An ultrafine nano-silicon-based negative electrode material prepared based on in-situ high-temperature phase change in a confined microcavity and its preparation method

Abstract

The present invention provides a method for preparing an ultrafine nano-silicon-based negative electrode material based on in-situ high-temperature phase change within a specific confined microcavity and a preparation method thereof. The method involves mixing silicon and a conductive porous material in a solvent and then sand-grinding them. Solid particles are formed by reforming and granulating them, and a confined microcavity is constructed by coating. By transiently heating and cooling the silicon source, the silicon source is sublimated and condensed into microparticles of less than 10 nm, which are then embedded in the porous material to achieve extreme nano-scaling of silicon. This method effectively solves the problems of volume expansion, low conductivity, and poor cycle stability when silicon is used as a negative electrode material for lithium-ion batteries, improves electron transmission and cycle life, simplifies the process, reduces costs, and has good commercial prospects.

Description

Technical Field

[0001] The present invention belongs to the field of lithium-ion battery negative electrode materials, and specifically relates to an ultrafine nano-silicon-based negative electrode material prepared based on in-situ high-temperature phase change in a confined microcavity and a preparation method thereof. Background Art

[0002] Over the past three decades, lithium-ion batteries have achieved tremendous commercial success thanks to their high energy density, low self-discharge rate, long cycle life, and lightweight advantages. The lithium-ion battery industry continues to experience rapid growth, with widespread application in consumer electronics, new energy vehicles, and energy storage devices. Currently, graphite remains the mainstream anode material for lithium-ion batteries, but the theoretical specific capacity of conventional graphite electrodes is only 372 mAh / g, approaching the theoretical capacity ceiling. This severely limits the energy density of lithium-ion batteries and hinders their further improvement.

[0003] Compared with traditional graphite negative electrode materials, the theoretical specific capacity of silicon is as high as 4200mAh / g, which is 11.3 times that of graphite. Therefore, silicon-based negative electrode materials have higher energy density potential. In addition, the lithium insertion and removal potential of silicon-based negative electrodes (0.4Vv.Li / Li + ) is slightly higher than graphite (0.05Vvs.Li / Li +), thereby avoiding the surface lithium deposition phenomenon that may occur during charging. In addition, silicon is widely available, relatively low in cost, non-toxic and pollution-free. Compared with other negative electrode materials, silicon-based negative electrode materials are more competitive. However, during the charging and discharging process, the volume expansion rate of silicon is extremely high (about 300%). This drastic volume change will not only cause repeated cracking of silicon, but also cause silicon to lose its conductive connection with the electrode, resulting in mechanical powdering and cracking. Repeated volume changes will cause repeated reconstruction and growth of the solid electrolyte interface layer (SEI). Silicon nano-sizing can quickly relax stress, improve the fracture resistance of silicon, and to a certain extent alleviate the mechanical stress generated by silicon during the lithiation process. Nano-silicon has the advantages of short lithium ion diffusion distance, large surface area and fast grain boundary transport. However, when the specific surface area of ​​the silicon-based negative electrode is larger, the specific surface area of ​​the SEI film formed will also be larger, thereby consuming more lithium ions and reducing the first coulomb efficiency of the entire battery. In addition, nano-silicon is prone to agglomeration, which increases the distance for lithium ion transmission. Coupled with its inherently poor electrical conductivity, it becomes unstable after nano-sizing, which can easily lead to problems such as rapid capacity decay, low coulombic efficiency, poor electrical conductivity, and low reversible capacity, which seriously limits its application in lithium-ion battery negative electrode materials. To solve the above problems, the current main research direction is to combine it with other matrix materials, and some important progress has been made. Other matrices mainly involve carbon-based materials. The high electrical conductivity of carbon-based materials improves the electrical conductivity of the entire electrode. The porous structure of carbon-based materials can buffer the drastic volume expansion of nano-silicon. At the same time, the atoms in the carbon-based materials form structurally stable chemical bonds with the nano-silicon, forming a stable SEI, which improves the battery's specific capacity, cycle stability, and first coulombic efficiency.

[0004] At present, the typical preparation technologies of silicon-carbon composite materials mainly include chemical vapor deposition, mechanical alloying and solution method. Among them, vapor-deposited silicon-carbon negative electrode materials have significant room for cost reduction and relatively mature industrial mass production conditions in the future, so they have become the hottest negative electrode material track in the current new energy field. Chemical vapor deposition uses gas-phase chemical reactions to form a thin film on the surface of the substrate. In the production of silicon-carbon negative electrode materials, chemical vapor deposition uses high temperature to decompose silicon source gases such as silane, and by precisely controlling the reaction parameters, a uniform, high-purity silicon-carbon composite material is deposited on the surface of the carbon-based material. However, the requirements for equipment and reaction conditions are high, resulting in high production costs.

[0005] As a typical example, the silicon-carbon anode material SCC55 produced by Group 14 in the United States innovatively utilizes vapor deposition technology. It utilizes a nanocarbon skeleton as its primary structure, storing nanosilicon anodes within the carbon skeleton to stabilize the volume expansion of silicon particles during charge and discharge. However, this approach faces challenges such as inability to achieve continuous production, poor batch-to-batch consistency, and high costs, and has yet to achieve full-scale production. Professor Cui Yi's research group at Stanford University, while studying silicon-carbon materials, uses a two-step chemical vapor deposition method to first fabricate a carbon skeleton anode loaded with high-capacity crystalline silicon. The skeleton is then coated with a highly elastic polymer through a polymerization reaction to significantly enhance the electrode's mechanical strain resistance. Professor Cui Yi's team has also designed innovative structures to enhance the material's performance, such as yolk-shell and micro-pomegranate configurations. However, these advanced structures are relatively expensive, complex, and have low safety factors, which to some extent limit the application of silicon-carbon materials. It is worth noting that both Group 14 and Cui Yi's Amprius face safety issues in the use of silane. The safe large-scale use of this highly toxic and explosive gas is a key challenge in the industrial production of silicon-carbon negative electrodes.

[0006] In summary, the present invention will adopt a solid silicon source, overcome the key problems in traditional technology through innovative structural design and process improvement, and explore a method for preparing silicon-based negative electrode materials that is efficient, stable, and widely applicable, completely avoiding the use of silane gas, and is expected to show great prospects in the application of high-energy-density battery technology. Summary of the Invention

[0007] The purpose of the present invention is to develop an ultrafine nano-silicon-based negative electrode material and its preparation method based on in-situ high-temperature phase change in a confined microcavity, aiming to solve the problems of low utilization rate, low electron transport, and significant volume change during the preparation process of silicon as a negative electrode material for lithium-ion batteries.

[0008] The technical solutions adopted in the present invention are as follows:

[0009] A method for preparing ultrafine nano-silicon-based negative electrode materials based on in-situ high-temperature phase change in a specific confined microcavity comprises the following steps:

[0010] (1) uniformly mixing silicon and a conductive porous material in a solvent and preliminarily reducing their size to obtain a mixed slurry;

[0011] (2) reforming and granulating the mixed slurry obtained in step (1) to form solid particles, which provide a basis for the subsequent construction of the coating layer;

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

[0013] (4) The product obtained in step (3) is loaded into a rapid high-temperature reaction zone, and 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 sharply reduced in an instant. The silicon vapor is rapidly condensed in this process to form ultrafine nanoparticles below 10nm, which are effectively embedded in the interior of the porous conductive material.

[0014] The silicon in step (1) is nanosilicon or microsilicon with a particle size of 0.05-10 μm. The nanosilicon or microsilicon is a powder, suspension or solution of inorganic silicon or organic silicon, the inorganic silicon includes silicate, quartz, sodium silicate and silicon carbide, and the organic silicon includes methylsilane, vinylsilane, aminosilane and epoxysilane.

[0015] The silicon in step (1) is preferably nano-silicon with an average particle size of 50 nm. The smaller the size of the nano-silicon, the easier it is to gasify. In addition, based on existing industrial means, 50 nm nano-silicon can be obtained in batches and has a wide range of sources. The nano-scale size enables the silicon material to better adapt to volume changes during the charge and discharge process, thereby improving the energy density and first charge efficiency of the lithium-ion battery. In addition, the nano-silicon material has the excellent performance of long-cycle fast charging, which improves the convenience of battery use.

[0016] Optionally, the conductive porous material is one or more of a porous carbon material, a porous metal material, a porous conductive polymer, porous graphene, a porous oxide, a metal-organic framework, an aerogel, a covalent organic framework, or a carbon-coated porous material, preferably a porous carbon material. The voids within the porous carbon material can accommodate the volume expansion of silicon. Furthermore, the effective coating of silicon by the porous carbon material can greatly reduce the contact between silicon and the electrolyte, preventing the re-growth of the SEI film, thereby significantly improving the initial coulombic efficiency of the lithium battery.

[0017] Preferably, the porous carbon material is at least one of micro-mesoporous carbon, activated carbon, carbon aerogel, carbon nanotubes, graphene aerogel, ordered mesoporous carbon, activated carbon fiber, porous carbon balls, and carbonized polymer porous carbon, preferably activated carbon. Activated carbon has a well-developed internal pore structure, a large specific surface area, a 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 is particularly suitable for adsorbing particles with smaller molecular diameters. In addition, the interaction force between the molecules of activated carbon (van der Waals attraction) also promotes its adsorption capacity, so that more molecules are attracted and stay in the pores of the activated carbon.

[0018] Preferably, the porous metal material is at least one of foam aluminum, foam nickel, foam copper, 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 materials or conductive polymer-carbon material composite materials; 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 silicon dioxide, porous iron oxide, porous magnesium oxide, porous zinc oxide or porous lithium titanate; the metal organic framework is ZIF series, MIL series, NU series, HKUST-1, IRMOF series, UiO series, 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 aerogel; the carbon-coated porous material is at least one of carbon-coated porous carbon, carbon-coated porous carbon, 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 ceramics, 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, isopropyl alcohol, 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 milling. The rotation speed of the sand mill is 1-5000r / s, the sand milling time is 1-60h, the sand milling temperature is 15-100℃, and the sand milling pressure is 0.1-100MPa; the classifier frequency of the air mill is 0-103Hz, the fan frequency is 0-50Hz, and the feeding frequency is 0-50Hz; the ball mill cylinder rotation speed is 0-38r / min, and the ball loading capacity is 0-330t. Sand milling is preferred. The sand mill uses high-speed rotating grinding discs and grinding beads for grinding, which can quickly grind the material into the required particle size. It has the advantages of efficient grinding, high fineness, low cost, and continuous operation. Technological advances in sand mills have made them superior to ball mills in terms of grinding efficiency and product particle size distribution. In addition, Lin Wenzhong pointed out in his research that compared with other grinding equipment, such as air flow mills, sand mills have the advantages of 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, compression granulation, fluidized bed granulation, wet granulation, drum granulation, sol-gel granulation, electrochemical deposition granulation or solution impregnation granulation. Spray drying granulation technology is preferred, which can process a large amount of materials in a short time, has rapid drying ability, and achieves high yield and high efficiency production. Spray drying granulation sprays liquid or solution-like materials through a high-pressure nozzle and quickly dries them into tiny particles, which is convenient for subsequent coating, easy to operate and has strong stability. In addition, spray drying granulation technology has become a preferred technology due to its wide applicability, controllability of product quality, flexibility of operation and continuous automated operation. Preferably, the gas temperature range during the spray drying granulation process is 80-250°C, the air flow pressure is 0.01-5MPa, and the feed rate is 1-20rmp.

[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 negative electrode materials is closely related to the granulation size. Smaller particle size can provide more contact area, which is conducive to the embedding and extraction of lithium ions, thereby improving the cycle performance of the battery. However, smaller particle size will also increase the specific surface area in contact with the electrolyte, resulting in an increase in the charge consumed by the formation of the SEI film during the initial charge and discharge process, thereby causing an increase in irreversible capacity loss. Therefore, a reasonable particle size distribution is crucial to improving the initial capacity and efficiency of the battery.

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

[0025] The carbon coating layer is one of graphene, carbon nanotubes, amorphous carbon, and 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; and 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. Carbon has excellent electrical conductivity and enables rapid lithium ion transport. Furthermore, the carbon coating layer has good toughness, can adapt to stress changes caused by volume expansion, and has a certain degree of ductility, thus protecting the structural stability of the silicon-based material during the charge and discharge process.

[0027] Metal and metal oxide coatings utilize the excellent mechanical properties of metals and their alloys, such as high elastic modulus and high hardness, as well as good electrical conductivity, to mitigate the expansion effect of nano-silicon during cycling and improve its electrical conductivity. The metal coating can provide mechanical stress for silicon expansion, but it also requires the metal to have good electrical conductivity, be able to transport lithium ions to the silicon located in the center, and not chemically react with lithium ions and battery electrolytes. Compared to carbon coatings, metal and metal oxide coatings place higher demands on the choice of coating metal.

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

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

[0030] Optionally, the coating layer in step (3) has a thickness of 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 effect on the cycle stability of the silicon-based negative electrode material, can effectively inhibit the decomposition of the electrolyte on the surface of the silicon negative electrode, and well stabilize the SEI film structure on the surface of the silicon negative electrode, thereby significantly improving the cycle performance of the silicon-based negative electrode material. Preferably, the coating layer thickness is 30 nm and the stirring time is 4 h.

[0031] Optionally, when the coating method in step (3) is polymer carbon coating, a carbonization treatment is required: heating to a carbonization temperature of 500-900°C under an inert atmosphere and holding the temperature, followed by natural cooling to room temperature, with a heating rate of 1-20°C / min and a holding time of 0.1-72h. The specific operation of the carbonization treatment is to dry the product and place it in a tube furnace, heating to the carbonization temperature under an inert atmosphere and holding the temperature, and then waiting for the tube furnace to cool naturally to room temperature.

[0032] Optionally, 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.

[0033] Optionally, in step (4), the temperature is raised to 800-1000°C by at least one pulse, and the heating rate is 1×10 6 The temperature rises at a rate of -100°C / s. After reaching the target temperature, the system enters a hold phase with a duration of 0.01-200 seconds. After the hold phase, the system immediately begins cooling to form ultrafine nanoparticles. A single pulse duration ranges from 0.01s to 100s, representing the total time from the start of heating to the end of cooling, including the heating, hold, and cooling processes. Each pulse operation completes a complete heating-hold-cooling-cooling cycle. The number of pulses is unlimited, and the pulse interval ranges from 0.1s to 100s, representing the interval between the end of one pulse and the beginning of the next. During the hold phase, the temperature within the device rapidly rises from the starting temperature to the set target temperature, which is determined based on experimental requirements. After reaching the target temperature, the system enters a hold phase, where the temperature is maintained constant to ensure sufficient sublimation and diffusion of the silicon source. The hold time can be flexibly adjusted based on material properties and process requirements for optimal results. After the hold phase, the system immediately begins cooling, rapidly cooling the temperature to a safe level, prompting rapid condensation of the silicon vapor and the formation of ultrafine nanoparticles. During the preparation of battery materials, the heating and cooling rates have a significant impact on crystal nucleation and particle size. Faster heating and cooling rates can cause drastic changes in system temperature, accelerating crystal nucleation. Due to the short growth time, the resulting crystal particles are smaller. These small-particle crystals are beneficial for optimizing the material's microstructure, making the silicon particles more evenly distributed, thereby improving the material's uniformity and stability, and thus enhancing the battery's performance stability over multiple charge and discharge cycles. Silicon-based anode materials prepared using rapid heating technology have excellent mechanical stability and long cycle life. Controlling the heating rate can positively impact the performance of silicon-based anode materials.

[0034] Optionally, the cooling rate in step (4) is 1×10 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 selected from the group consisting of low vacuum, helium, argon, and nitrogen.

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

[0037] 1. Construction of specific confined microcavity structures:

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

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

[0040] Using transient high-temperature techniques (such as Joule heating and microwave heating), silicon is rapidly sublimated within a confined microcavity and instantly condensed into ultrafine nanoparticles less than 10nm. By controlling the temperature and the rate of heating and cooling, precise size control and uniform distribution of the silicon are achieved.

[0041] 3. Use 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 not only adsorb vaporized silicon, but also provide a good electron conduction path and physically buffer the volume expansion of silicon during charging and discharging, preventing material pulverization.

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

[0044] The coating layer (such as carbon layer and oxide layer) constructed on the surface of the material not only forms a confined microcavity, but also chemically interacts with silicon, enhancing the mechanical and chemical stability of the material and inhibiting structural fracture caused by volume changes of silicon.

[0045] This invention improves material utilization efficiency and conductivity by nanosizing silicon and uniformly distributing it within a porous structure, addressing the issues of volume expansion and poor conductivity in battery applications. The construction of confined microcavities and transient high-temperature phase transition technology combine to precisely control the material structure, thereby enhancing the cycling stability and electrochemical performance of the electrode material. This innovative approach opens new possibilities for the application of silicon-based anode materials in lithium-ion batteries.

[0046] The method proposed in the present invention for preparing ultrafine nano-silicon-based negative electrode materials based on in-situ high-temperature phase transition in a specific confined microcavity has the following advantages and outstanding effects compared to the existing technology:

[0047] First, by combining confined microcavities with high-temperature phase change technology, the structural stability and cycle life of the material are greatly enhanced, significantly improving the battery's cycling stability and reversible capacity. The uniform distribution and high conductivity of the material within the conductive porous structure significantly improve the battery's electrochemical performance, demonstrating higher energy density and charge-discharge efficiency.

[0048] Secondly, the invention simplifies the material preparation process, utilizing efficient material utilization and precise size control to reduce production costs and process complexity. This innovative method is applicable to lithium-ion batteries and broadens the application range of silicon-based negative electrode materials.

[0049] Furthermore, using transient heating technology, silicon undergoes a rapid phase transition within the coating under thermodynamically driven, non-steady-state conditions. The coating confines the vaporized silicon, while the conductive porous material rapidly adsorbs the vaporized silicon. 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 its conductivity, and suppress structural fracture caused by the large volume change of silicon, thereby avoiding the loss of active sites and forming a stable SEI. This further improves cycle stability while increasing electrode conductivity.

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

[0051] In summary, the present invention will adopt a solid silicon source, overcome the key problems in traditional technology through innovative structural design and process improvement, and explore a method for preparing silicon-based negative electrode materials that is efficient, stable, and widely applicable, completely avoiding the use of silane gas, and is expected to show great prospects in the application of high-energy-density battery technology. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0053] Figure 2 This 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 This 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 This is a cross-sectional SEM image of Example 1 of the present invention before the Joule heat pulse, showing the uniform distribution of silicon and carbon in the material and its dense internal structure before the Joule heat pulse.

[0056] Figure 5 This is a cross-sectional SEM image of Example 1 of the present invention after the Joule heat pulse, showing the changes in the internal structure of the material after the Joule heat pulse, with silicon vaporizing into nanoparticles and entering the porous carbon.

[0057] Figure 6 The figure shows the comparison of the rate performance of button cells assembled before and after Joule heat pulse treatment in Example 1 of the present invention.

[0058] Figure 7 The figure shows a comparison of the first discharge efficiency of button cells assembled before and after Joule heat pulse treatment in Example 1 of the present invention.

[0059] Figure 8 The present invention presents a comparison of the cycling performance of button cells assembled before and after Joule heat pulse treatment in Example 1 of the present invention, showing the capacity change of the battery at different cycle times, and the cycling stability of the sample treated with Joule heat is improved.

[0060] Figure 9 This is a graph showing the capacity change of the battery of Example 2 after 500 cycles.

[0061] Figure 10 This is a diagram of the battery cycle performance in Example 3.

[0062] Figure 11 This is the morphology of the silicon carbon sphere in Example 4.

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

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

[0065] Figure 14 This is a cross-sectional morphology diagram of the silicon particles in Example 7 when they are not completely vaporized. DETAILED DESCRIPTION

[0066] The following content describes and discloses the invention of the present application in detail with appropriate reference to the accompanying drawings, which provides a method for preparing ultrafine nano-silicon-based negative electrode materials based on in-situ high-temperature phase change in a confined microcavity. Certain unnecessary details may be omitted in the description, such as well-known matters and repeated descriptions of the same structure. This is done to avoid the description becoming lengthy so that those skilled in the art can better understand it. In addition, the drawings and the following description are intended to help those skilled in the art fully understand the present application, rather than to limit the subject matter described in the claims. Obviously, the embodiments described are only part of the present invention, not all embodiments. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should also fall within the scope of protection of the present invention.

[0067] Unless otherwise specified, all technical features and optional technical features in this application can be combined with each other to form a new technical solution. In order to make the purpose, technical solution 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, they are carried out according to conventional conditions or the conditions recommended by the manufacturer. Where the manufacturer of the reagents or instruments is not specified, they are conventional products that can be purchased commercially.

[0068] Example 1:

[0069] Mixed preparation: Weigh 50g of nano-silicon with an average particle size of 50nm and 50g of activated carbon, disperse them in 900g of ethanol, pour them into a sand mill, control the temperature to 25°C, and sand mill at 360r / s for 7h to obtain a silicon-carbon mixed slurry. Through this step, the size of the silicon-carbon material is initially reduced and highly evenly mixed. The density of the spray-dried sphere is controlled by controlling the silicon-carbon ratio and concentration. The loose interior may easily cause the coating to enter the interior during subsequent coating; too much nano-silicon and insufficient porosity of activated carbon may easily cause nano-silicon to condense and agglomerate on the surface. By controlling the temperature, oxidation is prevented, and the uniformity of the silicon-carbon mixing is adjusted by controlling the sand milling speed and time.

[0070] Spray drying: The mixed slurry is spray dried, and the gas temperature is controlled to be 150℃, the gas pressure is 0.2Mpa, and the feeding speed is 15rmp. In this step, the size of the manufactured spheres is controlled by controlling the gas pressure and feeding speed. If the size is too large, the coating layer will not be completely covered. If the size is too small, the coating layer thickness will be difficult to control. The scanning electron microscope (SEM) image of the obtained spherical silicon-carbon mixed material is as follows: Figure 1 As shown, it can be seen that the figure shows spherical particles without significant aggregation or agglomeration.

[0071] Figure 2A scanning electron microscope (SEM) image of the spherical silicon-carbon hybrid material obtained after spray drying is shown. The image shows uniform spherical particles, with large particles ranging in diameter from a few microns to over ten microns, and small particles less than a few microns in diameter. The particles are relatively evenly distributed, with no significant aggregation or agglomeration.

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

[0073] Figure 3 This image 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 deposits a large number of spherical particles on the material surface, with a relatively uniform distribution of particles.

[0074] Joule heat treatment: Take 0.1g of material and place it in an 8cm long carbon felt. The carbon felt is supported between the positive and negative electrodes of the Joule heat. The device is in a high vacuum state and the atmosphere is controlled to ensure that it is not oxidized during the instantaneous heating process. Start the Joule heat device power supply in a high vacuum atmosphere, adjust the current and voltage, and make the temperature rise to 940℃ instantly. Pulse for 30s multiple times to reach the sublimation point of nano-silicon. After the nano-silicon is vaporized, it is evenly diffused in the microcavity. If the temperature is too high, the internal pressure is high, which is easy to break through the coating and generate silicon carbide. If the temperature is too low, the nano-silicon is not completely vaporized. The pulse makes the nano-silicon evenly distributed and refined to an ultra-fine nanometer size below 10nm without agglomeration. If the time is too long, the coating is easy to break. If the time is too short, the vaporization is incomplete. The best experimental effect is achieved by adjusting the time and temperature.

[0075] Figure 4 A scanning electron microscope (SEM) image of carbon-coated spherical silicon-carbon hybrid particles before Joule heating is shown. The image reveals a very dense structure, with some irregular structural features, but a relatively uniform internal structure.

[0076] Figure 5 This scanning electron microscope (SEM) image shows spherical silicon-carbon hybrid material particles after Joule heating. After treatment, new pore structures form within and on the surface of the material. These pores are caused by the vaporization and nanocrystallization of silicon. The SEM images show that the material structure becomes more complex, with an increase in internal porosity.

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

[0078] Figure 6 The figure shows the relationship between the specific capacity and the number of cycles of the silicon-carbon composite material prepared in Example 1 of the present invention before and after Joule heat treatment at different charge and discharge rates (C-rate).

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

[0080] Vertical axis (Capacity, mAh / g): represents the specific capacity of the battery, in mAh / g, ranging from 0 to 2500mAh / g.

[0081] The curves are labeled:

[0082] Black solid dot curve: represents the battery performance after Joule heating treatment.

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

[0084] The "0.1C," "0.2C," "0.5C," "1C," "2C," and "5C" labeled in the figure represent different charge and discharge rates. Typically, the C-rate indicates how many times the rated capacity a battery is charged or discharged at. For example, 1C indicates complete charge and discharge within one hour. As can be seen, the specific capacity decreases as the C-rate increases. This is due to increased battery polarization and overpotential at high rates. However, the specific capacity of the battery treated with Joule heating is significantly higher than that of the untreated battery at all rates.

[0085] Rate cycling stability: After testing at different rates, the specific capacity of the battery can still be restored to a high level when it returns to a low rate (such as 0.1C), especially the battery after Joule heat treatment, which shows good rate cycling stability.

[0086] Figure 7 The relationship curve between voltage and specific capacity of the silicon-carbon composite material prepared by Example 1 of the present invention before and after Joule heat treatment during the first charge and discharge process is shown.

[0087] Horizontal axis (Specific Capacity, mAh / g): represents the specific capacity of the battery, in mAh / g, ranging from 0 to 2500mAh / g.

[0088] Vertical axis (Voltage, V vs. Li / Li+): represents the voltage of the battery relative to the voltage of lithium / lithium ions, ranging from 0V to 3V.

[0089] The two curves are:

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

[0091] Black solid line: represents the voltage-capacity curve of the battery during the first charge and discharge process before Joule heating treatment.

[0092] Voltage platform and specific capacity:

[0093] Before Joule heating treatment (black line): The battery has unclear voltage platforms at around 0.2V and 0.7V. The charge capacity before treatment is low, at about 1250mAh / g.

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

[0095] After Joule heating, the battery's voltage changes during charge and discharge are smoother, indicating a more stable electrochemical reaction. The battery's initial specific capacity increases significantly after heat treatment, demonstrating the positive effect of heat treatment on improving material performance.

[0096] Figure 8 The figure shows the cycle performance of button-type batteries assembled with the silicon-carbon composite material prepared in Example 1 of the present invention before and after Joule heat treatment.

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

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

[0099] In the figure, the black solid circles represent the Coulombic efficiency after Joule heating treatment, and the gray solid circles represent the Coulombic efficiency before Joule heating treatment.

[0100] The two curves are labeled:

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

[0102] Gray solid dot curve: represents the battery performance before Joule heat treatment, and the specific capacity is significantly lower 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 battery was tested at a current density of 1 A / g.

[0105] Example 2:

[0106] This example is essentially the same as Example 1, except that 25 g of nano-silicon and 50 g of porous carbon were weighed and dispersed in 675 g of ethanol, which was then poured into a sand mill. The capacity can be adjusted by varying the silicon-carbon ratio.

[0107] Figure 9 The capacity change of a battery with a silicon-carbon ratio of 1:2 after 500 cycles is demonstrated.

[0108] Example 3:

[0109] This embodiment is basically the same as embodiment 1, except that graphene is used instead of porous carbon. The high electrical conductivity of graphene can improve electron transfer efficiency and effectively improve cycle stability.

[0110] Figure 10 The battery cycling performance after graphene replaced porous carbon was demonstrated. The high conductivity of graphene can improve the electron transfer efficiency to effectively improve the cycling stability.

[0111] Example 4:

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

[0113] Figure 11 Shown are silicon carbon spheres after granulation using a fluidized bed.

[0114] Example 5:

[0115] This embodiment is essentially the same as embodiment 1, differing only in that the carbon coating is fabricated by 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 Scanning electron microscope (SEM) images of silicon-carbon hybrid particles coated by physical vapor deposition are shown. The carbon layer has a smooth surface and does not contain small carbon spheres produced by dopamine self-polymerization.

[0117] Example 6:

[0118] This embodiment is essentially the same as Example 1, differing only in that the silicon-carbon mixed particles are coated with dopamine, with the coating thickness controlled to 500 nm. The increased coating thickness allows the particles to withstand greater internal pressure, resist breakage, achieve higher transient heating temperatures, and increase internal phosphorus content.

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

[0120] Example 7:

[0121] This embodiment is basically the same as embodiment 1, with the only difference being that the Joule heating device power supply is started in an argon-filled atmosphere, the temperature is instantly raised to 1000°C, and multiple pulses of 5 seconds are applied. Different temperature and time conditions can regulate the degree of gasification of silicon particles.

[0122] Figure 14 It shows the cross-sectional morphology of silicon particles when they are not completely vaporized.

[0123] In summary, the present 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 causes silicon to rapidly vaporize and be adsorbed by a porous conductive material. The microcavity structure confines the vaporized silicon to the filling material within the cavity. After instantaneous condensation, nanoparticles are formed and confined within the pores, enhancing conductivity and buffering silicon expansion. This effectively suppresses structural fracture caused by volume change, avoids the loss of active sites, and thus improves cycling stability.

[0124] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent replacement or modification made by any person skilled in the art within the technical scope disclosed by the present invention and based on the technical solution and its conception shall be covered by the scope of protection of the present invention.

Claims

1. A method for preparing ultrafine nano-silicon-based negative electrode materials based on in-situ high-temperature phase change in a specific confined microcavity, characterized in that: The following steps are involved: (1) uniformly mixing silicon and a conductive porous material in a solvent and reducing their particle size to obtain a mixed slurry; (2) Re-granulating the mixed slurry to form solid particles; (3) coating the obtained particles to form a coating layer with a confined microcavity structure to limit the diffusion range of silicon after vaporization; (4) The coated product is loaded into the reaction zone, rapidly heated to the sublimation temperature of the silicon source so that it is evenly distributed in the confined microcavity, and rapidly cooled so that the silicon vapor quickly condenses into ultrafine nanoparticles with a particle size of less than 10 nm and is embedded in the porous conductive material.

2. The method according to claim 1, wherein The silicon described 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 micro-silicon is a powder, suspension or solution selected from silicate, quartz and silicon carbide, or a solution selected from vinyl silane, amino silane and epoxy silane.

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

5. The method according to claim 1, wherein The conductive porous material described in step (1) is one or more of a porous carbon material, a porous metal material, a porous conductive polymer, a porous oxide, a metal organic framework, a covalent organic framework or a carbon-coated porous material.

6. The method according to claim 5, characterized in that The porous carbon material is at least one of micro-mesoporous carbon and 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 balls 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 foam aluminum, foam nickel, foam copper, 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 materials or conductive polymer-carbon material composite materials; the porous oxide is at least one of porous titanium dioxide, porous tin oxide, porous silicon dioxide, porous iron oxide, porous magnesium oxide, porous zinc oxide or porous lithium titanate; the metal organic framework is at least one of 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 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, wherein The conductive porous material described 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, wherein 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.

17. The method according to claim 1, wherein 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, wherein The uniform mixing method described in step (1) is one of sand milling, ball milling or air flow milling.

19. The method according to claim 1, wherein The reforming granulation method described in step (2) is one of spray drying granulation, compression 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, wherein During the spray drying process of the spray drying granulation, the gas temperature is 80-250° C., the gas pressure is 0.01-5 MPa, and the injection speed is 1-20 rpm.

21. The method according to claim 1, wherein The particle size of the microparticles in step (2) ranges from 1 to 100 μm.

22. The method according to claim 1, wherein The coating layer in step (3) is one of a carbon coating layer, a metal coating layer, an oxide coating layer, a nitride coating layer and a polymer coating layer.

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

24. The method according to claim 1, wherein 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, wherein When the coating is a polymer coating, it needs to undergo carbonization treatment: heating to a carbonization temperature of 500-900 °C under an inert atmosphere and keeping warm, then naturally cooling to room temperature, with a heating rate of 1-20 °C / min and a holding time of 0.1-72 h.

26. The method according to claim 1, wherein 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, wherein In step (4), the temperature is raised to 800-1000 °C by at least one pulse, and the heating rate is 1×10 6 -100 ℃ / s. After reaching the target temperature, the system enters the insulation stage with a insulation time of 0.01-200 s. After the insulation stage, the temperature is immediately lowered to form ultrafine nanoparticles.

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

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

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

31. An ultrafine nano-silicon-based negative electrode material prepared based on in-situ high-temperature phase change in a specific confined microcavity, characterized in that: The method according to any one of claims 1 to 30 is used for preparation.

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