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

Compared with Zn²⁺, the current mainly reported charge carrier for zinc hybrid capacitors, small-hydrated-sized and light-weight NH₄⁺ is expected as a better one to mediate cathodic interfacial electrochemical behaviors, yet has not been unraveled. Here we propose an NH₄⁺-modulated cationic solvation strategy to optimize cathodic spatial charge distribution and achieve dynamic Zn²⁺/NH₄⁺ co-storage for boosting Zinc hybrid capacitors. Owing to the hierarchical cationic solvated structure in hybrid Zn(CF₃SO₃)₂–NH₄CF₃SO₃ electrolyte, high-reactive Zn²⁺ and small-hydrate-sized NH₄(H₂O)₄⁺ induce cathodic interfacial Helmholtz plane reconfiguration, thus effectively enhancing the spatial charge density to activate 20% capacity enhancement. Furthermore, cathodic interfacial adsorbed hydrated NH₄⁺ ions afford high-kinetics and ultrastable C‧‧‧H (NH₄⁺) charge storage process due to a much lower desolvation energy barrier compared with heavy and rigid Zn(H₂O)₆²⁺ (5.81 vs. 14.90 eV). Consequently, physical uptake and multielectron redox of Zn²⁺/NH₄⁺ 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.