Mesoporous β-MnO₂ air electrode modified with pd for rechargeability in lithium-air battery

The electrochemical performance and electrode reactions using ordered mesoporous β-MnO₂ modified with Pd as a cathode catalyst for rechargeable Li-air batteries was reported. Well-ordered mesoporous β-MnO₂ was prepared using mesoporous silica KIT-6 as a template under hydrothermal synthesis of Mn(NO₃)₂H₂O. The obtained mesoporous β-MnO₂ shows narrow pore size distribution of 1 nm. With the dispersion of small amounts of Pd to β-MnO₂, mesoporous β-MnO₂ exhibited a high initial discharge capacity of 817 mAhg_-cat. with high reversible capacity. Charging potential is suppressed at 3.6 V vs. LiLi™, which is highly effective for preventing the decomposition of organic electrolyte. The mesoporous β-MnO₂Pd 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 Li₂O ₂ followed by Li₂O after discharge to 2.0 V vs. LiLi™. 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.