Whereas almost superior electrochemical performances could be achieved only in exquisite nanostructures, hierarchical 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°-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 proposed strategy would be highly attractive for utilizing electroactive sites toward electrochemical functions.