Concunrent manipulation of anion and cation adsorption kinetics in pancake-like carbon achieves ultrastable potassium ion hybrid capacitors

Abstract

Potassium ion hybrid capacitors (KIHCs) are one of the most promising candidate for large scale energy storage owing to the merits of high energy/power density, natural abundance and low cost. However, the sluggish ion adsorption kinetics on both electrodes results in unfavorable performance of KIHCs. Herein, we prepared bi-functional hierarchical porous P/N co-doped pancake-like carbon (PN-PanC), which exhibits superior K+/FSI− storage performance. Specifically, the PN-PanC delivers high specific capacity (385.8 mAh g−1 at 100 mA g−1), stable cycling capability (2000 cycles with an average attenuation rate of 0.21 ‰ at 1000 mA g−1) for anode application, and remarkable specific capacity (94.2 mAh g−1 at 100 mA g−1) when evaluated as cathode. The origins of the concurrently enhanced K+/FSI− storage are studied by ex-situ XPS, in-situ Raman, EIS analysis and DFT calculations, which could be attributed to the synergy of hierarchical porous structure, exposed active sites, tuned electronic structure and enhanced ion adsorption kinetics. Importantly, the KIHCs devices exhibit both high energy density (155.9 Wh kg−1 at 76.1 W kg−1) and high power density (11,309.1 W kg−1 with 22.0 Wh kg−1 retained) with ultra-long lifespan (93.4% capacity retention at 500 mA g−1 after 20 K cycles).