Free radical excited cross-linked composite hard carbon material as well as preparation method and application thereof

Abstract

The invention provides a free radical excited cross-linked composite hard carbon material as well as a preparation method and application thereof, and relates to the technical field of negative electrode materials. The composite hard carbon material is prepared from lignin and asphaltene as raw materials through lignin activation, wet ball milling, drying and calcination. Through the preparation method of free radical pre-excitation-wet ball-milling crosslinking, collaborative optimization of the sodium storage capacity, the first-week coulombic efficiency, the cycling stability and the rate capability of the composite hard carbon material is realized. Moreover, the preparation process of the composite hard carbon material provided by the invention has the advantages of good process stability, strong controllability, low cost, environmental friendliness and the like, is easy for large-scale production, meets the technical index requirements of industrial application of sodium ion batteries, and has a wide market application prospect.

Description

Technical Field

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

[0002] With the global energy structure transformation and the rapid development of renewable energy, large-scale energy storage technology has become a key support for ensuring energy security and achieving carbon neutrality. Lithium-ion batteries, due to their high energy density and excellent cycle performance, are widely used in portable electronic devices and electric vehicles. However, lithium resources are unevenly distributed and limited in reserves on Earth. With the explosive growth of the electric vehicle and energy storage markets, the problems of lithium resource shortage and rising costs are becoming increasingly prominent. In contrast, sodium is abundant in the Earth's crust, widely distributed, and inexpensive, and has similar physicochemical properties to lithium. Therefore, sodium-ion batteries are considered the most promising next-generation energy storage technology, particularly suitable for cost-sensitive applications such as large-scale energy storage, low-speed electric vehicles, and two-wheeled vehicles.

[0003] In the key material system of sodium-ion batteries, the selection and performance optimization of the anode material is one of the core bottlenecks restricting its commercial application. Unlike lithium-ion batteries, sodium ions have a larger ionic radius, making it difficult to effectively embed into the interlayer structure of graphite anode materials. This results in low reversible capacity of graphite in sodium-ion batteries, which cannot meet the needs of practical applications. Therefore, developing high-performance anode materials suitable for sodium-ion batteries has become a research hotspot and technical challenge in this field.

[0004] Hard carbon materials, due to their disordered carbon layer stacking structure, large interlayer spacing, abundant micropores and defect structures, can provide ample storage sites for sodium ions, exhibiting high reversible sodium storage capacity and good cycle stability, and are considered the most commercially promising anode material for sodium-ion batteries. Hard carbon materials are typically prepared by high-temperature carbonization of thermosetting organic precursors such as biomass, resins, and polymers. Their microstructural characteristics include short-range ordered carbon layer stacking, large interlayer spacing, abundant closed-pore structures, and defect sites. According to existing research, the sodium storage mechanism of hard carbon mainly involves two processes: in the high-voltage ramp region, sodium ions are mainly adsorbed on defect sites and functional groups on the carbon layer surface; in the low-voltage plateau region, sodium ions are mainly stored by embedding between carbon layers and filling closed pores. The plateau capacity is closely related to the closed-pore structure of the material and is a key factor determining the total capacity of hard carbon.

[0005] Lignin is a major component of plant cell walls and is abundant in nature, second only to cellulose, with an annual production of tens of billions of tons. As a major byproduct of the papermaking and biomass refining industries, industrial lignin production exceeds 100 million tons annually, but currently, most of it is burned as low-value fuel, resulting in extremely low resource utilization. Lignin possesses abundant aromatic ring structures and oxygen-containing functional groups, and can be carbonized at high temperatures to form hard carbon materials with a high carbon yield. Therefore, converting industrial lignin into high-value-added sodium-ion battery anode materials can not only achieve high-value utilization of biomass resources but also significantly reduce the preparation cost of hard carbon materials, yielding significant economic and environmental benefits. In recent years, research on lignin-based hard carbon anode materials has made significant progress. Through optimizing carbonization processes, chemical pretreatment, and elemental doping, the sodium storage performance of lignin-derived hard carbon has been continuously improved, demonstrating promising application prospects.

[0006] However, lignin-derived hard carbon materials still suffer from significant performance defects: on the one hand, the initial coulombic efficiency of lignin-based hard carbon is generally low, due to the presence of numerous oxygen-containing functional groups and a high specific surface area on the material surface. During the first charge, a large amount of sodium ions are consumed to form a solid electrolyte interphase (SEI) film, leading to irreversible loss of active sodium. On the other hand, the cycle stability and rate performance of lignin-based hard carbon need improvement. It is prone to structural collapse and capacity decay during high-rate charge-discharge and long-term cycling, which is closely related to its low electronic conductivity and insufficient structural stability. To overcome these defects, researchers have attempted to combine lignin with other carbon sources, hoping to optimize the overall performance of the material through the synergistic effect of different carbon sources.

[0007] Asphalt is a carbonaceous material rich in aromatic compounds and polycyclic structures, including coal tar pitch, petroleum asphalt, and mesophase asphalt. It possesses high carbon content, good graphitization ability, and excellent electrical conductivity. During high-temperature carbonization, asphalt tends to form a soft carbon structure with a certain degree of graphitization. Its carbon layers are relatively ordered, with small interlayer spacing and a fast electron conduction rate, thus it is widely used in the modification of anode materials for lithium-ion and sodium-ion batteries. Theoretically, introducing asphalt into lignin-based hard carbon systems can improve the electronic conductivity, rate performance, and cycle stability of the material through the graphitized carbon layers derived from asphalt, while maintaining the high sodium storage capacity and rich pore structure of lignin hard carbon, achieving complementary and synergistic performance optimization.

[0008] Based on the above ideas, researchers have been exploring lignin-pitch composite hard carbon anode materials in recent years. However, existing lignin-pitch composite hard carbon preparation processes generally employ direct physical mixing or solvent-assisted mixing, resulting in limited improvement in sodium storage capacity. The intrinsic structure of the carbon source precursor is disrupted, affecting the performance of the final carbon material and leading to problems such as large fluctuations in material properties, poor repeatability, and uncontrollable structure, making it difficult to meet the quality stability requirements for industrial applications.

[0009] Therefore, there is an urgent need to develop a new preparation method and technical route to achieve effective cross-linking and synergistic compounding of lignin and pitch at the molecular level, so as to synergistically improve the sodium storage capacity, first-cycle coulombic efficiency, cycle stability and rate performance of composite hard carbon materials, and provide new ideas and solutions for the development of high-performance hard carbon anode materials for sodium-ion batteries. Summary of the Invention

[0010] In view of this, the present invention provides a free radical-excited crosslinked composite hard carbon material, its preparation method, and its application. The present invention achieves synergistic optimization of sodium storage capacity, first-cycle coulombic efficiency, cycling stability, and rate performance through a "free radical pre-excitation-wet ball milling crosslinking" preparation method, exhibiting significant technical advantages and good application value.

[0011] The first aspect of the present invention is to provide a free radical-induced crosslinked composite hard carbon material, which is obtained by using lignin and asphaltene as raw materials, and then activating lignin, wet ball milling, drying and calcining.

[0012] The second aspect of this invention provides a method for preparing a free radical-excited crosslinked composite hard carbon material, specifically comprising the following steps: S1. Lignin is heat-treated, cooled, and ground under an inert atmosphere. During this process, the lignin molecular structure breaks down, generating C and O free radicals, resulting in excited-state lignin containing a high concentration of C and O free radicals. S2. Mix the excited lignin from step S1 with asphaltene, and wet ball mill to obtain a uniform slurry; The uniform slurry from steps S3 and S2 is filtered, vacuum dried, ground, calcined, and cooled to obtain a free radical-induced crosslinked composite hard carbon material.

[0013] Preferably, in step S1, the inert atmosphere is a nitrogen atmosphere, the heat treatment heating rate is 5℃ / min, the heat treatment temperature is 300℃-600℃, more preferably 500℃, and the heat treatment holding time is 0.5-3 h, more preferably 1 h.

[0014] Preferably, in step S2, the amount of asphaltene used is 10 wt.%-50 wt.% of the excited lignin, more preferably 20 wt.%; the wet ball milling uses an alcohol solvent, the amount of which is 5-15 mL / g of material, more preferably 10 mL / g of material; the ball-to-material ratio of the wet ball milling is (20-70):1, more preferably 50:1; the rotation speed is 300-1000 r / min, more preferably 1000 r / min; and the milling time is 1-3 h, more preferably 2 h. More preferably, the alcohol solvent is anhydrous ethanol.

[0015] Preferably, in step S2, the asphalt is prepared as follows: petroleum asphalt is dissolved in n-heptane solvent, the amount of n-heptane solvent is 40 mL / g, and after magnetic stirring for 12 h, it is filtered and dried to obtain asphalt.

[0016] Preferably, in step S3, the vacuum drying temperature is 60℃-80℃, more preferably 60℃, the vacuum drying time is 2-12 h, and the moisture content of the dried material is <0.1%; the calcination heating rate is 5℃ / min, the calcination temperature is 1200℃-1500℃, more preferably 1300℃, and the calcination holding time is 2 h.

[0017] A third aspect of the present invention is to provide an application of a free radical-induced crosslinked composite hard carbon material as a negative electrode material for sodium-ion batteries, wherein the free radical-induced crosslinked composite hard carbon material is the free radical-induced crosslinked composite hard carbon material described above.

[0018] Compared with the prior art, the beneficial technical effects of the present invention are as follows: This invention utilizes pre-activation treatment to selectively break unstable chemical bonds in lignin molecules, generating high concentrations of carbon and oxygen free radicals. These excited-state free radicals undergo cross-linking reactions with free radicals in asphaltene during wet ball milling, forming covalent connections such as COC bridge bonds and CC bonds at room temperature, achieving molecular-level chemical cross-linking. This avoids the phase separation and active site coverage problems caused by traditional physical mixing methods.

[0019] The composite hard carbon material prepared by this invention has a reversible sodium storage capacity of 333.2 mAh / g, which is 20.4% higher than that of single lignin hard carbon. The first-cycle coulombic efficiency reaches 72.88%, an improvement of 17.4%. After 100 cycles, the capacity retention rate is greater than 90%, and the charge transfer impedance is reduced. It successfully achieves synergistic optimization of sodium storage capacity, first-cycle coulombic efficiency, cycling stability and rate performance.

[0020] The composite hard carbon material preparation process provided by this invention has advantages such as good process stability, strong controllability, low cost, and environmental friendliness. It is easy to scale up production, meets the technical requirements for the industrial application of sodium-ion batteries, and has broad market application prospects. Attached Figure Description

[0021] The present invention will be further described below with reference to the accompanying drawings.

[0022] Figure 1 The above are the electron paramagnetic resonance (EPR) spectra of excited-state lignin (NL), asphaltenes (PZ), and composite precursor (NLPZ20) of 20% asphaltenes in Example 1 of the present invention. Figure 2 The Fourier transform infrared (FTIR) spectra of excited-state lignin (NL), asphaltene (PZ), and composite precursor (NLPZ20) of 20% asphaltene in Example 1 of the present invention are shown. Figure 3 The X-ray photoelectron spectroscopy (XPS) spectra of excited-state lignin (NL), asphaltenes (PZ), and composite precursor (NLPZ20) with 20% asphaltenes in Example 1 of the present invention are shown. Figure 4 The image shows the scanning electron microscope (SEM) morphology of the hard carbon material after calcination in Example 1 of this invention. NL-1300 is the hard carbon material obtained by calcining excited-state lignin, PZ-1300 is the soft carbon material obtained by calcining asphaltene, and NLPZ20-1300 is the composite hard carbon material obtained by calcining a composite precursor obtained by wet ball milling of lignin with 20 wt.% asphaltene. Figure 5 The image shows the Fourier transform infrared (FTIR) spectrum of the hard carbon material after calcination in Example 1 of this invention. NL-1300 is the hard carbon material obtained by calcining excited-state lignin, PZ-1300 is the soft carbon material obtained by calcining asphaltene, and NLPZ20-1300 is the composite hard carbon material obtained by wet ball milling of lignin with 20wt.% asphaltene. Figure 6 The image shows the X-ray photoelectron spectroscopy (XPS) spectrum of the hard carbon material after calcination in Example 1 of this invention. In this image, NL-1300 is the hard carbon material obtained by calcining excited-state lignin, PZ-1300 is the soft carbon material obtained by calcining asphaltene, and NLPZ20-1300 is the composite hard carbon material obtained by calcining the composite precursor obtained by wet ball milling of lignin with 20 wt.% asphaltene. Figure 7The image shows the high-resolution XPS C1s spectrum of the hard carbon material after calcination in Example 1 of this invention. NL-1300 is the hard carbon material obtained by calcining excited-state lignin, PZ-1300 is the soft carbon material obtained by calcining asphaltene, and NLPZ20-1300 is the composite hard carbon material obtained by calcining a composite precursor obtained by wet ball milling of lignin with 20wt.% asphaltene. Figure 8 This is a pore size distribution diagram of the hard carbon material after calcination in Example 1 of the present invention. In this diagram, NL-1300 is the hard carbon material obtained by calcination of excited lignin, PZ-1300 is the soft carbon material obtained by calcination of asphaltene, and NLPZ20-1300 is the composite hard carbon material obtained by calcination of the composite precursor obtained by wet ball milling of lignin with 20wt.% asphaltene. Figure 9 The images show the X-ray diffraction (XRD) patterns of composite hard carbon materials with different asphaltene ratios in Example 1 of this invention. NL-1300 is a hard carbon material obtained by calcining excited-state lignin; NLPZ10-1300 is a composite hard carbon material obtained by wet ball milling of lignin with 10 wt.% asphaltene; NLPZ20-1300 is a composite hard carbon material obtained by wet ball milling of lignin with 20 wt.% asphaltene; NLPZ30-1300 is a composite hard carbon material obtained by wet ball milling of lignin with 30 wt.% asphaltene; NLPZ40-1300 is a composite hard carbon material obtained by wet ball milling of lignin with 40 wt.% asphaltene; NLPZ50-1300 is a composite hard carbon material obtained by wet ball milling of lignin with 50 wt.% asphaltene; and PZ-1300 is a soft carbon material obtained by calcining asphaltene. Figure 10 The images show the constant current charge-discharge (GCD) curves of composite hard carbon materials with different asphaltene ratios in Example 1 of this invention. NL-1300 is the hard carbon material obtained by calcining excited-state lignin; NLPZ10-1300 is the composite hard carbon material obtained by wet ball milling of lignin with 10 wt.% asphaltene; NLPZ20-1300 is the composite hard carbon material obtained by wet ball milling of lignin with 20 wt.% asphaltene; NLPZ30-1300 is the composite hard carbon material obtained by wet ball milling of lignin with 30 wt.% asphaltene; NLPZ40-1300 is the composite hard carbon material obtained by wet ball milling of lignin with 40 wt.% asphaltene; NLPZ50-1300 is the composite hard carbon material obtained by wet ball milling of lignin with 50 wt.% asphaltene; PZ-1300 is the soft carbon material obtained by calcining asphaltene. Test conditions: Current density: 0.1 C, Voltage range: 0.002-3.0 V vs Na / Na⁺, Electrolyte: 1 M NaClO4in DME; Figure 11This is a rate performance diagram of composite hard carbon materials with different asphaltene ratios in Example 1 of the present invention. NL-1300 is a hard carbon material obtained by calcining excited-state lignin; NLPZ10-1300 is a composite hard carbon material obtained by wet ball milling of lignin with 10 wt.% asphaltene; NLPZ20-1300 is a composite hard carbon material obtained by wet ball milling of lignin with 20 wt.% asphaltene; NLPZ30-1300 is a composite hard carbon material obtained by wet ball milling of lignin with 30 wt.% asphaltene; NLPZ40-1300 is a composite hard carbon material obtained by wet ball milling of lignin with 40 wt.% asphaltene; NLPZ50-1300 is a composite hard carbon material obtained by wet ball milling of lignin with 50 wt.% asphaltene; PZ-1300 is a soft carbon material obtained by calcining asphaltene. Test conditions: Rate: 0.1 C → 10 C → 0.1 C, Electrolyte: 1 M NaPF6in DME; Figure 12 This is a cycle performance diagram of composite hard carbon materials with different asphaltene ratios in Example 1 of the present invention. NL-1300 is a hard carbon material obtained by calcining excited-state lignin; NLPZ10-1300 is a composite hard carbon material obtained by wet ball milling of lignin with 10 wt.% asphaltene; NLPZ20-1300 is a composite hard carbon material obtained by wet ball milling of lignin with 20 wt.% asphaltene; and so on, NLPZ30-1300 is a composite of 30 wt.%; NLPZ40-1300 is a composite of 40 wt.%; NLPZ50-1300 is a composite of 50 wt.%; PZ-1300 is a soft carbon material obtained by calcining asphaltene; test conditions: current density: 0.1C, number of cycles: 100 cycles, temperature: 25℃, electrolyte: 1 M NaPF6in DME (100%). Figure 13 This is a battery charge-discharge curve of the composite hard carbon material in Comparative Example 1 of the present invention; Figure 14 This is a flowchart illustrating the preparation process of the free radical-induced crosslinking composite hard carbon material of this invention. Detailed Implementation

[0023] 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 of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0024] Unless otherwise specified, all experiments were repeated three times. Analysis of variance (ANOVA) and Duncan's multiple comparison analysis were performed using SPSS 21.0. Results are expressed as mean ± standard deviation, and p < 0.05 was considered statistically significant.

[0025] The preparation method of the asphalt used in Example 1 and the comparative example of the present invention is as follows: petroleum asphalt is dissolved in n-heptane solvent, the amount of n-heptane solvent is 40 mL / g, and after magnetic stirring for 12 h, it is filtered and dried to obtain asphalt.

[0026] Example 1: A method for preparing a free radical-excited crosslinked composite hard carbon material, comprising the following steps: S1. The lignin was placed in a tube furnace under a nitrogen atmosphere and heated to 500°C at a heating rate of 5°C / min and held for 1 h to obtain excited lignin. S2. The excited lignin from step S1 is mixed with 10 wt.%, 20 wt.%, 30 wt.%, 40 wt.%, and 50 wt.% asphaltene and added to a ball mill jar. Stainless steel balls (ball-to-material mass ratio 50:1) and anhydrous ethanol (10 mL / g material) are added to the jar and ball-milled at 500 r / min for 2 h to obtain a uniform slurry. S3. The uniform slurry from step S2 is filtered through a funnel to remove the grinding balls, placed in a petri dish, covered with plastic wrap and evenly perforated, and dried in a vacuum drying oven at 60°C for 2 h. The resulting composite precursor is ground evenly and then calcined at 1300°C for 2 h at a heating rate of 5°C / min under a nitrogen atmosphere. After natural cooling, the free radical excited crosslinked composite hard carbon material is obtained.

[0027] The excited-state lignin obtained in step S1 and the raw materials (lignin and asphaltenes) were characterized. The results showed that the excited-state lignin contained abundant oxygen functional groups and a large number of C and O free radicals. Figure 1 Asphaltene possesses a high degree of aliphatic chain and aromatic hydrocarbon structure, and is also rich in C and O free radicals. The precursor after wet ball milling achieves uniform composite of the two materials, and this process avoids the damage to the component structure caused by high-energy collisions.

[0028] Compared to hard carbon materials directly derived from the two precursors, the carbon layer structure of composite hard carbon is significantly optimized, with asphaltene-derived graphite carbon layers achieving uniform dispersion and a richer pore structure. Figure 4 Further analysis showed that the content of COC bonds, CC bonds, and oxygen in the composite hard carbon was higher than that in the direct calcination product of the raw materials (hard carbon obtained by calcining lignin and asphaltene separately). This is due to the bridging structure formed by free radical cross-linking. Figure 5 , 67). The composite hard carbon prepared by this method has a rich porous structure, with significantly increased pore volume and larger carbon layer spacing, which is beneficial for Na… + Embedding and intercalation ( Figure 8 , 9 Electrochemical performance tests showed that the composite hard carbon exhibited a sodium storage specific capacity of 333.2 mAh / g and a first-week coulombic efficiency of 72.88%, representing a 20.4% improvement in sodium storage performance and a 17.4% improvement in first-week coulombic efficiency compared to excited-state lignin-derived hard carbon. Simultaneously, its rate performance and cycle stability were significantly improved. Figure 10 , 11 12).

[0029] Comparative Example 1 The difference from Example 1 is that no lignin activation treatment was performed, and the resulting composite hard carbon had a sodium storage capacity of 285.6 mAh / g. (See Example 1) Figure 13 .

[0030] 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 free radical-excited crosslinked composite hard carbon material, characterized in that, The composite hard carbon material is obtained by using lignin and asphalt as raw materials, and is processed by lignin activation, wet ball milling, drying and calcination.

2. The method for preparing the free radical-excited crosslinked composite hard carbon material according to claim 1, characterized in that, Includes the following steps: S1. Lignin is heat-treated, cooled, and ground under an inert atmosphere. During this process, the lignin molecular structure breaks down, generating C and O free radicals, resulting in excited-state lignin containing a high concentration of C and O free radicals. S2. Mix the excited lignin from step S1 with asphaltene, and wet ball mill to obtain a uniform slurry; The uniform slurry from steps S3 and S2 is filtered, vacuum dried, ground, calcined, and cooled to obtain a free radical-induced crosslinked composite hard carbon material.

3. The preparation method according to claim 2, characterized in that, In step S1, the inert atmosphere is a nitrogen atmosphere.

4. The preparation method according to claim 2, characterized in that, In step S1, the heat treatment heating rate is 5℃ / min, the heat treatment temperature is 300-600℃, and the heat treatment holding time is 0.5-3 h.

5. The preparation method according to claim 2, characterized in that, In step S2, the amount of asphaltene used is 10wt.%-50wt.% of the excited-state lignin.

6. The preparation method according to claim 2, characterized in that, In step S2, the wet ball milling uses an alcohol solvent.

7. The preparation method according to claim 2, characterized in that, In step S2, the amount of alcohol solvent used is 5-15 mL / g of material.

8. The preparation method according to claim 2, characterized in that, In step S2, the ball-to-material ratio of the wet ball mill is (20-70):1, the rotation speed is 300-1000 r / min, and the ball milling time is 1-3 h.

9. The preparation method according to claim 2, characterized in that, In step S3, the vacuum drying temperature is 60℃, the vacuum drying time is 2-12 h, and the moisture content of the dried material is <0.1%; the calcination heating rate is 5℃ / min, the calcination temperature is 1300℃, and the calcination holding time is 2 h.

10. The application of a free radical-excited crosslinked composite hard carbon material as a negative electrode material for sodium-ion batteries, characterized in that, The free radical-induced crosslinked composite hard carbon material is the free radical-induced crosslinked composite hard carbon material according to claim 1 or the free radical-induced crosslinked composite hard carbon material prepared by the method according to any one of claims 2-9.

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