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.