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 NH 4 + and host materials has attracted widespread attention in aqueous energy storage, while few studies focus on high-performance NH 4 + storage anodes. Herein, we present a high-performance inset-type anode for aqueous ammonium-ion batteries (AIBs) based on Bi 2 SeO 5 nanosheets. A reversible NH 4 + /H + co-intercalation/deintercalation accompanied by hydrogen bond formation/breaking and a conversion reaction mechanism in layered Bi 2 SeO 5 is proposed according to ex situ characterizations. Accordingly, the optimized Bi 2 SeO 5 anode has a high reversible capacity of 341.03 mAh g –1 at 0.3 A g –1 in 1 M NH 4 Cl 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 NH 4 + and the host material. When the rocking-chair ammonium-ion battery is assembled using a MnO 2 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.