Engineering Kinetics-Favorable Carbon Sheets with an Intrinsic Network for a Superior Supercapacitor Containing a Dual Cross-linked Hydrogel Electrolyte

Despite the physicochemical advantages of two-dimensional (2D) carbons for supercapacitors, the inappropriate texture within 2D carbon materials suppresses the charge storage capability. Reported here are heteroatom-rich carbon sheets with the overall network engineered by molecular structure modulation and subsequent chemical activation of a three-dimensional (3D) cross-linked polymer. The 3D-to-2D reconstruction mechanism is unveiled. The architecture with a large active surface, fully interpenetrating and conductive network, and rich surface heteroatoms relieves well the ionic diffusion restriction within thick sheets and reduces the overall resistance, exhibiting fast transport kinetics and excellent stability. Indeed, high gravimetric capacitance (281.1 F g-1 at 0.5 A g-1), ultrahigh retention rate (92.5% at 100 A g-1), and impressive cyclability (89.7% retention after 20 000 cycles) are achieved by this material. It also possesses a high areal capacitance of 3.56 F cm-2 at 0.5 A g-1 under a high loading of 25 mg cm-2. When coupled with the developed dual cross-linked hydrogel electrolyte (Al-alginate/poly(acrylamide)/sodium sulfate), a quasi-solid-state supercapacitor delivers an energy density of 28.3 Wh kg-1 at 250.1 W kg-1, which is significantly higher than those of some reported aqueous carbon-based symmetric devices. Moreover, the device displays excellent durability over 10 000 charge/discharge cycles. The proposed cross-linked polymer strategy provides an efficient platform for constructing dynamics-favorable carbon architectures and attractive hydrogel electrolytes toward improved energy supply devices.