Nano-silicon composite negative electrode material based on carbon microspheres, and preparation method and application thereof

Abstract

The application discloses a nano-silicon composite negative electrode material based on a microporous carbon sphere in the field of electrochemical energy storage devices and a preparation method and application thereof. The composite negative electrode material adopts a three-layer structure design of a microporous carbon sphere carrier + a uniform nano-silicon layer + a carbonaceous conductive coating. The microporous carbon sphere carrier is a regular sphere, the specific surface area is large, and the pore diameter is 1.0-2.5 nm. The nano-silicon layer is uniformly deposited on the surface and the pore channel of the carbon sphere by a chemical vapor deposition method, the thickness is large, and the silicon mass content is 15%-35%. The carbonaceous conductive coating is an amorphous carbon layer or a three-dimensional conductive network of carbon nanotubes. The application further discloses a preparation method of the material, which comprises three core processes of microporous carbon sphere carrier preparation, nano-silicon layer CVD deposition and carbonaceous conductive coating construction. The composite material has a compacted density, an electronic conductivity of greater than or equal to 1C, a capacity retention rate of greater than or equal to 80% after 1000 cycles at a 1C rate, supports fast charging at 4C or above, can be used in high-energy-density lithium ion batteries, is especially suitable for fields of electric vehicles and high-end consumer electronics, and has a significant industrialization prospect.

Description

Technical Field

[0001] This invention relates to the field of electrochemical energy storage devices, specifically to a negative electrode material for lithium-ion batteries, particularly a silicon / carbon composite negative electrode material with high cycle stability, high compaction density and excellent fast charging performance, and its preparation method. Background Technology

[0002] Silicon (Si) is considered the most promising anode material for next-generation high-energy-density lithium-ion batteries due to its extremely high theoretical specific capacity (approximately 4200 mAh / g). However, silicon undergoes a volume expansion of over 300% during charge and discharge, leading to the pulverization of active materials, repeated rupture and regeneration of the solid electrolyte interphase (SEI) film, and collapse of the electrode structure. Ultimately, this results in rapid capacity decay and shortened cycle life, severely hindering its commercial application.

[0003] To alleviate the above problems, existing technologies typically employ silicon-carbon (Si / C) composite strategies, such as dispersing nano-silicon in a porous carbon matrix or carbon coating. However, these methods still have significant shortcomings: 1) Commonly used porous carbon (such as amorphous carbon) has limited mechanical strength, making it difficult to effectively constrain the volume change of silicon over a long period; 2) Silicon particles are unevenly dispersed in the carbon matrix, easily agglomerating and causing localized stress concentration; 3) The compaction density of composite materials is generally low (often lower than...). ), which limits the volumetric energy density of the battery; 4) the carbon matrix has insufficient conductivity, which affects the rate performance and fast charging capability of the battery.

[0004] Therefore, developing a novel silicon-carbon composite material that combines high structural stability, high silicon loading uniformity, high compaction density, and high conductivity is crucial for promoting the development of high-energy-density, long-life, and fast-charging lithium-ion batteries. Summary of the Invention

[0005] The purpose of this invention is to provide nano-silicon composite anode materials based on microporous carbon spheres, their preparation methods and applications, in order to solve the problems mentioned in the background art.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] (I) Nano-silicon composite anode material

[0008] The composite anode material comprises a microporous carbon sphere carrier, a nano-silicon layer, and a carbonaceous conductive coating. The specific design of each component is as follows:

[0009] Microporous carbon sphere carrier: has a regular spherical structure and a specific surface area of The aperture is mainly distributed in Particle size is The carrier is made from resin-based precursors (such as phenolic resin) or biomass-based precursors (such as coconut shell, sodium lignosulfonate) through carbonization and chemical activation (the activator is...). or It is made by physical activation, and its high specific surface area and rich microporous structure provide ample space for the uniform deposition of nano-silicon. At the same time, the spherical structure and high mechanical strength can effectively buffer the volume expansion of silicon.

[0010] Nanoscale silicon layer: uniformly deposited on the surface and within the pores of a microporous carbon sphere carrier using chemical vapor deposition, with a thickness of 0.05-5 nm. The silicon mass content in the composite material is 15%-35%. The ultrathin and uniform nanoscale silicon layer can prevent silicon particle agglomeration, reduce local stress concentration, and shorten the lithium ion diffusion path.

[0011] Carbonaceous conductive coating: This coating, applied to the outside of the nano-silicon layer, can be an amorphous carbon layer formed by pyrolytic carbon or a three-dimensional conductive network formed by carbon nanotubes. This coating improves the electronic conductivity of the composite material while further constraining the volume expansion of silicon, thus stabilizing the SEI film.

[0012] The compaction density of the composite anode material is no less than [amount missing]. The electronic conductivity is not less than It can effectively improve the volumetric energy density, rate performance and cycle stability of lithium-ion batteries.

[0013] (II) Preparation method of nano-silicon composite anode material

[0014] The preparation method includes the following three core steps:

[0015] S1: Preparation of microporous carbon sphere carriers:

[0016] S11: Provide a spherical resin precursor or a biomass precursor, wherein the spherical resin precursor is prepared by suspension polymerization, and the dispersant used in the suspension polymerization is selected from at least one of polyvinyl alcohol and hydroxypropyl methylcellulose, and the emulsifier is selected from at least one of sodium dodecyl sulfate and Tween 80.

[0017] S12: In an inert atmosphere, the precursor is pre-carbonized at 400-1000℃ to remove volatile components from the precursor and form a preliminary carbonized structure.

[0018] S13: Mix the pre-carbonized product with the activator, or perform activation treatment at 600-1000℃ in an activating atmosphere to regulate the pore structure of the carbon spheres;

[0019] S14: The activated product is acid-washed and water-washed until neutral, and then dried to obtain a microporous carbon sphere support.

[0020] S2: Deposited nano-silicon layer:

[0021] The microporous carbon sphere carrier is evenly spread in the CVD furnace, and after the system is evacuated, it is introduced with... , and The mixed reaction gases are reacted at 500-600℃ for 1-3 hours, causing the silane gas to decompose and be uniformly deposited on the surface and in the pores of the carbon spheres, forming a silicon-carbon composite precursor.

[0022] S3: Constructing a carbon-based conductive coating:

[0023] Carbonaceous conductive coatings can be constructed in two ways:

[0024] Method 1: Secondary carbon coating is performed by chemical vapor deposition, using acetylene as the carbon source gas, with a coating time of 0.1-3 hours, to form an amorphous carbon layer;

[0025] Method 2: Using chemical vapor deposition, in the presence of a catalyst (such as ferrocene), a catalyst is introduced... and Gas is used to grow carbon nanotubes on the surface of a nano-silicon layer, forming a three-dimensional conductive network.

[0026] (III) Application

[0027] This nano-silicon composite anode material can be used to prepare lithium-ion battery anodes, especially suitable for pouch cells. The energy density of this lithium-ion battery is no less than... It supports fast charging at 4C and above, and its capacity retention rate is no less than 80% after 1000 cycles at 1C. It can be widely used in electric vehicles, high-end consumer electronics and other fields.

[0028] Compared with the prior art, the beneficial effects of the present invention are:

[0029] 1) Excellent structural stability: The microporous carbon sphere carrier with regular spherical shape, high specific surface area, and specific pore size distribution in this invention not only serves as the framework for subsequent deposition, but its own characteristics (sphericity and porosity) are prerequisites for achieving uniform, ultrathin, and stable adhesion of the nano-silicon layer. The external carbon conductive coating forms a 'dual constraint mechanism' with the internal carbon sphere framework, synergistically suppressing the volume expansion of silicon and solving the problem of easy collapse of existing material structures.

[0030] 2) Uniform and controllable silicon distribution: The 'suspension polymerization-carbonization activation' process in this invention determines the intrinsic structure of the carrier; the feasibility and quality of the 'CVD silicon deposition' process directly depend on the carrier structure; the effect of the 'carbon coating construction' process is closely related to the surface state of the silicon layer. CVD technology can achieve atomic-level precision, ultrathin and uniform deposition of nano-silicon layers, which greatly improves the consistency and electrochemical stability of the material and avoids local stress concentration caused by silicon particle agglomeration.

[0031] 3) Excellent overall electrochemical performance: The stable structure of this invention ensures cycle life; the uniform ultrathin silicon layer improves the first efficiency and reduces side reactions; the high solid density and high electronic conductivity jointly support the excellent volumetric energy density and fast charging performance, which are comprehensively superior to existing silicon-carbon composite materials.

[0032] 4) Strong process scalability: The parameters of each preparation step are clear and controllable. From carbon ball synthesis to composite coating construction, it is suitable for large-scale industrial production and solves the problems of complex and difficult-to-scale existing preparation processes.

[0033] 5) Broad application prospects: This material provides a key material solution for the development of next-generation high-performance lithium-ion batteries, especially suitable for fields such as electric vehicles and high-end consumer electronics that have high requirements for battery energy density, cycle life and fast charging performance. Detailed Implementation

[0034] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0035] Example 1

[0036] Preparation of spherical phenolic resin microspheres (suspension polymerization method)

[0037] raw material:

[0038] Oil phase (dispersed phase): 100g phenolic resin (RF) prepolymer, 11.1g hexamethylenetetramine (HMTA) (mass ratio RF:HMTA≈9:1), 20g deionized water (used to adjust viscosity);

[0039] Aqueous phase (continuous phase): 500 mL deionized water, 5.0 g polyvinyl alcohol (PVA, dispersant), 0.25 g sodium dodecyl sulfate (SDS, emulsifier).

[0040] step:

[0041] S1.1 Aqueous phase preparation: Add PVA and SDS to 500 mL of deionized water, stir at 85 °C until completely dissolved to form a clear solution, and cool to room temperature for later use;

[0042] S1.2 Oil phase preparation: Mix RF prepolymer, HMTA and 20g deionized water, and stir in a 60℃ water bath for 30 minutes to form a homogeneous viscous mixture;

[0043] S1.3 Suspension polymerization: The aqueous phase was transferred to a three-necked flask equipped with a mechanical stirrer, condenser and thermometer, and the temperature was raised to 88°C and maintained; stirring was started and the speed was adjusted to 450 rpm to form a stable vortex; the oil phase mixture was slowly added dropwise to the aqueous phase. After the addition was completed, the reaction was continued at 88°C and 450 rpm for 3.5 hours. The formaldehyde and ammonia released by the thermal decomposition of HMTA promoted the cross-linking and curing of RF, and the droplets gradually solidified into solid microspheres.

[0044] S1.4 Separation and Drying: After the reaction was completed, heating was stopped and the mixture was cooled to room temperature. The supernatant was discarded, and the microspheres were washed three times with hot water at 60°C and then twice with deionized water at room temperature. The obtained microspheres were placed in an 80°C drying oven and dried for 24 hours to obtain light brown, regularly spherical phenolic resin microspheres.

[0045] Preparation of microporous carbon sphere supports (carbonization and activation)

[0046] step:

[0047] S2.1 Pre-carbonization: The above-mentioned dried resin microspheres are placed in a tube furnace and heated to 620°C at a heating rate of 5°C / min under an argon atmosphere, and held for 1.5 hours for pre-carbonization to obtain pre-carbonized carbon spheres.

[0048] S2.2 Chemical activation: Grind and mix the pre-carbonized carbon balls and potassium hydroxide (KOH) in a mortar at a mass ratio of 2.2:1 (carbon balls: KOH) until homogeneous;

[0049] S2.3 High-temperature activation: The mixture is transferred to a corundum boat, placed in a tube furnace, and heated to 720°C at 5°C / min under argon protection, and activated at this temperature for 1 hour;

[0050] S2.4 Post-treatment: After the activated product is naturally cooled to room temperature, it is soaked and stirred with 1M dilute hydrochloric acid for 12 hours to remove residual potassium salts. Then it is washed with a large amount of deionized water until the filtrate is neutral. Finally, the product is dried at 120°C for 12 hours to obtain the microporous carbon sphere support.

[0051] Characterization results: The obtained microporous carbon spheres have complete morphology, maintain a regular spherical shape, and the particle size distribution is mainly in the range of 2-5 μm. BET test shows that its specific surface area is as high as 2580 m² / g, the total pore volume is 1.18 cm³ / g, and the pore size distribution is mainly concentrated in the micropore range of 1.0-1.6 nm, which fully meets the requirements of high specific surface area and rich pore structure of carrier for high loading and uniform deposition of nano-silicon.

[0052] Chemical vapor deposition (CVD) of nano-silicon layers

[0053] step:

[0054] S3.1 Deposition process: The microporous carbon spheres were evenly spread in the quartz boat of the CVD furnace; after the system was evacuated to a background pressure of less than 10 Pa, a mixed reaction gas was introduced into the furnace with a gas flow ratio of SiH4:H2:N2=1:3.5:5.5; the furnace temperature was raised to 560℃, and the reaction was carried out under these conditions for 1.2 hours, so that the silane gas was decomposed and deposited on the surface and in the pores of the carbon spheres;

[0055] S3.2 Sample Acquisition: After the reaction was completed, the sample was cooled to room temperature under argon protection to obtain a preliminary silicon-carbon composite material, labeled as Si@C-0h.

[0056] Characterization results: TEM characterization showed that the nano-silicon layer was continuously and uniformly coated on the surface of the carbon spheres with a thickness of about 2.8 nm; elemental analysis (EDS) showed that the mass content of silicon in the composite material was about 23%.

[0057] Construction of secondary carbon coating

[0058] step:

[0059] S4.1 Secondary CVD carbon coating (1.5 hours): Take a portion of Si@C-0h material and place it in the CVD furnace again; introduce acetylene (C2H2) as the carbon source gas and perform secondary deposition at 720℃ for 1.5 hours; after deposition, cool in argon gas, and the resulting material is labeled as Si@C-1.5h;

[0060] S4.2 Secondary CVD carbon coating (2.5 hours): Take another portion of Si@C-0h material, except that the secondary deposition time is extended to 2.5 hours, the other conditions are exactly the same as S4.1, and the resulting material is labeled as Si@C-2.5h.

[0061] Characterization results: BET tests showed that the specific surface area of ​​the materials decreased significantly after secondary carbon coating. The specific surface area of ​​Si@C-1.5h was 82.5 m² / g, and that of Si@C-2.5h was 76.3 m² / g, confirming the successful coating of the dense carbon layer.

[0062] Example 2: Optimized deposition of microporous carbon spheres and their silicon / carbon composites prepared by high-solids-content suspension polymerization.

[0063] This embodiment further improves the carbon ball yield, structural strength, and electrical conductivity of the composite material by increasing the solid content of the reaction system, optimizing the dispersion and stabilization system, and adjusting the heat treatment and deposition parameters.

[0064] Preparation of high-solids-content spherical phenolic resin microspheres (improved suspension polymerization method)

[0065] raw material:

[0066] Oil phase (dispersed phase): 150g of phenolic resin (RF) prepolymer (increase the amount by 50%), 18.75g of hexamethylenetetramine (HMTA) (mass ratio RF:HMTA=8:1), and 30g of anhydrous ethanol (to replace part of the water to reduce the viscosity of the oil phase and promote dispersion).

[0067] Aqueous phase (continuous phase): 600 mL deionized water, 7.5 g polyvinyl alcohol (PVA, dispersant) (concentration increased to 1.25%), 0.15 g sodium dodecyl sulfate (SDS, emulsifier) ​​(amount reduced to minimize impact on final carbon sphere purity).

[0068] step:

[0069] S1.1 Aqueous phase preparation: Add PVA and SDS to 600 mL of deionized water, stir vigorously at 90 °C until completely dissolved, and cool for later use;

[0070] S1.2 Oil phase preparation: Mix RF prepolymer, HMTA and anhydrous ethanol, and stir in a 50°C water bath for 40 minutes to form a homogeneous mixture with suitable viscosity;

[0071] S1.3 Suspension polymerization: Add the aqueous phase to the reactor, heat to 88℃ and maintain; start stirring and adjust the speed to 550 rpm; add the oil phase mixture dropwise to the aqueous phase at a slower rate; after the dropwise addition is complete, react at a constant temperature of 88℃ and 550 rpm for 4 hours to ensure full cross-linking and curing;

[0072] S1.4 Separation and Drying: After the reaction is completed, the mixture is settled and decanted, then washed once with 1% hydrochloric acid solution to remove any possible residual alkali, and then washed successively with 60℃ hot water and room temperature deionized water until neutral; finally, it is vacuum dried at 85℃ for 36 hours to obtain dark brown spherical resin microspheres with a narrower particle size distribution (mainly 1-4μm).

[0073] Preparation of high-strength microporous carbon sphere carriers (enhanced heat treatment)

[0074] step:

[0075] S2.1 Stepped pre-carbonization: The dried resin microspheres are placed in a tube furnace and heated to 350°C at 3°C / min and held for 1 hour under argon atmosphere (to promote stable decomposition). Then, the temperature is increased to 650°C at 5°C / min and held for 1.5 hours for deep carbonization.

[0076] S2.2 Chemical activation: Pre-carbonized carbon balls and KOH are mixed at a mass ratio of 1.5:1 (carbon balls: KOH). This ratio is intended to balance activation efficiency and carbon loss.

[0077] S2.3 Short-time high-temperature activation: Under argon protection, the mixture is rapidly heated to 750°C at 10°C / min, and the activation time is shortened to 20 minutes;

[0078] S2.4 Post-treatment: Same as in Example 1, after acid washing, water washing and drying, microporous carbon spheres are obtained.

[0079] Characterization results: The obtained carbon spheres maintain excellent sphericity and higher mechanical strength; the BET specific surface area remains above 2500 m² / g; through short-time high-temperature activation, the proportion of mesopores (2-5 nm) increases slightly, which is beneficial for rapid ion transport.

[0080] Rapid deposition of nano-silicon layers and construction of CNT networks

[0081] step:

[0082] S3.1 Silicon layer deposition: The carbon ball support is placed in the CVD furnace; after the system is evacuated, a mixed gas with a flow rate ratio of SiH4:H2:N2=1:4:5 is introduced and reacted at 580℃ for 1 hour; by increasing the H2 ratio and temperature, a denser and more uniform silicon layer is rapidly deposited.

[0083] S3.2 In-situ growth of CNT conductive network: After silicon deposition, the material was not removed, and the gas was switched in the same CVD system; SiH4 and N2 were turned off, and H2 (200 sccm) and C2H2 (50 sccm) were introduced at 700℃, and ferrocene (dissolved in toluene and carried by a bubbler) was introduced as a catalyst precursor. After reacting for 15 minutes, interwoven carbon nanotubes (CNTs) were grown in situ on the surface of Si@C material, forming a three-dimensional conductive network; this sample was labeled as Si@C-CNT-F.

[0084] Characterization results: TEM showed that the silicon layer thickness was about 2-4 nm; SEM showed that the material surface was covered with a uniform CNT network structure; the electronic conductivity of the composite material was significantly higher than that of the amorphous carbon-coated sample in Example 1, reaching more than 8.0 S / cm.

[0085] Performance comparison and beneficial effects

[0086] Compared with Example 1, this example brings the following optimizations:

[0087] Improved precursor synthesis efficiency: Increased solid content and optimized dispersion system resulted in an approximately 30% increase in yield per unit reaction volume.

[0088] Carbon sphere structure reinforcement: Stepped pre-carbonization combined with short-time high-temperature activation improves the mechanical strength and structural stability of carbon spheres while maintaining a high specific surface area.

[0089] Efficient deposition process: Silicon deposition time is shortened and completed continuously in the same system as CNT growth, improving process efficiency;

[0090] Significantly enhanced conductivity: The direct construction of a three-dimensional conductive network of CNTs, rather than a dense carbon layer, provides the composite material with a better electron conduction path and a certain buffer space, showing greater potential in high-rate (e.g., above 4C) charge-discharge and long cycle life.

[0091] Example 3: Preparation of Microporous Carbon Spheres and Investigation of Composite Properties under Optimization Strategies for Dispersed Stable Systems

[0092] This embodiment explores the effects of changes in the dispersant and emulsifier system during suspension polymerization on the properties of the precursor and the final composite material. By replacing or adjusting the type of surfactant, fine control of the particle size distribution, surface properties, and pore characteristics of the final carbon spheres can be achieved.

[0093] Preparation of spherical resin microspheres based on different dispersion stabilization systems

[0094] 1.1 Alternative dispersant system (using hydroxypropyl methylcellulose (HPMC) instead of PVA)

[0095] Raw materials (aqueous phase alteration):

[0096] Oil phase (dispersed phase): 100g phenolic resin (RF) prepolymer, 10g hexamethylenetetramine (HMTA) (mass ratio RF:HMTA=10:1), 20g deionized water (used to adjust viscosity);

[0097] Aqueous phase (continuous phase): 500 mL deionized water, 4.0 g hydroxypropyl methylcellulose (HPMC, viscosity 4000 mPa·s), 0.2 g sodium dodecyl sulfate (SDS, emulsifier).

[0098] step:

[0099] S1.1 Aqueous phase preparation: HPMC was slowly added to a portion of cold water under vigorous stirring and dispersed. The mixture was then heated to 85°C to allow it to fully swell and dissolve. SDS was then added and mixed thoroughly.

[0100] S1.2 Suspension polymerization: The oil phase preparation and dropwise addition are the same as in Example 1; the reaction is carried out at 85°C and 450 rpm (the speed is appropriately reduced due to the high viscosity of the HPMC solution) for 3 hours; HPMC forms stronger steric hindrance at the reaction temperature, which is beneficial to obtaining microspheres with better monodispersity;

[0101] S1.3 Post-processing: Same as Example 1.

[0102] Effects: HPMC, as a dispersant, can form a stronger protective layer on the surface of droplets due to its thermogel properties, resulting in resin microspheres with higher sphericity, smoother surface, and narrower particle size distribution (1-3 μm).

[0103] 1.2 Alternative emulsifier system (using nonionic emulsifier Tween 80 instead of SDS)

[0104] Raw materials (aqueous phase alteration):

[0105] Oil phase (dispersed phase): 100g phenolic resin (RF) prepolymer, 10g hexamethylenetetramine (HMTA) (mass ratio RF:HMTA=10:1), 20g deionized water (used to adjust viscosity);

[0106] Aqueous phase (continuous phase): 500 mL deionized water, 5.0 g polyvinyl alcohol (PVA), 0.4 g Tween-80 (as an emulsifier to reduce interfacial tension).

[0107] step:

[0108] S1.1 Aqueous phase preparation: Dissolve PVA and Tween 80 in hot water at 85°C and stir until clear;

[0109] S1.2 Suspension polymerization: The operation is the same as in Example 1, and the reaction is carried out at 85°C and 520 rpm for 3 hours; the nonionic emulsifier Tween 80 is not sensitive to pH and electrolytes, and provides a more stable emulsification environment at different curing stages;

[0110] S1.3 Post-processing: Same as Example 1.

[0111] Effects: Tween 80 alters the properties of the oil / water interface film, subtly affecting the final surface morphology and hydrophilicity / hydrophobicity of the microspheres, indirectly influencing the surface chemical reactions in the subsequent carbonization process and the wetting and reaction uniformity of the activator (KOH).

[0112] Preparation of microporous carbon spheres (carbonization and activation)

[0113] The resin microspheres prepared by the two methods described above were subjected to pre-carbonization (600℃, 2h), KOH activation (carbon spheres: KOH = 2:1, 700℃, 0.5h), and post-treatment according to steps S2.1 to S2.4 in Example 1, respectively, keeping the carbonization and activation conditions consistent, so as to evaluate the influence of changes in the precursor dispersion stability system on the final carbon sphere structure separately.

[0114] Deposition of nano-silicon / carbon composite materials

[0115] Two types of carbon spheres were subjected to nano-silicon deposition (SiH4:H2:N2=1:3:6, 550℃, 1.5h) and secondary carbon coating (C2H2, 700℃, 2h) according to steps S3.1 and S4.1 in Example 1, respectively. The resulting materials were labeled as Si@C-HPMC-2h (derived from the HPMC system) and Si@C-Tween-2h (derived from the Tween 80 system), respectively.

[0116] Characterization results and performance analysis

[0117] Precursor and carbon sphere morphology: The carbon spheres in the HPMC system inherit the excellent monodispersity of the precursor, are regular in shape, and have a denser surface; the carbon spheres in the Tween 80 system have good morphology, but the surface chemistry varies slightly due to the difference in precursor.

[0118] Pore ​​structure characteristics (BET): The specific surface area of ​​both types of carbon spheres exceeds 2500 m² / g, which meets the requirements of the carrier; due to the potential differences in the surface properties and microstructure of the precursor, there are subtle differences in pore size distribution (especially mesoporous part) and pore shape, which can be characterized by the NLDFT model.

[0119] Electrochemical performance of composite materials: Si@C-HPMC-2h has advantages in cycling stability due to its uniform and regular support structure, which is conducive to achieving extremely uniform silicon layer deposition and ion transport. Si@C-Tween-2h has different trends in first coulombic efficiency (ICE) and rate performance due to the change in support surface properties, which affects the bonding force between silicon layer and carbon substrate or the formation of initial SEI.

[0120] Significance and beneficial effects of this embodiment

[0121] Process flexibility verification: It has been demonstrated that the core "suspension polymerization + carbonization activation + CVD deposition" technical route of this invention has good compatibility and adaptability to different dispersion and stability systems;

[0122] A new dimension in the regulation of material properties: It reveals that changing the surfactant in the precursor synthesis can be used as an auxiliary means to regulate the microstructure and electrochemical properties of the final composite material.

[0123] Expanded intellectual property portfolio: Different combinations of dispersants / emulsifiers constitute diverse specific implementation methods, enhancing the hierarchy and strength of patent protection scope;

[0124] Provides optimization directions: It provides additional process adjustment parameters for material customization for specific performance indicators (such as ultra-high rate and ultra-long cycle).

[0125] Example 4

[0126] To demonstrate the synergistic necessity of the three-layer structure and specific process of this invention, the following control sample was prepared and compared with Si@C-1.5h of Example 1.

[0127] 1. Control sample A (with silicon but without dense coating):

[0128] The Si@C-0h sample prepared in Example 1 (with silicon deposition completed but no secondary carbon coating) was directly used as the negative electrode active material for battery testing.

[0129] 2. Control sample B (physically mixed silicon-carbon):

[0130] Commercially available nano-silicon powder (particle size ~50 nm) and the microporous carbon sphere carrier prepared in Example 1 were mechanically ball-milled and mixed for 2 hours at a silicon-to-carbon mass ratio of 23:77. Subsequently, this mixture was subjected to acetylene CVD carbon coating for 1.5 hours under the same conditions as in Example 1, S4.1.

[0131] 3. Performance Comparison:

[0132] The test results are shown in the table below:

[0133] sample First Coulomb efficiency (%) 1C cycle 500 cycles capacity retention (%) Compacted density (g / cm³) Remark This invention (Si@C-1.5h) 86.5 88.2 1.25 Triple structure Control sample A 81.3 32.7 1.05 Without outer constraints, SEI is unstable. Control sample B 73.8 45.1 1.10 Uneven silicon dispersion, with severe localized expansion.

[0134] Conclusion: The cycling performance of control sample A (without outer layer) deteriorated sharply, proving that the external carbon coating is indispensable for maintaining long-term structural stability; the performance of control sample B (with core process replacement) decreased significantly.

[0135] Comparative Example

[0136] Comparative Example 1: An Attempt at Preparing Lignin-Based Porous Carbon

[0137] Using sodium lignosulfonate as a precursor, an attempt was made to prepare spherical carbon according to a method similar to Example 1. However, after carbonization at 1100℃, the microspheres collapsed severely, their structure was destroyed, and they could not be used as a carrier for silicon deposition. The porous carbon obtained by directly activating irregular lignin powder had a low yield (16-25%) and irregular morphology.

[0138] Comparative Example 2: Commercial Porous Carbon-Supported Silicon

[0139] Commercially available spherical porous carbon was purchased, and silicon was deposited under the same conditions as in Example 1, without secondary coating treatment. The resulting silicon layer exhibited generally poor uniformity and low overall electronic conductivity.

[0140] Performance testing and effect verification

[0141] The materials from the above examples and comparative examples were used as active materials, and mixed with conductive carbon black and binder (CMC / SBR) at a mass ratio of 90:5:5 to form a slurry. This slurry was then coated onto copper foil to form a negative electrode. A CR2032 coin cell was assembled using a lithium metal sheet as the counter electrode and tested. The test results are as follows:

[0142] I. Cyclic Performance

[0143] Tested at a 1C charge-discharge rate, the material in Comparative Example 2 had a high initial capacity but decayed rapidly; the Si@C-1.5h and Si@C-2.5h materials in Example 1 showed significantly improved cycle stability; the Si@C-CNT material in Example 2 exhibited the best performance, with a capacity retention of over 85% after 1000 cycles.

[0144] II. Rate and Fast Charging Performance

[0145] The 1Ah pouch battery made using the materials from Example 1 has an energy density exceeding 400Wh / kg. Under 4C fast charging conditions (i.e., 80% charge in 15 minutes), the battery can be charged to approximately 85% in 15 minutes, demonstrating excellent fast charging capabilities.

[0146] in conclusion

[0147] This invention successfully fabricates a high-performance nano-silicon composite anode material through a sophisticated triple-structure design of "microporous carbon sphere framework + CVD uniform silicon layer + high-conductivity carbon coating". This material effectively and synergistically solves key technical challenges of silicon anodes, such as volume expansion, short cycle life, and poor fast-charging performance. The process route is clear and controllable, demonstrating significant prospects for industrial application and providing strong material support for the development of next-generation high-performance lithium-ion batteries.

[0148] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A nano-silicon composite anode material, characterized in that, It includes a microporous carbon sphere carrier, a nano-silicon layer uniformly deposited on the surface and within the pores of the carrier, and a carbonaceous conductive coating covering the outside of the nano-silicon layer.

2. The nano-silicon composite anode material according to claim 1, characterized in that, The microporous carbon sphere carrier is a regular sphere with a specific surface area of to The pore size is mainly distributed between 1.0 nm and 2.5 nm, and the particle size is between 0.5 μm and 8 μm.

3. The nano-silicon composite anode material according to claim 2, characterized in that, The microporous carbon sphere carrier is made by carbonization and chemical activation of phenolic resin precursor with KOH; the nano-silicon layer is formed by chemical vapor deposition with a thickness of 0.5-5 nm; and the silicon content in the composite material is 15%-35% by mass.

4. The nano-silicon composite anode material according to any one of claims 1 to 3, characterized in that, The carbonaceous conductive coating is an amorphous carbon layer formed by pyrolytic carbon, or a three-dimensional conductive network formed by carbon nanotubes; the compaction density of the composite negative electrode material electronic conductivity .

5. A method for preparing a nano-silicon composite anode material as described in any one of claims 1 to 4, characterized in that, Includes the following steps: S1: Preparation of microporous carbon sphere carriers; S2: Deposit a nano-silicon layer on a carrier using chemical vapor deposition; S3: Construct a carbonaceous conductive coating.

6. The preparation method according to claim 5, characterized in that, Step S1 includes: S11 was prepared as a spherical phenolic resin precursor by suspension polymerization. S12 pre-carbonizes the precursor; S13 involves activating the pre-carbonized product by mixing it with KOH. S14 involves washing and drying the activated product.

7. The preparation method according to claim 6, characterized in that, In the suspension polymerization method, the dispersant is selected from polyvinyl alcohol or hydroxypropyl methylcellulose, and the emulsifier is selected from sodium dodecyl sulfate or Tween 80.

8. The preparation method according to claim 5, characterized in that, In step S2, the reactive gas for chemical vapor deposition contains and The reaction temperature is 500-600℃; in step S3, a secondary carbon coating is performed by chemical vapor deposition to form an amorphous carbon layer, or carbon nanotubes are grown in the presence of a catalyst to form a three-dimensional conductive network.

9. A lithium-ion battery, characterized in that, Its negative electrode comprises the nano-silicon composite negative electrode material as described in any one of claims 1-4.

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