The relationship between microstructure and electrochemical performance was investigated in sputter-deposited V2O5 thin-film cathodes. As-deposited and heat-treated films in unlithiated and lithiated states were studied by transmission electron microscopy, X-ray diffraction, and secondary ion mass spectroscopy. Film properties including orientation, grain size, and morphology were found to be strongly dependent on the heating rate during annealing. Large enhancements in the capacity-rate performance of coarser grained over nanocrystalline grained films were observed, contrary to expectations. Potential transient methods were used to investigate the mass-transport differences between these two distinct microstructures. Slow transport phenomena during phase transformation and interfacial impedances linked to differences in grain orientation and/or grain boundary content are proposed to explain the observed performance. (c) 2006 The Electrochemical Society.