Ambient Na-S Discharge Mechanisms in Glyme Electrolytes Identified with in-Situ Optical Microscopy

Abstract

Ambient Na-S systems have regained attention as global abundance of materials becomes a concern for Li-ion batteries.1 The fundamental Na-S system consists of a sulfur cathode, liquid electrolyte and a sodium anode, and it can be informed by discoveries in Li-S and Li metal battery research. Early Li-S research identified the propensity for various Li-S discharge products to solubilize in the electrolyte. This behavior proved crucial to performance. Because the analogous solubilized Na-S discharge products have distinct colors in the visible spectrum, we employ a specially designed in-situ electrochemical cell, developed at the Naval Research Laboratory,2 to track electrolyte color during discharge. This optical tracking allows the identification of the chronology of solubilized discharge products and assess the efficacy of promising electrolytes. The discharge products (Na2Sn, 8<n<1) and relative quantities are determined via their distinct colors, and UV-vis calibration, respectively. Since these behaviors prove strongly dependent on electrolyte solvent and salt concentration, the study is valuable to selection of the optimal composition for anode stability and cathode performance.1.Carter, R.; Oakes, L.; Douglas, A.; Muralidharan, N.; Cohn, A. P.; Pint, C. L., A Sugar-DerivedRoom-Temperature Sodium Sulfur Battery with Long Term Cycling Stability. Nano Letters 2017, 17 (3),1863-1869.2.Love, C. T.; Baturina, O. A.; Swider-Lyons, K. E., Observation of Lithium Dendrites at AmbientTemperature and Below. Ecs Electrochem Lett 2015, 4 (2), A24-A27.