Lithium–sulfur (Li–S) batteries are drawing major attention for their extremely high theoretical energy density—but two persistent bottlenecks have kept real-world devices from performing reliably. Sulfur reduction reaction (SRR) kinetics are slow, and polysulfide “shuttle” arises when soluble lithium polysulfides dissolve and migrate between electrodes. Together, these effects drive rapid capacity fade, weak rate capability, and short cycle life.
A research team from Chongqing University, City University of Hong Kong, and the Hong Kong University of Science and Technology reports a route to address both problems at the interface level. Their strategy, described as an electron-injection-softened approach, reshapes the electronic structure of a sulfur host to enable an unusually smooth SRR—aiming for a near barrier-free conversion rather than the usual energy-limited liquid–solid transitions.
In conventional cells, S₈ reduction proceeds through multiple steps that pass through long-chain LiPS intermediates and end in insoluble Li₂S₂/Li₂S products. Because these transformations involve substantial energy barriers, LiPSs accumulate and shuttle more easily, intensifying performance losses. The key challenge is to regulate how LiPSs bind, activate, and convert on the cathode surface—fast enough to prevent their migration.
The researchers designed a Co₉S₈–Mn₃O₄@CNF architecture where electron injection from Co₉S₈ softens the Mn₃O₄ surface. This “softening” changes which orbital interactions dominate during contact with LiPSs. Based on HSAB theory, O atoms on softened Mn₃O₄ preferentially interact with Li atoms in LiPSs via hard-to-hard interactions, while Mn sites—enhanced by Co₉S₈ electron injection—promote soft-to-soft orbital interactions with sulfur-containing species.
The result is a cascaded conversion pathway in which LiPSs are driven toward Li₂S₂/Li₂S formation with far less resistance than in standard mechanisms. By bypassing the conventional barrier-limited liquid–solid transformation, the cathode accelerates interfacial electron transfer and reduces the time LiPSs remain soluble.
Electrochemical testing shows strong performance for the Co₉S₈–Mn₃O₄@CNF cathode, including an initial specific capacity of 761 mAh g⁻¹ at 5 C and stable cycling over 1000 cycles. The team further assembled a Li–S pouch cell delivering 2.22 Ah with an energy density of 389 Wh kg⁻¹ at a sulfur loading of 5.95 mg cm⁻², combining high areal capacity with excellent stability.
Beyond the device results, the work argues that electronic structure engineering can be used to directly control polysulfide chemistry at active sites. The authors suggest their interface modulation framework offers a general blueprint for designing next-generation electrochemical systems where reaction pathways and byproduct migration must be tightly managed.
Subject of Research: Lithium–sulfur batteries (SRR regulation via electron-injection-softened sulfur host)
Article Title: Nearly barrier-free cascaded sulfur reduction reaction realizes 2-Ah-level stable Lithium-sulfur pouch cell
News Publication Date: 26-Nov-2025
Web References: http://dx.doi.org/10.26599/NR.2025.94908170
References: 10.26599/NR.2025.94908170
Image Credits: Credit: Nano Research, Tsinghua University Press
Keywords
Lithium–sulfur batteries; sulfur reduction reaction; polysulfide shuttle; electron injection; electronic structure modulation; Co₉S₈–Mn₃O₄@CNF; HSAB theory; cascaded conversion; Li₂S₂/Li₂S
