Nanostructured Conductive Metal Organic Frameworks for Sustainable Low Charge Overpotentials in Li–Air Batteries

Abstract

Lithium-oxygen batteries are among the most attractive alternatives for future electrified transportation. However, their practical application is hindered by many obstacles. Due to the insulating nature of Li₂ O₂ product and the slow kinetics of reactions, attaining sustainable low charge overpotentials at high rates becomes a challenge resulting in the battery's early failure and low round trip efficiency. Herein, outstanding characteristics are discovered of a conductive metal organic framework (c-MOF) that promotes the growth of nanocrystalline Li₂ O₂ with amorphous regions. This provides a platform for the continuous growth of Li₂ O₂ units away from framework, enabling a fast discharge at high current rates. Moreover, the Li₂ O₂ structure works in synergy with the redox mediator (RM). The conductivity of the amorphous regions of the Li₂ O₂ allows the RM to act directly on the Li₂ O₂ surface instead of catalyst edges and then transport through the electrolyte to the Li₂ O₂ surface. This direct charge transfer enables a small charge potential of <3.7 V under high current densities (1-2 A g^-1 ) sustained for a long cycle life (100-300 cycles) for large capacities (1000-2000 mAh g^-1 ). These results open a new direction for utilizing c-MOFs towards advanced energy storage systems.