Dual Functionalities of Rb Cation in Lean Electrolyte Lithium Sulfur Batteries

Abstract

Achieving large discharge capacity and high cycling stability under high sulfur loading and lean electrolyte condition is critical for practical lithium sulfur batteries. However, it is impeded by the large overpotential for lithium sulfide (Li2S) nucleation at the cathode, caused by the sluggish reduction kinetics of lithium polysulfide and the short-circuit triggered by inhomogeneous Li electroplating at the anode. In this study, we report that adding rubidium cation to lean electrolyte in an additive level (0.05 M) can address the two challenges owing to the modifications of the cathode and anode surfaces by the formation of rubidium sulfide. At the sulfur cathode, the rubidium sulfide acts as a catalyst, accelerating the reduction of lithium polysulfides. At the Li metal anode, a rubidium sulfide-enriched inner SEI quickly passivates the surface, suppressing electrolyte decomposition and promoting uniform lithium deposition due to its lithiophilicity. The drop-in-solution leads to impressive results, delivering more than 3 mAh cm−2 over approximately 80 cycles at a sulfur loading of 3.8 mgsulfur cm−2 and an electrolyte to sulfur ratio of 3 μl mg−1.