Incorporating Near-Pseudocapacitance Insertion Ni/Co-Based Hexacyanoferrate and Low-Cost Metallic Zn for Aqueous K-Ion Batteries.

The limited availability of cathode materials with high specific capacity and significant cycling stability for aqueous K-ion batteries (AKIBs) hinder their further development owing to the large radius of K+ (1.38 Å). Prussian blue and its analogs with a three-dimensional frame structure possessing special energy storage mechanism are promising candidates as cathode materials for AKIBs. In this study, K0.2 Ni0.68 Co0.77 Fe(CN)6 ⋅ 1.8H2 O (KNCHCF) was prepared as a cathode material for AKIBs. Both the electrochemical activity of Co ions and the near-pseudocapacitance intercalation of KNCHCF enhance K+ storage. Therefore, KNCHCF exhibits a superior capacity maintenance rate of 86 % after 1000 cycles at a high current density of 3.0 A g-1 . The storage mechanism of K+ in AKIBs was revealed through ex situ X-ray diffraction, ex situ Fourier transform infrared spectroscopy, and ex situ X-ray photoelectron spectroscopy measurements. Moreover, the assembled K-Zn hybrid battery showed good cycling stability with 93.1 % capacity maintenance at 0.1 A g-1 after 50 cycles and a high energy density of 96.81 W h kg-1 . Hence, KNCHCF may be a potential material for the development of AKIBs.