Rational Precursor Crosslinking Engineering for High‐Performance Dual‐Carbon Sodium‐Ion Capacitors with Optimized Graphitic Microdomains and Pore Structures

Abstract Dual‐carbon sodium‐ion capacitors (SICs) represent cost‐effective, high‐energy‐density alternatives to traditional electrochemical double‐layer capacitors (EDLCs). Previous studies have been limited by the inability to tailor anode and cathode properties from a single precursor. In this work, a straightforward precursor regulation strategy is developed, synthesizing phenol‐furfural resins with tunable crosslinking degrees to simultaneously fabricate optimized hard carbon anodes and porous carbon cathodes for SICs. For the anode, highly crosslinked precursors demonstrate inherent advantages: the larger interlayer spacing in graphitic microdomains and greater volume of closed micropores, which enable the derived hard carbon 24H1400 to achieve a specific capacity of 337.8 mAh g −1 at 0.05 A g −1 , along with superior rate capability compared to low‐crosslinking‐derived anodes. As for the cathode, although low‐crosslinking‐derived porous carbons exhibit a higher specific surface area, this parameter proves irrelevant to electrochemical performance. Instead, the cathode A15H750 derived from moderately crosslinked precursors achieves optimal properties: a high microporosity ratio and abundant surface oxygen functional groups. This design delivers an exceptional specific capacity of 206.5 mAh g −1 at 0.1 A g −1 , coupled with satisfactory cycle and rate performance. Benefiting from optimal precursors regulation, the assembled SIC full cell 24H1400//A15H750 demonstrates exceptional performance, including reliable operational capability across an extended temperature range from −10 to 50 °C.