Ultrafine nano-silicon-based negative electrode material prepared on basis of in-situ high-temperature phase change in confinement microcavity, and preparation method therefor

Abstract

The present invention provides an ultrafine nano-silicon-based negative electrode material prepared on the basis of in-situ high-temperature phase change in a specific confinement microcavity, and a preparation method therefor. In the method, silicon and a conductive porous material are mixed in a solvent, then sanding is performed, solid particles are formed by means of reforming granulation, and a confinement microcavity is constructed by means of coating treatment. By means of transient heating and cooling, the silicon source is sublimated and desublimated into particles having a size of 10 nm or less, and the particles are embedded in the porous material, thereby achieving extreme nanometerization of silicon. The method effectively solves the problems such as volume expansion, low conductivity, and poor cycle stability when silicon is used as a negative electrode material of a lithium-ion battery, improves electron transport, prolongs cycle life, simplifies the process, reduces costs, and has good commercial prospects.

Description

A method for preparing ultrafine nano-silicon-based anode materials based on in-situ high-temperature phase transition within a confined microcavity. Technical Field

[0001] This invention belongs to the field of lithium-ion battery anode materials, specifically relating to a method for preparing ultrafine nano-silicon-based anode materials based on in-situ high-temperature phase transition within a confined microcavity. Background Technology

[0002] Over the past three decades, lithium-ion batteries have achieved tremendous commercial success due to their advantages such as high energy density, low self-discharge rate, long cycle life, and light weight. Currently, the lithium-ion battery industry continues its rapid growth, with widespread applications in consumer electronics, new energy vehicles, and energy storage devices. Graphite remains the mainstream anode material for lithium-ion batteries, but the theoretical specific capacity of traditional graphite electrodes is only 372 mAh / g, approaching the theoretical capacity ceiling and severely limiting the energy density of lithium-ion batteries, hindering further improvements.

[0003] Compared to traditional graphite anode materials, silicon boasts a theoretical specific capacity of 4200 mAh / g, 11.3 times that of graphite, thus exhibiting higher energy density potential. Furthermore, the lithium insertion / extraction potential of silicon-based anodes (0.4 V vs. Li / Li+) is slightly higher than that of graphite (0.05 V vs. Li / Li+), avoiding potential surface lithium plating during charging. Additionally, silicon is widely available, relatively inexpensive, and non-toxic and pollution-free. Compared to other anode materials, silicon-based anode materials are more competitive. However, silicon experiences extremely high volume expansion during charging and discharging (approximately 300%). This drastic volume change not only leads to repeated cracking of silicon but also causes it to lose its conductive connection with the electrode, resulting in mechanical pulverization and cracking. Repeated volume changes cause repeated reconstruction and growth of the solid electrolyte interphase (SEI). Silicon nanostructuring can rapidly relax stress, improve silicon's fracture resistance, and alleviate the mechanical stress generated during lithiation to some extent. Nano-silicon possesses advantages such as short lithium-ion diffusion distance, large surface area, and fast grain boundary transport. However, when the specific surface area of ​​the silicon-based anode is larger, the specific surface area of ​​the SEI film formed also increases, resulting in the consumption of more lithium ions and a decrease in the initial coulombic efficiency of the full cell. Furthermore, nano-silicon is prone to aggregation, increasing the lithium-ion transport distance. Coupled with its inherently poor conductivity, it is unstable after nano-sizing, easily leading to problems such as rapid capacity decay, low coulombic efficiency, poor conductivity, and low reversible capacity, severely limiting its application in lithium-ion battery anode materials. To address these issues, current research focuses on combining it with other matrix materials, and significant progress has been made. Other matrices primarily involve carbon-based materials. The high conductivity of carbon-based materials improves the overall conductivity of the electrode, the porous structure of carbon-based materials buffers the dramatic volume expansion of nano-silicon, and the formation of stable chemical bonds between atoms in carbon-based materials and nano-silicon forms a stable SEI, improving battery specific capacity, cycle stability, and initial coulombic efficiency.

[0004] Currently, typical preparation technologies for silicon-carbon composite materials mainly include chemical vapor deposition (CVD), mechanical alloying, and solution methods. Among these, CVD silicon-carbon anode materials have significant potential for cost reduction and relatively mature industrial mass production conditions, making them the most popular anode material track in the current new energy field. CVD uses a gas-phase chemical reaction to generate a thin film on the substrate surface. In the production of silicon-carbon anode materials, CVD utilizes high temperatures to decompose silicon source gases such as silanes. By precisely controlling reaction parameters, a uniform, high-purity silicon-carbon composite material is deposited on the surface of the carbon-based material. However, it requires sophisticated equipment and reaction conditions, resulting in high production costs.

[0005] As a prime example, Group 14 in the United States creatively utilizes chemical vapor deposition (CVD) technology to produce SCC55, a silicon-carbon anode material with a nano-carbon framework as its main structure. Nano-silicon anodes are stored within the carbon framework to stabilize the volume expansion of silicon particles during charging and discharging. However, this approach faces challenges such as the inability to achieve continuous production, poor batch-to-batch consistency, and high costs, preventing true mass production. Professor Yi Cui's research group at Stanford University, in their study of silicon-carbon materials, employed a two-step CVD method. They first prepared a carbon framework anode loaded with high-capacity crystalline silicon, and then coated the framework surface with a highly elastic polymer via polymerization to significantly improve the electrode's mechanical strain performance. Furthermore, Professor Cui's team designed innovative structures to enhance material performance, such as the yolk-shell structure and the micro-garnet configuration. However, the preparation costs of these advanced structures are relatively high, the fabrication processes are complex, and the safety factor is low, which limits the application of silicon-carbon materials to some extent. It is worth noting that both Group 14 and Cui Yi's Amprius company face safety issues related to the use of silane. The safe use of this highly toxic and explosive gas on a large scale is a major challenge in the industrial production of silicon-carbon anodes.

[0006] In summary, this invention utilizes a solid silicon source and overcomes key issues in traditional technologies through innovative structural design and process improvements. It explores a highly efficient, stable, and widely applicable method for preparing silicon-based anode materials, completely avoiding the use of silane gas, and is expected to show great promise in the application of high-energy-density battery technology. Summary of the Invention

[0007] The purpose of this invention is to develop an in-situ high-temperature phase transition method for preparing ultrafine nano-silicon-based anode materials within a confined microcavity, and to address the problems of low utilization, low electron transport, and significant volume changes in silicon as a lithium-ion battery anode material during its preparation.

[0008] The technical solution adopted in this invention is as follows:

[0009] A method for preparing ultrafine nano-silicon-based anode materials based on in-situ high-temperature phase transition within a specific confined microcavity includes the following steps:

[0010] (1) Silicon and conductive porous materials are uniformly mixed in a solvent and their size is initially reduced to obtain a mixed slurry;

[0011] (2) The mixed slurry obtained in step (1) is reformed and granulated to form solid microparticles, which provide a basis for the construction of the subsequent coating layer;

[0012] (3) The particles obtained by reforming and granulation in step (2) are coated. A coating shell with high mechanical strength, high toughness and high stability is selected to form a coating layer with a confined microcavity structure. The confined microcavity is tightly coated on the surface of the shell. It refers to the closed or semi-closed space constructed on the surface of the particles obtained by reforming and granulation through the coating layer, which is used to limit the diffusion range after silicon vaporization and achieve efficient utilization.

[0013] (4) Load the product obtained in step (3) into the rapid high-temperature reaction zone. The temperature is rapidly increased by a precisely controlled heating device so that the silicon source reaches the sublimation temperature in a very short time and is evenly distributed in the confined microcavity. After the sublimation process is completed, the rapid cooling system is immediately started. Through the rapid circulation of the cooling medium, the temperature in the reaction zone is rapidly reduced in an instant. The silicon vapor is rapidly condensed in this process to form ultrafine nanoparticles below 10 nm, which are effectively embedded into the interior of the porous conductive material.

[0014] The silicon mentioned in step (1) is nano-silicon or micron-silicon with a particle size of 0.05-10 μm. The nano-silicon or micron-silicon is an inorganic silicon or organosilicon powder, suspension or solution, wherein the inorganic silicon includes silicates, quartz, sodium silicate and silicon carbide, and the organosilicon includes methylsilane, vinylsilane, aminosilane and epoxysilane.

[0015] The silicon mentioned in step (1) is preferably nano-silicon with an average particle size of 50 nm. The smaller the size of nano-silicon, the easier it is to vaporize. In addition, based on existing industrial methods, 50 nm nano-silicon can be obtained in batches and is widely available. The nanoscale size allows silicon materials to better adapt to volume changes during charging and discharging, thereby improving the energy density and first-charge efficiency of lithium-ion batteries. Furthermore, nano-silicon materials have excellent long-cycle fast-charging performance, improving the convenience of battery use.

[0016] Optionally, the conductive porous material is one or more of porous carbon materials, porous metal materials, porous conductive polymers, porous graphene, porous oxides, metal-organic frameworks, aerogels, covalent organic frameworks, or carbon-coated porous materials, preferably porous carbon materials. The pores inside the porous carbon material can absorb the volume expansion of silicon. In addition, the effective coating of silicon by the porous carbon material can greatly reduce the contact between silicon and electrolyte, prevent the repeated growth of the SEI film, and thus greatly improve the first coulombic efficiency of the lithium battery.

[0017] Preferably, the porous carbon material is at least one of microporous carbon, activated carbon, carbon aerogel, carbon nanotubes, graphene aerogel, ordered mesoporous carbon, activated carbon fiber, porous carbon spheres, and carbonized polymer porous carbon, with activated carbon being the most preferred. Activated carbon has a well-developed internal pore structure, a large specific surface area, strong adsorption capacity, good chemical stability, and can be used in high-temperature and strong oxidant environments. The unique microporous structure of activated carbon gives it excellent adsorption capacity and makes it particularly suitable for adsorbing particles with small molecular diameters. In addition, the intermolecular interaction forces (van der Waals forces) of activated carbon also promote its adsorption capacity, causing more molecules to be attracted and retained in the pores of activated carbon.

[0018] Preferably, the porous metal material is at least one of aluminum foam, nickel foam, copper foam, porous titanium, porous gold, porous magnesium, porous iron, porous cobalt, porous tungsten, porous molybdenum, or porous alloy; the porous conductive polymer is at least one of polypyrrole, polyaniline, polythiophene and its derivatives, polythiophene-conductive polymer composite material, or conductive polymer-carbon material composite material; the porous graphene is at least one of three-dimensional graphene aerogel, porous reduced graphene oxide, or porous graphene foam; the porous oxide conductive material is at least one of porous titanium dioxide, porous tin oxide, porous silica, porous iron oxide, porous magnesium oxide, porous zinc oxide, or porous lithium titanate; and the metal-organic framework is ZIF series, MIL series, NU series, HKUST-1, IRMofF series, UiO series, or MOF-5. Or at least one of the PCN series; the covalent organic framework is at least one of COF-1, COF-5, COF-102, COF-108, TP-COFs, LZU-COF, NUS-COFs, PI-COFs, or TF-COFs; the aerogel is at least one of carbon-based, silicon-based, sulfur-based, metal oxide-based, metal-based, single-component, multi-component, inorganic, organic, or inorganic-organic aerogels; the carbon-coated porous material is at least one of carbon-coated porous carbon, carbon-coated porous char, carbon-coated porous metal, carbon-coated porous conductive polymer, carbon-coated porous graphene, carbon-coated porous oxide, carbon-coated metal-organic framework, carbon-coated covalent organic framework, carbon-coated porous polymer, carbon-coated porous glass, carbon-coated ceramic, carbon-coated zeolite, or porous carbon-coated bio-based porous material.

[0019] Optionally, the solvent in step (1) is one or more of ethanol, deionized water, isopropanol, propylene glycol methyl ether, N,N-dimethylformamide, N-methylpyrrolidone, ethyl acetate, cyclohexanone, and dichloromethane.

[0020] Optionally, in step (1), the mass ratio of silicon, conductive porous material and solvent is 1:0.1-100:1-100.

[0021] Optionally, the uniform mixing method described in step (1) is one of sand milling, ball milling, or air jet milling. The sand mill has a rotational speed of 1-5000 r / s, a milling time of 1-60 h, a milling temperature of 15-100 ℃, and a milling pressure of 0.1-100 MPa; the air jet mill has a classifier frequency of 0-103 Hz, a blower frequency of 0-50 Hz, and a feeding frequency of 0-50 Hz; the ball mill has a cylinder rotational speed of 0-38 r / min and a ball loading of 0-330 t. Sand milling is preferred. The sand mill uses a high-speed rotating grinding disc and grinding balls for grinding, which can quickly grind materials into the required particle size. It has advantages such as high efficiency, high fineness, low cost, and continuous operation. Technological advancements in sand mills have enabled them to outperform ball mills in terms of grinding efficiency and product particle size distribution. Furthermore, Lin Wenzhong's research indicates that sand mills, compared to other grinding equipment such as air jet mills, offer advantages such as low energy consumption, high fineness, strong continuity, and high efficiency.

[0022] Optionally, the reforming granulation method described in step (2) is one of spray drying granulation, pressure granulation, fluidized bed granulation, wet granulation, drum granulation, sol-gel granulation, electrochemical deposition granulation, or solution impregnation granulation. Spray drying granulation technology is preferred because it can process large quantities of materials in a short time, has rapid drying capabilities, and achieves high-yield and high-efficiency production. Spray drying granulation sprays liquid or solution-like materials through high-pressure nozzles, rapidly drying them into tiny particles, which facilitates subsequent coating, is simple to operate, and has strong stability. In addition, spray drying granulation technology is a preferred technology due to its wide applicability, controllable product quality, operational flexibility, and continuous automated operation. Preferably, the gas temperature range during the spray drying granulation process is 80-250 ℃, the gas flow pressure is 0.01-5 MPa, and the injection speed is 1-20 rmp.

[0023] Optionally, the particle size range of the microparticles in step (2) is 1-100 μm, preferably 1-20 μm. The cycle performance of silicon-based anode materials is closely related to the particle size. Smaller particle size can provide more contact area, which is beneficial for lithium ion insertion and extraction, thereby improving the cycle performance of the battery. However, smaller particle size also increases the specific surface area in contact with the electrolyte, resulting in more charge consumed in the formation of the SEI film during the initial charge and discharge process, thus causing greater irreversible capacity loss. Therefore, a reasonable particle size distribution is crucial for improving the initial capacity and efficiency of the battery.

[0024] Optionally, the coating layer mentioned in step (3) is one of the following: carbon coating layer, metal coating layer, oxide coating layer, nitride coating layer or polymer coating layer.

[0025] The carbon coating layer is one of graphene, carbon nanotubes, amorphous carbon, or graphite coating; the metal coating layer includes one of silver, tin, cobalt, aluminum, nickel, copper, zinc, titanium, gold, magnesium, iron, tungsten, molybdenum, and alloys; the oxide coating layer includes one of aluminum oxide, titanium oxide, zirconium oxide, silicon oxide, manganese oxide, magnesium oxide, nickel oxide, and cerium oxide; the nitride coating layer includes titanium nitride, silicon nitride, aluminum nitride, boron nitride, and zirconium nitride; the polymer coating layer includes one or more of dopamine, polyoxyethylene-polyoxypropylene-polyoxyethylene triblock copolymer, polyvinylidene fluoride, polyethyleneimine, polythiophene, polypyrrole, polyaniline, polyacrylonitrile, and polyethylene glycol.

[0026] Carbon coating is a common modification method. By covering the silicon surface with a layer of carbon, the conductivity of silicon-based anode materials can be effectively improved because carbon has excellent conductivity, enabling rapid lithium-ion transport. Furthermore, the carbon coating layer also possesses good toughness, can adapt to stress changes caused by volume expansion, and has a certain degree of ductility, thereby protecting the structural stability of the silicon-based material during charge and discharge processes.

[0027] Metal and metal oxide coatings utilize the high elastic modulus, high hardness, and other excellent mechanical properties of metals and their alloys, as well as their good electrical conductivity, to mitigate the expansion effect during the cycling process of nano-silicon and improve its conductivity. The metal coating layer can provide mechanical stress for silicon expansion, but it also requires the metal to have good electrical conductivity, enabling the transport of lithium ions to the central silicon layer, and it must not chemically react with lithium ions or the battery electrolyte. Compared to carbon coatings, metal and metal oxide coatings place higher demands on the selection of the coating metal.

[0028] Polymer coating, by forming a layer of high molecular polymer on the silicon surface, can also limit the volume change of silicon during charging and discharging to a certain extent, slow down the rupture of the SEI film, and thus improve the conductivity of silicon to a certain extent, but it is not as common as carbon coating and metal coating.

[0029] Optionally, the coating method in step (3) is one or more of the following: microemulsion coating, chemical plating, hydrothermal method, spray pyrolysis, electroplating, chemical vapor deposition, physical vapor deposition, electrochemical deposition, pyrolysis, and solution-gel method.

[0030] Optionally, the thickness of the coating layer in step (3) is 1-1000 nm, the stirring time is 1-8 h, and the mass ratio of the coating layer to the particles is 1:0.2-1:20. A coating layer of a certain thickness on the surface has a significant impact on the cycle stability of silicon-based anode materials. It can effectively inhibit the decomposition of the electrolyte on the surface of the silicon anode, and effectively stabilize the SEI film structure on the surface of the silicon anode, thereby significantly improving the cycle performance of silicon-based anode materials. Preferably, the coating layer thickness is 30 nm and the stirring time is 4 h.

[0031] Optionally, when the coating method described in step (3) is polymer carbon coating, a carbonization treatment is required: the product is heated to a carbonization temperature of 500-900 ℃ under an inert atmosphere and held at that temperature, and then naturally cooled to room temperature. The heating rate is 1-20 ℃ / min, and the holding time is 0.1-72 h. The specific operation of the carbonization treatment is to dry the product and place it in a tube furnace, heat it to the carbonization temperature under an inert atmosphere and hold it at that temperature, and then allow the tube furnace to cool naturally to room temperature after completion.

[0032] Optionally, the transient heating method described in step (4) is one of Joule heating, microwave heating, electric spark heating, plasma heating, infrared heating, combustion heating, thermal explosion heating, thin film electric heater heating, and electromagnetic pulse heating.

[0033] Optionally, in step (4), the temperature is increased to 800-1000 ℃ by at least one pulse, with a heating rate of 1×10⁻⁶. 6 The system operates at a speed of -100 ℃ / s. After reaching the target temperature, it enters a holding phase for 0.01-200 s. Immediately after the holding phase, cooling is initiated to form ultrafine nanoparticles. A single pulse duration of 0.01 s-100 s refers to the total time from the start of heating to the end of cooling, including the heating, holding, and cooling processes. Each pulse operation comprises a complete heating-holding-cooling cycle. The number of pulses is unlimited, and the pulse interval is 0.1 s-100 s, referring to the time interval between the end of one pulse and the start of the next. During the heating phase, the temperature inside the device rapidly rises from the initial temperature to the set target temperature, determined according to experimental requirements. After reaching the target temperature, the system enters a holding phase, maintaining a constant temperature to ensure sufficient sublimation and diffusion of the silicon source. The holding time can be flexibly adjusted according to material properties and process requirements to achieve optimal results. After the holding phase, the system immediately begins cooling, rapidly reducing the temperature to a safe level, promoting rapid condensation of silicon vapor and forming ultrafine nanoparticles. In the battery material fabrication process, the heating and cooling rates have a significant impact on crystal nucleation and particle size. Rapid heating and cooling rates lead to drastic temperature changes in the system, accelerating crystal nucleation. Due to the short growth time, the resulting crystal particles are smaller. These small crystal particles are beneficial for optimizing the material's microstructure, resulting in a more uniform distribution of silicon particles, thereby improving the material's uniformity and stability, and ultimately enhancing the battery's performance stability during multiple charge-discharge cycles. Silicon-based anode materials prepared using rapid heating technology exhibit excellent mechanical stability and long cycle life. Controlling the heating rate can positively influence the performance of silicon-based anode materials.

[0034] Optionally, the cooling rate in step (4) is 1×10⁻⁶. 6 -100℃ / s until room temperature.

[0035] Optionally, the atmosphere in the heating zone in step (4) is a non-oxidizing atmosphere, including a mixture of one or more gases such as low vacuum, helium, argon, and nitrogen.

[0036] The principle of this invention is based on in-situ high-temperature phase transition within a confined microcavity to prepare ultrafine nano-silicon-based anode materials, mainly involving the following key technical steps and mechanisms:

[0037] 1. Construction of confined microcavity structures:

[0038] A closed or semi-closed microcavity structure is formed by constructing a coating layer on the surface of a porous conductive material. This microcavity structure is used to limit the vaporization diffusion range and distribution path of silicon during the high-temperature phase transition process, thereby improving the utilization efficiency and distribution uniformity of silicon.

[0039] 2. In-situ high-temperature phase transition:

[0040] Transient high-temperature techniques (such as Joule heating and microwave heating) are used to rapidly sublimate silicon within a confined microcavity and instantly condense it into ultrafine nanoparticles smaller than 10 nm. By controlling the temperature and heating / cooling rates, precise size control and uniform distribution of silicon can be achieved.

[0041] 3. Application of conductive porous materials:

[0042] Materials with high conductivity and porous structures (such as porous carbon materials and metal-organic frameworks) are selected as the matrix. These porous materials can adsorb vaporized silicon, provide good electron conduction pathways, and physically buffer the volume expansion of silicon during charging and discharging, thus preventing the material from pulverizing.

[0043] 4. The function of the coating layer:

[0044] The coating layers (such as carbon layers and oxide layers) constructed on the material surface not only form confined microcavities, but also interact chemically with silicon, enhancing the mechanical and chemical stability of the material and suppressing structural cracking caused by volume changes in silicon.

[0045] This invention improves the utilization efficiency and conductivity of silicon by nano-sizing and uniformly distributing it in a porous structure, solving the problems of volume expansion and poor conductivity of silicon in battery applications. The construction of confined microcavities and transient high-temperature phase transition technology together achieve precise control over the material structure, thereby improving the cycle stability and electrochemical performance of the electrode material. This innovative method provides new possibilities for the application of silicon-based anode materials in lithium-ion batteries.

[0046] The method for preparing ultrafine nano-silicon-based anode materials based on in-situ high-temperature phase transition within a specific confined microcavity proposed in this invention has the following advantages and outstanding effects compared with existing technologies:

[0047] First, the combination of confined microcavity and high-temperature phase change technology greatly enhances the structural stability and cycle life of the material, significantly improving the cycle stability and reversible capacity of the battery. The uniform distribution and high conductivity of the material in the conductive porous structure significantly improve the electrochemical performance of the battery, exhibiting higher energy density and charge / discharge efficiency.

[0048] Secondly, this invention simplifies the material preparation process, reducing production costs and process complexity through efficient material utilization and precise dimensional control. This innovative method is applicable to lithium-ion batteries, broadening the application range of silicon-based anode materials.

[0049] Furthermore, using transient heating technology, silicon undergoes a rapid phase transition within the coating shell under thermodynamically driven unsteady conditions. The coating layer confines the vaporized silicon, while the conductive porous material rapidly adsorbs it. The nanoparticles formed after transient cooling, combined with the excellent mechanical properties of the conductive porous material, effectively limit the volume expansion of silicon, enhance conductivity, suppress structural breakage caused by the large volume change of silicon, avoid the loss of active sites, form a stable SEI, further improve cycle stability, and increase electrode conductivity.

[0050] Most importantly, this invention is completely different from the silane-based chemical vapor deposition technology used by Group 14 and Amprius, avoiding the use of highly toxic and explosive silanes, and will greatly promote the large-scale innovative preparation of silicon-carbon composite materials.

[0051] In summary, this invention utilizes a solid silicon source and overcomes key issues in traditional technologies through innovative structural design and process improvements. It explores a highly efficient, stable, and widely applicable method for preparing silicon-based anode materials, completely avoiding the use of silane gas, and is expected to show great promise in the application of high-energy-density battery technology. Attached Figure Description

[0052] Figure 1 is a basic schematic diagram of the preparation method of the present invention.

[0053] Figure 2 is a scanning electron microscope (SEM) image of the spherical silicon-carbon hybrid material obtained in Example 1 of the present invention.

[0054] Figure 3 is a scanning electron microscope (SEM) image of the spherical silicon-carbon hybrid material particles after carbon coating in Example 1 of the present invention.

[0055] Figure 4 is a cross-sectional SEM image of the material before the Joule thermal pulse in Embodiment 1 of the present invention, showing the uniform and dense internal structure of silicon and carbon in the material before the Joule thermal pulse.

[0056] Figure 5 is a cross-sectional SEM image of the material after a Joule thermal pulse in Embodiment 1 of the present invention, showing the changes in the internal structure of the material after the Joule thermal pulse, where silicon vaporizes into nanoparticles and enters the porous carbon.

[0057] Figure 6 shows a comparison of the rate performance of the coin cells assembled before and after Joule thermal pulse treatment in Embodiment 1 of the present invention.

[0058] Figure 7 shows a comparison of the initial discharge efficiency of the coin cells assembled before and after Joule thermal pulse treatment in Embodiment 1 of the present invention.

[0059] Figure 8 shows a comparison of the cycle performance of the coin cells assembled before and after Joule heat pulse treatment in Embodiment 1 of the present invention, showing the capacity change of the battery under different cycles, and the cycle stability of the sample treated by Joule heat is improved.

[0060] Figure 9 shows the capacity change of the battery in Example 2 after 500 cycles.

[0061] Figure 10 shows the battery cycle performance in Example 3.

[0062] Figure 11 is a morphology diagram of the silicon-carbon spheres in Example 4.

[0063] Figure 12 is a scanning electron microscope (SEM) image of the silicon-carbon hybrid particles in Example 5.

[0064] Figure 13 is a scanning electron microscope (SEM) image of the silicon-carbon hybrid particles whose shells were broken by gas in Example 6.

[0065] Figure 14 is a cross-sectional morphology diagram of the silicon particles in Example 7 when they were not completely vaporized. Detailed Implementation

[0066] The invention described herein, which provides a method for preparing ultrafine nano-silicon-based anode materials based on in-situ high-temperature phase transition within a confined microcavity, is described in detail below with appropriate reference to the accompanying drawings. Unnecessary details, such as well-known facts and repetitive descriptions of identical structures, may be omitted in the description. This is done to avoid making the description verbose and to facilitate better understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are intended to help those skilled in the art fully understand this application, and not to limit the subject matter of the claims. Obviously, the described embodiments are only a part of the invention, not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without inventive effort should also fall within the scope of protection of this invention.

[0067] Unless otherwise specified, all technical features and optional technical features in this application can be combined with each other to form new technical solutions. To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments used, unless otherwise specified by manufacturer, are all conventional products that can be purchased commercially.

[0068] Example 1

[0069] Preparation by mixing: Weigh 50 g of nano-silicon with an average particle size of 50 nm and 50 g of activated carbon, disperse them in 900 g of ethanol, pour the mixture into a sand mill, control the temperature to 25 ℃, and sand mill at 360 r / s for 7 h to obtain a silicon-carbon mixed slurry. Through this step, the size of the silicon-carbon material is initially reduced and highly uniformly mixed. The density of the spray-dried spheres is controlled by controlling the silicon-carbon ratio and concentration. If the interior is loose, the coating material will easily enter the interior during subsequent coating. If there is too much nano-silicon and the activated carbon is not porous enough, the nano-silicon will easily condense and agglomerate on the surface. The temperature is controlled to prevent oxidation, and the uniformity of silicon-carbon mixing is adjusted by controlling the sand mill speed and time.

[0070] Spray drying: The mixed slurry was spray-dried, with the gas temperature controlled at 150 ℃, the gas pressure at 0.2 MPa, and the injection rate at 15 rpm. This step controls the size of the manufactured spheres by controlling the gas pressure and injection rate. If the size is too large, the coating layer is difficult to complete; if the size is too small, the coating layer thickness is difficult to control. The scanning electron microscope (SEM) image of the obtained spherical silicon-carbon hybrid material is shown in Figure 1. It can be seen from the image that spherical particles are present, and no significant aggregation or agglomeration is observed.

[0071] Figure 2 shows a scanning electron microscope (SEM) image of the spherical silicon-carbon hybrid material obtained after spray drying. As can be seen in the image, the material presents uniform spherical particles, with the diameter of the large particles ranging from a few micrometers to tens of micrometers, and the diameter of the small particles within a few micrometers. The particle distribution is relatively uniform, and no significant aggregation or agglomeration is observed.

[0072] Carbon coating treatment: The powder obtained above is subjected to carbon coating treatment. 1g of dopamine and 1g of F127 (polyoxyethylene-polyoxypropylene-polyoxyethylene triblock copolymer) are added to a mixed solution of 50 ml of ethanol and deionized water (volume ratio 1:1), stirred evenly, 1g of spray-dried powder is added, stirred for 15 min, and then 1.5 mL of ammonia water is added and stirred for 1 h.

[0073] Figure 3 shows a scanning electron microscope (SEM) image of spherical silicon-carbon hybrid material particles after carbon coating. The image shows that the carbon coating process attaches a large number of spherical particles to the material surface, and the particle distribution is relatively uniform.

[0074] Joule heating: 0.1 g of material was placed in an 8 cm long carbon felt, which was then placed between the positive and negative electrodes of the Joule heating apparatus. The apparatus was kept under a high vacuum, and the atmosphere was controlled to prevent oxidation during the instantaneous heating process. The Joule heating apparatus was started under high vacuum, and the current and voltage were adjusted to instantly raise the temperature to 940 ℃. Multiple pulses were applied for 30 seconds to reach the sublimation point of the nano-silicon, causing the nano-silicon to vaporize and uniformly diffuse within the microcavity. Excessive temperature resulted in high internal pressure, which could easily break the coating layer and generate silicon carbide. Insufficient temperature led to incomplete vaporization of the nano-silicon. Pulsing ensured uniform distribution of the nano-silicon, refining it to ultrafine nanoscale sizes below 10 nm without agglomeration. Excessive time could cause the coating layer to rupture, while insufficient time resulted in incomplete vaporization. Optimal experimental results were achieved by adjusting the time and temperature.

[0075] Figure 4 shows a scanning electron microscope (SEM) image of the carbon-coated spherical silicon-carbon hybrid material particles before Joule heat treatment. The image shows that the particles have a very dense structure with some irregular structural features, and the internal structure is relatively uniform.

[0076] Figure 5 shows scanning electron microscopy (SEM) images of spherical silicon-carbon hybrid material particles after Joule heat treatment. After treatment, new porous structures formed inside and on the surface of the material, resulting from the vaporization and nanostructuring of silicon. The SEM images reveal a more complex material structure and an increase in internal porosity.

[0077] The silicon-carbon composite material prepared in Example 1 was used to assemble coin cells before and after Joule heating, and the electrochemical performance was tested. In the fabrication of the coin cells, a lithium metal sheet was selected as the counter electrode. The silicon-carbon electrode was prepared as follows: the silicon-carbon composite material, conductive agent SP, and binder PVDF were uniformly mixed at a mass ratio of 7:1.5:1.5, coated onto copper foil, and vacuum dried at 80 °C for 12 h. The dried electrode was then rolled, cut into 11 mm diameter discs, weighed, and placed in a vacuum glove box for coin cell assembly.

[0078] Figure 6 shows the relationship between the specific capacity and cycle number of the silicon-carbon composite material prepared using Example 1 of the present invention before and after Joule heat treatment. In the figure:

[0079] The horizontal axis (Cycle Number) represents the number of battery cycles, ranging from 0 to 40.

[0080] The vertical axis (Capacity, mAh / g) represents the battery's specific capacity, measured in mAh / g, ranging from 0 to 2500 mAh / g.

[0081] The curve is labeled as follows:

[0082] The black solid dot curve represents the battery performance after Joule heat treatment.

[0083] Gray solid square curve: represents the battery performance without Joule heat treatment.

[0084] The labels "0.1C", "0.2C", "0.5C", "1C", "2C", and "5C" in the diagram represent different charge / discharge rates. Typically, C-rate indicates how many times the battery's rated capacity it is charged / discharged at; for example, 1C means completing a charge / discharge cycle within one hour. It can be seen that as the C-rate increases, the specific capacity decreases, due to increased battery polarization and overpotential at higher rates. However, batteries that have undergone Joule heat treatment exhibit significantly higher specific capacities at all rates than untreated batteries.

[0085] Rate cycle stability: After being tested at different rates, the battery can still recover to a high level of specific capacity when it returns to a low rate (such as 0.1C). In particular, the battery after Joule heat treatment shows good rate cycle stability.

[0086] Figure 7 shows the voltage versus specific capacity curves of the silicon-carbon composite material prepared using Example 1 of the present invention before and after Joule heat treatment during the first charge-discharge process. In the figure:

[0087] The horizontal axis (Specific Capacity, mAh / g) represents the battery's specific capacity, measured in mAh / g, ranging from 0 to 2500 mAh / g.

[0088] The vertical axis (Voltage, V vs. Li / Li+) represents the battery voltage relative to the lithium / lithium-ion voltage, ranging from 0V to 3V.

[0089] The two curves are as follows:

[0090] The solid gray line represents the voltage-capacity curve of the battery during its first charge and discharge process after Joule heat treatment.

[0091] The solid black line represents the voltage-capacity curve of the battery during its first charge and discharge process before Joule heat treatment.

[0092] Voltage plateau and specific capacitance:

[0093] Before Joule heat treatment (black line): The battery has an indistinct voltage plateau at around 0.2V and 0.7V. The charge specific capacity before treatment is low, at around 1250 mAh / g.

[0094] After Joule heat treatment (gray line): After Joule heat treatment, the battery's charge-discharge plateau is more pronounced, and the specific charge capacity increases to nearly 1500 mAh / g. This indicates that heat treatment reduces the silicon particle size, improves utilization, and thus enhances lithium storage capacity and electrochemical activity.

[0095] The battery exhibits smoother voltage changes during charge and discharge after Joule heat treatment, indicating more stable electrochemical reactions in the material. The initial capacity of the battery significantly increases after heat treatment, demonstrating the positive effect of heat treatment on improving material performance.

[0096] Figure 8 shows the cycle performance of coin cells assembled using the silicon-carbon composite material prepared in Example 1 of this invention before and after Joule heat treatment. In the figure:

[0097] The horizontal axis (Cycle Number) represents the number of battery cycles, ranging from 0 to 300.

[0098] The left vertical axis (Specific Capacity, mAh / g) represents the battery's specific capacity, measured in mAh / g, ranging from 0 to 2500 mAh / g.

[0099] In the diagram, the solid black circles represent the coulombic efficiency after Joule heat treatment, and the solid gray circles represent the coulombic efficiency before Joule heat treatment.

[0100] The two curves are labeled as follows:

[0101] The black solid dot curve represents the battery performance after Joule heat treatment, showing a significant improvement in the battery's specific capacity after heat treatment.

[0102] The gray solid dot curve represents the battery performance before Joule heat treatment, with a significantly lower specific capacity than the result after heat treatment.

[0103] It can be seen that the initial specific capacity of the battery is not much different before and after Joule heat treatment, but after multiple cycles, the battery after Joule heat treatment shows a higher capacity retention rate, indicating that the heat treatment process significantly improves the cycle stability of the battery.

[0104] The current density for battery testing was 1 A / g.

[0105] Example 2

[0106] This embodiment is basically the same as Embodiment 1, except that: 25 g of nano-silicon and 50 g of porous carbon are weighed and dispersed in 675 g of ethanol, and then poured into a sand mill. The capacity can be adjusted by changing the silicon-carbon ratio.

[0107] Figure 9 shows the capacity change of a battery with a silicon-to-carbon ratio of 1:2 after 500 cycles.

[0108] Example 3

[0109] This embodiment is essentially the same as Embodiment 1, except that graphene is used instead of porous carbon. Graphene's high electrical conductivity can improve electron transport efficiency and effectively improve cycle stability.

[0110] Figure 10 shows the battery cycle performance after graphene replaces porous carbon. The high conductivity of graphene can improve electron transport efficiency, thereby effectively improving cycle stability.

[0111] Example 4

[0112] This embodiment is basically the same as Embodiment 1, except that the mixed slurry is granulated using a fluidized bed. A fluidized bed can also aggregate silicon and carbon into spherical composites.

[0113] Figure 11 shows silicon carbide spheres after fluidized bed granulation.

[0114] Example 5

[0115] This embodiment is essentially the same as Embodiment 1, except that the carbon coating layer is fabricated using physical vapor deposition. Physical vapor deposition allows for precise film thickness control and uniform deposition, resulting in a pure carbon film with low impurity content, which helps improve electrochemical properties.

[0116] Figure 12 shows a scanning electron microscope (SEM) image of silicon-carbon hybrid particles coated by physical vapor deposition. The carbon layer surface is smooth and there are no small carbon spheres generated by dopamine self-polymerization.

[0117] Example 6

[0118] This embodiment is basically the same as Embodiment 1, except that: dopamine is used to coat the silicon-carbon mixed particles, and the coating thickness is controlled at 500 nm. Increasing the coating thickness allows it to withstand greater internal pressure, making it less prone to breakage, enabling higher transient heating temperatures, and allowing for an increase in internal phosphorus content.

[0119] Figure 13 shows a scanning electron microscope (SEM) image of gas breaking through the shell due to insufficient shell thickness and excessive internal pressure. Therefore, when designing materials, it is necessary to select an appropriate coating thickness based on the specific material properties and internal phosphorus content to effectively limit the internal silicon vapor and maintain the integrity of the shell.

[0120] Example 7

[0121] This embodiment is basically the same as Embodiment 1, except that: the Joule heating device is started in an atmosphere filled with argon gas, and the temperature rises instantly to 1000 ℃. Multiple pulses of 5 s are applied. Different temperature and time conditions can control the degree of vaporization of silicon particles.

[0122] Figure 14 shows the cross-sectional morphology when the silicon particles are not fully vaporized.

[0123] In summary, this invention provides a method for preparing ultrafine nano-silicon-based anode materials based on in-situ high-temperature phase transition within a confined microcavity. Transient heating rapidly vaporizes silicon, which is then adsorbed by a porous conductive material. The microcavity structure confines the vaporized silicon within the cavity to fill the material. Upon instantaneous condensation, nanoparticles are formed and confined within the pores, enhancing conductivity, buffering silicon expansion, effectively suppressing structural breakage caused by volume changes, avoiding loss of active sites, and thus improving cycle stability.

[0124] The above description is merely 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 concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing ultrafine nano-silicon-based anode materials based on in-situ high-temperature phase transition within a specific confined microcavity, characterized in that, Includes the following steps: (1) Silicon and conductive porous materials are uniformly mixed in a solvent and their particle size is reduced to obtain a mixed slurry; (2) The mixed slurry is reformed and granulated to form solid microparticles; (3) The obtained particles are coated to form a coating layer with a confined microcavity structure to limit the diffusion range after silicon vaporization; (4) Load the coated product into the reaction zone, rapidly heat it to the sublimation temperature of the silicon source so that it is evenly distributed in the confined microcavity, and rapidly cool it so that the silicon vapor can be rapidly condensed into ultrafine nanoparticles with a particle size of less than 10 nm, which are embedded in the porous conductive material.

2. The method according to claim 1, characterized in that, The silicon mentioned in step (1) is nano-silicon or micro-silicon with a particle size of 0.05-10 μm.

3. The method according to claim 2, characterized in that, The nano-silicon or micron-silicon is selected from silicates, quartz and silicon carbide, and is in the form of powder, suspension or solution, or is a solution selected from vinylsilane, aminosilane and epoxysilane.

4. The method according to claim 3, characterized in that, The silicate is sodium silicate.

5. The method according to claim 1, characterized in that, The conductive porous material mentioned in step (1) is one or more of the following: porous carbon material, porous metal material, porous conductive polymer, porous oxide, metal-organic framework, covalent organic framework or carbon-coated porous material.

6. The method according to claim 5, characterized in that, The porous carbon material is at least one of microporous carbon or ordered mesoporous carbon.

7. The method according to claim 5, characterized in that, The porous carbon material is activated carbon.

8. The method according to claim 5, characterized in that, The porous carbon material is carbonized polymer porous carbon.

9. The method according to claim 5, characterized in that, The porous carbon material is at least one of carbon nanotubes, porous carbon spheres, or activated carbon fibers.

10. The method according to claim 5, characterized in that, The porous carbon material is porous graphene.

11. The method according to claim 10, characterized in that, The porous graphene is one of three-dimensional graphene aerogel, porous reduced graphene oxide, or porous graphene foam.

12. The method according to claim 5, characterized in that, The porous metal material is at least one of aluminum foam, nickel foam, copper foam, porous titanium, porous gold, porous magnesium, porous iron, porous cobalt, porous tungsten, porous molybdenum, or porous alloy; the porous conductive polymer is at least one of polypyrrole and its derivatives, polyaniline and its derivatives, polythiophene and its derivatives, polythiophene-conductive polymer composite material, or conductive polymer-carbon material composite material; the porous oxide is at least one of porous titanium dioxide, porous tin oxide, porous silica, porous iron oxide, porous magnesium oxide, porous zinc oxide, or porous lithium titanate; the metal-organic framework is at least one of the ZIF series, MIL series, NU series, HKUST-1, IRMOF series, UiO series, MOF-5, or PCN series; the covalent organic framework is at least one of COF-1, COF-5, COF-102, COF-108, TP-COFs, LZU-COF, NUS-COFs, PI-COFs, or TF-COFs.

13. The method according to claim 5, characterized in that, The carbon-coated porous material is at least one of the following: carbon-coated porous carbon, carbon-coated porous metal, carbon-coated porous conductive polymer, carbon-coated porous oxide, carbon-coated metal-organic framework, carbon-coated covalent organic framework, carbon-coated porous glass, carbon-coated ceramic, carbon-coated zeolite, or porous carbon-coated bio-based porous material.

14. The method according to claim 1, characterized in that, The conductive porous material mentioned in step (1) is aerogel.

15. The method according to claim 14, characterized in that, The aerogel is at least one of carbon-based, silicon-based, sulfur-based, metal oxide-based, or metal-based aerogels.

16. The method according to claim 1, characterized in that, In step (1), the solvent is one or more of the following: ethanol, deionized water, isopropanol, propylene glycol methyl ether, N,N-dimethylformamide, N-methylpyrrolidone, ethyl acetate, cyclohexanone, and dichloromethane.

17. The method according to claim 1, characterized in that, In step (1), the mass ratio of silicon, conductive porous material and solvent is 1:0.1-100:

1.

18. The method according to claim 1, characterized in that, The uniform mixing method described in step (1) is one of sand milling, ball milling or air jet milling.

19. The method according to claim 1, characterized in that, The reforming granulation method described in step (2) is one of the following: spray drying granulation, pressure granulation, fluidized bed granulation, wet granulation, drum granulation, sol-gel granulation, electrochemical deposition granulation, or solution impregnation granulation.

20. The method according to claim 19, characterized in that, During the spray drying process of the spray drying granulation, the gas temperature is 80-250 ℃, the gas flow pressure is 0.01-5 MPa, and the injection speed is 1-20 rpm.

21. The method according to claim 1, characterized in that, The particle size range of the microparticles in step (2) is 1-100 μm.

22. The method according to claim 1, characterized in that, The coating layer mentioned in step (3) is one of the following: carbon coating layer, metal coating layer, oxide coating layer, nitride coating layer and polymer coating layer.

23. The method according to claim 1, characterized in that, The coating treatment method described in step (3) is one or more of the following: microemulsion coating, chemical plating, hydrothermal method, spray pyrolysis, electroplating, chemical vapor deposition, physical vapor deposition, electrochemical deposition, pyrolysis, and solution-gel method.

24. The method according to claim 1, characterized in that, In step (3), the thickness of the coating layer is 1-1000 nm, and the mass ratio of the coating layer to the particles is 1:0.2-1:

20.

25. The method according to claim 22, characterized in that, When the coating layer is a polymer coating layer, it needs to undergo carbonization treatment: heat to a carbonization temperature of 500-900 ℃ under an inert atmosphere and hold at that temperature, then cool naturally to room temperature. The heating rate is 1-20 ℃ / min and the holding time is 0.1-72 h.

26. The method according to claim 1, characterized in that, The transient heating method in step (4) is one of Joule heating, microwave heating, electric spark heating, plasma heating, infrared heating, combustion heating, thermal explosion heating, thin film electric heater heating, and electromagnetic pulse heating.

27. The method according to claim 1, characterized in that, In step (4), the temperature is increased to 800-1000 ℃ by at least one pulse, with a heating rate of 1×10⁻⁶. 6 -100 ℃ / s. After reaching the target temperature, the system enters the heat preservation stage, which lasts for 0.01-200 s. After the heat preservation stage ends, the system immediately performs a cooling operation to form ultrafine nanoparticles.

28. The method according to claim 1, characterized in that, The cooling rate in step (4) is 1×10 6 -100 ℃ / s until room temperature.

29. The method according to claim 1, characterized in that, In step (4), the atmosphere in the reaction zone is a non-oxidizing atmosphere, including one or a mixture of helium, argon, and nitrogen.

30. The method according to claim 1, characterized in that, The atmosphere in the reaction zone during step (4) is a low vacuum.

31. An ultrafine nano-silicon-based anode material prepared based on in-situ high-temperature phase transition within a specific confined microcavity, characterized in that, It is prepared by the method according to any one of claims 1-30.

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