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

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.