Mechanistic understanding of lithium-anode protection by organosulfide-based solid-electrolyte interphases and its implications

Abstract

Maximizing the energy density of Li-based batteries to power our future is predicated on the use of Li-metal as the anode. To improve the longevity of the Li anode, it is critical to regulate the electrolyte–Li metal interface through the solid-electrolyte interphase (SEI). Organopolysulfides have been shown to form favorable SEIs but the mechanism of Li protection is poorly understood. In this work, we first elucidate how the organic thiolate-rich SEI homogenizes Li flux and enables uniform Li deposition. We then utilize methyl, phenyl, and allyl-based polysulfides as model compounds to investigate the effect of the functional groups on the electrodeposition of Li. It is found that aliphatic, conjugated functional groups promote the formation of thiolates, can form polymeric, flexible SEI, provide oxidative stability, and effectively incorporate inorganic phases, thus forming a robust SEI. Diallyl polysulfide is used as a model compound to demonstrate that the improved cycling of the Li-metal anode can prolong the life of Li‖LiFePO₄ coin cells as well as Li‖S and anode-free Ni‖Li₂S pouch cells when cycled with realistic cell-assembly parameters. This work provides guidelines for the design of future organosulfur materials that could enable long-lasting Li-metal batteries.