A phosphorus-carbon composite material, a preparation method thereof and application thereof

Abstract

The application provides a preparation method of a phosphorus-carbon composite material, comprising the following steps: dispersing a carbon source and a phosphorus source in an organic solvent, and then shaping to obtain a precursor of the carbon source coated phosphorus nano phase; and then performing low-temperature pyrolysis pretreatment on the precursor, and then slowly heating to carbonize the precursor in an inert atmosphere to obtain the phosphorus-carbon composite material. The application also provides application examples of the phosphorus-carbon composite material. In the phosphorus-carbon composite material prepared by the application, the phosphorus phase is uniformly distributed in the carbon phase in a nanometer size and is densely coated by the carbon phase, so that a series of problems caused by the volume expansion of phosphorus can be effectively inhibited, and reliable contact between the phosphorus and the carbon can be ensured, and therefore the electrochemical cycle performance of the final phosphorus-carbon composite material is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of energy storage materials, and particularly relates to a phosphorus-carbon composite material, a preparation method thereof and an application thereof. Background Art

[0002] Phosphorus-based anode materials can be used in high specific energy lithium / sodium / potassium ion batteries due to their high specific capacity, good electrochemical kinetics and compatibility with the electrochemical system, and have broad application prospects. However, the practical application of phosphorus-based anode materials faces two prominent problems: First, the low conductivity of phosphorus is not conducive to the electrochemical reaction of the battery, affecting the capacity performance and rate performance; Second, phosphorus faces severe volume changes (~300%) and complex phase transformation processes during the charge-discharge cycle, resulting in serious structural instability and pulverization problems of phosphorus-based anode materials during the electrochemical reaction process, leading to the detachment of active phosphorus from electrical contact, the continuous destruction / generation of the SEI on the anode surface, and the continuous consumption of alkali metal ions, thereby causing battery structure damage, unstable internal resistance and continuous irreversible loss of capacity.

[0003] Composite of elemental phosphorus with conductive and porous carbon-based materials is an effective solution to solve the above problems. The highly conductive carbon material can improve the conductivity of the phosphorus-based anode, thereby improving the electrochemical reaction kinetics of the anode; The carbon phase with relatively good mechanical stability and strength can relieve the deformation stress of the phosphorus phase or inhibit the violent expansion of the phosphorus phase, thereby suppressing the pulverization of the phosphorus phase to a certain extent and improving the structural stability of the anode.

[0004] To achieve the uniform composite and reliable contact of the phosphorus-carbon two-phase, currently two main synthesis routes are mainly used: high-energy mechanical ball milling mixing method and chemical vapor deposition method. The mechanical ball milling mixing method is to mix specific carbon materials with good physical and chemical properties (such as Ketjen black, carbon nanotubes, reduced graphene oxide) and phosphorus-based materials in a certain proportion, and then carry out ball milling under the protection of an inert atmosphere. The ball milling method is simple and easy to operate. It makes the phosphorus phase and carbon phase uniformly mixed through mechanical processing. And under the conditions of long time and high power, a small amount of chemical bonds may further generate between phosphorus and carbon, enhancing the interaction between the two phases. However, the processing process requires the protection of inert gas and high energy consumption for a long time, with high costs and low yields (laboratory scale). Moreover, the size uniformity of the finally prepared phosphorus-carbon composite particles is also poor. Therefore, the electrochemical performance is usually not ideal, and it is difficult to achieve industrial-scale large-scale production. The chemical vapor deposition method is mainly used for the preparation of red phosphorus-carbon composite materials. Utilizing the property that red phosphorus sublimes at 416 °C, red phosphorus is heated in a closed container to generate phosphorus vapor. The phosphorus vapor condenses and is adsorbed by specific carbon materials, and finally a phosphorus-carbon composite material is obtained. This method has relatively good controllability, the size uniformity of the final product is stronger, and the phosphorus-carbon mixing is more uniform. However, the single yield of the vapor deposition method is low (in the order of hundreds of milligrams), and the interaction between phosphorus and carbon is weak. Similarly, it is impossible to achieve the large-scale preparation of battery-grade phosphorus-based anode materials. In addition, a large amount of flammable and toxic white phosphorus will be generated during the condensation process of phosphorus vapor, with relatively serious safety hazards. Therefore, in order to achieve the large-scale preparation of phosphorus-carbon anode materials, it is urgent to develop a method for efficiently preparing high-performance phosphorus-carbon composite materials with low costs. Summary of the Invention

[0005] The technical problem solved by the present invention lies in providing a preparation method for a phosphorus-carbon composite material. The phosphorus-carbon composite material prepared by the present application has good stability and good electrochemical cycling performance.

[0006] In view of this, the present application provides a preparation method for a phosphorus-carbon composite material, including the following steps:

[0007] Disperse a carbon source and a phosphorus source in an organic solvent, and then shape them to obtain a precursor with a phosphorus nanophase coated with the carbon source.

[0008] Perform low-temperature pyrolysis pretreatment on the precursor, and then slowly raise the temperature to carbonize the precursor in an inert atmosphere to obtain a phosphorus-carbon composite material.

[0009] Preferably, the carbon source is selected from one or more of polymer macromolecules, biomass, mesophase pitch, sugars, and metal-organic framework materials, and the phosphorus source is selected from one or more of nanosheets of phosphorus allotropes, nanowires of phosphorus allotropes, nanoparticles of phosphorus allotropes, and phosphorus-containing compounds; the mass ratio of the carbon source to the phosphorus source is 0.5:1 to 20:1.

[0010] Preferably, the particle size of the phosphorus source is 30 to 500 nm.

[0011] Preferably, the raw materials for dispersion further include an additive, and the additive is a carbon nanomaterial accounting for 0.1 to 1 wt% of the total mass of the carbon source and the phosphorus source, and the carbon nanomaterial is selected from one or more of carbon nanotubes, carbon nanosheets, and graphene oxide.

[0012] Preferably, the shaping method is selected from freeze-drying, water impregnation, or electrospinning.

[0013] Preferably, the temperature of the low-temperature pyrolysis pretreatment is 160 to 320 °C, and the low-temperature pyrolysis pretreatment is specifically heat-insulated at 150 to 170 °C, 230 to 250 °C, and 310 to 330 °C for 1 to 300 min respectively; according to the type and chemical properties of the precursor, the atmosphere of the low-temperature pyrolysis pretreatment is air or an inert gas.

[0014] Preferably, the process of slowly heating to carbonize the precursor is specifically as follows:

[0015] The precursor obtained by the low-temperature pyrolysis pretreatment is heated to 1000 to 1200 °C at a heating rate of 1 to 10 °C / min, and is heat-insulated at 400 °C, 600 °C, 800 °C, and 1000 °C for 1 to 300 min respectively during this period.

[0016] This application also provides a phosphorus-carbon composite material prepared by the preparation method described above, including a phosphorus nanophase and a carbon phase. The surface of the phosphorus nanophase is coated with the carbon phase, and there is physical contact or chemical bonding between the phosphorus nanophase and the carbon phase.

[0017] Preferably, the mass ratio of the phosphorus nanophase to the carbon phase is 1:0.5 to 1:20.

[0018] This application also provides a secondary metal ion battery, including a positive electrode and a negative electrode. The material of the negative electrode is selected from the phosphorus-carbon composite material described above or the phosphorus-carbon composite material.

[0019] This application provides a preparation method of a phosphorus-carbon composite material. First, a carbon source and a phosphorus source are dispersed in an organic solvent, and then shaped to obtain a precursor with a carbon phase coating a phosphorus nanophase. Then, a low-temperature pyrolysis pretreatment and a heat treatment process are carried out in sequence to obtain a phosphorus-carbon composite material; the phosphorus phase prepared in this application is uniformly distributed in the carbon phase in nanoscale and is densely coated by the carbon phase, thereby effectively suppressing the problems caused by the volume expansion of phosphorus and ensuring reliable contact between phosphorus and carbon, and finally improving the electrochemical cycling performance of the phosphorus-carbon composite material.

[0020] Furthermore, in the low-temperature pyrolysis pretreatment and heat treatment processes of this application, a slow heating rate combined with segmented heat preservation is adopted, and a large batch preparation with a single yield of ten grams can be achieved through common heating devices. The process is simple and can be scaled up for large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 Transmission electron microscope photograph of the phosphorus-carbon composite nanoparticles prepared in Example 3 and distribution maps of carbon and phosphorus elements;

[0022] Figure 2 Energy spectrum analysis results of the element content of the phosphorus-carbon composite nanoparticles prepared in Example 3;

[0023] Figure 3 Raman spectrum analysis of the phosphorus-carbon composite nanoparticles (AC@RP) prepared in Example 3 and the phosphorus-carbon composite particles (AC+RP) prepared by ball milling in Example 4;

[0024] Figure 4 Rate performance discharge capacity curves and Coulomb efficiency curves of the Li║AC@RP half-cell assembled in Example 5 and the Li║AC+RP half-cell as a control;

[0025] Figure 5 Scanning electron microscope photograph and element distribution map of the self-supporting phosphorus-carbon three-dimensional felt prepared in Example 7;

[0026] Figure 6 Long cycle test discharge capacity curves and Coulomb efficiency curves of the self-supporting phosphorus-carbon three-dimensional felt prepared in Example 7 and the phosphorus-carbon three-dimensional felt prepared by vapor deposition method for lithium half-cells; DETAILED DESCRIPTION OF THE EMBODIMENTS

[0027] To further understand the present invention, the preferred embodiments of the present invention will be described below in conjunction with examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, rather than limiting the claims of the present invention.

[0028] Aiming at the problems of the weak effect of the current phosphorus-carbon composite material, easy shedding and inactivation of phosphorus leading to irreversible capacity loss of the negative electrode, and high preparation yield cost, the present invention provides a preparation method of a phosphorus-carbon composite material. Through low-temperature pyrolysis pretreatment and heat treatment with a slow heating rate, the phosphorus phase in the prepared phosphorus-carbon composite material is uniformly distributed in the carbon matrix in nanoscale and is densely coated by the carbon phase, thereby effectively suppressing the problems caused by phosphorus volume expansion, improving the stability of the phosphorus-carbon composite material, and ultimately improving the electrochemical cycling performance of the phosphorus-carbon composite material. Specifically, the embodiments of the present invention disclose a preparation method of a phosphorus-carbon composite material, including the following steps:

[0029] Disperse the carbon source and the phosphorus source in an organic solvent, and then shape them to obtain a precursor of a carbon source-coated phosphorus nanophase;

[0030] Perform low-temperature pyrolysis pretreatment on the precursor, and then slowly heat it up to carbonize the precursor in an inert atmosphere to obtain a phosphorus-carbon composite material.

[0031] In the preparation process of the phosphorus-carbon composite material, in this application, first, the carbon source and the phosphorus source are dispersed in an organic solvent, and then shaped to obtain a precursor of a carbon source-coated phosphorus nanophase. In the above process, the carbon source is selected from polymer macromolecules, biomass, mesophase pitch, sugars, and metal-organic framework materials; for example, the polymer macromolecule can be polyacrylonitrile, the biomass can be pectin, and the sugar can be glucose; in a specific embodiment, the carbon source is selected from glucose or polyacrylonitrile. The phosphorus source is one or more of nanosheets of phosphorus allotropes, nanowires of phosphorus allotropes, nanoparticles of phosphorus allotropes, and phosphorus-containing compounds. Specifically, the phosphorus allotropes are selected from one or more of red phosphorus, black phosphorus, violet phosphorus, yellow phosphorus, orange phosphorus, green phosphorus, and blue phosphorus; the phosphorus-containing compound can be various phosphates, phosphorus anhydrides, and phosphorus acid compounds. In a specific embodiment, the phosphorus source is selected from red phosphorus. The mass ratio of the carbon source to the phosphorus source is 0.5:1 to 20:1. Specifically, the mass ratio of the carbon source to the phosphorus source is 1:1 to 6:1. In the mixing process, a carbon nanomaterial can also be added as an additive, and its content is 0.1 to 1 wt% of the total mass of the carbon source and the phosphorus source; the carbon nanomaterial is selected from one or more of carbon nanotubes, carbon nanosheets, and graphene oxide.

[0032] According to the present invention, after mixing the above raw materials, depending on the nature of the carbon source, it is preferably shaped by freeze-drying, water impregnation or spinning to obtain a precursor of a carbon source-coated phosphorus nanophase. The above freeze-drying, water impregnation and spinning methods are carried out according to the methods well-known to those skilled in the art, and this application has no special restrictions on this.

[0033] The present application then performs low-temperature pyrolysis treatment on the obtained carbon-source-coated phosphorus nanophase precursor, and then slowly raises the temperature in an inert atmosphere to carbonize the precursor, thereby obtaining a phosphorus-carbon composite material. During this process, the carbon source in the carbon-source-coated nanophase precursor is converted into an amorphous carbon phase as the pyrolysis process proceeds, while the phosphorus phase physically sublimes into phosphorus vapor and then redistributes in the pores of the amorphous carbon. The temperature of the low-temperature pyrolysis pretreatment is 160-320°C. Specifically, the low-temperature pyrolysis pretreatment is independently maintained at 150-170°C, 230-250°C, and 310-330°C for 1-300 min respectively. Specifically, the carbon-source-coated phosphorus nanophase precursor is heated to 160°C at a rate of 1-10°C / min, maintained for 1-300 min, then heated to 240°C at a rate of 1-10°C / min, maintained for 1-300 min, and then heated to 320°C at a rate of 1-10°C / min. Depending on the difference in the composition of the organic precursor, the above process is carried out in an oxidizing atmosphere (air) or an inert atmosphere (nitrogen, argon, etc.).

[0034] Then, the obtained precursor is slowly heated to carbonize the precursor in an inert atmosphere to obtain a phosphorus-carbon composite material. Specifically, the precursor obtained by low-temperature pyrolysis pretreatment is heated to 1000-1100°C at a heating rate of 1-10°C / min, and is independently maintained at 400°C, 600°C, 800°C, and 1000°C for 1-300 min respectively during this period; more specifically, the precursor obtained by low-temperature pyrolysis pretreatment is heated to 400°C at a heating rate of 1-10°C / min, maintained for 1-300 min, then heated to 600°C at a heating rate of 1-10°C / min, maintained for 1-300 min, then heated to 800°C at a heating rate of 1-10°C / min, maintained for 1-300 min, and finally heated to 1000°C at a heating rate of 1-10°C / min, maintained for 1-300 min. Depending on the different structures of the precursor, the phosphorus-carbon composite material can be particles, agglomerates, or three-dimensional carbon fiber felts.

[0035] During the low-temperature pyrolysis pretreatment process, the carbon-source organic matter removes hydrogen and oxygen atoms in the long-chain structure, and the carbon atom long chain gradually reconstructs to form a four-membered ring or a six-membered ring structure, that is, a ladder structure. During this process, the micropores existing in the structure shrink and close, realizing a denser coating of the phosphorus nanophase; during the subsequent heat treatment and stepwise heating process, the structural nitrogen atoms and structural hydrogen atoms in the organic matter are further removed, gradually forming a dense and continuous amorphous carbon structure; at the same time, the phosphorus nanophase volatilizes due to heat and condenses on the pore walls of the internal micropores of the amorphous carbon, realizing a reliable combination between phosphorus and carbon. The above-mentioned slow heating and holding methods of the low-temperature pyrolysis pretreatment and heat treatment processes in the present application make the amorphous carbon component more uniform and the structure more continuous, which can not only fully coat the red phosphorus nanophase but also enable alkali metal ions to diffuse in its structure.

[0036] The present application also provides a phosphorus-carbon composite material prepared by the above method, which includes a phosphorus nanophase and a carbon phase, and the surface of the phosphorus nanophase is coated with a carbon phase, and there is physical contact or chemical bonding between the carbon phase and the phosphorus nanophase.

[0037] In the phosphorus-carbon composite material, the mass ratio of the phosphorus nanophase to the carbon phase is 0.5:1 to 20:1. Specifically, the mass ratio of the phosphorus nanophase to the carbon phase is 1:1 to 6:1.

[0038] Furthermore, the present application also provides a secondary metal ion battery, which includes a positive electrode and a negative electrode, and the material of the negative electrode is selected from the phosphorus-carbon composite material of the above solution.

[0039] The preparation method of the phosphorus-carbon composite material provided by the present application has a simple process, relatively low cost and high yield; in terms of raw materials, the materials used as carbon sources include biomass, mesophase pitch, polyacrylonitrile, etc. commonly used in the current ion negative electrode industry, which are widely sourced and inexpensive; the materials used as phosphorus sources include various common phosphorus allotropes; in terms of the preparation process, only a heating device capable of introducing an inert atmosphere (such as nitrogen, argon, etc.) is required, with a short production cycle, low energy consumption and simple equipment; in terms of yield, a single yield of ten grams can be achieved even in laboratory-scale production, and the yield can be arbitrarily increased with the volume of the heating container. Therefore, this method is suitable for industrial large-scale preparation.

[0040] The phosphorus-carbon composite material prepared by the present application can obtain phosphorus-carbon composite materials with different structures (such as micron-sized particles, three-dimensional felts, etc.) by designing raw materials with different geometric structure sizes according to the requirements of the battery system. Finally, the prepared phosphorus-carbon composite material has a uniform structure, and the nanoscale phosphorus phase is uniformly dispersed in the carbon matrix and densely coated with an amorphous carbon phase. Therefore, the electrical contact between phosphorus and carbon is reliable, improving the rate performance of the composite material. During the charge and discharge process, lithium / sodium / potassium metal ions pass through the amorphous carbon film to contact and react with phosphorus, and the volume expansion of phosphorus can be alleviated by the microstructure change of the amorphous carbon, thus maintaining the structural integrity of the phosphorus nanophase and improving the structural stability of the negative electrode material.

[0041] Experimental results show that taking the phosphorus-carbon particle sample with a phosphorus content of 25% as an example, in a lithium-ion battery, this negative electrode can provide a reversible capacity of 400 mAh / g at a rate current density of 2C, which is significantly better than the phosphorus-carbon negative electrode material obtained by mechanical ball milling (110 mAh / g); while the phosphorus-carbon three-dimensional felt with a phosphorus content of 21% stably outputs a reversible capacity of 510 mAh / g at a current density of 0.5C, the capacity retention rate after 300 cycles is 76.52%, and the Coulomb efficiency is 99.79 ± 0.22%; as a control, the phosphorus-carbon composite three-dimensional felt prepared by chemical vapor deposition outputs a capacity of 340 mAh / g after 300 cycles, the capacity retention rate is 53.01%, and the Coulomb efficiency is 99.58 ± 0.46%.

[0042] To further understand the present invention, the phosphorus-carbon composite material, its preparation method and its application provided by the present invention will be described in detail below in conjunction with embodiments. The protection scope of the present invention is not limited by the following embodiments.

[0043] Example 1

[0044] Preparation of composite particle precursor: Put 100-mesh red phosphorus raw material into an industrial sand mill and grind it for 1 h to obtain red phosphorus nanoparticles with a particle size of 50 - 300 nm. Stir and mix in water according to the mass ratio of phosphorus:glucose of 1:5 (total raw material amount is 20 g), and then dry it to obtain a mixed solid of glucose@phosphorus.

[0045] Example 2

[0046] Put the solid obtained in Example 1 into a heating furnace, heat it up to 160 °C at a heating rate of 10 °C / min, keep it warm for 300 min, and then still heat it up to 240 and 320 °C at a heating rate of 10 °C / min, and keep it warm for 300 min respectively.

[0047] Example 3

[0048] Put the raw material after low-temperature treatment in Example 2 into a heating device protected by an inert atmosphere, and still heat it up at a heating rate of 10 °C / min to pyrolyze and carbonize the raw material. During this period, keep it warm at four stages of 400 °C, 600 °C, 800 °C, and 1000 °C respectively, and the holding time for each stage is 300 min to obtain a phosphorus-carbon composite block, and then grind it for 30 min to obtain submicron-sized phosphorus-carbon composite particles (marked as AC@RP).

[0049] Use transmission electron microscopy combined with energy spectrum analysis to analyze the morphology and elements of AC@RP, and the results are as Figure 1 and Figure 2 shown; from the element distribution map, the phosphorus phase is evenly distributed in the carbon matrix, and the phosphorus content is 25 wt%.

[0050] Example 4

[0051] In order to compare with the performance of AC@RP prepared by the segmented pyrolysis method, the red phosphorus nanoparticles prepared in Example 1 and amorphous carbon particles (also prepared with glucose as the carbon source) were ball-milled at a rotation speed of 600 rpm for 24 h in an argon atmosphere to obtain phosphorus-carbon composite particles, marked as AC+RP. Use Raman to analyze the two kinds of particles of AC@RP and AC+RP, and the results are as Figure 3As shown; judging from the D peak and G peak of the Raman curve, the main components of both types of materials are amorphous carbon. However, phosphorus is exposed on the surface of the ball-milled sample AC+RP and is not coated with a carbon film, so the characteristic peak of red phosphorus appears; while in the AC@RP prepared by segmented pyrolysis, red phosphorus is completely coated, so no red phosphorus signal is shown.

[0052] Example 5

[0053] The two types of particles were respectively made into a slurry according to the same ratio, that is, the mass ratio of phosphorus-carbon particles: Ketjen black: PVDF was 92:4:4, and the slurry was scraped on the surface of a carbon-coated copper foil and dried to obtain an electrode with a phosphorus-carbon composite active material surface loading of 4.5 mg / cm 2 ; Using these two types of electrodes as working electrodes and a lithium sheet as a reference / counter electrode to assemble a half-cell. A solution of 100 μL of 1 mol / L lithium hexafluorophosphate (LiPF6) dissolved in ethylene carbonate / diethyl carbonate (EC:DEC = 1:1 volume ratio) was used as the electrolyte, and Celgard 2400 was used as the separator to assemble a standard button cell CR2032; the prepared cells were subjected to a rate charge-discharge test, and the charge-discharge voltage range was 0.001 to 2 V. The discharge specific capacity and Coulomb efficiency of the two groups of cell samples are as Figure 4 shown.

[0054] From Figure 4 it can be seen that the AC@RP composite negative electrode still has a discharge specific capacity of 400 mAh / g at a current density of 2C, which is much higher than 110 mAh / g of AC+RP, indicating that the AC@RP with carbon film completely coating phosphorus obtained by segmented pyrolysis has significantly better rate performance (or electrochemistry kinetics) than AC+RP prepared by ball milling; judging from the Coulomb efficiency, Li║AC@RP is also better than the Li║AC+RP half-cell, proving that the reversibility of lithium insertion in the AC@RP composite negative electrode is better and there are fewer electrode side reactions. It is speculated that the reason should be the unique structure of the carbon film completely coating phosphorus achieved by pyrolysis, which ensures the structural integrity of phosphorus and reliable electrical contact, and also improves

[0055] Example 6

[0056] Preparation of three-dimensional felt precursor: The red phosphorus nanoparticles prepared in Example 1 were dissolved in N,N-dimethylformamide according to the mass ratio of phosphorus: polyacrylonitrile of 1:4, and electrospinning was carried out to obtain a three-dimensional non-woven fabric with a thickness of 50 - 1000 μm. The steps of Example 2 and 3 were repeated to obtain a phosphorus-carbon composite three-dimensional felt, marked as CF@RP.

[0057] CF@RP was observed using scanning electron microscopy combined with energy spectrum analysis, and the results are as Figure 5 shown. The phosphorus content in the product is 21 wt%. As a control, the same content of red phosphorus was vapor-deposited into the porous three-dimensional carbon felt structure by chemical vapor deposition method, marked as CF+RP.

[0058] Example 7

[0059] Using the CF@RP and CF-RP prepared in Example 6 as the working electrodes respectively, a lithium sheet as the reference / counter electrode to assemble a half-cell. A solution of 100 μL of 1 mol / L lithium hexafluorophosphate (LiPF6) dissolved in ethylene carbonate / diethyl carbonate (EC:DEC = 1:1 volume ratio) was used as the electrolyte, and Celgard 2400 was used as the separator to assemble a standard button cell CR2032. The prepared batteries were subjected to a long cycle test of rate charge and discharge, and the charge and discharge voltage range was 0.001 - 2 V, and the current density was kept constant at 0.5 C. The discharge specific capacity and Coulomb efficiency of the two groups of battery samples are as Figure 6 shown.

[0060] As Figure 6 shown by the capacity and Coulomb efficiency curves, Li║CF@RP stably outputs a reversible capacity of 510 mAh / g at a current density of 0.5 C, the capacity retention rate after 300 cycles is 76.52%, and the Coulomb efficiency is 99.79 ± 0.22%; while Li║CF+RP outputs a capacity of 340 mAh / g after 300 repeated charge and discharges, the capacity retention rate is 53.01%, and the Coulomb efficiency is 99.58 ± 0.46%. The difference in the performance of the two groups of battery samples once again proves that the unique structure of the carbon completely coating phosphorus obtained by the segmented pyrolysis method designed in this application has special advantages in maintaining the electrochemical stability of the active material and improving the reversibility of lithium insertion.

[0061] The description of the above embodiments is only used to help understand the method and its core idea of the present invention. It should be pointed out that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and modifications can be made to the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

[0062] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be obvious to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to these embodiments shown herein, but will be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a phosphorus-carbon composite material, comprising the following steps: The carbon source and phosphorus source are dispersed in an organic solvent and then shaped to obtain a precursor of carbon source-coated phosphorus nanophase; the carbon source is selected from glucose or polyacrylonitrile, and the phosphorus source is selected from red phosphorus. The precursor is subjected to low-temperature pyrolysis pretreatment, and then slowly heated in an inert atmosphere until the precursor is carbonized to obtain a phosphorus-carbon composite material. The low-temperature pyrolysis pretreatment specifically involves independently holding at 150~170℃, 230~250℃ and 310~330℃ for 1~300 min respectively; The process of slowly heating to carbonize the precursor specifically involves heating the precursor obtained from low-temperature pyrolysis pretreatment to 1000-1200℃ at a heating rate of 1-10℃ / min, and independently holding it at 400℃, 600℃, 800℃ and 1000℃ for 1-300min respectively.

2. The preparation method according to claim 1, characterized in that, The mass ratio of the carbon source to the phosphorus source is 0.5:1 to 20:

1.

3. The preparation method according to claim 1, characterized in that, The phosphorus source has a particle size of 30~500nm.

4. The preparation method according to claim 1, characterized in that, The dispersed raw materials also include additives, which are carbon nanomaterials at 0.1 to 1 wt% of the total mass of the carbon source and the phosphorus source, and the carbon nanomaterials are selected from one or more of carbon nanotubes, carbon nanosheets and graphene oxide.

5. The preparation method according to claim 1, characterized in that, The shaping method is selected from freeze drying or spinning.

6. The preparation method according to claim 1, characterized in that, Depending on the type and chemical properties of the precursor, the atmosphere for the low-temperature pyrolysis pretreatment is air or an inert gas.

7. The phosphorus-carbon composite material prepared by the preparation method according to any one of claims 1 to 6 comprises a phosphorus nanophase and a carbon phase, wherein the surface of the phosphorus nanophase is coated with the carbon phase, and there is physical contact or chemical bonding between the phosphorus nanophase and the carbon phase.

8. The phosphorus-carbon composite material according to claim 7, characterized in that, The mass ratio of the phosphorus nanophase to the carbon phase is 1:0.5 to 1:

20.

9. A metal-ion secondary battery, comprising a positive electrode and a negative electrode, characterized in that, The material of the negative electrode is selected from the phosphorus-carbon composite material according to any one of claims 1 to 6 or the phosphorus-carbon composite material according to any one of claims 7 to 8.

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