Facilitating Kinetics by Multifunctional Solid-State Electrolyte in Lean-Electrolyte Lithium-Sulfur Batteries

Lithium-sulfur batteries are considered one of the promising next-generation rechargeable batteries due to their high theoretical specific capacity of 1675 mAh g^-1 and the use of low-cost sulfur. Considering practical aspects including cost and energy density, the electrolyte/sulfur (E/S) ratio should be decreased to less than 3 µL mg^-1. Under lean-electrolyte conditions, sulfur cathodes suffer from low ionic conductivity due to the high viscosity of the electrolyte, sluggish sulfur reaction kinetics, and poor infiltration of highly concentrated catholyte. This also induces poor cycle life because the irreversible insulating Li₂S can passivate the host materials and deteriorate the reactivity of active materials during cycling. Here, we propose a multifunctional sulfide-based solid electrolyte as an effective polysulfide catalyst for lean lithium-sulfur batteries. The superionic solid electrolyte Li₁₀GeP₂S₁₂ (LGPS) provides a lithium-transporting pathway in cathodes due to its higher ionic conductivity compared to that of highly concentrated liquid catholyte. Additionally, density functional theory (DFT) calculations show that LGPS has the ability to absorb polysulfide intermediates, providing an immobilizing effect. The solid electrolyte as a catalyst facilitates the process of solid-liquid-solid conversion including the nucleation and growth of Li₂S, thereby decreasing charge transfer resistance. The kinetically improved composite electrode shows a high areal capacity of 6.13 mAh cm^-2 with high sulfur loading of 8.1 mg cm^-2 and a low E/S ratio of 2.9 µL mg^-1. This work demonstrates that a superionic solid electrolyte used as a catalyst can enhance the kinetics of lean lithium-sulfur batteries through its catalytic effect and high ionic conductivity.