Quicker and More Zn²⁺ Storage Predominantly from the Interface

Aqueous zinc-ion batteries are highly desirable for large-scale energy storage because of their low cost and high-level safety. However, achieving high energy and high power densities simultaneously is challenging. Herein, a VO_x sub-nanometer cluster/reduced graphene oxide (rGO) cathode material composed of interfacial V-O-C bonds is artificially constructed. Therein, a new mechanism is revealed, where Zn²⁺ ions are predominantly stored at the interface between VO_x and rGO, which causes anomalous valence changes compared to conventional mechanisms and exploits the storage ability of non-energy-storing active yet highly conductive rGO. Further, this interface-dominated storage triggers decoupled transport of electrons/Zn²⁺ ions, and the reversible destruction/reconstruction allows the interface to store more ions than the bulk. Finally, an ultrahigh rate capability (174.4 mAh g⁻¹ at 100 A g⁻¹, i.e., capacity retention of 39.4% for a 1000-fold increase in current density) and a high capacity (443 mAh g⁻¹ at 100 mA g⁻¹, exceeding the theoretical capacities of each interfacial component) are achieved. Such interface-dominated storage is an exciting way to build high-energy- and high-power-density devices.