Investigation of transition metal oxide thin film cathodes for Li-ion battery applications

Li-ion batteries have become a wide-spread energy storage source for portable electronic devices such as cell phones, laptops and implantable medical devices. Hence the demand for lightweight devices with long life and high energy density has increased over the years. One approach for responding to this demand is thin film batteries. Discovery of new and improved cathode materials for energy storage, can improve the overall performance of Li-ion batteries. This study investigates transition metal oxides as cathode (positive electrode) materials for Li-ion battery applications. Two main approaches for fabricating thin film cathodes were used in this doctoral research. First, glancing angle sputter deposition (GLAD) was used in comparison to conventional rf magnetron sputtering to fabricate nanostructured LiMn2O4 and LiCoO2 thin film cathodes. The morphology, crystal structure and electrochemical response of the fabricated thin film cathodes were studied via scanning electron microscopy, X-ray diffraction, and cyclic voltammetry and galvanostatic measurements. In the second part of this work, NMC materials libraries were fabricated via the combinatorial synthesis and characterized using high-throughput XRD and EDX. A new high-throughput method, called the E-D-R approach, for full compositional mapping (including Li content) in thin films was introduced. The obtained compositional data was correlated with the structural data from high-throughput X-ray diffraction measurements; those compositions which show a layered (R3¯m) structure and are therefore most interesting for Li-battery applications (for cathode (positive) electrodes) were rapidly identified.