Overview of Research Progress and Development of Cathode Materials for Aqueous Na‐Ion Batteries

ABSTRACT Aqueous sodium‐ion batteries (ASIBs) have now been viewed as the promising energy storage technique for the grid application due to their intrinsic safety and cost‐effectiveness. However, their energy density and cycling stability are still unsatisfactory accompanied by the narrow electrochemical stability window of water and parasitic side reactions at electrode–electrolyte interfaces. The cathode material is a decisive factor in battery design, as it directly governs both the reversible capacity and structural integrity of ASIBs. This review systematically surveys the cathode materials developed for ASIBs, covering two major classes: transition metal oxides and polyanionic compounds. For transition metal oxides, we highlight compositional engineering strategies that could stabilize the host structure upon cycling. For polyanionic compounds, the “inductive effect” is discussed as a key principle that elevates operating voltages while enhancing structural rigidity. The representative modification approaches including carbon coating, nanostructuring, and cation substitution are critically evaluated for many typical compounds. By consolidating structure–property relationships and sodium storage mechanisms across these material families, this review provides rational design guidelines to inspire the development of high‐performance, durable, and sustainable ASIB cathodes for grid‐scale energy storage.