Ultrathin Two-Dimensional Metal–Organic Framework Nanosheets with the Inherent Open Active Sites as Electrocatalysts in Aprotic Li–O₂ Batteries

Abstract

Ultrathin two-dimensional metal-organic frameworks (2D MOFs) have the potential to improve the performance of Li-O₂ batteries with high O₂ accessibility, open catalytic active sites, and large surface areas. To obtain highly efficient cathode catalysts for aprotic Li-O₂ batteries, a facile ultrasonicated method has been developed to synthesize three kinds of 2D MOFs (2D Co-MOF, Ni-MOF, and Mn-MOF). Contributing from the inherent open active sites of the Mn-O framework, the discharge specific capacity of 9464 mAh g^-1 is achieved with the 2D Mn-MOF cathode, higher than those of the 2D Co-MOF and Ni-MOF cathodes. During the cycling test, the 2D Mn-MOF cathode stably operates more than 200 cycles at 100 mA g^-1 with a curtailed discharge capacity of 1000 mAh g^-1, quite longer than those of others. According to further electrochemical analysis, we observe that the 2D Mn-MOF outperforms 2D Ni-MOF and Co-MOF due to a superior oxygen reduction reactions and oxygen evolution reactions activity, in particular, the efficient oxidation of both LiOH and Li₂O₂. The present study provides new insights that the 2D MOF nanosheets can be well applied as the Li-O₂ cells with high energy density and long cycling life.