In situ Electrochemical Transformation of MoO₂/Mo₄O₁₁@Mo for High-Capacity Aqueous Zinc-Ion Batteries

Taking advantage of the variable valence states of molybdenum, this work develops a MoO₂/Mo₄O₁₁@Mo heterostructure as a highly efficient cathode, aiming to boost the electrochemical performance of aqueous zinc-ion batteries (AZIBs). It is noteworthy that during the initial charge-discharge cycle, in situ electrochemical conversion occurs between Mo₄O₁₁ and Mo, resulting in the formation of a stable MoO₂@Mo interfacial structure that significantly enhances the electrode's electrochemical kinetics. Furthermore, combined with multiple ex situ characterizations, the reversible Zn²⁺ insertion/extraction dynamic mechanism within the MoO₂ lattice is elucidated. Benefiting from progressive in situ phase transformation and structural reconstruction, the electrode exhibits a high specific capacity and robust cycling stability (291 mAh g^-1 at 0.5 A g^-1 with 60% capacity retention after 200 cycles), as well as excellent rate capability (148 mAh g^-1 at 3 A g^-1 with 77% capacity retention after 1500 cycles). Capacity evolution analysis reveals that the activation process under high-rate conditions is delayed yet sustained, mitigating the rapid initial capacity decay commonly observed in conventional materials and improving cycling durability. This work validates the efficacy of heterostructure design combined with in situ conversion strategies in optimizing Zn²⁺ storage kinetics and provides crucial insights into the development of advanced molybdenum-based cathodes for aqueous zinc-ion batteries.