Modeling the discharge behavior of a lithium-sulfur battery

In lithium-sulfur (Li-S) batteries, the discharge performance depends greatly on a number of cell design parameters because of the complex reaction mechanisms in the cathode. Electrolyte-to-sulfur (E/S) ratio and carbon-to-sulfur (C/S) ratio in the cell are key examples of these critical design factors that define the Li-S battery performance. Here, a 1-D electrochemical model is reported to calculate the dependence of the discharge behavior of a Li-S battery on the E/S and C/S ratios. Proposed model describes the complex kinetics through two electrochemical and two dissolution/precipitation reactions. Concentration variations in the cathode are also taken into account in the model. Characteristic aspects of the discharge profile of a Li-S battery -the two distinct voltage plateaus and the voltage dip in between- are captured in the predicted voltage curve. Similar trends on the discharge performance of the Li-S cell with varying E/S and C/S ratios are projected; both voltage and discharge capacity of the Li-S battery are improved substantially with increasing C/S or E/S ratio up to a certain point, whereas, the dependence of the discharge performance on these factors is less substantial at higher ratios. This model offers a mechanistic interpretation of the influence of cell design on the Li-S battery performance.