Lithium vanado-phosphate glasses: Structure and dynamics properties studied by molecular dynamics simulations

Lithium vanado-phosphate glasses have been designated as possible cathode material for the next generation of solid state batteries, due to their high conductivity and mixed electronic-ionic conducting behaviours, which derive from the small polaron hopping between the vanadium ions with different valence state and the lithium ion diffusion. Therefore, the understanding of the behaviour of these glasses at the atomistic level can be an important aspect in designing compositions for these applications. To reach this goal, the structure and lithium ion diffusion behaviour in lithium vanado-phosphate glasses with mixed V4 + and V5 + ions were studied using molecular dynamics simulations. The results show that vanadium oxide generally plays an intermediate role in glass structure while there are subtle details depending on its concentration and oxidation states. The phosphorus network is depolymerized by the content of vanadium oxide, but phosphorus ions always contribute to the glass network, interposing to vanadium polyhedra. The V4 +OV5 + linkages, responsible for the polaron hopping mechanism, show a linear dependence to the V2O5/P2O5 ratio, which highlights a strong role of the interaction between the former ions. The lithium ion diffusion was studied by mean square displacement calculations and it was found that the self-diffusion coefficient just depends on the Li content.