Composite hard carbon material and preparation method and application thereof

Abstract

The invention provides a composite hard carbon material as well as a preparation method and application thereof, and relates to the technical field of carbon materials. The composite hard carbon material is prepared from at least two heterogeneous carbon sources through stirring, ultrasonic dispersion, spray drying and high-temperature calcination, the air inlet temperature of the spray drying is 130-180 DEG C, the spray pressure is 0.2-0.4 MPa, and the temperature of a cooler is-15-25 DEG C. Through a unique free radical crosslinking mechanism, deep integration of lignin, asphalt and other dissimilar carbon sources at a molecular level is realized, so that the composite precursor presents highly uniform spherical particle characteristics, has excellent flowing property and uniform stacking density, and the spherical composite precursor is calcined to serve as a sodium ion battery negative electrode material, so that the sodium ion battery negative electrode material has a good application prospect. The sodium storage specific capacity is obviously improved, and the material has good cycling stability and rate capability and has a good application prospect.

Description

Technical Field

[0001] This invention relates to the field of carbon materials technology, and in particular to a composite hard carbon material, its preparation method, and its application. Background Technology

[0002] Carbon / carbon composites (C / C composites) are composite materials formed by reinforcing a carbon or graphite matrix with carbon or graphite fibers. With the rapid development of new energy technologies, especially the rise of sodium-ion battery technology, hard carbon materials have received widespread attention as the most commercially promising anode material for sodium-ion batteries.

[0003] Due to the scarcity of lithium resources and rising prices, sodium-ion batteries have regained public attention and are showing great application potential in grid energy storage and low-speed vehicles, complementing lithium-ion batteries. However, in the anode materials of sodium-ion batteries, the mainstream graphite anode material used in lithium-ion batteries cannot meet the requirements because the atomic radius of sodium ions is more than 35% larger than that of lithium ions.

[0004] Hard carbon materials are abundant and inexpensive, and possess higher lithium storage capacity and superior rate performance than graphite anodes in lithium-ion batteries. However, hard carbon generally suffers from low coulombic efficiency and poor rate performance in the first week of battery use, and its specific capacity still has considerable room for improvement.

[0005] Currently, hard carbon materials prepared from a single carbon source have relatively low sodium storage capacity, making it difficult to meet the requirements of high-performance sodium-ion batteries. Furthermore, hard carbon materials obtained by traditional methods often exhibit irregular morphology and uneven particle size distribution, affecting their processing and electrochemical performance. In the preparation of carbon / carbon composite materials, poor compatibility between different carbon source materials is often a problem, making direct mixing difficult to achieve uniform molecular-level composites. Therefore, existing composite hard carbon preparation methods are often complex, requiring multiple steps, increasing production costs and technical difficulty.

[0006] Therefore, developing a method that can effectively solve the compatibility problem of dissimilar carbon sources, achieve uniform composite at the molecular level, and prepare high-performance spherical hard carbon materials through a simple process is of great significance for improving the performance of sodium-ion battery anode materials. Summary of the Invention

[0007] In view of this, the present invention provides a composite hard carbon material, its preparation method, and its application. The present invention effectively solves the compatibility problem of dissimilar carbon sources by combining ultrasonic dispersion with spray drying, achieving uniform molecular-level composite composition between dissimilar carbon sources. The resulting high-performance spherical hard carbon material, obtained through calcination, can significantly improve the performance of sodium-ion batteries and has promising application prospects.

[0008] The first aspect of the present invention is to provide a composite hard carbon material, which is obtained by stirring, ultrasonically dispersing, spray drying and high-temperature calcination of at least two dissimilar carbon sources.

[0009] Preferably, the heterogeneous carbon source is lignin and pitch.

[0010] The second aspect of this invention is to provide a method for preparing a composite hard carbon material, specifically comprising the following steps: A heterogeneous carbon source is mixed with anhydrous ethanol and stirred until homogeneous. The mixture is then ultrasonically dispersed to obtain a dispersion. The dispersion is then spray-dried to obtain a spherical composite precursor. The spherical composite precursor is then calcined at high temperature and cooled to obtain a composite hard carbon material.

[0011] Preferably, the heterogeneous carbon source is composed of lignin and pitch, and the mass ratio of lignin to pitch is (1-3):(1-2), more preferably 2:1.

[0012] Preferably, the anhydrous ethanol is of analytical grade.

[0013] Preferably, the mass-to-volume ratio of the heterogeneous carbon source to anhydrous ethanol is 1 g:(30-60) mL, more preferably 1 g:40 mL.

[0014] Preferably, the stirring speed is 200-500 rpm and the stirring time is 8-12 h. Preferably, the stirring speed is 400 rpm and the stirring time is 12 h.

[0015] Preferably, the ultrasonic power for ultrasonic dispersion is 100-300 W, and the ultrasonic time is 2 h. More preferably, ultrasonication is performed for 30 min first, followed by shaking, and then ultrasonication is continued for another 90 min to form a uniform dispersion.

[0016] Preferably, the dispersion is fed into the spray drying device by a peristaltic pump at a pumping rate of 4-8 mL / min.

[0017] Preferably, the spray drying inlet air temperature is 130℃-180℃, the spray pressure is 0.2-0.4 MPa, and the cooler temperature is -25℃ to -15℃. More preferably, the spray drying inlet air temperature is 130℃, the spray pressure is 0.3 MPa, and the cooler temperature is -20℃. This invention adjusts the particle size of the feed by adjusting the spray pressure.

[0018] Preferably, the remaining spherical composite precursors are stored in a dry environment to prevent moisture absorption.

[0019] Preferably, the high-temperature calcination is carried out in a nitrogen atmosphere, with a heating rate of 5°C / min and a high-temperature calcination temperature of 1100°C-1500°C. Preferably, the high-temperature calcination temperature is 1300°C.

[0020] A third aspect of the present invention is to provide an application of a composite hard carbon material as a negative electrode material for sodium-ion batteries. The composite hard carbon material is the composite hard carbon material described above. The composite hard carbon material as a negative electrode can improve the sodium storage capacity, cycle stability and rate performance of sodium-ion batteries.

[0021] This invention firstly constructs a highly uniform dispersion system of dissimilar carbon sources by magnetic stirring and ultrasonic dispersion in anhydrous ethanol medium, effectively solving the compatibility problem caused by the immiscibility of the two materials and creating an ideal reaction environment for subsequent composite processing. Secondly, during spray drying, the instantaneous thermal effect generated under suitable temperature conditions promotes efficient in-situ free radical polymerization between oxygen free radicals in lignin molecules and aliphatic carbon free radicals in asphalt, forming stable and strong CO covalent bonds, thereby achieving deep structural integration and chemical composite of dissimilar carbon source materials at the molecular level. Finally, the unique atomization mechanism of spray drying technology ensures that the final product has excellent spherical morphology and highly uniform particle size distribution, significantly improving the material's flow properties and processing performance, laying a solid structural foundation for the subsequent high-temperature calcination treatment and practical application of the material.

[0022] Compared with the prior art, the beneficial technical effects of the present invention are as follows: This invention overcomes the technical barriers to composite materials between immiscible materials by achieving deep molecular-level integration of lignin and dissimilar carbon sources such as pitch through a unique free radical crosslinking mechanism, forming a stable COC covalent bond structure. Regarding product morphology control, the composite precursor prepared by this invention exhibits highly uniform spherical particles with a particle size precisely controlled within the 5-10 μm range, possessing excellent flow properties and uniform packing density, providing an ideal physical basis for subsequent processing applications. In terms of process technology, the entire preparation process of this invention requires only two simple steps: dispersion and spray drying, to obtain high-quality spherical composite precursors. The process is simple and efficient, eliminating the need for complex post-processing steps, significantly reducing production costs and technical difficulty. In terms of final performance, after calcination at 1300℃, the resulting composite hard carbon material exhibits a sodium storage capacity as high as 330.8 mAh / g, representing a 29.8% improvement compared to single lignin-derived hard carbon materials. Furthermore, it significantly outperforms single lignin-derived hard carbon materials in key indicators such as cycle stability and rate performance. Attached Figure Description

[0023] The present invention will be further described below with reference to the accompanying drawings.

[0024] Figure 1 The images shown are SEM images of lignin, pitch, and spherical composite precursors from Example 1 of the present invention, where (a) is lignin, (b) is pitch, and (c) is the spherical composite precursor. Figure 2 XPS spectra of lignin (L), pitch (P), and spherical composite precursor (LP21) in Example 1 of this invention; Figure 3 The NMR spectrum, infrared spectrum, XPS O1s spectrum and EPR spectrum of lignin (L), pitch (P) and spherical composite precursor (LP21) in Example 1 of the present invention are shown, wherein (a) is the NMR spectrum, (b) is the infrared spectrum, (c) is the XPS O1s spectrum and (d) is the EPR spectrum. Figure 4 The images shown are SEM and TEM images of carbon materials made from calcined lignin, pitch, and spherical composite precursors in Example 1 of this invention. (a) is an SEM image of carbon materials made from calcined lignin, (b) is an SEM image of carbon materials made from calcined pitch, (c) is an SEM image of carbon materials made from calcined spherical composite precursors (composite hard carbon materials), (d) is a TEM image of carbon materials made from calcined lignin, (e) is a TEM image of carbon materials made from calcined pitch, and (f) is a TEM image of carbon materials made from calcined spherical composite precursors (composite hard carbon materials). Figure 5 The infrared spectrum of carbon material after calcination at 1300℃ using lignin (L-1300), pitch (P-1300), and spherical composite precursor (LP21-1300) in Example 1 of the present invention. Figure 6 The images shown are SEM and TEM images of the composite hard carbon materials of Comparative Examples 1 and 2 of the present invention, wherein (a) is the SEM image of the composite hard carbon material prepared by high-energy ball milling, (b) is the SEM image of the composite hard carbon material prepared by solvent evaporation, (c) is the TEM image of the composite hard carbon material prepared by high-energy ball milling, and (d) is the TEM image of the composite hard carbon material prepared by solvent evaporation. Figure 7 The graph shows a comparison of the sodium storage electrochemical performance of different hard carbon materials. Spray drying is the spray drying method of Example 1, Ball-milling is the high-energy ball milling method of Comparative Example 1, Solvent evaporation is the solvent evaporation method of Comparative Example 2, and Liglin is the electrochemical performance of hard carbon materials derived from a single lignin raw material under the same conditions. Figure 8 The XRD patterns of different hard carbon materials in Example 2 of this invention are shown. Figure 9The Raman spectra of different hard carbon materials in Example 2 of this invention; Figure 10 The first three GCD curves of the sodium-ion half-cell assembled with carbon materials in Example 2 of this invention; Figure 11 This is a cycle performance graph of a sodium-ion half-cell assembled with carbon materials according to Example 2 of the present invention; Figure 12 This is a rate performance spectrum of a sodium-ion half-cell assembled with carbon materials according to Example 2 of the present invention. Figure 13 The NMR spectrum, infrared spectrum, XPS O1s spectrum and EPR spectrum of the composite hard carbon materials of Comparative Example 1 (LP21-Q) and Comparative Example 2 (LP21-E) of this invention are shown, wherein (a) is the NMR spectrum, (b) is the infrared spectrum, (c) is the XPS O1s spectrum and (d) is the EPR spectrum. Figure 14 Comparison of the properties of composite hard carbon materials obtained at different calcination temperatures in Example 3 of this invention. Detailed Implementation

[0025] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. The raw materials used in the following embodiments and comparative examples of the present invention are all commercially available.

[0026] Example 1: A method for preparing a composite hard carbon material, comprising the following steps: Lignin and asphalt were mixed at a mass ratio of 2:1, and then mixed with anhydrous ethanol at a material-to-liquid ratio of 1 g:40 mL. The mixture was covered with plastic wrap and magnetically stirred at 400 rpm for 12 h. After stirring, the mixture was ultrasonically dispersed for 2 h under ultrasonic power of 200 W to obtain a dispersion. The dispersion was then pumped into a spray drying device using a peristaltic pump at a pumping rate of 8 mL / min, a spray pressure of 0.3 MPa, an inlet air temperature of 130℃, and a cooler temperature of -20℃. After spray drying, a spherical composite precursor was obtained. The spherical composite precursor was then calcined at 1300℃ for 2 h under a nitrogen atmosphere at a rate of 5℃ / min to obtain a composite hard carbon material.

[0027] The specific capacity of the composite hard carbon material obtained in Example 1 was tested to be 330.8 mAh / g.

[0028] The SEM images of lignin (L), bitumen (P), and spherical composite precursor (LP21) used in Example 1 are shown below. Figure 1 As shown, the XPS spectrum is as follows Figure 2 As shown; NMR spectrum, infrared spectrum, XPS O1s spectrum and EPR spectrum are as follows Figure 3 As shown.

[0029] Depend on Figure 3 The NMR and infrared spectra show that the composite material retains more oxygen functional groups. The low wavenumber shift of the -OH infrared peak is attributed to the presence of C free radicals near the oxygen functional groups. The electron-withdrawing ability leads to changes in bond energy. The XPS O1s spectrum shows an increase in the COC content of the composite carbon material. Combined with the decrease in the LP21 aliphatic C free radical content in the EPR spectrum and the O free radicals in lignin itself, spray drying achieves chemical cross-linking (COC) through the integration between free radicals, and the oxygen content is increased.

[0030] The raw materials lignin and pitch were calcined separately using a spherical composite precursor method. The SEM and TEM images of the calcined carbon materials are shown below. Figure 4 As shown, the infrared spectrum is as follows Figure 5 As shown.

[0031] Depend on Figure 4 It is known that after spray drying achieves molecular-level integration, directly calcined carbon materials can achieve a more disordered carbon layer structure and a richer pore volume due to the existence of the rigid COC structure and the full cross-linking of oxygen functional groups and C free radicals.

[0032] Comparative Example 1: Preparation of Composite Hard Carbon Materials by High-Energy Ball Milling Lignin and pitch were mixed in a mass ratio of 2:1 and placed in a ball mill jar. Stainless steel balls with a mass ratio of 30:1 were added and ball milled at 1000 rpm for 2 hours to obtain a composite carbon material. The composite carbon material was then calcined and cooled to obtain a composite hard carbon material. The calcination method was the same as in Example 1.

[0033] Comparative Example 2: Preparation of Composite Hard Carbon Materials by Solvent Evaporation Method The dispersion was placed in a water bath and evaporated at a constant temperature of 60°C to obtain a composite carbon material. Then, the composite carbon material was placed in a vacuum drying oven and dried at 60°C for 1 h to obtain a composite carbon material. The composite carbon material was calcined and cooled to obtain a composite hard carbon material. The preparation method of the dispersion was the same as in Example 1, and the calcination method was the same as in Example 1.

[0034] SEM and TEM images of the composite hard carbon materials obtained in Comparative Examples 1 and 2 are shown below. Figure 6 As shown.

[0035] The composite hard carbon materials obtained in Examples 1, 1, and 2 were used as negative electrode materials and mixed with Super P and PVDF in an 8:1:1 ratio. The mixture was dissolved in NMP and coated onto copper foil. After drying, the slurry was cut into 12 mm electrode discs and used as negative electrode sheets to assemble sodium-ion half-cells of the same specifications. The sodium storage electrochemical performance of different hard carbon materials was compared as follows: Figure 7 As shown. The electrolyte used was 1 M NaClO4 in DMC:EC:DEC = 1:1:1 v / v%.

[0036] The NMR, infrared, XPS, O1s, and EPR spectra of the composite hard carbon materials obtained in Comparative Examples 1 and 2 are as follows: Figure 13 As shown. By Figure 13 It can be seen that solvent evaporation and high-energy ball milling are simply mixing of raw materials and do not involve cross-linking at the molecular integration level.

[0037] Example 2 The difference from Example 1 is that the mass ratio of lignin to pitch is 1:2, 1:1, and 3:1, respectively, denoted as LP12-1300, LP11-1300, and LP31-1300. The XRD patterns of each material are as follows: Figure 8 As shown, the Raman spectrum is as follows Figure 9 As shown, LP21-1300 is the material prepared in Example 1, L-1300 is the carbon material obtained after calcining lignin raw material, and P-1300 is the carbon material obtained after calcining pitch raw material. The calcination methods of lignin raw material and pitch raw material are the same as in Example 1.

[0038] The composite hard carbon material from Example 2 was used as the negative electrode material and mixed with Super P and PVDF in an 8:1:1 ratio. The mixture was dissolved in NMP and coated onto copper foil. After drying, the slurry was cut into 12 mm electrode discs to serve as negative electrode sheets for assembling sodium-ion half-cells of the same specifications. The electrolyte was 1 M NaClO4 in DMC:EC:DEC = 1:1:1 v / v%. The first three GCD curves for different hard carbon materials are shown below. Figure 10 As shown in the figure, the cycle performance graph is as follows: Figure 11 As shown, the rate performance spectrum is as follows: Figure 12 As shown.

[0039] Example 3 The difference from Example 1 is that the samples calcined at 1100℃, 1200℃, 1400℃, 1500℃, and 1300℃ were tested using the composite hard carbon material obtained in Example 1.

[0040] The performance comparison diagram of the composite hard carbon material obtained at different calcination temperatures in this embodiment is shown below. Figure 14 As shown.

[0041] Comparative Example 3 The difference from Example 1 is that the spray drying inlet air temperature is 100°C and the cooler temperature is -25°C.

[0042] The sodium storage capacity of the obtained composite hard carbon material was tested to be 296.83 mAh g. -1 .

[0043] Comparative Example 4 The difference from Example 1 is that the spray drying inlet air temperature is 200°C and the cooler temperature is -20°C.

[0044] The sodium storage capacity of the obtained composite hard carbon material was tested to be 288.61 mAh g. -1 .

[0045] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A composite hard carbon material, characterized by, The composite hard carbon material is obtained by stirring, ultrasonic dispersion, spray drying and high-temperature calcination of at least two heterogeneous carbon sources. The spray drying inlet temperature is 130-180 DEG C, the spray pressure is 0.2-0.4 MPa, and the cooler temperature is -25 to -15 DEG C.

2. The method for preparing the composite hard carbon material according to claim 1, characterized in that, The method comprises the following steps: The heterogeneous carbon sources are mixed with anhydrous ethanol, stirred uniformly, and then ultrasonically dispersed to obtain a dispersion liquid, the dispersion liquid is spray dried to obtain a spherical composite precursor, and the spherical composite precursor is calcined at high temperature, and then cooled to obtain the composite hard carbon material.

3. The production method according to claim 2, characterized by, The mass-volume ratio of the heterogeneous carbon sources to anhydrous ethanol is 1 g:(30-60)mL.

4. The production method according to claim 3, characterized by, The mass-volume ratio of the heterogeneous carbon sources to anhydrous ethanol is 1 g:40 mL.

5. The preparation method according to claim 2, characterized in that, The stirring speed is 200-500 rpm, and the stirring time is 8-12 h.

6. The preparation method according to claim 2, characterized in that, The ultrasonic dispersion power is 100-300 W, and the time is 2 h.

7. The preparation method according to claim 2, characterized in that, The spray drying inlet temperature is 130-180 DEG C, the spray pressure is 0.2-0.4 MPa, and the cooler temperature is -25 to -15 DEG C.

8. The preparation method according to claim 2, characterized in that, The high-temperature calcination is carried out in a nitrogen atmosphere, the heating rate is 5 DEG C / min, and the high-temperature calcination temperature is 1100-1500 DEG C.

9. The production method according to claim 8, characterized by, The high-temperature calcination temperature is 1300 DEG C.

10. Use of a composite hard carbon material as a negative electrode material for sodium-ion batteries, characterized in that, The composite hard carbon material is the composite hard carbon material of claim 1 or the composite hard carbon material prepared by the method of any one of claims 2-9.

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