Designing with Li₂S in Lithium-Sulfur Batteries: From Fundamental Chemistry to Practical Architectures

Lithium-sulfur (Li-S) batteries deliver gravimetric energy densities considerably higher than those of conventional lithium-ion systems while relying on low-cost, earth-abundant materials. Despite decades of progress, their commercialization remains hindered by intrinsic challenges such as the insulating nature of sulfur and lithium sulfide (Li₂S), formation and dissolution of soluble polysulfides, and instability of lithium-metal anodes. Among these, the use of Li₂S as a pre-lithiated cathode has redefined the landscape of Li─S chemistry by offering a pathway toward lithium-free and anode-free architectures that are compatible with the existing manufacturing infrastructure. This perspective revisits the Li₂S electrochemistry from a conceptual and design standpoint. The perspective emphasizes multiscale strategies for atomic-level catalytic engineering, mesoscale electrode architectures, and electrolyte-interface control, which collectively determine Li₂S activation and reversibility. The perspective also examines emerging approaches that integrate Li₂S cathodes with graphite, silicon, and solid-state configurations to enable safe, high-energy, and manufacturable Li─S technologies. Finally, this perspective discusses the evolving roles of redox mediators, machine learning-based discovery, and sustainable synthesis in bridging the gap between laboratory breakthroughs and industrial viability. Collectively, these insights frame Li₂S not only as an alternative, cathode, but also as a platform for reimagining Li─S electrochemistry in the post-lithium-metal era.