Mesoporous beta-MnO2 Air Electrode Modified with Pd for Rechargeability in Lithium-Air Battery

The electrochemical performance and electrode reactions using ordered mesoporous beta-MnO2 modified with Pd as a cathode catalyst for rechargeable Li-air batteries was reported. Well-ordered mesoporous beta-MnO2 was prepared using mesoporous silica KIT-6 as a template under hydrothermal synthesis of Mn(NO3)(2) center dot H2O. The obtained mesoporous beta-MnO2 shows narrow pore size distribution of 1 nm. With the dispersion of small amounts of Pd to beta-MnO2, mesoporous beta-MnO2 exhibited a high initial discharge capacity of 817 mAh/g(-cat). with high reversible capacity. Charging potential is suppressed at 3.6 V vs. Li/Li+, which is highly effective for preventing the decomposition of organic electrolyte. The mesoporous beta-MnO2/Pd electrode shows good rate capability and cycle stability. Ex-situ and in-situ XRD results suggested that the observed capacity comes primarily from the oxidation of Li+ to Li2O2 followed by Li2O after discharge to 2.0 V vs. Li/Li+. Electron spin resonance measurements suggest that the formation of superoxide anion radicals contributs to the oxidation of Li+ and the radicals were recovered during charge. Ex-situ FTIR measurement suggested that no electrolyte decomposition was observed and no Li2CO3 was formed during discharge when ethylene carbonate (EC)-diethyl carbonate (DEC) (3:7), which is highly stable for Li-air battery, was used as the electrolyte. (C) 2011 The Electrochemical Society. [DOI: 10.1149/2.090112jes]