Preparation And Lithium Storage Of Nanostructured Si And Ge Materials

Anode,as one of the key components for Li-ion batteries,greatly affects the electrochemical performances of batteries.Due to the low capacity of 372 mAh/g,the commercialized graphite anode limits the improvement of energy density for Li-ion batteries.Si and Ge with high theoretical specific capacities,are regraded as viable candidates for anode materials in place of graphite.However,Si and Ge suffer from large volume changes during the frequent insertion and extraction of Li-ion.The large volume changes cause extreme pulverization of the electrode materials as well as electrical disconnection,leading to a rapid capacity fading of electrode.Previously researches show that the nanostructured Si and Ge materials can present remarkable improvement of the cyclability and rate performance compared with the Si,Ge materials in the form of bulk.In this thesis,our work is aimed to prepare high-performance Si-based and Ge-based Li-ion battery anode materials.The electrochemical performance of Si and Ge anodes can be greatly improved via the preparation of the nanostructured current-collector and nanostructured active materials followed by the subsequent surface coating of organic materials.The work and results are as follows:1.The Cu nanowires were grown on the surface of Cu foam skeleton through galvanostatic-anodization followed by a H2 thermal reduction process.The as-fabricated Cu nanowires were uniformly anchored on the Cu foam framework,forming an ideal three-dimensional nanostructured current-collector.The Si and Ge were coated onto the Cu nanowires through the PECVD and electron beam evaporation,forming the nanostructured anode,respectively.And the obtained binder-free anodes showed outstanding electrochemical properties such as good cyclability and excellent rate performance.The as-obtained nanostructured Si anode exhibits high reversible capacity of 2003 mAh/g after 80 cycles at the current density of 2 A/g,and excellent rate ability such as high reversible capacity of 1470 mAh/g at a high current density of 10 A/g.The as-prepared nanostructured Ge anode exhibits a reversible capacity of 844 mAh/g after 200 cycles at a current density of 2 A/g and outstanding rate ability such as high reversible capacity of 758 mAh/g even at a high current density of 10 A/g.2.We have prepared the PEDOT-PSS coated nanostructured Ge anodes for lithium storage application.The nanostructured Ge anodes were fabricated by depositing Ge film onto the CuO nanorods array.Afterward,PEDOT-PSS was coated by spin-coating method.By limiting the voltage cut-off window,the CuO nanorods could irreversibly react with Li-ion only in the initial discharge progress and become a Cu/LiO mixture.Due to the good conductivity of the formed metallic Cu,the lithiated-CuO cores could act as the role of the current collector.The obtained binder-free electrodes show excellent cycle stability,which exhibits a reversible capacity of 640 mAh/g after 1000 cycles at a current density of 2 A/g.The excellent cyclability can be ascribed to the synergetic effect of the distinctive nanostructure and the surface PEDOT-PSS coating.Notably,the surface PEDOT-PSS coating can significantly facilitate the cycling stability of the electrode.