Progress in and application prospects of advanced and cost-effective iron (Fe)-based cathode materials for sodium-ion batteries

Sodium-ion batteries (SIBs) have received extensive attention in recent years and are expected to become one of the alternatives to lithium-ion batteries (LIBs). Among the various cathode materials for SIBs, iron-based materials have become the most suitable ones for grid-scale energy storage-conversion systems due to the rich natural abundance of sodium, low cost, high safety, and non-toxicity. To date, many studies have been conducted on iron-based cathode materials, and some progress has been made. To facilitate further research and development of such types of iron-based SIB cathode materials toward practical applications, we have prepared this comprehensive review to better understand the properties of various iron-based cathode materials and further improve their electrochemical performance. In this paper, the research progress in iron-based cathode materials for SIBs, including oxides, polyanionic compounds, Prussian blue compounds, and Na-free cathode materials, is systematically summarized in terms of their synthesis, characterization, functional mechanisms, and performance validation/optimization. Several technical challenges are analyzed with the proposed strategies for overcoming the challenges toward practical applications of iron-based cathode materials in SIBs.