Achieving commercial-level mass loading in ternary-doped holey graphene hydrogel electrodes for ultrahigh energy density supercapacitors

Enabling fast ion diffusion in thick electrodes (100-200 mu m, similar to 10 mg cm(-2)) is critical for their practical application in state-of-the-art supercapacitors (SCs). We developed a three-dimensional (3D) boron, nitrogen, and phosphorus ternary-doped holey graphene hydrogel (BNP-HGH) film to achieve an optimized porous structure with a high electrical conductivity, large ion accessible surface area, efficient electron and ion transport pathways, as well as high ion adsorption capacity. The binder-free BNP-HGH electrode can deliver a specific capacitance of 350 F g(-1) and a volumetric capacity of 234 F cm(-3), which are the best performance reported so far for graphene-based SCs using an organic electrolyte. Fully packaged SCs using the BNP-HGH electrodes with a commercial level graphene mass loading (150 mu m, similar to 10 mg cm(-2)) can deliver ultrahigh stack gravimetric and volumetric energy densities of 38.5 Wh kg(-1) and 57.4 Wh L-1, respectively, which are comparable to those of lead-acid batteries (35-40 Wh kg(-1) and 50-90 Wh L-1) while maintaining an ultrahigh power density of 83 kW kg(-1) (similar to 55 kW L-1) as well as a long cycle life (81.3% capacitance retention over 50,000 cycles). The high energy and power densities bridge the gap between traditional SCs and batteries, and should be very useful in practical applications.