A comprehensive review on double-redox reaction towards high-performance polyanionic sodium-ion batteries
Polyanionic cathode materials are widely considered as potential cathode materials for sodium-ion batteries due to their strong three-dimensional framework and intrinsic thermal safety. Nevertheless, the limitation of the specific capacity and energy density hindered their application, which can be ascribed to the common reliance of single-electron redox reaction of the transition metal. By realizing the reversible double redox reaction of vanadium-based and manganese-based polyanion cathodes, researchers have successfully opened up a new way to break through the long-term performance limitations. Recent studies disclose that vanadium and manganese-based polyanionic cathodes exhibit the possibility of realizing a reversible double-redox reaction, which opened up new avenues to overcome the capacity dilemma. However, many fundamental issues remain unclear, including insufficient structural stability at high operating voltages, irreversible structural evolution induced by sodium extraction, sluggish electronic and ionic transport kinetics, and Jahn–Teller distortion. Therefore, it is imperative to summarize recent work in order to clarify the pathway for future investigation. In this review, the key challenges associated with the activation of the double-redox reaction are outlined, followed by the realization and regulation of the double-redox reaction in polyanionic cathode materials. A systematic summary of recent studies is performed for both vanadium and manganese-based compounds, which could contribute to the fundamental understanding of the double-redox reaction mechanism. Combined with the modification strategy and future perspective, this review provides insights into the rational design of polyanionic cathodes with a reversible double-redox reaction. It also offers insights into the development of high-energy-density cathode materials for next-generation sodium-ion batteries.