In situ self-activation synthesis of binary-heteroatom co-doped 3D coralline-like microporous carbon nanosheets for high-efficiency energy storage in flexible all-solid-state symmetrical supercapacitors

Flexible solid-state supercapacitors have been considered one of the non-substitutable power supply devices for flexible and even wearable electronics. However, the highly capacitive behavior of carbon-based solid-state capacitors is restricted by the incompatible characteristics of the highly accessible surface area, efficient ion transport paths and superior electrical conductivity in carbonaceous electrodes. Herein, we propose a facile, effective strategy for the preparation of N/O dual-doped microporous carbon nanosheets (NMCNSs) with a 3D microstructure to solve the mutual competitiveness of necessary features for highly capacitive carbons. This strategy is a simple, template-free one-step heat-treatment process of organic salts, which combines the self-activation by the in situ formed activating agent to generate developed microporosity and the synergistic effect of gas blowing to hinder the aggregation of carbon sheets. The resulting NMCNSs exhibit an interconnected nonaggregated sheet-like morphology, a high surface area of 1900.5 m2 g−1 with an exceptionally large microporosity of 93%, and multiscale micropore systems with ultramicropores of 0.45–0.80 nm and supermicropores of 0.85–1.58 nm. The assembled NMCNS-based symmetric aqueous supercapacitors present a remarkable capacitive performance in KOH and Na2SO4 electrolytes. Meanwhile, we compare their electrochemical capacitive behaviors in various electrolytes and summarize a valuable reference for the potential application of NMCNS electrodes in different system supercapacitors. The constructed flexible NMCNS-based solid-state capacitors exhibit an excellent capacitive performance including high energy density, superb rate capability and outstanding long-term cycle stability. More importantly, the devices also possess an exceptional mechanical and thermal robustness, which can normally work under consecutive high bending cycles and at various ambient temperatures of 0–50 °C.