MOF-Derived Hollow Carbon Supported Nickel-Cobalt Alloy Catalysts Driving Fast Polysulfide Conversion for Lithium-Sulfur Batteries.

ABSTRACT

Transition-metal compounds can be used as electrocatalysts to expedite polysulfide conversion effectively in lithium-sulfur batteries. However, insufficient conductivity and tedious preparation process still limit their practical applications. In this work, NiCo alloy nanoparticles embedded in hollow carbon spheres (NiCo@HCS) are fabricated via a facile, template-free strategy from the NiCo-metal-organic framework (MOF) precursor and used as electrocatalysts for separator modification. NiCo@HCS can not only improve the adsorption capacity of polysulfides by d-band deviation to the Fermi level but also reduce the energy barrier in the process of catalytic polysulfide conversion. Due to favorable three-dimensional (3-D) morphology, improved adsorption, and promoted kinetics of NiCo@HCS, the battery containing the NiCo@HCS-modified separator gives a starting capacity of 1377 mAh g-1 at 0.2C, which is retained by 72% over 500 charge/discharge operations at 1.0C current density. Moreover, the battery's start capacity reaches 1180 mAh g-1 (5.9 mAh cm-2) with a high sulfur content of 5.0 mg cm-1 at 0.2C.