Silicon-based Composite As Anode Materials For Lithium Ion Batteries

Nowadays, traditional resources of fossil energies are becoming increasinglyscarce and accompanied with the environmental pollution crisis, which makesustainable development object face significant challenges. Therefore, more and moreresearchers are devoted to the development of new green energy. Since thebreakthrough in early1990s, lithium ion batteries have been widely used in differentfileds, which play important roles in people’s daily life. It is meaningful to developlithium ion batteries with properties of high specific capacity, excellent cyclability,low cost and environmental emissions. Currently, the capacity of carbon materials isdifficult to improve due to the limitations of its low theoretical capacity as the anodematerial of lithium ion batteries. To find new kinds of anode materials with highperformance seems necessary, among which silicon is considered as one of the mostpotential anode material. However, what we can not neglect is the large volumeexpansion of silicon during the charge-discharge process which results in the poorcycle performance. In this thesis, two kinds of silicon based composite materials arereported to improve electrochemical properties of silicon for the exploration of itsapplication prospects in the energy storage. The main contents are as follows:Single-crystalline silicon nanowires were prepared via metal-assisted chemicaletching method, and the preliminary characterized results were proved to behomogeneous silicon nanowires. Then, the C/Si composite was prepared by amodified soft-template method with following annealing process. The crystalstructures and morphologies and microstructures were characterized by XRD、Raman、SEM、TEM, respectively. The electrochemical performance of initialreversible capacity and cyclic stability for the composite were superior than puresilicon nanowires, which show a reversible capacity of529.3mAh/g even after100cycles. The excellent performance of the C/Si composite was due to the improvementof the electronic conductivity from carbon matrix and the ability to buffer largevolume expansion with the framework of carbon.TiO2/Si composite was fabricated via a a modified sol-gel method withfollowing heat-treatment process. The morphology and microstructure of thecomposite were characterized and the results reveal that the composite ishomogeneous in which the silicon nanoparticles are covered by TiO2. Moreover, theelectrochemical properties of the composite show excellent cyclic stability and rate capability compared with pristine silicon nanoparticles. The excellent performance isattributed to the outer coating layers and interconnected TiO2and silicon networks,which can accommodate large volume expansion and result in the improvement ofcyclic stability during charge-discharge process.