High-performance coal-based hard carbon negative electrode based on precursor fluidity regulation and preparation method thereof

Abstract

The invention discloses a high-performance coal-based hard carbon negative electrode based on precursor fluidity regulation and a preparation method thereof, and the method comprises the following steps: 1, hydropyrolysis pretreatment: carrying out heat treatment on a coal-based precursor in a hydrogen-containing reducing atmosphere to obtain a plasticized coal intermediate with significantly improved thermoplasticity; and 2, high-temperature carbonization: carrying out carbonization treatment on the plasticized coal intermediate in an inert atmosphere to obtain the coal-based hard carbon negative electrode material. According to the method, through the hydropyrolysis pretreatment step, hydrogen molecules are used as molecular scissors to depolymerize the precursor, so that path transformation from rigid solid-phase pyrolysis to plastic-phase transformation and reconstruction is realized, and a coal-derived carbon structure is easier to form a carbon microcrystalline structure with higher consistency in subsequent carbonization; the amorphous carbon content of the final product is obviously reduced. According to the structural optimization, the high reversible specific capacity and the high first coulombic efficiency of the material are achieved at the same time, and the inherent contradiction that the coal-based hard carbon performance is difficult to cooperate is solved.

Description

Technical Field

[0001] This invention belongs to the field of electrode material preparation technology, and relates to a coal-based hard carbon material and its preparation method, specifically to a high-performance coal-based hard carbon anode based on precursor flowability regulation and its preparation method. Background Technology

[0002] Hard carbon materials are considered ideal candidates for anodes in sodium-ion batteries due to their suitable interlayer spacing and excellent electrochemical stability. Among numerous carbon precursors, coal (especially low-rank coal) shows great application potential due to its abundant carbon source, low cost, and the presence of graphite-like microcrystalline units in its microstructure. However, the inherent complex three-dimensional cross-linked macromolecular structure of coal makes it prone to forming a highly disordered carbon skeleton during direct high-temperature carbonization, resulting in its electrochemical performance, especially reversible specific capacity and initial coulombic efficiency, failing to meet the requirements of high-performance sodium-ion batteries.

[0003] To achieve precise control over the microstructure of the final carbon material, precursor pretreatment has become a key technological approach in this field. Currently, pretreatment strategies based on different mechanisms are being widely explored. One mainstream approach focuses on stabilizing and solidifying the molecular network of the precursor by introducing chemical bridging bonds or functional groups. For example, pre-oxidation treatment is a typical example, which successfully introduces oxygen-containing functional groups such as carbonyl groups (C=O) and ether bonds (COC) into precursors like pitch through heat treatment in air. These functional groups effectively inhibit the migration and rearrangement of carbon atoms at high temperatures, preventing graphitization shrinkage of the carbon layer, thereby contributing to the formation of a non-graphitized carbon structure with large interlayer spacing and significantly improving carbon yield.

[0004] However, for carbon precursors with more complex structures, such as bituminous coal, its components include both aromatic macromolecules that tend towards local graphitization and aliphatic compounds that inhibit long-range ordering. In this case, using a single pre-oxidation strategy to increase the overall cross-linking degree may not be able to effectively reconcile its inherent and inconsistent structural evolution tendencies, that is, it may be difficult to fundamentally intervene in the nucleation and growth pathways of its carbon microcrystals.

[0005] Therefore, for complex precursors such as bituminous coal, developing a novel pretreatment method that can effectively regulate their initial cross-linking state and guide their carbon microcrystals to evolve towards a higher degree of bulk phase consistency is of great significance for breaking through existing technological bottlenecks and fully releasing the performance potential of coal-based hard carbon materials. Summary of the Invention

[0006] The purpose of this invention is to provide a high-performance coal-based hard carbon anode based on precursor flowability regulation and its preparation method, so as to solve the technical problem in the prior art that the carbon framework disorder caused by the inherent stubbornness of the complex cross-linked macromolecular structure of coal leads to the difficulty in synergistic improvement of sodium storage capacity and first coulombic efficiency.

[0007] The objective of this invention is achieved through the following technical solution:

[0008] A method for preparing a high-performance coal-based hard carbon anode based on precursor flowability regulation includes the following steps:

[0009] Step 1, Hydropyrolysis Pretreatment: The coal-based precursor is heat-treated in a reducing atmosphere containing hydrogen to obtain a plasticized coal intermediate with significantly improved thermoplasticity, wherein:

[0010] The coal-based precursor is bituminous coal or sub-bituminous coal with an oxygen content of less than 25 wt%.

[0011] The reducing atmosphere is a mixture of hydrogen and an inert gas, wherein the hydrogen gas fraction is 1-10%.

[0012] The heat treatment temperature is 420~480℃, preferably 450~480℃, and the holding time is 0.5~3 hours;

[0013] After the heat treatment and heat preservation are completed, the temperature can be raised to 700~900℃ for a short period of isothermal treatment to further stabilize the carbon structure.

[0014] The core function of the hydropyrolysis pretreatment is to enhance the molecular-level fluidity of the precursor by selectively depolymerizing the macromolecular structure of coal with hydrogen, thereby laying the foundation for the directional growth and structural homogenization of carbon microcrystals in the subsequent carbonization process.

[0015] Step 2, High-Temperature Carbonization: The plasticized coal intermediate obtained in Step 1 is carbonized under an inert atmosphere to obtain a coal-based hard carbon anode material. The carbonization process involves a heating rate of 1~5℃ / min, a temperature of 1150~1350℃, and a processing time of 2~6h. The coal-based hard carbon anode material can be used as an anode active material in electrochemical energy storage devices, which are sodium-ion batteries or sodium-ion hybrid capacitors.

[0016] Compared with the prior art, the present invention has the following advantages:

[0017] (1) This invention recognizes that for coal with an inherent oxygen content that is already at a low to medium level, the key bottleneck in structural optimization is not the removal of large amounts of oxygen, but rather breaking its stubborn three-dimensional cross-linked network. This invention utilizes hydrogen pyrolysis pretreatment steps, employing hydrogen molecules as molecular scissors to depolymerize the precursor, achieving a path transformation from rigid solid-phase pyrolysis to plastic phase transformation and reconstruction. This makes it easier for the coal-derived carbon structure to form a more consistent carbon microcrystalline structure during subsequent carbonization, resulting in a significant reduction in the amorphous carbon content of the final product (down to below 10%). The above structural optimization enables the material to achieve both high reversible specific capacity (up to 320 mAh / g or more) and high initial coulombic efficiency (up to 87% or more), resolving the inherent contradiction of the difficulty in synergistic performance of coal-based hard carbon.

[0018] (2) The process of this invention is simple, the required equipment is conventional, and because it targets depolymerization rather than deep deoxygenation, the amount of hydrogen used is small. While achieving high performance, it also takes into account the advantage of low cost, making it suitable for large-scale industrial production. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the preparation process of high-performance coal-based hard carbon anodes based on precursor flowability regulation.

[0020] Figure 2 The image shows the X-ray diffraction pattern of the coal-based hard carbon anode material prepared in Example 1.

[0021] Figure 3 The charge-discharge curves of the coal-based hard carbon material prepared in Example 1 used as the negative electrode of a sodium-ion battery are shown.

[0022] Figure 4 The X-ray diffraction pattern of the coal-based hard carbon anode material prepared in Comparative Example 2 is shown.

[0023] Figure 5 The charge-discharge curves of the coal-based hard carbon material prepared in Comparative Example 2 used as the negative electrode of a sodium-ion battery are shown. Detailed Implementation

[0024] The technical solution of the present invention will be further described below with reference to the accompanying drawings, but it is not limited thereto. Any modifications or equivalent substitutions to the technical solution of the present invention that do not depart from the spirit and scope of the technical solution of the present invention should be covered within the protection scope of the present invention.

[0025] Example 1

[0026] Step 1: Hydropyrolysis Pretreatment: Take 10 grams of bituminous coal (oxygen content of 24.8 wt% based on elemental analysis) and place it in a horizontal tube furnace. Continuously introduce a 5% hydrogen-argon mixture (v / v) into the furnace. Then heat from room temperature to 460°C at a heating rate of 10°C / min and hold at this temperature for 1 hour; then continue heating to 800°C, hold at this temperature for 5 minutes, and then naturally cool to room temperature (<60°C) under continuous ventilation (the atmosphere can be switched to nitrogen). Remove the solid product to obtain hydropyrolyzed coal char.

[0027] Step 2, High-Temperature Carbonization: The hydropyrolyzed coal char was placed in a high-temperature tubular furnace and heated from room temperature to 1200℃ at a heating rate of 5℃ / min under argon atmosphere protection, and held at this temperature for 2 hours. After the reaction was completed, it was naturally cooled to room temperature. The resulting black solid product was ground and passed through a 400-mesh sieve to obtain coal-based hard carbon anode material, denoted as sample S1.

[0028] Example 2

[0029] The only difference between this embodiment and Embodiment 1 is that in step 1, the temperature of the hydrogenation pyrolysis pretreatment is 480°C, and the resulting product is denoted as sample S2.

[0030] Example 3

[0031] The only difference between this embodiment and Embodiment 1 is that in step 1, the holding time for the hydrogenation pyrolysis pretreatment is 2 hours, and the resulting product is denoted as sample S3.

[0032] Example 4

[0033] The only difference between this embodiment and Embodiment 1 is that in step 1, the coal-based precursor is sub-bituminous coal.

[0034] Comparative Example 1

[0035] This comparative example uses a direct high-temperature carbonization method without hydrogenation pyrolysis pretreatment. 10 grams of bituminous coal from the same batch as in Example 1 was placed directly into a high-temperature tubular furnace. Under an argon atmosphere, the temperature was increased from room temperature to 1200°C at a rate of 5°C / min and held at this temperature for 2 hours. After the reaction was complete, the mixture was allowed to cool naturally to room temperature. The resulting black solid product was ground and passed through a 400-mesh sieve to obtain the control sample, designated as sample D1.

[0036] Comparative Example 2

[0037] The only difference between this comparative example and Example 1 is that in step 1, the 5% hydrogen-argon mixture is replaced with pure argon, and the resulting product is denoted as sample D2.

[0038] Performance testing and data analysis

[0039] The samples obtained from Examples 1-3, Comparative Example 1, and Comparative Example 2 were subjected to material characterization and electrochemical performance testing. Their key performance data are summarized in Table 1. To clearly demonstrate the effects of the present invention, the test results of representative samples (Example 1, Comparative Example 1, and Comparative Example 2) are shown below. Figures 1-4 As shown.

[0040]

[0041] Structural advantages: Hydrogenation treatment effectively promotes precursor depolymerization and structural rearrangement.

[0042] As shown in Table 1, the amorphous carbon content (~10%) of samples S1, S2, and S3 was significantly lower than that of samples D1 (18.1%) and D2 (18.6%). This crucial evidence indicates that hydrogen acted as molecular scissors during pretreatment, effectively breaking the cross-linking bonds in the coal precursor, allowing it to depolymerize and release small molecule compounds. This deep depolymerization enabled the carbon skeleton to undergo sufficient ordered rearrangement during subsequent high-temperature carbonization, transforming it into short-range graphite microcrystals with higher crystallinity consistency.

[0043] In contrast, sample D2 (pretreated in an inert atmosphere) largely retained the inherent three-dimensional cross-linked macromolecular network of coal during heat treatment due to the lack of hydrogen depolymerization. This rigid network structure limited its rearrangement capacity during subsequent carbonization, resulting in a large amount of amorphous precursors failing to be fully converted into ordered carbon microcrystals. Ultimately, a high proportion of amorphous carbon remained in the carbonization products, which is detrimental to the rapid transport and storage of sodium ions.

[0044] Performance advantages: Achieve synergistic improvement in high capacity and high initial efficiency.

[0045] Sample S1 exhibits a reversible specific capacity of 326 mAh / g, significantly higher than that of directly carbonized sample D1 (268 mAh / g) and inert atmosphere pretreated sample D2 (293 mAh / g). This is attributed to the short-range, wide-interlayer-spacing carbon microcrystal structure formed by hydrogenation depolymerization and the abundant storage sites provided by the associated closed pores, while the reduced amorphous carbon content increases the accessibility of sodium ions to the carbon microcrystals within the particles.

[0046] First-cycle coulombic efficiency: Samples S1 and S3 achieved first-cycle efficiency of 87% and 88%, respectively, significantly better than the comparative sample. This is mainly because hydrogenation treatment purified the carbon framework, reducing irreversible side reactions caused by unstable dangling bonds and functional groups on the surface of amorphous carbon regions, thus forming a more stable SEI film.

[0047] Compared with sample D1 of Comparative Example 1, the necessity of the hydropyrolysis pretreatment step is demonstrated.

[0048] Compared with sample D2 of Comparative Example 2, this demonstrates the core depolymerization role of hydrogen in the pretreatment, an effect that cannot be achieved by inert atmosphere heat treatment.

[0049] In summary, this invention successfully solves the core problem of excessively high amorphous carbon content in the final product due to insufficient precursor depolymerization by using a hydrogenation-depolymerization and plasticization route for low-oxygen coal, thereby synergistically improving the material's conductivity, sodium storage capacity, and initial efficiency.

Claims

1. A method for preparing a high-performance coal-based hard carbon anode based on precursor flowability regulation, characterized in that... The method includes the following steps: Step 1, Hydrogenation pyrolysis pretreatment: The coal-based precursor is heat-treated in a reducing atmosphere containing hydrogen to obtain a plasticized coal intermediate with significantly improved thermoplasticity. Step 2, High-temperature carbonization: The plasticized coal intermediate obtained in Step 1 is carbonized under an inert atmosphere to obtain coal-based hard carbon anode material.

2. The preparation method of high-performance coal-based hard carbon anode based on precursor flowability regulation according to claim 1, characterized in that... The coal-based precursor is bituminous coal or sub-bituminous coal with an oxygen content of less than 25 wt%.

3. The method for preparing a high-performance coal-based hard carbon anode based on precursor flowability regulation according to claim 1, characterized in that... The reducing atmosphere is a mixture of hydrogen and an inert gas, wherein the hydrogen component is 1-10%.

4. The method for preparing a high-performance coal-based hard carbon anode based on precursor flowability regulation according to claim 1, characterized in that... The heat treatment temperature is 420~480℃, and the holding time is 0.5~3 hours.

5. The method for preparing a high-performance coal-based hard carbon anode based on precursor flowability regulation according to claim 4, characterized in that... The heat treatment temperature is 450~480℃.

6. The method for preparing a high-performance coal-based hard carbon anode based on precursor flowability regulation according to claim 1, characterized in that... After the heat treatment and heat preservation are completed, the temperature is further increased to 700~900℃ for a short period of constant temperature treatment.

7. The method for preparing a high-performance coal-based hard carbon anode based on precursor flowability regulation according to claim 1, characterized in that... The carbonization process involves a heating rate of 1~5℃ / min, a temperature of 1150~1350℃, and a time of 2~6h.

8. A coal-based hard carbon anode prepared by the method according to any one of claims 1-7.

9. The application of a coal-based hard carbon anode prepared by the method of any one of claims 1-7 as an anode active material in an electrochemical energy storage device.

10. The application of the coal-based hard carbon anode as the anode active material according to claim 9 in an electrochemical energy storage device, characterized in that... The electrochemical energy storage device is a sodium-ion battery or a sodium-ion hybrid capacitor.

Images