The Nanoscale Structure of the Electrolyte-metal Oxide Interface

(a) Sketches of the molecular species comprising the LiPF6 in EC:DMC electrolyte that was investigated. (b) Comparison of the experiment (XRR, red) and simulation (MD, blue) electron density profiles for 0 M and 1 M LiPF6 in EC:DMC at the sapphire, and graphite interface, respectively. (c) Schematic illustration of the first layer molecular reorientation with increasing LiPF6 concentration.

Scientific Achievement

Observation of molecular layering and insight into Li-ion salt concentration dependence of molecular orientation at metal-oxide electrolyte interfaces relevant to Li-ion batteries.

Significance and Impact

Detailed understanding of the electrolyte-electrode interface and electric double layer in Li-ion batteries will inform strategies to mitigate capacity losses associated with interfaces and can help improve charging times in batteries.

Next steps are charged interfaces – understand  how electric field controls molecular organization (electrical double layer) and the initial formation and subsequent growth of the solid-electrolyte interface layer (reaction of electrolyte).

Research Details

  • Combined interface sensitive X-ray reflectivity (XRR) with molecular dynamics (MD) simulations to gain insight into the sapphire interface with Li-ion battery liquid electrolytes and found good agreement between experiment and simulation.
  • Observed layering of electrolyte molecules with molecules in the first interfacial layer aligned parallel to the interface.
  • Investigated how varying lithium hexafluorophosphate (LiPF6) salt concentrations in ethylene carbonate (EC) and dimethyl carbonate (DMC) impacted interfacial molecular organization.
  • With increasing LiPF6 concentration, found a reorientation of solvent molecules in the presence of ions.

DOI: 10.1039/C7EE02724A

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