Layer-by-Layer Stacked (NH₄)₂V₄O₉·0.5H₂O Nanosheet Assemblies with Intercalation Pseudocapacitance for High Rate Aqueous Zinc Ion Storage

Rechargeable aqueous zinc-ion batteries have become an emerging candidate for large-scale energy storage due to their low cost and high safety, the lack of suitable advanced cathode materials with high specific capacity, and desirable long cycle life, as well as the elusive intercalation mechanism, which hinders their potential applications. Herein, a layer-by-layer stacked (NH4)2V4O9·0.5H2O nanosheet assembly is engineered and prepared by a mild hydrothermal protocol, demonstrating ultrahigh rate capability (101 mAh g–1 at 15 A g–1), a high discharge capacity of 374.3 mAh g–1 at 0.2 A g–1, and desirable cycling stability at high rates (84% after 1000 cycles at 5 A g–1). Benefiting from the stable and stacked layer structure, the zinc-ion charge storage is revealed to be boosted by intercalation pseudocapacitance behavior with the capacitive contribution as high as 78.1% of the total capacity at 1 mV s–1. The ex situ analyses confirm the good reversibility with the continuous cointercalation reaction mechanism of H+ and Zn2+ as well as water molecules. This study provides a feasible protocol to engineer the cathode material with superior Zn-storage performance, providing inspiration for developing suitable cathodes beyond zinc-ion batteries.