Ion insertion into electrode materials can be used to store energy in battery applications. In this thesis, photoelectron spectroscopic and x-ray absorption spectroscopic methods have been used to study the change of the electronic structure of host materials during electrochemical ion insertion.
Specifically, the properties of ion insertion into nanoporous TiO2 were studied. It is demonstrated that the insertion of Li ions results in a reduction of the Ti4+ sites in TiO2 to Ti3+ sites close to the inserted Li ion. The intensity of the Ti3+ is directly correlated to the number of inserted electrons. It is also shown that the two phases resulting from moderate insertion can be detected by studying the electronic structure of inserted Li ions and the behavior observed can be correlated with electrochemical measurements.
Insertion of ions into tungsten oxides is a potential candidate for smart window and display applications. Ion insertion into these materials was, also studied with electron spectroscopic methods. The insertion of H+ reduces W6+ to W5+ and further insertion results in a reduction to W4+. Cyclic voltammerty shows two reduction peaks where the first peak implies reduction of W6+ to W5+ and the second peak can be associated with further reduction to W4+.
During the first charge/discharge cycles of a battery based on graphite anodes a solid electrolyte interface layer is formed on the electrode surface. This layer consumes some of the charge carrying Li ions, hence decreases the capacity of the battery. A careful characterization of this layer has been performed to aid in the further development of this type of battery.