Binder-free Co-Ni hexacyanoferrate as a battery-type electrode material for hybrid supercapacitors

In this study, Co-Ni hexacyanoferrate (CoxNi3-xHCF) electrodes with different Co and Ni ratios were directly synthesized on Ni foam (NF) via a simple and cost-effective hydrothermal approach, and their physical and electrochemical properties were studied. The binder-free CoxNi3-xHCF@NF composites exhibited battery-like electrochemical storage mechanisms. Among them, the CoNi2HCF@NF composite exhibited the better charge storage properties with a specific capacity of 817 C g(-1) at 1 A g(-1). Furthermore, a hybrid supercapacitor (HSC) device with a CoNi2HCF@NF composite as the battery type and activated carbon as supercapacitor electrodes delivered a high energy density of 36 Wh Kg(-1) at a power density of 1056 W kg(-1 )along with good cycling performance. This study introduces a feasible method to design such binder-free materials with optimized synergetic effects that are beneficial for designing next-generation HSC devices.