RuO2/MnO2 Bifunctional Electrocatalysts Supported on CNT with Cathode-Separator monolith for Pragmatic Li-O2 Batteries: High-Rate and High-Areal-Capacity with Improved Cycle Life

Abstract

Though lithium-oxygen (Li-O2) batteries have very high energy density (about 3.5 kWh kg-1), many obstacles such as low energy efficiency, poor cycle performance and poor rate capability are exist to make Li-O2 batteries widely used. And these problems become severe especially at high areal mass loading. Now, researches were widely done in Li-O2 batteries field but most researches use low areal mass loading cathode. For practical usage of Li-O2 batteries, high areal capacity and mass loading are essential so many researches were unsuitable for commercialization. In this research, air cathode with high areal mass loading was fabricated and this cathode shows unprecedentedly high capacity at high rate along with long cycle life. A separator-carbon nanotube (CNT) monolith-type cathode was fabricated and high areal capacity was achieved, but the high overpotential and poor cycle performance make CNT-only separator monolith cathode unsuitable for pragmatic usage. So we adopted RuO2/MnO2 solid catalysts on the CNT (RMCNT), and sufficient cycle performance, low overpotential and high energy efficiency were obtained. RMCNT have catalytic effects in both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) and completely decompose Li2CO3 and LiOH which were byproducts that were made at discharge process and clogged surface of cathode. High mass loading, binder-free, intimate contact with separator, and most importantly, catalysts for reversibility were obtained by this separator-RMCNT monolith. Together, these features provide a remarkably long cycle life at unprecedentedly high capacity and high rate: 315, 45, and 40 cycles, with areal capacity limits of 1.5, 3.0, and 4.5 mAh cm− 2, respectively. At a rate of 1.5 mA cm− 2, Cycling is possible even at the curtailing capacity of 10 mAh cm− 2.