Phosphorus-doped porous carbon / silicon composite negative electrode material and preparation method thereof

Abstract

The invention provides a phosphorus-doped porous carbon / silicon composite negative electrode material and a preparation method thereof, and belongs to the technical field of new energy battery electrode materials. The preparation method comprises the following steps: preparing dextrin into a homogeneous solution; adding a phytic acid solution to construct a hydrogen bond cross-linked network; melamine is introduced for dissolution; adding sodium chloride for dispersion to obtain a mixed solution; transferring the mixed solution into a reaction kettle, forming a microsphere primary blank through thermally-driven self-assembly, and filtering and washing to obtain a hydrothermal product; heating and carbonizing the hydrothermal product in a nitrogen atmosphere, cooling, washing to remove the sodium chloride template, and performing vacuum drying to obtain the nitrogen and phosphorus co-doped porous carbon microspheres. Adding the nitrogen and phosphorus co-doped porous carbon microspheres and red phosphorus into a quartz tube, vacuumizing and sealing, and carrying out staged gas phase loading to obtain red phosphorus loaded carbon microspheres; and mixing the red phosphorus loaded carbon microspheres with silicon nanoparticles and dextrin in an ethanol medium, performing ball milling, performing spray drying, and performing gas-phase carbon coating to obtain the phosphorus-doped porous carbon / silicon composite negative electrode material.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of new energy battery electrode materials, in particular to a phosphorus-doped porous carbon / silicon composite negative electrode material and a preparation method thereof. BACKGROUND

[0002] Lithium ion batteries are widely used in various electronic devices due to their high energy density, high working voltage, and long cycle stability. Among various negative electrode materials, phosphorus-based negative electrode materials have become an important research direction for achieving high energy density and high rate performance in the future due to their high theoretical specific capacity, excellent rate performance, and relatively low cost.

[0003] Elemental phosphorus mainly has three allotropes: white phosphorus, black phosphorus, and red phosphorus. Black phosphorus is difficult to prepare and expensive, white phosphorus is extremely unstable in air and difficult to handle, while red phosphorus is not only low in price, excellent in lithium storage performance, and relatively stable. However, as an insulator of electrons and ions, it cannot be directly used as an electrode active material. Therefore, how to overcome the insulating property of red phosphorus, fully utilize its low cost and high lithium storage capacity, and develop a lithium ion battery negative electrode material based on red phosphorus is of great significance for the research and development of lithium ion batteries. SUMMARY

[0004] To solve the problems mentioned in the background, the present application provides a preparation method of a phosphorus-doped porous carbon / silicon composite negative electrode material, which produces a deep synergistic effect in microstructure, conductive network, and interface chemistry of silicon, phosphorus, and carbon. Finally, a battery negative electrode material with high specific capacity, excellent rate performance, and ultra-long cycle life is successfully prepared.

[0005] Specifically, A preparation method of a phosphorus-doped porous carbon / silicon composite negative electrode material, comprising the following steps: Step 1: 100-120 parts by mass of dextrin is added to 300-400 parts of deionized water to prepare a homogeneous solution; 60-65 parts of phytic acid solution is added to build a hydrogen bond crosslinking network under controlled conditions; 40-45 parts of melamine is introduced to control the dissolution under controlled conditions; 150-170 parts of sodium chloride is added to control the dispersion under controlled conditions, and a mixed solution is obtained; Step 2: The mixed solution obtained in step 1 is transferred to a reaction kettle, and a microsphere embryo is formed by heat-driven self-assembly under controlled conditions. After filtration and washing, a hydrothermal product is obtained; Step 3: The hydrothermal product is carbonized under nitrogen atmosphere, and after cooling, the sodium chloride template is removed by washing, and vacuum drying is performed to obtain nitrogen and phosphorus co-doped porous carbon microspheres; Step 4, take 100-120 parts of the nitrogen and phosphorus co-doped porous carbon microspheres obtained in step 3 and 80-85 parts of red phosphorus, add them to a quartz tube, vacuum seal, and control the conditions to obtain red phosphorus loaded carbon microspheres by stage-by-stage gas phase loading; Step 5, take 100-120 parts of the red phosphorus loaded carbon microspheres obtained in step 4, mix them with 15-16 parts of silicon nanoparticles and 5-5.5 parts of dextrin in 200-250 parts of an ethanol medium, ball mill, spray dry, and then heat solidify the dextrin to form microspheres, and then perform gas phase carbon coating on the composite particles to obtain a phosphorus doped porous carbon / silicon composite negative electrode material.

[0006] Further, the phytic acid solution in step 1 is a 50%-55% mass fraction aqueous phytic acid solution.

[0007] Further, after adding the phytic acid solution in step 1, heat to 55-65°C, and react for 30-40 min to construct a hydrogen bond crosslinking network; after adding the melamine, heat to 80-85°C and stir for 1-1.5 h until completely dissolved; after adding the sodium chloride, control the stirring rate to 5000-6000 rpm, and stir for 10-15 min until completely dispersed.

[0008] Further, in step 2, control the filling degree to be ≤70% when transferring the mixed solution to the reaction kettle; heat to 220-230°C at a rate of 5°C, and keep the temperature for 12-14 h, and then cool to 80°C to discharge, vacuum filter, and wash with 80°C deionized water for 3-5 times.

[0009] Further, in step 3, the temperature increasing and carbonizing process is a gradient temperature increasing process, first heat to 300°C at a rate of 5°C, keep the temperature for 1 h, then heat to 750°C at a rate of 3°C, keep the temperature for 2 h; after cooling to room temperature, wash with deionized water to remove the sodium chloride template; the temperature of the vacuum drying process is controlled to be 80°C, and the drying time is 12 h.

[0010] Further, in step 4, the stage-by-stage gas phase loading process includes: stage 1, heat to 416°C at a rate of 10°C / min, keep the temperature for 4 h; stage 2, cool to 260°C at a rate of 5°C / min, keep the temperature for 8 h; stage 3, cool to <60°C in the furnace, and then break the vacuum.

[0011] Further, in step 4, when vacuum sealing, the length of the quartz tube is left with an expansion space of 30%-33%.

[0012] Further, in step 5, the spray drying control conditions are an inlet temperature of 180-190°C, an outlet temperature of 70-80°C, and a powder particle size of 8-15 μm.

[0013] Further, in step 5, the gas phase carbon coating control conditions are that the carbon source is selected from acetylene, the temperature is 650-660°C, and the treatment time is 1-1.2 h.

[0014] The application further provides the phosphorus-doped porous carbon / silicon composite negative electrode material prepared by the preparation method.

[0015] Compared with the prior art, the application has the beneficial features that: 1. The application constructs a "core-shell-bridge" three-level composite structure, three-dimensional porous nitrogen and phosphorus co-doped carbon microspheres as the core framework, the internal through porous structure provides sufficient space for the loading of red phosphorus, and the red phosphorus is firmly anchored through the strong P-C covalent bond, effectively buffering the volume expansion of red phosphorus in the cycle and preventing the active material from pulverizing and falling off. Meanwhile, the carbon framework also serves as a dispersion matrix, uniformly limiting the silicon nanoparticles on its surface and in its pores, greatly relieving the volume effect of the silicon material. The physical confinement effect of the carbon framework and the chemical bonding effect of the P-C bond cooperate to ensure the integrity of the electrode structure in long-period cycling, thereby realizing high specific capacity while ensuring cycle stability.

[0016] Synergistic mechanism: first, the three-dimensional porous carbon microspheres constructed by the sodium chloride template method have internal nanoscale channels that are mutually connected, providing a preset space for the storage of red phosphorus. When the red phosphorus is filled into these channels by the gas deposition method, the volume expansion in the charge and discharge process will be limited and constrained by the hard carbon wall, thereby converting the macroscopic volume change into local stress in the microcavity, avoiding the pulverizing destruction of the entire electrode. Secondly, pure physical contact will fail due to stress fatigue in long-term cycling, and in the gas loading stage, the application promotes the chemical reaction between the gaseous molecules and the defect carbon atoms (introduced by nitrogen doping or mechanical ball milling) at the edge of the carbon framework through the annealing process, forming a strong P-C covalent bond, and the introduction of nitrogen atoms can promote the adsorption of phosphorus atoms by the carbon matrix. This upgrades the red phosphorus and the carbon framework from "physical adsorption" to "chemical anchoring", greatly enhancing the bonding energy of the interface and effectively preventing the shedding and loss of the active material in the cycle. Finally, in the silicon-carbon composite stage, the hydroxyl groups (-OH) on the surface of the dextrin as a biological binder and the hydroxyl groups in the oxide layer (SiO2) on the surface of the silicon nanoparticles undergo dehydration condensation reaction to form a Si-O-C covalent bond bridge. This makes the silicon particles and the carbon microspheres no longer have simple mechanical contact, but achieve firm chemical connection, ensuring efficient transmission of electrons and ions between the interfaces and inhibiting the agglomeration of the silicon particles.

[0017] 2、The present application constructs a high-efficiency three-dimensional network for the rapid transmission of electrons and ions through the multi-level structure of the material. The nitrogen and phosphorus co-doped carbon skeleton significantly improves the intrinsic electronic conductivity. The nitrogen doping provides abundant free electrons, and the phosphorus doping expands the carbon layer spacing, promoting the embedding and extraction of lithium ions. Subsequently, the thin layer of amorphous carbon coated by chemical vapor deposition further forms a continuous and strong conductive network outside the composite particles, greatly reducing the interface impedance and polarization of the electrode. The internal doping modification and external uniform coating work together to ensure that electrons and ions can quickly reach every active site under high-rate charging and discharging conditions, thereby giving the material excellent rate performance.

[0018] Synergistic mechanism: First, the doping behavior of nitrogen and phosphorus atoms in the carbon lattice has a synergistic effect. Nitrogen atoms have a stronger attraction to electrons than carbon atoms, and doping will make the adjacent carbon atoms carry partial positive charges, which is more conducive to adsorbing lithium ions and reducing the migration energy barrier. At the same time, the incorporation of phosphorus atoms will expand the carbon layer spacing, providing a more spacious "channel" for the embedding and extraction of lithium ions, and improving the ionic conductivity. Together, they optimize the charge transport capability of the carbon skeleton itself. Second, the thin layer of amorphous carbon deposited by vapor deposition is like a conductive outer layer wrapped around each composite particle, and all the particles are "welded" into a continuous conductive whole. This greatly reduces the contact resistance between particles, ensuring that electrons can quickly transport to every active particle, especially at high-rate discharge, where this effect is crucial.

[0019] 3、The present application optimizes the interface between the electrode material and the electrolyte. The carbon coating layer deposited by vapor deposition greatly reduces the specific surface area of the composite material, reducing the contact surface with the electrolyte and effectively inhibiting the excessive growth of the solid-state electrolyte interface film (SEI), significantly improving the first coulombic efficiency. Second, the strong P-C and Si-O-C bonds prevent red phosphorus and silicon from falling off the carbon base during the cycling process, preventing the continuous exposure of fresh interfaces and the repeated rupture and reconstruction of the SEI film, ensuring the stability of the interface film. The synergistic effect of the two ensures the stability of the interface state during long-term cycling of the battery, which is the key to long life. In addition, nitrogen doping changes the electron cloud distribution of the surrounding carbon atoms, making them exhibit electron deficiency (positive charge). The gas-phase molecules will undergo bond polarization during heating, exhibiting a certain negative charge. According to the Lewis acid-base theory, there is a strong adsorption between the electron-deficient carbon sites (Lewis Acid) and the electron-rich phosphorus species (Lewis Base). This force makes molecules more inclined to concentrate near the defect sites of the carbon skeleton, creating a favorable local high-concentration environment and driving force for the subsequent chemical reaction to form P-C bonds. DETAILED DESCRIPTION

[0020] In order to make the purposes, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below in conjunction with the embodiments of the present application. Obviously, the described embodiments are some embodiments but not all of the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the protection scope of the present application.

[0021] In order to facilitate those skilled in the art to implement the present application, some reagents used in the examples and comparative examples will be described as follows: Dextrin: Zhengzhou Yinhe Dextrin Co., Ltd. Phytic acid: Nanjing Songguan Biological Technology Co., Ltd. Melamine: Shandong Han Yue Chemical Co., Ltd. Sodium chloride: Taizhou Bai Chuan Chemical Co., Ltd. Silicon nanoparticles: 40-60 nm, Zhongnuo New Material (Beijing) Technology Co., Ltd. Acetylene: Qingdao Fuda Gas Co., Ltd.

[0022] Example 1 A phosphorus-doped porous carbon / silicon composite negative electrode material, the preparation steps of which comprise: Step 1: 100 parts of dextrin is added to 300 parts of deionized water to stir at a speed of 300 rpm until transparent, to configure a homogeneous solution; 60 parts of a 50% mass fraction phytic acid solution is added, heated to 55°C, and reacted for 30 min to build a hydrogen bond crosslinking network; 40 parts of melamine is introduced, heated to 80°C, and stirred for 1 h until completely dissolved; 150 parts of sodium chloride is added, stirred at 5000 rpm for 15 min, and high-speed shearing is dispersed to obtain a mixed solution; Step 2: The mixed solution obtained in step 1 is transferred to a reaction kettle, the filling degree is 70%, heated to 220°C at a rate of 5°C, and kept for 12 h, then cooled to 80°C to discharge, to form microsphere initial embryo by heat-driven self-assembly; vacuum suction filtration is performed, and the hydrothermal product is washed with 80°C deionized water for 3 times to obtain a hydrothermal product; Step 3: The hydrothermal product is first heated to 300°C at a rate of 5°C under a nitrogen atmosphere (200 mL / min), kept for 1 h to remove bound water; then heated to 750°C at a rate of 3°C, kept for 2 h to carbonize / activate; after cooling to room temperature, the sodium chloride template is removed by washing with deionized water until the conductivity of the filtrate is <10 μS / cm; vacuum drying at 80°C for 12 h to obtain nitrogen and phosphorus co-doped porous carbon microspheres; Step 4: 100 parts of the nitrogen and phosphorus co-doped porous carbon microspheres obtained in step 3 and 80 parts of red phosphorus are added to a quartz tube (diameter 50 mm), vacuumed to 10 -3Sealing at about 400 Pa, leaving 30% expansion space; phase 1, heating to 416℃ at 10℃ / min, holding for 4 h; phase 2, cooling to 260℃ at 5℃ / min, holding for 8 h; phase 3, cooling to 59℃ in the furnace, then breaking the vacuum, to obtain red phosphorus loaded carbon microspheres; Step 5, 100 parts of the red phosphorus loaded carbon microspheres obtained in step 4 were mixed with 15 parts of silicon nanoparticles and 5 parts of dextrin in 200 parts of an ethanol medium for ball milling at a speed of 350 rpm for 3 h; then the dextrin was heat cured to form microspherical composite particles after spray drying, with the control conditions for spray drying being an inlet temperature of 180℃, an outlet temperature of 70℃, and a powder particle size of 8-15 μm; the composite particles were placed in a CVD furnace, acetylene (20 mL / min) and nitrogen (200 mL / min) were introduced, and treatment was carried out at 650℃ for 1 h, with the thickness of the deposited carbon layer being controlled at about 5 nm, to obtain a phosphorus doped porous carbon / silicon composite negative electrode material.

[0023] Example 2 A phosphorus doped porous carbon / silicon composite negative electrode material, the preparation steps of which include: Step 1, 120 parts of dextrin were added to 400 parts of deionized water to be stirred at a speed of 300 rpm until transparent, to configure a homogeneous solution; 65 parts of a 55% phytic acid solution were added, heated to 65℃, and reacted for 40 min to construct a hydrogen bond crosslinking network; 45 parts of melamine were introduced, heated to 85℃, and stirred for 1.5 h until completely dissolved; 170 parts of sodium chloride were added, stirred at a speed of 6000 rpm for 15 min, and high-speed shearing dispersion was carried out, to obtain a mixed solution; Step 2, the mixed solution obtained in step 1 was transferred to a reaction kettle, the filling degree was 65%, heating was carried out at a rate of 5℃ to 230℃, and holding was carried out for 14 h, then cooling was carried out to 80℃ to discharge, and microspherical embryos were formed by heat driven self-assembly, the hydrothermal product was obtained by vacuum suction filtration and washing with 80℃ deionized water for 5 times; Step 3, the hydrothermal product was first heated to 300℃ at a rate of 5℃ under a nitrogen atmosphere (200 mL / min), holding for 1 h to remove bound water; then heating was carried out to 750℃ at a rate of 3℃, holding for 2 h for carbonization / activation; after cooling to room temperature, the sodium chloride template was removed by washing with deionized water until the conductivity of the filtrate was <10 μS / cm; vacuum drying was carried out at 80℃ for 12 h, to obtain nitrogen and phosphorus co-doped porous carbon microspheres; Step 4, 120 parts of the nitrogen and phosphorus co-doped porous carbon microspheres obtained in step 3 were added to a quartz tube (diameter 50 mm) together with 85 parts of red phosphorus, vacuum was applied to 10 -3Pa sealing, leaving 33% expansion space; staged vapor loading, stage 1, heating to 416℃ at 10℃ / min, holding for 4 h; stage 2, cooling to 260℃ at 5℃ / min, holding for 8 h; stage 3, cooling to 55℃ in the furnace, then breaking the vacuum, to obtain red phosphorus loaded carbon microspheres; Step 5, 120 parts of the red phosphorus loaded carbon microspheres obtained in step 4 were mixed with 16 parts of silicon nanoparticles and 5.5 parts of dextrin in 250 parts of an ethanol medium and ball-milled at a speed of 350 rpm for 3 h; then, after spray drying, the dextrin was heat cured to form microspherical composite particles, the spray drying control conditions being an inlet temperature of 190℃ and an outlet temperature of 80℃, and the powder particle size being 8-15 μm; the composite particles were placed in a CVD furnace, acetylene (20 mL / min) and nitrogen (200 mL / min) were introduced, and the temperature was raised to 660℃ and maintained for 1.2 h, to obtain a phosphorus-doped porous carbon / silicon composite negative electrode material, with a carbon layer thickness of about 5 nm.

[0024] Example 3 A phosphorus-doped porous carbon / silicon composite negative electrode material, the preparation steps of which include: Step 1, 110 parts of dextrin were added to 350 parts of deionized water to form a homogeneous solution by stirring at a speed of 300 rpm until transparent; 65 parts of a 55% phytic acid solution were added, heated to 60℃, and reacted for 35 min to construct a hydrogen bond crosslinking network; 45 parts of melamine were introduced, heated to 85℃, and stirred for 1.5 h until completely dissolved; 160 parts of sodium chloride were added, stirred at a speed of 5500 rpm for 10 min, and high-speed shearing was performed to obtain a mixed solution; Step 2, the mixed solution obtained in step 1 was transferred to a reaction kettle, the filling degree was 68%, the temperature was raised to 225℃ at a rate of 5℃ / min, and held for 12 h; then, the temperature was cooled to 80℃ and the product was discharged, to form a microsphere precursor by heat-driven self-assembly; the product was washed with 80℃ deionized water 4 times, and a hydrothermal product was obtained; Step 3, the hydrothermal product was first heated to 300℃ at a rate of 5℃ / min under a nitrogen atmosphere (200 mL / min), held for 1 h, and then heated to 750℃ at a rate of 3℃ / min, held for 2 h, to carbonize / activate; after cooling to room temperature, the product was washed with deionized water to remove the sodium chloride template, until the conductivity of the filtrate was <10 μS / cm; the product was vacuum dried at 80℃ for 12 h, to obtain nitrogen and phosphorus co-doped porous carbon microspheres; Step 4, 110 parts of the nitrogen and phosphorus co-doped porous carbon microspheres obtained in step 3 were added to a quartz tube (diameter 50 mm) together with 85 parts of red phosphorus, vacuumed to 10 -3Pa sealing, leaving 30% expansion space; gas phase loading in stages, stage 1, heating to 416℃ at 10℃ / min, holding for 4 h; stage 2, cooling to 260℃ at 5℃ / min, holding for 8 h; stage 3, cooling to 55℃ in the furnace, then breaking the vacuum, to obtain red phosphorus-loaded carbon microspheres; Step 5, 110 parts of the red phosphorus-loaded carbon microspheres obtained in step 4 were mixed with 15 parts of silicon nanoparticles and 5 parts of dextrin in 230 parts of an ethanol medium and ball-milled at a speed of 350 rpm for 3 h; then the dextrin was heat-cured to form microspherical composite particles after spray drying, the spray drying control conditions were an inlet temperature of 185℃ and an outlet temperature of 75℃, and the powder particle size was 8-15 μm; the composite particles were placed in a CVD furnace, acetylene (20 mL / min) and nitrogen (200 mL / min) were introduced, and the particles were treated at 650℃ for 1 h, the thickness of the deposited carbon layer was controlled at about 5 nm, and a phosphorus-doped porous carbon / silicon composite negative electrode material was obtained.

[0025] Comparative Example 1 A negative electrode material, the preparation steps of which include: mixing 85 parts of red phosphorus with 15 parts of silicon nanoparticles and 5 parts of dextrin in 230 parts of an ethanol medium and ball-milling at a speed of 350 rpm for 3 h; then heat-curing the dextrin to form microspherical composite particles after spray drying, the spray drying control conditions were an inlet temperature of 185℃ and an outlet temperature of 75℃, and the powder particle size was 8-15 μm; the composite particles were placed in a CVD furnace, acetylene (20 mL / min) and nitrogen (200 mL / min) were introduced, and the particles were treated at 650℃ for 1 h, the thickness of the deposited carbon layer was controlled at about 5 nm, and a phosphorus-doped porous carbon / silicon composite negative electrode material was obtained.

[0026] The negative electrode materials obtained in Examples 1-3 and Comparative Example 1 were applied to batteries for performance testing.

[0027] Battery assembly: the negative electrode material, conductive agent (SP), CMC and SBR were mixed in a mass ratio of 95:1.5:1.5:2, coated on a copper foil to obtain a negative electrode sheet. The positive electrode active material lithium cobaltate, conductive agent (SP) and PVDF were mixed in a mass ratio of 96.5:2:1.5, coated on an aluminum foil to obtain a positive electrode sheet. The electrolyte was 1 mol / L LiPF6+EC+EMC, and the separator was a polyethylene / propylene composite microporous membrane. They were assembled into batteries, and the electrochemical performance of each group of batteries was tested on a Wuhan LanDian CT2001A battery tester.

[0028] The electrochemical performance test results are shown in Table 1 below: Table 1 Performance sample Initial discharge specific capacity, mAh / g Initial coulombic efficiency Capacity retention after 1 C cycling for 1000 cycles 5C rate capacity (vs. 0.1 C) Example 1 1508 83% 80% 75% Example 2 1479 82% 80% 77% Example 3 1493 83% 81% 75% Comparative Example 1 1332 74% 6% 11% According to the test results in the above table, although the first discharge specific capacity of Examples 1-3 is lower than that of Comparative Example 1, the battery stability and life of Examples 1-3 are found to be longer in the subsequent tests.

[0029] Finally, it should be noted that the above examples are only used to illustrate the technical solutions of the present application, and are not intended to limit the present application; although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that the technical solutions recorded in the foregoing examples can still be modified, or some or all of the technical features can be replaced by equivalents; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for preparing a phosphorus-doped porous carbon / silicon composite negative electrode material, characterized in that: The steps include: Step 1: adding 100 to 120 parts by mass of dextrin to 300 to 400 parts of deionized water to prepare a homogeneous solution; adding 60 to 65 parts of phytic acid solution and controlling the conditions to construct a hydrogen bond cross-linking network; introducing 40 to 45 parts of melamine and controlling the conditions to dissolve it; adding 150 to 170 parts of sodium chloride and controlling the conditions to disperse it to obtain a mixed solution; Step 2: The mixed solution obtained in step 1 is transferred to a reactor, and the conditions are controlled to form microsphere embryos through heat-driven self-assembly, and a hydrothermal product is obtained after filtering and washing; Step 3: heating the hydrothermal product under a nitrogen atmosphere to carbonize it, cooling it, washing it to remove the sodium chloride template, and vacuum drying it to obtain nitrogen-phosphorus co-doped porous carbon microspheres; Step 4: 100-120 parts of the nitrogen-phosphorus co-doped porous carbon microspheres obtained in step 3 and 80-85 parts of red phosphorus are added to a quartz tube, vacuum-sealed, and gas-phase loaded in stages under controlled conditions to obtain red phosphorus-loaded carbon microspheres; Step 5: Take 100-120 parts of the red phosphorus-loaded carbon microspheres obtained in step 4, mix them with 15-16 parts of silicon nanoparticles and 5-5.5 parts of dextrin in 200-250 parts of ethanol medium, and ball mill them. After spray drying, the dextrin is thermally cured to form microsphere-level composite particles. The composite particles are gas-phase carbon-coated to obtain a phosphorus-doped porous carbon / silicon composite negative electrode material.

2. The preparation method according to claim 1, characterized in that The phytic acid solution in step 1 is a phytic acid aqueous solution with a mass fraction of 50% to 55%.

3. The preparation method according to claim 1, characterized in that After adding the phytic acid solution in step 1, the temperature is raised to 55-65° C., and the reaction is carried out for 30-40 minutes to construct a hydrogen bond cross-linking network; after adding melamine, the temperature is raised to 80-85° C. and stirred for 1-1.5 hours until it is completely dissolved; after adding sodium chloride, the stirring speed is controlled at 5000-6000 rpm and stirred for 10-15 minutes until it is completely dispersed.

4. The preparation method according to claim 1, characterized in that When the mixed solution in step 2 is transferred to the reactor, the filling degree is controlled to be ≤70%; the temperature is increased to 220-230°C at a heating rate of 5°C, kept warm for 12-14 hours, then cooled to 80°C, discharged, vacuum filtered, and washed with 80°C deionized water for 3-5 times.

5. The preparation method according to claim 1, characterized in that In step 3, the carbonization process is a gradient heating process, first heating to 300°C at a heating rate of 5°C, keeping warm for 1 hour, then heating to 750°C at a heating rate of 3°C, keeping warm for 2 hours; after cooling to room temperature, washing with deionized water to remove the sodium chloride template; the vacuum drying process temperature is controlled at 80°C and dried for 12 hours.

6. The preparation method according to claim 1, characterized in that The staged gas phase loading process in step 4 includes: stage 1, heating to 416°C at 10°C / min and keeping at this temperature for 4 hours; stage 2, cooling to 260°C at 5°C / min and keeping at this temperature for 8 hours; stage 3, cooling to <60°C with the furnace and then breaking the vacuum.

7. The preparation method according to claim 1, characterized in that During the sealing in step 4, the quartz tube retains 30% to 33% expansion space in its length.

8. The preparation method according to claim 1, characterized in that The spray drying control conditions in step 5 are as follows: inlet temperature 180-190°C, outlet temperature 70-80°C, and powder particle size 8-15 μm.

9. The preparation method according to claim 1, characterized in that The control conditions for gas-phase carbon coating in step 5 are that the carbon source is selected from acetylene, and the temperature is 650-660° C. for 1-1.2 hours.

10. A phosphorus-doped porous carbon / silicon composite negative electrode material, characterized in that: The method is as described in any one of claims 1 to 9.