A hard carbon negative electrode material for multi-coal composite sodium battery, preparation method and application

Abstract

The present invention belongs to the technical field of sodium-ion batteries and discloses a multi-coal composite sodium battery hard carbon negative electrode material, preparation method, and application. Based on three coal raw materials with different characteristics, the hard carbon material with excellent structure and good performance is prepared by utilizing their respective compositional characteristics, pyrolysis characteristics, and structural characteristics. The overall preparation method is simple, large-scale production is easy, and no highly polluting chemical reagents are required. As a sodium-ion battery negative electrode material, the reversible specific capacity is as high as 350 mAh / g, and it exhibits ultra-high rate performance.

Description

Technical Field

[0001] The present invention belongs to the technical field of sodium ion batteries, and in particular relates to a hard carbon negative electrode material for a multi-coal composite sodium battery, a preparation method and an application thereof. Background Art

[0002] Sodium-ion batteries have become the most promising new type of battery due to their advantages in sodium resource reserves and the potential for lower material costs than lithium. Among them, hard carbon has become the mainstream negative electrode material for sodium-ion batteries due to its disordered structure, large interlayer spacing and abundant voids, which can efficiently accommodate sodium ions with a larger radius. Hard carbon has an important impact on the performance and cost of sodium-ion batteries. At present, the mainstream preparation method of hard carbon is based on biomass raw materials, but biomass raw materials have the problems of high cost and poor batch stability, which restricts the industrial development of sodium batteries. In contrast, coal has the advantages of abundant reserves, low price and high yield, and is a very promising alternative to biomass raw materials.

[0003] However, coal raw materials have a more ordered microcrystalline structure, and conventional hard carbon preparation processes cannot form a large sodium storage space. Therefore, the defect of low capacity performance has become a key factor restricting the development of coal-based hard carbon. Although there are currently various capacity enhancement methods, such as activation pore formation, gas phase coating, and blending with other materials, they all have problems such as high chemical reagent costs, harsh preparation process conditions, limited capacity enhancement effects, or poor rate performance. Based on this, the present invention proposes a new process to address the above problems. Summary of the Invention

[0004] In order to solve the above technical problems, the present invention provides a method for preparing hard carbon negative electrode materials for multi-coal composite sodium batteries. By utilizing the specific composition, structural characteristics and bonding properties of different coal types, the method rationally expands the active sites of the material and optimizes the structural characteristics of the particles, so that the obtained coal-based hard carbon can achieve a significant capacity improvement while still maintaining high kinetic properties.

[0005] In order to achieve the above-mentioned object of the invention, the technical solution adopted by the present invention is as follows:

[0006] In a first aspect of the present invention, the present invention provides a method for preparing a hard carbon negative electrode material for a multi-coal composite sodium battery, comprising:

[0007] S1. Grinding and pelletizing the first, second, and third types of coal respectively, and then acid-washing and purifying them. Among the three types of coal, the first type of coal serves as a matrix skeleton, the second type of coal has the lowest degree of coalification and is used for catalytic activation of the first type of coal, and the third type of coal contains a liquid-phase binding component;

[0008] S2. Evenly mixing the first type of coal and the second type of coal, calcining them in a closed environment and an inert gas atmosphere, and naturally cooling them to room temperature to obtain a mixed coal powder, wherein the calcination temperature is 700-1000° C., and the materials are kept dynamically mixed during the calcination process;

[0009] S3, uniformly mixing the mixed pulverized coal and the third type of coal and calcining them in an inert gas atmosphere at a calcination temperature of 400-600° C., maintaining dynamic mixing of the materials during the calcination process, and naturally cooling to room temperature after calcination to obtain a precursor pulverized coal;

[0010] S4. calcining the precursor coal powder at a calcination temperature of 1100-1500° C. and naturally cooling to room temperature after calcination to obtain a hard carbon negative electrode material.

[0011] Preferably, the first type of coal includes one or more of anthracite, lean coal, lean coal, weakly sticky coal, non-sticky coal, and long flame coal; the second type of coal includes lignite; and the third type of coal includes one or more of coking coal, fat coal, gas coal, and gas-fat coal.

[0012] Preferably, in step S1, the particle size of the first type of coal after grinding is 3-6 μm, the particle size of the second type of coal after grinding is 2-4 μm, and the particle size of the third type of coal after grinding is 1-3 μm.

[0013] Preferably, in step S2, the mass ratio of the first type of coal to the second type of coal is (1-5):1.

[0014] Preferably, in step S2, the heating rate during the calcination process is 1-5°C / min, and the holding time is 2-5 h.

[0015] Preferably, in step S3, the mass ratio of the mixed coal powder to the third type of coal is 100:(3-8).

[0016] Preferably, in step S3, the heating rate during the calcination process is 1-5°C / min, and the holding time is 2-5 h.

[0017] Preferably, in step S4, the heating rate during the calcination process is 1-10°C / min.

[0018] In the second aspect of the present invention, the present invention provides a multi-coal composite sodium battery hard carbon negative electrode material, which is prepared by the above-mentioned preparation method, and preferably has an average particle size of 5 to 10 μm.

[0019] In the third aspect of the present invention, the present invention proposes an application of a hard carbon negative electrode material for a multi-coal composite sodium battery, and the prepared hard carbon negative electrode material is applied to a sodium ion battery to prepare a sodium ion battery negative electrode material.

[0020] Beneficial effects

[0021] The present invention uses three types of coal raw materials with different characteristics as the basis, and utilizes their respective compositional properties, pyrolysis properties, and structural characteristics to prepare a hard carbon material with excellent structure and good performance. The overall preparation method is simple, large-scale production is easy, and no highly polluting chemical reagents are required. As a negative electrode material for sodium ion batteries, the reversible specific capacity is as high as 350 mAh / g, and it exhibits ultra-high rate performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Shown is the SEM image of the hard carbon material prepared in Example 1. DETAILED DESCRIPTION

[0023] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the specific embodiments of the present invention will be described below with reference to the accompanying drawings. Obviously, the embodiments described below are only some embodiments of the present invention. For those skilled in the art, other drawings and other embodiments can be obtained based on these drawings without inventive work.

[0024] This invention proposes a multi-coal composite sodium battery hard carbon anode material. This material utilizes the specific composition, structural characteristics, and bonding properties of different coal types to rationally expand the material's active sites and optimize the particle structure. Specifically, the raw materials for the multi-coal composite sodium battery hard carbon anode material include a first coal type, a second coal type, and a third coal type. The first coal type serves as a matrix skeleton, the second coal type catalytically activates the first coal type, and the third coal type bonds the first and second coal types to form secondary particles and coats and modifies surface openings.

[0025] The first type of coal is preferably a highly coalified type with a low volatile content, high density, high carbon content, and good electrical conductivity, which can serve as a matrix skeleton. In some embodiments, the first type of coal includes one or more of anthracite, lean coal, lean coal, slightly caking coal, non-caking coal, and long flame coal.

[0026] The second type of coal preferably uses the coal with the lowest degree of coalification, that is, the second type of coal includes lignite.

[0027] The third type of coal is preferably a type of coal with high cohesiveness, which has strong cohesive properties and forms a large amount of fluid colloid when heated to reconcile the melting properties of the first and second types of coal. In some embodiments, the third type of coal includes one or more of coking coal, fat coal, gas coal, and gas-fat coal.

[0028] Based on the above raw materials, the present invention proposes a method for preparing a hard carbon negative electrode material for a multi-coal composite sodium battery as follows:

[0029] S1. Grind and pelletize the first type of coal, the second type of coal, and the third type of coal respectively, and then acid-wash and purify them;

[0030] S2. Evenly mix the first type of coal and the second type of coal, place them in a closed environment and calcine them in an inert gas atmosphere at a temperature of 700 to 1000° C., maintain dynamic mixing of the materials during the calcination process, and naturally cool them to room temperature after calcination to obtain a mixed coal powder;

[0031] S3, uniformly mixing the mixed pulverized coal and the third type of coal and calcining them in an inert gas atmosphere at a calcination temperature of 400-600° C., maintaining dynamic mixing of the materials during the calcination process, and naturally cooling to room temperature after calcination to obtain a precursor pulverized coal;

[0032] S4. calcining the precursor coal powder at a calcination temperature of 1100-1500° C. and naturally cooling to room temperature after calcination to obtain a hard carbon negative electrode material.

[0033] The present invention uses low-cost and abundant coal as raw material, has a simple preparation process and mild conditions, and is easy to scale up industrially. It is a technical route with great cost advantages.

[0034] The present invention selects coal types with complementary properties and mixes and calcines them in a specific order to achieve structural optimization and performance modification of the target material. The method first calcines a first coal type with a second coal type. The first coal type, with its high density, high carbon content, and excellent conductivity, serves as the matrix skeleton of the hard carbon material. The second coal type, with its abundant inherent porosity, provides ample sodium storage space. Furthermore, the second coal type contains a high content of active components (such as humus) and moisture. During the first calcination, it catalytically activates the first coal type, increasing the porosity and structural defects of the mixed coal powder. After the mixed coal powder is calcined, a third coal type (a highly caking coal type) is added. During the second calcination, the third coal type releases a liquid-phase caking component, which binds the first and second coal types into secondary particles. The surface pores of the coal powder are then coated and modified. The resulting precursor coal powder is finally calcined and carbonized to produce a hard carbon anode material that not only exhibits high capacity but also maintains excellent rate performance under high-rate charge and discharge conditions.

[0035] Preferably, in step S1, the particle size of the first type of coal after grinding is 3-6 μm, the particle size of the second type of coal after grinding is 2-4 μm, and the particle size of the third type of coal after grinding is 1-3 μm.

[0036] In step S1, acid washing and purification is to reduce the ash content of hard carbon to avoid the negative effect of high ash content of coal powder on battery performance. Acid washing and purification is a conventional process for coal processing and will not be described in detail in this invention.

[0037] Preferably, in step S2, the mass ratio of the first type of coal to the second type of coal is (1-5):1.

[0038] The calcination temperature in step S2 is 700-1000°C, below the carbonization temperature. Under these calcination conditions, the volatile matter produced by the second type of coal catalyzes and activates the first type of coal in a closed environment. This closed environment helps minimize volatile matter loss and maintains a dynamic mixing state, ensuring a smooth reaction between the first and second types of coal. Preferably, the first and second types of coal are calcined in a rotary kiln.

[0039] Preferably, in step S2, the heating rate during the calcination process is 1-5°C / min, and the holding time is 2-5 hours. The inert gas atmosphere can be an atmosphere formed by nitrogen, helium, or the like.

[0040] Preferably, in step S3, the mass ratio of the mixed coal powder to the third type of coal is 100:(3-8). It should be noted that the mass ratio of the mixed coal powder to the third type of coal in step S3 actually refers to the ratio of the mass of the mixed coal powder obtained after the first type of coal and the second type of coal are mixed and calcined to the mass of the third type of coal.

[0041] The calcination temperature in step S3 is 400-600°C, lower than that in step S2. This prevents the liquid-phase binding components precipitated from the third type of coal from coking and affecting fluidity. Calcination in step S3 does not require a closed environment; instead, dynamic mixing of the materials is necessary during the calcination process to ensure sufficient contact between the liquid-phase binding components precipitated from the third type of coal and the mixed coal powder. For example, the mixed coal powder and the third type of coal can be calcined in a reactor equipped with a stirring mechanism.

[0042] Preferably, in step S3, the heating rate during the calcination process is 1-5°C / min, and the holding time is 2-5 hours. The inert gas atmosphere can be an atmosphere formed by nitrogen, helium, or the like.

[0043] The present invention prepares a precursor coal powder by sequentially mixing the three types of coal in steps S2 and S3, and then performs a final calcination and carbonization in step S4 to produce a hard carbon material. Preferably, in step S4, the calcination process is performed at a heating rate of 1 to 10°C / min. The calcination and carbonization are also performed in an inert gas atmosphere.

[0044] The hard carbon negative electrode material prepared by the present invention has the structural characteristics of secondary particles, has a rich pore structure, and an average particle size of 5 to 10 μm. The hard carbon negative electrode material prepared by the present invention can be used in sodium ion batteries to make battery negative electrodes.

[0045] The technical solutions of the present invention are described in detail below using specific embodiments. Experimental methods in the following examples, where specific conditions are not specified, were performed according to conventional conditions in the art or according to conditions recommended by the manufacturer. Raw materials and reagents used, unless otherwise specified, were obtained from commercial sources such as conventional markets.

[0046] Example 1

[0047] Long flame coal (i.e., the first type of coal), lignite (i.e., the second type of coal) and coking coal (i.e., the third type of coal) are all ground and granulated, and then acid-washed and purified. The average particle size of the long flame coal after grinding is 5 μm, the average particle size of the lignite after grinding is 2 μm, and the average particle size of the coking coal after grinding is 1 μm.

[0048] Long flame coal and lignite were evenly mixed in a mass ratio of 3:1, placed in a rotary kiln and calcined in an inert gas atmosphere with a heating rate of 3°C / min, a calcination temperature of 800°C, and a holding time of 2 h. During the calcination process, the materials were kept dynamically mixed. After calcination, the mixture was naturally cooled to room temperature to obtain mixed coal powder.

[0049] The mixed coal powder and coking coal were evenly mixed in a mass ratio of 100:5 and placed in a reactor for calcination in an inert gas atmosphere. The heating rate was 3°C / min, the calcination temperature was 600°C, and the holding time was 2 h. The materials were kept dynamically mixed during the calcination process. After calcination, the mixture was naturally cooled to room temperature to obtain the precursor coal powder.

[0050] The precursor coal powder was placed in a box furnace and calcined at a heating rate of 5 ° C / min, a calcination temperature of 1400 ° C, and a holding time of 5 h. After calcination, it was naturally cooled to room temperature to obtain a hard carbon negative electrode material, such as Figure 1 shown.

[0051] Example 2

[0052] Anthracite (i.e. the first type of coal), lignite (i.e. the second type of coal) and fat coal (i.e. the third type of coal) are all ground and granulated, and then acid-washed and purified. Among them, the average particle size of long flame coal after grinding is 5μm, the average particle size of lignite after grinding is 3μm, and the average particle size of coking coal after grinding is 2μm.

[0053] Anthracite and lignite were evenly mixed in a mass ratio of 3:1, placed in a rotary kiln and calcined in an inert gas atmosphere with a heating rate of 3°C / min, a calcination temperature of 700°C, and a holding time of 2 h. During the calcination process, the materials were kept dynamically mixed. After calcination, the mixture was naturally cooled to room temperature to obtain mixed coal powder.

[0054] The mixed coal powder and fat coal were evenly mixed in a mass ratio of 100:3 and placed in a reactor for calcination in an inert gas atmosphere. The heating rate was 3°C / min, the calcination temperature was 500°C, and the holding time was 2 h. The materials were kept dynamically mixed during the calcination process. After calcination, the mixture was naturally cooled to room temperature to obtain the precursor coal powder.

[0055] The precursor coal powder was placed in a box furnace for calcination at a heating rate of 5°C / min, a calcination temperature of 1400°C, and a holding time of 5 h. After calcination, it was naturally cooled to room temperature to obtain a hard carbon negative electrode material.

[0056] Example 3

[0057] The lean coal (i.e. the first type of coal), lignite (i.e. the second type of coal) and gas coal (i.e. the third type of coal) are all ground and granulated, and then acid washed and purified. Among them, the average particle size of the long flame coal after grinding is 5μm, the average particle size of the lignite after grinding is 3μm, and the average particle size of the coking coal after grinding is 2μm.

[0058] Lean coal and lignite were evenly mixed in a mass ratio of 3:1, placed in a rotary kiln and calcined in an inert gas atmosphere with a heating rate of 3°C / min, a calcination temperature of 700°C, and a holding time of 2 h. During the calcination process, the materials were kept dynamically mixed. After calcination, the mixture was naturally cooled to room temperature to obtain mixed coal powder.

[0059] The mixed coal powder and gas coal were evenly mixed in a mass ratio of 100:3 and placed in a reactor for calcination in an inert gas atmosphere. The heating rate was 3°C / min, the calcination temperature was 500°C, and the holding time was 2 h. The materials were kept dynamically mixed during the calcination process. After calcination, the mixture was naturally cooled to room temperature to obtain the precursor coal powder.

[0060] The precursor coal powder was placed in a box furnace for calcination at a heating rate of 5°C / min, a calcination temperature of 1400°C, and a holding time of 5 h. After calcination, it was naturally cooled to room temperature to obtain a hard carbon negative electrode material.

[0061] Comparative Example 1

[0062] Compared with Example 1, this comparative example only uses the first type of coal and the third type of coal.

[0063] The long flame coal (ie, the first type of coal) and the coking coal (ie, the third type of coal) are both ground and granulated, and then acid washed and purified. The average particle size of the long flame coal after grinding is 5 μm, and the average particle size of the coking coal after grinding is 1 μm.

[0064] The long flame coal was placed in a rotary kiln and calcined in an inert gas atmosphere with a heating rate of 3°C / min, a calcination temperature of 800°C, a holding time of 2 h, and naturally cooled to room temperature after calcination.

[0065] Long flame coal and coking coal were evenly mixed in a mass ratio of 100:5 and placed in a reactor for calcination in an inert gas atmosphere. The heating rate was 3°C / min, the calcination temperature was 600°C, and the holding time was 2 h. The materials were kept dynamically mixed during the calcination process. After calcination, the mixture was naturally cooled to room temperature to obtain precursor coal powder.

[0066] The precursor coal powder was placed in a box furnace and calcined at a heating rate of 5°C / min, a calcination temperature of 1400°C, and a holding time of 5 h. After calcination, it was naturally cooled to room temperature to obtain a hard carbon material.

[0067] Comparative Example 2

[0068] Compared with Example 1, this comparative example only uses the first type of coal and the second type of coal.

[0069] The long flame coal (ie, the first type of coal) and the lignite (ie, the second type of coal) are both ground and granulated, and then acid washed and purified. The average particle size of the long flame coal after grinding is 5 μm, and the average particle size of the lignite after grinding is 2 μm.

[0070] Long flame coal and lignite were evenly mixed in a mass ratio of 3:1, placed in a rotary kiln and calcined in an inert gas atmosphere with a heating rate of 3°C / min, a calcination temperature of 800°C, and a holding time of 2 h. During the calcination process, the materials were kept dynamically mixed. After calcination, the mixture was naturally cooled to room temperature to obtain mixed coal powder.

[0071] The mixed coal powder was placed in a reactor and calcined in an inert gas atmosphere at a heating rate of 3°C / min, a calcination temperature of 600°C, and a holding time of 2 h. During the calcination process, the materials were kept dynamically mixed. After calcination, the materials were naturally cooled to room temperature to obtain the precursor coal powder.

[0072] The precursor coal powder was placed in a box furnace and calcined at a heating rate of 5°C / min, a calcination temperature of 1400°C, and a holding time of 5 h. After calcination, it was naturally cooled to room temperature to obtain a hard carbon material.

[0073] Comparative Example 3

[0074] Compared with Example 1, this comparative example only uses the first type of coal.

[0075] The long flame coal (ie the first type of coal) is ground into particles and then acid washed and purified, wherein the average particle size of the long flame coal after grinding is 5 μm.

[0076] The long flame coal was placed in a rotary kiln and calcined in an inert gas atmosphere with a heating rate of 3°C / min, a calcination temperature of 800°C, a holding time of 2 h, and naturally cooled to room temperature after calcination.

[0077] The calcined long flame coal was placed in a reactor and calcined in an inert gas atmosphere at a heating rate of 3°C / min, a calcination temperature of 600°C, and a holding time of 2 h. After calcination, it was naturally cooled to room temperature.

[0078] The secondary calcined long flame coal was placed in a box furnace for calcination at a heating rate of 5°C / min, a calcination temperature of 1400°C, and a holding time of 5 h. After calcination, it was naturally cooled to room temperature to obtain a hard carbon material.

[0079] Comparative Example 4

[0080] Compared with Example 1, this comparative example only uses the second type of coal.

[0081] The lignite (i.e. the second type of coal) is ground into particles and then acid-washed and purified, wherein the average particle size of the lignite after grinding is 2 μm.

[0082] The lignite was placed in a rotary kiln and calcined in an inert gas atmosphere with a heating rate of 3°C / min, a calcination temperature of 800°C, a holding time of 2 h, and naturally cooled to room temperature after calcination.

[0083] The calcined lignite was placed in a reactor and calcined in an inert gas atmosphere at a heating rate of 3°C / min, a calcination temperature of 600°C, and a holding time of 2 h. After calcination, it was naturally cooled to room temperature.

[0084] The secondary calcined lignite was placed in a box furnace for calcination at a heating rate of 5°C / min, a calcination temperature of 1400°C, and a holding time of 5 h. After calcination, the material was naturally cooled to room temperature to obtain a hard carbon material.

[0085] Comparative Example 5

[0086] Compared with Example 1, in this comparative example, the first type of coal, the second type of coal and the third type of coal are directly mixed and placed in a closed environment for calcination.

[0087] Long flame coal (i.e., the first type of coal), lignite (i.e., the second type of coal) and coking coal (i.e., the third type of coal) are all ground and granulated, and then acid-washed and purified. The average particle size of the long flame coal after grinding is 5 μm, the average particle size of the lignite after grinding is 2 μm, and the average particle size of the coking coal after grinding is 1 μm.

[0088] Long flame coal, lignite and coking coal were evenly mixed in a mass ratio of 15:5:1, placed in a rotary kiln and calcined in an inert gas atmosphere with a heating rate of 3°C / min, a calcination temperature of 800°C, and a holding time of 2 h. During the calcination process, the materials were kept dynamically mixed. After calcination, the mixture was naturally cooled to room temperature to obtain a precursor coal powder.

[0089] The precursor coal powder was placed in a box furnace and calcined at a heating rate of 5°C / min, a calcination temperature of 1400°C, and a holding time of 5 h. After calcination, it was naturally cooled to room temperature to obtain a hard carbon material.

[0090] Comparative Example 6

[0091] Compared with Example 1, in this comparative example, the first type of coal, the second type of coal and the third type of coal are directly mixed and placed in an open environment for calcination.

[0092] Long flame coal (i.e., the first type of coal), lignite (i.e., the second type of coal) and coking coal (i.e., the third type of coal) are all ground and granulated, and then acid-washed and purified. The average particle size of the long flame coal after grinding is 5 μm, the average particle size of the lignite after grinding is 2 μm, and the average particle size of the coking coal after grinding is 1 μm.

[0093] Long flame coal, lignite and coking coal were evenly mixed in a mass ratio of 15:5:1, placed in a reactor and calcined in an inert gas atmosphere with a heating rate of 3°C / min, a calcination temperature of 800°C, and a holding time of 2 h. During the calcination process, the materials were kept dynamically mixed. After calcination, the mixture was naturally cooled to room temperature to obtain a precursor coal powder.

[0094] The precursor coal powder was placed in a box furnace and calcined at a heating rate of 5°C / min, a calcination temperature of 1400°C, and a holding time of 5 h. After calcination, it was naturally cooled to room temperature to obtain a hard carbon material.

[0095] The hard carbon materials prepared in Examples 1-3 and Comparative Examples 1-6 were subjected to performance testing, and the particle size and specific surface area of ​​the negative electrode active materials prepared above were tested with reference to the standard "GBT24533-2019".

[0096] The hard carbon material prepared above was ground and mixed with carbon black and PVDF in a mass ratio of 8:1:1, and then coated on the surface of copper foil and then vacuum dried. Metal sodium was used as the counter electrode, a glass fiber diaphragm was used as the diaphragm, and sodium perchlorate was used as the electrolyte salt of the electrolyte. The button battery was assembled in a glove box. The button battery model was CR2032. The assembled button battery was charged and discharged at a current of 0.1C in a battery test system, and the 0.1C reversible capacity of the battery was recorded. Then, the battery was charged and discharged at currents of 1C, 2C and 3C respectively. The battery capacity (1C, 2C, 3C) measured at different rates was divided by the 0.1C reversible capacity to obtain the capacity retention rate at different rates. The test results are shown in Table 1.

[0097] Table 1 Test results of hard carbon materials obtained in Examples 1-3 and Comparative Examples 1-6

[0098] <![CDATA[Specific surface area (m 2 / g)]]> Average particle size (μm) 0.1C reversible capacity (mAh / g) First coulombic efficiency (%) 1C capacity retention rate (%) 2C capacity retention rate (%) 3C capacity retention rate (%) Example 1 5 7 359 92 89 85 80 Example 2 4 8 351 93 91 86 83 Example 3 4 8 355 92.5 90 85 81 Comparative Example 1 3.8 6 250 93 91 86.5 82 Comparative Example 2 17 5 320 86 85 78 75 Comparative Example 3 8 5 247 90 89 86 80 Comparative Example 4 23 4 310 84 84 79 72 Comparative Example 5 7 8 325 88 85 76 73 Comparative Example 6 3 7 282 91 92 87 80

[0099] According to the data in Table 1, the hard carbon material prepared based on the method of the present invention has a controllable specific surface area, high capacity and good rate performance, indicating that the combination of multiple coal types constructs a rich sodium storage space in the hard carbon structure, and the reasonable structural design effectively promotes the transmission efficiency of sodium ions, thereby exhibiting ultra-high rate performance.

[0100] Comparing the test results of Example 1 with Comparative Example 1 reveals that the lack of the second coal type in Comparative Example 1 prevents the remaining two coal types from achieving high capacity. This is primarily due to the high degree of coalification of the first and third coal types, resulting in limited sodium storage sites. The remaining coal types are not catalytically activated by the highly active components of lignite, resulting in a low sodium storage capacity for the resulting hard carbon material.

[0101] Comparing the test results of Example 1 and Comparative Example 2 reveals that the lack of the third coal species in Comparative Example 2 compromises the rate performance of the hard carbon material, and also somewhat affects the 0.1C reversible capacity, which is associated with an increase in specific surface area and a decrease in initial coulombic efficiency. This is primarily due to the lack of coking coal's binding effect, which prevents the formation of a secondary particle structure, significantly impacting kinetic performance and reducing rate performance. Furthermore, the absence of liquid components precipitated during the calcination process prevents surface modification of the material, leading to an increase in specific surface area and a decrease in initial coulombic efficiency.

[0102] By comparing the test results of Example 1 and Comparative Examples 3 and 4, it can be seen that Comparative Examples 3 and 4 use single-component long flame coal and lignite respectively. Due to the limitations of their respective intrinsic structural characteristics, they lack the synergistic effect of multiple coal types and can only exhibit lower capacity and lower rate performance.

[0103] By comparing the test results of Example 1 and Comparative Example 5, it can be seen that in Comparative Example 5, the three types of coal are not mixed and calcined in a specific order, and a secondary particle structure with high dynamic performance cannot be formed. The rate performance is greatly affected and the capacity cannot be fully utilized.

[0104] By comparing the test results of Example 1 and Comparative Example 6, it can be seen that Comparative Example 6 did not mix and calcine the three types of coal in a specific order, and also lacked the calcination process in a closed environment, namely a rotary kiln, and was unable to fully exert the catalytic activation effect of lignite. Although the material has a high rate performance, the overall sodium storage space is limited, resulting in a significant reduction in capacity.

[0105] The embodiments provided by the present invention are described in detail above. Specific examples are used herein to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only used to help understand the core idea of ​​the present invention. It should be pointed out that for ordinary technicians in this technical field, without departing from the principles of the present invention, the present invention can also be improved and modified in a number of ways, and these improvements and modifications also fall within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing a hard carbon negative electrode material for a multi-coal composite sodium battery, characterized in that: include: S1. Grinding and pelletizing a first type of coal, a second type of coal, and a third type of coal, respectively, and then acid-washing and purifying the first type of coal, wherein the first type of coal serves as a matrix skeleton and includes one or more of anthracite, lean coal, lean coal, weakly caking coal, non-caking coal, and long flame coal; the second type of coal has the lowest degree of coalification and includes lignite, and is used for catalytic activation of the first type of coal; the third type of coal contains a liquid-phase binding component and includes one or more of coking coal, fat coal, gas coal, and gas-fat coal; S2. Evenly mixing the first type of coal and the second type of coal, calcining them in a closed environment and an inert gas atmosphere, and naturally cooling them to room temperature to obtain a mixed coal powder, wherein the calcination temperature is 700-1000° C., and the materials are kept dynamically mixed during the calcination process; S3, uniformly mixing the mixed pulverized coal and the third type of coal and calcining them in an inert gas atmosphere at a calcination temperature of 400-600° C., maintaining dynamic mixing of the materials during the calcination process, and naturally cooling to room temperature after calcination to obtain a precursor pulverized coal; S4. calcining the precursor coal powder at a calcination temperature of 1100-1500° C. and naturally cooling to room temperature after calcination to obtain a hard carbon negative electrode material.

2. The preparation method according to claim 1, characterized in that In step S1 , the particle size of the first type of coal after grinding is 3 to 6 μm, the particle size of the second type of coal after grinding is 2 to 4 μm, and the particle size of the third type of coal after grinding is 1 to 3 μm.

3. The preparation method according to claim 1, characterized in that In step S2, the mass ratio of the first type of coal to the second type of coal is (1-5):

1.

4. The preparation method according to claim 1, characterized in that In step S2, the heating rate during the calcination process is 1-5°C / min, and the holding time is 2-5 h.

5. The preparation method according to claim 1, characterized in that In step S3, the mass ratio of the mixed coal powder to the third type of coal is 100:(3-8).

6. The preparation method according to claim 1, characterized in that In step S3, the heating rate during the calcination process is 1-5°C / min, and the holding time is 2-5 h.

7. The preparation method according to claim 1, characterized in that In step S4, the heating rate during the calcination process is 1-10°C / min.

8. A multi-coal composite sodium battery hard carbon negative electrode material, characterized in that: Prepared by the preparation method according to any one of claims 1 to 7.

9. An application of a hard carbon negative electrode material for a multi-coal composite sodium battery, characterized in that: The hard carbon negative electrode material prepared by the preparation method according to any one of claims 1 to 7 is applied to a sodium ion battery.

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