Rational design of protective In2O3 layer-coated carbon nanopaper membrane: Toward stable cathode for long-cycle Li-O-2 batteries

To date, lithium-oxygen batteries (LOBs) using porous carbon materials as the air cathode have been widely studied. However, a fundamental issue of carbon electrode still remains; the carbon surface is unstable and is highly reactive in contact with Li2O2, resulting in the formation of irreversible byproducts (e.g., Li2CO3). To address this issue, we investigated the use of surface protection layers for improving the cycling stability of porous carbon-based LOB cathode. We employed atomic layer deposition (ALD) for conformal coating of two types of overlayers (In2O3 and TiN), i.e., oxide and nitride thin film, on an electrospun carbon nanopaper (CNp) membrane. The LOB cell with In2O3-coated CNp exhibited much enhanced cycling performance (over 140 cycles) compared with pristine CNp and TiN-coated CNp as control samples (less than 60 cycles for both cases). To further improve cell efficiency by reducing overpotentials, the surface of In2O3-coated CNp electrode was functionalized by catalytic RuOx nanoparticles, which enables stable and complete discharging and recharging reactions below 4.2 V for an extended period of 165 cycles. Interestingly, after each discharge, nanosheet-like Li2O2 growth was observed on In2O3-coated CNps, which is advantageous for enhanced cycle life. This work demonstrates that use of a free-standing, high surface area carbon membrane, that is conformally encapsulated by a highly conductive and stable oxide protection layer, is essential for enhanced Li-O-2 cell performance by preventing direct contact between underneath carbon and electrolyte.