Harvesting honeycomb-like carbon nanosheets with tunable mesopores from mild-modified coal tar pitch for high-performance flexible all-solid-state supercapacitors

Abstract Versatile topology structures and hierarchical pore configuration are highly desired for supercapacitive carbons, but there is a daunting challenge to synthesize the material that works well on both fronts synchronously via an efficient and template-free route. Herein, honeycomb-like porous carbon nanosheets with tunable mesopores are fabricated from coal tar pitch through a sequential solvent extraction-mild modification-activation process without any templates. Engineering design of molecular spacing of pitch is implemented by grafting rosin structures on the edge of oxidized polycyclic aromatic hydrocarbons under mild condition, which avoids molecular excessive stacking and further promotes K+ etching and intercalation during activation. As-obtained carbon nanosheets show a well-defined honeycomb nanosheet features together with rich tunable mesopores specific in sizes of 2–5 nm. Benefiting from the synergy of hierarchical micro-architectures, the optimized carbon nanosheets deliver an ultra-high specific capacitance of 411.2 F g−1 and an excellent rate performance. As-assembled symmetrical flexible all-solid-state supercapacitor with PVA/KCl membrane electrolyte exhibits a high energy density of 12.3 W h kg−1 at a power density of 249.5 W kg−1, as well as a superior long-term durability over 50,000 cycles. This work paves the path from bulk cheap precursors to high-value carbon nanosheets engaged in high-performance flexible supercapacitive devices.