Phosphate ions functionalized metal-organic framework-derived cobalt oxide with improved redox reactivity for high-performance alkaline aqueous Zn-ion batteries

Alkaline aqueous Zn/Co3O4 batteries (AZCBs) have captured significant attention within the field of scalable grid energy storage due to their high output voltage (>1.8 V), superior safety profile, and low manufacturing cost. Nevertheless, the intrinsic Co3O4 material experiences limitations in terms of low electronic conductivity and insufficient active sites, consequently constraining its electrochemical performance in AZCBs. To address this challenge, this investigation focuses on the use of phosphate ions functionalized Co3O4 (referred to as PCO) material derived from cobalt-based metal-organic frameworks (Co-MOFs) as a cathode electrode in AZCBs. Both theory calculations and experimental verification illustrate that the functionalization with phosphate ion enhances the active sites for electrochemical redox reactions and increases the electrical conductivity of intrinsic Co3O4. Consequently, a pouch cell configuration of PCO-2||Zn with the optimized PCO-2 sample as cathode exhibits a high capacity of 162.0 mAh g(-1), a maximum energy density of 265.7 Wh kg(-1), a maximum power density of 16.39 kW kg(-1). Furthermore, excellent long-term stability is observed, with the capacity retention rate reaching 92.3 % over 5000 cycles at a high current density of 5 A g(-1). Additionally, the constructed fibrous flexible solid-state device also demonstrates notable long-term stability, with a capacity retention of 96 % after 2000 cycles under a high current density of 10 mA cm(-2), and performs well under different deformation statuses. This successful approach may hold potential for the exploration of other cathode materials, such as Mn or V-based compounds, which may exhibit high performance in aqueous zinc-based batteries.