Electrolyte Decomposition in Li-S Cells

Abstract

Li-S cells are attractive due to their high potential gravimetric energy density, but they achieve only low cycle numbers. A major reason for this is a continuous electrolyte decomposition during cycling. As low electrolyte/sulfur ratios are required for high gravimetric energy density, this electrolyte decomposition reduces the obtainable cycle number to below 50.  It is therefore extremely important to evaluate, reduce or ideally prevent this electrolyte decomposition by utilizing new electrolyte (additives), separators and protection layers. Applying in-situ mass spectroscopy, the electrolyte decomposition has been characterized for Li-S cells with lithium metal anode, silicon anode and carbon anode with various electrolyte compositions, electrodes and cycling parameters. Electrolyte cracking leads to gaseous substances, some of which are created continuously while others show a maximum depending on the state of charge. Standard ether-based Li-S electrolytes (e.g. DME:DIOX) are unstable with Li metal anodes and will always limit the obtainable cycle number unless further protection devices are applied.  The attached figure demonstrates specific gaseous substances created in a Li-S cell during cycling between 1.8-2.6 V at 0.6 mA/cm². Figure 1