Effect of Electrolyte-to-Sulfur Ratio in the Cell on the Li-S Battery Performance

The effect of electrolyte-to-sulfur (E/S) ratio on the electrochemical and cell- and systems-level performance of a Li-S battery is investigated through modeling efforts. A 1-D electrochemical model is proposed predicting the cell voltage at 60% discharge depth. In the model, increasing electrolyte amount improves the cell voltage by linearly increasing the cathode exchange current density, which is the single kinetic model parameter. Moreover, cathode specific capacity is either defined as a linear function of the E/S ratio or taken constant in the performance models. Increasing E/S ratio enhances the cell- and systems-level specific energy and energy density until 9 mL/g S when cathode specific capacity depends on the E/S ratio. However, when the cathode specific capacity is constant at 1200 mAh/g S, battery performance decreases continuously with increasing electrolyte amount. The effect of other critical design parameters -cathode thickness, carbon-to-sulfur ratio, S loading and excess Li%- are also considered in the analysis.