New Anode Materials For Lithium-ion Battery Research

With the looming exhaustion of traditional fuels and growing threaten of environment pollution, revolution in the energy area is not only necessary but urgent. The development and utilization of novel energy has gained more and more attentions. Rechargeable lithium ion battery is one of the most appealing types of all existing novel energy due to its high energy density, long calendar life, low pollution and so on,. It has been widely used in high-tech areas. Nowadays, graphite is the most popular anode material in commercial lithium batteries. To improve the performance of the battery, researchers has been devoted to fabricate and test new anode materials such as alloys, oxides, nitrides, phosphides and selenides.Pursuing high performance lithium storage materials is one of the primary directions in lithium battery development. Due to their particular dimension effect and large specific surface area, nano-materials are considered as next generation electrode materials for lithium ion batteries. This thesis will focus on the fabrication and investigation of a few nano-sized thin film materials fabricated by pulsed laser deposition (PLD) technology or radio frequency magnetron sputtering. Charge/discharge measurements and cyclic voltammograms were used to investigate cycle performance and electrochemical properties of the materials. X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED) and X-ray photoelectron spectroscopy (XPS) were employed to detect the composition and structure information of the materials in certain electrochemical states.Pulsed Laser Deposition (PLD) is a well-developed route to synthesis inorganic films. Comparing to the powder electrodes, thin film electrodes has their advantages such as no additives and binders. It can be considered an effective way to build an "ideal" system for gaining insights of the active materials. Here, WO3, InSe, Cr2O3-InP and Fe2O3-Se thin film electrodes have been successfully fabricated by PLD and radio frequency magnetron sputtering methods. Their electrochemical reaction mechanism with lithium was discussed.1. Fabrication and electrochemical properties of WO3 nanocomposite thin film. We fabricated the WO3 thin film by RF magnetron sputtering deposition. The reversible capacity was 626 mAh/g after 60 cycles. After characterizing the composition and structure of the thin film in first charge and discharge, we found that their initial discharge process is an irreversible reaction and produced nanosized Li2O and W. In the charge process, the nanosized metallic W plays an important role in enhancing the electrochemical activity of WO3 toward the formation/decomposition of Li2O.2. Fabrication and electrochemical properties of InSe thin film. We fabricated the InSe thin film by pulse laser deposition. The reversible capacity was 410mAh/g at a current density of 0.05mA/cm2. Composition and structure changed after the first discharge and charge processes. Metallic In and Li reacted with each other to produce InLi in the first discharge step. In the charge process, InLi discomposed to give metallic In and In drove the decomposition of Li2Se3. Fabrication and electrochemical properties of Cr2O3-InP nanocomposite thin film. Cr2O3-InP nanocomposite thin film was fabricated by pulse laser deposition for the first time. Electrochemical performance and reaction mechanism were investigated. For Cr2O3-InP, we found 568mAh/g. After characterizing the composition and structure of the thin film after discharging and charging, we found the metallic Cr, InLi and Li3P after the first discharging process. During the charging process, there was an interesting anion exchange mechanism and a new compound CrP was produced rather than Cr2O3.4. Fabrication and electrochemical properties of Fe2O3-Se nanocomposite thin film. Fe2O3-Se nanocomposite thin film was fabricated by pulse laser deposition. Electrochemical characterization showed a large irreversible capacity which could achieve 650mAh/g after 20 cycles. Electrochemical and structural characterization indicated that the charging and discharging of the thin film contained multi-step reactions. Metallic Fe, Li2O and Li2Se could be found after the first discharge. After charging, there were FeSe and Fe2O3, and the ratio is about 2.6. This is an interesting anion competition (Se and O) reaction mechanism which contributes to its larger capacity and better cycle performance than pure Fe2O3.The in-depth investigation of electrochemical properties on these nanosized thin films in this thesis is helpful to uncover electrochemical reaction essences of these materials. It has certain directive significance for developing new kinds of high performance lithium storage materials.