Balancing surface adsorption and diffusion of lithium-polysulfides on nonconductive oxides for lithium–sulfur battery design

TLDR

Lithium–sulfur batteries promise up to six times the specific energy of conventional lithium‑ion batteries, but face key challenges such as polysulfide dissolution, sulfur volume expansion, and uncontrolled lithium sulfide deposition, which metal‑oxide nanostructure cathodes can mitigate by suppressing the shuttle effect and enabling controlled sulfide deposition. The study aims to establish mechanistic insights and selection criteria for oxides that balance sulfide adsorption and diffusion to improve lithium‑sulfur battery performance. The authors synthesize nonconductive metal‑oxide nanoparticle‑decorated carbon flakes using a biotemplating method and propose oxide selection criteria that balance sulfide adsorption and diffusion. Cathodes incorporating MgO, CeO₂, and La₂O₃ exhibit improved cycling, with polysulfide capture occurring via monolayer chemisorption and enhanced surface diffusion driving higher sulfide deposition efficiency.

Abstract

Abstract Lithium–sulfur batteries have attracted attention due to their six-fold specific energy compared with conventional lithium-ion batteries. Dissolution of lithium polysulfides, volume expansion of sulfur and uncontrollable deposition of lithium sulfide are three of the main challenges for this technology. State-of-the-art sulfur cathodes based on metal-oxide nanostructures can suppress the shuttle-effect and enable controlled lithium sulfide deposition. However, a clear mechanistic understanding and corresponding selection criteria for the oxides are still lacking. Herein, various nonconductive metal-oxide nanoparticle-decorated carbon flakes are synthesized via a facile biotemplating method. The cathodes based on magnesium oxide, cerium oxide and lanthanum oxide show enhanced cycling performance. Adsorption experiments and theoretical calculations reveal that polysulfide capture by the oxides is via monolayered chemisorption. Moreover, we show that better surface diffusion leads to higher deposition efficiency of sulfide species on electrodes. Hence, oxide selection is proposed to balance optimization between sulfide-adsorption and diffusion on the oxides.