Modified silicon-carbon composite material, negative electrode sheet, and battery

Abstract

This invention discloses a modified silicon-carbon composite material, an anode sheet, and a battery. The modified silicon-carbon composite material includes porous carbon, ring-patterned graphite nanoparticles, and silicon nanoparticles. The silicon nanoparticles are located within the pores of the porous carbon, and / or, within the pores of the ring-patterned graphite nanoparticles, and / or, in the pores between adjacent ring-patterned graphite nanoparticles. In the provided modified silicon-carbon anode material, the introduction of ring-patterned graphite nanoparticles into the porous carbon matrix improves conductivity through the ordered structure of the ring-patterned graphite nanoparticles, enhances ion conduction through the porous structure, and allows silicon to be deposited in the pores of the ring-patterned graphite nanoparticles, suppressing Si expansion and maximizing silicon capacity, thereby improving the conductivity, rate performance, and cycle performance of the silicon-carbon anode.

Description

Technical Field

[0001] This invention belongs to the field of secondary battery materials technology, specifically relating to modified silicon-carbon composite materials, negative electrode sheets, and batteries. Background Technology

[0002] With the rapid development of the new energy industry, mobile phones, new energy vehicles, drones, robots, and other fields have placed increasingly higher demands on the energy density, fast charging performance, and safety of batteries. Silicon boasts a theoretical specific capacity of up to 4200 mAh / g, approximately 10 times that of graphite, and a relatively low voltage plateau, making it the most promising anode material currently available. Silicon is abundant in nature, offering advantages in terms of resource availability and low cost. Silicon anode materials have undergone iterative advancements from first-generation silicon-oxygen, second-generation pre-magnesium / pre-lithium silicon-oxygen, to third-generation CVD vapor-deposited silicon-carbon. The third-generation CVD silicon-carbon anode material is composed of porous carbon, nano-silicon particles, and a carbon coating layer. The porous carbon provides a space for the nano-silicon, and the silicon precursor is deposited on the inner wall of the porous carbon through vapor-phase decomposition, forming nano-sized silicon particles, thus greatly mitigating volume expansion. The final carbon coating layer prevents direct contact between the silicon particles and the electrolyte, significantly improving the first coulombic efficiency of the silicon-carbon anode material, which is now widely used in consumer electronics. However, silicon, as an intrinsic semiconductor, has low electrical conductivity. The porous carbon currently used has a hard carbon structure, where the carbon arrangement is disordered, increasing the difficulty of lithium-ion and electron transport and resulting in poor rate performance. In addition, due to the limited mechanical properties of porous carbon, the carbon skeleton is prone to cracking after repeated charge and discharge cycles, which in turn leads to volume expansion and gas generation problems.

[0003] To improve the electrical and ion-conducting properties of porous carbon, graphitization catalyzed by transition metals can be employed; high-temperature graphitization can promote the formation of splined carbon (SP) using pitch / coal-based soft porous carbon. 2 Hybridization enhances intrinsic conductivity and cycle performance; doping with conductive metals / agents creates point or surface contacts, forming a highly conductive matrix that significantly increases electron transport speed through high-speed conductive channels; fast-ion conductors are coated onto the surface of silicon-carbon particles through spray drying or conductive polymer synthesis. All these methods involve adding conductive materials to the interior / surface of silicon-carbon anode particles, increasing the contact area between electrons and active materials, constructing a multi-dimensional electron transport structure, and allowing silicon nanoparticles to utilize their capacity more efficiently.

[0004] Existing technologies significantly improve conductivity, but the ordered carbon striations in highly graphitized materials hinder ion transport. In particular, two-dimensional materials like graphene can cause a decrease in initial efficiency and exacerbate side reactions. Currently, to meet the commercial demand for high energy density, there are increasingly higher requirements for the silicon content of silicon anode materials. However, this increased silicon content leads to problems such as "floating silicon" and expansion. While the above preparation methods, by adding conductive agents, have a clear advantage in improving conductivity, they still fall short in improving ion transport pathways and providing more space for silicon expansion. Faced with stringent market demands, materials that combine high conductivity and ion conduction with low expansion are urgently needed. Summary of the Invention

[0005] The present invention aims to solve the above-mentioned problems of the prior art, and its purpose is to provide modified silicon-carbon composite materials, negative electrode sheets, and batteries.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, a modified silicon-carbon composite material is provided, comprising porous carbon, ring-patterned graphite nanoparticles, and silicon nanoparticles, wherein the silicon nanoparticles are located within the pores of the porous carbon, and / or, the silicon nanoparticles are located within the pores of the ring-patterned graphite nanoparticles, and / or, the silicon nanoparticles are located in the pores between adjacent ring-patterned graphite nanoparticles.

[0007] In a second aspect, a negative electrode sheet is provided, comprising a negative electrode active material, said negative electrode active material being a modified silicon-carbon composite material as described in the first aspect.

[0008] Thirdly, a battery is provided, including the negative electrode sheet described in the second aspect.

[0009] Compared with the prior art, one or more of the above technical solutions can achieve at least one of the following beneficial effects: In the provided modified silicon-carbon anode material, ring-patterned graphite nanoparticles are introduced into a porous carbon matrix. The ordered structure of the ring-patterned graphite nanoparticles improves the conductivity, while the porous structure improves the ion conduction performance. At the same time, silicon can be deposited in the pores of the ring-patterned graphite nanoparticles, which inhibits Si expansion and makes full use of silicon capacity more efficiently, thereby improving the conductivity, rate performance and cycle performance of the silicon-carbon anode. Attached Figure Description

[0010] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0011] Figures 1-3This is a TEM image of the ring-patterned graphite nanoparticles prepared in step S1 of Example 1.

[0012] Figure 4 The image shows the Raman spectrum of the annular graphite nanoparticles prepared in step S1 of Example 1.

[0013] Figure 5 The image shows the Raman spectrum of the porous carbon composite material prepared in step S2 of Example 3.

[0014] Figure 6 This is a TEM image of the porous carbon containing ring-patterned graphite nanoparticles prepared in step S2 of Example 9.

[0015] Figure 7 This is a TEM image of the annular graphite nanoparticles prepared in step S1 of Example 10. Detailed Implementation

[0016] Some embodiments of the present invention provide a modified silicon-carbon composite material comprising porous carbon, ring-patterned graphite nanoparticles and silicon nanoparticles, wherein the silicon nanoparticles are located within the pores of the porous carbon, and / or, the silicon nanoparticles are located within the pores of the ring-patterned graphite nanoparticles, and / or, the silicon nanoparticles are located in the pores between adjacent ring-patterned graphite nanoparticles. In the provided modified silicon-carbon composite material, the ring-patterned graphite nanoparticles are interconnected or connected to porous carbon and nano-silicon, providing a fast and continuous electron transport channel for the silicon nanoparticles. Furthermore, it provides a flexible nano-confined space for the silicon nanoparticles located between or within adjacent ring-patterned graphite nanoparticles, effectively absorbing and mitigating the expansion effect of the silicon particles. Simultaneously, the ring-patterned graphite nanoparticles overlap or combine with the porous carbon framework to form a flexible three-dimensional constraint network. This network can strongly lock the silicon nanoparticles located within and between the ring-patterned graphite nanoparticles, preventing them from agglomerating, detaching, or losing electrical contact with the conductive network during repeated volume contraction and expansion. In addition, the ring-patterned graphite nanoparticles encapsulating the silicon particles can physically isolate the silicon from direct, large-area contact with the electrolyte, reducing the uncontrollable decomposition of the electrolyte on the silicon surface. This helps form a more stable SEI film on the surface of the ring-patterned graphite nanoparticles. A stable SEI film can reduce side reactions, decrease irreversible capacity loss, and further improve the initial coulombic efficiency and cycle life.

[0017] It should be noted that the name of ring-patterned graphite nanoparticles comes from the fact that the lattice stripes on their surface are regular concentric graphite structures, hence the name ring-patterned graphite nanoparticles.

[0018] In some preferred embodiments, the primary particles of the annular graphite nanoparticles are one or more of the following: spherical, near-spherical, bowling ball-shaped, and columnar.

[0019] In some preferred embodiments, the average size of the primary particles of the annular graphite nanoparticles is 5~200nm, preferably 10~100nm, such as 10nm, 15nm, 20nm, 25nm, 30nm, 35nm, 40nm, 45nm, 50nm, 55nm, 60nm, 65nm, 70nm, 75nm, 80nm, 85nm, 90nm, 95nm, 100nm, etc.

[0020] In some preferred embodiments, the primary particles of the annular graphite nanoparticles are connected by branches, and / or, the primary particles of the annular graphite nanoparticles are distributed in clusters; and / or, the primary particles of the annular graphite nanoparticles are distributed as single particles.

[0021] The ring-shaped graphite nanoparticles, distributed as single particles, are isolated on porous carbon. They exhibit high graphitization and few defects. These nanoparticles, embedded within the porous carbon, physically shield the active sites on the carbon surface. Furthermore, the resulting SEI film is thinner and more stable, reducing side reactions and lithium loss. The isolated ring-shaped graphite nanoparticles also form conductive islands. When silicon nanoparticles are adjacent to these nanoparticles, electrons can rapidly transfer from silicon to the porous carbon framework through the nanoparticles without traversing the low-conductivity inner layer of the porous carbon. This point-to-point contact significantly reduces local contact resistance, facilitating high-rate discharge. The primary particles of the ring-shaped graphite nanoparticles connected by branches can form a long-range conductive network to achieve an efficient conductive path. At the same time, the branches can more easily provide a stable porous structure for ion transport. In addition, they can also build an elastic liner within the porous carbon channels. Although porous carbon has rigid pores to accommodate the expansion of silicon, after repeated cycles, the pore walls are prone to microcracks due to local stress concentration, leading to structural degradation. The ring-shaped graphite nanoparticles connected by branches continuously adhere to the inner surface of the pore walls, forming a flexible and deformable conductive framework. When silicon expands and compresses the pore walls, these ring-shaped graphite nanoparticles can be compressed like springs, absorbing strain energy. When silicon contracts, they return to their original shape, significantly reducing fatigue damage to the pore walls and extending the cycle life of the composite material. Multiple graphite rings in a ring-patterned graphite nanoparticle cluster can share stress. When a silicon particle expands, the entire cluster undergoes synergistic deformation. This local collective buffering mechanism allows the porous carbon to withstand high local expansion stress without cracking. However, if the cluster is too large or too dense, it often blocks the transport channels of the porous carbon, preventing the electrolyte from penetrating deeper into the silicon particles. At the same time, lithium-ion diffusion is hindered, resulting in capacity decay and rate reduction.

[0022] In some preferred embodiments, at least some of the primary particles of the ring-patterned graphite nanoparticles contain pores, and / or, at least some of the primary particles of adjacent ring-patterned graphite nanoparticles contain pores. The presence of pores within the primary particles of the ring-patterned graphite nanoparticles and the presence of pores between some of the primary particles of adjacent ring-patterned graphite nanoparticles allows these pores to accommodate silicon nanoparticles, further improving the buffering effect on silicon and enhancing the cycling performance of the silicon-carbon composite material.

[0023] In some preferred embodiments, the primary particles of the annular graphite nanoparticles are connected by branched particles to form secondary particles, and / or, the clustered large particles formed by the clustered distribution of the primary particles of the annular graphite nanoparticles constitute secondary particles.

[0024] In some preferred embodiments, the carbon atoms on the surface of the ring-patterned graphite nanoparticles are arranged in an ordered ring shape.

[0025] In some preferred embodiments, the primary surface of each annular graphite nanoparticle includes one or more concentric carbon rings.

[0026] In some preferred embodiments, the carbon lattice stripes on the primary surface of the annular graphite nanoparticles are curved annular stripes, which are substantially parallel to each other and have a concentric orientation.

[0027] In some preferred embodiments, the ID / IG ratio of the annular graphite nanoparticles is not greater than 1.1, more preferably not greater than 1.05, and even more preferably not greater than 1.

[0028] In some preferred embodiments, there may be or may not be pores between the primary particles of two adjacent annular graphite nanoparticles; when there are no pores between the primary particles of two adjacent annular graphite nanoparticles, the connection region between the primary particles of two adjacent annular graphite nanoparticles is an annular graphite sheet structure (i.e., annular carbon stripes).

[0029] In some preferred embodiments, the average pore size between adjacent annular graphite nanoparticles is 2~20nm, such as 2nm, 4nm, 6nm, 8nm, 10nm, 12nm, 14nm, 16nm, 18nm, 20nm, etc.; preferably, the pore size is 2~10nm.

[0030] In some preferred embodiments, the pore shape between adjacent annular graphite nanoparticles is columnar, worm-like, or spherical.

[0031] In some preferred embodiments, the annular graphite nanoparticles are distributed inside the porous carbon, and / or the annular graphite nanoparticles are distributed on the surface of the porous carbon.

[0032] In some preferred embodiments, the mass ratio of porous carbon to ring-patterned graphite nanoparticles is 0.95~0.6:0.05~0.4, for example, 0.95:0.05, 0.9:0.1, 0.85:0.15, 0.8:0.2, 0.75:0.25, 0.7:0.3, 0.65:0.35, 0.6:0.4, etc., preferably 0.9~0.7:0.1~0.3. Due to the high specific surface area and nanoscale size of ring-patterned graphite nanoparticles, if their proportion as the main material is too high, the mechanical properties of the particles decrease, they are prone to pulverization, and their expansion and compressive strength both decrease. When used as a filler within porous carbon, it can effectively alleviate stress and reduce expansion. Ring-patterned graphite nanoparticles themselves have the advantage of high electrical conductivity, and their branched structure can serve as high-speed conductive channels. If their proportion is too low, the improvement in conductivity will not be significant.

[0033] In some preferred embodiments, with the content of the silicon-carbon composite material being 100%, the silicon content in the silicon-carbon composite material is 15% to 80%; preferably 30% to 70%.

[0034] In some preferred embodiments, the specific surface area of ​​the silicon-carbon composite material is 0.05~55m². 2 / g; preferably 0.5~10m 2 / g.

[0035] In some preferred embodiments, the surface of the silicon nanoparticles is coated with one or more of the following: a carbon layer, a conductive polymer layer, a metal oxide layer, and a non-metallic compound layer.

[0036] In some embodiments, the carbon layer is amorphous carbon and / or graphitized carbon.

[0037] In some embodiments, the conductive polymer is made of one or more of polyaniline, polypyrrole, polydopamine, polythiophene, etc.

[0038] In some embodiments, the metal oxide layer is made of ZrO2, SnO2, CeO2, TiO2, Al2O3, or SiO2. x One or more of the following.

[0039] In some embodiments, the non-metallic compound layer is made of one or more materials such as Si3N4 and SiC.

[0040] In some embodiments, the porous carbon is one or more of the following: irregular block, perfect sphere, near-sphere, polyhedron, worm-shaped, etc.

[0041] In some preferred embodiments, the particle size Dv50 of the porous carbon is 3~15μm, preferably 5~9μm.

[0042] Some embodiments provide a method for preparing modified silicon-carbon composite materials, including: (1) A mixture of carbon source vapor and inert gas, and a mixture of water vapor and inert gas are mixed in an insulated pipeline. As the inert gas enters the high-temperature reaction zone, the reaction takes place (causing the carbon source vapor to crack the CH bonds and break them, and carbon atoms to aggregate into nuclei, while the water vapor vaporizes and etches the carbon in the cracking products to create pores). After the reaction is completed, the solid product is collected to obtain ring-patterned graphite nanoparticles. (2) The annular graphite nanoparticle material is mixed evenly with the polymer solution, and after solidification, the solidified product is coarsely crushed, then carbonized under a nitrogen atmosphere, and then finely crushed and classified. After activation treatment by passing water vapor at high temperature, porous carbon containing annular graphite nanoparticles is obtained. (3) The porous carbon and silicon precursor are contacted in a nitrogen atmosphere to deposit nano-silicon particles, which are embedded in the pores of the annular graphite nanoparticles and / or porous carbon to obtain a modified silicon-carbon composite matrix. Optionally, it further includes: coating the modified silicon-carbon composite matrix.

[0043] In the above preparation process, the aggregation morphology of the ring-patterned graphite nanoparticles is controlled by adjusting the pyrolysis temperature, carbon source concentration, water vapor concentration, and cooling method. When the temperature is high or the carbon source concentration is high, the primary particles collide with each other to form a branched network structure.

[0044] In some embodiments, in step (1), the carbon source vapor is formed by the constant-temperature vaporization of the carbon source liquid carried by the first inert gas, and the water vapor is formed by the constant-temperature water bubbling carried by the second inert gas; the two gases are mixed through a heat-insulating pipeline before entering the high-temperature reaction zone.

[0045] In some embodiments, the outlet of the high-temperature reaction zone is equipped with a rapid cooling device to quickly cool the reaction products.

[0046] In some embodiments, the carbon source is one or more of toluene, xylene, ethylbenzene, naphthalene, anthracene, phenanthrene, cyclohexane, pitch, and light coal tar; the inert gas is not limited to nitrogen, argon, etc.

[0047] In some embodiments, in step (1), the temperature of the carbon source vapor is 25~300℃, for example 25℃, 60℃, 100℃, 150℃, 200℃, 250℃, 300℃, etc., and the temperature of the carbon source vapor is related to the properties of the carbon source itself; the flow rate of the inert gas introduced into the carbon source vapor is 2~500mL / min, for example 2mL / min, 10mL / min, 30mL / min, 50mL / min, 80mL / min, 100mL / min, 120mL / min, 150mL / min, 180mL / min, 200mL / min, 250mL / min, 300mL / min, 350mL / min, 400mL / min, 450mL / min, 500mL / min, etc.

[0048] In some embodiments, in step (1), the temperature of the water vapor is 70~100℃, for example 70℃, 80℃, 90℃, 100℃, etc.; the flow rate of the inert gas introduced into the water vapor is 0.5~50mL / min, for example 0.5mL / min, 1mL / min, 2mL / min, 3mL / min, 4mL / min, 5mL / min, 8mL / min, 10mL / min, 12mL / min, 15mL / min, 18mL / min, 20mL / min, 25mL / min, 30mL / min, 35mL / min, 40mL / min, 45mL / min, 50mL / min, etc.

[0049] In some embodiments, in step (1), the temperature of the heat-insulating pipeline is 100~350℃, for example 100℃, 120℃, 150℃, 180℃, 200℃, 220℃, 250℃, 280℃, 300℃, 320℃, 350℃, etc., and is not lower than the boiling point of the carbon source used.

[0050] In some embodiments, in step (1), the temperature of the tubular furnace is 800~1500℃, for example 800℃, 900℃, 1000℃, 1200℃, 1500℃, etc.; the thermal decomposition time is 0.5~4h, for example 0.5h, 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h, etc.

[0051] In some embodiments, in step (2), the curing temperature is 80~200℃; the curing time is 3~48h.

[0052] In some embodiments, in step (2), the carbonization temperature is 600~900℃; the carbonization time is 1~6h.

[0053] In some embodiments, in step (2), the activation temperature is 800~900℃; the activation time is 1~6h.

[0054] In some embodiments, in step (3), the temperature at which the silicon precursor contacts the porous carbon is 150~1000℃ and the time is 1~100 h.

[0055] In some embodiments, the silicon-containing precursor is selected from at least one of the following materials: silane, silane, propane, halosilane, polysilane, polysiloxane, polycarbosilane, thiophene and its derivatives, silanium and its derivatives, etc.

[0056] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to the accompanying drawings and preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0057] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0058] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0059] Example 1 After purging with nitrogen, the tubular furnace was heated to 900℃ at a rate of 5℃ / min and held constant. Simultaneously, toluene was kept at a constant temperature of 60℃ and transported by nitrogen at a rate of 80mL / min to form stable toluene vapor. A separate nitrogen stream was used to bubble 80℃ pure water at a rate of 8mL / min to carry saturated water vapor. The two vapor streams mixed in a 120℃ insulated tubing before entering the tubular furnace, where the reaction lasted 120min. During the two-phase gas mixing and contact, toluene under an inert atmosphere underwent high-temperature decomposition to generate branched primary particles. The water vapor in the system underwent a mild vaporization etching reaction with the amorphous carbon within it, constructing a porous structure in situ. After the reaction, the furnace was kept under nitrogen protection and allowed to cool naturally to room temperature. The nanoparticles were collected from the furnace wall and the exhaust gas absorption device.

[0060] The obtained transmission electron microscopy data of nanoparticles are as follows Figures 1-3 As shown, by Figure 1 It can be seen that the primary particles of the ring-patterned graphite nanoparticles have a spherical or columnar morphology, with a particle size ranging from 10 to 30 nm. Pores exist between some adjacent ring-patterned graphite nanoparticles, with a worm-like morphology and a pore size of 3 to 15 nm. The primary particles are linked by branches to form secondary particles, such as... Figure 3 As shown; the internal pores of the ring-patterned graphite nanoparticles are as follows Figure 2As shown, the annular graphite nanoparticles exhibit an irregular shape with pore sizes ranging from 2 to 10 nm. The carbon within these nanoparticles is arranged in an ordered ring pattern, and the carbon lattice fringes within the nanoparticles form a concentric circle structure. The carbon fringes within the nanoparticles are distributed in a long-range ordered banded pattern, primarily due to the water activation process etching amorphous carbon atoms between the fringes or some carbon atoms within individual microcrystals, opening pores between the fringes, which then rearrange into ordered fringes. The average particle size and average pore size of the primary particles were obtained from TEM data. Their Raman spectra are shown below. Figure 4 As shown.

[0061] Analysis revealed that in the aforementioned process, the carbon source vapor undergoes rapid decomposition under an inert high-temperature environment, breaking molecular chemical bonds and generating highly reactive carbon free radicals. These free radicals then undergo dehydrogenation, cyclization, condensation, and gas-phase nucleation, gradually removing hydrogen and stacking to form graphite microcrystals, ultimately generating primary particles. Simultaneously, the multiple active sites and steric hindrance of the molecular structure disrupt the regular growth trend of carbon, promoting multi-angle and multi-directional condensation and aggregation of carbon free radicals. Furthermore, the primary carbon particles continuously collide in the high-temperature gas phase, fusing and extending at active defect sites, ultimately leading to the growth of the primary particles into a typical branched aggregate structure. Mixing water vapor into the carbon source vapor allows for rapid carbon source decomposition and rearrangement of the carbon structure, while the water vapor physically etches further pores, resulting in branched, porous, ring-patterned graphite nanoparticles.

[0062] Step S2: 1.5 g of the annular graphite nanoparticle material prepared in step S1 was mixed with 100 g of phenolic resin prepolymer in a homogenizer at room temperature for 6 hours. The Mw of the resin prepolymer was 700 and the solid content was 80%. After that, it was cured at 180°C for 6 hours. The network crosslinking of the phenolic resin improved the bonding strength with the internal annular graphite nanoparticles. Then, it was coarsely crushed and carbonized at 600°C under nitrogen for 2 hours. After fine crushing, it was water activated and held at 850°C for 2 hours to obtain a porous carbon composite material. Some of the pores of the annular graphite nanoparticles were filled by the polymer, so that the average pore size of the porous carbon was lower than that of the annular graphite nanoparticles. The particle size and micropore data are shown in Table 2. Step S3: Take the porous carbon from step S2, place the substrate in a tube furnace, and heat it to 580°C at 5°C / min under a N2 atmosphere. Then, introduce a 25% SiH4-N2 mixed gas and maintain the temperature for 18 hours. Change the atmosphere to N2, place the substrate in the tube furnace again, and heat it to 650°C. Introduce methane gas for carbon coating for 2 hours. Change the atmosphere back to N2, cool it to room temperature, and obtain the silicon-carbon anode material. Test the electrochemical performance of the silicon-carbon anode material. The coin cell data are shown in Table 3.

[0063] Example 2 The difference between this embodiment and Embodiment 1 is that the amount of ring-patterned graphite nanoparticles used in step S2 is adjusted to 3 grams, while other aspects remain unchanged.

[0064] Example 3 The difference between this embodiment and Embodiment 1 is that the amount of ring-patterned graphite nanoparticles used in step S2 is adjusted to 4.8 grams, while other aspects remain unchanged.

[0065] The Raman diagram of the porous carbon composite material obtained in step S2 is as follows: Figure 5 As shown. Comparison Figure 4 and Figure 5 It can be seen that the prepared textured graphite nanoparticles have a relatively small ID / IG ratio, and the ring-textured graphite nanoparticles have an ID / IG ratio of less than 1. The G peak represents the degree of ordered graphitization, and the G peak is more prevalent and sharper, indicating a clear graphitized structure with ordered carbon stripes inside. In contrast, the porous carbon composite material in Example 3, due to the introduction of disordered carbon after the carbonization of phenolic resin, shows a decrease in the degree of order in the carbon arrangement, an increase in the ID / IG ratio, an increase in the proportion of disordered carbon, and an overall decrease in order.

[0066] Example 4 The difference between this embodiment and Embodiment 1 is that the subsequent introduction of 25% SiH4-N2 mixed gas in step S3 and the maintenance at 580°C for 18 hours is adjusted to 22 hours, while other aspects remain unchanged.

[0067] Example 5 The difference between this embodiment and Embodiment 1 is that in step S3, a 25% SiH4-N2 mixed gas is subsequently introduced and the temperature is maintained at 580°C for 18 hours, which is then adjusted to 10 hours, while other aspects remain unchanged.

[0068] Example 6 The difference between this embodiment and Embodiment 1 is as follows: the nitrogen flow rate for introducing water vapor in step S1 is set to 2 mL / min, the water vapor temperature is 80°C, the nitrogen flow rate for introducing toluene vapor is 60 mL / min, the toluene vapor temperature is 60°C, and the tube furnace temperature is set to 800°C. The obtained nanoparticles were analyzed, and the results are shown in Table 1. Lowering the pyrolysis temperature weakens the water etching effect and reduces the pore size. Simultaneously, reducing the carbon source vapor flow rate results in insufficient carbon source supply, limiting particle growth and making dense packing more likely, leading to reduced porosity between branches.

[0069] Example 7 The difference between this embodiment and Embodiment 1 is as follows: the nitrogen flow rate for introducing water vapor in step S1 is set to 15 mL / min, the water vapor temperature is 80℃, the nitrogen flow rate for introducing toluene vapor is 100 mL / min, the toluene vapor temperature is 60℃, and the tube furnace temperature is set to 950℃. The obtained nanoparticles were analyzed, and the results are shown in Table 1. Increasing the pyrolysis temperature enhances the water etching effect, increases the pore size, and increases the carbon source vapor flow rate. Incomplete pyrolysis yields a large number of nanoparticles, increasing the probability of particle collisions, rapidly integrating chain-like structures, and increasing pore size, resulting in a more porous branched structure.

[0070] Comparing Examples 1, 6, and 7, it can be seen that annular graphite nanoparticles with different pore volumes and pore sizes can be obtained by controlling the reaction conditions. With increasing toluene concentration, the nucleation rate is faster, the prepared branches are more stable and have increased degrees of freedom, and the porosity between branches also increases. With increasing water vapor flow rate, the physical etching effect of water on the carbon interior and branch surface pore formation is more pronounced. When the tube furnace temperature increases, the toluene decomposition rate accelerates, the particle size of the initial particles increases, the branches are less prone to compression, and the porosity further increases. When the temperature, toluene concentration, and water vapor flow rate are decreased, the initial particle size is smaller, the flexibility is higher, the branches are more easily brought together, the inter-chain pores narrow, and the water etching effect weakens, resulting in a smaller pore size.

[0071] Example 8 Step S1: Same as step S1 in Example 1; Step S2: Dissolve 0.5 g of polyethylene glycol in 150 mL of water until completely dissolved. Mix 1.5 g of porous ring-patterned graphite nanoparticles and 100 g of water-soluble phenolic resin in a homogenizer at room temperature for 6 hours until completely dispersed, with the ring-patterned graphite nanoparticles completely coated by the phenolic resin. Then add the mixture to the above dispersion, heat to 90 degrees Celsius and stir for 1 hour. Under the action of the dispersant, a resin suspension is obtained. Add 5 g of hexamethylenetetramine powder, heat to 95 degrees Celsius, and obtain a light green slurry. Centrifuge and dry at 100 degrees Celsius to obtain a powder. Carbonize at 600 degrees Celsius under nitrogen for 2 hours, then activate with water and treat at 850 degrees Celsius for 2 hours to obtain a spherical porous carbon composite material. In the obtained spherical porous carbon composite material, the ring-patterned graphite nanoparticles are distributed inside the spherical porous carbon material. Step S3: Same as step S3 in Example 1.

[0072] Example 9 Step S1: After purging the tube furnace with nitrogen, the temperature was increased to 1100℃ at a rate of 5℃ / min and held constant for one hour. Toluene was then kept at a constant temperature of 40℃ and transported by nitrogen at a rate of 300mL / min to form toluene vapor. A separate nitrogen stream was introduced at a rate of 8mL / min through 80℃ pure water to carry saturated water vapor. The two streams were mixed in a 120℃ insulated tubing before entering the constant-temperature zone of the tube furnace. The outlet of the tube furnace was connected to an ice-water absorption device for rapid cooling. After the reaction, the toluene cracking reaction was terminated by purging with pure nitrogen. At 1100℃, toluene rapidly cracked, carbon atoms rearranged, and graphite sheets curled and wrapped layer by layer. Simultaneously, the extremely low concentration of toluene vapor nucleated individually, preventing adhesion. The collected nanoparticles were ultrasonically treated in ethanol to further disperse and depolymerize, followed by rotary evaporation to remove the solvent, yielding single-particle ring-patterned graphite nanoparticles. The TEM data of the porous carbon containing the single-particle ring-patterned graphite nanoparticles are shown below. Figure 6 As shown, ring-patterned graphite nanoparticles are distributed on the surface and inside of porous carbon.

[0073] Steps S2-S3: Same as steps S2-S3 in Example 1.

[0074] Example 10 Step S1: After purging the tube furnace with nitrogen, the temperature is increased to 800℃ at 5℃ / min and held constant for one hour. Then, toluene is kept at 80℃ and carried by nitrogen at 80mL / min to form toluene vapor. Separately, nitrogen is bubbled through 80℃ pure water at 1mL / min to carry saturated water vapor. The two gas streams are mixed in a 120℃ insulated tube and then enter the constant-temperature zone of the tube furnace. A collection device is connected to the outlet of the tube furnace to collect the nanoparticles inside the furnace wall and the exhaust gas absorption device, yielding clustered ring-patterned graphite nanoparticles. The TEM data of the obtained clustered ring-patterned graphite nanoparticles are shown below. Figure 7 As shown.

[0075] Analysis revealed that the high concentration of toluene vapor caused them to collide, entangle, and stack together, forming a dense cluster structure at high temperatures. This simultaneously reduced the flow rate of water vapor, weakening the pore-forming ability. Furthermore, the lack of physical etching between the nanospheres made them more prone to agglomeration.

[0076] Steps S2-S3: Same as steps S2-S3 in Example 1.

[0077] Comparative Example 1 Phenolic resin was cured at 180℃ for 6 hours, coarsely crushed and then carbonized at 600℃ under nitrogen for 2 hours. After fine crushing and water activation, it was kept at 850℃ for 2 hours to obtain porous carbon. The porous carbon was placed in a tube furnace and heated to 500°C at a rate of 5°C / min under a N2 atmosphere. A 25% SiH4-N2 mixture was then introduced, and the temperature was maintained at 580°C for 18 hours. The atmosphere was then changed to N2, and the substrate was placed back in the tube furnace and heated to 650°C. Methane gas was introduced for carbon coating for 2 hours. The atmosphere was then changed back to N2, and the material was cooled to room temperature to obtain a silicon-carbon anode material. The electrochemical performance of this silicon-carbon anode material was then tested.

[0078] Performance testing: Property testing of ring-patterned graphite nanoparticles: The morphology, average size, and average pore size of the primary particles of the annular graphite nanoparticles in each embodiment were obtained by TEM testing, and the results are shown in Table 1.

[0079] Porous carbon property testing: 1. Particle size test: The particle size of the porous carbon in each embodiment and comparative example was measured by a laser particle size analyzer MS3000. 0.5 ± 0.05 g of porous carbon powder was weighed using a 0.1% balance and poured into 100 ml of a 0.2% dispersant solution. The mixture was then stirred magnetically for 20 minutes at 500-550 rpm. The laser particle size analyzer was operated at 80% ultrasonic power and 3000 rpm. After background removal, the average value of three manually measured values ​​was obtained to obtain the porous carbon volume distribution data (Dv10, Dv50, Dv90). The Span data was calculated based on Span = (Dv90 - Dv50) / Dv10, and the results are shown in Table 2.

[0080] 2. Pore volume and specific surface area test: BET data for porous carbon in each embodiment and comparative example were obtained using a Bestech BSD-660M. 0.2 ± 0.02 g of porous carbon powder was weighed into sample tubes. The empty sample tube weighed m0, and the sample + sample tube weighed m1. The sample mass m = m0 - m1 was recorded. A purge head was attached to the end of each sample tube, and heating and purging were performed. Nitrogen purging was performed at 150°C for 30 minutes, followed by degassing at 300°C for 90 minutes. After cooling, the sample + sample tube m2 was weighed again after 5-10 minutes. The degassed sample mass m3 = m2 - m0. The sample type was selected as "ultrafine ultralight powder (extremely easily dispersed)," and the degassing setting was selected as "non-in-situ degassing / no degassing." In the isotherm report, P is the pressure after adsorption equilibrium, P0 is the saturated vapor pressure of the adsorbate at the adsorption temperature, P / P0=0.990 is selected as the total pore volume data and pore diameter <195.6nm is selected as the BET multi-point method automatic range P / P0=0.0149~0.1573 as the specific surface area data.

[0081] Physical and electrochemical performance testing of silicon-carbon composite materials: 1. Specific surface area test: The BET data of the silicon-carbon composite materials in each embodiment and comparative example were obtained by Bestech BSD-660M testing.

[0082] 2. Test of Si content in silicon-carbon anode materials: 3.0 g of silicon-carbon composite material was dried in an oven at 150℃ until constant weight, and the mass m1 was recorded. The dried composite material was then placed in a muffle furnace, heated to 1100℃ and held for 2 hours, cooled, and weighed, and the mass m2 was recorded. The Si content calculation formula is as follows: .

[0083] 3. Electrode and half-cell preparation and electrochemical performance testing: Using the silicon-carbon anode materials prepared in the above embodiments and comparative examples as anode active materials, anode sheets were prepared respectively. The anode sheets were used to prepare CR2032 coin cells using conventional methods, and the electrical performance of the cells was tested.

[0084] Specific testing methods include: Half-cell assembly: Assemble CR2032 coin cells in a glove box, using lithium metal sheets as the counter electrode, polypropylene microporous membranes as the separator, and LiPF6 dissolved in a mixture of ethyl carbonate (EC) and diethyl carbonate (DEC) (volume ratio EC:DEC=1:1), with a LiPF6 concentration of 1 mol / L.

[0085] The battery was charged and discharged using the LAND battery testing system: (1) Cyclic specific capacity and initial efficiency test: After the CR2032 button cell was left to stand for 6 hours, it was discharged at 0.1C to 0.005V and the specific capacity was recorded as Q1; then it was discharged at a constant voltage of 0.005V to the current cutoff of 0.01C and the specific capacity was recorded as Q2; after standing for 5 minutes, it was charged at a constant current of 0.1C to 0.8V and the specific capacity was recorded as Q3; after standing for 5 minutes, it was charged at a constant current of 0.1C to 1.5V and the specific capacity was recorded as Q4; after standing for 5 minutes, it was discharged at a constant current of 1.0C to 0.005V and the specific capacity was recorded as Q5; after standing for 2 hours, the thickness of the negative electrode sheet was measured in sequence and the average value was recorded as h1. Another coated and dried electrode sheet was taken and the thickness of the negative electrode sheet at 5 points was measured and the average value was recorded as h2. The specific capacity of the first lithium delithiation is the specific capacity (or mass specific capacity) of the electrode material. The ratio of the first lithium delithiation capacity to the first lithium insertion capacity is the first coulombic efficiency of the battery.

[0086] 1.5V initial efficiency = (Q3 + Q4) / (Q1 + Q2) * 100%; 1C rate discharge retention rate = Q5 / (Q3 + Q4) * 100%; (2) 1C Ratio Test: After the CR2032 coin cell was left to stand for 6 hours, it was discharged at 0.1C to 0.005V, left to stand for 5 minutes, and then charged at 0.1C to 1.5V. This cycle was repeated 3 times. Then, it was discharged at 1C to 0.005V, left to stand for 5 minutes, and then charged at 1C to 1.5V. This cycle was repeated 3 times. The data was recorded, and the 1C lithium intercalation retention rate was the 1C discharge specific capacity / 0.1C discharge specific capacity.

[0087] (3) Powder resistivity test: After compacting the silicon-carbon composite material with a pressure of 4.0 MPa, the ST2722-SD four-terminal powder resistivity tester was used. The test results are shown in Table 3.

[0088] (4) Electrode expansion rate: After the CR2032 type button cell was left to stand for 6 hours, it was discharged to 0.005V at 0.05C and then discharged to 0.005V at 0.01C. Then the button cell was disassembled in the glove box, the electrode was cleaned with DMC and the thickness of the electrode was measured. The expansion rate was calculated as: (thickness of electrode in the first fully charged state - thickness of fresh electrode) / thickness of fresh electrode × 100%.

[0089] The data of the annular graphite nanoparticle materials obtained in each embodiment and comparative example are shown in Table 1 below; the characterization parameters of the porous carbon prepared in each embodiment and comparative example are shown in Table 2 below; and the electrochemical and physical performance data of the silicon-carbon composite materials prepared in each embodiment and comparative example are shown in Table 3 below.

[0090] Table 1 Characterization parameters of ring-patterned graphite nanoparticles Table 2 Characterization parameters of porous carbon Table 3 Physical properties and electrochemical performance of silicon-carbon composite materials Examples 1-7 and 9-10 are bulk porous carbon, and Example 8 is spherical porous carbon. By dispersing ring-patterned graphite nanoparticles in a prepolymer solution and fixing the ring-patterned graphite nanoparticles inside the microspheres during the microsphere solidification process through suspension polymerization, this method is suitable for preparing porous carbon with spherical, near-spherical, polyhedral, and worm-shaped appearances.

[0091] Depend on Figures 1-2As shown in Table 1, the ring-patterned graphite nanoparticles have a relatively large pore size and a mesoporous structure. After combining with the polymer, they also introduce a mesoporous structure into the porous carbon. With increasing addition, the pore volume of the porous carbon increases, while the specific surface area decreases. The data for the porous carbon are shown in Table 2. When the ring-patterned graphite nanoparticles are single particles, there is no influence from the mesopores between the particles; the specific surface area is only affected by the pores within the ring-patterned graphite particles, resulting in a smaller decrease in specific surface area. In Example 10, the clustered ring-patterned graphite particles, due to the pores created by their own particle aggregation, also introduce some mesoporous structures into the porous carbon. However, the pores created by the aggregation between particles result in a less dense structure, easily leading to pulverization after expansion. In Comparative Example 1, without the introduction of ring-patterned graphite particles, the polymer-carbonized and activated carbon has a relatively large specific surface area, indicating microporous carbon.

[0092] And by Figures 1-2 As shown in Table 1, the average pore size distribution between adjacent ring-shaped graphite nanoparticles and within the ring-shaped graphite nanoparticles ranges from 2 to 30 nm, exhibiting a mesoporous structure that effectively buffers the volume expansion of silicon deposited within. The ring-shaped graphite nanoparticles integrate with the porous carbon framework via embedding, enhancing the bonding strength between ordered and disordered carbon and enabling rapid electron transfer within the carbon structure. Furthermore, the silicon within the pores of the ring-shaped graphite nanoparticles achieves a bonding similar to that with graphite, improving long-cycle performance.

[0093] The data from Example 1 and Comparative Example 1 in Table 3 show that the addition of ring-patterned graphite nanoparticles significantly improves the first-efficiency and rate performance of the silicon-carbon anode material, while alleviating expansion. TEM image analysis reveals that the ordered ring-shaped carbon arrangement within the ring-patterned graphite nanoparticles provides a neat and fast channel for electron transfer. Simultaneously, silicon particles deposited in the gaps between adjacent ring-patterned graphite nanoparticles, and even within the pores of the ring-patterned graphite nanoparticles, are effectively reduced by the double-layer constraint of the ring-patterned graphite nanoparticles and porous carbon. The data from Examples 1-3 in Table 3 show that with the increase of the ring-patterned graphite nanoparticle content, the first-efficiency and rate performance are further improved. The increased proportion of ring-patterned graphite nanoparticles within the porous carbon enhances the overall graphitization degree of the porous carbon, thus improving conductivity. Compared with Example 8, Example 1 shows that the resistivity of the perfect spherical porous carbon is low, and the resistivity is further reduced after the addition of ring-patterned graphite nanoparticles. The effect is obvious after a small amount of addition. The addition of ring-patterned graphite nanoparticles also improves the rate performance of the perfect spherical material and broadens the application of spherical silicon carbon in the power direction.

[0094] Comparing Examples 1, 9, and 10 in Table 3, it can be seen that the distribution of single-particle, branched, and clustered annular graphite nanoparticles affects rate performance. Specifically, the silicon-carbon anode material prepared with branched annular graphite nanoparticles exhibits improved rate performance, significantly reduced resistivity, and improved expansion. Analysis reveals that this is because individual particles are prone to conductive disconnection, and the specific surface area and pore volume resulting from the difficulty in dispersing clusters are caused by the physical aggregation or overlap of particles. This structural instability easily leads to loss of initial efficiency, resulting in increased resistivity and decreased rate performance. In contrast, branched annular graphite nanoparticles can form a long-range conductive network, achieving efficient conductive paths. Simultaneously, the branches more easily provide a stable porous structure for ion transport, increasing the lithium-ion insertion / extraction rate, mitigating lithium plating side reactions under fast charging conditions, and improving battery life.

[0095] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A modified silicon-carbon composite material, characterized in that, It includes porous carbon, ring-patterned graphite nanoparticles, and silicon nanoparticles, wherein the silicon nanoparticles are located within the pores of the porous carbon, and / or, the silicon nanoparticles are located within the pores of the ring-patterned graphite nanoparticles, and / or, the silicon nanoparticles are located in the pores between adjacent ring-patterned graphite nanoparticles.

2. The modified silicon-carbon composite material as described in claim 1, characterized in that, The primary particles of the ring-patterned graphite nanoparticles are one or more of the following: spherical, near-spherical, bowling ball-shaped, and columnar; the average size of the primary particles of the ring-patterned graphite nanoparticles is 5~200 nm.

3. The modified silicon-carbon composite material as described in claim 1, characterized in that, The primary particles of the ring-patterned graphite nanoparticles are connected by branches, and / or the primary particles of the ring-patterned graphite nanoparticles are distributed in clusters, and / or the primary particles of the ring-patterned graphite nanoparticles are distributed as single particles. And / or, the primary particles of the annular graphite nanoparticles are connected by branched particles to form secondary particles, and / or, the clustered large particles formed by the primary particle clusters of the annular graphite nanoparticles constitute secondary particles. And / or, at least some of the ringed graphite nanoparticles have pores within their primary particles and / or at least some of the primary particles of adjacent ringed graphite nanoparticles have pores between them.

4. The modified silicon-carbon composite material as described in claim 1, characterized in that, The carbon atoms on the surface of the ring-patterned graphite nanoparticles are arranged in an ordered ring shape. And / or, the primary particle surface of each annular graphite nanoparticle includes one or more concentric carbon rings; And / or, the carbon lattice stripes on the primary particle surface of the ring-patterned graphite nanoparticles are curved ring stripes, which are substantially parallel to each other and have a concentric orientation structure. And / or, there may be or may not be pores between the primary particles of two adjacent annular graphite nanoparticles; when there are no pores between the primary particles of two adjacent annular graphite nanoparticles, the connection region between the primary particles of two adjacent annular graphite nanoparticles is an annular lamellar structure.

5. The modified silicon-carbon composite material as described in claim 1, characterized in that, The average pore size between adjacent annular graphite nanoparticles is 2~20 nm; And / or, the pore shape between adjacent annular graphite nanoparticles is one or more of columnar, worm-like, or spherical.

6. The modified silicon-carbon composite material as described in claim 1, characterized in that, Ringed graphite nanoparticles are distributed inside porous carbon, and / or, ringed graphite nanoparticles are distributed on the surface of porous carbon; And / or, the mass ratio of the porous carbon to the ring-patterned graphite nanoparticles is 0.95~0.6:0.05~0.

4.

7. The modified silicon-carbon composite material as described in claim 1, characterized in that, The surface of the silicon nanoparticles is coated with one or more of the following: a carbon layer, a conductive polymer layer, a metal oxide layer, and a non-metallic compound layer. The carbon layer is amorphous carbon and / or graphitized carbon; The conductive polymer layer is made of one or more of polyaniline, polypyrrole, polydopamine, and polythiophene. The metal oxide layer is made of ZrO2, SnO2, CeO2, TiO2, Al2O3, and SiO2. x One or more of the following; The non-metallic compound layer is made of one or two of Si3N4 and SiC.

8. The modified silicon-carbon composite material as described in claim 1, characterized in that, With the modified silicon-carbon composite material content being 100%, the silicon content in the modified silicon-carbon composite material is 15%~80%; And / or, the specific surface area of ​​the modified silicon-carbon composite material is 0.05~55m². 2 / g; And / or, the porous carbon is one or more of the following: irregular block, spherical, near-spherical, polyhedral, and worm-shaped. And / or, the particle size Dv50 of the porous carbon is 3~15μm.

9. A negative electrode, characterized in that, Including the modified silicon-carbon composite material as described in any one of claims 1 to 8.

10. A battery, characterized in that, Includes the negative electrode as described in claim 9.

Images