Journal
JOURNAL OF PHYSICAL CHEMISTRY C
Volume 116, Issue 46, Pages 24476-24481Publisher
AMER CHEMICAL SOC
DOI: 10.1021/jp3086304
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Funding
- Fluid Interface Reactions, Structures and Transport (FIRST) Center, an Energy Frontier Research Center
- U.S. Department of Energy, Office of Science, Office of Basic Energy
- Office of Science of the U.S. Department of Energy [DE-AC02-05CH11231]
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Understanding the nature and formation of the solid electrolyte interphase (SEI) formed in electrochemical storage devices, such as Li-ion batteries, is most important for improving functionality. Few experiments exist that adequately probe the SEI, particularly in situ. We perform predictive ab initio molecular dynamics simulations of the anode electrolyte interface for several electrolytes and interface functionalizations. These show strongly differing effects on the reducibility of the electrolyte. Electrolyte reduction occurs rapidly, on a picosecond time scale. Orientational ordering of electrolyte near the interface precedes reduction. The reduced species depend strongly on surface functionalization and presence of LiPF6 salt While LiPF6 salt in ethylene carbonate is more stable at a hydrogen-terminated anode, oxygen/hydroxyl termination causes spontaneous dissociation to form LiF and other fluorophosphates. LiF migrates to the interface creating chainlike structures, consistent with experimental observations of LiF agglomeration. Inorganic products such as LiF and Li2CO3 migrate closer to the anode than purely organic components, consistent with their more ionic character. Significantly, we conclude that while the electrolyte reduction occurs at the molecular level near the interface, requiring specific alignments and proximity, the reducibility is governed by the average reduction potential barrier between the electrode (anode) and the electrolyte.
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