The Research Of Silicon Monoxide Composite With Graphene Oxide As Anode Material For Lithium Ion Batteries

Lithium-ion batteries have a lot of advantages such as high energy density,long cycle life,no memory effect,which makes it have been widely used in portable electronic devices?such as mobile phones,dig ital cameras,camcorders,notebook computers,etc.?and power tools and other fields,and gradually to the electric bicycles.Among all the new anode materials,silicon has been drawing people's attention for its super-high theoretical capacity(4200 mAh·g^-1),thus silicon is considered to be the next generation of commercial anode materials,and the current commercial anode material is graphite with therotical capacity of 378 mAh·g^-1.However,the pulverization and failure phenomenon caused by the volume c hange always happen in silicon-based anode materials during charging and discharging process.The structure of amorphous SiO is homogeneous and consist of amorphous silicon cluters surrounded uniformly by SiO4 suboxide matrix.The init ial columbic efficiency of SiO is 50%⁵3% owing to the formation of the Li₂ O and Li₄SiO₄ in the first cycle.While the electron conductivity of pure SiO is 1.78*10-14 ?·cm-1,and this value means that SiO is a kind of insulator.Therefore,this paper will focus on the following aspects: the synthesis and electrochemical properties of SiO /grapheme oxide compound,the synthesis and electrochemical properties of mill-SiO /grapheme oxide compound in different ratio,and the doping of N i,B,and Li elements into mill-SiO/grapheme oxide compound.This paper stars from the morphology,composit ion,and electrochemical properties of raw material SiO with particle size of 20 ?m.The initial discharge capacity,charge capacity,in itia l effic iency of SiO is 1591 mAh·g^-1,798 mAh·g^-1 and only 50 %.After 50 electrochemical cycles,the capacity of SiO was maintained in 190 mAh·g^-1 with retained capacity rate of only 24%.Therefore,the fabrication of SiO /reduced grapheme oxide was taken into consideration to improve the electrochemical properties,but the results shown that SiO and SiO/reduced grapheme oxide can't be qualified anode materials used in lithium-ion batteries,because the layered lithiation-the failure of lithiated layer problem would appear repeatedly because of the large size of SiO.Thus,the SiO with 20 ?m was prepared by high-energy ball milling to decrease its size into 5³00 nm in order to solve the lithiation-the failure of lithiated layer problem fundamentally.After decreasing the size into nanoscale,the mill-SiO /reduced grapheme oxide compounds in different ratio was synthesized by hydrothermal reaction.Among all the mill-SiO /reduced graphene oxide compounds with different ratio,the compound in the ratio 6 had good properties: 1853 mAh·g^-1 of first discharging capacity,1 077 mAh·g^-1 of first charging capacity,58% of init ial columbic effic iency,743 mAh·g^-1 of capacity after 100 cycles,and capacity retention of 68.9%.In order to improve the initial efficiency of mill-SiO /reduced grapheme oxide compound in the ratio 6,N i,B,and Li elements were doped into the compound.All the experiment data shown that the best preparing condit ion was pyrolyzing the compound with doping elements under 500 °C in the tube furnace.compared to the SiO,SiO/reduced grapheme oxide compound,and milled SiO/ reduced grapheme oxide compound,the electrochemical properties of the doping compound has been increased significantly by 1636 mAh·g^-1 of first discharging capacity,1021 mAh·g^-1 of first charging capacity,62% of initia l colu mbic efficiency,720 mAh·g^-1 of capacity after 100 cycles,and capacity retention of 71%.