Assessment and progress of polyanionic cathodes in aqueous sodium batteries

Abstract

Aqueous sodium-ion batteries are expected to be competitive technologies for large-scale energy storage applications due to the extraordinary sodium abundance, low manufacturing cost and high safety. However, only a few materials have been reported for the positive electrode and there is an urgent need to develop new, practical host materials with satisfactory performance. Polyanionic compounds [e.g., Na₃V₂(PO₄)₃] have shown promising performance as positive electrode materials in non-aqueous electrolyte-based sodium-ion batteries, yet they possess limitations in aqueous systems. Herein we provide an assessment of the materials along with the latest ground-breaking advances of polyanion-type compounds as potential positive electrode materials for aqueous sodium-ion batteries. Particular emphasis is placed on the electrolyte regulation and cell design to address the compatibility issues from the technical and scientific point of view, which would make aqueous sodium batteries advantageous over non-aqueous systems. Lastly, we provide an outlook on the challenges and research directions to incorporate polyanionic compounds in the development of high energy aqueous batteries for grid-scale applications.