Resolving water-induced deactivity and fragility of Prussian blue by eutectic chemistry for upgraded sodium storage

Despite the alluring prospect of Prussian blue (PB) cathode for Na-ion batteries (NIBs), the abundant existence of structural water molecules in the lattice framework greatly downgrades its capacity output and cycling performance, which remains a troublesome issue. Herein, we propose a novel eutectic chemistry strategy to mitigate the water-induced challenges of PB for advanced Na-ion storage. The unique eutectic medium network provides a nonaqueous and highly viscous environment for ab initio refraining water incorporation into the PB framework and greatly retarding the crystallization, thereby producing high-quality crystals with reduced water content as low as 4.9 wt%. The structurally favorable traits endow the water-deficient PB with an elevated capacity of 131.4 mAh g−1 at 0.2 C, and more impressively, an ultralong lifespan over 10,000 cycles. A deep insight into the mechanistic enhancement by eutectic chemistry on sodiation kinetics and structural stability is unraveled. Furthermore, the obsolete eutectic solvent can be recycled to prepare water-deficient PB without noticeable performance sacrifice, thereby paving a sustainable, economic, and green avenue for boosting the development of PB-based NIBs.