Advanced Electrolyte and Electrode Enabling High Energy Lithium Sulfur Batteries

Currently, sulfur encapsulation in high surface area, nanoporous conducting carbon is the most widely studied approach to improve the cycling stability of Li-S batteries. However, the relatively large amount of high surface area carbon results in two fundamental problems with this approach. First, a large amount of electrolyte volume to sulfur (E/S) ratio (typically > 20 mlE/gs) is needed to fully wet the porous sulfur cathode. Second, the large amount use of high surface area carbon greatly decreases the overall energy density in the system, especially for volumetric energy density, and makes it difficult to compete with other battery technologies. Here, we found the E/S ratio plays a critical role in the cycling stability of Li-S batteries. Owing to the insulating nature of S/Li2S, lowering E/S ratio increases the charge carrier transfer resistance on the interface, causing poor rechargeability and sustainability of sulfur cathode. An ammonium-based electrolyte additive is identified to effectively address the passivation issue of Li2S under low E/S ratio. To further solve the critical passivation issue of cathode especially under lean electrolyte condition, we proposed a new approach that does not depend on the conventional sulfur encapsulation with high surface area carbon was proposed to reduce electrolyte absorption. The new approach generates a large spherical porous agglomerated particles with self-sustaining structures to avoid cathode passivation, leading ~100% sulfur utilization with good cycling (Nature Energy 2, 813, 2017).