Hierarchical Porous N-doped Graphene Monoliths for Flexible Solid-State Supercapacitors with Excellent Cycle Stability

N-doped-graphene-assembled (NG-assembled) monoliths with hierarchical porous structure and outstanding electrochemical properties are desired for making high-performance flexible supercapacitors. Herein, we report a microwave-assisted synthesis of NG monoliths (M-NGM) with a unique nanosac-in-sheet structure as flexible electrodes, which are assembled to form a solid-state supercapacitor without using current collectors. Because of the hierarchical porous structure, good conductivity (15 S cm–1), and abundant nitrogen amount (6.6 wt %), the M-NGM-based flexible solid-state supercapacitor provides the super-high-capacitive behavior and excellent energy density. Together with the great cycle stability (capacitance retention of 100% after 10 000 galvanostatic charge–discharge cycles) and mechanical robustness (∼97% bending capacitance retention), the performances of the M-NGM-based supercapacitor are superior to current carbon-material-based flexible supercapacitors. It provides a facile route to prepare an excellent nitrogen-doped graphene monolith for flexible solid-state supercapacitors.