Defect regulation in bimetallic oxide cathodes for significantly improving the performance of flexible aqueous Zn-ion batteries

Bimetallic oxides have received extensive attention as cathode materials in aqueous zinc-ion batteries (AZIBs) due to their effective multi-electron storage mechanism. However, their capacity still falls short of the current demand. In this study, through reasonable structural design, we synthesized spherical glucose-derived carbon-regulated defect state Zn₃V₃O₈ (ZVO) bimetallic oxide (CS@ZVO) cathode. Such a design avoids the layered accumulation of electrode materials, which prevents the structural collapse during the cycle process, leading to a significant improvement in the cycle stability of AZIBs. Additionally, the introduction of glucose-derived carbon can shift the valence state of vanadium in the ZVO bimetallic oxide cathode towards reduction, thereby significantly improving its Zn-ion storage capacity. The resulting CS@ZVO cathode manifests a high discharge capacity of 154 mAh g⁻¹ at 1 A g⁻¹ after 100 cycles and a stable lifespan of 2000 cycles at 5 A g⁻¹. We also constructed a flexible and foldable AZIB using a hydrogel electrolyte, which operates with a specific capacity of up to 230 mAh g⁻¹ at 0.5 A g⁻¹ and can be bent and folded arbitrarily when working. This strategy for regulating the valence state of bimetallic oxides offers a promising path for the development of cathode materials in flexible AZIBs.