Study On Modification Of Coal-based Carbon Anode Material For Sodium-ion Battery

Sodium-ion batteries are considered as a new type of secondary battery for large-scale energy storage applications due to their abundant resources,widespread distribution,low cost,and similar physical and chemical properties to lithium.Developing high-performance,low-cost carbon-based anode electrode materials is an important challenge for the commercialization of sodium-ion batteries.Coke coal is a high-quality amorphous carbon precursor with abundant reserves and high carbon content.However,the relatively regular microcrystalline structure of coke coal pyrolysis carbon,fewer sodium storage active sites,and poor electrochemical performance seriously affect the application of coke coal-based carbon anode materials in sodium-ion batteries.In this paper,using coke coal as raw material,the structural disorder of coke coal pyrolysis carbon is controlled by constructing heterostructure microcrystalline structures,flexible self-supporting integrated electrodes,and pitch coated modification methods,creating sodium storage active sites,and improving the electrochemical sodium storage performance of coal-based carbon materials.（1）Study on preparation and sodium storage performance of coal-based heterostructure microcrystalline carbon materials assisted by molten salt.Using coke coal as precursor,by introducing the second precursor-sucrose and fully cross-linking with molten salt system,the heterostructure microcrystalline structure is constructed to improve the structural disorder of carbon materials and improve the electrochemical sodium storage performance of coal-based carbon materials.Compared with coal-based carbon（BCoal-700）,the sodium storage capacity of coal-based heterostructure microcrystalline structure（BCoal-SM-700）constructed by molten salt method was increased from 125.4 m Ah g^-1 to 286.5 m Ah g^-1,and the cycle and rate performance were excellent,when assembled into a sodium-ion hybrid capacitor,it exhibits an energy density of 103 Wh kg^-1.The molten salt process is simple,and can be recycled and reused,which is in line with the concept of environmental protection and suitable for large-scale production.Therefore,the coal/sucrose heterostructure microcrystalline carbon materials prepared by this method is a potential anode electrode materials for sodium-ion batteries.（2）Preparation and sodium storage performance of cotton fabric/coke coal integrated carbon electrode.A flexible self-supporting integrated carbon electrode material（DC-B-1200）was obtained by loading coke coal onto a flexible cotton fabric substrate by liquid phase impregnation and further carbonizing at high temperature.Due to the synergistic effect between cotton fabric and coke coal,DC-B-1200 exhibits a structural feature of long carbon layers distributed around short range disordered carbon layers.Compared with the non-impregnated cotton fabric carbon material（DC-12000）,the sodium storage performance of the carbon material DC-B-1200 impregnated with coke coal has been significantly improved.The reversible capacity at 0.1 C has increased from 243.5 m Ah g^-1 to 318.1 m Ah g^-1,and the initial coulomb efficiency has increased to 88.7%.At 1 C magnification,the specific capacity can still maintain 93.1 m Ah g^-1.Matched and assembled with O₃Na Ni_1/3Fe_1/3Mn_1/3O₂ positive electrode to form a sodium-ion full battery,the energy density is up to 250 Wh kg^-1,indicating that the cotton fabric/coke coal carbon composite material prepared by liquid phase impregnation and high-temperature carbonization is an ideal flexible electrode for sodium-ion batteries,and has good application prospects in high energy density energy storage devices.（3）Preparation and sodium storage properties of pitch modified coke coal-based carbon anode materials.Through alkali activation treatment of coke coal,a microporous structure is constructed,and a coal-based carbon material with a closed pore structure is further obtained by melting and plugging the pores with pitch.The smaller closed pore structure can block the entry of solvent molecules,allowing sodium ions to fill the pores in the form of bare ions,effectively inhibiting the decomposition of electrolyte in the pores and the formation of SEI films,thereby improving the initial coulomb efficiency.At the same time,closed pore structures provide more sodium storage active sites,thereby improving electrochemical performance.The sodium storage capacity of the coal-based carbon material（ABC-700）without pitch modification is only 195.3 m Ah g^-1.In contrast,after adding pitch to melt and plug the pores,the electrochemical sodium storage performance of the sample is significantly improved,with the reversible sodium storage capacity of CABC-P-2.5-1-1000 reaching 290.0 m Ah g^-1,the initial coulomb efficiency increasing from 52.2%to 78.0%,and the plateau capacity increasing from 66.2 m Ah g^-1 to 130.4 m Ah g^-1,while exhibiting good cycle and rate performance,it is shown that melting and pore filling of pitch is an effective strategy for modifying coal-based carbon materials.