Methanol–Li2S Multiplexing: A Mechanism for Suppressing Reaction Potential and Enhancing Cathode Stability in Lithium–Sulfur Batteries

Lithium sulfide (Li2S) is a cathode material with great potential to surpass the current lithium-ion technology, boasting a high specific capacity comparable to a typical lithium–sulfur battery and raising the cycling ability while being capable of mitigating safety concerns associated with lithium metal anodes. However, it suffers from a high first-charge overpotential, stemming from the strong ionic bonds that prevent lithium–sulfur dissociation. Dissolution with a fluid medium is a facile approach to raise the capacity utilization and suppress the reaction overpotential, often attributed to the refinement of particle size, where, nevertheless, the interaction between Li2S and commonly used alcohol solvent is often overlooked. This study highlights this critical aspect by examining the interactions between Li2S and methanol, revealing its multifunctional roles beyond a mere solvent. Li2S forms a multiplex with methanol in solution and remains stable through conventional drying, where the final products in conjunction can aid with the delithiation process significantly. Our results further show that when utilizing methanol, the first-charge overpotential of the Li2S cathode can be suppressed from 3.8 V to as low as 2.35 V, superior to those by various other methods, such as the particle engineering methods, which require higher energy input. Material characterization and electrochemical testing further demonstrate the great potential to control the drying of Li2S–methanol multiplexes to modulate the active material product during cathode fabrication, supported by simulation studies to present a comprehensive understanding of optimizing Li2S-based LSBs. The present study demonstrates a framework to engineer Li2S particles and their reaction not as a bulk material but on a molecular level.