DFT Calculations of reaction energies and activation barriers were performed using DMol in Materials Studio at the m-GGA/TPSS level of theory. Reaction barriers were calculated using the doublynudged elastic band (DNEB) method as implemented in FlexTS/DMol 3 , with barrierless (E a = 0) reactions confirmed as such by observing a monotonically decreasing energy landscape along the reaction path. Calculations were run in a simulated solution-phase environment as implemented in COSMO, using the extrapolated dielectric constant for pure ethylene carbonate at 298 K of = 95.3. MD Simulations were run using Materials Studio Forcite 22 as a constant-number, -volume, and -temperature (NVT) ensemble, with an integration timestep of 1 fs and the temperature maintained at 298 K with a Berendsen thermostat. The COMPASSIII forcefield was used, with PPPM electrostatic summation. Geometry optimizations were also performed with Materials Studio Forcite. better performing simulations. Growth of a heterogeneous SEI structure that spans tens of nanometres is observed, in line with experimental findings.