MOF-derived NiCo2S4 and carbon hybrid hollow spheres compactly concatenated by electrospun carbon nanofibers as self-standing electrodes for aqueous alkaline Zn batteries

Abstract

The development of high-performance cathode materials is of great importance for aqueous alkaline Zn batteries (AZBs) but also remains a great challenge. Herein, we demonstrate the rational design and synthesis of NiCo₂S₄ nanoparticles and hollow carbon hybrid spheres compactly concatenated by carbon fibers (denoted as NiCo₂S₄/HCS@CFs) through an innovative combination of metal–organic framework (MOF)-derived strategy and electrospinning technique. The as-synthesized NiCo₂S₄/HCS@CF film is flexible, lightweight, and free of any polymer binders, which offers multilevel advantages including high electrical conductivity, abundant electroactive sites, fast ion diffusion, facile electrolyte permeability and robust structural stability. When evaluated as self-standing cathode electrodes, as expected, the resulting NiCo₂S₄/HCS@CFs//Zn batteries exhibit an extremely high capacity of 343.1 mA h g⁻¹ at a current density of 3.8 A g⁻¹ (based on the NiCo₂S₄ active material), as well as superior rate performance and decent cycling performance. Moreover, the corresponding quasi-solid-state batteries are also fabricated to confirm the potential for practical applications. Remarkably, the energy densities of NiCo₂S₄/HCS@CFs//Zn batteries are 563.2 W h kg⁻¹ and 49.1 mW h cm⁻³ (liquid) and 504.1 W h kg⁻¹ and 43.9 mW h cm⁻³ (quasi-solid-state). What's more, density functional theory (DFT) calculations reveal that NiCo₂S₄/HCS@CFs have strong adsorption ability for OH⁻ ions. This work not only highlights the importance of developing advanced flexible and lightweight cathode electrodes for aqueous AZBs, but also provides some insights into electrode designs for other energy storage devices.