On the Chemomechanical Behavior in Solid-State Sodium Sulfur Batteries

Abstract

Sodium-sulfur batteries are promising for grid energy storage applications thanks to their high theoretical capacity, their abundance in the Earth’s crust and raw materials being cost effective. Unfortunately, their practical application is limited by several technical challenges, especially polysulfide shuttling phenomenon and accompanied volume expansion, which can lead to serious capacity degradation [1]. In this case, solid-state sodium-sulfur battery (S4B) can effectively suppress the shuttle phenomenon [2]. However, the poor triple-phase contact among active material, solid electrolytes and electroconductive agent limits the battery performance. During cycling, the complete conversion of one mole S8 into eight mole Na2S expands its volume by 260 %, and contracts upon dissociation [1].This phenomenon causes the chemo-mechanical failure, results in contact lost within the cathode composite and decreases the reversible capacity. In contrast to solid-state Li-S batteries [3][4], the understanding in case of S4B is lacking. In this study, the battery using composite cathode preparing by ball milling achieved the first discharge capacity of 1640 mAh/g and 50 mA/g current density which is close to the theoretical capacity of sulfur. This is owing to the homogeneous distribution of sulfur within the electrode and intimate contact of sulfur, solid electrolyte, and conductive carbon. Upon cycling the chemo-mechanical impact on the global performance of S4B has been studied using operando XRD, SAXS, WAXS, and electrochemical dilatometry.