Engineering Anionic Aggregation in Dilute Electrolyte for High Performance Layered Oxide Cathodes for Sodium‐Ion Batteries

Abstract Sodium‐ion batteries (SIBs) have garnered increasing attention due to their distinctive advantages. However, they still confront a series of technical challenges, particularly in cycle stability and energy density. Notably, layered oxide cathode materials experience irreversible structural changes during electrochemical processes, which significantly hinders SIBs from achieving their theoretical metrics. Here, we developed a dilute 0.5 M high‐entropy electrolyte. Remarkably, despite its low salt concentration, this electrolyte features an anion‐rich solvation sheath and forms distinctive “clusters”, facilitating the creation of an inorganic‐rich and dense cathode electrolyte interphase (CEI). This CEI layer effectively passivates the electrode and prevents solvent co‐intercalation. Importantly, the high‐entropy dilute electrolyte enables the layered oxide cathode NaNi 1/3 Mn 1/3 Fe 1/3 O 2 (NaNMF) to maintain an excellent capacity retention of 90% after 250 cycles and exhibits remarkable electrochemical performance at both high and low temperatures. The innovative structural design of anionic aggregates in dilute high‐entropy electrolytes represents a pivotal advancement, offering substantial promise for the development of cost‐effective and high‐energy‐density SIBs in the future.