Regulating Li₂S Deposition by Ostwald Ripening in Lithium-Sulfur Batteries

The lithium-sulfur (Li-S) batteries have attracted tremendous attention from both academia and industry for their high energy density and environmental benignity. However, the cell performance suffers from the passivation of the conductive matrix caused by uncontrolled lithium sulfide (Li₂S) deposition. Therefore, regulation of Li₂S deposition is essential to advanced Li-S batteries. In this work, the role of temperature in regulating Li₂S deposition is comprehensively investigated. At room temperature (25 °C), Li₂S exhibits a two-dimensional (2D) growth mode. The dense and insulating Li₂S film covers the conductive surface rapidly, inhibiting the charge transfer for subsequent polysulfide reduction. Consequently, the severe passivation of the conductive surface degrades the cell performance. In contrast, three-dimensional (3D) Li₂S is formed at a high temperature (60 °C) because of a faster Ostwald ripening rate at an elevated temperature. The passivation of the conductive matrix is mitigated effectively, and the cell performance is enhanced significantly, thanks to the formation of 3D Li₂S. Ostwald ripening is also valid for Li-S cells under rigorous conditions. The cell working at 60 °C achieves a high specific capacity of 1228 mA h g^-1 under the conditions of high S loading and a lean electrolyte (S loading = 3.6 mg cm^-2, electrolyte/sulfur ratio = 3 μL mg^-1), which is substantially higher than that at 25 °C. This work enriches the intrinsic understanding of Li₂S deposition in Li-S batteries and provides facile strategies for improving the cell performance under practical conditions.