Recent progress and prospects of NASICON framework electrodes for Na-ion batteries

Sodium-ion batteries (SIBs) have emerged as the most promising energy storage devices for large-scale grid and electric vehicle applications. This is because of the natural abundance, high availability, and cheap resources of Na. Since the electrochemical performance of the battery is heavily dependent on the capacity, storage reversibility and structural stability of the cathode, various materials have been explored for SIB cathode. Among them, NASICON-framework oxides have shown immense potential owing to the 3D open-framework structure, which remains stable upon the extraction/insertion of large sodium ions. Besides, the [PO4]3- units introduce a strong inductive effect, resulting in higher redox potential compared to other layered oxides. Nevertheless, the poor electronic and ionic conductivities are the major drawbacks of these materials. Various compositions are reported, and several advanced processing methods are employed to overcome these challenges. This review discusses the experimental and theoretical studies performed to establish the storage mechanism and sodium diffusion pathways inside the NASICON-structured oxides. Particular emphasis has been given to the multiple strategies used to understand the correlations between the structure, chemistry, processing, and underlying mechanism in these electrodes, which eventually affect the energy density and cycling performance of batteries. Moreover, this article also reviews the work done in evaluating the performance of full sodium-ion battery cells utilizing NASICON-structured cathode and other materials as an anode.