The growing desire for large-scale stationary electrical power storage is driving research interest into Na-ion batteries, due to the greater abundance and lower cost of Na versus Li. This article focuses on advances achieved in the development of positive electrode (cathode) materials for such batteries. As for Li-ion batteries, layered transition metal oxide systems have traditionally dominated the research in this area, although following the development of LiFePO₄ for Li-ion batteries, there has been considerable interest in Na transition metal phosphate/sulfate/silicate systems among other materials.