Predicting stable lithium iron oxysulphides for battery cathodes

Cathode materials that have high specific energies and low manufacturing costs are vital for the scaling up of lithium-ion batteries (LIBs) as energy storage solutions. We perform an extensive computational search for iron-based oxysulphides using ab initio random structure searching (AIRSS). Several new oxysulphide phases have been discovered which are predicted to be less than 50 meV/atom from the convex hull. Among the predicted phases, two anti-Ruddlesden-Popper structured materials Li2Fe2S2O and Li4Fe3S3O2 have been found to be attractive as they have high theoretical capacities. With band gaps as low as about 2.0 eV, they are expected to exhibit good electronic conductivities. Climbing-image NEB calculations show that the Li-ion transport in these materials has low activation barriers between 0.3 eV and 0.5 eV. The richness of new materials in the Li-Fe-S-O phase field illustrate the great opportunity in these mixed anion systems for energy storage applications and beyond.