Porous hollow ZnCo2S4 nanosheet arrays derived from metal-organic framework as efficient cathode for lithium oxygen batteries

Highlights: • 3D porous ZnCo₂S₄ nanosheet arrays with hollow structure are fabricated as bifunctional catalyst for LOBs. • More surface-exposed Co³⁺ induced by Zn introduction augments the ORR and OER catalytic activity remarkably. • The ZnCo₂S₄ cathode exhibits extremely high discharge capacity of 9505 mAh g^-1 at 100 mA g^-1. • The discharge product Li₂O₂ displays unique morphology of large discs with interconnected nanosheets. -- Abstract: Rechargeable non-aqueous lithium oxygen batteries (LOBs) have attracted extensive attention as the most promising next-generation battery technologies due to their extremely high theoretical energy density. However, their practical applications are hampered by sluggish reaction kinetics and severe parasitic reactions, resulting from the insulating and insoluble discharge product-Li₂O₂. Herein, self-standing ZnCo₂S₄ nanosheet arrays derived from metal-organic framework (MOF) via low-temperature solvothermal sulfuration method, are fabricated as efficient cathode for LOBs. The hollow structure of ZnCo₂S₄ nanosheet formed during sulfuration provides more catalytic sites and alleviates stress during repeated discharge/charge progress, while three-dimensional (3D) porous architecture inheriting from MOF shortens the transportation pathway of Li⁺ and O₂ in electrolyte. Compared with pure CoS derived from Co-MOF, more Co³⁺ exposes on ZnCo₂S₄ surface due to the introduction of Zn, enhancing the catalytic activity distinctly. Benefitting from the bifunctional catalytic performance, the ZnCo₂S₄ cathode exhibits an extremely high initial discharge capacity of 9505 mAh g⁻¹ at 100 mA g⁻¹. Additionally, it also achieves a smaller overpotential of 1.02 V under a cutoff capacity of 1000 mAh g⁻¹ and a longer cycle life of 90 cycles at 100 mA g⁻¹. This work provides new insights into designing efficient bifunctional catalyst for LOBs.