The Optimized Synthesis Of Carbon Spheres For The Anode Of Sodium-ion Batteries

Lithium-ion batteries(LIBs)are widely used in small-sized electronic equipment and large-scale power gride application due to their high energy density and proven technology.With the extensive use of LIBs,the demand for lithium is also increasing dramatically.But the reserves of lithium resources in the crust is limited.Therefore,new energy storage technologies are urgently needed to relieve the pressure of lithium resource shortage.Sodium,located in group IA in the periodic table,has similar physical and chemical properties to lithium.Considering the wide abundance,widely distributed and low cost of sodium resource,sodium-ion batteries(SIBs)have recently been considered as an alternative to LIBs for the large-scale stationary energy storage applications.However,the radius of sodium ion is much larger than that of lithium ion.Therefore,it’s critical to find suitable anode materials for SIBs.Carbonaceous materials are considered to be excellent anode materials for both LIBs and SIBs due to their relatively high capacity,chemical stability,nontoxicity,low cost and abundance.Among them,carbon materials with spherical shape are beneficial to the uniform distribution of current and can achieve a high rate performance,due to their unique morphology.In this thesis,we studied the carbon spheres from two aspects,including porosity and heteroaotm doping,and the prepared samples were used as anode materials for SIBs to investigate their electrochemical performances.The major content of the thesis is summarized as follow:1.porous carbon spheres(PCSs)with large specific surface area and adjustable pore structure were synthesized through a facile hydrothermal treatment of D-Glucose monohydrate precursor via the reaction with Na2MoO4·2H2O and applied as anode materials for SIBs.The PCS,120 sample possessed the largest specific surface area and smallest Rct,and showed the excellent cycling performances and rate performances.A reversible capacity of 249.9 mA h g-1 after 50 cycles at a current density of 50 mA g-1 and a long cycling life at a high current density of 500 mAg-1 were achieved.2.Sulfur-doped carbon spheres with hierarchical micro/mesopores(S-MCSs)and different S content were successfully synthesized through a two-step strategy including a sol-gel process by using resorcinol-formaldehyde(RF)as a carbon source and tetraethoxysilane(TEOS)as an assistant pore-forming agent,and a subsequent heat-treatment with sulfur,and then the prepared samples were used as anode materials for SIBs.It was found that the sample sulfurated at 600℃ had the highest S content and exhibited excellent cycling performances and rate performances.A high reversible capacity of 443 mA h g-1 was obtained after 50 cycles at a current density of 50 mA g-1 and even at a high current density of 2.5 A g-1,a reversible capacity of 238 mAh g-1 was achieved.