Ultra-fine nanophosphorus-carbon negative electrode material prepared on basis of in-situ high-temperature phase change in confined microcavities, and preparation method therefor

Abstract

The present invention provides an ultra-fine nanophosphorus-carbon negative electrode material prepared on the basis of in-situ high-temperature phase change in confined microcavities, and a preparation method therefor. The method aims at solving the problems of large volume expansion, poor conductivity, poor cycle stability and the like when phosphorus is used as a negative electrode material of an alkali metal-ion battery. By constructing confined microcavities on the surface of a porous conductive material and using a transient high-temperature phase change technique, phosphorus can be uniformly distributed and nanocrystallized. The method comprises: mixing phosphorus and a conductive porous material in a solvent, and then performing sand milling; forming solid particles by means of reforming and granulation; constructing confined microcavities by means of coating treatment; performing transient heating in a high-temperature apparatus, so that a phosphorus source is rapidly sublimated and uniformly distributed; and finally, performing heat preservation and conversion in a sealed container. In this way, the stability of the material is improved. The method not only enhances the utilization rate of phosphorus and the conductivity of the material, but also prolongs the service life of a battery and enhances the energy density of the battery, and has the advantages of simplifying a production process and reducing the production costs.

Description

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

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

[0002] Phosphorus, as a novel anode material for alkali metal-ion batteries, has attracted widespread attention due to its extremely high theoretical capacity (2596 mAh / g) and suitable charge-discharge platform. However, phosphorus exhibits high volume expansion (>300%) during charge-discharge, is prone to pulverization, and suffers from poor conductivity. Furthermore, its nano-sizing leads to instability, resulting in rapid capacity decay, low coulombic efficiency, and limited reversible capacity, thus restricting its application in alkali metal battery anode materials. To address these issues, current research focuses on combining phosphorus with other matrix materials, and some effective results have been achieved. Other matrices primarily involve carbon-based materials. The high conductivity of carbon-based materials improves the overall conductivity of the electrode, while the porous structure of carbon-based materials buffers the volume expansion of red phosphorus. Simultaneously, chemical bonds are formed between the atoms in the carbon-based materials and red phosphorus, stabilizing the structure.

[0003] Commonly used methods include mechanical ball milling and evaporative condensation. Mechanical ball milling involves accurately weighing phosphorus and carbon sources in a specific ratio, placing them in a milling jar, adding an appropriate amount of milling media (grinding balls), and sealing the jar in an inert atmosphere (such as argon) to prevent oxidation. Then, high-energy ball milling is performed at a set speed and time, allowing the phosphorus and carbon to fully mix and alloy under mechanical force, forming a composite material. Chinese patent application CN202311542975.2 provides a polymer-coated phosphorus-carbon composite material, its preparation method, and its application. This composite material mainly solves the problems of volume expansion, structural instability, severe electrolyte consumption, and poor conductivity that existing phosphorus-carbon composite materials easily exhibit during charging and discharging, especially the difficulty in achieving uniform material coating in existing processes. However, this method suffers from uneven mixing, easy agglomeration of fine particles, high energy consumption and long processing time during ball milling, which easily leads to material oxidation, increasing process complexity and cost. Evaporative condensation involves heating phosphorus and carbon sources in a sealed container under vacuum or an inert atmosphere, causing phosphorus to sublimate. Sublimated phosphorus gas condenses on a carbon substrate, forming a phosphorus layer covering the carbon material. However, this method suffers from low phosphorus source utilization due to easy condensation on the container wall, uneven phosphorus distribution on the carbon substrate, and difficulty in size control. Furthermore, it easily generates harmful gases, increasing safety and environmental requirements. Chinese patent application CN202311677198.2 provides a phosphorus-carbon composite anode material, its preparation method, and its application. This method involves depositing a phosphorus source onto a carbon source using chemical vapor deposition (CVD) to obtain a phosphorus-carbon composite anode material suitable for use as a sodium-ion battery anode. However, this method is complex and requires strict control of parameters such as vacuum, temperature, and time during production. Moreover, the high cost of CVD equipment may affect cost-effectiveness in large-scale production. Therefore, a technology that can efficiently utilize the phosphorus source, precisely control phosphorus size, and achieve uniform composite formation is needed. Summary of the Invention

[0004] The purpose of this invention is to develop a method based on in-situ high-temperature phase transition within a confined microcavity to prepare ultrafine nano-phosphorus carbon anode materials, aiming to solve the problems of low utilization rate and difficulty in size control when phosphorus is used as an anode material in alkali metal ion batteries.

[0005] The technical solution adopted in this invention is as follows:

[0006] A method for preparing ultrafine nano-phosphorus-carbon anode materials based on in-situ high-temperature phase transition within a confined microcavity includes the following steps:

[0007] (1) After adding phosphorus and conductive porous materials to a solvent and stirring, the mixture is sand-milled. Through high-speed rotation and the mutual impact of the grinding balls, highly uniform mixing is achieved and the size is initially reduced.

[0008] (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;

[0009] (3) The particles obtained by reforming and granulation in step (2) are coated to form a coating layer with a confined microcavity structure. The confined microcavity 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 range of phosphorus gasification and achieve efficient utilization.

[0010] (4) Load the product obtained in step (3) into the heating zone of the transient high temperature device for transient heating, so that the phosphorus source sublimates rapidly and diffuses evenly in the confined microcavity; cool instantly, the phosphorus vapor condenses rapidly to form ultrafine nanoparticles, and enters the porous conductive material.

[0011] (5) Transfer the product obtained in step (4) to a sealed container for heat preservation and conversion, and control the atmosphere to reduce the generation of by-products.

[0012] Optionally, 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 graphene, porous oxide conductive material, metal-organic framework, covalent organic framework, and carbon-coated porous material;

[0013] Optionally, the phosphorus source in step (1) is selected from one or more of red phosphorus, black phosphorus, white phosphorus, cellulose phosphorus, purple phosphorus, blue phosphorus, green phosphorus, phosphoric acid, phosphate, phosphate, phosphide, and organophosphorus compounds, preferably red phosphorus;

[0014] Optionally, the solvent in step (1) is one or more of ethanol, deionized water, isopropanol, propylene glycol methyl ether, N,N-dimethylformamide (DMF), N-methylpyrrolidone (NMP), ethyl acetate, cyclohexanone, and dichloromethane.

[0015] Optionally, the porous carbon mentioned in step (1) includes at least one of: activated carbon, carbon aerogel, carbon nanotubes, graphene aerogel, ordered mesoporous carbon, activated carbon fibers, porous carbon spheres, and carbonized polymer porous carbon; the porous metal material includes at least one of: aluminum foam, nickel foam, copper foam, porous titanium, porous gold, porous copper, porous magnesium, porous iron, porous cobalt, porous tungsten, porous molybdenum, and porous alloy; the porous conductive polymer includes at least one of: polypyrrole, polyaniline, polythiophene and its derivatives, polythiophene-conductive polymer composite material, and conductive polymer-carbon material composite material; the porous graphene includes at least one of: three-dimensional graphene aerogel, porous reduced graphene oxide, and porous graphene foam; the porous oxide conductive material includes: porous titanium dioxide, porous tin oxide, porous silica, porous iron oxide, porous magnesium oxide, and porous oxide. The metal-organic framework includes at least one of zinc and porous lithium titanate; the metal-organic framework includes at least one of the following: ZIF series, MIL series, NU series, HKUST-1, IRMO series, UiO series, MOF-5, and PCN series; the covalent organic framework includes at least one of COF-1, COF-5, COF-102, COF-108, TP-COFs, LZU-COF, NUS-COFs, PI-COFs, and TF-COFs; the carbon-coated porous material includes at least one of the following: carbon-coated porous carbon, carbon-coated porous metal materials, carbon-coated porous conductive polymers, carbon-coated porous graphene, carbon-coated porous oxide conductive materials, carbon-coated metal-organic frameworks, carbon-coated covalent organic frameworks, carbon-coated porous polymers, carbon-coated porous glass and ceramics, carbon-coated zeolites, and porous carbon-coated bio-based porous materials.

[0016] Optionally, in step (1), the mass ratio of phosphorus to conductive porous material is 1:0.1 to 1:100; the mass ratio of solvent to phosphorus carbon is 1:1 to 1:100; the milling speed is 1 r / s to 5,000 r / s; the milling time is 1 h to 24 h; and the milling temperature is 15 ℃ to 100 ℃.

[0017] Optionally, the reforming granulation method in step (2) includes existing granulation methods such as pressure granulation, spray drying granulation, and fluidized bed granulation, with a granulation size of 100 nm-100 μm.

[0018] Optionally, the coating layer in step (3) includes one or more of the following: carbon coating layer, metal coating layer, alloy coating layer, oxide coating layer, carbide coating layer, nitride coating layer, polymer coating layer, composite material coating layer, and organic coating layer.

[0019] Optionally, the coating method described in step (3) includes existing coating methods such as chemical vapor deposition, physical vapor deposition, and electrochemical deposition. The key to material design and optimization lies in constructing a stable microcavity structure through different coating methods to effectively control and utilize phosphorus vapor. Regardless of the coating material or technology used, the core objective is to restrict the escape of phosphorus vapor from the interior, allowing it to enter the porous conductive material through capillary force and pressure difference. This process ensures the full utilization of phosphorus vapor, maximizes the utilization rate of phosphorus source, reduces losses, and improves material performance.

[0020] Optionally, the coating thickness in step (3) is 0.01 μm-5 μm, and the mass ratio of the coating to the particles is 1:0.2~1:20. The design of the coating thickness is crucial. When the internal phosphorus content is too high and the coating thickness is insufficient, the shell may rupture due to the accumulation of internal gas and increased pressure. The structural integrity and performance stability of the material will also be affected, which will not only lead to an increase in specific surface area and more lithium ions being consumed, but also reduce the initial efficiency of the battery. Therefore, when designing the material, an appropriate coating thickness must be selected according to the specific material characteristics and internal phosphorus content to effectively resist internal gas pressure and maintain structural integrity, thereby enhancing the stability and lifespan of the battery during cycle use. In addition, the heating and cooling rates of the material also need to be optimized. Too rapid heating may quickly generate a large amount of internal gas, while the cooling process may cause gas condensation or volume reduction. These factors should be considered comprehensively to avoid material failure or performance degradation during cycle use. Through refined coating design and heat treatment process adjustment, the stability and lifespan of the material in practical applications can be ensured. For example, based on experimental data analysis, the minimum required coating thickness and optimal heating / cooling rates under different phosphorus content conditions can be determined to achieve the best performance. This not only maintains the integrity of the material structure but also provides higher performance and reliability in applications such as batteries.

[0021] Optionally, the transient heating method described in step (4) includes existing transient heating methods such as Joule heating, microwave heating, and plasma heating. During the heating process, a heating method capable of rapid heating is typically used, its key advantage being the ability to quickly heat the material and then rapidly cool it. This instantaneous cooling is crucial for the formation of the material's crystal structure because it significantly increases the nucleation rate and shortens the crystal growth time, thereby effectively generating nanoscale phosphorus particles. Nanoscale phosphorus particles not only help improve the material's conductivity but also significantly improve its overall performance in battery applications, particularly cycle stability.

[0022] Optionally, in step (4), the temperature is raised to 350 ℃ to 1000 ℃ by at least one pulse, with a heating rate of 1×106 ℃ / s to 100 ℃ / s. After reaching the target temperature, the system enters a heat preservation stage, with a heat preservation time of 0.01 s to 200 s. After the heat preservation stage ends, a cooling operation is immediately performed, cooling down to room temperature at a cooling rate of 1×106 ℃ / s to 100 ℃ / s to form ultrafine nanoparticles. The duration of a single pulse is 0.01 s to 100 s, which refers to the total time from the start of heating to the end of cooling, including the heating, heat preservation, and cooling processes. Each pulse operation includes a complete heating-heat preservation-cooling cycle. The number of pulses is unlimited, and the pulse interval is 0.1 s to 100 s, which refers to the time interval between the end of one pulse and the start of the next pulse. During the heating stage, the temperature inside the device rapidly rises from the initial temperature to the set target temperature, which is determined according to the experimental requirements. Once the target temperature is reached, the system enters a heat preservation phase, maintaining a constant temperature to ensure sufficient sublimation and diffusion of the phosphorus source. The heat preservation time can be flexibly adjusted according to material characteristics and process requirements to achieve optimal results. After the heat preservation phase, the system immediately begins cooling, rapidly reducing the temperature to a safe level, promoting rapid condensation of phosphorus vapor and forming ultrafine nanoparticles. In the battery material preparation process, the heating and cooling rates have a significant impact on crystal nucleation and particle size. Faster heating and cooling rates lead to drastic temperature changes in the system, accelerating crystal nucleation. Due to the shorter growth time, the formed crystal particles are smaller. These small crystal particles are beneficial for optimizing the microstructure of the material, resulting in a more uniform distribution of phosphorus particles, thereby improving the uniformity and stability of the material, and ultimately enhancing the performance stability of the battery during multiple charge-discharge cycles.

[0023] 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.

[0024] Optionally, the heat preservation temperature in step (5) is 100 ℃~400 ℃, the heat preservation time is 1 h~24 h, and the heat preservation atmosphere is a mixture of one or more gases selected from vacuum, argon, nitrogen and helium.

[0025] The principle of this invention is based on in-situ high-temperature phase transition within a confined microcavity to prepare ultrafine nano-phosphorus-carbon anode materials, mainly involving the following key technical steps and mechanisms:

[0026] 1. Construction of confined microcavity structures:

[0027] 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 range and distribution path of phosphorus during high-temperature phase transition, thereby improving phosphorus utilization efficiency and distribution uniformity.

[0028] 2. In-situ high-temperature phase transition:

[0029] Transient high-temperature techniques (such as Joule heating and microwave heating) are used to rapidly sublimate and condense phosphorus into nanoparticles within a confined microcavity. By controlling the temperature and heating / cooling rates, precise size control and uniform distribution of phosphorus can be achieved.

[0030] 3. Application of conductive porous materials:

[0031] Materials with high conductivity and porous structures (such as porous carbon materials and metal-organic frameworks) are selected as the matrix. These materials can adsorb and vaporize phosphorus, provide good electron conduction pathways, and physically buffer the volume expansion of phosphorus during charging and discharging, thus preventing the material from pulverizing.

[0032] 4. The function of the coating layer:

[0033] The coating layer (such as a carbon layer or oxide layer) constructed on the material surface forms a confined microcavity, which enhances the mechanical and chemical stability of the material, suppresses structural breakage caused by phosphorus volume changes, and improves the initial efficiency.

[0034] 5. Thermal insulation conversion steps:

[0035] The prepared material is placed in a sealed environment for heat preservation to reduce the generation of by-products.

[0036] This invention improves the utilization efficiency and conductivity of materials by nano-sizing and uniformly distributing phosphorus within a porous structure, solving the problems of volume expansion and poor conductivity associated with phosphorus 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 offers new possibilities for the application of phosphorus-based anode materials in sodium-ion, lithium-ion, and potassium-ion batteries.

[0037] The method for preparing ultrafine nano-phosphorus-carbon anode materials based on in-situ high-temperature phase transition within a confined microcavity proposed in this invention has the following advantages and outstanding effects compared with existing technologies:

[0038] 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.

[0039] 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 various alkali metal ion batteries, including sodium-ion, lithium-ion, and potassium-ion batteries, broadening the application range of phosphorus-based anode materials.

[0040] Furthermore, using transient heating technology, phosphorus undergoes a rapid phase transition under thermodynamically driven unsteady conditions. The coating layer confines the vaporized phosphorus, 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 phosphorus, enhance conductivity, suppress structural breakage caused by the large volume change of phosphorus, avoid the loss of active sites, and further improve cycling stability.

[0041] In summary, this invention overcomes key problems in traditional technologies through innovative structural design and process improvements, providing a highly efficient, stable, and widely applicable method for preparing phosphorus-carbon anode materials, demonstrating great potential and advantages in battery technology applications. Attached Figure Description

[0042] Figure 1 is a scanning electron microscope (SEM) image of the spherical phosphorus-carbon hybrid material obtained in Example 1 of the present invention.

[0043] Figure 2 shows the X-ray diffraction (XRD) patterns of the spherical phosphorus-carbon hybrid material particles before and after copper plating in Example 1 of the present invention.

[0044] Figure 3 shows a cross-sectional scanning electron microscope (SEM) image of the spherical phosphorus-carbon hybrid material particles of Example 1 of the present invention after copper plating and before Joule thermal pulse treatment.

[0045] Figure 4 is a cross-sectional SEM image of the spherical phosphorus-carbon hybrid material particles of Embodiment 1 of the present invention after a Joule thermal pulse.

[0046] Figure 5 is a scanning electron microscope (SEM) image of the spherical phosphorus-carbon hybrid material of Example 4 of the present invention after physical vapor deposition of a carbon layer.

[0047] Figure 6 shows a scanning electron microscope (SEM) image of Embodiment 2 of the present invention, which illustrates that due to the increased phosphorus content and insufficient copper shell thickness, excessive internal pressure caused gas to break through the shell.

[0048] Figure 7 shows transmission electron microscopy (TEM) images of the interior of phosphorus carbon at different single pulse times and temperatures in Embodiment 6 of the present invention.

[0049] Figure 8 shows the cycle performance curves of the spherical phosphorus-carbon hybrid material particles of Example 1 of the present invention before and after the Joule thermal pulse in a coin cell.

[0050] Figure 9 shows the relationship between the specific capacity (mAh / g) and cycle number of the coin cell assembled with spherical phosphorus-carbon hybrid material particles before and after Joule thermal pulse in Example 1 of the present invention at different charge-discharge rates (C-rate).

[0051] Figure 10 shows the relationship between voltage and specific capacity (mAh / g) of the coin cell assembled with phosphorus-carbon composite material before and after Joule heat treatment prepared in Example 1 of the present invention during the first charge and discharge process.

[0052] Figure 11 shows a comparison of the cycle performance of coin cells assembled with phosphorus-carbon composite materials before and after Joule heat treatment using the materials prepared in Example 2 of this invention.

[0053] Figure 12 shows the cycle performance of a coin cell assembled with the phosphorus-carbon composite material after Joule heat treatment prepared in Example 3 of the present invention.

[0054] Figure 13 shows the relationship between voltage and specific capacity (mAh / g) of coin cells assembled with different heat preservation times after using the Joule thermal pulse obtained in Example 7 of the present invention during the first charge and discharge process. Detailed Implementation

[0055] The invention described herein, which provides a method for preparing ultrafine nano-phosphorus-carbon 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.

[0056] 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.

[0057] Example 1:

[0058] Preparation by mixing: Weigh 50 g of red phosphorus and 50 g of porous carbon, disperse them in 900 g of ethanol, pour the mixture into a sand mill, control the temperature to 25 ℃, and mill at 2000 r / s for 2 h to obtain a phosphorus-carbon mixed slurry. By controlling the phosphorus-carbon ratio and concentration, the density of the spray-dried spheres can be adjusted. A loose internal structure makes it easy for the coating material to penetrate the interior during subsequent coating; too much red phosphorus results in insufficient porosity in the porous carbon, easily leading to the condensation and agglomeration of red phosphorus on the surface. During this process, oxidation must be prevented, and uniform mixing must be ensured by adjusting the milling speed and time.

[0059] Spray drying: The mixed slurry is spray-dried, with the gas temperature controlled at 150 ℃, the gas pressure at 0.2 MPa, and the injection rate at 15 rpm, to obtain spherical phosphorus-carbon mixtures. By adjusting the gas pressure and injection rate, the size of the spheres and the uniformity of the coating layer can be controlled. 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.

[0060] Figure 1 shows a scanning electron microscope (SEM) image of the spherical phosphorus-carbon mixture obtained after spray drying. As can be seen in the image, the material consists of uniform spherical particles, with the large particles ranging from a few micrometers to tens of micrometers in diameter, and the small particles having a diameter within a few micrometers. The particle distribution is relatively uniform, and no significant aggregation or agglomeration is observed.

[0061] Electroless copper plating: Spherical phosphorus-carbon composite material particles are coated with copper using an electroless copper plating solution. 1g of the spherical phosphorus-carbon composite material is placed in 50ml of a 20g / L stannous chloride sensitization solution and stirred for 10 min. Then, it is immersed in 50ml of an electroless copper plating solution with a copper salt concentration of 3.8g / L for 10 min. Finally, it is dried to form a coating layer with a confined microcavity structure, with a thickness controlled at 200 nm. This step mainly controls the thickness by controlling the amount of copper plating solution and the plating time. Excessive thickness affects battery performance, while insufficient thickness makes it susceptible to being broken by the gas generated after sublimation.

[0062] Figure 2 shows the X-ray diffraction (XRD) patterns of spherical phosphorus-carbon composite particles before and after copper plating. In the figure, the horizontal axis represents the 2θ angle, and the vertical axis represents the diffraction intensity. The XRD curve of the unplated material does not show significant diffraction peaks, while the curve after copper plating shows obvious characteristic peaks of copper crystals at positions close to 43.3° and 50.4°, indicating that the copper plating process was successful.

[0063] Joule heating: 0.2 g of material was placed in a 5 cm long carbon felt, which was then placed between the positive and negative electrodes of an open Joule heating device inside a glove box. The glove box was filled with high-purity argon gas, with water and oxygen content below 0.01 ppm to control the atmosphere and prevent oxidation during the instantaneous heating process. The Joule heating device was started in the argon-filled atmosphere, and the voltage and current parameters were adjusted to 80V and 15A, respectively, to rapidly raise the temperature to 450 °C within 0.1 seconds. Five 1-second pulse heating cycles were then performed to reach the sublimation point of red phosphorus, causing the red phosphorus to vaporize and diffuse within the microcavity. After the sublimation process, a rapid cooling system was immediately activated. Rapid circulation of the cooling medium caused the temperature in the reaction zone to drop sharply and instantaneously. The phosphorus vapor rapidly condensed to room temperature during this process, forming ultrafine nanoparticles that effectively embedded themselves into the porous conductive material. In this step, if the temperature is too high, the internal pressure is too great, which may break through the coating layer; if the temperature is too low, the red phosphorus will not vaporize completely. By precisely controlling the heating time and temperature, the red phosphorus is ensured to be evenly distributed, refined to an ultrafine nanoscale size, and without agglomeration.

[0064] Figure 3 shows a cross-sectional scanning electron microscope (SEM) image of the spherical phosphorus-carbon hybrid material particles after copper plating before Joule heat treatment. The image shows that the cross-sectional structure of the particles is very dense and contains some irregular structural features. The copper plating process forms a dense copper layer on the material surface with a relatively uniform internal structure.

[0065] Post-processing: The product obtained in step 4 was sealed and transferred to a tube furnace, argon gas was introduced, and the furnace was kept at 260 °C for 12 h to ensure complete stabilization of red phosphorus.

[0066] Figure 4 shows a cross-sectional scanning electron microscope (SEM) image of the spherical phosphorus-carbon hybrid material particles after Joule heat treatment. After treatment, new porous structures formed inside and on the surface of the material, which are caused by the vaporization and nanostructuring of red phosphorus. The SEM images reveal that the material structure has become more complex, with an increase in internal porosity.

[0067] Example 2: Same as Example 1, except that the mass ratio of red phosphorus to porous carbon is 2:1.

[0068] Example 3: Same as Example 1, except that porous graphene is used instead of porous carbon. Graphene's high electrical conductivity improves electron transport efficiency, effectively enhancing cycle stability. Example 4: Same as Example 1, except that the carbon coating is fabricated using physical vapor deposition (PVD). PVD allows for precise film thickness control and uniform deposition, resulting in a pure carbon film with low impurity content, which helps improve electrochemical performance. It also uses fewer harmful chemicals, resulting in a relatively smaller environmental impact.

[0069] Figure 5 shows a scanning electron microscope (SEM) image of phosphorus-carbon mixed particles formed by physical vapor deposition. The carbon layer has a smooth and dense surface and an intact shell.

[0070] Example 5: Same as Example 1, except that the copper plating thickness is 500 nm. Increased copper plating 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.

[0071] Figure 6 shows a scanning electron microscope (SEM) image of gas breaking through the shell due to insufficient copper 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 internal phosphorus vapor and maintain the integrity of the shell.

[0072] Example 6: Same as Example 1, except that the single pulse time of the Joule heat treatment is 10 s and the temperature is 500 ℃. Different temperature and time conditions can control the particle distribution of different particle sizes.

[0073] Figure 7 shows transmission electron microscopy (TEM) images of the interior of phosphorus carbon at different temperatures and for different single pulse times. The particle size and distribution of the internal phosphorus particles can be controlled by adjusting the time and temperature. When the temperature and time are not suitable, the internal phosphorus particles will aggregate.

[0074] Example 7: Same as Example 1, except that the holding time in the tube furnace is 24 hours. By adjusting the holding time, fewer by-products are produced, thereby increasing the overall capacity of the battery.

[0075] Tests and Results

[0076] We selected the phosphorus-carbon composite materials prepared in Examples 1, 2, 3, and 7, and assembled them into coin cells before and after transient heat treatment, respectively, and conducted electrochemical performance tests. In the fabrication of the coin cells, lithium metal sheets were selected as the counter electrode. The preparation method of the phosphorus-carbon electrode sheet is as follows: the phosphorus-carbon composite material, conductive agent SP, and binder PVDF were uniformly mixed at a mass ratio of 8:1:1, coated onto copper foil, and vacuum dried at 80 °C for 12 hours. The dried electrode sheet was then rolled, cut into circular pieces with a diameter of 11 mm, weighed, and placed in a vacuum glove box for coin cell assembly.

[0077] Test results of Example 1:

[0078] Figure 8 shows the cycle performance of coin cells assembled using the phosphorus-carbon composite material prepared in Example 1 of this invention before and after Joule heat treatment. In the figure:

[0079] The horizontal axis (Cycle Number) represents the number of battery cycles, from 0 to 100.

[0080] The left vertical axis (Specific Capacity, mAh / g) represents the battery's specific capacity, measured in mAh / g, ranging from 0 to 4000 mAh / g.

[0081] The right vertical axis (Coulombic Efficiency %) represents the battery's coulombic efficiency, expressed as a percentage (%), ranging from 0% to 100%.

[0082] In the diagram, the black hollow circles represent the coulombic efficiency after Joule heat treatment, and the gray hollow circles represent the coulombic efficiency before Joule heat treatment.

[0083] The two curves are labeled as follows:

[0084] 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.

[0085] 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.

[0086] 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.

[0087] The trend of coulombic efficiency shows that the coulombic efficiency after Joule heat treatment is higher than that before Joule heat treatment in the first cycle (first charge and discharge). However, in long cycles, the difference in coulombic efficiency between the two is not significant.

[0088] The current density of the battery test was 0.26 A / g.

[0089] Figure 9 shows the relationship between the specific capacity and the number of cycles of the phosphorus-carbon composite material prepared using Example 1 of the present invention before and after Joule heat treatment. In the figure:

[0090] The horizontal axis (Cycle Number) represents the number of battery cycles, ranging from 0 to 70.

[0091] The vertical axis (Specific Capacity, mAh / g) represents the battery's specific capacity, measured in mAh / g, ranging from 0 to 1600 mAh / g.

[0092] The curve is labeled as follows:

[0093] The black solid dot curve represents the battery performance after Joule heat treatment.

[0094] Hollow dot curve: represents the performance of a battery without Joule heat treatment.

[0095] The labels "0.1C", "0.2C", "0.5C", "1C", and "2C" in the diagram represent different charge / discharge rates. Typically, C-rate indicates how many times the battery's rated capacity it is charged and 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.

[0096] 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.

[0097] First-charge-discharge comparison before and after Joule heat treatment: Figure 10 shows the voltage-specific capacity relationship curves of the phosphorus-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:

[0098] The horizontal axis (Specific Capacity, mAh / g) represents the battery's specific capacity, measured in mAh / g, ranging from 0 to 3000 mAh / g.

[0099] The vertical axis (Voltage, V vs. Li / Li+) represents the battery voltage relative to the lithium / lithium-ion voltage, ranging from 0V to 2.5V.

[0100] The two curves are as follows:

[0101] Solid line: Represents the voltage-capacity curve of the battery during the first charge and discharge process after Joule heat treatment.

[0102] Dashed line: Represents the voltage-capacity curve of the battery during its first charge and discharge process before Joule heat treatment.

[0103] Voltage plateau and specific capacitance:

[0104] Before Joule heat treatment (dashed line): The battery has an indistinct voltage plateau at around 1.2V and 0.6V. The charge specific capacity before treatment is low, at around 1200 mAh / g.

[0105] After Joule heat treatment (solid 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 red phosphorus particle size, improves utilization, and thus enhances lithium storage capacity and electrochemical activity.

[0106] 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.

[0107] Test results of Example 2:

[0108] Figure 11 shows a comparison of the cycling performance of the phosphorus-carbon composite material prepared using Example 2 of the present invention before and after Joule heat treatment. In the figure:

[0109] The horizontal axis (Cycle Number) represents the number of battery cycles, ranging from 0 to 100.

[0110] The left vertical axis (Specific Capacity, mAh / g) represents the battery's specific capacity, ranging from 0 to 3000 mAh / g.

[0111] The right-hand vertical axis (Coulombic Efficiency, %) represents the battery's coulombic efficiency, ranging from 0% to 100%.

[0112] In the diagram, the black hollow circles represent the coulombic efficiency after Joule heat treatment, and the gray hollow circles represent the coulombic efficiency before Joule heat treatment.

[0113] The curves in the figure are:

[0114] The black solid dot curve represents the battery performance after Joule heat treatment.

[0115] The gray hollow dot curve represents the battery performance before Joule heat treatment.

[0116] Specific capacity change trend:

[0117] After Joule heat treatment: The initial specific capacity of the battery is about 1970 mAh / g. As the number of cycles increases, the specific capacity gradually decreases, but it still remains at about 1134 mAh / g at the 100th cycle, showing good cycle stability.

[0118] Before Joule heat treatment: The battery has a low initial specific capacity of about 1800 mAh / g. As the number of cycles increases, the specific capacity decreases significantly, dropping to about 627 mAh / g by the 100th cycle, showing poor cycle performance.

[0119] The trend of coulombic efficiency shows that the coulombic efficiency in the first cycle after Joule heat treatment is higher than that before treatment, but the difference between the two is not significant during long cycles.

[0120] Comparison of treatment effects: Compared with Example 1, the initial capacity of the battery in Example 2 increased due to the increased phosphorus content. However, excessively high phosphorus content can lead to agglomeration in the porous carbon, thereby reducing phosphorus utilization and causing a decline in cycle performance. Therefore, it is necessary to adjust the pore volume and specific surface area of ​​the porous carbon to achieve the optimal phosphorus content.

[0121] Test results of Example 3:

[0122] Figure 12 shows the cycling performance of the phosphorus-carbon composite material after Joule heat treatment prepared using Example 3 of the present invention. In the figure:

[0123] The horizontal axis (Cycle Number) represents the number of battery cycles, ranging from 0 to 50.

[0124] The left vertical axis (Specific Capacity, mAh / g) represents the battery's specific capacity, ranging from 0 to 3000 mAh / g.

[0125] The right-hand vertical axis (Coulombic Efficiency, %) represents the battery's coulombic efficiency, ranging from 0% to 100%.

[0126] The gray hollow circles in the figure represent the coulomb efficiency after Joule heat treatment.

[0127] The black solid dot curve represents the battery performance after Joule heat treatment, showing the stability of the battery's charge and discharge after heat treatment.

[0128] It can be seen that using porous graphene as a porous conductive substrate results in better cycle performance, and the cycle retention rate is improved compared with that of porous carbon as a conductive substrate.

[0129] The current density of the battery test was 0.26 A / g.

[0130] Test results of Example 7:

[0131] Comparison of first-cycle capacity of materials with different heat preservation times: Figure 13 shows the voltage-specific capacity relationship curves of phosphorus-carbon composite materials prepared using Example 7 of the present invention with different heat preservation times during the first charge-discharge process. In the figure:

[0132] The horizontal axis (Specific Capacity, mAh / g) represents the battery's specific capacity, measured in mAh / g, ranging from 0 to 3000 mAh / g.

[0133] The vertical axis (Voltage, V vs. Li / Li+) represents the battery voltage relative to the lithium / lithium-ion voltage, ranging from 0V to 2.5V.

[0134] The two curves are as follows:

[0135] Solid line: Represents the voltage-capacity curve of the battery during the first charge and discharge process after 24 hours of heat preservation.

[0136] Dashed line: Represents the voltage-capacity curve of the battery during the first charge and discharge process after 12 hours of heat preservation.

[0137] It can be seen that the heat preservation time is conducive to the conversion of more by-products into red phosphorus, thereby increasing the content of red phosphorus, improving capacity, and reducing by-products generated during battery cycling.

[0138] In summary, this invention provides a method for preparing ultrafine nano-phosphorus-carbon anode materials based on in-situ high-temperature phase transition within a confined microcavity. Transient heating rapidly vaporizes phosphorus, which is then adsorbed by the porous conductive material. The microcavity structure confines the vaporized phosphorus within the cavity. Upon instantaneous condensation, nanoparticles are formed and confined within the pores, enhancing conductivity, buffering phosphorus expansion, effectively suppressing structural breakage caused by volume changes in phosphorus, avoiding loss of active sites, and thus improving cycle stability.

[0139] 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 ultra-fine nano-phosphorus-based negative electrode material based on in-situ high-temperature phase transition in a confined microcavity, characterized in that, Includes the following steps: (1) After adding phosphorus and conductive porous materials to a solvent and stirring, the mixture is sand-milled. Through high-speed rotation and the mutual impact of the grinding balls, highly uniform mixing is achieved and the size is initially reduced. (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; (3) The particles obtained by reforming and granulation in step (2) are coated to form a coating layer with a confined microcavity structure. The confined microcavity 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 range of phosphorus gasification and achieve efficient utilization. (4) Load the product obtained in step (3) into the heating zone of the transient high temperature device for transient heating, so that the phosphorus source sublimates rapidly and diffuses evenly in the confined microcavity; cool instantly, the phosphorus vapor condenses rapidly to form ultrafine nanoparticles, and enters the porous conductive material. (5) Transfer the product obtained in step (4) to a sealed container for heat preservation and conversion, and control the atmosphere to reduce the generation of by-products.

2. The method according to claim 1, characterized in that, The phosphorus mentioned in step (1) is selected from one or more of red phosphorus, black phosphorus, white phosphorus, cellulose phosphorus, purple phosphorus, blue phosphorus, green phosphorus, phosphoric acid, phosphate, phosphide, and organophosphorus compounds.

3. The method according to claim 1, characterized in that, The conductive porous material mentioned in step (1) includes one or more of the following: porous carbon materials, porous metal materials, porous conductive polymers, porous graphene, porous oxide conductive materials, metal-organic frameworks, covalent organic frameworks, and carbon-coated porous materials.

4. The method according to claim 3, characterized in that, The porous carbon material mentioned in step (1) is selected from at least one of activated carbon, carbon aerogel, carbon nanotubes, graphene aerogel, ordered mesoporous carbon, activated carbon fiber, porous carbon spheres, and carbonized polymer porous carbon; the porous metal material is selected from at least one of aluminum foam, nickel foam, copper foam, porous titanium, porous gold, porous magnesium, porous iron, porous cobalt, porous tungsten, porous molybdenum, and porous alloy; the porous conductive polymer is selected from at least one of polypyrrole, polyaniline, polythiophene and its derivatives, polythiophene-conductive polymer composites, and conductive polymer-carbon material composites; the porous graphene is selected from at least one of three-dimensional graphene aerogel, porous reduced graphene oxide, and porous graphene foam; the porous oxide conductive material is selected from at least one of porous titanium dioxide, porous tin oxide, porous silica, porous iron oxide, porous magnesium oxide, porous zinc oxide, and porous titanate. At least one of lithium; the metal-organic framework is selected from at least one of the ZIF series, MIL series, NU series, HKUST-1, IRMO series, UiO series, MOF-5, and PCN series; the covalent organic framework is selected from at least one of COF-1, COF-5, COF-102, COF-108, TP-COFs, LZU-COF, NUS-COFs, PI-COFs, and TF-COFs; the carbon-coated porous material is selected from at least one of carbon-coated porous carbon, carbon-coated porous metal materials, carbon-coated porous conductive polymers, carbon-coated porous graphene, carbon-coated porous oxide conductive materials, carbon-coated metal-organic frameworks, carbon-coated covalent organic frameworks, carbon-coated porous polymers, carbon-coated porous glass and ceramics, carbon-coated zeolites, and porous carbon-coated bio-based porous materials.

5. The method according to claim 1, characterized in that, The solvent in step (1) is selected from one or more of ethanol, deionized water, isopropanol, propylene glycol methyl ether, N-dimethylformamide (DMF), N-methylpyrrolidone (NMP), ethyl acetate, cyclohexanone, and dichloromethane.

6. The method according to claim 1, characterized in that, The mass ratio of phosphorus to conductive porous material in step (1) is 1:0.1 to 1:

100.

7. The method according to claim 1, characterized in that, The mass ratio of the solvent to phosphorus carbon in step (1) is 1:1 to 1:

100.

8. The method according to claim 1, characterized in that, The grinding speed in step (1) is 1 r / s to 5000 r / s, the grinding time is 1 hour to 24 hours, and the grinding temperature is 15 ℃ to 100 ℃.

9. The method according to claim 1, characterized in that, The size of the microparticles in step (2) is 100 nm to 100 μm.

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

11. The method according to claim 10, characterized in that, The carbon coating layer mentioned in step (3) includes graphene, carbon nanotubes, amorphous carbon, and graphite coating; the metal coating layer includes aluminum, nickel, copper, zinc, titanium, gold, magnesium, iron, tungsten, molybdenum, and alloy coating; the oxide coating layer includes aluminum oxide, titanium oxide, zirconium oxide, silicon oxide, manganese oxide, magnesium oxide, nickel oxide, and cerium oxide coating; the nitride coating layer includes titanium nitride, silicon nitride, aluminum nitride, boron nitride, and zirconium nitride coating; and the polymer coating layer includes one or more of polyvinylidene fluoride, polyethyleneimine, polythiophene, polypyrrole, polyaniline, polyacrylonitrile, and polyethylene glycol.

12. The method according to claim 1, characterized in that, The thickness of the coating layer in step (3) is 0.01 μm-5 μm, and the mass ratio of the coating layer to the particles is 1:0.2 to 1:

20.

13. The method according to claim 1, characterized in that, In step (4), the temperature is increased to 350-1000 °C by at least one pulse, the temperature increase rate is 1x10 6 °C / s-100 °C / s, after reaching the target temperature, the system enters a holding stage, the holding time is 0.01 s-200 s, after the holding stage, the temperature is immediately decreased to room temperature at a rate of 1x10 6 °C / s-100 °C / s, and ultrafine nanoparticles are formed.

14. The method according to claim 1, characterized in that, The duration of a single pulse is 0.01 s-100 s, which 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 includes a complete heating-holding-cooling cycle. The number of pulses is unlimited. The pulse interval is 0.1 s-100 s, which refers to the time interval between the end of one pulse and the start of the next pulse.

15. The method according to claim 1, characterized in that, The atmosphere in the heating zone mentioned in step (4) is a non-oxidizing atmosphere, a low vacuum, or a mixture of one or more of helium, argon, and nitrogen.

16. The method according to claim 1, characterized in that, The heat preservation temperature in step (5) is 100 ℃ to 400 ℃, the heat preservation time is 1 hour to 24 hours, and the heat preservation atmosphere is a mixture of one or more gases selected from vacuum, helium, argon and nitrogen.

17. A method for preparing ultrafine nano-phosphorus-based anode materials based on in-situ high-temperature phase transition within a confined microcavity, characterized in that, Prepared according to the method of any one of claims 1-16.

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