Journal
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
Volume 138, Issue 25, Pages 7918-7931Publisher
AMER CHEMICAL SOC
DOI: 10.1021/jacs.6b02882
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Funding
- Office of Vehicle Technologies of the U.S. Department of Energy under the Batteries for Advanced Transportation Technologies (BATT) Program [DE-AC02-05CH11231, 7057154]
- European Commission (EC)
- ERC [259619 PHOTO EM, 312483 ESTEEM2]
- Schiff Foundation
- nanoDTC Associate
- Weizmann Institute of Science - National Postdoctoral Award for Advancing Women in Science
- EU
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The solid electrolyte interphase (SEI) of the high capacity anode material Si is monitored over multiple electrochemical cycles by Li-7, F-19, and C-13 solid-state nuclear magnetic resonance spectroscopies, with the organics dominating the SEI. Homonuclear correlation experiments are used to identify the organic fragments -OCH2CH2O-, -OCH2CH2-, -OCH2CH3, and -CH2CH3 contained in both oligomeric species and lithium semicarbonates ROCO2Li, RCO2Li. The SEI growth is correlated with increasing electrode tortuosity by using focused ion beam and scanning electron microscopy. A two-stage model for lithiation capacity loss is developed: initially, the lithiation capacity steadily decreases, Li+ is irreversibly consumed at a steady rate, and pronounced SEI growth is seen. Later, below 50% of the initial lithiation capacity, less Si is (de)lithiated resulting in less volume expansion and contraction; the rate of Li+ being irreversibly consumed declines, and the Si SEI thickness stabilizes. The decreasing lithiation capacity is primarily attributed to kinetics, the increased electrode tortuousity severely limiting Li+ ion diffusion through the bulk of the electrode. The resulting changes in the lithiation processes seen in the electrochemical capacity curves are ascribed to non-uniform lithiation, the reaction commencing near the separator/on the surface of the particles.
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