Lithium-sulfur (Li-S) batteries are low cost and high energy density but face challenges including lithium polysulfide (LiPS) shuttling and high electrolyte consumption. Unlike the conventional dissolution-deposition reaction mechanism, the quasi-solid-solid sulfur reaction (QSSSR) can mitigate shuttling and reduces reliance on electrolyte volume. However, QSSSR suffers from sluggish sulfur reaction kinetics, leading to poor cycling stability and rate performance in Li-S batteries.

To address this, Associate Professor Yatao Liu from Beijing University of Chemical Technology, in collaboration with Prof. Quanquan Pang and Prof. Ruqiang Zou at Peking University, designed a novel electrolyte for Li-S batteries using cyclopentyl methyl ether (CPME) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) as the base electrolyte, with tetramethylthiuram monosulfide (BDTS) as an additive. The LiTFSI-CPME electrolyte is weakly solvating, significantly reducing LiPS solubility and enabling quasi-solid-solid sulfur reactions, thereby fundamentally suppressing LiPS shuttling. The lithium solvation structure contains abundant contact ion pairs (CIPs), promoting TFSI⁻ anion decomposition on the lithium surface to form an inorganic-rich SEI layer, effectively inhibiting lithium dendrite growth.

BDTS acts as a phase mediator, whose reduction products bind with quasi-solid-phase LiPS, enabling surface-localized solvation of LiPS to enhance their electrochemical activity. Under this mechanism, sulfur electrodes exhibit quasi-solid-solid reactions, while localized surface dissolution of LiPS ensures rapid reaction kinetics. Li-S batteries using the BDTS-LiTFSI-CPME electrolyte demonstrate exceptional cycling stability and rate capability, delivering a capacity of 494 mAh/g at 16C. The 2.4 Ah pouch cell achieves a high energy density of 331 Wh/kg.

Electrolyte design is critical to Li-S battery development. This work proposes an innovative strategy using CPME as the main solvent and LiTFSI as the salt to construct a weakly solvating electrolyte, while introducing BDTS as a functional phase mediator. This approach enables sulfur electrodes to undergo quasi-solid-solid reactions with localized LiPS dissolution at the surface, resolving sluggish kinetics and significantly improving electrochemical performance. Notably, BDTS as a phase mediator can be universally applied to other weakly solvating or sparingly solvating electrolytes to enhance sulfur reaction kinetics.

Figure 1. Electrolyte design for lithium-sulfur batteries, and schematics of the proposed surface-localized solvation-mediated QSSSR.

Reference: Liu, Y.; An, Y.; Fang, C.; Ye, Y.; An, Y.; He, M.; Jia, Y.; Hong, X.; Liu, Y.; Gao, S.; Hao, Y.; Chen, J.; Zheng, J.; Lu, Y.; Zou, R.; Pang, Q. Surface-localized phase mediation accelerates quasi-solid-state reaction kinetics in sulfur batteries. Nat. Chem. 2025, 17, 614–623. https://doi.org/10.1038/s41557-025-01735-w.

About Yatao Liu: Yatao Liu is an Associate Professor at the College of Chemical Engineering, Beijing University of Chemical Technology (Prof. Yunfeng Lu’s group). His research focuses on lithium-sulfur batteries, lithium-ion batteries, and sodium-ion batteries. He has published nearly 30 papers in journals including Nature Chemistry, Joule (2 papers), Advanced Materials, Advanced Energy Materials, and Advanced Science. He currently serves as a Youth Editorial Board Member for Exploration, Energy & Environmental Materials, and Carbon Neutralization. Students are welcome to join his team. Contact: liuyatao@buct.edu.cn.