Tuning the Solvation Structure in Water‐Based Solution Enables Surface Reconstruction of Layered Oxide Cathodes toward Long Lifespan Sodium‐Ion Batteries

Abstract Layered oxides of sodium‐ion batteries suffer from severe side reactions on the electrode/electrolyte interface, leading to fast capacity degradation. Although surface reconstruction strategies are widely used to solve the above issues, the utilization of the low‐cost wet chemical method is extremely challenging for moisture‐sensitive Na‐based oxide materials. Here, the solvation tuning strategy is proposed to overcome the deterioration of NaNi 1/3 Mn 1/3 Fe 1/3 O 2 in water‐based solution and conduct the surface reconstruction. When capturing the water molecules by the solvation structure of cations, here is Li + , the structural collapse and degradation of layered oxides in water‐based solvents are greatly mitigated. Furthermore, Li(H 2 O) 3 EA + promotes the profitable Li + /Na + exchange to build a robust surface, which hampers the decomposition of electrolytes and the structural evolution upon cycling. Accordingly, the lifespan of Li‐reinforced materials is prolonged to three times that of the pristine one. This work represents a step forward in understanding the surface reconstruction operated in a water‐based solution for high‐performance sodium layered oxide cathodes.