Investigation into the Solvation of Lithium Anions and the Search for a Connection with Electrode Passivation Behavior

Tuesday, May 13, 2014: 11:40
Bonnet Creek Ballroom I, Lobby Level (Hilton Orlando Bonnet Creek)
A. V. Cresce, K. Xu, S. M. Russell (U.S. Army Research Laboratory), N. Urban (US Army Research Laboratory), and E. Wikner (Wake Forest University)

Recently published studies have shown that there is a complex relationship between a lithium ion and its solvent molecules in  two-solvent electrolyte systems. Cyclic carbonates like ethylene carbonate are stable in the Li+ solvation sheath while linear carbonates like dimethyl carbonate move in and out frequently, reflecting a difference in coordinating stability with Li+. Because of this bias in Li+ coordinating ability, a correlation can be drawn between the composition of the Li+solvation sheath and the resulting composition of the passivating solid electrolyte interphase that forms on the graphitic anode of a Li-ion battery during the first charge.

We are investigating the solvation condition of the anion in the Li-ion electrolyte system with the goal of identifying a potential correlation between the solvation condition of the anion (including PF6-, BF4-, ClO4-, and TFSI-) and the formation and composition of a cathode passivation layer.

Our previous work indicated that although typical electrolyte anions are poorly coordinated, both PF6- and BF4- showed a preference for the low-permittivity linear carbonate ethyl methyl carbonate over the high-permittivity solvent ethylene carbonate. The PF6-results are summarized in Fig. 1. This result spurred further investigation into the solvation condition of the anion, accomplished using electrospray mass spectrometry, linear voltammetry, x-ray photoelectron spectroscopy, and density functional theory simulations of anion-solvent cluster stability.

We will attempt to show a correlation between the stability of anion-solvent clusters with the composition and formation of the cathode interphase layer.