Accurate Quantum Chemical Reaction Energies for Lithium-Mediated Electrolyte Decomposition and Evaluation of Density Functional Approximations

An important concern related to the performance of Li-ion
batteries
is the formation of a solid electrolyte interphase on the surface
of the anode. This film is formed from the decomposition of electrolytes
and can have important effects on the stability and performance. Here,
we evaluate the decomposition pathway of ethylene carbonate and related
organic electrolyte molecules using a series of density functional
approximations and correlated wave function (WF) methods, including
the coupled-cluster theory with single, double, and perturbative triple
excitations [CCSD(T)] and auxiliary-field quantum Monte Carlo (AFQMC).
We find that the transition state barrier associated with ring opening
varies widely across different functionals, ranging from 3.01 to 17.15
kcal/mol, which can be compared to the value of 12.84 kcal/mol predicted
by CCSD(T). This large variation underscores the importance of benchmarking
against accurate WF methods. A performance comparison of all of the
density functionals used in this study reveals that the M06-2X-D3
(a meta-hybrid GGA), CAM-B3LYP-D3 (a range-separated hybrid), and
B2GP-PLYP-D3 (a double hybrid) perform the best, with average errors
of about 1.50–1.60 kcal/mol compared to CCSD(T). We also compared
the performance of the WF methods that are more scalable than CCSD(T),
finding that DLPNO–CCSD(T) and phaseless AFQMC with a DFT trial
wave function exhibit average errors of 1.38 and 1.74 kcal/mol, respectively.