Stability of Solid Electrolyte Interphase Components on Lithium Metal and Reactive Anode Material Surfaces

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-4/Li(s) potential. Interfacial reactions represent one way to trigger the intrinsic thermodynamic instability. Both Li2CO3 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 LixSi surfaces. Our studies suggest that the innermost SEI layer on lithium metal surfaces should be a thin layer of Li2O, the only thermodynamically and kinetically stable component (in the absence of a fluoride source). This work should also be relevant to inadvertent lithium plating during battery cycling and SEI evolution on LixSi surfaces.