CN103184587B - Method for preparing microporous LiFePO4/C fibers by spinning with three-screw banburying extruder - Google Patents

Abstract

A method for preparing microporous LiFePO ₄ /C ultrafine fibers by spinning with a three-screw internal mixing extruder, mixing iron source, lithium source, reducing agent, carbon source, and complexing agent, and introducing the three-screw internal mixing and extruding The supercritical fluid is introduced into the three-screw banbury extruder to mix with the above-mentioned blend and maintain a certain pressure, so that the blend is reacted and synthesized in the supercritical fluid, compacted by the screw compression section and gradually formed Homogeneous body, the homogeneous body is extruded from the spinneret hole of the die head through the entrance area, hole flow area and puffing area of the meltblown die to form ultra-fine microporous fibers, and the fibers obtained after natural cooling are put into a calciner to make Obtain LiFePO ₄ /C ultrafine microporous fibers. The prepared microporous LiFePO ₄ /C fiber can meet the needs of lithium battery-based textile, electrical, electronic, mechanical, medical, chemical, food, aerospace and other related fields.

Description

Method for preparing microporous LiFePO4/C fibers by spinning with three-screw banburying extruder

technical field

The invention relates to a method for preparing microporous LiFePO ₄ /C fibers by spinning with a three-screw banburying extruder.

Background technique

Lithium iron phosphate LiFePO ₄ can reversibly insert and extract lithium ions, the voltage of Fe ²⁺ /Fe ³⁺ relative to metal lithium is 3.4 V, and the theoretical specific capacity of this material is 170 mA·h/g. Because LiFePO ₄ has the advantages of non-toxicity, environmental friendliness, rich source of raw materials and low price, good cycle and thermal stability, etc., it will soon be used in lithium batteries. However, the conductivity of LiFePO ₄ is only on the order of 10 ^-9 S/cm, and lithium ions are affected by the close packing of oxygen atoms, which is unfavorable for the diffusion and transfer of lithium ions during charge and discharge. At present, the research on LiFePO ₄ cathode materials is mainly focused on improving its electronic and ion conductivity, including uniform coating of conductive agents such as carbon, metal or conductive polymer with good dispersion performance on the outside of the particles, and improving the particle surface and inter-particle conductivity. The apparent conductivity of the particle is doped with metal ions to reduce the conduction band energy level of the solid material or cause ion vacancies to increase the intrinsic conductivity of the material to synthesize nanomaterials and reduce the diffusion distance of electrons or ions in the material. Common synthesis methods of LiFePO ₄ include high-temperature solid-state reaction, sol-gel method, and solvothermal method. High-temperature solid-phase synthesis is often used in industrial production. However, the quality stability of this method is not easy to control during the synthesis process. In order to obtain a more uniform product, multi-step calcination and grinding are required.

Facing the increasingly scarce petroleum energy crisis, finding environmentally friendly, low-carbon, sustainable renewable energy is an urgent research and solution task. Lithium-ion batteries as chemical energy storage have been widely researched and developed due to their advantages of high voltage, high energy density, long cycle life and no memory effect. However, the current commercial Lithium Ion Batteries (Lithium Ion Batteries) are mainly used in low-power products, and there are still many challenges and problems for high-power applications, such as high polarization effects and high capacity under high-rate charge and discharge. Attenuation problem. For the cathode material LiFePO ₄ , it has attracted much attention due to its advantages such as high plateau voltage, environmental protection, abundant manganese resources, and relatively low cost. Ordinary micron-sized LiFePO ₄ suffers from low rate capability due to its long Li-ion diffusion path, which affects its high-power applications. In recent years, the functionalization of nanomaterials has received extensive attention, and it is also considered to be an effective way to improve the application of high-power electrode materials. Because it greatly shortens the diffusion length of lithium ions, it reduces the polarization effect under high rate charge and discharge.

With the rapid development of blending and dispersing processing, the requirements for the refinement of various components in processing, the dispersion effect and the mixing state of the final mixture are becoming higher and higher. Correspondingly, there are a wide variety of methods to adapt to different mixing process requirements. Advanced mixing equipment, such as twin-screw extruders, disc extruders, planetary screw extruders, and reciprocating single-screw mixing extruders that have been introduced to the market in the past two years, and screw vibration continuous mixers , these devices play a very good role in the field of modification. It should be affirmed that mechanical equipment is an important tool for completing mixing and dispersing processes and realizing modification. the

The appearance of the three-screw internal mixing extruder provides a new technical platform for the mixing and dispersion process, because the three screws arranged in an equilateral triangle form a closed space in the central area. Since the screw element has three heads, when the screw rotates In one cycle, on any section of the screw, the area of the central section will change from small to large three times. For example, the area of the section is the smallest at 0°, becomes the largest when it rotates 60°, and then gradually decreases to the smallest at 120°. Such a cycle, such as the screw length neck ratio is 30, when the screw speed is 500 rpm, the number of changes per minute is 30×3×500=45000 times, that is, 45000 pressure pulses. Obviously, the twin-screw has only one meshing point, and the three-screw has three meshing points. In this regard, a three-screw extruder is equivalent to three twin-screw extruders. Shearing, combined with heater heating, will quickly plasticize the material. At the same time, since the compression ratio reaches 43 times each time, it forms a specific super strong function of compacting and dispersing. the

The single screw has no meshing zone, the double screw has one meshing zone, the three-screw arranged in line has two meshing zones, and the three-screw arranged in a triangle has three meshing zones. The increase in the meshing area of the three-screw extruder doubles the rolling area, and the efficient extrusion, crushing, kneading, calendering, and stretching effects are formed on the material during operation. Therefore, every revolution of the screw will increase the times of material mixing, homogenization, kneading and shearing, and the equipment has stronger mixing, melting and dispersing mixing capabilities. It is this efficient mixing effect that makes the three-screw no need The large diameter and large length-to-diameter ratio of single-screw or twin-screw can obtain the production conditions of the same quality and output, which fully reflects the high-efficiency mixing and homogenization characteristics, compact structure and economy of the three-screw extruder. the

With the wide application of blends and the increasing market demand, people's performance requirements for blend materials are also increasing, but most of the components of blends are thermodynamically incompatible and incompatible. The dispersed phase domain of the blend is coarse, the interface between the two phases is weak, the mechanical properties are poor, and the practical value is reduced. However, the microstructure of the product can be improved and the performance of the product can be improved through different processing conditions. the

The mixing and extrusion process of the three-screw blend will inevitably affect the dispersion form of the dispersed phase in the matrix and the interface between the two phases. On the one hand, the high-speed movement of the axial threads of the three-screw dynamic mixing extruder of the blend causes the diffusion and movement of the macromolecular segments, which reduces the macromolecular segments, the mutual entanglement between the segments and the Molecular slip resistance makes molecular unentanglement and orientation easier, the interface area between the dispersed phase and the continuous phase increases, the distribution of dispersed phase particles is more uniform, and the shape is more regular; on the other hand, the three-screw dynamic mixing extrusion of the blend The periodic change of the meshing gap of the extruding screw causes the particles of the dispersed phase in the gap to be vibrated and ground, and the resulting pure extensional flow field is also conducive to the crushing of the dispersed phase, thereby reducing the particle size of the dispersed phase and improving the dispersion and mixing effect . the

The development of melt-blown fiber production technology and the expansion of product application fields have promoted the use of high-performance polymers to meet the special needs of industrial textiles, such as small fiber fineness, high temperature resistance, chemical resistance, good strength and elasticity, Requirements for the comfort of medical products and the safety of contact with food. the

Supercritical fluid refers to a fluid with unique physical properties different from liquid or gas above the critical temperature and critical pressure of a certain substance. It has both the characteristics of gas and the characteristics of liquid. Therefore, it can be said that supercritical fluid It is the third fluid that exists outside the two fluid states of gas and liquid. Supercritical fluid has a density close to that of liquid, so it has a strong solvent strength, and has a viscosity close to that of gas. Its fluidity is much better than that of liquid, and its mass transfer coefficient is much larger than that of liquid. Moreover, the density, solvent strength, viscosity and other properties of the fluid can be adjusted conveniently through the change of pressure and temperature, so it has a wide application prospect. Extraction using supercritical _CO2 has been extensively studied and industrially applied. Although the use of supercritical CO ₂ in polymer processing is not much, it has received considerable attention and extensive research, such as the polymerization reaction of supercritical CO ₂ as the medium, the use of supercritical CO ₂ to add additives to polymers, supercritical CO 2 _CO2 swelling polymerization to obtain blends and composites, polymer fractionation, extraction of oligomers and solvents, preparation of microspheres and microfibrils, crystallization, etc.

The use of supercritical fluids in the preparation of microporous polymers has the following advantages:

(1) The mass transfer coefficient is high, and the equilibrium concentration can be reached in a short time, thus shortening the processing time and making the industrial application of microporous polymer preparation possible.

(2) At the same temperature, a higher equilibrium concentration can be achieved by using supercritical CO ₂ , so higher cell density and smaller cell diameter can be obtained.

(3) Since the supercritical fluid dissolves into the polymer, the viscosity of the polymer can be greatly reduced, thereby reducing the melt blown pressure and improving the fluidity of the melt. the

By changing the temperature or pressure of the supercritical fluid, any density between the gaseous state and the liquid state can be obtained; near the critical point, small changes in pressure and temperature can lead to large changes in density. Since viscosity, dielectric constant, diffusivity, and solvency are all related to density, pressure and temperature can be conveniently adjusted to control the physical and chemical properties of supercritical fluids. The preparation of microporous polymers is mainly based on the gas supersaturation method. The basic process is: firstly, high-pressure gas (CO ₂ and N ₂ ) is dissolved in the polymer to form a polymer/gas saturated system; The nuclei are initiated and grown at the same time; finally, the microporous structure is finalized by methods such as quenching. The improvement of traditional foam physical foaming lies in the strict control of process parameters such as temperature, pressure, and time, so that a large number of gas nuclei can be triggered at the same time without merging into large bubbles, thereby obtaining a microporous structure. The process of preparing microporous polymers by using the principle of supersaturation mainly includes sub-step method, semi-continuous method and continuous methods such as extrusion, injection molding and rotational molding according to the continuous degree of operation. The step-by-step method and the semi-continuous method are mainly used in theoretical research because the time required to form a polymer/gas saturated system is determined by the diffusion rate of gas to the polymer matrix, so it takes a long time and cannot meet the needs of industrial production. The emergence of the continuous method consistent with the actual three-screw mixer extruder melt-blowing process makes the practical application of microporous LiFePO ₄ /C fibers possible. The mechanical properties of microporous LiFePO ₄ /C fibers mainly depend on the microporous structure (including: pore size, pore density, pore distribution, and pore orientation) and molecular chain orientation. By optimizing the process and controlling the microporous structure and molecular chain orientation, microporous LiFePO ₄ /C fibers with excellent performance can be obtained.

Contents of the invention

The purpose of the present invention is to provide a method for preparing microporous LiFePO ₄ /C ultrafine fibers by spinning with a three-screw banburying extruder, so as to meet the needs of lithium battery-based textile, electrical, electronic, mechanical, medical, chemical, The needs of related fields such as food and aerospace.

To achieve the above object, the technical scheme adopted in the present invention is as follows:

The method for preparing microporous LiFePO ₄ /C fibers by spinning with a three-screw banburying extruder of the present invention is characterized in that it comprises the following steps:

(1) Weigh the iron source: lithium source: reducing agent: carbon source: complexing agent in a molar ratio of 0.8~1.2:0.8~1.2:0.8~1.2:0.4~0.6:0.1~0.3, and introduce it into the three-screw Banbury extruder mixes and obtains blend;

(2) Introduce the supercritical fluid into the three-screw banburying extruder to mix with the above-mentioned blend and maintain the pressure at 7-17 MPa, so that the blend reacts in the supercritical fluid, and then compacts through the screw compression section and gradually into a homogeneous body;

(3) In the filter part, the homogeneous body passes through the filter medium to filter out impurities and catalysts remaining after polymerization;

(4) In the metering pump part, the homogeneous body is metered by the gear metering pump to precisely control the fiber fineness and uniformity;

(5) The homogeneous body is extruded from the spinneret hole of the die head through the entrance area of the melt blown die head, the hole flow area and the puffing area;

(6) When the homogeneous solid stream extruded from the spinneret hole of the die head expands due to the sudden drop in ambient pressure, it is drawn by the high-speed hot air flow on both sides, and the melt stream in a viscous flow state At the same time, the air at room temperature on both sides is mixed with the drafting hot air flow, so that the melt stream is cooled and solidified to form ultra-fine microporous fibers;

(8) After natural cooling, the obtained fibers are placed in a calciner, and pre-calcined at 250-400 ° C for 4-6 hours in a mixed gas flow atmosphere with a volume fraction of 5% H ₂ gas and 95% N ₂ gas, and then Calcined at 600° C. for 9-11 hours in the above-mentioned mixed air flow atmosphere, and cooled down to room temperature with the furnace to obtain LiFePO ₄ /C ultrafine microporous fibers.

The iron sources mentioned are FePO ₄ ·2H ₂ O, Fe(NO ₃ ) ₃ ·9H ₂ O, ferrous oxalate, ferrous acetate, Fe ₂ O ₃ , etc., but not limited thereto.

The Li source is LiH ₂ PO ₄ , Li ₂ CO ₃ , LiNO _{3 ,} etc., but not limited thereto.

The carbon source is polypropylene, sucrose, PVA or PVP, etc., but not limited thereto. the

The complexing agent is NH ₄ H ₂ PO ₄ , glycine, etc., but not limited thereto.

The supercritical fluid is supercritical N _{2 ,} H ₂ O or supercritical CO ₂ .

When the supercritical fluid is supercritical _N2 , its temperature is 50-380°C, its pressure is 7-40MPa, and the mass ratio of supercritical _N2 to the blend is 1:400-1:10.

When the supercritical fluid is supercritical H ₂ O, its temperature is 330-380° C., its pressure is 19-24 MPa, and the mass ratio of supercritical H ₂ O to the blend is 1:80-1:30.

When the supercritical fluid is supercritical CO ₂ , its temperature is 50-380° C., its critical pressure is 7-40 MPa, and the mass ratio of supercritical CO ₂ to the blend is 1:100-1:10.

The pressure difference between the homogeneous body and the outside is 7-40 MPa, and the melt blowing rate is 10-2000 cm ³ /s.

The advantages of the present invention are remarkable, and the method for preparing polymer microporous LiFePO4/C fibers by spinning with a three-screw banbury extruder of the present invention can produce ultrafine (20-90000nm) microporous LiFePO4/C fibers fiber. The advantages of the present invention are remarkable, and the method for preparing polymer microporous LiFePO4/C fibers by spinning with a three-screw banbury extruder of the present invention can produce ultrafine (20-90000nm) microporous LiFePO4/C fibers fiber. The prepared microporous LiFePO4/C fibers can meet the needs of lithium battery-based textiles, electrical, electronic, mechanical, medical, chemical, food, aerospace and other related fields. the

Description of drawings

Figure 1 is a schematic diagram of the method for preparing microporous LiFePO ₄ /C fibers by supercritical fluid melt-blown spinning.

Detailed ways

Below in conjunction with specific embodiment, further illustrate the present invention. the

Example 1

Weigh Fe(NO ₃ ) ₃ 9H ₂ O: LiNO ₃ : NH ₄ H ₂ PO ₄ : sucrose: PVA(PVP) at a molar ratio of 0.8:0.8:0.8~1.2:0.4:0.1, and introduce it into the three-screw banburying The extruder is mixed to obtain a blend; the supercritical fluid with a temperature of 50-380 ° C and a pressure of 7-40 MPa is introduced into the three-screw internal mixer extruder to mix with the above blend and maintain a certain pressure (7-17 MPa) , the mass ratio of supercritical _CO2 to the blend is 1:100~1:10. The blend is synthesized by reaction in a supercritical fluid. Then it is compacted by the screw compression section and gradually becomes a homogeneous body; the homogeneous body should pass through the filter medium to filter out impurities and residual catalyst after polymerization. The homogeneous body is metered by a gear metering pump to precisely control the fineness and uniformity of the fibers. As shown in Figure 1, the arrow A in the figure indicates the injection direction of the homogeneous mixture melt, the arrow B indicates the flow direction of the hot air for drawing, and the arrow C indicates the flow direction of the cold air. The homogeneous body is extruded from the spinneret hole of the melt blowing die through the entrance zone 1, the hole flow zone 2 and the puffing zone 3, and the melt blowing rate is 10-2000 cm ³ /s. The homogeneous body thin stream extruded from the spinneret hole of the die head expands due to the sudden drop in ambient pressure, and at the same time is drawn by the high-speed hot air flow at 290-320 °C on both sides, and the melt thin stream in a viscous flow state The stream is drawn down rapidly. At the same time, the air at room temperature on both sides is mixed with the drafting hot air flow, so that the melt stream is cooled and solidified to form ultra-fine microporous fibers. The above fibers are calcined to obtain LiFePO ₄ /C fibers, and the LiFePO ₄ /C fibers can be directly used as lithium battery cathode materials.

Example 2

Weigh Fe(NO ₃ ) ₃ 9H ₂ O : LiNO ₃ : NH ₄ H ₂ PO ₄ : sucrose: PVA(PVP) at a molar ratio of 1.2:1.2:1.2:0.6:0.3, and import into three-screw banburying extrusion Machine mixing to obtain a blend; 80 ° C, 16 MPa supercritical CO ₂ supercritical fluid into the three-screw mixer extruder to mix with the above blend and maintain a certain pressure (7-17 MPa), supercritical CO ₂ The mass ratio to the blend is 1:100~1:10. The blend is synthesized by reaction in a supercritical fluid. Then it is compacted by the screw compression section and gradually becomes a homogeneous body; the homogeneous body should pass through the filter medium to filter out impurities and catalysts remaining after polymerization; the homogeneous body is measured by a gear metering pump for melt measurement to precisely control fiber fineness. degree and uniformity; the homogeneous body is extruded from the die spinneret hole through the melt-blown die head entrance area, hole flow area and puffing area; the homogeneous body fine flow extruded from the die head spinneret hole is suddenly While reducing the expansion and expansion, the melt stream in the viscous state is rapidly thinned by the drafting of the high-speed hot air flow on both sides. At the same time, the air at room temperature on both sides is mixed with the drafting hot air flow, so that _the melt stream is cooled and solidified to form ultra-fine microporous fibers; the above fibers are calcined to obtain LiFePO ₄ /C fibers, which can be used directly. C fiber is used as the positive electrode material of lithium battery.

Example 3

Weigh Fe(NO ₃ ) ₃ 9H ₂ O: LiNO ₃ : NH ₄ H ₂ PO ₄ : sucrose: PVA(PVP) at a molar ratio of 0.8:0.8:0.8~1.2:0.4:0.1, and introduce it into the three-screw banburying The extruder is mixed to obtain a blend; the supercritical fluid of 50 ° C and 7 MPa supercritical N ₂ is introduced into the three-screw mixer extruder to mix with the above blend and maintain a certain pressure (7-17 MPa), supercritical N The mass ratio of ₂ to the blend is 1:100~1:10. The blend is synthesized by reaction in a supercritical fluid. Then it is compacted by the screw compression section and gradually becomes a homogeneous body; the homogeneous body should pass through the filter medium to filter out impurities and residual catalyst after polymerization. The homogeneous body is metered by a gear metering pump to precisely control the fineness and uniformity of the fibers. The homogeneous body is extruded from the spinneret hole of the die head through the entrance area of the melt blown die head, the hole flow area and the puffing area. While the homogeneous solid stream extruded from the spinneret hole of the die head expands due to the sudden drop in ambient pressure, it is drawn by the 290°C high-speed hot air flow on both sides, and the melt stream in a viscous flow state is drawn Thin quickly. At the same time, the air at room temperature on both sides is mixed with the drafting hot air flow, so that the melt stream is cooled and solidified to form ultra-fine microporous fibers. The above fibers are calcined to obtain the LiFePO ₄ /C target product, and the LiFePO ₄ /C can be directly used as the positive electrode material of the lithium battery.

Example 4

Weigh Fe(NO ₃ ) ₃ 9H ₂ O : LiNO ₃ : NH ₄ H ₂ PO ₄ : sucrose: PVA(PVP) at a molar ratio of 1.2:1.2:1.2:0.6:0.3, and introduce it into a high-pressure liner Mix evenly in the reactor. Import into a three-screw banburying extruder and mix to obtain a blend; introduce a supercritical fluid of 80 °C and 16 MPa supercritical N into a three _- screw banbury extruder to mix with the above blend and maintain a certain pressure (7-17 MPa), the mass ratio of supercritical N ₂ to the blend is 1:100~1:10. The blend is synthesized by reaction in a supercritical fluid. Then it is compacted by the screw compression section and gradually becomes a homogeneous body; the homogeneous body should pass through the filter medium to filter out impurities and catalysts remaining after polymerization; the homogeneous body is measured by a gear metering pump for melt measurement to precisely control fiber fineness. degree and uniformity; the homogeneous body is extruded from the die spinneret hole through the melt-blown die head entrance area, hole flow area and puffing area; the homogeneous body fine flow extruded from the die head spinneret hole is suddenly While reducing the expansion and expansion, the melt stream in the viscous state is rapidly thinned by the drafting of the high-speed hot air flow on both sides. At the same time, the air at room temperature on both sides is mixed with the drafting hot air flow, so that the melt stream is cooled and solidified to form ultra-fine microporous fibers; the above fibers are calcined to obtain LiFePO ₄ /C ultra-fine fibers, and the LiFePO 4 /C ultra-fine fibers can be directly used ₄ /C superfine fiber is used as the positive electrode material of lithium battery.

Claims (6)

1. A method for preparing microporous LiFePO ₄ /C fibers by spinning with a three-screw banburying extruder, characterized in that: comprise the steps: (1) Weigh iron source: lithium source: reducing agent: carbon source: complexing agent with a molar ratio of 0.8~1.2: 0.8~1.2: 0.8~1.2: 0.4~0.6: 0.1~0.3, and introduce it into the three-screw Banbury extruder mixes and obtains blend; (2) Introduce the supercritical fluid into the three-screw banburying extruder to mix with the above-mentioned blend and maintain the pressure at 7-17 MPa, so that the blend reacts in the supercritical fluid; then compact it through the screw compression section and gradually into a homogeneous body; (3) In the filter part, the homogeneous body passes through the filter medium to filter out impurities and catalysts remaining after polymerization; (4) In the metering pump part, the homogeneous body is metered by the gear metering pump to precisely control the fiber fineness and uniformity; (5) The homogeneous body is extruded from the spinneret hole of the die head through the entrance area of the melt blown die head, the hole flow area and the puffing area; (6) While the homogeneous thin stream extruded from the spinneret hole of the die head expands due to the sudden drop in ambient pressure, it is drawn by the high-speed hot air flow on both sides, and the thin melt stream in a viscous flow state is drawn Rapid thinning; at the same time, the air at room temperature on both sides is mixed with the drafting hot air flow, so that the melt stream is cooled and solidified to form ultra-fine microporous fibers; (7) After natural cooling, the obtained fibers are placed in a calciner, and pre-calcined at 250-400 ° C for 4-6 hours in a mixed gas flow atmosphere with a volume fraction of 5% H ₂ gas and 95% N ₂ gas, and then Calcined at 600°C for 9-11 hours in the above-mentioned mixed air flow atmosphere, and cooled to room temperature with the furnace to obtain LiFePO ₄ /C ultrafine microporous fibers; The pressure difference between the homogeneous body and the outside is 7-40 MPa, and the melt blowing rate is 10-2000 cm ³ /s. 2. the method for preparing microporous LiFePO ₄ /C fibers by spinning with a three-screw banburying extruder according to claim 1, characterized in that: the iron source is FePO _{2H 2} O, Fe(NO _{3 )} One of 3.9H ₂ O, ferrous oxalate, ferrous acetate or Fe ₂ O ₃ ; the Li source is one of LiH ₂ PO ₄ , Li ₂ CO ₃ or LiNO ₃ ; The carbon source is any one of polypropylene, sucrose, PVA or PVP; The complexing agent is NH ₄ H ₂ PO ₄ or glycine. 3. The method for preparing microporous LiFePO ₄ /C fibers by spinning with a three-screw banburying extruder according to claim 1 or 2, characterized in that: the supercritical fluid is supercritical N ₂ , supercritical H ₂ O or supercritical CO ₂ . 4. the application three-screw banbury extruder spinning according to claim 3 prepares the method for microporous _LiFePO4 /C type fiber, it is characterized in that: described supercritical fluid is supercritical N _When , its temperature is 50~380℃, the pressure is 7~40MPa, the mass ratio of supercritical _N2 to the blend is 1:400-1:10. 5. the method for preparing microporous LiFePO ₄ /C fibers by spinning with a three-screw banburying extruder according to claim 3, characterized in that: when the supercritical fluid is supercritical H ₂ O, its temperature The temperature is 330~380℃, the pressure is 19~24MPa, and the mass ratio of supercritical H ₂ O to the blend is 1:80-1:30. 6. the application three-screw banbury extruder spinning according to claim 3 prepares the method for microporous LiFePO ₄ /C type fiber, it is characterized in that: described supercritical fluid is supercritical CO _When , its temperature is 50~380℃, the critical pressure is 7~40MPa, and the mass ratio of supercritical CO ₂ to the blend is 1:100~1:10.