Assessment of Li-S Battery Performance as a Function of Electrolyte-to-Sulfur Ratio

Abstract

Lithium-Sulfur (Li-S) battery performance is greatly sensitive to cell design as a result of the highly complex reaction and shuttle mechanisms within the cathode. Electrolyte-to-sulfur (E/S) ratio is one of the key design parameters that have a great impact on the performance of Li-S batteries. Here, an integrated research methodology coupling experimental characterization and electrochemical modeling is applied to forecast the relation between the E/S ratio and the discharge capacity, cycling performance and cell- and system-level specific energy and energy density of the Li-S battery. The highest initial discharge capacity is achieved with an E/S ratio of 20 μl mg−1, whereas, the best capacity retention is observed for 13 μl mg−1. This experimentally obtained link between the E/S ratio and the discharge performance is taken into consideration in the proposed cell- and system-level performance models. Lower E/S ratios lead to higher battery performance at the cell and system level. Consequently, an E/S ratio of 13 μl mg−1 presents the best performance as the impact of E/S ratio not only on the peak discharge capacity and capacity retention but also on the specific energy and energy density at the cell and system level are all considered.

Carbon‐to‐sulfur ratio in the cell controls the discharge capacity, cycling performance and energy density of a lithium‐sulfur battery

“…As discussed in our previous study, for high E/S ratios, the electrolyte weight/volume dominates the pack weight/ volume and the system-level performance becomes less sensitive to the other design factors. 31 The best systemlevel metrics are projected with the lowest C/S and E/S ratios of 0.5 and 6 μL mg À1 , respectively, even though this cell provided a lower peak discharge capacity compared to the others. This result supports our discussion that the Wh L À1 or Wh kg À1 for the battery packs should be a prior concern in Li-S cathode design; optimizing the E/S or C/S ratio based on the peak discharge capacities may be misleading.…”

“…Increasing the C/S ratio from 2 to 3.5 also leads to inferior cycling performance as Figure 4A presents. Previously, we reported that the best capacity retention and cell‐ and system‐level performance are achieved for the Li‐S cell with an E/S ratio of 13 μL mg −1 31 …”

“…In order to design the battery pack according to the given design equations, the current‐voltage relationship in the cell needs to be determined. For this reason, a 1D electrochemical model is offered 31 . The described system‐level performance model uses this electrochemical model (governing equations and model parameters are given in Tables S3 and S4, respectively) to determine the overpotential as well as the area‐specific impedance of all cell components.…”

How to Model the Cathode Area in Lithium‐Sulfur Batteries?

“…As a consequence of the complex reaction and degradation mechanisms in the cathode, the electrochemical performance of Li−S batteries is directly related to materials and cell design [16–19] . Therefore, the design of the Li−S cathode plays a vital role in the achievement of high cycling performance and energy density [5] .…”

“…[7,12,15] As a consequence of the complex reaction and degradation mechanisms in the cathode, the electrochemical performance of LiÀ S batteries is directly related to materials and cell design. [16][17][18][19] Therefore, the design of the LiÀ S cathode plays a vital role in the achievement of high cycling performance and energy density. [5] Electrolyte-to-sulfur (E/S) ratio is one of the key cathode design parameters as it determines the polysulfide electrolyte concentration on the cathode surface, which affects the precipitation/dissolution reactions and the shuttle mechanism.…”