Tuning the Solvation Structure in Water-Based Solution Enables Surface Reconstruction of Layered Oxide Cathodes...

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_1/3Mn_1/3Fe_1/3O₂ 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(H₂O)₃EA⁺ 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.