Leveraging Sodium Storage of Water-Deficient Prussian Blue Analogues by Deep Eutectic Chemistry

Prussian Blue and its analogues (PB/PBAs) are of remarkable prospect as low-cost and high-capacity cathode materials for sodium-ion batteries. However, traditional aqueous synthesis incurs massive structural water and defects in the framework that downgrade the performance and hinder the way to commercialization. Herein, we demonstrate nonaqueous deep eutectic chemistry for finely synthesizing a diverse family of high-quality PB/PBAs with boosted sodium energy. The reaction system essentially refrains water incorporation into crystal framework, thus reducing the water content to 5.7% (vs 19.8% for the counterpart). Such an ingenious cathode design enables unprecedented electrochemical sodium storage activity and stability, including a superhigh reversible capacity of 151 mAh g^–1 and an ultralong 9000-cycling lifespan. Furthermore, the role of structural water on sodium storage mechanism and working failure behavior of the cathode are systematically unveiled. This work affords a fresh synthesis paradigm for rational design of high-performance PB/PBAs toward sustainable battery communities beyond sodium chemistry.