As one of promising candidates for achieving a higher capacity Li ion battery electrode, transition metal oxides can electrochemically react with lithium to form lithium oxide and reduced metal phases as a so-called conversion reaction. Despite its higher energy density and use of cheaper materials than conventional intercalation materials, conversion materials have been commercially limited by several factors, including its slow, diffusion-limited kinetics, poor cycling performance driven by substantial structural re-organization and corresponding large volume changes, and Coulombic inefficiency—especially in the first cycle. In addition, there are substantial deviations in redox potentials for conversion reactions in oxides with respect to the thermodynamically expected values (E_therm~ 2 V). It is obvious that the interfacial processes play a critical role in the overall conversion reaction which enlists charge/mass transport through a complex network of metal-rich and lithia-rich domains and consequent nucleation/growth.

To understand and control the reaction kinetics, we have studied nanoscale model electrodes that take advantage of a geometrically well-defined, simple and reproducible structure, which enables us to investigate more readily the correlation between electrochemical reactivity and electrode microstructure. Using epitaxial thin films, we explore the role of strain and initial metal oxide surface structure on the potential for lithiation. To control transport and phase-separation, we have also examined various nanoscale oxide structures including spheres, cylinders and lamellae structures. These electrodes are prepared by combining the rich phase-space of self-assembled block copolymers with sequential infiltration synthesis via atomic layer deposition. Traditional scanning probe methods are combined with both in situ x-ray diffraction and small angle scattering to investigate the controlled phase separation of a conversion reaction. These results provide deeper knowledge of the reaction kinetics and new perspective on the energy loss mechanisms in conversion reaction while helping develop strategies for improving the viability of conversion materials.