The objectives of this proposal are to understand the reactions occurring at the electrode/electrolyte interphases in lithium-oxygen (Li-O2) batteries, and to investigate the transform mechanisms of lithium nickel manganese cobalt oxide (NMC) cathode materials for Li-ion batteries during synthesis processes. In nonaqueous Li-O2 batteries, recent reports indicated that the battery cycling can be performed via LiOH formation and decomposition by adding water and LiI as additives in electrolytes or through LiO2 by using Ir-decorated graphene electrode, both of which are different from the traditional pathway of formation of Li2O2. However, the proposed mechanism for cycling LiOH is not convincing and there is no direct experimental XRD evidence for LiO2. We also found that the temperature below and above 0 degrees C has significant effects on the discharge behaviors of the Li-O2 battery but the true mechanisms are unclear. Therefore, the investigations in Li-O2 batteries will be focused on (1) the mechanisms of oxygen reduction reaction (ORR) at the air electrode/electrolyte interphase in the temperature ranges below and above 0?C, (2) the effects of selected catalysts and moisture with and without LiI additive in electrolytes on ORR and oxygen evolution reaction (OER) at air electrode/electrolyte interphases and the cycling stability of related Li-O2 cells, and (3) the Li/electrolyte interphases during Li-O2 operations. In Li-ion batteries, the studies include (1) the phase transformation and Ni segregation in Li-rich Mn-rich (LMR) layered cathode materials during synthesis process to find out the Ni-segregation layer formation process, (2) the phase transformation mechanisms and morphological changes of Ni-rich LiNixMnyCozO2 (NMC) cathode materials during synthesis to find out the optimized calcination temperature for cathode materials synthesis, and (3) the conditions that the NMC particles start to form cracks and show deteriorated cycling stability when cycled to high voltages. All of the work is leveraged with the strong capabilities in PNNL including energy storage materials, characterizations and computational calculations.