  Lithium ion batteries (LIB) can feature reactive anodes that operate at low
potentials, such as lithium metal or silicon, passivated by solid electrolyte
interphase (SEI) films. SEI is known to evolve over time as cycling proceeds.
In this modeling work, we focus on the stability of two main SEI components,
lithium carbonate (Li2CO3) and lithium ethylene dicarbonate (LEDC). Both
components are electrochemically stable but thermodynamically unstable near the
equilibrium Li+/Li(s) potential. Interfacial reactions represent one way to
trigger the intrinsic thermodynamic instability. Both Li(2)CO(3) and LEDC are
predicted to exhibit exothermic reactions on lithium metal surfaces, and the
barriers are sufficiently low to permit reactions on battery operation time
scales. LEDC also readily decomposes on high Li-content Li(x)Si surfaces. Our
studies suggest that the innermost SEI layer on lithium metal surfaces should
be a thin layer of Li(2)O -- the only thermodynamically and kinetically stable
component (in the absence of a fluoride source). This work should also be
relevant to inadvertant lithium plating during battery cycling, and SEI
evolution on Li(x)Si surfaces.
