Coupling of reasonable micro-defect structure and multiple chemisorption sites for boosting the K+ storage capacity in dual-carbon potassium ion hybrid capacitors

Abstract

Construction of hierarchical porous (meso‑microporous) carbonaceous anodes with reasonable-sized defects and rich active sites is important for enhancing K+ storage capacity. Here, we propose a strategy that can expand the microporous defects and synchronously introduce multiple chemisorption sites to synthesize phosphorus-nitrogen double-doped foamed porous carbon (PN-FPC). Interlaced and interconnected macropores in PN-FPC can effectively promote long-range mass transfer, while ultrathin carbon bubble walls with abundant meso‑micropores and chemisorption sites can maximize the utilization of active sites. Density-functional theory (DFT) calculations show that the P, N double-doped synergistically rational micro-defect structure significantly contributes to the reversible adsorption-desorption of K+. More importantly, the potassium-ion hybrid capacitors (PIHCs) composed of P, N double-doped activated porous carbon (PN-FAPC) as cathode and pre-activated PN-FPC as anode exhibited ultra-high energy density (155.6 Wh kg−1), power density (17,000 W kg−1), and ultra-long lifetime (90.9 % capacity retention after 10,000 cycles). This study not only provides new insights for the convenient synthesis of advanced carbonaceous anode materials, but also provides a deeper understanding for revealing the charge storage mechanism of PIHCs.