Effect of morphology and functionalization on the electrochemical properties of oxide anode materials for lithium-ion batteries

In the present thesis, potential anode materials for lithium-ion batteries are studied with respect to their physical and electrochemical properties. The focus is on the relationship between particle size, morphology, functionalization and electrochemical properties. In this context, the intercalation material Li${}_3$VO${}_4$, the conversion-based transition metal oxides MoO${}_2$, V${}_2$O${}_3$, CoFe${}_2$O${}_4$ and Mn${}_3$O${}_4$ as well as ZnO as a representative of the alloy-forming materials were investigated. The physical characterization of the pristine as well as electrochemically cycled materials was performed by X-ray diffraction, scanning electron microscopy and magnetization measurements. The electrochemical measurement methods used were cyclic voltammetry and galvanostatic cycling. In total, the presented results show, that the electrochemical properties of anode materials can be improved significantly by morphological modification and realising carbon composites. In the case of Li${}_3$VO${}_4$ and MoO${}_2$ smaller particles exhibit higher electrochemical activities. The pseudo-capacitive charge storage observed for hierarchically structured V${}_2$O${}_3$/C microspheres allows good performance even at high charge rates. In the case of the composites with hollow carbon spheres and nanotubes, the contributions of the transition metal oxides lead to higher specific capacities. Moreover, encapsulation of CoFe${}_2$O${}_4$ in carbon nanotubes proves to be a successful strategy to counteract the negative effects of conversion processes on cycling stability.