Alleviated mechanical structure decay and accelerated transport kinetics via KNCHCF@NiHCF core–shell structure for aqueous potassium-ion batteries

Abstract

The sluggish ion transport and mechanical decay caused by K⁺ intercalation can hinder the K⁺ storage ability of Prussian blue analogs (PBAs), potential cathode materials for potassium-ion batteries (PIBs). The construction of composite materials using adjustable chemical components of PB is an effective method to improve cycling stability. In this study, a core–shell structure of KNiCoFe(CN)₆@NiFe(CN)₆ (KNCHCF@NiHCF) was prepared to utilize the inertness of Ni²⁺ and the stability of Fe–CN–Ni bonds and enhance the performance of PBAs. Different concentrations of NiHCF coating (Ni-0, Ni-2, Ni-5, and Ni-60) were introduced into the outer layer of KNCHCF using a simple solution precipitation method. The aforementioned core–shell structure and the corresponding built-in electric field enhanced the structural stability and K⁺/e⁻ transport kinetics of the fabricated materials. And Ni-5 exhibited the best electrochemical performance with excellent durable cycling stability and rate performance. Furthermore, the reversible single-phase insertion and extraction reaction of K⁺ storage mechanism within the Ni-5 cathode was revealed using ex-/in-situ characterization techniques. This strategy may facilitate the development of other cathode materials for rechargeable metal ion batteries.