Conversion-Based Cathode Materials for Rechargeable Sodium Batteries

Conversion-based electrode materials for rechargeable sodium batteries (RSBs) have received considerable attention because of their potentially higher energy densities than those of conventional intercalation-based electrode materials. This would overcome generally lower energy densities of RSBs than those of lithium-ion batteries. However, they often suffer from large volume changes, sluggish Na-ion kinetics, and large overpotential in their reaction. Intensive research has thus focused on improving the electrochemical performance through a number of approaches, including analyses of the reaction mechanisms during charge/discharge, engineering the electrode materials in terms of their nanostructuring or compositing, and searching for new candidate materials. This review presents an overview of the approaches used to explore conversion electrode materials for RSBs, in particular focusing on those with relative high redox potential that could be possibly used as cathodes, followed by a discussion of the challenges and perspectives involving future research directions for these materials.