Quantitative Delineation of the Low Energy Decomposition Pathway for Lithium Peroxide in Lithium-Oxygen Battery.

Identification of a low-potential decomposition pathway for lithium peroxide (Li2O2) in nonaqueous lithium-oxygen (Li-O2) battery is urgently needed to ameliorate its poor energy efficiency. In this study, experimental data and theoretical calculations demonstrate that the recharge overpotential (η RC) of Li-O2 battery is fundamentally dependent on the Li2O2 crystallization pathway which is intrinsically related to the microscopic structural properties of the growing crystals during discharge. The Li2O2 grown by concurrent surface reduction and chemical disproportionation seems to form two discrete phases that have been deconvoluted and the amount of Li2O2 deposited by these two routes is quantitatively estimated. Systematic analyses have demonstrated that, regardless of the bulk morphology, solution-grown Li2O2 shows higher η RC (>1 V) which can be attributed to higher structural order in the crystal compared to the surface-grown Li2O2. Presumably due to a cohesive interaction between the electrode surface and growing crystals, the surface-grown Li2O2 seems to possess microscopic structural disorder that facilitates a delithiation induced partial solution-phase oxidation at lower η RC (<0.5 V). This difference in η RC for differently grown Li2O2 provides crucial insights into necessary control over Li2O2 crystallization pathways to improve the energy efficiency of a Li-O2 battery.