Silicon-carbon negative electrode material, preparation method thereof and battery
By constructing a carbon nanotube conductive network and a double-layer elastic polymer coating in silicon-carbon anode materials, the problem of volume change in silicon-based anode materials during charge and discharge processes was solved, achieving efficient structural self-repair and improved conductivity, thereby enhancing the cycle stability and high-rate performance of lithium-ion batteries.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-19
- Publication Date
- 2026-04-03
AI Technical Summary
Silicon-based anode materials undergo large volume changes during charge and discharge, leading to increased electrode material crushing and electrolyte consumption, reduced cycle life, and low electronic conductivity and lithium-ion diffusion rate, which limits their performance under high current and high power conditions.
A conductive network of in-situ grown CNTs and a double elastic polymer self-healing coating layer were constructed. The volume expansion was buffered and the structure self-healed by the carbon nanotube conductive network on the surface of nitrogen-doped silicon nanoparticles and the coating of the elastic polymer layer.
It improves the cycle life and high-rate performance of lithium-ion batteries, suppresses the pulverization of active materials and electrolyte consumption, and enhances the overall structural integrity and conductive network connectivity of the battery.
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Figure CN121790342A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of lithium-ion batteries, specifically to a silicon-carbon anode material, its preparation method, and a battery. Background Technology
[0002] Lithium-ion batteries are rechargeable batteries that primarily function by the reciprocating movement of lithium ions between the positive and negative electrodes. During charging and discharging, Li... + It intercalates and deintercalates back and forth between the two electrodes: while during charging, Li + During discharge, the lithium is extracted from the positive electrode and inserted into the negative electrode through the electrolyte, making the negative electrode lithium-rich; the opposite occurs during discharge. Due to its advantages of good environmental compatibility, long cycle life, and low self-discharge rate, lithium-ion batteries have become the most commonly used energy storage devices and are widely used in portable devices and electric vehicles.
[0003] Among the materials studied to date, Si-based materials have the highest theoretical specific capacity. The resulting alloy is LixSi, where x ranges from 0 to 4.4, and the theoretical specific capacity of pure silicon is 4200 mAh / g. Silicon has a slightly higher voltage plateau than graphite, making it less prone to surface lithium plating during charging, thus offering superior safety compared to graphite electrodes. Furthermore, silicon is one of the most abundant elements in the Earth's crust, widely available and inexpensive. Unlike graphite, silicon alloys do not exhibit solvation, and their low lithium intercalation potential, low atomic weight, high energy density, and high Li molar fraction in Li-Si alloys contribute to their superior stability compared to other metals and materials, making silicon a highly promising anode material to replace graphite in the near future. Therefore, developing silicon-based anodes is extremely attractive.
[0004] However, silicon anode materials have yet to achieve widespread commercial application. While possessing many advantages, silicon anode materials also have several disadvantages. First, silicon anode materials undergo volume changes exceeding 300% during charge and discharge. Such high volume expansion and contraction can easily lead to electrode material pulverization, detachment from the current collector and electrode conductive network. Simultaneously, the volume change creates new surfaces, requiring the formation of new solid-electrolyte interfaces (SEIs), resulting in significant electrolyte consumption and a substantial reduction in cycle life. Furthermore, silicon's conductivity and lithium-ion diffusion rate are lower than graphite, which limits its performance under high current and high power conditions.
[0005] This material primarily achieves its properties by doping nitrogen into the silicon nanoparticles, forming amorphous silicon nanoparticles. Nitrogen doping effectively improves the conductivity of the silicon nanoparticles. The most significant design feature is the coating of the internal silicon nanoparticles with an organic polymer network, along with in-situ generation of carbon nanotubes on the silicon nanoparticle surface. Finally, a carbon layer and an elastic polymer network are applied to the surface of the silicon-carbon material. This structural design not only ensures the integrity of the overall silicon-carbon material structure during cell cycling but also guarantees the integrity of the internal silicon nanoparticles and their connection to the overall conductive network, thereby improving the battery's cycle performance. Summary of the Invention
[0006] In view of this, the present invention provides a carbon anode material and its preparation method, as well as a battery, to solve the problems mentioned in the background art. By constructing an in-situ grown CNT conductive network and an inner and outer double elastic polymer self-healing coating layer, the rate performance of the silicon-carbon anode material is significantly improved, while dynamic buffering and structural self-healing of volume expansion during charging and discharging are achieved, thereby greatly improving the cycle life of lithium-ion batteries.
[0007] To achieve the above objectives, the present invention provides the following technical solution: In a first aspect, the present invention discloses a silicon-carbon anode material, comprising a shell layer and a core layer, wherein the shell layer comprises a first elastic polymer layer covering the core layer, a carbon skeleton covering the first elastic polymer layer, and a second elastic polymer layer covering the carbon skeleton.
[0008] As a further aspect of the present invention: the core layer comprises a nitrogen-doped silicon nanoparticle core and a carbon nanotube conductive network grown in situ on the surface of the silicon nanoparticle core.
[0009] As a further aspect of the present invention: the first elastic polymer layer includes a pore-forming agent and a first elastic polymer coated on the pore-forming agent; and / or, the pore-forming agent is one or more of ammonium bicarbonate, magnesium carbonate, polymethyl methacrylate, and polystyrene; And / or, the first elastic polymer is one or more of polydopamine, polyacrylic acid, and polyurethane.
[0010] As a further aspect of the present invention: the second elastic polymer layer is one or more of polydopamine, polyacrylic acid, and polyurethane.
[0011] Secondly, this invention discloses a method for preparing a silicon-carbon anode material, comprising the following steps: S1: Provides nitrogen-doped silicon nanoparticles; S2: Carbon nanotubes are grown in situ on the surface of the nitrogen-doped silicon nanoparticles to obtain primary composite particles; S3: A pore-forming agent and a first elastic polymer layer are sequentially coated on the surface of the primary composite particles to form secondary composite particles; S4: The secondary composite particles are combined with porous carbon materials to form a carbon skeleton and obtain tertiary composite particles. S5: Coat the surface of the tertiary composite particles with a carbon layer to obtain quaternary composite particles; S6: Coat the surface of the fourth-level composite particles with a second elastic polymer layer to obtain the self-healing nitrogen-doped silicon-carbon anode material.
[0012] As a further aspect of the present invention: In step S1, the nitrogen-doped silicon nanoparticles are prepared by plasma-enhanced chemical vapor deposition, with a silicon source to nitrogen source ƒ volume ratio of 1:(1-5) and a deposition temperature of 250-700℃; the mass percentage of nitrogen in the nitrogen-doped silicon nanoparticles is 0.2-2%, and the D50 particle size is 10-100nm.
[0013] As a further aspect of the present invention: step S2 specifically involves: immersing the nitrogen-doped silicon nanoparticles in a metal catalyst solution, removing and drying them, and then reacting them at 400-800°C under a carbon source gas atmosphere for 10-60 minutes to grow carbon nanotubes in situ; and / or, The metal catalyst is at least one of ferric nitrate, ferric sulfate, and ferric oxide, and the concentration of the metal catalyst solution is 0.1-10M.
[0014] As a further aspect of the present invention: the length of the carbon nanotube is 10-100 nm, and its mass accounts for 5-25% of the total mass of the primary composite particles.
[0015] As a further aspect of the present invention: step S3 specifically includes: S3a: The primary composite particles and the pore-forming agent are mixed at a mass ratio of 2:(3-7), dispersed in a solvent, and then dried to uniformly coat the particle surface with the pore-forming agent, forming a pore-forming agent coating layer. S3b: Disperse the pore-forming agent-coated particles in a first elastic polymer solution and cure at 60-150℃ for 10-24h to form the first elastic polymer layer.
[0016] As a further aspect of the present invention: the pore-forming agent is selected from one or more of ammonium bicarbonate, magnesium carbonate, PMMA, and PS.
[0017] As a further aspect of the present invention: the first elastic polymer is selected from one or more of polydopamine, polyacrylic acid, and polyurethane; the first elastic polymer layer accounts for 1-10% of the total mass of the secondary composite particles.
[0018] As a further embodiment of the present invention: Step S4 specifically involves: mixing the secondary composite particles with porous carbon material at a mass ratio of (1-2):1, and reacting at 150-250°C for 6-12 hours to construct the carbon framework; And / or, the porous carbon material accounts for 30-60% of the total mass of the tertiary composite particles; And / or, the particle size of the porous carbon material is 500-1000 nm.
[0019] As a further aspect of the present invention: in step S5, the carbon layer is formed by mixing the tertiary composite particles with a carbon precursor solution, followed by hydrothermal reaction or low-temperature drying, and then carbonizing at 300-600°C under an inert atmosphere; and / or, The carbon precursor is selected from one or more of glucose, phenolic resin, and asphalt; and / or, The carbon layer accounts for 2-10% of the total mass of the four-stage composite particles.
[0020] As a further aspect of the present invention: step S6 specifically involves immersing the fourth-level composite particles in a second elastic polymer solution and curing them at 60-150°C for 10-24 hours to form a second elastic polymer layer; and / or, The second elastic polymer is selected from one or more of polydopamine, polyacrylic acid, and polyurethane; and / or, The second elastic polymer layer accounts for 1-10% of the total mass of the self-healing nitrogen-doped silicon-carbon anode material.
[0021] Thirdly, the present invention discloses a lithium-ion battery, wherein the negative electrode comprises the aforementioned self-healing nitrogen-doped silicon-carbon negative electrode material.
[0022] Compared with the prior art, the beneficial effects of the present invention are: The self-healing nitrogen-doped silicon-carbon anode material prepared in this invention exhibits synergistically enhanced comprehensive electrochemical performance. Its core effects are reflected in two aspects: First, through nitrogen bulk doping and in-situ growth of carbon nanotubes on the surface of silicon particles, a stable three-dimensional conductive network is constructed, improving the intrinsic electronic conductivity and ion migration rate of the material, enabling the battery to maintain high capacity and stability even under high-rate charge-discharge conditions. Second, an innovative composite structure is introduced, consisting of a pore-forming agent reserving buffer space and inner and outer double-layer elastic polymer coating. This structure not only effectively adapts to and buffers the huge volume changes of silicon during lithium insertion / extraction, but also achieves self-repair of microcracks through the elasticity of the polymer layer, thereby greatly suppressing the pulverization and shedding of active materials, as well as the continuous consumption of electrolyte caused by repeated SEI film formation.
[0023] Based on the above mechanism, this invention successfully solves the problem of poor cycle stability in silicon-based anode materials. Compared with traditional silicon-carbon materials or single-coating structures, this material exhibits extremely low electrode sheet expansion rate and significantly optimized capacity retention during long-term cycling. This enables lithium-ion batteries equipped with this anode to possess high energy density, excellent rate performance, and ultra-long cycle life, providing a key material solution for next-generation high-performance power batteries and energy storage devices. Attached Figure Description
[0024] Figure 1 The graph shows the battery capacity retention rate as a function of cycle number for Examples 1-3 and Comparative Example 4. Figure 2 The discharge capacity retention rates of Examples 1-3 and Comparative Example 2 at different discharge rates; Figure 3 The difference in cell expansion rate between Examples 1-3 and Comparative Example 1 under full charge. Detailed Implementation
[0025] To facilitate understanding of the present invention, a more comprehensive description will be given below with reference to specific embodiments. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the disclosure of the present invention.
[0026] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.
[0027] Example 1 (1) Cleaned single-crystal silicon and high-melting-point quartz substrate were placed in the reaction chamber of the radio frequency plasma enhanced chemical vapor deposition system. After the chamber was evacuated, high-purity argon gas was introduced and the temperature of the reaction chamber was controlled at 250℃. The radio frequency power was adjusted to 50W, and silane (SiH4) was introduced to deposit the silicon sublayer. The silane gas flow rate was controlled at 5 mL / min, and the deposition time was 5h. At the same time as the silicon sublayer was deposited, ammonia gas diluted with hydrogen to a concentration of 1% was introduced as a doping gas to dope the silicon sublayer, so as to obtain nitrogen-doped silicon nanoparticles A with a D50 of 20 nm. (2) The obtained nano-silicon powder was immersed in 0.1M ferric nitrate solution and dried at low temperature in an inert atmosphere at 100℃. After drying, the powder was placed in a CVD furnace, acetylene gas was introduced, and carbon nanotubes were grown in situ at 600℃ for 30 min to obtain carbon nanotube-modified nano-silicon particles B. (3) The obtained nano-silicon particles B are mixed with the pore-forming agent ammonium bicarbonate at a mass ratio of 5:2, ultrasonically dispersed in an ethanol solution for 10 min, and then spray-dried at 350℃ to prepare nano-silicon particles C coated with the pore-forming agent. (4) The obtained nano-silicon particles C were immersed in dopamine-Tris buffer (pH=8.5) and polymerized for 12 hours. By precisely controlling the polymerization time and monomer concentration, the first elastic polymer layer accounted for 6% of the total mass of the composite nano-silicon particles C. The PDA layer was solidified at 60°C to obtain the composite nano-silicon particles E. (5) The above-mentioned composite nano-silicon particles D are mixed with 500nm porous carbon material (petroleum coke) at a mass ratio of 3:2, and dispersed in a mixed solution of polyethylene glycol and PAA. The low-temperature carbon skeleton is constructed at 200℃ by hydrothermal method to obtain composite silicon-carbon composite material A. (6) The silicon-carbon composite material A was ultrasonically treated in a glucose solution for 60 min, and the surfactant CTAB was added. The mixed solution was transferred to a stainless steel hydrothermal reactor lined with polytetrafluoroethylene, with the filling degree controlled at 70%-80%. After reacting at 200℃ for 8 h, it was naturally cooled to room temperature. The product (Si@C composite) was collected by centrifugation and washed three times with deionized water and ethanol to remove unreacted glucose and byproducts. It was then dried under vacuum at 60-80℃ for 12 h to obtain the composite silicon-carbon material B. (7) The obtained composite silicon-carbon material B is immersed in dopamine-Tris buffer (pH=8.5) for 12 hours and cured at 60°C to form a second elastic polymer coating layer, so that the second elastic polymer layer accounts for 6% of the total mass of the final self-healing nitrogen-doped silicon-carbon composite material, and a self-healing nitrogen-doped silicon-carbon composite material is obtained. (8) The nitrogen-doped silicon-carbon composite material prepared above is mixed with commercial graphite material at a specific capacity of 600 mAh / g, and then mixed with sodium carboxymethyl cellulose (CMC) and polyacrylic acid (PAA) at a mass ratio of 95:3:2. After coating, rolling, slitting and other processes, it is assembled into a lithium-ion battery.
[0028] Example 2 (1) The cleaned single-crystal silicon and high-melting-point quartz substrate were placed in the reaction chamber of the radio frequency plasma enhanced chemical vapor deposition system. After the chamber was evacuated, high-purity argon gas was introduced. The temperature of the reaction chamber was controlled at 250℃, the radio frequency power was adjusted to 50W, and silane (SiH4) was introduced to deposit the silicon sublayer. The silane gas flow rate was controlled at 5 mL / min, and the deposition time was 5h. At the same time as the silicon sublayer was deposited, ammonia gas diluted with hydrogen to a concentration of 1% was introduced as a doping gas to dope the silicon sublayer, so as to obtain nitrogen-doped silicon nanopowder A with a D50 of 20 nm. (2) The obtained nano-silicon powder A was immersed in a 0.1M ferric nitrate solution and dried at low temperature in an inert atmosphere at 100℃. After drying, the powder was placed in a CVD furnace and acetylene gas was introduced to carry out in-situ growth of carbon nanotubes at 600℃ for 30 min to obtain carbon nanotube-modified nano-silicon particles B.
[0029] (3) The obtained nano-silicon particles B and the pore-forming agent ammonium bicarbonate were mixed at a mass ratio of 7:2 and ultrasonically dispersed in an ethanol solution for 10 min. Then, the nano-silicon particles C coated with the pore-forming agent were prepared by spray drying at 350℃.
[0030] (4) The obtained nano-silicon particles C are immersed in an N-methylpyrrolidone (NMP) solution of polyurethane (PU) and cured at 60°C for 24 hours to form a first elastic polymer coating layer. By controlling the solution concentration and the number of dips, the first elastic polymer layer accounts for 10% of the total mass of the composite nano-silicon particles C, thus obtaining the composite nano-silicon particles E.
[0031] (5) The above-mentioned composite nano-silicon particles D and 500nm porous carbon material (petroleum coke) are mixed and dispersed in a mixed solution of polyethylene glycol and PAA at a mass ratio of 1:1. The carbon skeleton is constructed at a low temperature of 200℃ by hydrothermal method to obtain composite silicon-carbon composite material A.
[0032] (6) The silicon-carbon composite material A was ultrasonically treated in an ethanol solution of phenolic resin for 60 min. After removing the solvent by rotary evaporation, the mixture was carbonized in a tube furnace at 500 °C for 2 hours under an inert atmosphere to form a carbon coating layer. The product was collected by centrifugation, washed three times with deionized water and ethanol, and dried under vacuum at 60-80 °C for 12 hours to obtain the composite silicon-carbon material B.
[0033] (7) The obtained composite silicon-carbon material B is immersed in an aqueous solution of polyacrylic acid (PAA) and cured at 60°C for 24 hours to form a second elastic polymer coating layer. By controlling the solution concentration, the second elastic polymer layer accounts for 10% of the total mass of the final self-healing nitrogen-doped silicon-carbon composite material, thus obtaining the self-healing nitrogen-doped silicon-carbon composite material.
[0034] (8) The self-healing nitrogen-doped silicon-carbon composite material prepared above is mixed with commercial graphite material at a specific capacity of 600 mAh / g, and then mixed with sodium carboxymethyl cellulose (CMC) and polyacrylic acid (PAA) at a mass ratio of 95:3:2. After coating, rolling, slitting and other processes, it is assembled into a lithium-ion battery.
[0035] Example 3 (1) Cleaned single-crystal silicon and high-melting-point quartz substrate were placed in the reaction chamber of a radio frequency plasma enhanced chemical vapor deposition system. After the chamber was evacuated, high-purity argon gas was introduced. The temperature of the reaction chamber was controlled at 250℃, and the radio frequency power was adjusted to 50W. Silane (SiH4) was introduced to deposit the silicon sublayer. The silane gas flow rate was controlled at 5 mL / min, and the deposition time was 5h. At the same time as the silicon sublayer was deposited, ammonia gas diluted with hydrogen to a concentration of 1% was introduced as a doping gas to dope the silicon sublayer, resulting in nitrogen-doped silicon nanoparticles A with a D50 of 20 nm.
[0036] (2) The obtained nano-silicon powder A was immersed in a 0.1M ferric nitrate solution and dried at low temperature in an inert atmosphere at 100℃. After drying, the powder was placed in a CVD furnace and acetylene gas was introduced to carry out in-situ growth of carbon nanotubes at 600℃ for 30 min to obtain carbon nanotube-modified nano-silicon particles B.
[0037] (3) The obtained nano-silicon particles B and the pore-forming agent ammonium bicarbonate were mixed at a mass ratio of 3:2 and ultrasonically dispersed in an ethanol solution for 10 min. Then, the nano-silicon particles C coated with the pore-forming agent were prepared by spray drying at 350℃.
[0038] (4) The obtained silicon nanoparticles C were immersed in dopamine-Tris buffer (pH=8.5) for 12 hours and then cured at 60°C to form a PDA layer. By precisely controlling the polymerization time and monomer concentration, the first elastic polymer layer accounted for 1% of the total mass of the composite silicon nanoparticles C, thus obtaining the composite silicon nanoparticles E.
[0039] (5) The above-mentioned composite nano-silicon particles D and 500nm porous carbon material (petroleum coke) are mixed and dispersed in a mixed solution of polyethylene glycol and PAA at a mass ratio of 2:1. The carbon skeleton is constructed at a low temperature of 200℃ by hydrothermal method to obtain composite silicon-carbon composite material A.
[0040] (6) The silicon-carbon composite material A was ultrasonically mixed with a pyridine solution of asphalt for 60 min. After removing the solvent by rotary evaporation, it was carbonized in a tube furnace at 600 °C for 2 hours under an inert atmosphere to form a carbon coating layer. The product was collected by centrifugation and washed three times with quinoline and ethanol to remove uncarbonized light components. It was then vacuum dried at 60-80 °C for 12 hours to obtain the composite silicon-carbon material B.
[0041] (7) The obtained composite silicon-carbon material B was immersed in dopamine-Tris buffer (pH=8.5) for 6 hours and then cured at 60°C to form a PDA layer. By precisely controlling the polymerization time, the second elastic polymer layer accounted for 1% of the total mass of the final self-healing nitrogen-doped silicon-carbon composite material, and the final product was obtained.
[0042] (8) The self-healing nitrogen-doped silicon-carbon composite material prepared above is mixed with commercial graphite material at a specific capacity of 600 mAh / g, and then mixed with sodium carboxymethyl cellulose (CMC) and polyacrylic acid (PAA) at a mass ratio of 95:3:2. After coating, rolling, slitting and other processes, it is assembled into a lithium-ion battery.
[0043] Comparative Example 1 Commercially available silicon-carbon anode material (Lanxi Zhide S310) and commercially available graphite material were mixed at a specific capacity of 600 mAh / g, and then mixed with sodium carboxymethyl cellulose (CMC), polyacrylic acid (PAA), and conductive carbon black (SP) at a mass ratio of 94:3:2:1 to form a slurry. After coating, rolling, slitting and other processes were carried out in the same manner as in Example 1, the mixture was assembled into a lithium-ion battery.
[0044] Comparative Example 2 Steps (1), (2), and (3) are the same as in Example 1.
[0045] (4) The above-mentioned nano-silicon particles C and 500nm porous carbon material (petroleum coke) are mixed and dispersed in a mixed solution of polyethylene glycol and PAA at a mass ratio of 3:2. The carbon skeleton is constructed at a low temperature of 200℃ by hydrothermal method to obtain the composite silicon-carbon composite material A.
[0046] (5) The silicon-carbon composite material A was ultrasonically treated in a glucose solution for 60 min, and the surfactant CTAB was added. The mixed solution was transferred to a stainless steel hydrothermal reactor lined with polytetrafluoroethylene, with the filling degree controlled at 70%-80%. After reacting at 200℃ for 8 h, it was naturally cooled to room temperature. The product (Si@C composite) was collected by centrifugation and washed three times with deionized water and ethanol to remove unreacted glucose and byproducts. It was dried under vacuum at 60-80℃ for 12 h to obtain the composite silicon-carbon material B.
[0047] (6) The obtained composite silicon-carbon material B was immersed in dopamine-Tris buffer (pH=8.5) for 12 hours and then cured at 60°C to form a PDA layer, thus obtaining the final comparative material.
[0048] (7) The comparative material prepared above is mixed with commercial graphite material at a capacity of 600 mAh / g, and then mixed with sodium carboxymethyl cellulose (CMC) and polyacrylic acid (PAA) at a mass ratio of 95:3:2. After coating, rolling, slitting and other processes, the mixture is assembled into a lithium-ion battery.
[0049] Comparative Example 3 (1) Provide ordinary nano-silicon powder A with D50 of 20 nanometers.
[0050] (2) The obtained ordinary nano-silicon powder A was immersed in a 0.1M ferric nitrate solution and dried at low temperature in an inert atmosphere at 100℃. After drying, the powder was placed in a CVD furnace and acetylene gas was introduced to carry out in-situ growth of carbon nanotubes at 600℃ for 30 min to obtain ordinary nano-silicon particles B modified with carbon nanotubes.
[0051] (3) The obtained nano-silicon particles B and the pore-forming agent ammonium bicarbonate were mixed at a mass ratio of 5:2 and ultrasonically dispersed in an ethanol solution for 10 min. Then, the nano-silicon particles C coated with the pore-forming agent were prepared by spray drying at 350℃.
[0052] (4) The obtained nano-silicon particles C were immersed in dopamine-Tris buffer (pH=8.5) for 12 hours and then cured at 60°C to form a PDA layer, thus obtaining composite nano-silicon particles E.
[0053] (5) The above-mentioned composite nano-silicon particles D and 500nm porous carbon material (petroleum coke) are mixed and dispersed in a mixed solution of polyethylene glycol and PAA at a mass ratio of 3:2. The carbon skeleton is constructed at a low temperature of 200℃ by hydrothermal method to obtain composite silicon-carbon composite material A.
[0054] (6) The silicon-carbon composite material A was ultrasonically treated in a glucose solution for 60 min, and the surfactant CTAB was added. The mixed solution was transferred to a stainless steel hydrothermal reactor lined with polytetrafluoroethylene, with the filling degree controlled at 70%-80%. After reacting at 200°C for 8 h, it was naturally cooled to room temperature. The product (Si@C composite) was collected by centrifugation and washed three times with deionized water and ethanol to remove unreacted glucose and byproducts. It was dried under vacuum at 60-80°C for 12 h to obtain the composite silicon-carbon material B.
[0055] (7) The obtained composite silicon-carbon material B was immersed in dopamine-Tris buffer (pH=8.5) for 12 hours and cured at 60°C to form a PDA layer, thus obtaining the final comparison material.
[0056] (8) The comparative material prepared above is mixed with commercial graphite material at a specific capacity of 600 mAh / g, and then mixed with sodium carboxymethyl cellulose (CMC) and polyacrylic acid (PAA) at a mass ratio of 95:3:2. After coating, rolling, slitting and other processes, the mixture is assembled into a lithium-ion battery.
[0057] Comparative Example 4 Step (1) is the same as in Example 1.
[0058] (2) The obtained nano-silicon powder A and the pore-forming agent ammonium bicarbonate were mixed at a mass ratio of 5:2 and ultrasonically dispersed in an ethanol solution for 10 min. Then, the nano-silicon particles C coated with the pore-forming agent were prepared by spray drying at 350℃.
[0059] (3) The obtained nano-silicon particles C were immersed in dopamine-Tris buffer (pH=8.5) for 12 hours and then cured at 60°C to form a PDA layer, thus obtaining composite nano-silicon particles E.
[0060] (4) The above-mentioned composite nano-silicon particles D, 500nm porous carbon material (petroleum coke), and commercial carbon nanotubes of medium mass as in Example 1 (the total amount of which is determined by calculating the weight gain of CNTs grown in Example 1) are mixed and dispersed in a mixed solution of polyethylene glycol and PAA at a mass ratio of 3:2:1. The carbon skeleton is constructed at low temperature of 200°C by hydrothermal method to obtain composite silicon-carbon composite material A.
[0061] (5) The silicon-carbon composite material A was ultrasonically treated in a glucose solution for 60 min, and the surfactant CTAB was added. The mixed solution was transferred to a stainless steel hydrothermal reactor lined with polytetrafluoroethylene, with the filling degree controlled at 70%-80%. After reacting at 200℃ for 8 h, it was naturally cooled to room temperature. The product (Si@C composite) was collected by centrifugation and washed three times with deionized water and ethanol to remove unreacted glucose and byproducts. It was dried under vacuum at 60-80℃ for 12 h to obtain the composite silicon-carbon material B.
[0062] (6) The obtained composite silicon-carbon material B was immersed in dopamine-Tris buffer (pH=8.5) for 12 hours and cured at 60°C to form a PDA layer, thus obtaining the final comparative material.
[0063] (7) The comparative material prepared above is mixed with commercial graphite material at a capacity of 600 mAh / g, and then mixed with sodium carboxymethyl cellulose (CMC) and polyacrylic acid (PAA) at a mass ratio of 95:3:2. After coating, rolling, slitting and other processes, the mixture is assembled into a lithium-ion battery.
[0064] Test case The batteries assembled in the examples and comparative examples were subjected to long-cycle performance testing, rate performance testing, and electrode sheet expansion rate testing. The testing methods are as follows: Long-cycle performance testing: Hundreds or even thousands of cycles were performed under the same conditions (e.g., 1C charge / discharge rate, voltage range 2.5-4.2V), and the capacity retention rate after each cycle was recorded. Test results are available in [link to test results]. Figure 1 .
[0065] Rate performance testing: The battery was charged and discharged at different current densities (e.g., from 0.2C, 0.5C, 1C, 2C, to 5C), cycling for 5-10 cycles at each rate, and finally returned to a low rate (e.g., 0.2C) to observe the capacity recovery. The discharge capacity at different rates was recorded. Test results are shown below. Figure 2 .
[0066] Electrode sheet expansion rate test: The electrode sheets prepared in the examples and comparative examples are assembled into a specific battery or measured in an in-situ measuring device. Their thickness is measured after a certain number of cycles (e.g., after full charging), and compared with the thickness before cycling to calculate the expansion rate. Test results are shown below. Figure 3 .
[0067] Although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.
[0068] Therefore, the above description is only a preferred embodiment of this application and is not intended to limit the scope of this application; that is, all equivalent modifications made in accordance with the scope of the claims of this application shall be within the protection scope of the claims of this application.
Claims
1. A silicon-carbon anode material, comprising a shell layer and a core layer, characterized in that, The shell consists of a first elastic polymer layer covering the core layer, a carbon skeleton covering the first elastic polymer layer, and a second elastic polymer layer covering the carbon skeleton.
2. The silicon-carbon anode material according to claim 1, characterized in that, The core layer comprises a nitrogen-doped silicon nanoparticle core and a carbon nanotube conductive network grown in situ on the surface of the silicon nanoparticle core.
3. The silicon-carbon anode material according to claim 1, characterized in that, The first elastic polymer layer includes a pore-forming agent and a first elastic polymer coated on the pore-forming agent; and / or, the pore-forming agent is one or more of ammonium bicarbonate, magnesium carbonate, polymethyl methacrylate, and polystyrene; And / or, the first elastic polymer is one or more of polydopamine, polyacrylic acid, and polyurethane.
4. The silicon-carbon anode material according to claim 1, characterized in that, The second elastic polymer layer is one or more of polydopamine, polyacrylic acid, and polyurethane.
5. The method for preparing the silicon-carbon anode material according to any one of claims 1-4, characterized in that, Includes the following steps: S1: Provides nitrogen-doped silicon nanoparticles; S2: Carbon nanotubes are grown in situ on the surface of the nitrogen-doped silicon nanoparticles to obtain primary composite particles; S3: A pore-forming agent and a first elastic polymer layer are sequentially coated on the surface of the primary composite particles to form secondary composite particles; S4: The secondary composite particles are combined with porous carbon materials to form a carbon skeleton and obtain tertiary composite particles. S5: Coat the surface of the tertiary composite particles with a carbon layer to obtain quaternary composite particles; S6: Coat the surface of the fourth-level composite particles with a second elastic polymer layer to obtain the self-healing nitrogen-doped silicon-carbon anode material.
6. The preparation method according to claim 5, characterized in that, In step S1, the nitrogen-doped silicon nanoparticles are prepared by plasma-enhanced chemical vapor deposition, with a silicon source to nitrogen source volume ratio of 1:(1-5) and a deposition temperature of 250-700℃; the mass percentage of nitrogen in the nitrogen-doped silicon nanoparticles is 0.2-2%, and the D50 particle size is 10-100nm.
7. The preparation method according to claim 5, characterized in that, Step S2 specifically involves: immersing the nitrogen-doped silicon nanoparticles in a metal catalyst solution, removing and drying them, and then reacting them at 400-800°C under a carbon source gas atmosphere for 10-60 minutes to grow carbon nanotubes in situ; and / or, The metal catalyst is at least one of ferric nitrate, ferric sulfate, and ferric oxide, and the concentration of the metal catalyst solution is 0.1-10M.
8. The preparation method according to claim 7, characterized in that, The carbon nanotubes have a length of 10-100 nm and their mass accounts for 5-25% of the total mass of the primary composite particles.
9. The preparation method according to claim 5, characterized in that, Step S3 specifically includes: S3a: The primary composite particles and the pore-forming agent are mixed at a mass ratio of 2:(3-7), dispersed in a solvent, and then dried to uniformly coat the particle surface with the pore-forming agent, forming a pore-forming agent coating layer. S3b: Disperse the pore-forming agent-coated particles in a first elastic polymer solution and cure at 60-150℃ for 10-24h to form the first elastic polymer layer.
10. The preparation method according to claim 5, characterized in that, The pore-forming agent is selected from one or more of ammonium bicarbonate, magnesium carbonate, PMMA, and PS.
11. The preparation method according to claim 9, characterized in that, The first elastic polymer layer accounts for 1-10% of the total mass of the secondary composite particles.
12. The preparation method according to claim 5, characterized in that, Step S4 specifically involves mixing the secondary composite particles with porous carbon material at a mass ratio of (1-2):1 and reacting them at 150-250°C for 6-12 hours to construct the carbon framework. And / or, the porous carbon material accounts for 30-60% of the total mass of the tertiary composite particles; And / or, the particle size of the porous carbon material is 500-1000 nm.
13. The preparation method according to claim 5, characterized in that, In step S5, the carbon layer is formed by mixing the tertiary composite particles with a carbon precursor solution, followed by hydrothermal reaction or low-temperature drying, and then carbonizing at 300-600°C under an inert atmosphere; and / or, The carbon precursor is selected from one or more of glucose, phenolic resin, and asphalt; and / or, The carbon layer accounts for 2-10% of the total mass of the four-stage composite particles.
14. The preparation method according to claim 5, characterized in that, Step S6 specifically involves: immersing the fourth-level composite particles in a second elastic polymer solution and curing them at 60-150°C for 10-24 hours to form a second elastic polymer layer; and / or, The second elastic polymer layer accounts for 1-10% of the total mass of the self-healing nitrogen-doped silicon-carbon anode material.
15. A lithium-ion battery, characterized in that, Its negative electrode comprises the carbon negative electrode material as described in any one of claims 1-4.