Synergistic Role of Transition Metals and Polyanionic Frameworks in Phosphate-Based Cathode Materials for Sodium-Ion Batteries

Abstract: Ongoing research in the area of advanced cathode materials for sodium-ion batteries (SIBs) is expected to reduce reliance on lithium-ion batteries (LIBs), providing more affordable and sustainable energy storage solutions. Polyanionic compounds have emerged as promising options due to their stable structure and ability to withstand high-voltage conditions as well as fast charging capabilities. This review offers a thorough discussion of phosphate-based polyanionic cathodes for SIBs, exploring their structure, electrochemical performance with various transition metals, and existing challenges. We discuss different polyanionic frameworks, such as ortho-phosphates, fluoro-phosphates, pyro-phosphates, mix pyro-phosphates, and NASICON-based phosphates, highlighting their unique structural characteristics and ability to perform well across a wide potential range. Further, we delve into the mechanisms governing sodium storage and tunability of redox potentials in polyanionic materials, providing insights into the factors that affect their electrochemical performance. Finally, we outline future research directions and potential avenues for the practical applications of polyanionic high-voltage cathodes in sodium-ion battery technologies.