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

Abstract 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, K 0.2 Ni 0.68 Co 0.77 Fe(CN) 6 ⋅ 1.8H 2 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.