Rational Design of a Dual-Function Hybrid Cathode Substrate for Lithium-Sulfur Batteries

Abstract

Reliable sulfur cathodes hold the key to realize high-performance lithium-sulfur (Li-S) batteries, yet the electrochemical inefficiency and instability arising from the poor conductivity of sulfur and lithium sulfide together with polysulfide shuttle remain challenging. Here, a unique three-dimensional (3D) hybrid sponge with chemically coupled nickel disulfide-reduced graphene oxide (NiS2-RGO) framework is rationally developed as an effective polysulfide reservoir through a biomolecule-assisted self-assembly synthesis. An optimized amount of NiS2 (~ 18 wt.%) with porous nanoflower-like morphology is uniformly in-situ grown on the RGO substrate, providing abundant active sites to adsorb and localize polysulfides. The improved polysulfide adsorptivity from sulfiphilic NiS2 is confirmed by experimental data and first-principle theoretical calculations. Moreover, due to the chemical coupling between NiS2 and RGO formed during the in-situ synthesis, the conductive RGO substrate offers a 3D electron pathway to facilitate charge transfer towards the NiS2-polysulfide adsorption interface, triggering a fast redox kinetics of polysulfide conversion and excellent rate performance (C/20 – 4C). Therefore, the self-assembled hybrid structure simultaneously promotes static polysulfide-trapping capability and dynamic polysulfide-conversion reversibility. As a result, the 3D porous sponge enables a high sulfur content (75 wt.%) and a remarkably high sulfur loading (up to 21 mg cm-2) and areal capacity (up to 16 mA h cm-2), exceeding most of the reported values in the literature involving either RGO or metal sulfides/other metal compounds (sulfur content of < 60 wt.% and sulfur loading of < 3 mg cm-2). This integrated hybrid system could be extended to other metal-sulfides and it provides a new possibility to engineer advanced sulfur cathodes for high-performance Li-S technology with a necessary high sulfur loading. Figure 1