NSLS-II Friday Lunchtime Seminar

The demands on low cost and high energy density rechargeable batteries for both transportation and large-scale stationary energy storage are stimulating more research toward new battery systems such as metal, metal-sulfur, metal-air, and multivalent batteries. Since sulfur is an earth-abundant material with low cost and has a high theoretical capacity, Li-S battery chemistry has attracted significant interest during the past decade. The Li-S battery utilizes electrochemical conversion of sulfur (S8) to lithium sulfide (Li2S), going through multiple electron transfer processes associated with long- and short-chain polysulfide (Li2Sx) intermediates. It is well known that the long-chain polysulfides can be dissolved into electrolyte with aprotic organic solvents and migrated to the Li anode side. This so-called "shuttle effect" is considered as the main reason for the capacity loss and low coulombic efficiency of the Li-S system. A lot of efforts have been made on how to overcome the problem of polysulfide dissolution through new sulfur-based material and electrolyte, as well as cell engineering. Sulfurized polyacrylonitrile (SPAN) is a promising material capable of suppressing polysulfide dissolution in Li-S batteries with carbonate-based electrolytes. However, undesirable spontaneous formation of soluble polysulfides may arise in the ether-based electrolyte, and the conversion of sulfur in SPAN during the lithiation/delithiation process is yet to be understood clearly. In this talk, our recent characterization study on the SPAN cathode material in Li-S battery using spatially-resolved X-ray fluorescence (XRF) microscopy combined with X-ray absorption spectroscopy (XAS) will be present. The morphology changes and the redistribution of sulfur and polysulfide in both the SPAN cathode and lithium metal anode were monitored through the XRF images, while the chemical state changes of SPAN and sulfur-containing interfacial layer (i.