Abstract
Use of fluorinated ether (TFEE) based electrolyte in lithium-sulfur (Li-S) batteries enables high-energy Li–S cells at low electrolyte loading by significantly reducing the polysulfide shuttle phenomenon. The molecular level origin for the change in polysulfide solubility was found to be poor Li+ ion solvation ability of the fluorinated ethers as analyzed by COSMO-RS computations for several electrolytes.1
There are still several questions open about the mechanism of operation of such cells. How is impedance and its limitations different from the conventional polysulfide solvating electrolytes? Which process during the operation of such cells is the bottle-neck for cell performance? What is the mechanism of Li2S deposition? Is lithium stripping and deposition limited by the poor Li+ ion solvation ability?
In order to understand the cell performance with TFEE electrolyte, an impedance spectroscopy study was conducted on simplified cell geometry model systems. The basic principles elucidated through that approach were then used to understand the workings of the conventional mesoporous carbon cathode cell setup. Charge transfer reaction and diffusion contributions were evaluated and the change due to Li2S deposition analyzed. Finally, Li metal stripping and deposition analysis was performed, which showed beneficial effects of the fluorinated solvent on the SEI.
References:
1 S. Drvarič Talian, S. Jeschke, A. Vizintin, K. Pirnat, I. Arčon, G. Aquilanti, P. Johansson, R. Dominko, Chem. Mater. 29 (2017) 10037–10044.
Figure 1