The importance of the solid–electrolyte interphase (SEI) for reversible operation of Li-ion batteries has been well established, but the understanding of its chemistry remains incomplete. The current consensus on the identity of the major organic SEI component is that it consists of lithium ethylene di-carbonate (LEDC), which is thought to have high Li-ion conductivity, but low electronic conductivity (to protect the Li/C electrode). Here, we report on the synthesis and structural and spectroscopic characterizations of authentic LEDC and lithium ethylene mono-carbonate (LEMC). Direct comparisons of the SEI grown on graphite anodes suggest that LEMC, instead of LEDC, is likely to be the major SEI component. Single-crystal X-ray diffraction studies on LEMC and lithium methyl carbonate (LMC) reveal unusual layered structures and Li+ coordination environments. LEMC has Li+ conductivities of >1 × 10−6 S cm−1, while LEDC is almost an ionic insulator. The complex interconversions and equilibria of LMC, LEMC and LEDC in dimethyl sulfoxide solutions are also investigated.
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Crystallographic data for the structures reported in this work have been deposited at the Cambridge Crystallographic Data Centre (CCDC) under deposition nos. CCDC 1847784 (LEMC) and CCDC 1847785 (LMC). Copies of the data can be obtained free of charge via www.ccdc.cam.ac.uk/structures. Data supporting the findings of this study are available within this paper and its Supplementary Information, and are available from the corresponding author upon reasonable request. The MAS NMR experimental and GIPAW calculated data for this study are provided as a supporting dataset from WRAP, the Warwick Research Archive Portal at http://wrap.warwick.ac.uk/120226.
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The authors thank the DOE for funding this research through the EFRC (NEES-II) and Energy Hub (JCESR). B.W.E. thanks J. Davis for many helpful discussions. A.M. thanks the University of Warwick for a Chancellor’s International Scholarship. The UK 850 MHz solid-state NMR Facility used in this research is funded by EPSRC and BBSRC, as well as the University of Warwick, including via part funding through Birmingham Science City Advanced Materials Projects 1 and 2 supported by Advantage West Midlands (AWM) and the European Regional Development Fund (ERDF). O.B. acknowledges support via NASA agreement NND16AA29I.
The authors declare no competing interests.
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Wang, L., Menakath, A., Han, F. et al. Identifying the components of the solid–electrolyte interphase in Li-ion batteries. Nat. Chem. 11, 789–796 (2019). https://doi.org/10.1038/s41557-019-0304-z
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