Critical Void Dimension of Carbon Frameworks to Accommodate Insoluble Products of Lithium-Oxygen Batteries.

Abstract

High-energy density lithium-oxygen batteries (LOBs) seriously suffer from poor rate capability and cyclability due to the slow oxygen-related electrochemistry and uncontrollable formation of lithium peroxide (Li2O2) as an insoluble discharge product. In this work, we accommodated the discharge product in macro-scale voids of a carbon-framed architecture with meso-dimensional channels on the carbon frame and open holes connecting the neighboring voids. More importantly, we found that a specific dimension of the voids guaranteed high capacity and cycling durability of LOBs. The best LOB performances were achieved by employing the carbon-framed architecture having voids of 0.8 μm size as the cathode of the LOB when compared with the cathodes having voids of 0.3 and 1.4 μm size. The optimized void size of 0.8 μm allowed only a monolithic integrity of lithium peroxide deposit within a void during discharging. The deposit was grown to be a yarn ball-looking sphere exactly fitting the shape and size of the void. The good electric contact allowed the discharge product to be completely decomposed during charging. On the other hand, the void space was not fully utilized due to the mass transfer pathway blockage at the sub-optimized 0.3 μm and the formation of multiple deposit integrities within a void at the sur-optimized 1.4 μm. Consequently, the critical void dimension at 0.8 μm was superior to other dimensions in terms of the void space utilization efficiency and the lithium peroxide decomposition efficiency, disallowing empty space and side reactions during discharging.