Doping Regulation Stabilizing δ-MnO₂ Cathode for High-Performance Aqueous Aluminium-ion Batteries

δ-MnO₂ is a promising cathode material for aqueous aluminium-ion batteries (AAIBs) for its layered crystalline structure with large interlayer spacing. However, the excellent Al ion storage performance of δ-MnO₂ cathode remains elusive due to the frustrating structural collapse during the intercalation of high ionic potential Al ion species. Here, it is discovered that introducing heterogeneous metal dopants with high bond dissociation energy when bonded to oxygen can significantly reinforce the structural stability of δ-MnO₂ frameworks. This reinforcement translates to stable cycling properties and high specific capacity in AAIBs. Vanadium-doped δ-MnO₂ (V-δ-MnO₂) can deliver a high specific capacity of 518 mAh g⁻¹ at 200 mA g⁻¹ with remarkable cycling stability for 400 cycles and improved rate capabilities (468, 339, and 285 mAh g⁻¹ at 0.5, 1, and 2 A g⁻¹, respectively), outperforming other doped δ-MnO₂ materials and the reported AAIB cathodes. Theoretical and experimental studies indicate that V doping can substantially improve the cohesive energy of δ-MnO₂ lattices, enhance their interaction with Al ion species, and increase electrical conductivity, collectively contributing to high ion storage performance. These findings provide inspiration for the development of high-performance cathodes for battery applications.