Carbon hydrangeas with typical ionic liquid matched pores for advanced supercapacitors

Pore–ion size matching between carbon electrodes and electrolytes is crucial for superior energy storage. However, it remains a great challenge to engineer carbons with perfectly compatible pore dimension for desired electrolytes. Herein we design a simple synthetic route to obtain carbon hydrangeas integrated with unique geometry, high surface areas, N/O doping, and more importantly, well-developed pore structure. The narrow primary subnanopores of 0.80 nm are exactly matched the cation sizes (EMIM+, 0.76 nm) of 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMIMTFSI) and 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIMBF4) ionic liquid electrolytes. Besides, the secondary pores of 0.50 nm are size-exclusively accessible for small BF4− anions (0.48 nm) but exclude larger TFSI− (0.79 nm), giving enhanced ion diffusion/adsorption kinetics. The solid-state supercapacitor based on EMIMBF4 gel electrolyte achieves an ultrahigh specific energy of 101.2 Wh kg−1 (29.2% enhancement against the use of EMIMTFSI), superior to the most values of recently reported carbon-based supercapacitors. This study opens new horizons to develop functionalized carbons with perfectly ion-comparable pore architecture, moving toward advanced energy storage systems.