Monitoring polysulfide solubility and diffusion in fluorinated ether based electrolytes by operando Raman spectroscopy

Polysulfide (PS) solubility is a key property of Li-S battery electrolytes for the conversion reaction(s) at the electrolyte-electrode interface. When PSs shuttle between the composite C/S cathode and the lithium metal anode, however, this leads to a continuous loss of active material and thus rapid capacity fading. In order to restrict the shuttle effect, fluorinated ethers have recently been proposed as a remedy; by only sparsely dissolving PSs they physically block the diffusion. We show here how the diffusion of PSs in fluorinated ethers, as monitored by operando Raman spectroscopy, is selective and that only short-chain PS (S42-) are soluble and diffuse. This fundamental observation can be used to further leverage the practical performance of Li-S batteries by novel electrolyte design.