Facile Synthesis of Porous Bimetallic Co-Ni Fluorides for High-Performance Asymmetric Supercapacitors

Exploring specific electrode active materials with excellent kinetic properties is important for high performance supercapacitors. Herein, a novel nickel-cobalt fluoride (Ni1-xCoxF2) with porous nanoprisms structure is synthesized through step-wised recrystallization and ion-exchange reactions with polyvinyl pyrrolidone (PVP) morphology control agent. The synergistic effect of bimetallic redox centers promotes the reconstruction of the electronic coordination, leading to apparent discrepancy on the microstructure and morphology of Ni1-xCoxF2 with different stoichiometric ratios of Ni/Co. The micro-porous structure also provides sufficient interfaces and active sites for efficient electrolyte penetration and ion diffusion, improving its electrochemical performance. Among the synthesized samples, Ni0.5Co0.5F2, with Ni/Co ratio of 1:1, achieves the highest specific capacity of 1979.6 F g-1 at 1.0 A g-1 and remarkable long-term cycling stability of 932 F g-1 residual after 30,000 cycles at 20 A g-1. The supercapacitor with Ni0.5Co0.5F2 and activated carbon as positive and negative electrodes, respectively, delivers a high specific capacitance of 107.3 F g-1 at 1 A g-1, outstanding cycling stability of 90.07% capacity retention after 30,000 cycles and a maximum energy density of 48.3 Wh kg-1 at the power density of 952.9 W kg-1. Flexible asymmetric all-solid-state supercapacitor based on PVA/KOH gel electrolyte is assembled, which delivers a specific capacitance of 41.0 F g-1 at 1 A g-1 and shows promising application in flexible electronic devices.