Ultrathin Manganese-Based Metal-Organic Framework Nanosheets: Low-Cost and Energy-Dense Lithium Storage Anodes with the Coexistence of Metal and Ligand Redox Activities

We herein demonstrate the fabrication of Mn- and Ni-based ultrathin metal organic framework nanosheets with the same coordination mode (termed "Mn-UMOFNs" and "Ni-UMOFNs", respectively) through an expedient and versatile ultrasonic approach and scrutinize their electrochemical properties as anode materials for rechargeable lithium" batteries for the first time. The obtained Mn-UMOFNs with structure advantages over NiUMOFNs (thinner nanosheets, smaller metal-ion radius, higher specific surface area) exhibit high reversible capacity (1187 mAh g(-1) at 100 mA g(-1) for 100 cycles), excellent rate capability (701 mAh g(-1) even at 2 A g(-1)), rapid Li diffusion coefficient (2.48 X 10(-9) cm(2) s(-1)) and a reasonable charge discharge profile with low,average operating potential at 0.4 V. On the grounds of the low-cost and environmental benignity of Mn metals and terephthalic acid linkers, our Mn-UMOFNs show alluring promise as a low-cost high-energy anode material for delithiation chemistry of Mn-UMOFNs was unequivocally studied by a combination of magnetic measurements, electron paramagnetic resonance, and synchrotron-based soft X-ray spectroscopy (O K-edge and Mn L-edge) experiments, the results of which substantiate that both the aromatic chelating ligands and the Mn2+ centers participate in lithium storage.