<i>In Situ</i> Engineering of a Multifunctional Cathode–Electrolyte Interphase for Advanced Sodium-Ion Batteries

Layered transition metal oxides have been considered promising cathode candidates for sodium-ion batteries due to their exceptional specific capacity and tunable composition. Nevertheless, their commercialization faces critical challenges, including irreversible phase transitions, hygroscopic degradation, and thermal runaway risks. To address these limitations, we propose a strategy for the in situ construction of an artificial cathode–electrolyte interphase (CEI) layer, which facilitates rapid Na+ diffusion kinetics and suppresses detrimental interfacial side reactions. The modified Na2/3Ni1/3Mn2/3O2 electrode delivers a remarkable reversible capacity of 150 mAh g–1 at 0.1 C while maintaining 84% capacity retention over 200 cycles at 1 C (vs 67% for pristine). Notably, the CEI-modified cathode exhibits significant air tolerance, retaining 96% of initial capacity after 7-day ambient exposure. Furthermore, thermal analysis confirms enhanced thermal stability of the battery, effectively mitigating safety concerns. The work establishes a universal paradigm for stabilizing electrode materials, providing critical insights for developing robust sodium-ion battery systems.