Automatic Generation of Chemical Mechanisms for Electrochemical Systems: Solid Electrolyte Interphase Formation in Lithium Batteries

Electrolytes in many lithium ion batteries decompose
at the low
potentials near the anode. The decomposition products form a layer
termed the solid electrolyte interphase (SEI). The composition and
growth of the SEI layer significantly affect both the capacity fade
and safety of lithium ion batteries. However, SEI formation and growth
kinetics are not well understood. In this work, we present an extension
of the Reaction Mechanism Generator (RMG) software to automatically
generate mechanisms for SEI formation. We extend RMG’s solvation
correction framework to account for kinetic solvent effects and demonstrate
the accuracy of our technique. We calculate thermochemical parameters
for 252 species and rate coefficients for 69 reactions, most with
associated solvation corrections. This and additional quantum chemistry
data are used to extend RMG’s thermodynamic group additivity
and solute parameter estimation schemes to handle lithiated species
and add 14 new reaction families to RMG. RMG is additionally extended
to simulate electrocatalytic systems. Lastly, we demonstrate RMG on
the decomposition of acetonitrile and ethylene carbonate near a battery
anode. While this framework does not yet resolve individual ions,
as appropriate thermochemistry estimators are not available, and thus,
cannot yet resolve more complex electrochemical pathways, RMG is able
to generate reasonable pathways for SEI formation that match literature
pathways and products. In particular, RMG identifies a new important
reaction pathway that is not present in literature.