Boosting the Zinc-Ion Storage Capability of NH₄V₃O₈ via Cation-Defect Engineering

Ammonium vanadate (NVO) is regarded as one of the most promising cathodes for aqueous zinc-ion batteries (AZIBs) by virtue of its favorable theoretical capacity and comparatively stable layered structure. Nevertheless, the crowded NH4+ cation in the interlayer would partially occupy the transfer routes of Zn2+, and the strong electrostatic interaction contributed by the excessive NH4+ would further lower the mobility of Zn2+, thus resulting in the sluggish kinetics of Zn2+ and inferior rate performances. Herein, cation-modulated engineering is proposed and achieved via a facile thermal-treatment process. By modulating the number of NH4+ cations, the interlayer spacing of NH4V3O8 is significantly broadened and the migration barrier of Zn2+ is effectively reduced. As a result, the proposed NH4V3O8 cathode with moderate NH4+ removal exhibits the favorable capacity of 375 mAh g–1 at 2 A g–1, while ∼363 mAh g–1 could be maintained after 1000 cycles, corresponding to a superior capacity retention of ∼97%, suggesting the significantly boosted electrochemical properties contributed by the cation-modulated engineering. Moreover, the related ex-situ characterizations substantiate the Zn2+/H2O co-intercalation mechanism of the proposed NVO cathode. This work sheds light on the potential of the cation-modulation strategy on accelerating the kinetics of zinc-ions and improving the electrochemical properties of ammonium vanadate-based cathodes and further broadens the application potentials of vanadium-based cathodes in rechargeable AZIBs.