Ab initio characterization of the electrochemical stability and solvation properties of condensed-phase ethylene carbonate and dimethyl carbonate mixtures

Abstract

A central challenge in the refinement of lithium- ion batteries is to avoid cathode- induced oxidative decompn. of electrolyte solvents, such as ethylene carbonate (EC) and di-Me carbonate (DMC). We study the oxidn. potentials of neat EC, neat DMC, and 1:1 mixts. of EC and DMC using the newly developed projection- based embedding method, which we demonstrate to be capable of correcting qual. inaccuracies in the electronic densities and ionization energies obtained from conventional Kohn- Sham d. functional theory (DFT) methods. Our wavefunction- in- DFT embedding approach enables accurate calcn. of the vertical ionization energy (IE) of individual mols. at the CCSD(T) level of theory, while explicitly accounting for the solvent using a combination of DFT and mol. mechanics interactions. We find that the ensemble- averaged distributions of vertical IEs are consistent with a linear response interpretation of the statistics of the solvent configurations, enabling detn. of both the intrinsic adiabatic oxidn. potential of the solvents and the corresponding solvent reorganization energies. Interestingly, we demonstrate large contributions to the solvation properties of DMC from quadrupolar interactions, resulting in a much larger solvent reorganization energy than that predicted using dielec. continuum models. Demonstration that the solvation properties of EC and DMC are governed by fundamentally different intermol. interactions provides insight into key aspects of lithium- ion batteries, including electrolyte decompn. processes, solid- electrolyte interphase formation, and the local solvation environment of lithium cations.

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