Current progress of Na4Fe3(PO4)2(P2O7): Key issues, modifications, and perspectives

Abstract

The sodium-ion battery (SIB) cathode material, Na₄Fe₃(PO₄)₂(P₂O₇) (NFPP), has become a focal material in both academia and industry due to its low cost, long lifespan, and high safety. In the recent three years, substantial efforts have been devoted to promoting the practical applications of NFPP by optimizing its electrochemical performance and disclosing the reaction mechanisms. Various modification strategies and their effect mechanisms have been explored, and the performance evaluation of NFPP has progressively advanced from laboratory-scale coin cells to practical pouch cell configurations. Nevertheless, there remains a lack of systematic reviews comprehensively assessing the developmental status and application readiness of NFPP. This review critically examines NFPP’s fundamental structural characteristics and proposes four key development issues. Then, the latest research advances are introduced with explicit differentiation of design strategies and their mechanistic impacts. Notably, we provide a dedicated discussion on NFPP’s current pouch cell performance metrics, while highlighting two critical yet underexplored research directions (enhancing air stability and improving tap density) for commercial viability.