Cathodes for Sodium-Ion Batteries

Abstract

Advances in lithium-ion battery (LIBs) technology have improved living conditions around the globe. However, there are increasing concerns regarding the sustainability and criticality of materials (lithium and cobalt) for LIBs. Considering sodium's superiority in cost and abundance, the development of electrode materials for sodium-ion batteries (NIBs) has been intensively revisited. Limited types of structures are suitable for intercalation sodium ions due to their preferential sixfold coordination. Layered transition metal oxides and polyanion compounds can hold sodium cations in six-coordinated geometry. Additionally, Prussian Blue analogs (PBAs) with open interstitial sites exhibit Na-ion insertion properties. Sodium layered metal oxides demonstrate advantages such as high capacities and low price, but also exhibit problems like low operating voltage or structural instability upon multiple phase transitions during charge–discharge cycles. Polyanion-type compounds exhibit 3D structures with open channels that facilitate the diffusion of alkali metal ions. Moreover, the highly stable frameworks for reversible Na-ion insertion assure a good cyclability. PBAs possess two metal centers coordinated by cyano-groups. Tailoring the metal centers in this three-dimensional framework provides a tool to vary the redox potential of the compound and the size of the interstitial cavities. These three classes of compounds will be described in this chapter considering their composition, structure, electrochemical performance, sustainability, and cost.