A bulk Ba2Co3F10 electrode: three-dimensional ion tunnels facilitate atomic-scale redox toward high-performance electrochemical capacitors

Whereas almost superior electrochemical performances could be achieved only in exquisite nanostructures, hi-erarchical structures and mesoporous electrode materials in terms of surface electroactive sites and redox, it seems extremely challenging or even impossible for realizing high performances in a large-size bulk material. Herein we report a new bulk material Ba2Co3F10 with large ion tunnels along a, b and 24.3 degrees-tilted c (i.e. [106]) directions are built. Such three-dimensional ion tunnels facilitate unimpeded diffusion for OH- in electrolyte entering Ba2Co3F10 lattice and permit all electroactive Co2+ sites participating atomic-scale electrochemical redox, following an ionic intercalation kinetics mechanism with a high capacitive contribution. The fabricated asymmetric supercapacitor (ASC) exhibits an ultrahigh energy density, significantly 2-3 folds higher than almost all existing bulk ASC systems, rendering the Ba2Co3F10 for the first promising bulk material as high-performance supercapacitors. Given layer/tunnel structures extensively exist in transition-metal compounds, currently pro-posed strategy would be highly attractive for utilizing electroactive sites toward electrochemical functions.