Identification of lithium-sulfur battery discharge products through 6Li and 33S solid-state MAS and 7Li solution NMR spectroscopy

Li-6 and S-33 solid-state magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy was used to identify the discharge products in lithium-sulfur (Li-S) battery cathodes. Cathodes were stopped at different potentials throughout battery discharge and measured ex-situ to obtain chemical shifts and T-2 relaxation rates of the products formed. The chemical shifts in the spectra of both Li-6 and S-33 NMR demonstrate that long-chain, soluble lithium polysulfide species formed at the beginning of discharge are indistinguishable from each other (similar chemical shifts), while short-chain, insoluble polysulfide species that form at the end of discharge (Presumably Li2S2 and Li2S) have a different chemical shift, thus distinguishing them from the soluble long-chain products. T-2 relaxation measurements of discharged cathodes were also performed which resulted in two groupings of T-2 rates that follow a trend and support the previous conclusions that long-chain polysulfide species are converted to shorter chain species during discharge. Through the complementary techniques of 1-D Li-6 and S-33 solid-state MAS NMR spectroscopy, solution Li-7 and H-1 NMR spectroscopy, and T2 relaxation rate measurements, structural information about the discharge products of Li-S batteries is obtained. (C) 2014 Elsevier B.V. All rights reserved.