Silicon-based negative electrode material with multi-level composite structure and preparation method and application thereof

Abstract

The application discloses a kind of silicon-based negative electrode material of multistage composite structure and its preparation method and application, belong to lithium battery technical field.The application provides a kind of silicon-based negative electrode material of multistage composite structure and its preparation method and application to solve the problems, such as poor dispersibility of nano-silicon in the existing silicon-based negative electrode, poor resistance to expansion capacity of single-stage structure, which is 15-38 μm particle in particle size, and is sequentially surface layer carbon, high porosity filling carbon and silicon-carbon microcapsule from surface to inside;Silicon-carbon microcapsule is composed of ultrafine silicon particles and high-density filling carbon;High porosity filling carbon is a disordered structure carbon-based material, accounting for 18-25wt%;Surface layer carbon is a semi-ordered structure carbon-based material, with a thickness of 20-30nm.The application realizes two-stage dispersion treatment of ultrafine silicon particles and design of multistage composite structure, so that the ultrafine silicon particles are distributed in a monodisperse state, avoiding particle pulverization and electrode sheet cracking, and effectively improving battery performance.

Description

Technical Field

[0001] This invention belongs to the field of lithium battery technology, specifically relating to a silicon-based anode material with a multi-level composite structure, its preparation method, and its application. Background Technology

[0002] Silicon-based anodes have attracted widespread attention and research due to their high specific capacity, and their industrialization is currently progressing rapidly. Among silicon-based anodes, nano-silicon-carbon anodes are a novel type of silicon-based anode material developed using nano-silicon as a substrate, possessing a relatively mature market and broad application prospects. Currently, silicon-based anodes, represented by nano-silicon-carbon anodes, mainly employ spray drying technology. Their product characteristics include high capacity, with conventional products typically exceeding 1000 mAh / g. In practical applications, they are often blended with graphite products to achieve a capacity of 420-450 mAh / g. To more efficiently develop silicon-based anodes with superior performance, the research and industry communities have conducted research and development on various processes for silicon anodes.

[0003] 202210514967.6 discloses a method for spray granulation of a ground nano-silicon mixed solution in a spray dryer, followed by isothermal calcination to obtain a silicon-carbon anode material for lithium-ion batteries, with performance improved by adding dispersants. 202310292291.5 discloses a silicon-carbon composite anode material prepared by spray drying using graphitized mesophase carbon microspheres, silicon powder, and artificial graphite powder as raw materials, featuring a composite modification layer of tetrafluoroaluminate and carbon coating, which effectively inhibits electrolyte corrosion of the silicon material. 202310538608.9 discloses a nano-silicon-carbon composite anode material where alumina is used to coat the nano-silicon, forming an artificial SEI coating layer on the nano-silicon surface, mitigating lithium ion consumption during cycling due to the formation of a "natural" SEI layer.

[0004] The above-mentioned method for preparing silicon-based anodes via spraying has the following two technical problems: First, the nano-silicon in the silicon-based anode has poor dispersion, resulting in severe agglomeration of nano-silicon particles. During charging and discharging, this agglomeration causes significant stress concentration, which further leads to particle pulverization, electrode cracking, and failure. Second, the composite structures of the above-mentioned silicon-based anodes are all single-level composite structures, that is, nano-silicon is simply coated inside to form a single-level composite. This type of composite has very limited ability to resist the volume expansion of nano-silicon. After multiple cycles, the single-level composite structure will gradually fail, resulting in a rapid decline in the cycle performance and rate performance of the silicon-based anode. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of existing silicon-based anodes, such as poor dispersion of nano-silicon and poor resistance to expansion in single-level composite structures, and to provide a silicon-based anode material with a multi-level composite structure and excellent cycle and rate performance, as well as its preparation method and application.

[0006] This invention first provides a multi-level composite silicon-based anode material, which consists of particles with a particle size of 15–38 μm. From the surface inwards, each particle comprises a surface carbon layer, highly porous carbon-filled particles, and silicon-carbon microcapsules. The silicon-carbon microcapsules are composed of ultrafine silicon particles and high-density carbon-filled particles. The ultrafine silicon particles are monodispersed within the high-density carbon-filled particles, which are semi-disordered carbon-based materials. The highly porous carbon-filled particles are disordered carbon-based materials, accounting for 18–25% of the mass of the silicon-based anode material. The surface carbon layer is a semi-disordered carbon-based material with a thickness of 20–30 nm.

[0007] In the aforementioned multi-level composite silicon-based anode material, the silicon-carbon microcapsules are spherical or near-spherical.

[0008] In the aforementioned multi-level composite silicon-based anode material, the silicon-carbon microcapsules have a particle size of 0.8–1.3 μm.

[0009] In the aforementioned multi-level composite silicon-based anode material, the ultrafine silicon particles are sheet-like high-purity nano-silicon with a particle size of 30-50 nm.

[0010] In the aforementioned multi-level composite silicon-based anode material, the oxidation degree of the ultrafine silicon particles is <6%.

[0011] The present invention also provides a method for preparing the above-mentioned multi-level composite silicon-based anode material, which includes the following steps:

[0012] A. Microcapsule preparation: Ultrafine silica particles were added to a chitosan aqueous solution and stirred at low speed for the first time. Then, cinnamaldehyde and water-soluble phenolic resin were added, followed by sodium dodecyl sulfonate, Span 85, Tween 80 and oil phase. Then, the mixture was stirred at high speed for the second time. The mixture was demulsified and then centrifuged and washed to obtain microcapsules.

[0013] B. Preparation of silicon-carbon microcapsules: The microcapsules obtained in step A are subjected to vacuum drying and curing treatment. Then, under an inert atmosphere, the temperature is first raised to 450-550℃ and kept at that temperature, and then raised to 1000-1200℃ and kept at that temperature. After natural cooling to room temperature, silicon-carbon microcapsules are obtained.

[0014] C. Preparation of silicon-carbon microcapsules containing highly porous carbon-filled material: The silicon-carbon microcapsules obtained in step B are added to an aqueous solution of highly porous carbon-filled precursor. After stirring, a spray precursor with a solid content of 25% to 35% is obtained. Then, spray granulation is performed. After granulation, the temperature is raised to 800 to 900°C under an inert atmosphere and kept at that temperature. Then, the temperature is naturally cooled to room temperature to obtain silicon-carbon microcapsules containing highly porous carbon-filled material.

[0015] D. Preparation of surface carbon and particles: The silicon-carbon microcapsules containing highly porous carbon obtained in step C are mixed evenly with petroleum-based spinnable pitch and kneaded. After kneading, the mixture is heated to 1050-1180℃ under an inert atmosphere and kept at that temperature. Then, it is naturally cooled to room temperature to form surface carbon and obtain particles, which are silicon-based anode materials with a multi-level composite structure.

[0016] In the preparation method of the above-mentioned multi-level composite silicon-based anode material, in step A, the mass fraction of the chitosan aqueous solution is 3.2wt% to 4.5wt%.

[0017] In the preparation method of the above-mentioned multi-level composite silicon-based anode material, in step A, the mass ratio of the ultrafine silicon particles to the chitosan aqueous solution is 1:4.5 to 6.5.

[0018] In the preparation method of the above-mentioned multi-level composite silicon-based anode material, in step A, the mass ratio of the ultrafine silicon particles to cinnamaldehyde is 1:0.005-0.008.

[0019] In the preparation method of the above-mentioned multi-level composite silicon-based anode material, in step A, the mass ratio of the ultrafine silicon particles to the water-soluble phenolic resin is 1:0.6-0.75.

[0020] In the preparation method of the above-mentioned multi-level composite silicon-based anode material, in step A, the mass ratio of the ultrafine silicon particles to sodium dodecyl sulfonate, Span 85, and Tween 80 is 1:0.001~0.002:0.001~0.013:0.001~0.015.

[0021] In the preparation method of the above-mentioned multi-level composite silicon-based anode material, in step A, the oil phase is at least one of phenyl silicone oil, n-hexane, cyclohexane, liquid paraffin, and toluene.

[0022] In the preparation method of the above-mentioned multi-level composite silicon-based anode material, in step A, the mass ratio of the ultrafine silicon particles to the oil phase is 1:25-35.

[0023] In the preparation method of the silicon-based anode material with the above-mentioned multi-level composite structure, in step A, the rotation speed of the first low-speed stirring is 1000-1200 rpm.

[0024] In the preparation method of the silicon-based anode material with the above-mentioned multi-level composite structure, in step A, the time for the first low-speed stirring is 30 to 40 minutes.

[0025] In the preparation method of the silicon-based anode material with the above-mentioned multi-level composite structure, in step A, the rotation speed of the second high-speed stirring is 1800-2300 rpm.

[0026] In the preparation method of the silicon-based anode material with the above-mentioned multi-level composite structure, in step A, the second high-speed stirring time is 4 to 7 hours.

[0027] In the preparation method of the silicon-based anode material with the above-mentioned multi-level composite structure, in step B, the temperature of the vacuum drying and curing treatment is 200-250℃.

[0028] In the preparation method of the above-mentioned multi-level composite silicon-based anode material, in step B, the vacuum drying and curing treatment time is 6-9 hours.

[0029] In the preparation method of the silicon-based anode material with the above-mentioned multi-level composite structure, step B involves heating to 450-550°C at a heating rate of 2-3°C / min.

[0030] In the preparation method of the silicon-based anode material with the above-mentioned multi-level composite structure, step B involves heat treatment at 450–550°C for 0.5–2 hours.

[0031] In the preparation method of the silicon-based anode material with the above-mentioned multi-level composite structure, step B involves heating to 1000-1200℃ at a heating rate of 5-8℃ / min.

[0032] In the preparation method of the silicon-based anode material with the above-mentioned multi-level composite structure, step B involves heat treatment at 1000-1200℃ for 2-4 hours.

[0033] In the preparation method of the silicon-based anode material with the above-mentioned multi-level composite structure, in step C, the highly porous carbon precursor is at least one of sucrose, glucose, water-soluble starch, citric acid, or cyclodextrin.

[0034] In the preparation method of the silicon-based anode material with the above-mentioned multi-level composite structure, the mass ratio of the ultrafine silicon particles used in step A to the high-porosity carbon-filled precursor in the aqueous solution of the high-porosity carbon precursor used in step C is 1:1.2 to 1.5.

[0035] In the preparation method of the silicon-based anode material with the above-mentioned multi-level composite structure, in step C, the stirring speed is 400-700 rpm.

[0036] In the preparation method of the silicon-based anode material with the above-mentioned multi-level composite structure, the stirring time in step C is 1 to 2 hours.

[0037] In the preparation method of the silicon-based anode material with the above-mentioned multi-level composite structure, in step C, the conditions for spray granulation are: inlet temperature 140-180℃ and linear velocity 140-210m / s.

[0038] In the preparation method of the silicon-based anode material with the above-mentioned multi-level composite structure, in step C, the temperature is raised to 800-900℃ at a heating rate of 3-5℃ / min.

[0039] In the preparation method of the silicon-based anode material with the above-mentioned multi-level composite structure, in step C, the heat treatment time at 800-900℃ is 2-5 hours.

[0040] In the preparation method of the above-mentioned multi-level composite silicon-based anode material, the mass ratio of ultrafine silicon particles used in step A to petroleum-based spinnable pitch used in step D is 1:0.08-0.13.

[0041] In the preparation method of the silicon-based anode material with the above-mentioned multi-level composite structure, in step D, the mixing speed is 300-500 rpm.

[0042] In the preparation method of the above-mentioned multi-level composite silicon-based anode material, in step D, the time for uniform mixing is 20-50 min.

[0043] In the preparation method of the silicon-based anode material with the above-mentioned multi-level composite structure, in step D, the kneading speed is 1200-1500 rpm.

[0044] In the preparation method of the silicon-based anode material with the above-mentioned multi-level composite structure, the kneading time in step D is 10-20 min.

[0045] In the preparation method of the silicon-based anode material with the above-mentioned multi-level composite structure, step D involves heating to 1050-1180℃ at a heating rate of 3-5℃ / min.

[0046] In the preparation method of the silicon-based anode material with the above-mentioned multi-level composite structure, in step D, the heat treatment time at 1050-1180℃ is 2-5 hours.

[0047] The present invention also provides a lithium-ion battery anode sheet, which includes the silicon-based anode material with the above-mentioned multi-level composite structure.

[0048] The present invention also provides a lithium-ion battery comprising the above-described lithium-ion battery negative electrode sheet.

[0049] The beneficial effects of this invention are:

[0050] This invention addresses the dispersion problem of nano-silicon by employing a two-stage dispersion treatment on ultrafine silicon particles, resulting in a near-monodispersed distribution of these particles. This fundamentally solves the dispersion problem and significantly reduces particle pulverization and electrode cracking caused by stress concentration due to silicon particle contact. Furthermore, to address the poor expansion resistance of single-stage composite structures, this invention incorporates a multi-stage composite structure design. This includes rigid confinement of high-density carbon filler, flexible buffering of high-porosity carbon filler, and interface protection of semi-disordered carbon-based materials. These measures further effectively reduce particle pulverization and electrode cracking, improving cycle life, rate capability, and other performance characteristics. Attached Figure Description

[0051] Figure 1 This is a schematic diagram of the multi-level composite silicon-based anode material prepared according to the present invention.

[0052] Figure 2 The diagram shows the cycle performance of the silicon-based anode material with a multi-stage composite structure in Example 1 of the present invention, and the silicon-based anode materials in Comparative Examples 1 and 2. Detailed Implementation

[0053] Specifically, a multi-level composite silicon-based anode material comprises particles with a diameter of 15–38 μm. These particles, from the surface inwards, consist of a surface carbon layer, highly porous carbon-filled particles, and silicon-carbon microcapsules. The silicon-carbon microcapsules are composed of ultrafine silicon particles and high-density carbon-filled particles. The ultrafine silicon particles are monodispersed within the high-density carbon-filled particles, which are semi-disordered carbon-based materials. The highly porous carbon-filled particles are disordered carbon-based materials, accounting for 18–25% of the mass of the silicon-based anode material. The surface carbon layer is a semi-disordered carbon-based material with a thickness of 20–30 nm.

[0054] To address the issue of poor expansion resistance in single-stage composite structures, this invention employs a multi-stage composite structure design. The first stage involves the combination of high-density carbon filler within silicon-carbon microcapsules and ultrafine silicon particles. The high-density carbon filler is in direct contact with the silicon particles, while the ultrafine silicon particles are monodispersed within the high-density carbon filler. This high-density carbon filler provides stronger rigid restraint on the volume expansion of the ultrafine silicon particles, reducing particle pulverization. The second stage involves the combination of silicon-carbon microcapsules and disordered, highly porous carbon filler. This highly porous carbon filler provides flexible buffering against the expansion of ultrafine silicon particles at the particle scale of the silicon-carbon anode material. The disordered structure and high porosity enhance the buffering capacity against volume expansion and ensure rapid electrolyte penetration, thereby guaranteeing efficient capacity utilization. The third stage involves a surface carbon layer made of a semi-disordered carbon-based material. This reduces surface side reactions, minimizes lithium-ion consumption, and forms a more dense and uniform interfacial protective film, thus providing stable interfacial protection for the silicon-based anode material. Through the synergistic effect of the rigid confinement of high-density carbon filling, the flexible buffer of high-porosity carbon filling, and the interface protection of semi-disordered carbon-based materials, particle pulverization and electrode cracking are effectively reduced, and cycle and rate performance are improved.

[0055] In the multi-level composite silicon-based anode material of this invention, the inventors innovatively designed microcapsules and silicon-carbon microcapsules, and carried out two-level dispersion treatment on ultrafine silicon particles to obtain spherical or near-spherical silicon-carbon microcapsules with a particle size of 0.8 to 1.3 μm.

[0056] In this invention, the initial raw material ultrafine silicon particles have an oxidation degree of 2.5% to 3%, a particle size of 30 to 48 nm, and a shape controlled as flakes. After subsequent dispersion, calcination, spraying, and other treatments, ultrafine silicon particles that meet the requirements of the finished product are obtained. The finished product consists of flake-shaped high-purity nano-silicon with a particle size of 30 to 50 nm and an oxidation degree of <6% (the oxidation degree will be higher than that of the initial ultrafine silicon particles, while the particle size and shape remain basically unchanged).

[0057] To obtain the silicon-based anode material with a specially constructed multi-level composite structure according to the present invention, the present invention also provides a method for preparing the silicon-based anode material with the above-mentioned multi-level composite structure, which includes the following steps:

[0058] A. Microcapsule preparation: Ultrafine silica particles are added to a chitosan aqueous solution and stirred at low speed for the first time. Then, cinnamaldehyde and water-soluble phenolic resin are added, followed by sodium dodecyl sulfonate, Span 85, Tween 80 (three surfactants), and the oil phase. Then, the mixture is stirred at high speed for the second time. The mixture is demulsified (usually using isopropanol), then centrifuged and washed (usually using isopropanol for washing, 3-5 times) to obtain microcapsules.

[0059] B. Preparation of silicon-carbon microcapsules: The microcapsules obtained in step A are subjected to vacuum drying and curing treatment (drying and curing are carried out simultaneously, generally using a vacuum oven). Then, under an inert atmosphere, the temperature is first raised to 450-550℃ and kept at that temperature, and then raised to 1000-1200℃ and kept at that temperature. After that, the temperature is naturally cooled to room temperature to obtain silicon-carbon microcapsules.

[0060] C. Preparation of silicon-carbon microcapsules containing highly porous carbon-filled material: The silicon-carbon microcapsules obtained in step B are added to an aqueous solution of highly porous carbon-filled precursor. After stirring, a spray precursor with a solid content of 25% to 35% is obtained. Then, spray granulation is performed. After granulation, the temperature is raised to 800 to 900°C under an inert atmosphere and kept at that temperature. Then, the temperature is naturally cooled to room temperature to obtain silicon-carbon microcapsules containing highly porous carbon-filled material.

[0061] D. Preparation of surface carbon and particles: The silicon-carbon microcapsules containing highly porous carbon obtained in step C are mixed evenly with petroleum-based spinnable pitch and kneaded. After kneading, the mixture is heated to 1050-1180℃ under an inert atmosphere and kept at that temperature. Then, it is naturally cooled to room temperature to form surface carbon and obtain particles, which are silicon-based anode materials with a multi-level composite structure.

[0062] To address the dispersibility issue of nano-silicon, this invention employs a two-stage dispersion process for ultrafine silicon particles. The first stage of dispersion involves the structural design of microcapsules with specific particle sizes and silicon-carbon microcapsules. This initial dispersion of the ultrafine silicon particles within different silicon-carbon microcapsules significantly reduces contact and agglomeration between particles. Therefore, in step A of this invention, after adding the ultrafine silicon particles to the chitosan aqueous solution, a first low-speed stirring is performed, with the stirring speed controlled at 1000–1200 rpm, typically for 30–40 minutes. The process involves two stages of dispersion to ensure the material meets the requirements for secondary dispersion. The secondary dispersion stage involves ultrafine silicon particles with high specific surface energy. After primary dispersion, the material undergoes strong bonding with the hydroxymethyl and hydroxyl groups in the phenolic resin, ensuring that the ultrafine silicon particles are essentially monodisperse within the microcapsules during microcapsule preparation. Furthermore, these particles are monodisperse within the silicon-carbon microcapsules, forming a water-in-oil microcapsule structure. Therefore, in step A of this invention, the second high-speed stirring speed is controlled at 1800–2300 rpm, typically for 4–7 hours. This invention fundamentally solves the problem of nano-silicon dispersibility through two-stage dispersion treatment.

[0063] Furthermore, this invention also features an innovative formulation design. In step A, the chitosan aqueous solution has a mass fraction of 3.2 wt% to 4.5 wt%, and the mass ratio of ultrafine silica particles to the chitosan aqueous solution is controlled at 1:4.5 to 6.5. The mass ratio of ultrafine silica particles to cinnamaldehyde is controlled at 1:0.005 to 0.008, the mass ratio of ultrafine silica particles to water-soluble phenolic resin is controlled at 1:0.6 to 0.75, and the mass ratio of ultrafine silica particles to sodium dodecyl sulfonate, Span 85, and Tween 80 is controlled at 1:0.001 to 0.002:0.001 to 0.013:0.001 to 0.015. The oil phase is at least one of phenyl silicone oil, n-hexane, cyclohexane, liquid paraffin, and toluene, and the mass ratio of ultrafine silica particles to the oil phase is 1:25 to 35. Thus, through two-stage dispersion treatment, the ultrafine silica particles are basically in a monodisperse state, resulting in a water-in-oil microcapsule structure.

[0064] In step B of this invention, the microcapsules obtained in step A are first dried and cured in a vacuum at 200–250°C for 6–9 hours (drying and curing are carried out simultaneously, generally using a vacuum oven). Then, under an inert atmosphere, the temperature is raised to 450–550°C at a heating rate of 2–3°C / min and held for 0.5–2 hours. Finally, the temperature is raised to 1000–1200°C at a heating rate of 5–8°C / min and held for 2–4 hours. This process yields silicon-carbon microcapsules that meet the requirements, maximizing the compatibility and affinity between the two reaction raw materials (silicon-carbon microcapsules and highly porous carbon precursor) in step C, which is more conducive to the implementation of step C.

[0065] In step C of this invention, the high-porosity carbon-filled precursor is at least one of sucrose, glucose, water-soluble starch, citric acid, or cyclodextrin. After being prepared into an aqueous solution, it is then stirred with the silicon-carbon microcapsules obtained in step B at 400-700 rpm (generally stirred for 1-2 hours) to disperse evenly. By controlling the mass ratio of the ultrafine silicon particles used in step A to the high-porosity carbon-filled precursor in the aqueous solution of the high-porosity carbon-filled precursor used in step C to be 1:1.2-1.5, the solid content of the resulting spray precursor slurry is 25%-35%.

[0066] In step C of this invention, the conditions for controlling spray granulation are: inlet temperature 140-180℃, linear velocity 140-210m / s, and then heating to 800-900℃ at a heating rate of 3-5℃ / min and holding for 2-5 hours. This allows for the acquisition of silicon-carbon microcapsules containing highly porous carbon, which meets the requirements. This ensures that the compatibility and affinity between the two reaction raw materials (silicon-carbon microcapsules containing highly porous carbon and petroleum-based spinnable pitch) in step D are optimal, which is more conducive to the implementation of step D.

[0067] In step D of this invention, the mass ratio of the ultrafine silicon particles used in step A to the petroleum-based spinnable pitch used in step D is controlled to be 1:0.08-0.13. The mixture is stirred at 300-500 rpm until it is evenly dispersed (generally stirred for 20-50 min). Then it is transferred to a fusion machine for kneading. The kneading conditions are controlled to be: kneading at 1200-1500 rpm for 10-20 min. Finally, the temperature is raised to 1050-1180℃ at a heating rate of 3-5℃ / min and held for 2-5 h to obtain a silicon-based anode material with a multi-level composite structure and a special structure.

[0068] The silicon-based anode material with a special structure obtained by the innovative design of this invention has excellent performance and is more suitable for preparing lithium-ion battery anode sheets. Therefore, this invention also provides a lithium-ion battery anode sheet, which includes the above-mentioned silicon-based anode material with a multi-level composite structure.

[0069] Based on the above-mentioned negative electrode sheet, the present invention further provides a lithium-ion battery, which includes the above-mentioned lithium-ion battery negative electrode sheet.

[0070] The present invention will be further described in detail below through embodiments, but the scope of protection of the present invention is not limited to the embodiments described herein.

[0071] Example 1

[0072] The method for preparing the multi-level composite silicon-based anode material provided in this embodiment includes the following steps:

[0073] (1) Microcapsule preparation: 1000g of ultrafine silicon particles with a particle size of 35nm were added to 4500g of chitosan solution with a mass fraction of 3.5wt%. After stirring at 1100rpm for 35min, 7g of cinnamaldehyde and 750g of water-soluble phenolic resin were added. Then, 1g of sodium dodecyl sulfonate, 1g of Span 85, 1g of Tween 80 and 30000g of phenyl silicone oil were added. The mixture was stirred at 1900rpm for 5h. Isopropanol was used to demulsify the stirred material. Then, the mixture was centrifuged and washed three times with isopropanol to obtain microcapsules.

[0074] (2) Preparation of silicon-carbon microcapsules: The microcapsules obtained in step (1) were dried and cured in a vacuum oven at 220°C for 8 hours, then transferred to a calcination furnace. Under an inert atmosphere, the temperature was increased to 500°C at a heating rate of 2.5°C / min and held for 1 hour. Then, the temperature was increased to 1150°C at a heating rate of 7°C / min and held for 3 hours. The microcapsules were then naturally cooled to room temperature to obtain silicon-carbon microcapsules.

[0075] (3) Preparation of silicon-carbon microcapsules with high porosity-filled carbon: The silicon-carbon microcapsules from step (2) were added to a sucrose aqueous solution containing 1500g of sucrose. After stirring at 500rpm for 1h, a spray precursor with a solid content of 30% was obtained. Then, spray granulation was carried out at an inlet temperature of 140℃ and a linear velocity of 200m / s. After granulation, the microcapsules were transferred to a calcining furnace and heated to 800℃ at a heating rate of 5℃ / min under an inert atmosphere and held for 3h. After natural cooling to room temperature, silicon-carbon microcapsules with high porosity-filled carbon were obtained.

[0076] (4) Preparation of surface carbon and particles: The silicon-carbon microcapsules containing high-porosity carbon obtained in step (3) and 130g of petroleum-based spinnable pitch are mixed at high speed at 400rpm for 30min, and then transferred to a kneading machine for kneading. The kneading conditions are: kneading at 1300rpm for 15min. After kneading, the mixture is transferred to a calcining furnace and heated to 1050℃ at a heating rate of 5℃ / min under an inert atmosphere and kept at that temperature for 3h. The mixture is then naturally cooled to room temperature to form surface carbon and prepare silicon-based anode material particles with a multi-level composite structure.

[0077] The silicon-based anode material with a multi-level composite structure prepared by the above embodiments has a particle size of 38 μm, a silicon-carbon microcapsule particle size of 1.3 μm, a surface carbon thickness of 30 nm, a high porosity-filled carbon content of 25% of the particles by mass, and an oxidation degree of 5.5% for the ultrafine silicon particles.

[0078] A slurry was prepared using a multi-stage composite silicon-based anode material, modified polyacrylic acid, and conductive carbon black at a mass ratio of 7:2:1. After coating, the slurry was dried in a vacuum oven at 110℃ for 12 hours. Pure lithium sheets were used as the counter electrode, and the electrolyte was 1M LiPF6 with an EC:EMC:FEC ratio of 7:2.2:0.8. The separator was a porous polypropylene membrane. After assembling CR2032 coin cells, the first cycle was performed at a rate of 0.1C, and the second cycle onwards at a rate of 0.3C. Capacity testing was also conducted at a rate of 2.5C.

[0079] Figure 2 The graph shows the cycling performance of the silicon-based anode material with a multi-stage composite structure in Example 1 of the present invention, and Comparative Examples 1 and 2. After 200 cycles, the capacity of Example 1 of the present invention is maintained at 79.2%, while the capacity of Comparative Examples 1 and 2 is maintained at 55.7% and 23.5%, respectively, after 200 cycles.

[0080] Other performance indicators of the silicon-based anode material with a multi-level composite structure obtained by Example 1 of the present invention are shown in Table 1.

[0081] Example 2

[0082] The method for preparing the multi-level composite silicon-based anode material provided in this embodiment includes the following steps:

[0083] (1) Microcapsule preparation: 1000g of ultrafine silicon particles with a particle size of 45nm were added to 6500g of chitosan solution with a mass fraction of 3.5wt%. After stirring at 1100rpm for 38min, 6g of cinnamaldehyde and 720g of water-soluble phenolic resin were added. Then, 1.5g of sodium dodecyl sulfonate, 1g of Span 85, 1g of Tween 80 and 35000g of n-hexane were added. The mixture was stirred at 2000rpm for 4h. Isopropanol was used to demulsify the stirred mixture. The mixture was then centrifuged and washed with isopropanol 4 times to obtain microcapsules.

[0084] (2) Preparation of silicon-carbon microcapsules: The microcapsules obtained in step (1) were dried and cured in a vacuum oven at 230°C for 8 hours, then transferred to a calcination furnace. Under an inert atmosphere, the temperature was increased to 500°C at a heating rate of 2.5°C / min and held for 1 hour. Then, the temperature was increased to 1100°C at a heating rate of 5°C / min and held for 3 hours. The microcapsules were then naturally cooled to room temperature to obtain silicon-carbon microcapsules.

[0085] (3) Preparation of silicon-carbon microcapsules with high porosity-filled carbon: The silicon-carbon microcapsules from step (2) were added to a glucose aqueous solution containing 1400g of glucose. After stirring at 400rpm for 2h, a spray precursor with a solid content of 25% was obtained. Then, spray granulation was carried out at an inlet temperature of 150℃ and a linear velocity of 210m / s. After granulation, the microcapsules were transferred to a calcination furnace and heated to 800℃ at a heating rate of 5℃ / min under an inert atmosphere and held for 3h. After natural cooling to room temperature, silicon-carbon microcapsules with high porosity-filled carbon were obtained.

[0086] (4) Preparation of surface carbon and particles: The silicon-carbon microcapsules containing high-porosity carbon obtained in step (3) and 120g of petroleum-based spinnable pitch are mixed at high speed at 500rpm for 30min, and then transferred to a kneading machine for kneading. The kneading conditions are: kneading at 1200rpm for 20min. After kneading, the mixture is transferred to a calcining furnace and heated to 1100℃ at a heating rate of 5℃ / min under an inert atmosphere and kept at that temperature for 3h. The mixture is then naturally cooled to room temperature to form surface carbon and prepare silicon-based anode material particles with a multi-level composite structure.

[0087] The silicon-based anode material with a multi-level composite structure prepared by the above embodiments has a particle size of 30 μm, a silicon-carbon microcapsule particle size of 1.1 μm, a surface carbon thickness of 25 nm, a high porosity-filled carbon content of 22% of the particles by mass, and an oxidation degree of 4.3% for the ultrafine silicon particles.

[0088] The battery assembly and testing of the silicon-based anode material with a multi-level composite structure obtained in Example 2 are the same as those in Example 1. The performance indicators of the silicon-based anode material with a multi-level composite structure obtained in Example 2 are shown in Table 1.

[0089] Example 3

[0090] The method for preparing the multi-level composite silicon-based anode material provided in this embodiment includes the following steps:

[0091] (1) Microcapsule preparation: 1000g of ultrafine silicon particles with a particle size of 30nm were added to 5500g of chitosan solution with a mass fraction of 3.5wt%. After stirring at 1000rpm for 30min, 5g of cinnamaldehyde and 700g of water-soluble phenolic resin were added. Then, 2g of sodium dodecyl sulfonate, 1g of Span 85, 1g of Tween 80 and 25000g of cyclohexane were added. The mixture was stirred at 2300rpm for 7h. Isopropanol was used to demulsify the stirred mixture. After centrifugation and washing with isopropanol 5 times, microcapsules were obtained.

[0092] (2) Preparation of silicon-carbon microcapsules: The microcapsules obtained in step (1) were dried and cured in a vacuum oven at 200°C for 8 hours, then transferred to a calcination furnace. Under an inert atmosphere, the temperature was increased to 500°C at a heating rate of 3°C / min and held for 1 hour. Then, the temperature was increased to 1000°C at a heating rate of 6°C / min and held for 3 hours. The microcapsules were then naturally cooled to room temperature to obtain silicon-carbon microcapsules.

[0093] (3) Preparation of silicon-carbon microcapsules with high porosity-filled carbon: The silicon-carbon microcapsules from step (2) were added to an aqueous solution of water-soluble starch containing 1300g of water-soluble starch. After stirring at 700rpm for 1h, a spray precursor with a solid content of 35% was obtained. Then, spray granulation was carried out at an inlet temperature of 180℃ and a linear velocity of 140m / s. After granulation, the microcapsules were transferred to a calcining furnace and heated to 800℃ at a heating rate of 5℃ / min under an inert atmosphere and held for 3h. After natural cooling to room temperature, silicon-carbon microcapsules with high porosity-filled carbon were obtained.

[0094] (4) Preparation of surface carbon and particles: The silicon-carbon microcapsules containing high-porosity carbon obtained in step (3) and 90g of petroleum-based spinnable pitch are mixed at high speed at 300rpm for 30min, and then transferred to a fusion machine for kneading. The kneading conditions are: kneading at 1400rpm for 15min. After kneading, the mixture is transferred to a calcining furnace and heated to 1180℃ at a heating rate of 5℃ / min under an inert atmosphere and kept at that temperature for 3h. The mixture is then naturally cooled to room temperature to form surface carbon and prepare silicon-based anode material particles with a multi-level composite structure.

[0095] The silicon-based anode material with a multi-level composite structure prepared by the above embodiments has a particle size of 25 μm, a silicon-carbon microcapsule particle size of 1 μm, a surface carbon thickness of 21 nm, a high porosity-filled carbon content of 19% of the particles by mass, and an oxidation degree of 5.7% for the ultrafine silicon particles.

[0096] The battery assembly and testing of the silicon-based anode material with a multi-level composite structure obtained in Example 3 are the same as those in Example 1. The performance indicators of the silicon-based anode material with a multi-level composite structure obtained in Example 3 are shown in Table 1.

[0097] Example 4

[0098] The method for preparing the multi-level composite silicon-based anode material provided in this embodiment includes the following steps:

[0099] (1) Microcapsule preparation: 1000g of ultrafine silicon particles with a particle size of 50nm were added to 5000g of chitosan solution with a mass fraction of 3.5wt%. After stirring at 1200rpm for 40min, 8g of cinnamaldehyde and 650g of water-soluble phenolic resin were added. Then, 1.5g of sodium dodecyl sulfonate, 1g of Span 85, 1g of Tween 80 and 32000g of liquid paraffin were added. The mixture was stirred at 1800rpm for 6h. Isopropanol was used to demulsify the stirred material. Then, the mixture was centrifuged and washed with isopropanol 4 times to obtain microcapsules.

[0100] (2) Preparation of silicon-carbon microcapsules: The microcapsules obtained in step (1) were dried and cured in a vacuum oven at 250°C for 8 hours, then transferred to a calcination furnace. Under an inert atmosphere, the temperature was increased to 500°C at a heating rate of 2°C / min and held for 1 hour. Then, the temperature was increased to 1200°C at a heating rate of 8°C / min and held for 3 hours. The microcapsules were then naturally cooled to room temperature to obtain silicon-carbon microcapsules.

[0101] (3) Preparation of silicon-carbon microcapsules with high porosity-filled carbon: The silicon-carbon microcapsules from step (2) were added to a citric acid solution containing 1200g of citric acid. After stirring at 600rpm for 2h, a spray precursor with a solid content of 30% was obtained. Then, spray granulation was carried out at an inlet temperature of 170℃ and a linear velocity of 160m / s. After granulation, the microcapsules were transferred to a calcination furnace and heated to 800℃ at a heating rate of 5℃ / min under an inert atmosphere and held for 3h. After natural cooling to room temperature, silicon-carbon microcapsules with high porosity-filled carbon were obtained.

[0102] (4) Preparation of surface carbon and particles: The silicon-carbon microcapsules containing high-porosity carbon obtained in step (3) and 80g of petroleum-based spinnable pitch were mixed at high speed at 400rpm for 30min and then transferred to a kneading machine. The kneading conditions were: kneading at 1500rpm for 10min. After kneading, the mixture was transferred to a calcining furnace and heated to 1150℃ at a heating rate of 5℃ / min under an inert atmosphere and held for 3h. The mixture was then naturally cooled to room temperature to form surface carbon and produce silicon-based anode material particles with a multi-level composite structure.

[0103] The silicon-based anode material with a multi-level composite structure prepared by the above embodiments has a particle size of 15 μm, a silicon-carbon microcapsule particle size of 0.8 μm, a surface carbon thickness of 20 nm, a high porosity-filled carbon content of 18% of the particles by mass, and an oxidation degree of 4.6% for the ultrafine silicon particles.

[0104] The battery assembly and testing of the multi-level composite silicon-based anode material obtained in Example 4 were the same as those in Example 1. The performance indicators of the multi-level composite silicon-based anode material obtained in Example 4 are shown in Table 1.

[0105] Comparative Example 1

[0106] The preparation method of the silicon-based anode material provided in this comparative example includes the following steps:

[0107] (1) Microcapsule preparation: 1000g of ultrafine silicon particles with a particle size of 35nm were added to 4500g of chitosan solution with a mass fraction of 3.5wt%. After stirring at 1100rpm for 35min, 7g of cinnamaldehyde and 750g of water-soluble phenolic resin were added. Then, 1g of sodium dodecyl sulfonate, 1g of Span 85, 1g of Tween 80 and 30000g of phenyl silicone oil were added. The mixture was stirred at 1900rpm for 5h. Isopropanol was used to demulsify the stirred material. Then, the mixture was centrifuged and washed three times with isopropanol to obtain microcapsules.

[0108] (2) Preparation of silicon-carbon microcapsules: The microcapsules obtained in step (1) were dried and cured in a vacuum oven at 220°C for 8 hours, then transferred to a calcination furnace. Under an inert atmosphere, the temperature was increased to 500°C at a heating rate of 2.5°C / min and held for 1 hour. Then, the temperature was increased to 1150°C at a heating rate of 7°C / min and held for 3 hours. The microcapsules were then naturally cooled to room temperature to obtain silicon-carbon microcapsules.

[0109] (3) Preparation of surface carbon and particles: The silicon carbon microcapsules obtained in step (2) and 130g of petroleum-based spinnable pitch were mixed at high speed at 400rpm for 30min, and then transferred to a kneading machine. The kneading conditions were: kneading at 1300rpm for 15min. After kneading, the mixture was transferred to a calcining furnace and heated to 1050℃ at a heating rate of 5℃ / min under an inert atmosphere and kept at that temperature for 3h. The mixture was then naturally cooled to room temperature to form surface carbon and silicon-based anode material particles were obtained.

[0110] The silicon-based anode material prepared by the above comparative example has a particle size of 32 μm, a silicon-carbon microcapsule particle size of 1.3 μm, a surface carbon thickness of 30 nm, and an oxidation degree of 5.5% for its ultrafine silicon particles.

[0111] The battery assembly and testing of the silicon-based anode material obtained in Comparative Example 1 were the same as those in Example 1. The performance indicators of the silicon-based anode material obtained in Comparative Example 1 are shown in Table 1.

[0112] Comparative Example 2

[0113] The preparation method of the silicon-based anode material provided in this comparative example includes the following steps:

[0114] (1) 1000g of ultrafine silicon particles with a particle size of 35nm were added to a sucrose aqueous solution containing 1500g of sucrose. After stirring at 500rpm for 1h, a spray precursor with a solid content of 30% was obtained. Then, spray granulation was carried out at an inlet temperature of 140℃ and a linear velocity of 200m / s. After granulation, the product was transferred to a calcining furnace and heated to 800℃ at a heating rate of 5℃ / min under an inert atmosphere and held for 3h. The product was then allowed to cool naturally to room temperature.

[0115] (2) Preparation of surface carbon and particles: The product obtained in step (1) and 130g of petroleum-based spinnable pitch were mixed at high speed at 400rpm for 30min and then transferred to a kneading machine for kneading. The kneading conditions were: kneading at 1300rpm for 15min. After kneading, the mixture was transferred to a calcining furnace and heated to 1050℃ at a heating rate of 5℃ / min under an inert atmosphere and kept at that temperature for 3h. The mixture was then naturally cooled to room temperature to form surface carbon and silicon-based anode material particles were obtained.

[0116] The silicon-based anode material prepared by the above comparative example has a particle size of 28 μm, a surface carbon thickness of 30 nm, a high porosity-filled carbon content of 55% of the particles by mass, and an oxidation degree of 5.5% for the ultrafine silicon particles.

[0117] The battery assembly and testing of the silicon-based anode material obtained in Comparative Example 2 were the same as those in Example 1. The performance indicators of the silicon-based anode material obtained in Comparative Example 2 are shown in Table 1.

[0118] Table 1. Comparison of performance indicators between the embodiments and comparative examples.

[0119]

Claims

1. A silicon-based anode material with a multi-level composite structure, characterized in that: It consists of particles with a diameter of 15-38 μm, which are composed of surface carbon, highly porous carbon-filled carbon, and silicon-carbon microcapsules. The silicon-carbon microcapsules are composed of ultrafine silicon particles and high-density carbon-filled carbon. The ultrafine silicon particles are monodispersed in the high-density carbon-filled carbon, which is a carbon-based material with a semi-disordered structure. The highly porous carbon-filled carbon is a carbon-based material with a disordered structure, accounting for 18-25% of the mass of the silicon-based anode material. The surface carbon is a carbon-based material with a semi-disordered structure and a thickness of 20-30 nm. Its preparation method includes the following steps: A. Microcapsule preparation: Ultrafine silica particles were added to a chitosan aqueous solution and stirred at low speed for the first time. Then, cinnamaldehyde and water-soluble phenolic resin were added, followed by sodium dodecyl sulfonate, Span 85, Tween 80 and oil phase. Then, the mixture was stirred at high speed for the second time. The mixture was demulsified and then centrifuged and washed to obtain microcapsules. B. Preparation of silicon-carbon microcapsules: The microcapsules obtained in step A are subjected to vacuum drying and curing treatment. Then, under an inert atmosphere, the temperature is first raised to 450~550℃ and kept at that temperature, and then raised to 1000~1200℃ and kept at that temperature. After natural cooling to room temperature, silicon-carbon microcapsules are obtained. C. Preparation of silicon-carbon microcapsules containing highly porous carbon: The silicon-carbon microcapsules obtained in step B are added to an aqueous solution of highly porous carbon precursor. After stirring, a spray precursor with a solid content of 25%~35% is obtained. Then, spray granulation is performed. After granulation, the temperature is raised to 800~900℃ under an inert atmosphere and kept at that temperature. Then, the temperature is naturally cooled to room temperature to obtain silicon-carbon microcapsules containing highly porous carbon. D. Preparation of surface carbon and particles: The silicon-carbon microcapsules containing highly porous carbon obtained in step C are mixed evenly with petroleum-based spinnable pitch and kneaded. After kneading, the mixture is heated to 1050~1180℃ under an inert atmosphere and kept at that temperature. Then, it is naturally cooled to room temperature to form surface carbon and obtain particles, which are silicon-based anode materials with a multi-level composite structure.

2. The silicon-based anode material with a multi-level composite structure according to claim 1, characterized in that: At least one of the following must be met: The silicon-carbon microcapsules are spherical or near-spherical in shape. The silicon-carbon microcapsules have a particle size of 0.8~1.3μm; The ultrafine silicon particles are sheet-like high-purity nano-silicon with a particle size of 30~50nm; The oxidation degree of the ultrafine silicon particles is <6%.

3. The silicon-based anode material with a multi-level composite structure according to claim 1, characterized in that: In step A, at least one of the following must be satisfied: The chitosan aqueous solution has a mass fraction of 3.2 wt% to 4.5 wt%. The mass ratio of the ultrafine silica particles to the chitosan aqueous solution is 1:4.5~6.5; The mass ratio of the ultrafine silicon particles to cinnamaldehyde is 1:0.005~0.008; The mass ratio of the ultrafine silicon particles to the water-soluble phenolic resin is 1:0.6~0.75; The mass ratio of the ultrafine silicon particles to sodium dodecyl sulfonate, Span 85, and Tween 80 is 1:0.001~0.002:0.001~0.013:0.001~0.015; The oil phase is at least one of phenyl silicone oil, n-hexane, cyclohexane, liquid paraffin, and toluene; The mass ratio of the ultrafine silicon particles to the oil phase is 1:25~35.

4. The silicon-based anode material with a multi-level composite structure according to claim 1, characterized in that: In step A, at least one of the following must be satisfied: The first low-speed stirring speed is 1000~1200 rpm; The first low-speed stirring time is 30-40 minutes; The second high-speed stirring speed is 1800~2300 rpm; The second high-speed stirring time is 4-7 hours.

5. The silicon-based anode material with a multi-level composite structure according to claim 1, characterized in that: In step B, at least one of the following must be satisfied: The temperature for the vacuum drying and curing process is 200~250℃; The vacuum drying and curing process takes 6-9 hours. Heating to 450-550℃ at a heating rate of 2-3℃ / min; Heat treatment at 450~550℃ for 0.5~2 hours; Heating to 1000-1200℃ at a heating rate of 5-8℃ / min; Heat treatment at 1000~1200℃ for 2~4 hours.

6. The silicon-based anode material with a multi-level composite structure according to claim 1, characterized in that: In step C, at least one of the following must be satisfied: The highly porous carbon precursor is at least one of sucrose, glucose, water-soluble starch, citric acid, or cyclodextrin. The mass ratio of the ultrafine silicon particles used in step A to the high-porosity carbon precursor in the aqueous solution of the high-porosity carbon precursor used in step C is 1:1.2~1.5; The stirring speed is 400~700 rpm; The stirring time is 1-2 hours; The conditions for spray granulation are: inlet temperature 140~180℃, linear velocity 140~210m / s; Heating to 800-900℃ at a heating rate of 3-5℃ / min; The heat treatment time at 800~900℃ is 2~5 hours.

7. The silicon-based anode material with a multi-level composite structure according to claim 1, characterized in that: In step D, at least one of the following must be satisfied: The mass ratio of the ultrafine silica particles used in step A to the petroleum-based spinnable pitch used in step D is 1:0.08~0.13; The mixing speed is 300~500 rpm; The time for uniform mixing is 20-50 minutes; The kneading speed is 1200~1500 rpm; The kneading time is 10-20 minutes; Heating to 1050~1180℃ at a heating rate of 3~5℃ / min; The heat treatment time at 1050~1180℃ is 2~5 hours.

8. A negative electrode sheet for a lithium-ion battery, characterized in that: The negative electrode sheet comprises a silicon-based negative electrode material with a multi-level composite structure as described in any one of claims 1 to 7.

9. A lithium-ion battery, characterized in that: The lithium-ion battery includes the lithium-ion battery negative electrode sheet as described in claim 8.

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