Investigations of lithium insertion into transition metal oxide cathodes

Abstract

To the pursuit of powerful lithium ion battery for integration into future automobiles and various advanced applications, new generation cathode with good storage ability and sustainability is intensively studied and explored. Transition metal oxides with ordered rocksalt structure are one the mostly investigated candidates, which are able to insert/extract lithium ions with good structural tolerance for low power applications. However, the practicality of ordered rocksalt-based materials for high power applications are still restrained several intrinsic issues. Therefore, advancement in current lithium ion batteries technology are demanded to fulfill the application requirements. In this thesis, preparation of several lithium transition metal oxides with rocksalt structure by different synthesis methods is presented. Their electrochemical properties as lithium ion battery cathode are discussed. This thesis aims to address the core issues related to ordered rocksalt-based materials from two perspectives, i.e. applicability of nanomaterials in improving the battery performance and comprehensive studies on the effect of cation substitution on the electrochemical characteristics. Another aim is to extend the investigation into feasibility of disordered-rocksalt based material to be applied as lithium ion battery cathode, which includes detailed studies on the effect of cation ordering on the electrochemical properties. Based on the results of systematic experiments in ordered-rocksalt based material (lithium trivanadate, Li1.2V3O8) with different morphology, the electrochemical performance of rocksalt-based cathodes is highly dependent on the particle size and morphology of intercalation host. Optimum cation substitution on ordered rocksalt-based Li1.2V3O8 demonstrates the possibility to circumvent the structural instability issues and further enhance lithium storage capabilities, indicating their promising potential to replace conventional LiCoO2 cathode. The study is then extended to exploration of lithium intercalation into partially disordered rocksalt-based Li2NiTiO4. To deepen the understanding of lithium insertion mechanism in correlation with structural properties, detailed characterizations on cycled electrodes are conducted.