In situ synchrotron XRD and sXAS studies on Li-S batteries with ionic-liquid and organic electrolytes

Lithium-sulfur (Li-S) batteries are a promising technology capable of reaching high energy density of 500-700 Wh kg-1, however the practically achievable performance is still lower than this value. This hindrance can be attributed to a lack of understanding of the fundamental electrochemical processes during Li-S battery cycling, in particular the so-called redox shuttle effect which is due to the relatively high solubility of polysulfide intermediates in the electrolyte. Herein, the effects of LiNO3 as an additive as well as C4mpyr-based ionic liquids (ILs) in electrolyte formulations for Li-S cells are analysed using in situ X-ray powder diffraction (XRD) and ex situ soft X-ray absorption spectroscopy (sXAS) techniques. Whilst LiNO3 is known for its protective properties on the lithium anode in Li-S cells, our studies have provided further evidence for suppression of Li2S deposition when using LiNO3 as an additive, as well as affecting the solid electrolyte interphase (SEI) layer at a molecular level. Moreover, the detected sulfur species on the surface of the anode and cathode, after a few cycles are compared for IL and organic- based electrolytes.