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.