Sepiolite as a novel polysulfide trapper for energy applications: an electrochemical, X-ray spectroscopic and DFT study.

Capacity retention is a critical property to enhance in electrochemical storage systems applied to renewable energy. In lithium-sulfur (Li-S) batteries, the capacity fade resulting from the shuttle effect of polysulfides is a major obstacle to their practical application. Sepiolite, an eco-friendly earth-abundant clay with suitable surface chemistry for anchoring and retaining various molecules and structures, was studied as a cathode additive to mitigate the shuttle effect using experimental and theoretical approaches. Electrochemical measurements, spectroscopy, and calculations were performed to describe the mechanism and interfaces involved in polysulfide retention using 2 wt% of sepiolite as an additive in Li-S batteries. The results showed that the addition of sepiolite significantly improved the capacity retention during battery cycling. Spectroscopic analysis revealed that the effective sepiolite-polysulfide interface was governed by oxidized sulfur species. Additionally, studies showed a highly exothermic adsorption both inside and outside the sepiolite pore. This study demonstrates the potential use of eco-friendly, low-cost, non-toxic, natural, and abundant materials as additives to increase capacity retention.