Controllable Configuration of Constitutional Units in Vanadium/Iron-Based Polyanionic Compounds for Sodium-Ion Storage.

Sodium-ion batteries (SIBs) are considered one of the most promising next-generation energy storage solutions. Among various electrode materials, vanadium/iron-based polyanionic compounds show significant potential as SIB cathodes due to their stable structures and high operating voltages, yet challenges persist in electron/Na transport and energy density. Although doping is an effective solution, the structure-activity relationship between dopant-induced configuration of octahedral/tetrahedral units and electrochemical performance remains poorly understood. Herein, the effects of composition and connection type of octahedral and tetrahedral constitutional units on Na-storage properties are systematically re-evaluated. By establishing descriptors and systematic analysis, the regulatory roles of octahedral/tetrahedral units are elucidated, establishing a fresh research perspective to describe the intrinsic impact of doping types on the structure-activity relationship. Additionally, other modification strategies are discussed to complement the research on the constitutional unit. In industrial applications, balancing electrochemical performance with air stability, cost, and large-scale production remains challenging, creating novel configuration compositions, controlling the structural arrangement of constitutional units, combined with interface and microstructural adjustments, are proposed to achieve multiscale modifications. Simultaneously, theoretical simulations will be employed to predict/validate their efficacy, providing insights for the rational design of high-performance and low-cost polyanionic compounds for sustainable SIBs.