Electrochemistry of lithium-oxygen batteries using microelectrode voltammetry

The electrochemistry of non-aqueous lithium-oxygen (Li-O2) batteries on both reduction and oxidation was investigated using carbon black and single-walled nanotube (SWNT) microcavity electrodes. Two oxidative peaks were observed on oxidation (charge). The first peak at 3.0-3.7 V vs. Li/Li+ was limited in storable charge (∼8 × 103 C cm−3). The oxidation potential of this first peak was independent of Li2O2 thickness (as measured by total charge on reduction) and assigned to interfacial Li2O2, lying between the bulk of the Li2O2 and the carbon surface. A second peak between 4.0 and 4.6+ V showed significant discharge product thickness dependence on oxidation potential and was assigned to bulk Li2O2, away from the carbon surface. On reduction (discharge), deposition of the interfacial Li2O2 showed a significant overpotential indicated by the ratio of interfacial/bulk Li2O2 formed at varying reduction potentials. SWNT were shown to effectively decrease the Li-O2 average charge overpotential for a given charge by increasing the electrode surface area available for formation of interfacial discharge products.