Dept. of Chemistry and Biochemistry and the Materials Science Program Seminar
- Friday, February 15, 2019 at 3:10pm
- Chemistry & Biochemistry Building, Byker - view map
Bryan Eichhorn from the Dept. of Chemistry and Biochemistry, University of Maryland, College Park, MD will present "Unravelling the Solid-Electrolyte-Interphase (SEI) Chemistry in Li-ion and Li-S Batteries."
The solid-electrolyte-interphase (SEI) that forms spontaneously between the electrode and electrolyte of virtually all organic-based batteries is critically important to battery function and stability but remains the least understood of all battery components. The role of stable SEIs for reversible operation of Li-ion batteries (LIBs) and the sulfur-based cathodes of Li-S batteries has been well-established, but their compositions and formation mechanisms are debated fiercely. The major organic SEI component of LIB anodes is believed by many to be lithium ethylene di-carbonate (LEDC), which is thought to have a high Li-ion conductivity but a low electronic conductivity thus protecting the Li/C electrode. Through comprehensive analysis of authentic and synthetic SEI components (single crystal and powder XRD, FTIR, elemental analysis, solid-state and liquid 1D and 2D NMR), we show that the previously synthesized “LEDC” chemical standards are actually lithium ethylene mono-carbonate (LEMC) which is most likely formed from a simple chemical pathway available in LIBs. Direct comparisons of authentic SEI grown on graphite anodes (1M LiPF6 in ethylene carbonate/dimethyl carbonate) suggest that LEMC, instead of LEDC, is likely the major SEI component. Single crystalline x-ray diffraction (XRD) studies on LEMC and LMC reveal unusual layered structures and Li+ coordination environments. LEMC has Li+ conductivities of above 10-6 S/cm similar to LiPON, while LEDC is almost an ionic insulator. The complex interconversions, equilibria and aggregation of LMC, LEMC and LEDC in dimethyl sulfoxide (DMSO) solutions are also briefly discussed. Surprisingly, the SEI layer in sulfur cathodes also consist of LEMC, which is formed by a completely different mechanism.
- Department of Chemistry and Biochemistry