NH4+-Modulated Cathodic Interfacial Spatial Charge Redistribution for High-Performance Dual-Ion Capacitors

Abstract Compared with Zn 2+ , the current mainly reported charge carrier for zinc hybrid capacitors, small-hydrated-sized and light-weight NH 4 + is expected as a better one to mediate cathodic interfacial electrochemical behaviors, yet has not been unraveled. Here we propose an NH 4 + -modulated cationic solvation strategy to optimize cathodic spatial charge distribution and achieve dynamic Zn 2+ /NH 4 + co-storage for boosting Zinc hybrid capacitors. Owing to the hierarchical cationic solvated structure in hybrid Zn(CF 3 SO 3 ) 2 –NH 4 CF 3 SO 3 electrolyte, high-reactive Zn 2+ and small-hydrate-sized NH 4 (H 2 O) 4 + induce cathodic interfacial Helmholtz plane reconfiguration, thus effectively enhancing the spatial charge density to activate 20% capacity enhancement. Furthermore, cathodic interfacial adsorbed hydrated NH 4 + ions afford high-kinetics and ultrastable C‧‧‧H (NH 4 + ) charge storage process due to a much lower desolvation energy barrier compared with heavy and rigid Zn(H 2 O) 6 2+ (5.81 vs. 14.90 eV). Consequently, physical uptake and multielectron redox of Zn 2+ /NH 4 + in carbon cathode enable the zinc capacitor to deliver high capacity (240 mAh g −1 at 0.5 A g −1 ), large-current tolerance (130 mAh g −1 at 50 A g −1 ) and ultralong lifespan (400,000 cycles). This study gives new insights into the design of cathode–electrolyte interfaces toward advanced zinc-based energy storage.