Study Of Si/C And Ge/C Composites Based Anodes For Lithium-ion Batteries

Lithium-ion batteries（LIBs）are widely applied in portable electronic devices and electric vehicles due to their high energy storage density,long cycle life,pollution-free to environment,and so on.One of the key LIBs technologies is to develop new anode materials with higher specific capacity.Silicon is the most promising anode materials for LIBs because of its abundant reserves and its theroretical capacity ten times higher than that of commercial graphite.However,the volume expansion and pulverization problem during charge/discharge processes limit its commercialization process.Currently,the main strategies of improving the performance of Si anode materials are the structure designs towards nanoscale,porosity and composite with other materials.In this dissertation,several Si/C and Ge/C composites have been prepared by physical sputtering deposition,and their physical properties and electrochemical performances have been investigated.These researches show great referential significance in improving the cycling performance of Si,Ge-based LIBs.The research contents are as follows:1.Pure Si and Si/C film anodes were prepared by magnetron sputtering deposition under room temperature（RT）and the performances as anodes for LIBs were investigated.The comparison of pure silicon anodes with different thicknesses implies that the thinner pure silicon anode with 100 nm possesses better electrochemical performance.Seven layers Si/C alternate-layered structure possesses faster activation rate,which could be ascribed to the insert of carbon films.2.The C/Si/C/Si/C（10 nm/50 nm/10 nm/50 nm/10 nm）structure anode grown at RT performs an excellent cyclic performance that 88.45%capacity was maintained after145 cycles.It is believed that the carbon films mainly act as coats and conductive agents,which promote its cyclic performance.Moreover,the same structure anodes grown at high temperature perform a higher specific capacity,in which the highest one of the anodes was grown at 100 ^oC.So that 100 ^oC is denoted as the best activation temperature for Si/C anodes.3.It has very important significances to investigate the morphological evolution of graphene-based Ge QDs in the development of anodes for LIBs.The evolution of graphene-based Ge QDs was studied by control the amounts of Ge deposition under 500^oC.The results of surface topographies and statistics indicate that Ge QDs have good uniform distribution and high density(3.52×10¹⁰/cm²)with deposition of 300 s,and the heights and bottom diameters are 1.0².0 nm and 30⁴0 nm,respectively.The Raman spectra reveal that with the increase of deposition amount,the crystallinity of Ge QDs turns better,and Ge-induced defects are reduced.X-ray photoelectron spectroscopy（XPS）indicates that the surfaces of Ge QDs have suffered severe oxidation.The existence of Ge-C bonds also proves the interaction of Ge and C atoms.