P, n co-doped high-compacted coal-based soft / hard carbon negative electrode material and preparation method thereof

Abstract

The application discloses P, N co-doped high-compaction coal-based soft / hard carbon negative electrode material, and a preparation method of the material, and belongs to the technical field of new energy materials. The method comprises the following steps: selecting lump coal and strong cohesive coal as raw material coal, and crushing the lump coal and the strong cohesive coal; uniformly mixing the crushed lump coal and the strong cohesive coal to obtain a coal-based precursor; after removing ash from the coal-based precursor, the coal-based precursor is mixed with a dopant and a coating agent in a solid phase to obtain a P, N co-doped coal-based precursor; the P, N co-doped coal-based precursor is calcined under a protective gas atmosphere to obtain a P, N co-doped coal-based soft / hard carbon matrix A; the matrix A is crushed and subjected to secondary granulation to obtain a P, N co-doped coal-based soft / hard carbon matrix B; and the matrix B is subjected to magnetic removal and screening classification to obtain a P, N co-doped coal-based soft / hard carbon composite negative electrode material. The P, N co-doped high-compaction coal-based soft / hard carbon negative electrode material has the characteristics of high capacity, high first coulomb efficiency and high compaction density.

Description

Technical Field

[0001] This invention belongs to the technical field of soft / hard carbon anode materials, and relates to a P, N co-doped high-pressure coal-based soft / hard carbon anode material. This invention also relates to a method for preparing the above-mentioned anode material. Background Technology

[0002] With the rapid development of electric vehicles and renewable energy storage technologies, sodium-ion batteries have attracted widespread attention as a promising energy storage device. The performance of sodium-ion batteries is limited by the performance of their electrode materials. Currently, graphite is the most commonly used anode material for lithium-ion batteries, but its sodium storage capacity is limited, and its cycle stability needs improvement, making it unsuitable for sodium-ion batteries. Therefore, developing novel high-performance anode materials for sodium-ion batteries is of great significance.

[0003] Coal-based soft / hard carbon materials, as a novel type of carbon material, are inexpensive, widely available, and possess high specific surface area, good conductivity, and abundant pore structure, thus being considered a promising anode material for sodium-ion batteries. However, the sodium storage capacity of pure coal-based soft / hard carbon materials in sodium-ion batteries still needs improvement. For example, the sodium storage capacity of Zhongke Haina, after one-step carbonization of anthracite, is only 220 mAh / g. To address this issue, researchers have attempted to improve the performance of coal-based soft / hard carbon materials by doping with other elements (such as N, O, S, P, B, Mn, etc.), as doping can introduce new defects into the coal-based soft / hard carbon, increasing pores and setting more sodium storage sites, thereby improving sodium storage capacity. However, existing preparation methods often have some problems, such as high costs due to complex doping processes (e.g., hydrothermal methods, spray methods, sand milling methods, etc.), the high risk of doping with P, and the reduction in compaction due to the increased defects caused by doping with N and other elements.

[0004] With the declining cost of lithium-ion batteries, sodium-ion batteries can only remain competitive by achieving higher cost-effectiveness, increasing capacity while reducing costs. Therefore, how to safely and cost-effectively dope sodium-ion battery anode materials to improve their performance has become a new research hotspot. Phosphorus-based materials are the anode materials with the highest sodium storage performance (theoretical specific capacity 2596 mAh / g), making phosphorus doping the best way to improve capacity. However, phosphorus-based materials have a series of drawbacks, such as the flammability of red phosphorus, the toxicity of white phosphorus, and the difficulty in preparing black phosphorus. Poor conductivity and poor cycle performance due to easy expansion (≥300%) during charge and discharge limit their application in large-scale energy storage. Low-cost doping of phosphorus into coal-based soft / hard carbon materials has become an important solution to improve the cost-effectiveness of coal-based anode materials. Furthermore, oxygen doping, nitrogen doping, and sulfur doping have all been proven effective in modifying coal-based materials. A certain proportion of doping increases the defect degree of the material, leading to reduced compaction, which is a major challenge in battery fabrication.

[0005] In the manufacture of sodium-ion batteries, compaction density has a significant impact on battery performance. Experiments have shown that compaction density is closely related to the specific capacity, efficiency, internal resistance, and cycle performance of the battery. Finding the optimal compaction density is crucial for battery design. Generally, the higher the compaction density, the greater the battery capacity; therefore, compaction density is considered one of the important indicators of material performance. Thus, increasing the compaction density of coal-based soft / hard carbon is considered one of the important ways to improve its capacity. Summary of the Invention

[0006] The purpose of this invention is to provide a P, N co-doped high-pressure compacted coal-based soft / hard carbon anode material with high capacity, high initial coulombic efficiency, and high compaction density.

[0007] Another objective of this invention is to provide a method for preparing the above-mentioned negative electrode material, which has the characteristics of simple and easy operation, low cost, and industrial production capability.

[0008] The technical solution adopted in this invention is a method for preparing P, N co-doped high-pressure coal-based soft / hard carbon anode materials, specifically implemented according to the following steps:

[0009] Step 1: Select lump coal and strongly caking coal as raw coal, and crush them;

[0010] Step 2: Mix the crushed lump coal and strongly caking coal from Step 1 evenly to obtain a coal-based precursor;

[0011] Step 3: Remove the ash from the coal-based precursor obtained in Step 2;

[0012] Step 4: Mix the coal-based precursor obtained in Step 3 with the dopant and coating agent in a solid phase to obtain a P and N co-doped coal-based precursor.

[0013] Step 5: Under a protective gas atmosphere, calcine the P, N co-doped coal-based precursor obtained in step 4 to obtain P, N co-doped coal-based soft / hard carbon matrix A.

[0014] Step 6: Crush the P, N co-doped coal-based soft / hard carbon matrix A obtained in Step 5 and perform secondary granulation to obtain P, N co-doped coal-based soft / hard carbon matrix B.

[0015] Step 7: Demagnetize and classify the P, N co-doped coal-based soft / hard carbon matrix B obtained in Step 6 to obtain the P, N co-doped coal-based soft / hard carbon composite anode material.

[0016] The invention is further characterized by:

[0017] In step 1, the strongly caking coal is coal with a caking index G greater than 65. The lump coal and strongly caking coal are crushed to an average particle size D50 of 5.0 to 8.0 μm.

[0018] In the coal-based precursor of step 2, the mass ratio of lump coal to strongly caking coal is 4-5:1.

[0019] Step 3 specifically involves:

[0020] The coal-based precursor powder obtained in step 2 is added to dilute hydrochloric acid and reacted fully. After filtration to pH=7, it is added to dilute hydrofluoric acid or sodium hydroxide solution and reacted fully. After filtration to pH=7, it is dried.

[0021] In step 4, the dopant is one or a mixture of several of the following: ammonium phosphate, ammonium hydrogen phosphate, sodium ammonium phosphate, and ammonium polyphosphate.

[0022] In step 4, the coating agent is one or a mixture of several of petroleum asphalt, coal tar pitch, phenolic resin, epoxy resin, polyacrylonitrile, and styrene-butadiene rubber.

[0023] In step 4, the mass ratio of the coal-based precursor, dopant, and coating agent is 100:5 to 25:5 to 10.

[0024] Step 5 specifically involves:

[0025] The P, N co-doped coal-based precursor obtained in step 4 was placed in a high-temperature atmosphere furnace and heated to 150–400°C at a rate of 1–5°C / min under a protective gas atmosphere. The temperature was maintained for 2.0–4.0 h. Then, the temperature was increased to 1100–1300°C at a rate of 1–5°C / min and maintained for 2.0–4.0 h. After the heat treatment, the furnace was allowed to cool naturally to room temperature to obtain P, N co-doped coal-based soft / hard carbon matrix A.

[0026] The protective gas is selected from one or a mixture of nitrogen, helium, neon, argon, krypton, or xenon, with a gas flow rate of 0.4–1.2 m³ / s. 3 / h.

[0027] In step 6, the average particle size D50 of the secondary granulation particles is 7.0–15.0 μm.

[0028] Another technical solution adopted in this invention is a P and N co-doped high-pressure coal-based soft / hard carbon anode material, which is prepared by the above-mentioned preparation method.

[0029] The beneficial effects of this invention are:

[0030] (1) The method of the present invention uses lump coal as the raw material for the preparation of coal-based soft / hard carbon. It is widely available and inexpensive. Incorporating all coal-based raw materials into the preparation system is beneficial to reducing the production cost of composite anode materials and broadening the application field of coal-based materials.

[0031] (2) The method of the present invention combines a general type of coal with a small amount of strongly cohesive coal to prepare a coal-based carbon material with multi-level pores, which reduces the breakage rate of the coal-based carbon material, improves the strength and compaction density of the coal-based carbon material, and indirectly improves its energy density in battery systems.

[0032] (3) The method of the present invention uses low-cost ammonium phosphate salts as dopants. Their application fields are generally fertilizers, flame retardants and other fields. They are widely available, stable in properties, safe and environmentally friendly. Using them as P and N dopants is inexpensive, significantly improves capacity, and is easy to mass-produce.

[0033] (4) The method of the present invention adopts one-step carbonization, introducing nitrogen atoms and phosphorus atoms into the carbon interlayer and micropore defects of coal-based soft / hard carbon materials to form covalent bonds. Nitrogen atom doping generates a large number of highly electronegative active sites at the doping sites, effectively enhancing the electron transport performance and electrochemical reaction activity of coal-based hard carbon. Phosphorus atom doping effectively increases the carbon interlayer spacing of coal-based soft / hard carbon, effectively promoting the material to obtain more disordered micropore defect structures under high temperature conditions, providing more sodium storage active sites for sodium ions, and effectively improving the discharge specific capacity, rate charge and discharge performance and low temperature performance of the composite material.

[0034] (5) The method of the present invention combines the coal blending process and the carbonizable binder to improve the uniformity and strength of the raw materials, increase the compaction density, enhance the inhibition of phosphorus volume expansion in the carbon matrix during the cycle, improve the conductivity, and significantly improve the electrochemical performance.

[0035] (6) The present invention has a short preparation process, simple process, low production cost, easy industrial production, green and environmentally friendly, and improves the disadvantages of long process, high cost and high alkali pollution of alkali activation process, while significantly improving performance. Attached Figure Description

[0036] Figure 1 This is a flowchart of the method of the present invention;

[0037] Figure 2 This is a SEM image of the negative electrode material prepared in Example 1 of the present invention;

[0038] Figure 3 This is a SEM image of the negative electrode material prepared in Example 2 of the present invention;

[0039] Figure 4 This is a flowchart of Comparative Example 1 of the present invention;

[0040] Figure 5 XRD diffraction patterns of different coal raw material precursors;

[0041] Figure 6 This is a SEM image of the negative electrode material prepared in Comparative Example 1 of this invention;

[0042] Figure 7 This is a SEM image of the negative electrode material prepared in Comparative Example 2 of this invention;

[0043] Figure 8 This is a SEM image of the negative electrode material prepared in Comparative Example 3 of this invention. Detailed Implementation

[0044] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0045] The preparation method of P, N co-doped high-pressure coal-based soft / hard carbon anode material of the present invention is as follows: Figure 1 As shown, please follow these steps:

[0046] Step 1: Crushing the raw coal:

[0047] Lump coal is crushed to an average particle size D50 of 5.0–8.0 μm, and strongly caking coal with a caking index G greater than 65 is crushed to an average particle size D50 of 5.0–8.0 μm.

[0048] The lump coal can be one or a mixture of several types of lump coal, such as anthracite, bituminous coal, lignite, and semi-coke (low-temperature coal carbonization feedstock). Strongly caking coal refers to coal that provides good caking properties during calcination. Specifically, the strongly caking coal used in this invention refers to coal with a caking index G greater than 65, including bituminous coal, gas-bituminous coal, some gas coal, 1 / 3 coking coal, and the more caking portion of coking coal. This type of coal typically has a high plastic layer thickness or a high Oya expansion degree, enabling it to act as a base coal in coal blending, enhancing the caking properties of the blend, and thus contributing to the formation of high-strength coal-based soft / hard carbon.

[0049] Step 2, Coal Blending:

[0050] The crushed lump coal and strongly caking coal from step 1 are compounded at a mass ratio of 4 to 5:1 and mixed evenly to obtain a coal-based precursor.

[0051] Step 3: Remove ash:

[0052] Add the coal-based precursor powder obtained in step 2 to a certain proportion of dilute hydrochloric acid and react fully. After filtering to pH=7, add a certain proportion of dilute hydrofluoric acid or sodium hydroxide solution and react fully. After filtering to pH=7, dry.

[0053] Step 4, Mix:

[0054] The impurity-removed coal-based precursor powder obtained in step 3 is mixed with dopant and coating agent in a solid phase to obtain P and N co-doped coal-based precursor.

[0055] The dopant is one or a mixture of several of the following: ammonium phosphate, ammonium hydrogen phosphate, sodium ammonium phosphate, and ammonium polyphosphate.

[0056] The coating agent is a carbonizable binder, which is one or a mixture of several of petroleum asphalt, coal tar pitch, phenolic resin, epoxy resin, polyacrylonitrile, and styrene-butadiene rubber.

[0057] The mass ratio of coal-based precursor powder, dopant, and coating agent is 100:5~25:5~10;

[0058] The equipment used for mixing is one of the following: mechanical fusion machine, V-type mixer, drum mixer, or cone mixer.

[0059] Step 5, calcination:

[0060] The P, N co-doped coal-based precursor obtained in step 4 was placed in a high-temperature atmosphere furnace and heated to 150–400°C at a rate of 1–5°C / min under a protective gas atmosphere. The temperature was maintained for 2.0–4.0 h. Then, the temperature was increased to 1100–1300°C at a rate of 1–5°C / min and maintained for 2.0–4.0 h. After the heat treatment, the furnace was allowed to cool naturally to room temperature to obtain P, N co-doped coal-based soft / hard carbon matrix A.

[0061] The protective gas is selected from one or a mixture of nitrogen, helium, neon, argon, krypton, or xenon, with a gas flow rate of 0.4–1.2 m³ / s. 3 / h;

[0062] Step 6, Secondary granulation:

[0063] The P, N co-doped coal-based soft / hard carbon matrix A obtained in step 5 is pulverized to obtain P, N co-doped coal-based soft / hard carbon matrix B; the average particle size D50 of the secondary granulation particles is 7.0 to 15.0 μm.

[0064] Step 7: Demagnetization and sieving.

[0065] The P, N co-doped coal-based soft / hard carbon matrix B obtained in step 6 is sieved and classified to obtain the final product, P, N co-doped coal-based soft / hard carbon composite anode material.

[0066] The working principle of the method of this invention is as follows:

[0067] This invention uses lump coal and strongly caking coal in a certain proportion as raw materials, ammonium phosphate salts as dopants, and carbonizable binders as coating agents. A solid-phase mixing coating method is employed, followed by a one-step high-temperature calcination, pulverization, and sieving process to prepare high-capacity P / N co-doped coal-based soft / hard carbon with high mechanical strength, excellent processing performance, large carbon interlayer spacing, and numerous sodium storage activity defects. One-step calcination achieves low-cost preparation.

[0068] In step 1, the raw materials are selected as needed, and all conventional lump coals are acceptable. The raw coal is crushed into micro powder with a narrow particle size distribution and good surface morphology. After crushing, the particle size distribution is controlled to have an average particle size D50 of 5.0 to 8.0 μm.

[0069] In step 2, the pulverized lump coal and highly caking coal from step 1 are blended in a certain proportion. This coal blending process can integrate the properties of different coals, thereby improving their performance in preparing anode materials. For example, adding a certain amount of coking coal, which melts at high temperatures, can uniformly wet and penetrate the surface and interior of the coal powder. This helps maintain the strength of the coal-based soft / hard carbon and inhibits the expansion of phosphorus during cycling. At the same time, some impurities with poor thermal stability in the high-volatile coal powder at this stage gradually undergo thermal decomposition, carbonization, or gasification, and are then discharged with the protective gas, creating coal precursors with different pore sizes.

[0070] In step 3, acid / alkali washing removes impurities and simultaneously regulates the microscopic pore spacing of coal powder, activates pore formation to increase defects, and enhances the disordered arrangement of carbon atoms, thereby achieving the dual purpose of material purification and increasing sodium storage active sites. On the other hand, the pores after acid washing effectively prevent the orderly rearrangement of carbon atoms in coal powder during heat treatment, thus inhibiting its graphitization process.

[0071] In step 4, P and N dopants and coating agents are mixed with coal precursors in a certain proportion. Solid-phase mixing is used at this time, and ammonium phosphate salts are selected as dopants because they are low in cost and can safely and uniformly introduce P and N into the coal-based precursors. At this time, it is still physical mixing, and the doping and coating effects are formed in a unified manner during high-temperature treatment.

[0072] In step 5, nitrogen and phosphorus atoms are introduced into the carbon interlayers and micropore defects through a one-step carbonization method, forming covalent bonds. Phosphorus doping increases the interlayer spacing of the coal-based hard carbon and helps suppress the directional growth of graphene domains under subsequent high-temperature conditions, resulting in a richer, disordered microporous defect structure, thus providing more sodium-storing active sites for sodium ions. The carbonizable binder, after being softened by heating, fully wets and penetrates the surface and defects of the phosphorus-nitrogen co-doped coal-based hard carbon material, while simultaneously coating the surface to reduce resistivity and specific surface area. Furthermore, it eliminates interparticle frictional stress, thereby increasing compaction density and effectively enhancing the mechanical strength of the secondary particles in the final product, giving the composite material good cycle stability. The carbon atoms at the interface of the P / N co-doped coal-based soft / hard carbon material generated by high-temperature calcination of the coal-based precursor, dopant, and carbonizable binder rearrange to form a stable chemical bond structure, thus linking and recombining the phosphorus-nitrogen co-doped coal-based hard carbon material.

[0073] In step 6, the matrix A obtained in step 5 is crushed to achieve secondary granulation.

[0074] In step 7, the matrix B obtained in step 6 is demagnetized to control the magnetic material within a certain range, generally below 100 ppm; sieving is performed to control the particle size within a certain range, so that the composite material exhibits macroscopic isotropy, which can effectively improve the uniformity and stability of the material structure and is suitable for sodium ions to be inserted and extracted during high-rate charging and discharging.

[0075] Example 1:

[0076] Step 1, Lump Coal Crushing: The Wuzhou lump coal is crushed by airflow to an average particle size D50 of 5.0-7.0 μm to obtain Wuzhou lump coal powder;

[0077] Coking coal (caking index G=70) was pulverized by air jet milling to an average particle size D50 of 5.0-7.0 μm to obtain coking coal (G=70) powder.

[0078] Step 2, Coal Blending:

[0079] The pulverized Wuzhou lump coal powder and fat coal powder from step 1 are compounded at a mass ratio of 5:1 and mixed evenly to obtain a coal-based precursor.

[0080] Step 3: Remove ash:

[0081] The coal-based precursor powder was mixed with 1 mol / L dilute hydrochloric acid at a ratio of 1:2 and stirred for 24 hours. After positive pressure filtration, the mixture was repeatedly washed with water until the pH reached 7. After positive pressure filtration, hydrofluoric acid and water were added according to the ratio of material: HF: H2O = 10 g: 2 mL: 100 mL. After stirring for 24 hours, the mixture was filtered under positive pressure and repeatedly washed with water until the pH reached 7. After positive pressure filtration, the mixture was dried in an 80℃ high-temperature oven.

[0082] Step 4, Mix:

[0083] The impurity-removed coal-based precursor powder obtained in step 3 is mixed with the dopant ammonium phosphate and the coating agent coal tar pitch in a solid phase.

[0084] The mass ratio of the coal-based precursor powder, dopant, and coating agent is 100:10:10.

[0085] The equipment used in the hybrid process is a mechanical fusion machine;

[0086] Step 5, calcination:

[0087] The P and N co-doped coal-based precursor obtained in step 4 was placed in a high-temperature atmosphere furnace and heated to 250°C at a rate of 2°C / min under a protective gas atmosphere. It was then kept at a constant temperature for 2.0 h, and then heated to 1100°C at a rate of 2°C / min. It was kept at a constant temperature for 2.0 h. After the heat treatment was completed, the furnace was allowed to cool naturally to room temperature to obtain P and N co-doped coal-based soft / hard carbon matrix A.

[0088] Nitrogen gas was selected as the protective gas, with a flow rate of 1.0 m³ / s. 3 / h;

[0089] Step 6, Secondary granulation:

[0090] The P, N co-doped coal-based soft / hard carbon matrix A obtained in step 5 is pulverized; the average particle size D50 of the secondary granulation particles is 7.0–10.0 μm.

[0091] Step 7: Demagnetization and sieving.

[0092] The P, N co-doped coal-based soft / hard carbon matrix B obtained in step 6 is sieved and classified to obtain the final product, P, N co-doped coal-based soft / hard carbon composite anode material.

[0093] The composite anode material obtained in Example 1 was subjected to physical and electrochemical performance tests. The electrochemical performance test method was as follows: The composite anode material, Super P, CMC, and SBR were mixed in a mass ratio of 94:1.5:2:2.5 to form a slurry. A 120µm four-sided coating tool was used to coat the black slurry onto copper foil. The membrane was then dried in a vacuum drying oven at 100°C for 2 hours. The electrode membrane was punched into a disc with a radius of 0.6mm using a punching machine. Sodium metal was used as the counter electrode, and 1mol / L NaClO4 and EC+DEC (1:1 vol%) were used as the electrolyte. A PP / PE / PP three-layer separator was used. The membrane was assembled into a CR2016 type button cell in a glove box. The above button cell was subjected to constant current charge-discharge tests at a current density of 0.1C (1C = 300mAh / g) and a voltage range of 2-0.005V.

[0094] The compacted density of the negative electrode material powder was measured to be 1.2 g / cm³. 3 The initial charge capacity at 0.1C is 275mAh / g, the initial efficiency is 89.7%, and the specific surface area of ​​the material, as measured by nitrogen adsorption-desorption testing, is 3.5m². 2 / g, the test results are summarized in Table 1.

[0095] like Figure 2 The image shown is a SEM image of the material prepared in Example 1. As can be seen from the image, the product prepared in Example 1 has a smooth surface and fewer cracks.

[0096] Example 2:

[0097] Step 1, Lump coal crushing: Xinjiang lignite is crushed by air jet milling to an average particle size D50 of 6.0-8.0 μm to obtain Xinjiang lignite coal powder;

[0098] Fat coal (caking index G=70) is pulverized by air jet milling to an average particle size D50 of 6.0-8.0 μm to obtain fat coal (G=70) powder;

[0099] Step 2, Coal Blending:

[0100] The Xinjiang lignite powder and coking coal powder pulverized in step 1 were compounded at a mass ratio of 4:1 and mixed evenly to obtain a coal-based precursor.

[0101] Step 3: Remove ash:

[0102] The coal-based precursor powder was mixed with 1 mol / L dilute hydrochloric acid at a ratio of 1:2 and stirred for 24 hours. After positive pressure filtration, the mixture was repeatedly washed with water until the pH reached 7. After positive pressure filtration, hydrofluoric acid and water were added according to the ratio of material: HF: H2O = 10 g: 2 mL: 100 mL. After stirring for 24 hours, the mixture was filtered under positive pressure and repeatedly washed with water until the pH reached 7. After positive pressure filtration, the mixture was dried in an 80℃ high-temperature oven.

[0103] Step 4, Mix:

[0104] The impurity-removed coal-based precursor powder obtained in step 3 is mixed with the dopant ammonium polyphosphate and the coating agent petroleum asphalt in a solid phase.

[0105] The mass ratio of coal-based precursor powder, dopant, and coating agent is 100:10:8;

[0106] The equipment used in the hybrid process is a mechanical fusion machine;

[0107] Step 5, calcination:

[0108] The P and N co-doped coal-based precursor obtained in step 4 was placed in a high-temperature atmosphere furnace and heated to 350°C at a rate of 2°C / min under a protective gas atmosphere. It was then kept at the same temperature for 2.0 h and then heated to 1200°C at a rate of 2°C / min. After the heat treatment was completed, the furnace was allowed to cool naturally to room temperature to obtain P and N co-doped coal-based soft / hard carbon matrix A.

[0109] Nitrogen gas was selected as the protective gas, with a flow rate of 1.2 m³ / s. 3 / h;

[0110] Step 6, Secondary granulation:

[0111] The P, N co-doped coal-based soft / hard carbon matrix A obtained in step 5 was pulverized; the average particle size D50 of the secondary granulation particles was 8.0 μm.

[0112] Step 7: Demagnetization and sieving.

[0113] The P, N co-doped coal-based soft / hard carbon matrix B obtained in step 6 is sieved and classified to obtain the final product, P, N co-doped coal-based soft / hard carbon composite anode material.

[0114] The composite anode material obtained in Example 2 was tested for physical and electrochemical properties using the same method as in Example 1. The compacted density of the anode material powder was measured to be 1.02 g / cm³. 3 The initial charge capacity at 0.1C is 295mAh / g, the initial efficiency is 89.3%, and the specific surface area of ​​the material, measured by nitrogen adsorption-desorption testing, is 2.9m². 2 / g, the test results are summarized in Table 1.

[0115] like Figure 3 The image shown is an SEM image of the material prepared in Example 2. As can be seen from the image, the product prepared in Example 2 has a smooth surface and fewer cracks.

[0116] Example 3:

[0117] Step 1, Lump coal crushing: Xinjiang lignite is crushed by air jet milling to an average particle size D50 of 6.0-7.0 μm to obtain Xinjiang lignite coal powder;

[0118] Taixi anthracite was pulverized by airflow to an average particle size D50 of 8.0 μm to obtain Taixi anthracite powder;

[0119] Coal (caking index G=70) was pulverized by air jet milling to an average particle size D50 of 8.0 μm to obtain coal powder (G=70);

[0120] Step 2, Coal Blending:

[0121] The Xinjiang lignite powder, Taixi anthracite powder and fat coal powder pulverized in step 1 were compounded in a mass ratio of 5:3:2 and mixed evenly to obtain a coal-based precursor.

[0122] Step 3: Remove ash:

[0123] The coal-based precursor was mixed with 1 mol / L dilute hydrochloric acid at a ratio of 1:2 and stirred for 24 hours. After positive pressure filtration, the mixture was repeatedly washed with water until the pH reached 7. After positive pressure filtration, hydrofluoric acid and water were added according to the ratio of material: HF: H2O = 10 g: 2 mL: 100 mL. After stirring for 24 hours, the mixture was filtered under positive pressure and repeatedly washed with water until the pH reached 7. After positive pressure filtration, the mixture was dried in an 80℃ high-temperature oven.

[0124] Step 4, Mix:

[0125] The impurity-free coal-based precursor powder obtained in step 3 is mixed with the dopant ammonium polyphosphate and the coating agent phenolic resin in a solid phase.

[0126] The mass ratio of coal-based precursor powder, dopant, and coating agent is 100:10:5.

[0127] The equipment used in the hybrid process is a mechanical fusion machine;

[0128] Step 5, calcination:

[0129] The P and N co-doped coal-based precursor obtained in step 4 was placed in a high-temperature atmosphere furnace and heated to 400°C at a rate of 2°C / min under a protective gas atmosphere. It was then kept at a constant temperature for 2.0 h, and then heated to 1250°C at a rate of 2°C / min. After the heat treatment was completed, the furnace was allowed to cool naturally to room temperature to obtain P and N co-doped coal-based soft / hard carbon matrix A.

[0130] Nitrogen gas was selected as the protective gas, with a flow rate of 1.2 m³ / s. 3 / h;

[0131] Step 6, Secondary granulation:

[0132] The P, N co-doped coal-based soft / hard carbon matrix A obtained in step 5 was pulverized; the average particle size D50 of the secondary granulation particles was 8.0 μm.

[0133] Step 7: Demagnetization and sieving.

[0134] The P, N co-doped coal-based soft / hard carbon matrix B obtained in step 6 is sieved and classified to obtain the final product, P, N co-doped coal-based soft / hard carbon composite anode material.

[0135] The composite anode material obtained in Example 3 was tested for physical and electrochemical properties using the same method as in Example 1. The compacted density of the anode material powder was measured to be 1.3 g / cm³. 3 The initial charge capacity at 0.1C is 290mAh / g, the initial efficiency is 89.7%, and the specific surface area of ​​the material, measured by nitrogen adsorption-desorption testing, is 3.1m². 2 / g, the test results are summarized in Table 1.

[0136] Example 4

[0137] Step 1, Lump coal crushing: The long-flame coal is crushed by airflow to an average particle size D50 of 5.0μm to obtain long-flame coal powder;

[0138] Yangquan anthracite was pulverized by airflow to an average particle size D50 of 8.0 μm to obtain Yangquan anthracite powder.

[0139] Coal (caking index G=70) was pulverized by air jet milling to an average particle size D50 of 8.0 μm to obtain coal powder (G=70);

[0140] Step 2, Coal Blending:

[0141] The long-flame coal powder, Yangquan anthracite coal powder, and fat coal powder pulverized in step 1 are compounded in a mass ratio of 5:4:2 and mixed evenly to obtain a coal-based precursor.

[0142] Step 3: Remove ash:

[0143] The coal-based precursor was mixed with 1 mol / L dilute hydrochloric acid at a ratio of 1:2 and stirred for 24 hours. After positive pressure filtration, the mixture was repeatedly washed with water until the pH reached 7. After positive pressure filtration, hydrofluoric acid and water were added according to the ratio of material: HF: H2O = 10 g: 2 mL: 100 mL. After stirring for 24 hours, the mixture was filtered under positive pressure and repeatedly washed with water until the pH reached 7. After positive pressure filtration, the mixture was dried in an 80℃ high-temperature oven.

[0144] Step 4, Mix:

[0145] The impurity-free coal-based precursor powder obtained in step 3 is mixed with the dopant ammonium polyphosphate and the coating agent phenolic resin in a solid phase.

[0146] The mass ratio of coal-based precursor powder, dopant, and coating agent is 100:5:5;

[0147] The equipment used in the hybrid process is a mechanical fusion machine;

[0148] Step 5, calcination:

[0149] The P and N co-doped coal-based precursor obtained in step 4 was placed in a high-temperature atmosphere furnace and heated to 300°C at a rate of 2°C / min under a protective gas atmosphere. It was then kept at a constant temperature for 2.0 h, and then heated to 1250°C at a rate of 2°C / min. After the heat treatment was completed, the furnace was allowed to cool naturally to room temperature to obtain P and N co-doped coal-based soft / hard carbon matrix A.

[0150] Nitrogen gas was selected as the protective gas, with a flow rate of 0.4 m³ / s. 3 / h;

[0151] Step 6, Secondary granulation:

[0152] The P, N co-doped coal-based soft / hard carbon matrix A obtained in step 5 was pulverized; the average particle size D50 of the secondary granulation particles was 8.0 μm.

[0153] Step 7: Demagnetization and sieving.

[0154] The P, N co-doped coal-based soft / hard carbon matrix B obtained in step 6 is sieved and classified to obtain the final product, P, N co-doped coal-based soft / hard carbon composite anode material.

[0155] The composite anode material obtained in Example 4 was tested for physical and electrochemical properties using the same method as in Example 1. The compacted density of the anode material powder was measured to be 1.3 g / cm³. 3 The initial charge capacity at 0.1C is 285mAh / g, the initial efficiency is 89.1%, and the specific surface area of ​​the material, as measured by nitrogen adsorption-desorption testing, is 3.5m². 2 / g, the test results are summarized in Table 1.

[0156] Comparative Example 1:

[0157] The preparation method of the unblended / undoped coal-based soft / hard carbon composite anode material in this comparative example is as follows: Figure 4 As shown, it includes the following steps:

[0158] Step 1: Weigh a certain amount of Wuzhou lump coal and perform air jet milling to make the particle size within a certain range (D50 is 5-8μm);

[0159] Step 2: Mix the Wuzhou lump coal powder after air jet milling with 1 mol / L dilute hydrochloric acid at a ratio of 1:2 and stir for 24 hours. Then, filter under positive pressure and repeatedly wash with water until pH=7. After positive pressure filtration, add hydrofluoric acid and water according to the ratio of material:HF:H2O=10g:2mL:100mL, stir for 24 hours, filter under positive pressure, and repeatedly wash with water until pH=7. After positive pressure filtration, dry in an 80℃ high-temperature oven.

[0160] Step 3: Place the acid-washed low-ash coal powder into a high-temperature tubular furnace, and introduce inert gas into the high-temperature furnace until the pressure inside the high-temperature furnace is greater than the standard atmospheric pressure and the purity of the inert gas inside the high-temperature furnace is ≥98%. Open the gas outlet of the high-temperature furnace to keep the inert gas flowing.

[0161] Step 4: Heat the high-temperature furnace to 350℃ at a heating rate of 2℃ / min, and hold at 350℃ for 2 hours; continue heating the high-temperature furnace to 1150℃ at a heating rate of 2℃ / min, and hold at 1150℃ for 2 hours; after holding, the carbon anode material product of lump coal is obtained.

[0162] Step 5: After the material from step 4 is calcined, cool it to room temperature at 5℃ / min, crush and screen it to obtain coal-based soft / hard carbon with an average particle size D50 of 8-9.0μm.

[0163] The physical and chemical properties of the unblended / undoped phosphorus-nitrogen coal-based hard carbon composite anode material obtained in Comparative Example 1 were tested using the same method as in Example 1. The tap density of the anode material powder was measured to be 1.0 g / cm³. 3 The initial charge capacity at 0.1C was 260 mAh / g, with an initial efficiency of 88%. The specific surface area of ​​the material in Comparative Example 1, measured by nitrogen adsorption-desorption testing, was 6.7 m².2 / g, the test results are summarized in Table 1.

[0164] Comparative Example 2:

[0165] The only difference was that the raw material in Comparative Example 1 was replaced with lignite, while everything else remained the same.

[0166] The composite anode material obtained in Comparative Example 2 was tested for physical and chemical properties using the same method as in Example 1. The tap density of the anode material powder was measured to be 0.83 g / cm³. 3 The initial charge capacity at 0.1C was 269.4 mAh / g, with an initial efficiency of 86.5%. The specific surface area of ​​the material in Comparative Example 1, measured by nitrogen adsorption-desorption testing, was 6.7 m². 2 / g, the test results are summarized in Table 1.

[0167] Comparative Example 1 used Wuzhou lump coal with low defect degree as a precursor, resulting in a low reversible specific capacity of only 260 mAh / g, but high compaction and first-efficiency performance. Comparative Example 2 used lignite with high defect degree as a precursor, resulting in a high reversible specific capacity, but low compaction and first-efficiency performance. This shows that the electrochemical performance of different precursors varies significantly. Therefore, selecting a suitable lump coal precursor is crucial to the performance of the final product. Figure 5 The figure shows the XRD diffraction patterns of different coal precursors, where HM is lignite, YQM is Yangquan anthracite, PSM is lean coal, and TXM is Taixi anthracite. It can be seen that the number and types of diffraction impurity peaks of different precursor materials are different, which corresponds to the different electrochemical properties of different precursors.

[0168] Figure 6 This is a SEM image of the material prepared in Comparative Example 1 (Wuzhou lump coal coated with one-step carbonization). Figure 7 The SEM images of the materials prepared in Comparative Example 2 (one-step carbonization of lignite) show that, using only a one-step carbonization process, the surface of the Wuzhou lump coal is relatively smooth, and its surface fragmentation is less than that of lignite. Figure 7 Less lignite; a comparison of the SEM images with those of Example 1 (Wuzhou lump coal blended with coal tar pitch) shows that the finished product prepared by the method of Example 1 of this invention has significantly fewer broken particles, a smoother and flatter surface, and fewer pores.

[0169] Comparative Example 3:

[0170] It is basically the same as Example 1, except that no coal blending was performed, that is, no coking coal powder was added.

[0171] The composite anode material obtained in Comparative Example 3 was tested for physical and chemical properties using the same method as in Example 1. The compacted density of the anode material powder was measured to be 0.95 g / cm³. 3The initial charge capacity at 0.1C is 270mAh / g, the initial efficiency is 89.1%, and the specific surface area of ​​the material, measured by nitrogen adsorption-desorption testing, is 3.1m². 2 / g, the test results are summarized in Table 1.

[0172] Figure 8 The SEM image of the material prepared in Comparative Example 3 is shown. Compared with the SEM image of Example 1, it can be seen that the material surface has a few pores when no coal is added, while the surface of the material prepared by the coal-added coating process in Example 1 is smoother.

[0173] Comparative Example 4:

[0174] It is basically the same as Example 1, except that no dopant ammonium phosphate is added.

[0175] The composite anode material obtained in Comparative Example 4 was tested for physical and chemical properties using the same method as in Example 1. The compacted density of the anode material powder was measured to be 1.33 g / cm³. 3 The initial charge capacity at 0.1C is 260mAh / g, the initial efficiency is 89.1%, and the specific surface area of ​​the material, as measured by nitrogen adsorption-desorption testing, is 3.5m². 2 / g, the test results are summarized in Table 1.

[0176] Comparative Example 5:

[0177] It is basically the same as Example 1, except that no carbonizable binder coal tar pitch is added.

[0178] The composite anode material obtained in Comparative Example 5 was tested for physical and chemical properties using the same method as in Example 1. The tap density of the anode material powder was 1.1 g / cm³. 3 The initial charge capacity at 0.1C was 280mAh / g, and the initial efficiency was 84.9%. The specific surface area of ​​Example 1, measured by nitrogen adsorption-desorption testing, was 9.5m². 2 / g, the test results are summarized in Table 1.

[0179] Table 1. Material performance test results

[0180]

[0181]

[0182] As can be seen from Table 1, the performance of the anode materials prepared from the same type of lump coal raw material using the method of the present invention is improved to a certain extent; the compaction density of the finished coal-based soft / hard carbon materials prepared in Examples 1-4 of the present invention is 1.02-1.3 g / cm³. 3The compaction density of the materials prepared by the one-step carbonization method using the same coal raw material in Comparative Examples 1-2 was higher than that of the materials prepared by the same coal raw material without blending in Comparative Example 3. Comparative Example 4 involved blending coal but without adding any dopants, resulting in a significantly higher compaction density, but also a significantly lower reversible specific capacity. Comparative Example 5, without the addition of a carbonizable binder, coal tar pitch, had a large specific surface area of ​​9.5 m². 2 / g will lead to an increase in side reactions after the material surface comes into contact with it, which is detrimental to the material's first-efficiency. In summary, the method of the present invention, by blending coal, adding dopants and carbonizable binders, can increase the reversible specific capacity while reducing the compaction density. The coal blending process and the addition of binders can comprehensively improve performance and optimize the low compaction and high specific surface area problems caused by the addition of dopants.

[0183] Example 1 of the present invention: compaction 1.2 g / cm³ 3 Comparative Example 1, compacted to 1.0 g / cm³ 3 This indicates that the combined effects of doping, coal blending process, and the addition of binders significantly improve compaction and reversible specific capacity.

[0184] Comparative Example 1: Compacted at 1.0 g / cm³ 3 However, its reversible specific capacity is low, only 260mAh / g; Comparative Example 2 has a compaction capacity of 0.83g / cm³. 3 The reversible specific capacity was 269.4 mAh / g, which was higher than that of Comparative Example 1. The analysis is that the raw materials with higher coalification degree have fewer defects, so the compaction is higher. However, the capacity of raw materials with higher coalification degree is lower after one-step carbonization. Therefore, under the same process, the compaction and capacity of the same coal raw materials are inversely proportional.

Claims

1. A method for preparing P, N co-doped high-pressure coal-based soft / hard carbon anode materials, characterized in that, The specific steps are as follows: Step 1: Select lump coal and strongly caking coal as raw coal, and crush them; Step 2: Mix the crushed lump coal and strongly caking coal from Step 1 evenly to obtain a coal-based precursor; Step 3: Remove the ash from the coal-based precursor obtained in Step 2; Step 4: Mix the coal-based precursor obtained in Step 3 with the dopant and coating agent in a solid phase to obtain a P and N co-doped coal-based precursor. Step 5: Under a protective gas atmosphere, calcine the P, N co-doped coal-based precursor obtained in step 4 to obtain P, N co-doped coal-based soft / hard carbon matrix A. Step 6: Crush the P, N co-doped coal-based soft / hard carbon matrix A obtained in Step 5 and perform secondary granulation to obtain P, N co-doped coal-based soft / hard carbon matrix B. Step 7: Demagnetize and classify the P, N co-doped coal-based soft / hard carbon matrix B obtained in Step 6 to obtain P, N co-doped coal-based soft / hard carbon composite anode material. In the coal-based precursor of step 2, the mass ratio of lump coal to strongly caking coal is 4~5:1; Step 3 specifically involves: Add the coal-based precursor powder obtained in step 2 to dilute hydrochloric acid and react fully. After filtering to pH=7, add it to dilute hydrofluoric acid or sodium hydroxide solution and react fully. After filtering to pH=7, dry it. In step 4, the dopant is one or a mixture of several of the following: ammonium phosphate, ammonium hydrogen phosphate, sodium ammonium phosphate, and ammonium polyphosphate. In step 4, the coating agent is one or a mixture of several of petroleum asphalt, coal tar pitch, phenolic resin, epoxy resin, polyacrylonitrile, and styrene-butadiene rubber. In step 4, the mass ratio of the coal-based precursor, dopant, and coating agent is 100:5 to 25:5 to 10. Step 5 specifically involves: The P, N co-doped coal-based precursor obtained in step 4 was placed in a high-temperature atmosphere furnace and heated to 150–400°C at a rate of 1–5°C / min under a protective gas atmosphere. The temperature was maintained for 2.0–4.0 h. Then, the temperature was increased to 1100–1300°C at a rate of 1–5°C / min and maintained for 2.0–4.0 h. After the heat treatment, the furnace was allowed to cool naturally to room temperature to obtain P, N co-doped coal-based soft / hard carbon matrix A. The protective gas is selected from one or a mixture of nitrogen, helium, neon, argon, krypton, or xenon, with a gas flow rate of 0.4–1.2 m³ / s. 3 / h.

2. The method for preparing P, N co-doped high-pressure coal-based soft / hard carbon anode material according to claim 1, characterized in that, In step 1, the strongly caking coal is coal with a caking index G greater than 65, and the lump coal and strongly caking coal are crushed to an average particle size D50 of 5.0 to 8.0 μm.

3. The method for preparing P, N co-doped high-pressure coal-based soft / hard carbon anode material according to claim 1, characterized in that, In step 6, the average particle size D50 of the secondary granulation particles is 7.0–15.0 μm.

4. A P / N co-doped high-pressure coal-based soft / hard carbon anode material, characterized in that, It is prepared by any of the preparation methods described in claims 1-3.

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