Simple Framework for Simultaneous Analysis of Both Electrodes in Stoichiometric Lithium-Sulfur Batteries.

ABSTRACT

A battery is composed of two electrodes that depend on and interact with each other. However, galvanostatic charging-discharging measurement, the most widely used method for battery evaluation, cannot simultaneously reflect performance metrics [capacity, Coulombic efficiency (CE), and cycling stability] of both electrodes because the result is generally governed by the lower-capacity electrode of the cell, namely the limiting reagent of the battery reaction. In studying stoichiometric Li-S cells operating under application-relevant high-mass-loading and lean-electrolyte conditions, we take advantage of the two-stage discharging behavior of sulfur to construct a simple framework that allows us to analyze both electrodes simultaneously. The cell capacity and its decay are anode performance descriptors, whereas the first plateau capacity and cell CE are cathode performance descriptors. Our analysis within this frame identifies Li stripping/plating and polysulfide shuttling to be the limiting factors for the cycling performance of the stoichiometric Li-S cell. Using our newly developed framework, we examine various previously reported strategies to mitigate these bottleneck problems and find modifying the separator with a reduced graphene oxide layer to be an effective means, which improves the capacity retention rate of the cell to 99.7% per cycle.