Preparation And Electrochemical Properties Of New And Highly Efficient Composites For Lithium Ion Batteries

Recently,lithium-ion batteries have attracted much attention due to the rapid development of portable electronic devices,electric vehicles?EVs?,and hybrid electric vehicles?HEVs?.At present,most commonly used anode materials for commercial LIBs are based on graphite and other carbon materials.However,these materials possess low specific capacity?372 m A h g-1?and poor rate capability.Therefore,the design and synthesis of new anode materials are necessary to offer the promise of high performance lithium-ion batteries with higher efficiency,greater energy density and longer cycle life to meet various energy storage demands for transportations.In this article,silica-based and Fe₂O₃-based materials were chosen as research subjects to improve the specific capacity,cycling stability and rate performance for LIBs.The research contents of this paper are as follows:1?The Si@C composites were prepared by a simple coating method with Si nanoparticles as the cores.This synthesis involved the coating of a poly-dopamine layer by one step-assembly approach,and this poly-dopamine layer was carbonized at high temperature.The electrochemical properties of the electrode material were studied by assembling button cell.The results show that the Si@C composites prepared has an obvious core-shell structure.This Si@C composites electrode exhibits superior specific capacity and cycle performance then Si anode.The reversible capacity is 956.3 m Ah/g in the first cycle,and could remain 61.34% capacity after 20 cycles.2?The Si@void@C composites were also prepared by a simple coating method with Si nanoparticles as the cores.This synthesis involved the coating of a Si O₂ layer through self-assembly approach with TEOS,and the coating of a carbon layer through in-situ polymerization approach with dopamine and carbonized at high temperature,and then the etching of Si O₂ on the surface of the Si with HF.The electrochemical properties of the electrode material were studied by assembling button cell.The results show that the Si@void@C composites exist a void space between Si and C shell about thickness of 15 nm.This Si@void@C composites electrode exhibits superior specific capacity and cycle performance then Si and Si@C anode.The reversible capacity is 2336.59 m Ah/g in the first cycle,and could remain 75.5% capacity after 20 cycles.3?The Fe₂O₃ fibers were synthesized by the electrospinning technique assisted with anneal treatment.The PVP/ FeCl₃ solution was used as precursor which was electrospun into PVP/ FeCl₃ fibers and then obtained Fe₂O₃ fibers through anneal treatment.The electrochemical properties of the electrode material were studied by assembling button cell.The results show that the Fe₂O₃ fibers of the smallest diameter exhibits superior specific capacity and cycle performance than Fe₂O₃ particles anode.A high reversible capacity of 827.3 m Ah/g at a current density of 0.1 A/g and an excellent cyclic stability over 70 cycles at 2 A/g are shown by the Fe₂O₃ fibers.4?The Fe₂O₃/rGO composites were successfully synthesized by combining Fe₂O₃ fibers and rGO,which were also prepared by a modified Hummers method and far infrared reduction technique.The electrochemical properties of the electrode material were studied by assembling button cell.The results show that the Fe₂O₃/rGO composites have an obvious rod-shell structure,and exhibits superior specific capacity and cycle performance than Fe₂O₃ fibers anode.A high reversible capacity of 1180.69 m Ah/g at a current density of 0.1 A/g and an excellent cyclic stability over 1000 cycles at 5 A/g were shown by the Fe₂O₃/rGO composites electrode.