Study Of Carbon-based Composite As Anode Materials For Lithium-ion Battery

The hard carbon was coated with pitch pyrolitic carbon to improve firstcoulombic efficiency and reversible capacity in the thesis.In order to improve thefirst coulombic efficiency and reversible capacity of hard carbon,The pyrolyticprocess of pitch was researched and used to prepared the twice coated pitch/hardcarbon composite. Acetylene black was also researched to find the influence onfirst coulombic efficiency of hard carbon-based composite. At the same time,thepreparation method of graphene was also researched,to improve theelectrochemical performance,the si/graphene and si@c/graphene composite wasprepared by high-temperature method.The pitch pyrolitic carbon prepared by stytle2method showed the highestfirst coulombic efficiency of71.9%,which is hiher than the efficiency of hardcarbon（65.0%）; the pyrolitic carbon prepared by stytle4showed the highestreversible capacity,the first reversible capacity was251mAh·g^-1,after50cycle itwas dcreased to246mAh·g^-1with the capacity retention ratio of98%.then thepitch/hard carbon composite coated twice showed the high first coulombicefficiency of72.2%,high reversible capacity of252mAh·g^-1，and high capacityretention ratio of97.2%after30cycles.Silicon/hard carbon composite prepared by ball-milling showed perfectperformance while the mass ratio of silicon/hard carbon was1/8.the compositeshowed high first coulombic efficiency of72.3%and high reversible capacity of361mAh·g^-1,the reversible capacity remaining was240mAh·g^-1after50cyclesand the capacity retention ratio was66.5%,the influence on the first coulombicefficecy of acetylene black was also researched,it showed that the first irreversiblecoulombic efficiency contributed by acetylene black was about6.7%.Graphene was prepared by high temperature method,it showed goodelectrochemical performance and relatively thin sheets structure by SEM、TEMmeasurement and so on. It showed that the first reversible capacity was1157mAh·g^-1at charge&discharge current density of74.4mA·g^-1,and the capacitystill remaining was642mAh·g^-1after30cycles.while the charge&discharge currentdensity was as high as744mA·g^-1,it still exihibited perfect electrochemicalperformance,the first reversible capacity was581mAh·g^-1and still remained of537mAh·g^-1after10cycles.Nano silicon/graphene composite was pepared by high temperature method,the composite exhibited the first reversible capacity of998mAh·g^-1and410mAh·g^-1after50cycles; nano silicon@c/graphene composite was also prepared byhigh temperature method,the composite exihibited first reversible capacity of1337mAh·g^-1and420mAh·g^-1after50cycles.it showed enhanced electrochemicalperformance relative to nano silicon.