All geometry optimizations are performed at the ωB97X-D/def2-TZVP(-f) level of theory using Jaguar v11.4. The transition state (TS) of the EC decomposition pathway is obtained using the automatic transition state (AutoTS) search approach as detailed in Ref. 31. The transition states of the substituted ethylene carbonates (FEC and PC) are initially optimized with the eigenvector following method using ωB97X-D/6-31G* as a guess, followed by frequency analysis to verify the TS. Finally, these pre-optimized TS geometries were refined with eigenvector following utilizing ωB97X-D/def2-TZVP(-f). These geometries are used for all subsequent energy evaluations.