An Open-Framework Structured Material: [Ni(en)2]3[Fe(CN)6]2 as a Cathode Material for Aqueous Sodium- and Potassium-Ion Batteries

Open-framework structured materials such as Prussian blue analogues and sodium superionic conductor (NASICON) materials have been regarded as promising electrode candidates for aqueous batteries. These materials exhibit outstanding long cycle stability and high rate capacity retention, due to their high ion diffusive rate in the crystal and the stable structure maintenance in the electrochemical reaction process. Herein, an open-framework structured material [Ni(en)₂]₃[Fe(CN)₆]₂ (NienHCF) is prepared and first used as a cathode material for aqueous sodium- and potassium-ion batteries. The resultant material exhibits a high output potential and outstanding cycle performance (93.4% after 500 cycles at 1 A g^-1) in K-ion batteries. Meanwhile, the electrochemical reaction mechanism is investigated. After coupling with the activated carbon anode, the K-ion full cell has 91.5% capacity retention at 5 A g^-1 and retains 77.2% after 1000 cycles at 0.5 A g^-1, exhibiting the potential as an electrode material for rechargeable aqueous K-ion and Na-ion batteries.