The Preparation And Lithium/sodium Storage Performance Of Hard Carbon From Heavy Organic Matters Of Coal

Comparing with the traditional graphite anode materials,hard carbons,with the larger layer spacing and random stacked microstructure,show a higher capacity,excellent rate and cycle performance in Lithium/Sodium ion batteries.Among the raw materials of hard carbon,the heavy organic matters in coal measures,with the advantages of wide source,low price,high carbon content and high reactivity,is a kind of high quality carbon precursor.In this paper,a process for preparing hard carbon anode materials from heavy organic compounds of coal liquefaction residues was developed.The effects of carbonization temperature on the composition and microstructure of hard carbon was investigated.Moreover the relationship between microstructure and electrochemical properties of hard carbon was also discussed.The main research contents and results are as follows:The hard carbon uses as anode materials for lithium-ion batteries was prepared with heavy organic compounds of coal liquefaction residues by a simple chemical crosslinking modification,solidification and carbonization.As the carbonization temperature raises,the H/C ratio of the hard carbon material increases,the interlayer spacing decreases,the graphite crystallites become larger and the corresponding initial coulombic efficiency improves gradually while the lithium storage capacity declines.Hard carbon obtained at 1100 ? delievers the best electrochemical performance: the first reversible lithium storage capacity is 360 mAh g-1 with a initial columbic efficiency of 76.5 % at 100 mA g-1;a reversible capacity of 260 mAh g-1 is still achieved at current density of 5 A g-1 after 1200 cycles with the capacity retention rate as high as about 95%.The storage properties of the prepared hard carbon in sodium ion batteries was also studied.As carbonization temperature increases,similar to the lithium case,the sodium storage capacity decreases gradually while the efficiency of the initial coulombic efficiency increases.The hard carbon obtained at 1100? exhibits the best electrochemical performance: the first reversible sodium storage capacity is 217 mAh g-1 and an initial columbic efficiency of 59.2% is achieved at 100 mA g-1.In view of the problem of poor circulation and rate performance of hard carbon in sodium ion batteries,a strategy of graphene coating modification was proposed.The experimental results show that the presence of graphene leads to a more abundant pore structure and improves the conductivity of hard carbon effectively.The electrochemical characterization results demonstrate that graphene/carbon composites(HCG)exhibits an excellent rate performance and cycle stability.The reversible sodium capacity of 5%-HCG-800 and HC-800,under current density of 100 mA g-1 and 5 Ag-1,is 205 mAh g-1,95 mAh g-1 and 192 mAh g-1,23 mAh g-1,respectively.The capacity retention rates of 5%-HCG-800 and HC-800,after 2000 cycles,is about 83.8 % and 24.2% at 2 A g-1,respectively.