Smaller Sulfur Molecules Promise Better Lithium–Sulfur Batteries

TLDR

The lithium‑sulfur battery offers 4–5× the energy density of current lithium‑ion cells, but its practical use is limited by poor sulfur cathode conductivity and rapid capacity fade from soluble polysulfide intermediates. This study demonstrates that reducing sulfur to smaller allotropes can effectively mitigate these losses. Metastable S₂–S₄ molecules were synthesized within a conductive microporous carbon matrix, confining the sulfur species. The confined S₂–S₄ cathode eliminates the detrimental S₈→S₄(2–) transition, yielding Li‑S batteries with high specific capacity, excellent cycling stability, and superior rate capability, making them suitable for portable electronics, EVs, and large‑scale storage.

Abstract

The lithium-sulfur battery holds a high theoretical energy density, 4-5 times that of today's lithium-ion batteries, yet its applications have been hindered by poor electronic conductivity of the sulfur cathode and, most importantly, the rapid fading of its capacity due to the formation of soluble polysulfide intermediates (Li(2)S(n), n = 4-8). Despite numerous efforts concerning this issue, combatting sulfur loss remains one of the greatest challenges. Here we show that this problem can be effectively diminished by controlling the sulfur as smaller allotropes. Metastable small sulfur molecules of S(2-4) were synthesized in the confined space of a conductive microporous carbon matrix. The confined S(2-4) as a new cathode material can totally avoid the unfavorable transition between the commonly used large S(8) and S(4)(2-). Li-S batteries based on this concept exhibit unprecedented electrochemical behavior with high specific capacity, good cycling stability, and superior rate capability, which promise a practicable battery with high energy density for applications in portable electronics, electric vehicles, and large-scale energy storage systems.