Exploring the Janus structure to improve kinetics in sulfur conversion of Li-S batteries

Lithium-sulfur (Li-S) batteries with high theoretical capacity have been attracting attention as next-generation energy storage systems. The random deposition of electrically insulating solid lithium sulfide (Li2S) from lithium polysulfides (LiPSs) limits the complete conversion of sulfur. The introduction of sulfiphlic metal compounds to facilitate the conversion is not accompanied by morphological control over Li2S deposition. To tackle this issue, we demonstrate a Janus-structured particle of oxide/carbon that regulates the Li2S growth. The Janus particles are prepared by directional thermal deposition of MoO3 onto CNT-agglomerated spherical particles. Under potentiostatic discharge, we observe that Li2S is deposited predominantly on MoO2-coated regions on CNT particles, accompanied by high discharge capacity. As the deposition of Li2S is microscopically controlled, the diffusion path of ions/charges in the electrode is preserved. Moreover, it is confirmed that the adsorption and catalytic properties of MoO3 are greatly promoted by its lithiation during the charge/discharge process. Janus particle cathode cells achieve excellent performance, especially under kinetically limited conditions, such as ultra-high C-rates or high cathode sulfur densities.