Aqueous zinc–sodium hybrid battery based on high crystallinity sodium–iron hexacyanoferrate

Owing to their advantages of non-toxicity, non-flammability, and ultrahigh ionic conductivity, aqueous rechargeable batteries are regarded as promising candidates for energy storage systems (ESSs). Currently, electrode materials are key factors in determining the performance of aqueous batteries. In this study, a high crystallinity sodium–iron hexacyanoferrate (Na–FeHCF) with low vacancy and low water content was successfully synthesized. It can promote the rapid transfer of Na⁺ and maintain the structural stability during the repeated insertion/extraction cycles of Na⁺. Owing to these features, it presents better electrochemical performance than the ordinary one. Overall, the assembled aqueous zinc–sodium hybrid battery displays excellent electrochemical performance with an energy density of 132.5 Wh kg⁻¹ and cycling stability of 77.5% capacity retention after 800 cycles. These results show great promise for the aqueous hybrid batteries in application for ESSs.