Probing Electrochemical Cycling Stability of Li-ion Cathode Materials at Atomic-scale

Li-excess layered oxide high energy density materials are currently being considered as promising candidates for energy storage technologies in plug-in hybrid electric vehicles (PHEVs) or electric vehicles (EVs), owning to their high capacity (>250mAh/g), high energy density, and excellent safety.[1-3] Two major fundamental questions, however, must be resolved before their commercial implementation: one is the irreversible capacity loss during the first electrochemical charge and the other is the voltage decay after longtime cycling.[4] Much of the recent research focus has been devoted to addressing these two issues. Possible explanations for the observed performance loss have been proposed: the irreversible loss of oxygen from the structural lattice and surface phase transformations upon electrode/electrolyte reduction.[3,5] The underlying mechanisms controlling performance, however, are unclear due to a present lack of understanding of the material’s nm-scale characteristics.