  Oxidative decomposition of organic-solvent-based liquid electrolytes at
cathode material interfaces has been identified as a main reason for rapid
capacity fade in high-voltage lithium ion batteries. The evolution of "cathode
electrolyte interphase: (CEI) films, partly or completely consisting of
electrolyte decomposition products, has also recently been demonstrated to be
correlated with battery cycling behavior at high potentials. Using Density
Functional Theory (DFT) calculations, the hybrid PBE0 functional, and the (001)
surfaces of spinel oxides as models, we examine these two interrelated
processes. Consistent with previous calculations, ethylene carbonate (EC)
solvent molecules are predicted to be readily oxidized on the Li(x)Mn(2)O(4)
(001) surface at modest operational voltages, forming adsorbed organic
fragments. Further oxidative decompostion of such CEI fragments to release CO2
gas is however predicted to require higher voltages consistent with
Li(x)Ni(0.5)Mn(1.5)O(4) (LNMO) at smaller x values. We argue that multi-step
reactions, involving first formation of CEI films and then further oxidization
of CEI at higher potentials, are most relevant to capacity fade. Mechanisms
associated with dissolution or oxidation of native Li2CO3 films, which is
removed before the electrolyte is in contact with oxide surfaces, are also
explored.
