Unsaturated coordination modulation and enlarged pore size in nanoflower-like metal organic frameworks for enhanced lithium–oxygen battery performance

Abstract

Lithium–oxygen batteries (LOBs) have very high energy density, but reversibility and high capacity are difficult to achieve due to sluggish cathode dynamics. Efficient cathodic catalysts are an effective means to solve this problem. Metal–organic framework (MOF) catalysts cannot function well due to the narrow orbital arrangement of metal sites, resulting in weak orbital coupling with oxygen species. Selectively changing the metal nodes can modulate the electronic structure of MOFs and thus improve the catalytic activity, besides the enlarged pore size of MOFs also contributes to ion transfer and oxygen transport. Here, nanoflower-like Ni-MOFs were designed and Co ions were introduced into their skeleton while increasing the pore size to 1.65 times of the original. The introduction of Co ions altered the adsorption of LiO₂ intermediates, which led to the generation of part of the discharge products of the CoNi-MOF electrodes in a solution pathway to increase the specific capacity of the discharge (15 784.2 mA h g⁻¹). Furthermore, the Co-active sites played a significant role in facilitating the breakdown of Li₂O₂ throughout the oxygen evolution reaction (OER) process. On the other hand, the increase in pore size alleviated the clogging of the pores of the MOFs and thus prolonged the cycle life (186 cycles) under a specific capacity limit of 600 mA h g⁻¹ at a current of 500 mA g⁻¹. This work will provide new insights into the design of MOF-based electrocatalysts to address the sluggish cathode kinetics of LOBs and other air batteries.