Electrochemical Performance Of Si/C Omposite Anode As Anode For Li-ion Battery

Lithium-ion battery is a kind of secondary batteries which has high specificcapacity, long cycle life and being reliable.With the growing concerns of global energy,environmental protection, it is urgent for the high-capacity chemical power sources.Aswell as the rapid development of mobile and portable computers, Lithium-ion batteryhas attracted much attention and become a hot spots.Silicon with high lithium insertioncapacity is considered as a promising material for anode.But silicon has volume changeduring the charge and discharge, it may reduce the cycling performance.To prepare Si/Ccomposite materials is a way that can improve the electrochemical performance.In this study, phenolic resin and starch are used as carbon source, nano-silicon asthe raw materials of silicon. Silicon/Carbon composite materials are prepared bypyrolysis and ball milling.The preparations and the electrochemical properties ofcomposite materials have also been studied.The Si/C composite materials is obtained with phenolic resin as carbon source.Carbonized temperature, proportion of phenolic resin and ball milling time have beenstudied.The best phenolic resin Si/C composite material we get is which carbonized at850℃, phenolic resin: Si=3:1(by mass) and2hours of ball milling. It obtains794mAh/g and538mAh/g at the first cycle with68%of efficiency. After20cycles, thespectfic capacity is282mAh/g. On the basis, we use starch as carbon source.Differentconditions of preparation have also been studied. Such as carbonized temperature,proportion of Si and graphite, ball milling time.The best performance of starch Si/Ccomposite materials we found is the one which marked as1-4#85010h.The anodematerial carbonizes at850℃,Si:grathite=1:4(by mass) and has been milled for10hours.The electrodes are prepared by mixing85wt.%active material,5wt.%conductivegraphite,5wt%CMC and5wt.%SBR. The starch Si/C composite material under theconditions have obtained971mAh/g charge capacity and604mAh/g discharge capacityat the first cycle. After20cycles, the retention is466mAh/g.We also find that the performance of composite materials would be improvedwhen increasing the amount of graphite and extending the time of ball milling. Graphitecan make conductivity of the semiconductor silicon better, and its flexibility can alsomitigate the volume effect of Si. Ball milling can reduce the size, make closer contactwith silicon, carbon and graphite. It is beneficial for achieving good cyclic performance, as well as the stability of composite materials.