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Issue 8, 2013
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Influence of Li2O2 morphology on oxygen reduction and evolution kinetics in Li–O2 batteries

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Abstract

Understanding the origins of high overpotentials required for Li2O2 oxidation in Li–O2 batteries is critical for developing practical devices with improved round-trip efficiency. While a number of studies have reported different Li2O2 morphologies formed during discharge, the influence of the morphology and structure of Li2O2 on the oxygen evolution reaction (OER) kinetics and pathways is not known. Here, we show that two characteristic Li2O2 morphologies are formed in carbon nanotube (CNT) electrodes in a 1,2-dimethoxyethane (DME) electrolyte: discs/toroids (50–200 nm) at low rates/overpotentials (10 mA gC−1 or E > 2.7 V vs. Li), or small particles (<20 nm) at higher rates/overpotentials. Upon galvanostatic charging, small particles exhibit a sloping profile with low overpotential (<4 V) while discs exhibit a two-stage process involving an initially sloping region followed by a voltage plateau. Potentiostatic intermittent titration technique (PITT) measurements reveal that charging in the sloping region corresponds to solid solution-like delithiation, whereas the voltage plateau (E = 3.4 V vs. Li) corresponds to two-phase oxidation. The marked differences in charging profiles are attributed to differences in surface structure, as supported by X-ray absorption near edge structure (XANES) data showing that oxygen anions on disc surfaces have LiO2-like electronic features while those on the particle surfaces are more bulk Li2O2-like with modified electronic structure compared to commercial Li2O2. Such an integrated structural, chemical, and morphological approach to understanding the OER kinetics provides new insights into the desirable discharge product structure for charging at lower overpotentials.

Graphical abstract: Influence of Li2O2 morphology on oxygen reduction and evolution kinetics in Li–O2 batteries

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Publication details

The article was received on 24 Mar 2013, accepted on 22 May 2013 and first published on 22 May 2013


Article type: Paper
DOI: 10.1039/C3EE40998H
Citation: Energy Environ. Sci., 2013,6, 2518-2528
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    Influence of Li2O2 morphology on oxygen reduction and evolution kinetics in Li–O2 batteries

    B. M. Gallant, D. G. Kwabi, R. R. Mitchell, J. Zhou, C. V. Thompson and Y. Shao-Horn, Energy Environ. Sci., 2013, 6, 2518
    DOI: 10.1039/C3EE40998H

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