Glutaraldehyde crosslinked chitosan modified coal-based carbon material as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of coal-based carbon materials, and particularly relates to a glutaraldehyde crosslinked chitosan modified coal-based carbon material as well as a preparation method and application thereof. The preparation method of the glutaraldehyde cross-linked chitosan modified coal-based carbon material comprises the following steps: preparing chitosan-coated coal by taking chitosan and oxidized coal as raw materials, drying the chitosan-coated coal, grinding and sieving to obtain copolymer powder OCS; and dispersing the copolymer powder OCS in an acetic acid solution, and then adding a glutaraldehyde solution for reaction, so that glutaraldehyde and chitosan are subjected to Schiff base covalent cross-linking, and the glutaraldehyde cross-linked chitosan modified coal-based carbon material is obtained. The preparation method comprises the following steps: taking air oxidized coal as a carbon skeleton, realizing uniform coating by utilizing an electrostatic force effect of deprotonated amino and a negative charge functional group on the surface of the oxidized coal, then constructing a three-dimensional composite network by utilizing a Schiff base reaction of glutaraldehyde and a chitosan covalent cross-linking strategy, and carbonizing the obtained product to obtain the carbon-based composite material. The glutaraldehyde crosslinked chitosan modified coal-based carbon material is obtained.

Description

Technical Field

[0001] This invention belongs to the field of coal-based carbon materials technology, specifically relating to a glutaraldehyde crosslinked chitosan modified coal-based carbon material, its preparation method, and its application. Background Technology

[0002] Lithium-ion batteries have distinguished themselves due to their superior energy density, excellent cycle stability, and ultra-long lifespan. However, the scarcity of lithium reserves and their uneven geographical distribution have led to a sharp increase in the cost of lithium-ion batteries, limiting their deployment in large-scale energy storage applications. Therefore, exploring low-cost, green, and efficient alternative electrochemical energy storage technologies is of great significance for sustainable energy development.

[0003] Sodium-ion batteries (SIBs) have become an important supplement or potential alternative to lithium-ion batteries due to their advantages such as low-temperature operation, abundant and low-cost sodium sources, good fast-charging performance, and high safety, coupled with breakthroughs in energy density. However, the electrochemical performance of SIBs is still limited by key electrode materials and cannot meet the requirements of practical applications.

[0004] As a crucial component of SIBs (Self-Isolating Battery), the anode material plays a key role in electrochemical performance. It should possess high theoretical specific capacity, good cycle stability, and a suitable operating voltage to ensure the overall stability of the battery performance. Among numerous anode materials, hard carbon (HC) exhibits broad industrial application prospects due to its advantages such as low cost, good conductivity, stable physicochemical properties, and tunable structure.

[0005] Raw materials for preparing hard carbon include biomass and coal-based derivatives. However, biomass and polymers suffer from drawbacks such as low yield, low vibration density, and high cost. Coal, on the other hand, boasts advantages such as abundant reserves, low price, and controllable oxygen-containing functional groups, achieving carbon yields exceeding 70% and possessing a stable framework structure capable of supporting repeated sodium ion insertion and extraction. However, coal-based raw materials undergo softening, aromatization, and molecular rearrangement during carbonization, resulting in highly graphitized matrix carbon materials. Due to their high crystallinity and small interlayer spacing, their sodium storage performance is limited, with reversible capacities in SIBs typically below 300 mAh g⁻¹. -1 This means that the hard carbon materials prepared using current methods have low hard carbon capacity. Summary of the Invention

[0006] To develop a new strategy for preparing hard carbon materials and address the problem of low hard carbon capacity in products prepared by current methods, thereby obtaining high-performance hard carbon materials, this invention provides a glutaraldehyde-crosslinked chitosan-modified coal-based carbon material, its preparation method, and its applications. To achieve the above objectives, this invention adopts the following technical solution.

[0007] The first objective of this invention is to provide a method for preparing glutaraldehyde-crosslinked chitosan-modified coal-based carbon materials, comprising the following steps: Chitosan and oxidized coal were simultaneously added to a 1% (w / w) acetic acid solution to obtain a chitosan / oxidized coal mixed system; wherein the mass-volume ratio of chitosan, oxidized coal, and acetic acid solution was 0.07g~0.09g:1g:99mL~101mL. The oxidized coal was air-oxidized coal.

[0008] The pH of the mixture is adjusted to 7.8-8.2, and after stirring for 2.8-3.2 hours, the protonated amino groups of chitosan and the deprotonated carboxyl groups and / or phenolic hydroxyl groups on the surface of oxidized coal are electrostatically self-assembled to form a uniformly coated copolymer, thus obtaining chitosan-coated coal slurry.

[0009] After filtering the chitosan-coated coal slurry, the chitosan-coated coal is collected and washed until the filtrate is neutral. The chitosan-coated coal is dried, ground, and sieved to obtain copolymer powder OCS.

[0010] The copolymer powder OCS was dispersed in an acetic acid solution with a pH of 5.9-6.1, and then an 8% (w / w) glutaraldehyde solution was added to react, causing glutaraldehyde to undergo Schiff base covalent cross-linking with chitosan, and further interacting with oxygen-containing functional groups on the surface of oxidized coal to form a three-dimensional network, thus obtaining a glutaraldehyde-crosslinked chitosan-modified coal slurry; wherein the mass-volume ratio of the copolymer powder OCS, acetic acid solution and glutaraldehyde solution was 1g:49mL-51mL:2.8mL-3.2mL.

[0011] After filtering the glutaraldehyde-crosslinked chitosan-modified coal slurry, the upper precipitate was collected and washed until neutral to obtain glutaraldehyde-crosslinked chitosan-modified coal. The glutaraldehyde-crosslinked chitosan-modified coal was then carbonized and naturally cooled to obtain the glutaraldehyde-crosslinked chitosan-modified coal-based carbon material, denoted as COCSG.

[0012] The preparation method provided by this invention uses chitosan and oxidized coal as raw materials to prepare a chitosan / oxidized coal mixed system. The pH of the mixed system is then adjusted to 7.8-8.2, and stirred for 2.8-3.2 hours. This allows the protonated amino groups of chitosan to electrostatically self-assemble with the deprotonated carboxyl groups and / or phenolic hydroxyl groups on the surface of oxidized coal to form a uniformly coated copolymer, resulting in chitosan-coated coal. The chitosan-coated coal is then dried, ground, and sieved to obtain copolymer powder (OCS). The copolymer powder (OCS) is dispersed in an acetic acid solution with a pH of 5.9-6.1, and then an 8% (w / w) glutaraldehyde solution is added to react, causing glutaraldehyde and chitosan to undergo Schiff base covalent cross-linking. This further interacts with the oxygen-containing functional groups on the surface of oxidized coal to form a three-dimensional network, resulting in a glutaraldehyde-crosslinked chitosan-modified coal solution. The glutaraldehyde-crosslinked chitosan-modified coal is then carbonized and naturally cooled to obtain a glutaraldehyde-crosslinked chitosan-modified coal-based carbon material, denoted as COCSG.

[0013] This invention utilizes a progressive structural design involving electrostatic self-assembly, chemical cross-linking, and synergistic carbonization. It organically combines the nitrogen-doping advantages, structural cross-linking, and graphitization inhibition of chitosan with the high carbon yield and low cost of coal-based carbon. This systematically addresses the low hard carbon capacity issue from three levels: increasing active sites, optimizing pore structure, and controlling interlayer spacing. Compared to traditional physical mixing or single modification methods, the preparation method provided by this invention achieves precise positioning and efficient anchoring of nitrogen, resulting in a significant increase in the sodium storage capacity of the final material and enhanced cycle stability. This preparation method can improve the hard carbon capacity of coal-based materials, yielding materials with high hard carbon capacity / high-performance hard carbon materials.

[0014] Preferably, the glutaraldehyde-crosslinked chitosan-modified coal has a three-dimensional network structure and contains nitrogen; the three-dimensional network structure refers to the glutaraldehyde-crosslinked chitosan-modified coal being intertwined in three dimensions.

[0015] Preferably, the carbonization conditions are as follows: Under a nitrogen atmosphere, at 4.9℃ min -1 ~5.1℃ min -1 Heat to 1180℃~1220℃ and hold for 1.5h~2.5h.

[0016] Preferably, the reaction is carried out by adding an 8% (w / w) glutaraldehyde solution and stirring at 39°C to 41°C for 2.5 to 3.5 hours.

[0017] Preferably, the pH of the mixture is adjusted to 7.8-8.2 using a 1 mol / L NaOH and 0.1 mol / L HCl solution.

[0018] Preferably, the coal modified with glutaraldehyde crosslinked with chitosan is dried before carbonization.

[0019] Preferably, the drying temperature is 64℃~66℃; the drying time is ≥12h.

[0020] Preferably, the stirring time is 2.5h to 3.5h.

[0021] The second objective of this invention is to provide the preparation method described above for preparing glutaraldehyde-crosslinked chitosan-modified coal-based carbon materials.

[0022] A third objective of this invention is to provide the application of the glutaraldehyde-crosslinked chitosan-modified coal-based carbon material in the preparation of sodium-ion batteries.

[0023] The fourth objective of this invention is to provide a sodium-ion battery anode, which includes an active material, a conductive agent, and a binder; the active material has a mass fraction of 89% to 91% in the sodium-ion battery anode, and the conductive agent and binder have a combined mass fraction of 9% to 11% in the sodium-ion battery anode, totaling 100%.

[0024] The active material is the glutaraldehyde crosslinked chitosan modified coal-based carbon material as described in claim 6.

[0025] A fifth objective of the present invention is to provide a sodium-ion battery comprising the aforementioned sodium-ion battery negative electrode.

[0026] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention provides a glutaraldehyde-crosslinked chitosan-modified coal-based carbon material. The preparation method provided by this invention first uses chitosan and oxidized coal as raw materials, with oxidized coal as the carbon skeleton, to prepare chitosan-coated coal. After drying the chitosan-coated coal, it is ground and sieved to obtain copolymer powder OCS. The copolymer powder OCS is dispersed in an acetic acid solution with a pH of 5.9-6.1, and then an 8% (w / w) glutaraldehyde solution is added to react, causing glutaraldehyde and chitosan to undergo Schiff base covalent crosslinking, further interacting with oxygen-containing functional groups on the surface of oxidized coal to form a three-dimensional network, thus obtaining the glutaraldehyde-crosslinked chitosan-modified coal-based carbon material. That is, a three-dimensional composite network is constructed through a stepwise crosslinking strategy of chitosan and glutaraldehyde. The deprotonated amino groups (-NH3) are utilized... + Uniform coating is achieved through electrostatic interaction between glutaraldehyde and the negatively charged functional groups on the surface of oxidized coal. Then, glutaraldehyde is covalently cross-linked with chitosan via a Schiff base reaction to form a stable network. The resulting product is then carbonized to obtain chitosan-modified carbon material. This preparation method provided by the present invention can improve the hard carbon capacity of coal-based materials, obtaining materials with high hard carbon capacity / high-performance hard carbon materials.

[0027] 2. Among numerous strategies for suppressing the ordered growth of carbon microcrystals during coal pyrolysis and carbonization, pre-oxidation in the gas phase or liquid phase before carbonization is widely considered a crucial step in inhibiting excessive graphitization of the carbon layer due to its simplicity and suitability for mass production. However, whether coal is directly pre-oxidized or oxidized after separation, the uncontrollable oxidation and structural evolution caused by the complex molecular structure of coal hinders the design of high-performance hard carbon. Furthermore, this hard carbon structure results in low reversible capacity in sodium-ion batteries, with capacity mainly concentrated in the slope region. Various heteroatom doping methods (boron, phosphorus, iodine, fluorine, etc.) are also effective strategies for regulating the physicochemical properties of carbon-based materials, exhibiting high capacity and moderate initial coulombic efficiency (ICE). Nitrogen doping has been the most frequently reported, as nitrogen doping at oxygen sites introduces oxygen vacancies, thereby increasing the electron-hole concentration, enhancing the conductivity of hard carbon materials, promoting sodium ion migration, and ultimately improving rate performance.

[0028] Crosslinking strategies can form microporous hard carbon structures, significantly improving the storage performance of sodium-ion batteries. Chitosan is a non-toxic, biodegradable, and biocompatible natural polymer with wide applications in biomedicine, membranes, drug delivery systems, hydrogels, water treatment, and food packaging. As a natural nitrogen-containing polymer (containing approximately 8% nitrogen), its molecular chains are rich in amino and hydroxyl groups, making it highly suitable for chemical modification to construct complex molecular structures. A three-dimensional covalent network can be formed through crosslinking with the bifunctional groups of glutaraldehyde. This crosslinking not only provides mechanical stability, but the residual oxygen and nitrogen atom doping sites after chitosan carbonization can also enhance sodium storage activity. Furthermore, chitosan-hard carbon materials can form porous structures in situ during high-temperature carbonization, which is beneficial for electrolyte permeation and ion transport. The abundant oxygen and nitrogen elements work synergistically to significantly improve the wettability of the electrode surface and the interfacial reaction kinetics. By controlling the crosslinking density and carbonization process, the carbon interlayer spacing and defect concentration can be optimized, thereby improving the reversible intercalation capability and cycle stability of sodium ions, providing new ideas for the design of biomass-based anode materials.

[0029] This invention utilizes a progressive structural design involving electrostatic self-assembly, chemical cross-linking, and synergistic carbonization to organically combine the nitrogen-doping advantages of chitosan with the high carbon yield and low cost of coal-based carbon. It systematically addresses the low capacity of hard carbon from three levels: increasing active sites, optimizing pore structure, structural cross-linking, and inhibiting graphitization. Compared to traditional physical mixing or single modification methods, the preparation method provided by this invention achieves precise positioning and efficient anchoring of nitrogen, resulting in a significant increase in the sodium storage capacity of the final material and enhanced cycle stability. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the preparation process of the glutaraldehyde crosslinked chitosan modified coal-based carbon material in this invention.

[0031] Figure 2 This is a schematic diagram illustrating the mechanism of glutaraldehyde-crosslinked chitosan-modified coal-based carbon material (COCSG) in this invention; wherein: (a) Chitosan-coated oxidized coal; (b) is the reaction of glutaraldehyde crosslinking chitosan.

[0032] Figure 3 The image shows the infrared spectrum of glutaraldehyde-crosslinked chitosan-modified oxidized coal (OCSG) in this invention; where OCSG-X represents glutaraldehyde-crosslinked chitosan-modified oxidized coal with different chitosan coating amounts.

[0033] Figure 4 These are the TG-DTG curves of CS, OCS-8, and OCSG-8 in this invention; wherein: (a) TG for CS, OCS-8 and OCSG-8; (b) DTG curves for CS, OCS-8, and OCSG-8; CS stands for chitosan, OCS-8 refers to oxidized coal with a chitosan coating of 8%wt, and OCSG-8 refers to oxidized coal with a glutaraldehyde crosslinked chitosan coating of 8%wt.

[0034] Figure 5 These are the XPS total spectrum, C1s fitting plot, O1s fitting plot, and N1s fitting plot of OCSG-X in this invention; wherein: (a) is the OCSG-8XPS full spectrum; (b) is the C1s fitting plot; (c) is the O1s fitting plot; (d) is the N1s fitting plot; OCSG-X refers to glutaraldehyde-crosslinked chitosan-modified coal-based carbon materials with different chitosan coating amounts.

[0035] Figure 6 This is a graph showing the variation of elemental content of OCSG-X in this invention; where OCSG-X refers to glutaraldehyde-crosslinked chitosan-modified oxidized coal with different chitosan coating amounts.

[0036] Figure 7 These are enlarged SEM images of OC-260, OCS-8, a portion of OCS-8, COCS-8, COCSG-8, a portion of OCSG-8, COCSG-8, and a portion of COCSG-8 in this invention; wherein: (a) is a SEM image of OC-260; (b) is the SEM image of OCS-8; (c) is a magnified SEM image of a portion of the OCS-5 image; (d) is the SEM image of COCS-8; (e) is a magnified SEM image of a portion of COCSG-8; (f) is a magnified SEM image of a portion of OCSG-8; (g) is a SEM image of COCSG-8; (h) is a magnified SEM image of a portion of COCSG-8; OC-260 refers to oxidized coal at 260℃, OCS-8 refers to oxidized coal with 8% chitosan coating, COCS-8 refers to carbon material made by carbonizing oxidized coal with 8% chitosan coating at 1200℃ for 2 hours, (e) OCSG-8 refers to oxidized coal with 8% glutaraldehyde crosslinked chitosan coating, and COCSG-8 refers to carbon material prepared by carbonizing glutaraldehyde crosslinked chitosan modified oxidized coal at 1200℃ for 2 hours with different chitosan coating amounts.

[0037] Figure 8 The XRD pattern and peak fitting plot of COCSG-X in this invention are shown below; wherein: (a) is the overall XRD pattern of COCSG-X; (b) is the peak fitting plot of COCSG-X; COCSG-X is a carbon material prepared by carbonizing glutaraldehyde-crosslinked chitosan-modified oxidized coal at 1200℃ for 2 hours with different chitosan coating amounts.

[0038] Figure 9 This is a Raman spectroscopy and trend diagram of COCSG-X in this invention; wherein: (a) is the Raman plot of COCSG-X; (b) is d for COCSG-X 002 and I D / I G ; COCSG-X is a carbon material prepared by carbonizing glutaraldehyde-crosslinked chitosan-modified oxidized coal at 1200℃ for 2 hours with different chitosan coating amounts.

[0039] Figure 10 This is the BET diagram of COCSG-X in this invention; wherein: (a) is the specific surface area of ​​COCSG-2; (b) is the specific surface area of ​​COCSG-5; (c) is the specific surface area of ​​COCSG-8; (d) is the specific surface area of ​​COCSG-10; COCSG-X is a carbon material prepared by carbonizing glutaraldehyde-crosslinked chitosan-modified oxidized coal at 1200℃ for 2 hours with different chitosan coating amounts.

[0040] Figure 11 The charge-discharge curves of the COCSG-X series in this invention are shown below; wherein: (a) is a graph showing the relationship between the potential and specific capacitance of COCSG-X under constant battery charge and discharge conditions; (b) represents the total capacity of COCSG-X under constant battery charge and discharge conditions, and the ratio of ramp capacity to plateau capacity in the total capacity; COCSG-X is a carbon material prepared by carbonizing glutaraldehyde-crosslinked chitosan-modified oxidized coal at 1200℃ for 2 hours with different chitosan coating amounts.

[0041] Figure 12 This is a magnification chart of COCSG-X in this invention; wherein: (a) is the CCS multiplier. (b) The multiplier of COCSG-2; (c) represents the multiplier of COCSG-5; (d) represents the multiplier of COCSG-8; (e) represents the multiplier of COCSG-10; (f) represents the multiplier of COCSG-15; COCSG-X refers to carbon materials prepared by carbonizing glutaraldehyde-crosslinked chitosan-modified oxidized coal at 1200℃ for 2 hours with different chitosan coating amounts.

[0042] Figure 13 In this invention, COCSG-X is cyclically processed at 0.02 A / g; wherein, COCSG-X is a carbon material prepared by carbonizing glutaraldehyde-crosslinked chitosan-modified oxidized coal at 1200℃ for 2 hours with different chitosan coating amounts.

[0043] Figure 14 This is a CV curve of COCSG-X in the first three cycles at 0.1 mV / s in this invention; where: (a) is the CV curve of CCS; (b) shows the CV curve of COCSG-2; (c) shows the CV curve of COCSG-5; (d) shows the CV curve of COCSG-8; (e) shows the CV curve of COCSG-10; (f) shows the CV curve of COCSG-10; COCSG-X is a carbon material prepared by carbonizing glutaraldehyde-crosslinked chitosan-modified oxidized coal at 1200℃ for 2 hours with different chitosan coating amounts.

[0044] Figure 15 The diagram shows the CV curves of TTC and COCSG-8 coal-based carbon materials at different scan rates, and the linear relationship between log(i) and log(v); where: (a) is the CV curve of TC; (b) shows the CV curve of COCSG-8; (c) is the linear fit between log(i) and log(v) of the CV curve of TC; (d) shows the linear fit between log(i) and log(v) of the CV curve of COCSG-8; CT refers to carbon materials prepared by carbonizing oxidized coal at 1200℃ for 2 hours. COCSG-8 coal-based carbon materials are carbon materials prepared by carbonizing oxidized coal at 1200℃ for 2 hours with glutaraldehyde crosslinking chitosan and a chitosan-modified coating of 8%.

[0045] Figure 16 The image shows the EIS diagram of the COCSG-X material in this invention. The COCSG-X material is a carbon material prepared by carbonizing glutaraldehyde-crosslinked chitosan-modified oxidized coal at 1200℃ for 2 hours with different chitosan coating amounts. Detailed Implementation

[0046] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments, but this should not be construed as limiting the invention. Unless otherwise specified, the technical means used in the following embodiments are conventional means well known to those skilled in the art, and the materials, reagents, etc. used in the following embodiments are commercially available unless otherwise specified.

[0047] The reagents involved in the following examples are as follows: The lignite was supplied by Shaanxi Coal Yubei Coal Industry Co., Ltd.

[0048] High-purity nitrogen (≥99.999%) and high-purity argon (≥99.999%) were purchased from Shaanxi Longqing Gas Co., Ltd.

[0049] Hydrofluoric acid and concentrated hydrochloric acid, analytical grade, were purchased from Sinopharm Chemical Reagents.

[0050] Conductive carbon black (SuperP), industrial grade, purchased from Aladdin.

[0051] Glass fiber separator GF / D1823-19 Whatman. Copper foil, battery grade, purchased from Shenzhen Jingliang Copper Industry Co., Ltd.

[0052] Sodium perchlorate (NaClO4), battery grade, purchased from Kelude Experimental Equipment Technology Co., Ltd. Sodium block, 99.9%, purchased from Aladdin.

[0053] Example I. Methods 1. Preparation of coal-based hard carbon (1) Preparation of OCS materials: Prepare 100 mL of 1% (w / w) acetic acid solution. Add 0.08 g of chitosan and 1 g of coal oxide (OC) to the acetic acid solution to obtain a chitosan / coal oxide mixture. Adjust the pH of the chitosan / coal oxide mixture to 8 using 1 mol / L NaOH and 0.1 mol / L HCl solutions. After magnetic stirring for 3 hours, filter the mixture, collect the filtrate, wash it with deionized water until neutral, collect the filter cake, and dry it overnight in an oven at 65°C. Grind the final copolymer product in a mortar and pestle and pass it through a 200-mesh sieve to obtain copolymer powder OCS. Copolymer powder OCS is abbreviated as OCS.

[0054] Overnight stays refer to stays of 12 hours or more.

[0055] The method for obtaining oxidized coal is to oxidize lignite at a constant temperature of 260°C for 3 hours in an air atmosphere.

[0056] (2) Preparation of OCSG materials: 1 g of OCS was dissolved in 50 mL of acetic acid solution with pH 6. 3 mL of glutaraldehyde solution with mass percentages of 2%, 5%, 8%, 10%, and 15% was added. The mixture was magnetically stirred at 40 °C for 3 h. After filtration, the filtrate was collected. The filtrate was washed with deionized water until neutral and dried overnight at 65 °C in an oven. The sample was placed in a tube furnace and carbonized at 1200 °C for 2 h under a nitrogen atmosphere. The resulting sample is chitosan-coal oxide crosslinked carbon material, denoted as COCSG-X.

[0057] For comparative studies, oxidized coal was carbonized at 1200℃ for 2 hours, and the resulting sample was denoted as TC. The preparation method is described in [link to preparation method]. Figure 1 OCSG was carbonized at 1200℃ for 2 hours, and the resulting sample was designated COCSG. The preparation method is detailed below. Figure 1 .

[0058] Glutaraldehyde-crosslinked chitosan-coated oxidized coal is known as OCSG material, or simply OCSG.

[0059] 2. Preparation of electrode sheets and assembly of CR032 cells (1) Preparation of electrode sheets: COCSG-X, carbon black, and sodium alginate binder were precisely weighed in a mortar at a mass ratio of 90:5:5 and thoroughly mixed and ground to ensure uniform dispersion of each component. Deionized water was added gradually to adjust the slurry viscosity to meet coating requirements. The slurry was uniformly coated onto the copper foil current collector using a scraping method, controlling the wet film thickness. The coated current collector was dried overnight (12 hours) in a vacuum drying oven at 60℃ to ensure complete solvent evaporation and the formation of a uniform solid film, resulting in the coated current collector. After drying, the coated current collector was cut into 12mm diameter circular electrode sheets using a stamping machine, and copper sheets were also cut into 12mm diameter circular sheets for quality calibration. The mass of all electrode sheets was measured, and abnormal sheets with a mass deviation exceeding 2% were discarded to ensure the reliability of experimental data. The average mass of the remaining electrode sheets was taken as the reference value for substrate mass. The final active material mass was calculated using the following formula:

[0060] Mass of active material = mass of electrode sheet × 90%.

[0061] (2) Assembly of CR2032 button cell: Inside the glove box (H2O / O2 < 0.1ppm), a gasket and a spring are placed in the positive electrode shell in sequence. 60μL of 1mol / L NaClO4 / EC-DMC electrolyte is dropped into the middle of the gasket. After placing the negative electrode plate, another 60μL of electrolyte is dropped in and the separator is covered. Then, a sodium sheet with a diameter of 16mm is placed on the separator as the counter electrode. The negative electrode shell is then covered, and finally, the battery is sealed by applying 8MPa pressure through a sealing machine.

[0062] 3. Characterization of chemical composition (1) Elemental Analysis (EA): The industrial analysis of coal was conducted according to the national standard "Methods for Industrial Analysis of Coal" (GB / T212-2008). Elemental analysis of the coal samples was conducted according to the national standards "Determination of Carbon and Hydrogen in Coal" (GB / T476-2008), "Determination of Total Sulfur in Coal" (GB / T214-2007), and "Determination of Nitrogen in Coal" (GB / T19227-2008). The instrument used was an Elemantar Vario ELcube elemental analyzer manufactured by a German company. The contents of C, H, N, and S were obtained by averaging two parallel measurements, while the O content was obtained using the difference method.

[0063] (2) Fourier transform infrared spectroscopy analysis (FT-IR): The experimental instrument was a Thermo Scientific Nicoleti S5 infrared spectrometer, using the KBr pellet method. The thin slices were fixed in place with a sample holder and placed in the sample chamber of the infrared spectrometer. The instrument resolution was set to 4.0 cm⁻¹. -1 The number of scans was 32, and the spectral range was 400 cm⁻¹. -1~4000cm -1 Infrared spectra were obtained. The thin film referred to here is the KBr film of COCSG-X.

[0064] (3) X-ray photoelectron spectroscopy (XPS): XPS measurements were performed on a Thermo ESCALAB 250XI photoelectron spectrometer. The parameters were set as follows: X-ray source, voltage 16 kV, current 14.9 mA, beam diameter 650 μm, full-spectrum pass energy 100 eV, elemental high-resolution spectrum 30 eV, and charge calibration using C1s = 284.4 eV as the standard. Sensitivity correction was performed using the Shirley background subtraction method in Avantage software, and C1s was calibrated to 284.8 eV. XPS analysis of COCSG-X was then performed to ensure the accuracy and repeatability of the measurement results.

[0065] 4. Microstructure characterization (1) X-ray diffraction analysis (XRD): XRD data acquisition was performed on COCSG-X using an MSAL-XD2 X-ray diffractometer. The testing conditions were: Cu target Ka rays, λ = 0.15406 nm; accelerating voltage 40 kV; accelerating current 200 mA; testing range 5°–90°; scan rate 10°·min. The diverging slit was 1 mm, the receiving slit 0.30 mm, and a step scan was used with a step width of 0.029 and a scan rate of 2%·min. The scanning range was 5° to 70° (2θ). Origin 2018 software was used to perform peak fitting on the diffraction pattern, and the peak position, intensity, full width at half maximum (FWHM), and peak area were measured to calculate the d002, La, and Lc of the material.

[0066] (2) Raman spectroscopy: Raman spectroscopy can provide information on the chemical bonding and crystal structure characteristics of materials. Analyzing material structure through molecular vibrational scattering is non-invasive, non-destructive, and offers high resolution. A Thermo Fisher DXR laser confocal Raman spectrometer (532 nm laser wavelength) was used to resolve the defects and crystal microstructure information of COCSG-X.

[0067] (3) Specific surface area and pore structure test (BET): Using a Micromeritics ASAP2020 physical adsorption instrument (USA), after removing surface adsorbates by vacuum degassing at 200℃ for 12 h, the specific surface area of ​​the carbon material was calculated using the BET model (error ±5%). Key structural parameters of COCSG-X, such as specific surface area (BET model), pore volume, and pore size distribution, were analyzed to reveal the structure-activity relationship between its microstructure and electrochemical performance.

[0068] The BET model is publicly available in the literature: The BET model is publicly available in the literature.

[0069] (4) Small-angle scattering and wide-angle scattering (SAXS / WAXS): The COCSG-X was tested using an Eiger2R 1MXeuss 3.0 SAXS / WAXS, with a pixel side length of 75 μm, a copper target of 8.05 keV X-ray, and a wavelength of 1.54189 angstroms. The testing environment was: vacuum (<1 mbar); temperature: 24 degrees Celsius; detector-to-sample distance: 750 mm; spot center coordinates: x 540.1, z 639.4.

[0070] 5. Thermal stability analysis (TG) Using a NETZSCH STA449C integrated thermal analyzer, the temperature was increased to the final temperature (450℃, 1200℃) at a heating rate of 5℃ / min under a nitrogen / oxygen atmosphere to understand the key temperatures and stages of the heat treatment process of COCSG-X.

[0071] 6. Electrochemical performance testing (1) Constant current charge-discharge (GCD): The COCSG-X coin cell was subjected to constant current charge-discharge testing using the MHWX-2000 battery testing system from Xinwei Company. The test temperature was 26℃, and the voltage window was 0.01V~3.0V. This test reflects key parameters such as voltage change, capacity retention, reversible capacity, and initial charge-discharge efficiency, providing important data for evaluating the battery's electrochemical performance. By changing the current density, the battery's performance at different rates can be further tested, thereby evaluating its rate performance and cycle stability.

[0072] (2) Cyclic voltammetry (CV): Cyclic voltammetry tests were performed on COCSG-X using an electrochemical workstation (model CS350M) manufactured by COCSG. The test voltage range was set to 0.01V~3.0V. The electrochemical activity of the substance can be quantitatively described by the integrated peak area.

[0073] (3) Electrochemical impedance spectroscopy (EIS): The COCSG-X was tested using a Metrohm PGSTAT302N electrochemical workstation. The hard carbon anode was cycled a certain number of times in a half-cell, then discharged to 0.01V and held at a constant voltage for 1 hour. The EIS test frequency range of 100kHz to 0.01Hz was used to effectively evaluate its performance.

[0074] II. Results 1. Chemical composition of glutaraldehyde-chitosan crosslinked modified oxidized coal The mechanism of glutaraldehyde-chitosan crosslinking modification of oxidized coal is as follows: Figure 2 As shown, the surface of oxidized coal is rich in hydroxyl and carboxyl groups. In acidic aqueous solutions, the amino groups in chitosan molecules are protonated and dissolved, and then bond with the functional groups on the surface of oxidized coal through hydrogen bonds and electrostatic attraction. The amino groups of two chitosan molecules and the aldehyde group of one dialdehyde molecule are cross-linked through an aldehyde imine. The reaction generates C=N, thus constructing a three-dimensional cross-linked network structure. However, the hydroxyl groups (C-OH) in the chitosan backbone, due to their low reactivity and steric hindrance, usually do not participate in this type of covalent cross-linking reaction and remain in the composite system.

[0075] like Figure 3 As shown. In the infrared spectrum of the OCSG sample (OCSG material), at 3400 cm⁻¹ -1 The nearby strong broadband is a multiple absorption peak broadened by the stretching vibrations of the -NH and -OH functional groups. Oxidized coal, after surface modification with chitosan, has an absorption peak at 3400 cm⁻¹. -1 The increased absorption peak intensity at 1640 cm⁻¹ indicates that the relative content of -OH and NH functional groups in OCSG is higher than that in raw oxidized coal. This is mainly due to the abundant -OH and -NH₂ groups in the chitosan molecular structure. -1 The peak at 1640 cm⁻¹ belongs to C=C / C=N, and after the addition of glutaraldehyde, it reaches 1640 cm⁻¹. -1 The peak at that point first broadens and intensifies, indicating that glutaraldehyde binds to the -NH group on the chitosan chain via the dialdehyde group. 2 Schiff base reactions occur or the hydrogen bond network structure on the material surface is reconstructed, resulting in a broadening of its distribution.

[0076] like Figure 4 and Figure 5 As shown, the XPS total spectrum of OCSG shows C1s, N1s, and O1s diffraction peaks at 284 eV, 400 eV, and 530 eV, respectively, corresponding to electronic orbital transitions of C, N, and O elements. The total contents of O and N elements are 40.69% and 4.91%, respectively. The O content is 17% higher than that of OC. The C1s spectrum was fitted to five sub-peaks: CC / C=C (284.8 eV), CN / C=N (285 eV), CO (286.2 eV), C=O (287.9 ​​eV), and OC=O (289.0 eV). The relative content of CN / C=N is 13.70%, formed by the cross-linking of the aldehyde group of glutaraldehyde with the amino group of chitosan through Schiff base. The N1s spectrum was fitted to two sub-peaks: -NH2 / -NH (399.5 eV) and -NH3. + (401.1 eV). NH 2来源于 Unreacted amino groups, -NH3 in chitosan +This is due to the protonation of the amino groups in chitosan in acetic acid solution. TG-DTG curves of OC and OCSG show that the thermal stability of oxidized coal is significantly enhanced after cross-linking modification with chitosan and glutaraldehyde, with the carbon yield increasing from 30.79% to 53.92%, an increase of 23.13%. Therefore, it can be considered that glutaraldehyde, acting as a cross-linking agent, undergoes a Schiff base reaction with chitosan macromolecules while simultaneously undergoing an aldol reaction with oxidized coal, covalently cross-linking the three substances into a network. This inhibits chain slippage, delays the breakage of the carbon skeleton at high temperatures, and reduces the release of volatiles, thus enhancing the thermal stability of the material.

[0077] Elemental analysis was used to characterize the compositional properties of the OCSG-X material, and the data are as follows: Figure 6 As shown in Table 1.

[0078] The oxygen content was determined by subtraction. With increasing chitosan addition, the C content gradually decreased (65.89%~57.25%), while the contents of N, O, and H increased by 68.1% (0.91%~1.53%), 24.0% (30.68%~38.03%), and 33.8% (2.16%~2.89%), respectively. This trend is consistent with the changes in O1s and N1s observed in XPS characterization. The significant changes in elemental composition are mainly due to the structural characteristics of chitosan molecules and their chemical reactivity in the composite system. Chitosan molecules are rich in amino (-NH2) and hydroxyl (-OH) groups; the continuous introduction of chitosan directly increases the N, O, and H contents in the system.

[0079] Table 1. Elemental Content of OCSG-X Characterization techniques such as FT-IR and XPS revealed that the synergistic effect of chitosan and glutaraldehyde effectively reconstructed the surface chemical structure of oxidized coal. This reconstruction process involves multiple interaction mechanisms: ① Schiff base reaction to construct C=N covalent bonds; ② electrostatic attraction between amino and carboxyl groups. These reactions synergistically formed a complex cross-linked system rich in oxygen and nitrogen elements and with a significantly enhanced hydrogen bond density.

[0080] 2. Glutaraldehyde-chitosan crosslinking modified microcrystalline structure of coal-based carbon oxidants The morphology of the prepared OCSG-X was characterized using scanning electron microscopy (SEM), such as... Figure 7 As shown. Figure 7 As shown in (a), OC-260, after air oxidation, exhibits a typical polyhedral structure with clear geometric contours and sharp edges, while other samples such as OCS-8 show significantly blunted edges and rounded corners compared to OC-260. Figure 7As can be clearly seen in (b) and (c), the surface of the oxidized coal particles has a dense, layered coating structure. This is because the amino groups of chitosan are protonated in the acetic acid solution, and electrostatic interactions occur between chitosan and the electronegative functional groups (such as carboxyl and hydroxyl groups) on the surface of the oxidized coal, forming a uniform and stable composite system. From... Figure 7 As can be seen in (d), after direct pyrolysis of OCS-8, the surface of the chitosan-coal oxide composite material becomes rough and the edge lamellars warp. This may be attributed to the following factors: ① The initial interfacial bonding force between chitosan and coal oxide is weak, and the bonding between chitosan and coal oxide mainly relies on electrostatic attraction and hydrogen bonding, lacking the construction of a covalent cross-linked network; ② The pyrolysis of the intramolecular hydrogen bond network and crystal structure of chitosan during carbonization destroys the carbonization process.

[0081] from Figure 7 (e) and Figure 7 In (f), it can be observed that after the addition of glutaraldehyde, there is a clear interconnected structure on the surface. The original lamellar structure undergoes significant cross-linking and recombination, forming a fibrous interconnected network and generating a three-dimensional network structure. Figure 7 (g) and Figure 7 As can be seen from (h), many small pore structures appear after high-temperature carbonization. This is due to the condensation of the cross-linked network during the carbonization process and the generation of gas during the oxidation of coal. In summary, through the Schiff base reaction, the chitosan molecular chains are linked to form a uniform and stable three-dimensional cross-linked structure, causing the OCSG-8 structure to undergo a "passivation-rounding-network" transformation. The resulting three-dimensional structure can improve electrolyte wettability, construct a fast transport channel for sodium ions, and enhance the interfacial charge transfer kinetics and bulk sodium storage capacity of the material.

[0082] Figure 8 X-ray diffraction patterns of the chitosan COCSG-X carbon material are presented. The XRD patterns show two diffuse diffraction peaks of amorphous carbon near 24.1° and 43.4°, corresponding to the (002) and (100) crystal planes of the carbon-based material. The d-axis of the COCSG-X carbon material... 002The values ​​were 0.366 nm, 0.370 nm, 0.372 nm, 0.375 nm, 0.371 nm, and 0.368 nm, respectively. The CCS (002) interlayer spacing was the smallest, indicating a higher degree of structural order. The chitosan pre-oxidized coal crosslinked composite material showed a significant increase in peak intensity after the chitosan addition exceeded 8%, indicating a more ordered structure. This may be because excessive chitosan forms an overly thick coating layer, making it difficult for glutaraldehyde to penetrate into the interior to complete crosslinking. Uncrosslinked chitosan molecular chains can move freely at high temperatures, forming sp² hybrid carbon planes through deoxygenation, denitrification, and other reactions, promoting carbon layer stacking. The outer crosslinked region forms a disordered structure, while the inner uncrosslinked region forms an ordered structure through pyrolysis and polycondensation. The coexistence of the two leads to an increase in the overall intensity of the XRD (002) peak.

[0083] Further Raman spectroscopy analysis was conducted to analyze the lattice defect information of the material under different chitosan addition amounts. The Raman spectra of COCSG-X material are shown below. Figure 9 As shown in (a) above. All materials are at 1350cm. −1 (D peak) and 1590cm −1 Diffraction peaks are present at (G peak), corresponding to sp... 3 and sp 2 Characteristic peaks of hybrid carbon. Peak fitting was performed on the Raman spectrum of COCSG-X, and the results are shown in Table 2. With increasing chitosan content, the interlayer spacing and I... D / I G The value increases and then decreases, while the L value of carbon microcrystals decreases. a and L c The trend shows an increasing intensity, consistent with the conclusions obtained from the XRD diffraction pattern. This may be due to the synergistic effect of glutaraldehyde crosslinking chitosan to form a three-dimensional crosslinked network structure and the oxygen-containing functional groups introduced by oxidation—the C=N, C=O, and COC bonds formed through crosslinking can suppress the rearrangement of graphite crystallites at high temperatures through steric hindrance and defect introduction. Secondly, nitrogen, oxygen, and other elements introduced by the crosslinking agent embed into the carbon skeleton, disrupting the regularity of the graphite structure and introducing defects.

[0084] Table 2. Microcrystalline structure size parameters and Raman spectroscopy results of COCSG-X carbon materials. D / I G value A BET test analysis was performed on COCSG-X, and the results are as follows: Figure 10 As shown, with the gradual increase of chitosan addition, the specific surface area increased from 8.35 m² / s². 2 / g increased to 38.71m 2 / g. This can be attributed to the fact that the cross-linked structure of chitosan forms a large number of pores, which are retained during the carbonization process. Secondly, the higher the amount of chitosan added, the greater the volatile matter production, and the more open-cell structures are formed during carbonization.

[0085] 3. Sodium storage performance of glutaraldehyde-chitosan crosslinked modified carbon materials To investigate the influence of the microcrystalline structure of coal-based carbon materials with different degrees of crosslinking on their electrochemical performance, a half-cell of COCSG-X was assembled, and its electrochemical performance was tested. The half-cell was subjected to galvanostatic charge / discharge tests at a current density of 0.02 A / g on a Newway testing system.

[0086] like Figure 11 As shown in (a) and Table 3, the reversible capacity initially increases and then decreases with increasing chitosan content, with COCSG-8 exhibiting the highest reversible capacity (350.45 mAh / g) and plateau region. At chitosan content (2%–8%), the cross-linking reaction between chitosan and glutaraldehyde dominates. At this point, the cross-linked network gradually expands, forming a uniform three-dimensional structure, which transforms into a stable three-dimensional carbon skeleton after carbonization. This facilitates the exposure of active sites and the construction of ion transport channels. This structure enhances the mechanical stability and sodium ion conductivity of the material. The low-voltage plateau region is closely related to the filling of sodium ions in the nanopores. Based on whether the electrolyte can enter the pores, nanopores can be classified as open-pores and closed-pores. Open-pore structures can achieve effective electrolyte wetting and obtain rapid sodium ion diffusion kinetics, but this leads to a lower initial coulombic efficiency.

[0087] Secondly, with the expansion of the cross-linked network, more nitrogen doping and oxygen-containing functional groups are retained after pyrolysis, providing a large number of active sites for sodium ion intercalation. However, when the chitosan content exceeds 8%, the densified structure of the cross-linked network hinders the diffusion of glutaraldehyde inward, forming an outer cross-linked structure and an inner heterogeneous structure of chitosan. This leads to the decomposition of internal chitosan during pyrolysis, reducing interlayer spacing, graphitization, and the ordering of the carbon layer structure. The hard carbon structure generated by chitosan carbonization has poor ion transport kinetics, resulting in a decrease in reversible capacity and initial efficiency. The dense outer shell restricts electrolyte penetration and ion transport, leading to a decrease in reversible capacity. Secondly, the initial efficiency continues to decline. As shown by the BET results, the increase in specific surface area requires more sodium ions to form an SEI film, resulting in a decrease in initial efficiency. As can be seen from the figure, the main sodium storage behavior of the electrode material is the adsorption of Na+ by surface defects.

[0088] Table 3. COCSG-X charge / discharge curve data The shape of the charge-discharge curves shows that the reversible capacity of the COCSG-X carbon material mainly originates from the sodium storage behavior in the slope region within the voltage range of 0.01V to 3.0V, a characteristic corresponding to a rapid surface adsorption / desorption mechanism. Studies have shown that carbon-based anodes dominated by slope region capacity typically exhibit superior rate retention under high current loads. Rate performance tests of the COCSG-X series materials at current densities ranging from 0.02A / g to 2A / g yielded the following results: Figure 12 As shown.

[0089] As shown in the rate curve, the average reversible capacities after 5 cycles at a current density of 0.02 A / g are 182.2 mAh / g, 284.7 mAh / g, 319.3 mAh / g, 349.7 mAh / g, 332.83 mAh / g, and 280.9 mAh / g, respectively. After the rate test, with the current density returning to 0.02 A / g, the reversible capacities are 180.7 mAh / g, 280.4 mAh / g, 309.2 mAh / g, 348.9 mAh / g, 331.3 mAh / g, and 290.2 mAh / g, respectively. This demonstrates excellent rate performance, indicating that the electrode structure remained undamaged after the high-rate charge / discharge test, reflecting the structural stability of the material.

[0090] Figure 13 The cycling performance of COCSG-X under a constant current density of 0.02 A / g for 100 cycles was systematically evaluated. The COCSG-X carbon materials exhibited excellent cycling stability, with no significant capacity decay after 100 cycles. The initial reversible capacities were 184.5 mAh / g, 284.6 mAh / g, 314.8 mAh / g, 352.6 mAh / g, 332.1 mAh / g, and 282.3 mAh / g, respectively. After 100 cycles, the reversible capacities remained at 167.7 mAh / g, 267.8 mAh / g, 288.3 mAh / g, 334.3 mAh / g, 309.5 mAh / g, and 264.7 mAh / g, respectively, with capacity retention rates of 90.9%, 94.1%, 91.6%, 94.8%, 93.2%, and 93.8%. Of particular note is that the capacity retention of all samples exceeded 90%, which fully demonstrates the excellent structural stability of the material.

[0091] In summary, coal-based carbon materials obtained with different chitosan addition amounts exhibit different electrochemical properties due to differences in their physicochemical properties, while materials with a moderate degree of crosslinking show better performance in terms of reversible capacity and rate capability.

[0092] Cyclic voltammetry (CV) was used to further analyze the sodium storage information of the material. Figure 14The results of the first three cycles of COCSG-X at a scan rate of 0.1 mV / s are shown in the figure.

[0093] from Figure 14 As can be seen, a broad oxidation peak was observed in the range of 0.5V to 1.2V, and a corresponding reduction peak was observed at the same position. The redox peaks were relatively weak, which is because Na... + The main focus is on adsorption behavior on the carbon material surface. Secondly, the differences between the first and second / third cycles are minimal. Thirdly, a strong reduction peak appears between 0.5V and 1.2V and disappears in subsequent curves; this is because an SEI film forms on the electrode surface as discharge progresses.

[0094] Cyclic voltammetry tests (scan rates 0.1 mV / s to 1 mV / s) were conducted on sodium-ion half-cells assembled from CT and COCSG-8 cells. The differences in sodium storage mechanisms were revealed by analyzing the evolution of redox peak positions and kinetic parameters. With increasing scan rate, the oxidation peaks of both CT and COCSG-8 cells showed a positive shift, while the reduction peaks showed a negative shift, and the peak spacing significantly increased, indicating an intensified polarization effect. The b-value was calculated to determine whether the ion state during the electrochemical reaction was due to diffusion or capacitive control. The b-value was calculated using the following formula:

[0095] ; In the above formula, a The intercept; b is the slope; i is the current density, in A / g; v This is the scan rate, measured in V / s. When b is 0.5, it indicates that the electrochemical reaction mainly involves diffusion. When b is 1, it indicates that capacitive control is dominant, such as the adsorption of sodium ions by crystal defects and functional groups. The relationship between the current and the scan rate at 0.1 V was calculated through fitting, and the results are as follows: Figure 15 As shown. Calculations show that the b-values ​​for CT and COCSG-8 are 0.47 and 0.34, respectively. It can be seen that the b-values ​​of the samples are all close to 0.5, proving that sodium ion storage is mainly controlled by diffusion. This behavior primarily relies on sodium ions intercalating into the carbon layer to form sodium-intercalated compounds for storage.

[0096] To investigate the internal dynamics and interfacial structure of the electrode, electrochemical impedance spectroscopy (EIS) was used. The entire equivalent circuit of the COCSG-X carbon material was fitted using CS Analysis software, and the fitted curves are shown below. Figure 16As shown, the obtained parameter values ​​are summarized in Table 4. The table shows that Rs gradually increases with increasing chitosan content. COCSG-8 achieves the lowest Rct (169.8 Ω), which is likely due to the three-dimensional structure formed by cross-linking and the presence of the nanoporous structure promoting ion and charge transport. When the chitosan content is further increased, the smaller interlayer spacing hinders ion and charge diffusion, leading to an increase in internal resistance to 183.9 Ω.

[0097] Table 4. Fitting results of Nyquist plots 4. Comparison of sodium storage performance of glutaraldehyde-chitosan crosslinked modified carbon materials To further demonstrate the high sodium storage capacity of the prepared COCSG-8, its sodium storage performance at 0.02 A / g was compared with that of other coal-based carbon materials in the literature, and the results are shown in Table 5. The study found that the reversible capacity of the OCSG-8 material prepared in this paper is much greater than the adsorption data reported in the literature, indicating that the sodium storage performance of the oxidized coal-based carbon material was improved by the glutaraldehyde-chitosan crosslinking modification method.

[0098] Table 5 Comparison of sodium storage performance of coal-based carbon materials This invention utilizes a stepwise crosslinking strategy between chitosan and glutaraldehyde to construct a three-dimensional composite carbon material with pre-oxidized coal (OC-260) as the framework. The effects of the crosslinking mechanism on the material's chemical composition and microcrystalline structure were systematically revealed, and its electrochemical sodium storage behavior was investigated. The main conclusions are as follows: The negative charge on the surface of oxidized coal and the protonated chitosan (-NH3) + A uniform coating is formed through electrostatic interactions, and glutaraldehyde crosslinks to form molecular chains via Schiff base reactions (C=N bonds), constructing a stable three-dimensional network. This network enhances the interfacial stability of the material through the synergistic effect of hydrogen bonds, electrostatic interactions, and covalent bonds, suppressing the ordered arrangement of graphite crystallites during high-temperature carbonization, increasing the carbon yield to 53.92% (COCSG-8), and nitrogen doping to 1.42%. At low addition levels (≤ 8%): the crosslinked network dominates, CN / C=N bonds increase rapidly, interlayer spacing expands to 0.375 nm (COCSG-8), and defect density increases (I0.05). D / I G =1.22), the specific surface area increased to 20.16m². 2 / g, the reversible capacity increased from 284.87mAh / g to 350.45mAh / g, and the capacity ratio of the plateau region increased to 48.51%. High addition amount (>8%): Excessive chitosan densification and coating inhibits internal cross-linking, and after carbonization L aThe wavelength was increased to 2.90nm (COCSG-15), the interlayer spacing was reduced to 0.368nm, the reversible capacity was reduced to 280.65mAh / g, the platform capacity ratio was reduced to 42.31%, and the first-efficiency simultaneous effect was reduced to 68.22%.

[0099] It should be noted that when numerical ranges are involved in this invention, it should be understood that the two endpoints of each numerical range and any value between the two endpoints can be selected. To avoid redundancy, this invention describes preferred embodiments.

[0100] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments, all of which fall within the scope of the invention.

Claims

1. A method for preparing glutaraldehyde cross-linked chitosan modified coal-based carbon material, characterized in that, Comprising the following steps: adding chitosan and oxidized coal into 1% acetic acid solution at the same time to obtain a chitosan / oxidized coal mixed system; wherein the mass-volume ratio of chitosan, oxidized coal and acetic acid solution is 0.07g-0.09g:1g:99mL-101mL; adjusting the pH of the mixed system to 7.8-8.2, stirring, and then allowing the protonated amino groups of chitosan to self-assemble with the deprotonated carboxyl and / or phenolic hydroxyl groups on the surface of oxidized coal to form a uniform coated copolymer, thereby obtaining chitosan-coated coal; drying the chitosan-coated coal, grinding and sieving to obtain copolymer powder OCS; dispersing the copolymer powder OCS in an acetic acid solution with a pH of 5.9-6.1, and then adding 8% glutaraldehyde solution to react, thereby obtaining glutaraldehyde cross-linked chitosan-modified coal; wherein the mass-volume ratio of copolymer powder OCS, acetic acid solution and glutaraldehyde solution is 1g:49mL-51mL:2.8mL-3.2mL; carbonizing the glutaraldehyde cross-linked chitosan-modified coal to obtain the glutaraldehyde cross-linked chitosan-modified coal-based carbon material.

2. The production method according to claim 1, characterized by, The carbonization conditions are as follows: Ramp to 4.9°C min -1 Ramp to 5.1°C min -1 Ramp to 1180°C~1220°C and hold for 1.5h~2.5h.

3. The production method according to claim 1, characterized by, When adding 8% glutaraldehyde solution to react, the conditions are 39°C-41°C stirring for 2.5h-3.5h.

4. The method of claim 1, wherein, The temperature during drying is 64°C-66°C; the time during drying is ≥12h.

5. The preparation method according to claim 1, characterized in that, The stirring time is 2.5h-3.5h.

6. The glutaraldehyde cross-linked chitosan-modified coal-based carbon material prepared by the preparation method of any one of claims 1-5.

7. The use of the glutaraldehyde cross-linked chitosan-modified coal-based carbon material of claim 6 in the preparation of a sodium ion battery.

8. A sodium-ion battery anode, characterized in that, The negative electrode of the sodium ion battery comprises an active material, a conductive agent and a binder; the mass fraction of the active material in the negative electrode of the sodium ion battery is 89%-91%, and the mass fraction of the conductive agent and the binder in the negative electrode of the sodium ion battery is 9%-11% in total, accounting for 100%. The active material is the glutaraldehyde cross-linked chitosan-modified coal-based carbon material of claim 6.

9. A sodium-ion battery, characterized in that, The sodium ion battery negative electrode of claim 8. The sodium ion battery negative electrode of claim 8.

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