried to obtain silicon-carbon anode material.

[0080] Example 7

[0081] The preparation method of silicon-carbon anode material based on nanocellulose in this embodiment includes the following steps:

[0082] (1) Add 5g of wheat straw cellulose (purity 95%, particle size D50 is 65μm) to 200mL of deionized water, stir and treat with high-energy ultrasound for 2h, and then treat in a sand mill with 0.2mm zirconia beads for 1.5h to obtain dispersion A;

[0083] (2) Add 0.2g cobalt acetate and 0.2g 1-ethyl-3-methylimidazolium acetate to dispersion A, add sulfuric acid solution to adjust the pH to 1.5, and stir at 70℃ for 5h to obtain dispersion B;

[0084] (3) Add ammonia water to adjust the pH to 4.0, then add 8g of polydopamine and 0.25g of conductive carbon black and disperse evenly by ultrasonication; then add 0.25g of γ-aminopropyltriethoxysilane and 15g of micron-sized silicon (particle size D50: 0.5-2μm) and disperse evenly by ultrasonication. Stir at room temperature for 2h to obtain dispersion C.

[0085] (4) Spray dry the dispersion C, adjust the spray drying pressure to 0.2 MPa and the inlet temperature to 170℃ to obtain silicon-carbon precursor D;

[0086] (5) The silicon-carbon precursor D was carbonized and sintered at high temperature using a plasma-enhanced vapor deposition furnace at a heating rate of 5℃ / min. The carbonization was carried out at 850℃ for 2h, and then 5% acetylene / nitrogen mixed gas was introduced. The carbonization was carried out at 500℃ for 0.5h to obtain spherical silicon-carbon product E. Then it was dispersed in deionized water, the solid content was adjusted to 10%, and it was washed 4 times, each time for 0.5h. Then it was filtered and dried to obtain silicon-carbon anode material.

[0087] Comparative Example 1

[0088] The preparation method of the silicon-carbon anode material in this comparative example differs from that in Example 1 in that no ionic liquid is added in step (2), while the other steps are the same, as follows:

[0089] (1) Add 5g of cotton cellulose (purity 95%, particle size D50 is 30μm) to 200mL of deionized water, stir and treat with high-energy ultrasound for 2h, and then treat in a sand mill with 0.3mm zirconia beads for 2h to obtain dispersion A.

[0090] (2) Add 0.2g of zinc chloride to dispersion A, add oxalic acid solution to adjust the pH to 1.0, and stir at 60℃ for 2h to obtain dispersion B;

[0091] (3) Add ammonia water to adjust the pH to 3.0, then add 6g chitosan and 0.1g single-walled carbon nanotubes and ultrasonically disperse them evenly; then add 0.15g γ-aminopropyltriethoxysilane and 15g nano-silicon (particle size D50: 50-150nm) and ultrasonically disperse them evenly. Stir at room temperature for 2h to obtain dispersion C.

[0092] (4) Spray dry the dispersion C, adjust the spray drying pressure to 0.2 MPa and the inlet temperature to 180℃ to obtain silicon-carbon precursor D;

[0093] (5) The silicon-carbon precursor D was carbonized and sintered at high temperature using a plasma-enhanced vapor deposition furnace at a heating rate of 5℃ / min. The carbonization was carried out at 800℃ for 2h, and then 5% acetylene / nitrogen mixed gas was introduced. The deposition was carried out at 500℃ for 0.5h to obtain spherical silicon-carbon product E. Then it was dispersed in deionized water, the solid content was adjusted to 10%, and it was washed 3 times for 0.5h each time. The product was then filtered and dried to obtain silicon-carbon anode material.

[0094] Comparative Example 2

[0095] The preparation method of the silicon-carbon anode material in this comparative example differs from that in Example 1 in that the 5% acetylene / nitrogen mixed gas deposition is not performed in step (5), while the other steps are the same, as follows:

[0096] (1) Add 5g of cotton cellulose (purity 95%, particle size D50 is 30μm) to 200mL of deionized water, stir and treat with high-energy ultrasound for 1h, and then treat in a sand mill with 0.3mm zirconia beads for 2h to obtain dispersion A.

[0097] (2) Add 0.2g zinc chloride and 0.2g 1-ethyl-3-methylimidazolium acetate to dispersion A, add oxalic acid solution to adjust the pH to 1.0, and stir at 60℃ for 2h to obtain dispersion B;

[0098] (3) Add ammonia water to adjust the pH to 3.0, then add 6g chitosan and 0.1g single-walled carbon nanotubes and ultrasonically disperse them evenly; then add 0.15g γ-aminopropyltriethoxysilane and 15g nano-silicon (particle size D50: 50-150nm) and ultrasonically disperse them evenly. Stir at room temperature for 2h to obtain dispersion C.

[0099] (4) Spray dry the dispersion C, adjust the spray drying pressure to 0.2 MPa and the inlet temperature to 180℃ to obtain silicon-carbon precursor D;

[0100] (5) The silicon-carbon precursor D was carbonized and sintered at high temperature using a plasma-enhanced vapor deposition furnace at a heating rate of 5℃ / min and carbonized at 800℃ for 2h to obtain spherical silicon-carbon product E; then it was dispersed in deionized water, the solid content was adjusted to 10%, and it was washed 3 times for 0.5h each time. After filtration and drying, silicon-carbon anode material was obtained.

[0101] Application examples

[0102] The silicon-carbon anode material prepared according to this invention is mixed with conductive agent carbon black and binder (PAA) in a mass ratio of 8:1:1 to form a slurry, which is then uniformly coated onto copper foil and dried to form an electrode. A 1.0 mol / L electrolyte is used. -1A mixed organic solution of LiPF6 was used, with the solvent being EC:DEC:DMC (mass ratio 1:1:1), and the additive being 10% FEC. The separator was a microporous polypropylene membrane, and the positive electrode was a lithium sheet, which was then processed into a CR2032 coin cell.

[0103] (1) Battery first-efficiency performance

[0104] The first discharge test used 100mA / g to discharge to 0.005V, and then charged to 2.0V. Figure 4 The figures show the initial charge-discharge diagrams of the silicon-carbon anode materials based on nanocellulose obtained in Example 1 and the comparative examples. It can be seen that the battery assembled from the materials prepared in Example 1 achieved an initial charge specific capacity of 1956.6 mAh / g and an initial efficiency of 91.5%. The capacity utilization and initial efficiency of the materials in Comparative Examples 1 and 2 are significantly different from those of Example 1. Furthermore, the initial efficiency data for each example are shown in Table 1.

[0105] Table 1

[0106] First charge specific capacity (mAh / g) First-efficacy (%) Example 1 1956.6 91.5 Example 2 1346.5 83.2 Example 3 1852.3 90.4 Example 4 1246.5 83.5 Example 5 1918.6 90.5 Example 6 1752.7 87.3 Example 7 2086.3 90.8 Comparative Example 1 1823.3 86.5 Comparative Example 2 1756.3 84.4

[0107] As can be seen from the table, the silicon-carbon anode material prepared in Example 1 exhibits high capacity and first-pass coulombic efficiency, and from... Figure 2 The material exhibits well-formed spherical particles and a porous structure extending from the inside out. This invention demonstrates high coulombic efficiency even for silicon-oxygen raw materials with initially low coulombic efficiency, as shown in Examples 2, 4, and 6. In Comparative Example 1, no ionic liquid was added, resulting in a cellulose product with poor nano-sizing. During spray drying, the larger cellulose particles inhibited spheroidization, leading to the formation of particles like... Figure 3 The image shows relatively dispersed particles. (From...) Figure 4 , Figure 5 As can be seen from the initial charge-discharge diagrams and cycle diagrams of Example 1 and Comparative Examples 1 and 2, the dispersed structure of Comparative Example 1 and the lack of secondary conductive carbon modification on the surface of Comparative Example 2 result in lower initial efficiency. During the cycle, the silicon-carbon material of Comparative Example 1 is prone to electrode cracking, and the silicon-carbon material of Comparative Example 2, lacking surface carbon layer binding, will also break and fail. Therefore, the cycle stability is worse than that of Example 1.

[0108] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a silicon-carbon anode material based on nanocellulose, characterized in that, The steps are as follows: (1) Add cellulose to deionized water, and after stirring and high-energy ultrasonic treatment, grind to obtain dispersion A; (2) Add the hydrolysis catalyst and ionic liquid to dispersion A, adjust the pH to 1.0-2.0 with acid solution, and obtain dispersion B after heating and stirring; wherein the mass ratio of hydrolysis catalyst to ionic liquid is (2-5):(2-3); the ionic liquid is any one of 1-ethyl-3-methylimidazolium acetate, 1-allyl-3-methylimidazolium chloride, 1-butyl-3-methylimidazolium chloride, 1-ethyl-3-methylimidazolium hydrogen sulfate and 3-ethoxymethyl-1-methylimine hydrogen sulfate; (3) After adjusting the pH of dispersion B to 3.0-4.0, add carbon source and conductive agent; then add coupling agent and silicon source, and disperse to obtain dispersion C; wherein, the mass ratio of cellulose, carbon source, conductive agent, coupling agent and silicon source in dispersion C is 5:(6-8):(0.1-0.25):(0.15-0.5):(7.5-15); the concentration of carbon source is 30-40 g / L; (4) The dispersion C was spray-dried to obtain silicon carbide precursor D; (5) Silicon-carbon precursor D is sintered in nitrogen and carbonized by vapor deposition to obtain silicon-carbon product E; then, after washing and drying, silicon-carbon anode material is obtained; wherein, the sintering in nitrogen is carried out by heating to 700-1000℃ at a heating rate of 3-15℃ / min and holding for 2-6h; the deposition gas source in the carbonized vapor deposition sintering is a mixture of at least one of acetylene, ethylene, methane and ethane with nitrogen, and the temperature of the carbonized vapor deposition sintering is 500-800℃ and the time is 0.5-2h.

2. The method for preparing silicon-carbon anode material based on nanocellulose according to claim 1, characterized in that, In step (1), the cellulose is any one of cotton cellulose, wheat straw cellulose and corn straw cellulose, with a purity of 90-95% and a particle size D50 of 30-65μm; the high-energy ultrasonic treatment time is 1-4h.

3. The method for preparing silicon-carbon anode material based on nanocellulose according to claim 2, characterized in that, The hydrolysis catalyst in step (2) is any one of zinc chloride, ferric chloride, nickel chloride, cobalt chloride, zinc nitrate, nickel nitrate, cobalt acetate, and nickel acetate.

4. The method for preparing silicon-carbon anode material based on nanocellulose according to claim 3, characterized in that, The heating and stirring process in step (2) is carried out at a temperature of 60-90℃ for 2-8 hours.

5. The method for preparing silicon-carbon anode material based on nanocellulose according to claim 4, characterized in that, In step (3), the carbon source is any one of chitosan, citric acid, phytic acid, sucrose, polyethylene glycol, phenolic resin, polydopamine, and fructose; the conductive agent is any one of single-walled or multi-walled carbon nanotubes, hydroxyl carbon nanotubes, carboxyl carbon nanotubes, graphene oxide, graphene, conductive carbon black, and acetylene black; the coupling agent is any one of γ-aminopropyltriethoxysilane, 3-glycidyl etheroxypropylmethyldiethoxysilane, N1-(3-(trimethoxysilyl)propyl)ethane-1,2-diamine, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, and hexadecyltrimethylammonium bromide; and the silicon source is at least one of silicon suboxide, nano-silicon, and micron-silicon.

6. The method for preparing silicon-carbon anode material based on nanocellulose according to claim 5, characterized in that, In step (4), the spray drying spray pressure is 0.15-0.25 MPa and the inlet temperature is 160-200℃.

7. A silicon-carbon anode material prepared by the preparation method according to any one of claims 1-6, characterized in that, The silicon-carbon anode material has a porous structure from the inside out.

8. A lithium-ion battery, characterized in that, Including the silicon-carbon anode material as described in claim 7.

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