Effect of electrolyte properties on lithium-sulfur battery performance
Loading...
Date
2023
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Thesis (M.S.) - Bogazici University. Institute for Graduate Studies in Science and Engineering, 2023.
Abstract
Lithium-sulfur (Li-S) batteries take attraction due to their promising theoretical gravimetric and volumetric energy densities, besides the natural abundance, low toxicity, and low cost of sulfur. The properties of the electrolyte significantly affect the electrochemical performance since the cathode kinetics in a Li-S cell includes the formation of lithium polysulfide intermediates soluble in the electrolyte. Herein, the effect of electrolyte constituents, namely the solvent and the salt, on discharge performance was investigated experimentally and theoretically. First, the effect of salt and solvent type on the discharge capacity, cycle life, capacity retention, and cell resistance of a Li-S cell were experimentally characterized by using galvanostatic cycling and electrochemical impedance spectroscopy (EIS) methods for sulfolane and triglyme solvents, and LiTFSI, LiTF, and LiClO4 salts at different electrolyte-to-sulfur (E/S) ratios. LiTFSI salt leads to the best cycling performance in sulfolane-based electrolytes, with higher discharge capacities at all cycles for almost all E/S ratios. On the other hand, LiTF salt- containing cells have superior capacity retention at low E/S ratios for triglyme-based electrolytes. The discharge performance of a Li-S battery is highly influenced by both the solvent and the salt type, particularly at low E/S ratios. Given this, 1M LiTFSI in a sulfolane electrolyte system appears to be promising for achieving high performance at low E/S ratios. A zero-dimensional and a one-dimensional model were also built to investigate the effect of electrolyte properties on the discharge performance of a Li-S battery. In both models, the effect of electrolyte type and properties on discharge performance is implicitly described by the variation of chosen model variables. In the 0-D model, the discharge capacity can only be controlled by the S8 precipitation rate constant. In contrast, the influence of electrolyte characteristics on discharge capacity in the 1-D model may be controlled by the S8 precipitation rate parameters, kS8 and KspS8, as well as the diffusion coefficients. Both models can predict the effect of electrolyte characteristics on discharge performance, but the one-dimensional model contains more factors that influence the discharge curve.