Method for preparing sodium-ion battery hard carbon negative electrode with high cross-linked structure based on synergistic cross-linking of hydroxyl enriched lignin and oxidized asphalt

Abstract

The invention provides a method for preparing a sodium-ion battery hard carbon negative electrode with a high cross-linked structure based on cooperative cross-linking of hydroxyl enriched lignin and oxidized asphalt, and belongs to the technical field of preparation of sodium-ion battery negative electrode materials. The high-performance hard carbon negative electrode can be prepared without a solvent and an additional additive by optimizing a lignin pretreatment process and an asphalt pre-oxidation process and improving an asphalt-lignin cross-linking mode; by adopting the biomass derivative and petroleum asphalt composite carbon source, the method has the advantages of low cost, environmental protection and accessible raw materials; the sodium ion battery with the obtained hard carbon negative electrode has excellent electrochemical performance and is suitable for large-scale production of the sodium ion battery; and the practicability is high.

Description

Technical Field

[0001] This invention belongs to the field of sodium-ion battery anode material preparation technology, specifically relating to a method for preparing a highly cross-linked hard carbon anode for sodium-ion batteries based on the synergistic cross-linking of hydroxyl-enriched lignin and oxidized pitch. Background Technology

[0002] The demand for sodium-ion batteries in low-cost, large-scale energy storage is increasingly urgent. Hard carbon is currently the best-performing and most adaptable anode material for sodium-ion batteries. However, the core bottleneck in its preparation process has not yet been overcome, which seriously restricts its industrialization. In existing technologies, hard carbon is prepared using lignin and pitch as raw materials. However, the reaction synergy between lignin and pitch is insufficient during the preparation process, and the functional group matching degree between the two is low, resulting in a lack of driving force for precursor crosslinking. Furthermore, traditional composite methods have significant drawbacks. They either rely on volatile solvents such as ethanol and acetone for liquid-phase mixing, which involves cumbersome process steps and high solvent recovery costs, making it difficult to adapt to continuous industrial production; or they use simple solid-phase mixing, where lignin and pitch particles easily agglomerate and do not contact sufficiently, ultimately leading to uneven crosslinking and a loose, defective crosslinked network. These problems result in a chaotic pore structure in hard carbon materials (macropores account for over 30%) and poor cycle stability (capacity retention after 1000 cycles is often below 80%). Therefore, developing a solvent-free, simplified, and precisely matched lignin-asphalt synergistic crosslinking preparation method to address the problems of agglomeration and uneven crosslinking by directionally enhancing the reactivity of both materials and optimizing the crosslinking mechanism, thereby obtaining high-performance hard carbon materials, has become a core requirement for promoting the industrial application of sodium-ion batteries in the field of large-scale energy storage. Summary of the Invention

[0003] To address some shortcomings in existing technologies, this invention provides a method for preparing highly cross-linked hard carbon anodes for sodium-ion batteries based on the synergistic cross-linking of hydroxyl-enriched lignin and oxidized asphalt. This invention optimizes the lignin pretreatment process, the asphalt pre-oxidation process, and improves the asphalt-lignin cross-linking method, achieving the preparation of high-performance hard carbon anodes without solvents or additional additives. The invention uses a composite carbon source of biomass derivatives and petroleum asphalt, combining low cost, environmental friendliness, and readily available raw materials. The resulting hard carbon anode exhibits excellent electrochemical performance in sodium-ion batteries, making it suitable for large-scale production of sodium-ion batteries and demonstrating significant practicality.

[0004] To achieve the above-mentioned technical objectives, the present invention employs the following technical means: This invention first provides a method for preparing a highly cross-linked hard carbon anode for sodium-ion batteries based on the synergistic cross-linking of hydroxyl-enriched lignin and oxidized pitch, the method comprising: (1) Lignin pretreatment: Lignin was mixed with NaOH solution and stirred to react. After the reaction was completed, the mixture was filtered to remove the filter residue. The pH was then adjusted to 6.0 and allowed to stand. After standing, the mixture was washed with water until neutral, dried, and ground to obtain hydroxyl-enriched modified lignin. (2) Pre-oxidation of asphalt: Petroleum-based asphalt is crushed and placed in an oxidizing atmosphere, then heated for pre-oxidation treatment to obtain oxidized asphalt. (3) Crosslinking reaction: The obtained oxidized asphalt was ground and mixed with hydroxyl-enriched modified lignin and then pre-crosslinked in an inert gas atmosphere. The temperature was then raised to continue crosslinking. After the crosslinking was completed, the crosslinked product was obtained. (4) Carbonization reaction: The cross-linked product was crushed and heated in an inert gas atmosphere to carry out a carbonization reaction. After the reaction was completed, it was cooled to obtain a hard carbon anode for sodium-ion batteries with a highly cross-linked structure.

[0005] Preferably, in step (1), the solid-liquid ratio of lignin to NaOH solution is 1:8~12 (g / mL); the purity of the lignin is ≥92%, and the concentration of NaOH solution is 1~2 mol / L; The conditions for the stirring reaction are: constant temperature stirring at 60~90℃ for 2~6 hours.

[0006] Preferably, in step (1), a citric acid solution with a concentration of 0.5~1mol / L is used to adjust the pH value to 5~6 and the mixture is allowed to stand for precipitation for 2~4 hours; The drying conditions are: vacuum drying at 80~100℃ for 8~12 hours; The grinding conditions are: grinding to 100~200 mesh.

[0007] Preferably, in step (2), the petroleum-based asphalt includes petroleum-based asphalt with a softening point of 140~280℃; Crush petroleum-based bitumen to 80-100 mesh; The oxidizing atmosphere is an oxygen-nitrogen mixture, wherein the volume fraction of oxygen is 10-40%. The pre-oxidation treatment conditions are as follows: heating to 200-350℃ at a heating rate of 1-5℃ / min and holding for 1-8 hours.

[0008] Preferably, in step (3), the mass ratio of oxidized asphalt to hydroxyl-enriched modified lignin is 1:0.08~0.12; The inert gas is either nitrogen or argon. The conditions for the pre-crosslinking reaction are: heating to 300-400℃ at a rate of 2-6℃ / min for 1-4 hours; The conditions for continued crosslinking are: continue to crosslink at a rate of 2~6℃ / min to 450~600℃ for 1~4 hours.

[0009] Preferably, in step (4), the crosslinking product is crushed to 80-100 mesh; The conditions for the carbonization reaction are: heating to 1000-1500℃ at a heating rate of 1-5℃ / min and holding at that temperature for 1-4 hours.

[0010] This invention also provides a highly cross-linked sodium-ion battery hard carbon anode prepared by the above method, wherein the highly cross-linked sodium-ion battery hard carbon anode has a specific surface area of ​​5~100 m². 2 / g, the interlayer spacing (d) of the hard carbon anode material 002 The wavelength is 0.370~0.420 nm, I D / I G The value is 1.0~2.0.

[0011] This invention also provides the application of the above-mentioned highly cross-linked sodium-ion battery hard carbon anode in the preparation of sodium-ion batteries.

[0012] The present invention also provides a sodium-ion battery comprising the above-described highly cross-linked sodium-ion battery hard carbon anode.

[0013] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) This invention uses a grinding and mixing method to combine modified lignin and oxidized asphalt, avoiding the solvent recovery step in the traditional solvent method, thus reducing process costs and environmental pollution. Compared with traditional methods, it reduces process steps such as solvent recovery, additional additives, and plasma activation, resulting in lower equipment investment and a shorter production cycle. This method uses lignin with a purity ≥92% and petroleum asphalt as raw materials. First, the lignin is purified by alkali treatment to enrich and modify its hydroxyl groups, and the petroleum asphalt is pre-oxidized. The modified lignin and oxidized asphalt are fully contacted in a dispersion system, and deep cross-linking is achieved through esterification and etherification reactions of hydroxyl and oxidized functional groups. Finally, a highly disordered hard carbon material is obtained through carbonization. This invention uses a composite carbon source of biomass derivatives and petroleum asphalt, which combines low cost, environmental friendliness, and readily available raw materials. The resulting hard carbon anode exhibits excellent electrochemical performance in sodium-ion batteries and is suitable for large-scale production of sodium-ion batteries.

[0014] (2) The method of the present invention enriches active hydroxyl groups through lignin-oriented pretreatment (NaOH alkali dissolution ~ citric acid pH adjustment); asphalt is pre-oxidized in an oxidizing atmosphere at 200~350℃ to form carboxyl and hydroxyl groups; the modified lignin hydroxyl groups undergo esterification and etherification reactions with the carboxyl and hydroxyl groups of oxidized asphalt to form a deep cross-linked network, achieving cross-linking without additional additives, thus avoiding solvent volatilization pollution and additive residue problems, and significantly reducing raw material costs. Furthermore, the present invention achieves surface defect control (I) of hard carbon by adjusting the pre-cross-linking (300~400℃, 1~4h) and deep cross-linking (450~600℃, 1~4h) parameters to form a dense cross-linked network. D / I G =1.0~2.0), ensuring initial coulombic efficiency and cycle stability, resulting in high capacity and high initial coulombic efficiency of the prepared hard carbon, meeting the requirements of large-scale energy storage batteries. The battery has a reversible capacity of 260~340mAh / g at a current density of 30mA / g and an initial coulombic efficiency ≥70~90%.

[0015] (3) While simplifying the process, the interlayer spacing and electrochemical performance of the materials are comparable to those of traditional processes. Industrial Application Prospects: The process of this invention is compatible with existing industrial production lines for carbon materials and can be widely applied in fields such as photovoltaic energy storage, grid peak shaving, and low-speed electric vehicles, yielding significant economic and social benefits. Attached Figure Description

[0016] Figure 1 The XRD pattern of the hard carbon anode in a highly cross-linked sodium-ion battery is shown.

[0017] Figure 2 The Raman spectrum of a hard carbon anode in a highly cross-linked sodium-ion battery is shown.

[0018] Figure 3 The charge-discharge curves are for the hard carbon anode of a highly cross-linked sodium-ion battery. Detailed Implementation

[0019] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but the scope of protection of the present invention is not limited thereto. Example 1:

[0020] (1) Lignin pretreatment: 10g of lignin with a purity of 92% was mixed with 100mL of 1.5mol / L NaOH solution and stirred at 75℃ for 3.5h. After the reaction was completed, the residue was filtered, and the pH of the filtrate was adjusted to 6.0 with 0.8mol / L citric acid solution and allowed to stand for 2.5h. The precipitate was collected, washed with water until neutral, dried under vacuum at 90℃ for 10h, and ground to 180 mesh to obtain hydroxyl-enriched modified lignin.

[0021] (2) Pre-oxidation of asphalt: Petroleum-based asphalt with a softening point of 250℃ was crushed to 80-100 mesh and then placed in an oxidizing atmosphere. The temperature was increased to 300℃ at a rate of 2℃ / min and held for 3 hours for pre-oxidation treatment. After the treatment, oxidized asphalt rich in carboxyl and hydroxyl groups was obtained.

[0022] (3) Crosslinking reaction: The oxidized asphalt obtained in step (2) and the modified lignin obtained in step (1) were ground and mixed at a mass ratio of 1:0.1, placed in a tube furnace, and inert gas was introduced. The temperature was increased to 400℃ at 2℃ / min, and the pre-crosslinking reaction was carried out for 1h. After the reaction was completed, ester bonds (-COO-) were formed to construct a preliminary crosslinking network. The temperature was further increased to 500℃ at 5℃ / min, and crosslinking was carried out for 2h to form ether bonds (-O-) to obtain the crosslinking product.

[0023] (4) Carbonization reaction: The cross-linked product was crushed to 80-100 mesh, high-purity argon gas was introduced, the temperature was raised to 1400℃ at 5℃ / min and held for 2 hours, and then cooled to obtain hard carbon anode material.

[0024] The structural characteristics and properties of the obtained hard carbon were investigated: specific surface area 36 m² / g. 2 / g, interlayer spacing 0.39nm, I D / I G =1.26; reversible capacity at 30 mA / g current density is 291 mAh / g, and initial coulombic efficiency is 82%.

[0025] Example 2: This embodiment uses essentially the same steps as Example 1 to prepare the hard carbon anode material, with only the following differences: In step (2), the softening point of the asphalt is 160℃. It is placed in an oxidizing atmosphere and heated to 330℃ at a heating rate of 2℃ / min for 2 hours. In step (3), oxidized asphalt and modified lignin are ground and mixed at a mass ratio of 1:0.08, nitrogen is introduced, and the temperature is raised to 350℃ at 2℃ / min for 2h of pre-crosslinking reaction; the temperature is then raised to 480℃ at 2℃ / min for 3h to form crosslinking product. In step (4), the temperature is increased to 1300℃ at 2℃ / min and held for 2 hours, and then cooled to obtain hard carbon anode material.

[0026] The structural characteristics and properties of the obtained hard carbon were investigated: specific surface area 78 m² / g. 2 / g, interlayer spacing 0.402nm, I D / I G =1.38, reversible capacity at 30mA / g current density is 286mAh / g, and initial coulombic efficiency is 85%. This embodiment uses essentially the same steps as Example 1 to prepare the hard carbon anode material, with only the following differences:

[0027] In step (2), the softening point of the asphalt is 220℃, and the temperature is increased to 300℃ at a rate of 3℃ / min for 4 hours. In step (3), the mass ratio of asphalt to lignin is 1:0.12. The temperature is increased to 380℃ at 3℃ / min, and the pre-crosslinking reaction is carried out for 3h. The temperature is then increased to 500℃ at 2℃ / min, and the reaction is carried out for 2h to form the crosslinking product. In step (4), the temperature is increased to 1400℃ at 3℃ / min and held for 1 hour, and then cooled to obtain hard carbon anode material.

[0028] The structural characteristics and properties of the obtained hard carbon were investigated: specific surface area 28 m². 2 / g, interlayer spacing 0.388nm, I D / I G =1.28, reversible capacity at 30mA / g current density is 318mAh / g, and initial coulombic efficiency is 87%.

[0029] Comparative Example 1: This comparative example uses the traditional "solvent dissolution + crosslinking agent" process to prepare pitch-lignin hard carbon. In the preparation process, pitch and lignin are dissolved in ethanol (solid-liquid ratio 1:6), epichlorohydrin (10% of lignin mass) is added, the solvent is evaporated after mixing, and the subsequent carbonization process is the same as in Example 1.

[0030] The specific surface area is 87m². 2 / g, interlayer spacing 0.398nm, I D / I G =1.20, reversible capacity at 30mA / g current density is 318mAh / g, and initial coulombic efficiency is 80%.

[0031] In summary, this invention achieves the preparation of high-performance hard carbon anodes without solvents or additional additives by optimizing the lignin pretreatment process, the asphalt pre-oxidation process, and improving the asphalt-lignin crosslinking method. The invention utilizes a composite carbon source of biomass derivatives and petroleum asphalt, combining low cost, environmental friendliness, and readily available raw materials. The resulting hard carbon anode exhibits excellent electrochemical performance in sodium-ion batteries, making it suitable for large-scale production of sodium-ion batteries and demonstrating significant practicality.

[0032] The embodiments described above are preferred embodiments of the present invention, but the present invention is not limited to the above embodiments. Any obvious improvements, substitutions or modifications that can be made by those skilled in the art without departing from the essence of the present invention shall fall within the protection scope of the present invention.

Claims

1. A method for preparing a highly cross-linked hard carbon anode for sodium-ion batteries based on the synergistic cross-linking of hydroxyl-enriched lignin and oxidized pitch, characterized in that, The method includes: (1) Lignin pretreatment: Lignin was mixed with NaOH solution and stirred to react. After the reaction was completed, the mixture was filtered to remove the filter residue. The pH was then adjusted to 6.0 and allowed to stand. After standing, the mixture was washed with water until neutral, dried, and ground to obtain hydroxyl-enriched modified lignin. (2) Pre-oxidation of asphalt: Petroleum-based asphalt is crushed and placed in an oxidizing atmosphere, then heated for pre-oxidation treatment to obtain oxidized asphalt. (3) Crosslinking reaction: The obtained oxidized asphalt was ground and mixed with hydroxyl-enriched modified lignin and then pre-crosslinked in an inert gas atmosphere. The temperature was then raised to continue crosslinking. After the crosslinking was completed, the crosslinked product was obtained. (4) Carbonization reaction: The cross-linked product was crushed and heated in an inert gas atmosphere to carry out a carbonization reaction. After the reaction was completed, it was cooled to obtain a hard carbon anode for sodium-ion batteries with a highly cross-linked structure.

2. The method according to claim 1, characterized in that, In step (1), the solid-liquid ratio of lignin to NaOH solution is 1:8~12 (g / mL); the purity of the lignin is ≥92%, and the concentration of NaOH solution is 1~2 mol / L; The conditions for the stirring reaction are: constant temperature stirring at 60~90℃ for 2~6 hours.

3. The method according to claim 1, characterized in that, In step (1), the pH value is adjusted to 5-6 using a citric acid solution with a concentration of 0.5-1 mol / L and allowed to stand for precipitation for 2-4 hours; The drying conditions are: vacuum drying at 80~100℃ for 8~12 hours; The grinding conditions are: grinding to 100~200 mesh.

4. The method according to claim 1, characterized in that, In step (2), petroleum-based bitumen includes petroleum-based bitumen with a softening point of 140~280℃; Crush petroleum-based bitumen to 80-100 mesh; The oxidizing atmosphere is an oxygen-nitrogen mixture, wherein the volume fraction of oxygen is 10-40%. The pre-oxidation treatment conditions are as follows: heating to 200-350℃ at a heating rate of 1-5℃ / min and holding for 1-8 hours.

5. The method according to claim 1, characterized in that, In step (3), the mass ratio of oxidized asphalt to hydroxyl-enriched modified lignin is 1:0.08~0.12; The inert gas is either nitrogen or argon. The conditions for the pre-crosslinking reaction are: heating to 300-400℃ at a rate of 2-6℃ / min for 1-4 hours; The conditions for continued crosslinking are: continue to crosslink at a rate of 2~6℃ / min to 450~600℃ for 1~4 hours.

6. The method according to claim 1, characterized in that, In step (4), the crosslinked product is crushed to 80-100 mesh; The conditions for the carbonization reaction are: heating to 1000-1500℃ at a heating rate of 1-5℃ / min and holding at that temperature for 1-4 hours.

7. The highly cross-linked sodium-ion battery hard carbon anode prepared by the method according to any one of claims 1 to 6, characterized in that, The specific surface area of ​​the hard carbon anode is 5~100m². 2 / g, the interlayer spacing (d) of the hard carbon anode material 002 The wavelength is 0.370~0.420 nm, I D / I G The value is 1.0~2.

0.

8. The application of the highly cross-linked sodium-ion battery hard carbon anode according to claim 7 in the preparation of sodium-ion batteries.

9. A sodium-ion battery, characterized in that, The sodium-ion battery comprises the hard carbon anode of the sodium-ion battery with a highly cross-linked structure as described in claim 7.

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