Developments and prospects of conversion reaction-based anode materials in sodium-ion batteries

Recent advances in renewable energy and energy-storage technologies have increased the demand for high-performance, cost-effective, and sustainable electrochemical energy-conversion and storage systems. Sodium-ion batteries (SIBs), which leverage abundant and widely distributed sodium resources, are emerging as promising low-cost alternatives to lithium-ion batteries. Within SIB anodes, conversion-type materials-including metal sulfides, oxides, and phosphides-offer much higher theoretical capacities than intercalation-type materials, primarily because they undergo multi-electron transfer reactions. Nevertheless, their practical implementation is impeded by several critical challenges, such as large volumetric changes, low electronic and ionic conductivity, and unstable electrode-electrolyte interfaces; these issues result in poor cycle life and degraded rate capability. This review systematically summarizes recent research progress on various conversion-type anode materials, elucidates their reaction mechanisms, and analyzes the principal bottlenecks that hinder practical deployment. We discuss key optimization strategies in detail-including nanostructuring, surface/interface engineering, compositing with conductive matrices, and the combination of advanced characterization techniques with theoretical modeling. By providing a comprehensive overview and critical perspectives, this work aims to guide future fundamental and applied research and engineering efforts, thereby advancing the development of practical, high-energy-density, long-lived SIBs.