Reduced graphene oxide bubbles boosting 3D hierarchically porous carbon confined transition metal chalcogenides for high-performance Na/K-ion capacitors

Confining active nanoparticles in hierarchically porous carbon to construct intercalation and conversion coupling mechanisms is one promising way to achieve high-performance energy storage electrodes. However, this carbon with fragile mesoporous walls always suffer from fragmentation during the ion intercalation/deintercalation process, which would lead to the blocking of the whole electron transport network and the detachment of active particles, resulting in the capacity attenuation. Herein, reduced graphene oxide (rGO) bubbles are successfully introduced into N-doped hierarchically porous carbon (rGO-NPC) confined conversion-type nanoparticles to enhance their electrochemical performance. The rGO bubbles not only can afford an uninterrupted electron transport network, accelerating the reaction kinetics of active nanoparticles, and thus improving the capacity, but also can buffer the volume change of porous carbon, maintaining the integrity of electrode materials, and thereby, enhancing the cycling performance. With FeS2 as an example, when employed in Na/K-ion capacitors (SICs/KICs), the FeS2@rGO-NPC electrode can reach a high maximum energy/power density (110 Wh kg−1/20935 W kg−1 for SICs and 134 Wh kg−1/17973 W kg−1 for KICs) with a great cycling performance (82%/91% of capacitance retentions at 2 A g−1 after 10000/15000 cycles for SICs/KICs). This work indicates a promising way for designing porous carbon-based anodes with high-performance for alkali metal ions storage.