Li2S/C/SnS2 Composite-Based Cathode Material for Lithium-Sulfur Batteries

Abstract

The rapid developments in portable electronic devices, electric vehicles, and smart grids are driving the need for high-energy (>500 Wh kg−1) rechargeable batteries. Lithium-sulfur batteries (Li-S) are of interest due to their high theoretical energy density (2600 Wh kg−1 or 2800 Wh L−1), but their commercialisation is restricted by several technical challenges, including the use of the highly reactive lithium metal anode. Using Li2S as the cathode to couple with Li-free anodes, such as Si and intermetallic alloys, presents a realistic approach to avoiding the safety issues associated with metallic lithium. However, the low electrochemical activity of Li2S and the shuttling effect of lithium polysulfides (LiPS) prevent the realization of high capacity and good cyclic performance. The usual Li2S/carbon (C) composite cathode suffers gradual capacity fading over long-term cycling due to irreversible LiPS migration in lithium-sulfur batteries. Although the presence of C in the cathode composite provides a conductive path to utilize the active material, the irreversible migration of LiPS still exists. In this work, we introduce a polar SnS2 additive in the cathode composite (Li2S/C) via a highly scalable ball milling method to adsorb LiPS. The Li2S/C/SnS2 composite acts as a restriction for LiPS by chemisorption and provides a physical for LiPS shuttling. We have synthesized three types of cathode composites with different weight percentages of C and SnS2 while keeping the amount of Li2S constant, and studied their electrochemical performance in characteristic cells. We found that the Li2S/C(20%)/SnS2(5%) composite shows a high initial capacity of 711 mAh g−1 at 0.1C and retains a capacity of around 400 mAh g−1 after 100 cycles. In comparison, the Li2S/C(25%) composite delivered a capacity that was 100 mAhg−1 less than that of the Li2S/C(20%)/SnS2(5%) composite after 100 cycles. The approach and design presented in this work could lead to the development of effective shuttle suppression material additives for future Li-S.

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