Cobalt hexacyanoferrate enhanced by common ion effect for aqueous potassium-ion batteries

Abstract

Aqueous potassium-ion batteries (APIBs) are emerging as candidates for large-scale energy storage in virtue of their cost-efficiency, environmental friendliness and intrinsic security. Nevertheless, the shortage of high-capacity and long-cycle K+ hosts imposes restrictions on developing advanced APIBs. Herein, KCo[Fe(CN)6] (K-CoHCF) is synthesized through simple co-precipitation and applied as a novel cathode material for storage of K+ in APIBs. For building a strong host, Co(NO3)2 is introduced into the electrolyte to suppress the dissolution of Co ions and consolidate the lattice structure on account of “common ion effect”. Thus, benefitting from its firm open structure as well as two active redox couples, K-CoHCF exhibits desirable capacity of 89.2 mAh g−1 at 100 mA g−1, excellent rate performance and superior cycling stability with 87.0% capacity retention upon 1400 cycles. In addition, the highly reversible structural evolution and single-phase reaction mechanism of K-CoHCF are unraveled by a series of ex-situ tests during K+ insertion/extraction. Thus, this work establishes a feasible battery system with K-CoHCF as cathode and sheds light on further development of advanced APIBs for practical utilization.