Electrochemical Performance Research On Sn And Sn/C Intercalation Lithium Film Materials Prepared By Vacuum Sputtering

With the development of electric vehicles for decreasing environment pollution and portable electronic devices, there is an interest in developing new electrode materials with higher capacity, higher stability, higher safety and lower cost for lithium ion batteries. On the basis of reviewing the development of lithium ion battery and anode materials, this thesis selected tin-based materials as anode for lithium ion battery. Different types of Sn and Sn/C composite / multilayer films were prepared by vacuum sputtering on Cu foil. The composition, phase structure, electrochemical properties of films with different sputtering method and technology parameters are investigated by electrochemical methods in combination with X-Ray Diffraction (XRD), Scanning Electron Microscopy(SEM), Atomic Force Microscope (AFM), Inductively Coupled Plasma Spectroscopy(ICP). The new approach and work results to prepare a new type of tin-based films anode materials by vacuum sputtering.The influence of sputtering method on the micro structures and electrochemical properties of Sn thin films was investigated. The results showed that the discharge capacity of Sn electrode after 30 cycles by DC magnetron sputtering decreases to 98.9mAh/g, but the electrode by RF magnetron sputtering can keep 515mAh/g, the Sn electrode by RF magnetron sputtering shows better electrochemical properties.The influence of sputtering power on the deposition rates,microstructures and electrochemical properties of Sn thin films was studied. It has been found that the sputtering power and deposition rates exists approximately linear relationship; With increasing the sputtering power, the amorphous components of thin film decreased and the grains grow bigger, on 400W tin and copper diffusion generation of some alloys. For the sputtering power of 250W, Sn films optimum electrochemical performance: the frist cycle efficiency reached 70%, the reversible capacity retained 515mAh/g after 30 cycles.The influence of sputtering time on the microstructures and electrochemical properties of Sn thin films was studied. With increasing the sputtering time, the crystallization intensified. For the sputtering time of 15min, Sn films optimum electrochemical performance: the first cycle efficiency reached 69%, the reversible capacity retained 650mAh/g after 30 cycles. The influence of heat-treating on the microstructures and electrochemical properties of Sn thin films was investigated. Being annealed at 200℃of 8h, the Cu₆Snå’ŒCu₃Sn phases appearance, which will improve the binding energy between coating and the substrate and electrochemical properties.The different graphite content of Sn/C composite has been studied. With the increase of the graphite content, the Sn/C composite electrode of the first lithium intercalation capacity gradually reduced, the first cycle efficiency gradually increased and the first capacity loss declined.The micro-structure and electrochemical properties of Sn/C nano-multilayer has been studied. It has been found that the reversible capacity retained 250mAh/g after 30 cycles, form the second cycle, the charge and discharge efficiency is 95%, which can be ascribed to the mixable graphite provides a transmission path for lithium ion insertion. Moreover, the graphite films have an enforced function to tin body and decreased the breaking up of electrode.