Chemical and Morphological Changes of Li–O2 Battery Electrodes upon Cycling

We report considerable chemical and morphological changes of reaction products in binder-free, vertically aligned carbon nanotube (VACNT) electrodes during Li–O 2 battery cycling with a 1,2-dimethoxyethane (DME)-based electrolyte. X-ray absorption near edge structure (XANES) of discharged oxygen electrodes shows direct evidence for the formation of Li 2 CO 3 -like species at the interface between VACNTs and Li 2 O 2 but not significantly on the Li 2 O 2 surfaces exposed to the electrolyte. Although Li 2 O 2 and Li 2 CO 3 -like species were largely removed upon first charge, the oxidation kinetics became increasingly difficult during Li–O 2 cycling, which is accompanied by the accumulation of Li 2 CO 3 in the discharged and charged electrodes as evidenced by selected area electron diffraction (SAED) and transmission electron microscopy (TEM). Together, these results indicate that the irreversibility during Li–O 2 cycling in DME can be attributed largely to the growth of Li 2 CO 3 -like species associated with the reactivity between carbon and Li 2 O 2 or other reaction intermediates.