Physical characterization of tin composite oxides and related anode materials for lithium ion batteries

Abstract

This thesis addresses the issues concerning the excellent electrochemical performance exhibited by the tin-composite-oxide glass. Sn1.0Al0.42B0.56P0.40O3.6 as an anode material for rechargeable lithium ion batteries. The debate surrounding this material focuses on the nature of the lithium-tin interaction: whether it is ionic or intermetallic. The TCO anode material has been studied electrochemically, as well as by multinuclear Solid-State-NMR. X-ray Absorption Spectroscopy, and X-ray Scattering including Pair Distribution Function analysis. By examining electrode materials at various stages of discharge, corresponding to various levels of lithium insertion, the interactions between lithium, tin, oxygen, and the other components of the glass have been ascertained. The inserted lithium remains highly ionic throughout the first cycle of the cell, with no evidence for the formation of alloy phases. Extended cycling of the cell results in the formation of alloy-like domains in the parent materials. SnO, but not in the case of TCO. This demonstrates that the required structural rearrangements for the formation of Li-Sn phases are kinetically prohibited: and this to a greater extend in TCO than in SnO. Two key factors account for the electrochemical properties of TCO: 1) the participation of the glass framework in sequestering the electrochemically active tin centers and providing a flexible framework for the reversible insertion of lithium 2) the proximity of oxygen to tin is maintained throughout lithium insertion process, thus oxygen may act as a charge carrier. These factors are developed in the context of several models for the interactions in the electrode, drawing on the data obtained from the physical characterizations implemented here. A comparative study of the anode material NaMoO3 is also described.