Oxygen Vacancy-Enriched Bi₂SeO₅ Nanosheets with Dual Mechanism for Ammonium-Ion Batteries

Ammonium ions feature a light molar mass and small hydrated radius, and the interesting interaction between NH₄⁺ and host materials has attracted widespread attention in aqueous energy storage, while few studies focus on high-performance NH₄⁺ storage anodes. Herein, we present a high-performance inset-type anode for aqueous ammonium-ion batteries (AIBs) based on Bi₂SeO₅ nanosheets. A reversible NH₄⁺/H⁺ co-intercalation/deintercalation accompanied by hydrogen bond formation/breaking and a conversion reaction mechanism in layered Bi₂SeO₅ is proposed according to ex situ characterizations. Accordingly, the optimized Bi₂SeO₅ anode has a high reversible capacity of 341.03 mAh g^-1 at 0.3 A g^-1 in 1 M NH₄Cl electrolyte and an impressive capacity retention of 86.7% after 7000 cycles at 3 A g^-1, which is related to the existence of oxygen vacancies that enhance ion/electron transfer and promote the formation of hydrogen bonds between NH₄⁺ and the host material. When the rocking-chair ammonium-ion battery is assembled using a MnO₂ cathode, the device delivers an ultrahigh capacity of 140.73 mAh g^-1 at 0.15 A g^-1 and energy density of 207.13 Wh kg^-1 at the power density of 2985.07 W kg^-1. This work provides a promising strategy for designing high-performance anodes for next-generation AIBs.