Mille-feuille-like heterostructures through in situ cross-linking approach for high power density supercapacitor

[Display omitted] •Mille-feuille-like cobalt oxide/sulfide (MF-S) on Ni foam was prepared.•The heterostructure resulted from in situ cross-linking between PGMA-POEM and DETA.•Synergistic effect of well-ordered nanosheets/spheres led to high performance.•The solid-state, bendable MF2-S//AC ASC achieved an exceptional power density. Tailoring the heterostructure of transition metal compounds is considered a promising approach for developing high-performance electrode materials for energy storage devices. In this study, a mille-feuille-like cobalt oxide/sulfide (MF-S) on Ni foam comprising porous microspheres between interconnected nanosheet walls is successfully synthesized via a one-pot solvothermal process and sulfurization. The unique heterostructure is generated using in situ cross-linking during the solvothermal process, resulting from the reaction between the epoxy groups of the comb copolymer and amine group of diethylentrieamine (DETA). The comb copolymer consisting of poly(glycidyl methacrylate)–co-poly(oxyethylene methacrylate) (PGMA-POEM) is synthesized via free-radical polymerization and serves as the structure directing agents. The prepared MF-S electrode exhibits outstanding electrochemical performance with high specific capacitance (1138F g−1 or 142 mAh g−1 at 3 A g−1) and good cycle stability owing to the synergistic effect of well-ordered nanosheets and nanospheres. Moreover, the all-solid-state, bendable asymmetric supercapacitor fabricated with the MF-S and activated carbon electrodes achieves an exceptional power density of 35000 W kg−1 at a high energy density of 18.1 Wh kg−1 with excellent cycling stability (86.9%, 10,000 cycles).