Self-standing porous carbon electrodes mainly composed of mesopores with a three-dimensional hexagonal array exhibited superior lithium–oxygen battery performance under low electrolyte/areal capacity (E/C < 10 g A−1 h−1) conditions.

There is growing demand for practical implementation of lithium–oxygen batteries (LOBs) due to their superior potential for achieving higher energy density than that of conventional lithium‐ion batteries. Although recent studies demonstrate the stable operation of 500 Wh kg−1‐class LOBs, their cycle life remains fancy. For further improving the cycle performance of LOBs, the complicated chemical degradation mechanism in LOBs must be elucidated. In particular, the quantitative contribution of each cell component to degradation phenomenon in LOBs under lean‐electrolyte and high‐areal‐capacity conditions should be clarified. In the present study, the mass balance of the positive‐electrode reaction in a LOB under lean‐electrolyte and high‐areal‐capacity conditions is quantitatively evaluated. The results reveal carbon electrode decomposition to be the critical factor that prevents the prolonged cycling of the LOB. Notably, the carbon electrode decomposition occur during charging at voltages higher than 3.8 V through the electrochemical decomposition of solid‐state side products. The findings of this study highlight the significance of improving the stability of the carbon electrode and/or forming Li2O2, which can decompose at voltages lower than 3.8 V, to realize high‐energy‐density LOBs with long cycle life.

Lithium−oxygen batteries (LOBs) are promising nextgeneration rechargeable batteries due to their high theoretical energy densities. The optimization of the porous carbon-based positive electrode is a crucial challenge in the practical implementation of LOB technologies. Although numerous studies have been conducted regarding the relationships between LOB performance and the physicochemical properties of carbon electrodes, most of these studies evaluate the performances of the electrodes under unrealistic conditions with inappropriate technological parameters. In this study, we prepared carbon gel-based self-standing membranes as positive electrodes and evaluated their performances in LOBs under lean-electrolyte, high-areal-capacity conditions. We clarified the following three crucial points: (1) The nanometer-sized pores exhibited limited effects in improving the cycle performance, although they contributed in enhancing the discharge capacity. (2) The macro-sized pores displayed positive effects in enhancing the discharge capacity. (3) The crystallinity and/or surface functional groups influence the discharge potential and cycle life. The results of this study suggest the significance of controlling the physicochemical properties of a porous carbon-based positive electrode in preparing a LOB with a practically high energy density and an extended cycle life.