Hye Ryung Byon1

1, KAIST, Daejeon, , Korea (the Republic of)

The rechargeable lithium-oxygen (Li-O2) battery, providing theoretically high specific-energy-density calculated as ~3 kWh kg-1cell, is a promising future energy storage system. However, the over-potential is considerably severe during charge due to difficulty of Li2O2 decomposition (Li2O2(s) = 2Li+ + O2(g) + 2e, Erev = 2.96 V vs. Li+/Li), which is one of the greatest challenges for implementation of practical battery systems. Much effort has been devoted by incorporation of metal oxide promoters and soluble redox mediator. However, these additive materials give rise to side reactions and require high cost. Here I present a new strategy for decrease in charge over-potential by tailoring carbon electrodes. The oxygen functional groups implemented in carbon electrodes allow for growth of conformal and amorphous Li2O2 film during discharge, which rapidly decomposes in the following charge. In contrast, seamless and graphitized carbon electrode provides crystalline Li2O2 requiring higher overpotential for decomposition. This result is attributed to O2 and LiO2 adsorption affinity with respect to surface property of carbon, determining nucleation and growth pathway of Li2O2 during discharge. Further, morphological and structural characteristics of Li2O2 may greatly affect its ionic and electronic conductivities, enabling facile decomposition of Li2O2 toward amorphous structure. This study gives insights into design of carbon electrode surface toward the enhancement of discharge capacity, charge potential and cycling stability. It also paves the way for improvement of Li-O2 cell performance in the absence of additional promoters.