A Bifunctional Perovskite Promoter for Polysulfide Regulation toward Stable Lithium-Sulfur Batteries

Abstract

Lithium-sulfur (LiS) batteries are strongly considered as the next-generation rechargeable cells. However, both the shuttle of lithium polysulfides (LiPSs) and sluggish kinetics in random deposition of lithium sulfides (Li₂ S) significantly degrade the capacity, rate performance, and cycling life of LiS cells. Herein, bifunctional Ba_0.5 Sr_0.5 Co_0.8 Fe_0.2 O_3-δ perovskite nanoparticles (PrNPs) are proposed as a promoter to immobilize LiPSs and guide the deposition of Li₂ S in a LiS cell. The oxygen vacancy in PrNPs increases the metal reactivity to anchor LiPSs, and co-existence of lithiophilic (O) and sulfiphilic (Sr) sites in PrNP favor the dual-bonding (LiO and SrS bonds) to anchor LiPSs. The high catalytic nature of PrNP facilitates the kinetics of LiPS redox reaction. The PrNP with intrinsic LiPS affinity serves as nucleation sites for Li₂ S deposition and guides its uniform propagation. Therefore, the bifunctional LiPS promoter in LiS cell yields high rate performance and ultralow capacity decay rate of 0.062% (a quarter of pristine LiS cells). The proposed strategy to immobilize LiPSs, promotes the conversion of LiPS, and regulates deposition of Li₂ S by an emerging perovskite promoter and is also expected to be applied in other energy conversion and storage devices based on multi-electron redox reactions.

Keywords: bifunctional perovskite promoters; composite cathodes; lithium-sulfur batteries; polysulfide redox reactions; shuttle of polysulfide intermediates.