High-Performance Lithium-Sulfur All-Solid-State Batteries Enabled by Chemically Synthesized Lithium Polysulfide...

To achieve high specific energy and long lifespan in lithium-sulfur all solid-state batteries (Li-S ASSBs), it is pivotal to ensure high sulfur utilization and minimize volume change during cycling. In this work, we synthesize a partially lithiated sulfur material (S@Li₂S) by mechanical mixing sulfur with lithium sulfide (Li₂S). To our surprise, characterization techniques including Raman spectroscopy, solid-state nuclear magnetic resonance (ssNMR), and sulfur K-edge X-ray absorption near edge structure spectroscopy (XANES) reveal the formation of lithium polysulfide (Li₂S_n) species that can be stabilized at room temperature, previously thought to be unlikely in the solid-state. With enhanced reactivity, these lithium polysulfide cathode materials show much faster kinetics than S or Li₂S and are always present throughout the charge and discharge processes. Furthermore, molecular dynamics simulations indicate that different polysulfide species have similar densities. This explains the observed minimal volume change of S@Li₂S during cycling. Consequently, this cathode delivers a high specific capacity of 780 mAh g^-1, more than double that of sulfur (315 mAh g^-1), with an 85% capacity retention after 500 cycles. These mechanistic insights and cycling performance advancement contribute to the development of the high-performance, next-generation Li-S ASSBs.