Despite their high‐power density and cycling stability, supercapacitors remain fundamentally limited by low energy density, motivating asymmetric carbon–oxide architectures that nevertheless suffer from ion‐transport and durability constraints. In this work, pitch‐based activated carbon (PBAC) with a hierarchically engineered micro/mesoporous structure was synthesized via controlled KOH activation, yielding an ultrahigh specific surface area (SSA) of 2827 m 2 g −1 and an optimized mesopore fraction of 23%, which enables dense charge storage in micropores while facilitating rapid ion buffering through mesoporous channels. As a complementary positive electrode, NiO nanosheets were conformally deposited on nickel foam using a facile chemical bath deposition (CBD)–annealing process, providing abundant redox‐active sites for reversible Ni 2+ /Ni 3+ reactions. The resulting PBAC–NiO asymmetric supercapacitor (Asy‐K4) operates stably over a wide voltage window of 1.5 V and delivers a high specific capacitance of 265 F g −1 with an energy density of 82.9 Wh kg −1 at 0.2 A g −1 , while maintaining 72.1 Wh kg −1 at 1.0 A g −1 , demonstrating excellent rate capability. Moreover, the device retains 87.1% of its initial capacitance after 10,000 charge–discharge cycles, confirming robust long‐term durability. Electrochemical impedance spectroscopy (EIS) reveals a substantially reduced charge‐transfer resistance (11.3 vs. 23.3 Ω for the symmetric PBAC cell), highlighting the kinetic advantage of the asymmetric architecture. Compared with previously reported NiO//activated‐carbon asymmetric supercapacitor (ASC), the present Asy‐K4 system achieves a distinctly higher energy density while preserving low charge‐transfer resistance, demonstrating that rational micro/mesopore engineering in pitch‐derived carbons is a decisive factor for overcoming the conventional energy–power trade‐off in aqueous ASC.
Kim et al. (Thu,) studied this question.