MOF-derived hollow multi-shell NiCo2O4 spheres as high-performance cathodes for alkaline aqueous Zn batteries

Abstract

The development of high-performance cathode materials is crucial yet highly challenging for aqueous alkaline zinc batteries (AZBs). Herein, hollow multi-shell NiCo₂O₄ spheres (NiCo₂O₄-HMSs) with three to four interconnected shells were prepared through controllable thermal treatment of a metal–organic framework (MOF) precursor. Benefiting from their high specific surface area and unique hollow multi-shell architecture, these nanostructured oxides facilitate efficient electrolyte penetration and rapid ion/electron transport, while simultaneously exposing abundant electrochemically active sites, thereby enabling a markedly enhanced capacity. When assembled into a NiCo₂O₄-HMSs//Zn battery, the cathode delivers a high specific capacity of 152.8 mAh g⁻¹ at 2 A g⁻¹ and outstanding cycling durability, retaining 121.1 mAh g⁻¹ after 500 cycles at 6 A g⁻¹, markedly outperforming its single-shelled NiCo₂O₄ counterpart. The resulting device further achieves an energy density up to 264.3 Wh kg⁻¹ and a power density up to 24.7 kW kg⁻¹, demonstrating a favorable balance between energy output and rate capability. Electrochemical analyses reveal reduced interfacial resistance and mixed capacitive/diffusion-controlled charge storage with a pronounced surface-controlled contribution at elevated scan rates, consistent with accelerated reaction kinetics enabled by the multi-shell architecture. This work highlights that rational multi-shell structural engineering provides an effective route to improve energy/power characteristics and cycling stability of NiCo₂O₄-based cathodes for alkaline aqueous Zn batteries.