Au-nanocrystals-decorated δ-MnO2 as an efficient catalytic cathode for high-performance Li-O2 batteries.

A Li-O2 battery works based on the reversible formation and decomposition of Li2O2, which is insulating and highly reactive. Designing a catalytic cathode capable of controlling Li2O2 growth recently became a challenge to overcome this barrier. In this work, we present a new design of catalytic cathode by growing porous Au/δ-MnO2 electrocatalyst directly on a conductive substrate. We found that Au/δ-MnO2 can catalyze the directed growth of Li2O2 into a thin/small form, only inside porous δ-MnO2, and along the surface of δ-MnO2 sheets. We proposed the catalytic mechanism of Au/δ-MnO2, where Au plays a critical role in catalyzing the nucleation, crystallization and conformal growth of Li2O2 on δ-MnO2 sheets. Li-O2 batteries with an Au/δ-MnO2 catalytic cathode showed excellent electrochemical performance due to this favorable Li2O2 growth habit. The battery yielded a high capacity of 10,600 mA h g(-1) with a low polarization of 0.91 V at 100 mA g(-1). Superior cycling stability could be achieved in both capacity-limited (500 mA h g(-1), 165 times at 400 mA g(-1)) and unlimited (ca. 3000 mA h g(-1), 50 cycles at 800 mA g(-1)) modes.