Lithium Ion Materials for Energy Applications: Structural Properties from Neutron Diffraction

Cathode materials and solid electrolytes to be used in lithium batteries require a high ionic mobility of Li+ species in their crystal structures. This in turn depends on the order–disorder state of lithium and on its bonding environment. Neutron diffraction is the choice technique to study the structural features of polycrystalline lithium materials that control their performance in ion transport processes. The basic principles of ionic mobility in solids and of the Rietveld refinement methods for neutron diffraction data are briefly reviewed. Then two important families of lithium conductors are selected from the literature and thoroughly discussed: the LLTO perovskite-type LiLa2/3--/3TiO3 system and the Li1+Me2(PO4)3 Nasicon phases. Accurate neutron diffraction determinations of the corresponding crystal structures have been shown to provide a considerable insight into the mechanisms of Li+ ion transfer in such materials.