Molecular Trends in the Oxidative H Abstraction of Organic Molecules on Oxide Surfaces: Implications for Electrolyte Reactivity at the Positive Electrode in Li-Ion Batteries

Oxidative degradation of carbonate solvents via C–H activation is observed on late transition metal oxide positive electrodes in Li-ion batteries. However, analogous reactivity of other classes of organic molecules on oxides is not well understood. Here, we used density functional theory calculations to show how C–H activation changes from deprotonation to oxidative hydrogen abstraction as the lattice oxygen activity increases by moving the Fermi level closer to the oxygen 2p-band center. By using a set of 23 small molecules with 50 nonequivalent C–H bonds, spanning a broad range of functional groups and substitutions, we show how relevant energies of the isolated molecules impact the driving force for degradation reactions at the surface of LiNiO2, an oxide with high lattice oxygen activity. We demonstrated that C–H bond oxidation free energy, measured as the free energy to substitute a C–H bond with a C–OH bond for the isolated molecule, is the descriptor with the most predictive power for the C–H activation driving force on an oxide with highly reactive lattice oxygen. Using this descriptor, we identified promising S- and F-containing compounds with enhanced stability toward C–H activation. These results pave the way for a rational design of novel electrolytes that minimize degradation and impedance growth of Ni-rich LiNixMnyCo1–x–yO2 (NMC) electrodes.