Defect chemistry of alkali peroxides

O. Gerbig, R. Merkle

Solid Li2O2 forms as cathodic discharge product in the Li-O2-battery. Ionic and electronic transport and surface reaction determine the rate of formation/decomposition of Li2O2, potentially limiting the performance of such batteries. Generally, the defect chemistry of alkali and alkali earth peroxides is an unexplored field so far. The transport properties of Li2O2 and Na2O2 were investigated with a combination of ac impedance and dc polarization with selectively blocking electrodes. Li2O2 is found to be predominantly a Li ion conductor via lithium vacancies (Fig. 1(a)). Electronic transport proceeds via holes (strongly localized on a peroxide ion yielding superoxide species O2- as electronic defect centers). The semi-quantitative dependence of the relevant defect concentrations on pO2 is shown in Fig, 1(b), including defect interactions. Na2O2 exhibits a similar ionic conductivity, but significantly higher electronic conductivity (Fig. 1(c)).

Fig. 1: a): Ionic and electronic conductivity in Na2O2; (b) Kröger-Vink diagram for Li2O2 with donor-doping by impurities; (c) ionic and electronic conductivity in Na2O2.

Publications:

Oliver Gerbig , Rotraut Merkle , and Joachim Maier
Electron and Ion Transport In Li2O2
Adv. Mater. 25 (2013) 3129  DOI: 10.1002/adma.201300264

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