| AVS 62nd International Symposium & Exhibition | |
| Surface Science | Monday Sessions |
| Session SS-MoA |
| Session: | Organics and Ionic Liquids: Surfaces, Layers, Interfaces and Chirality |
| Presenter: | Wentao Song, University of Maryland, College Park |
| Authors: | W. Song, University of Maryland, College Park J.E. Reutt-Robey, University of Maryland, College Park |
| Correspondent: | Click to Email |
The Solid Electrolyte Interphase (SEI) formed at the Li-ion battery (LIB) anode plays a major role in battery cycle life and safety. The ethylene carbonate (EC) electrolyte is known to undergo reduction to a mixture of lithium salts at the onset of SEI formation, but the product branching and sensitivity to electrode structure have not been determined. We report the use of temperature programmed desorption (TPD) and reaction spectroscopy (TPRS) to quantify interactions between the molecular carbonates, ethylene carbonate (EC) and dimethyl carbonate (DMC), and model Li- C(0001) anode surfaces prepared in situ. Both EC and DMC interact weakly with the clean C(0001) surface with adsorption energies of 0.60 ± 0.06 and 0.64 ± 0.05 eV, respectively. Submetallic lithiation of C(0001) significantly increases the binding energies of molecular carbonates, and the range of measured values indicates EC solvation of lithium ions. In the presence of metallic lithium, 1.5 monolayers of EC undergoes complete decomposition, resulting in 70.% organolithium products and 30% inorganic lithium product. Further structural analysis of the early stage organolithium salt, lithium ethylene dicarbonate (LEDC), was performed with UHV-STM. A pulsed microaerosol molecular beam source permitted controlled deposition of LEDC (from dimethyl formamide solvent) on Ag(111). Elongated LEDC monolayer islands spontaneously form in three distinct 120 degree rotational domains, all aligned with the close-packed silver direction. Further deposition increases island size and density, with little change in island shape. Molecularly resolved STM images reveal a LEDC monolayer structure with a 1.1874 ± 0.0079 nm x 0.5793 ±0.0055 nm unit cell containing one LEDC. A structural model is presented that accounts for the anisotropy of the LEDC islands. The O-Li-O linkages in the structural model define the long-axis (fast growth direction) of the islands. The LEDC islands are thermally stable up to at least 80°C, and can be imaged over days under UHV. Preliminary STS measurements (performed in Z-V mode) are consistent with significant differences in the local density of electronic states for LEDC islands relative to the Ag(111) substrate.