Metal-Organic Frameworks Triggered High-Efficiency Li storage in Fe-Based Polyhedral Nanorods for Lithium-ion Batteries

Recently, metal organic framework (MOF) nanostructures have been frequently reported in the field of energy storage, specifically for Li-io nor Na-ion storage. By inter-separating the active sites of metal cluster and organic ligands, MOF nanostructures are exceptionally promising for realizing fast ion exchange and high-efficiency transportation and addressing the intricate issues that the energyintensive Li-ion batteries have faced over many years. The related ion-storage mechanism remains to be explored. Is the traditional redox reaction mechanism operative for these nanostructure, as it is for transitional metal oxide? Herein, taking [Fe3O(BDC)(3)(H2O)(2)(NO3)] n (Fe-MIL-88B) as an example, an Febased metal organic polyhedral nanorods of MIL-88 B structure was designed as an anode for Li-ion storage. When tested at 60 mA g (1), the nanoporous Fe-MIL-88 B polyhedral nanorods retained a reversible capacity of 744.5 mAh g (1) for more than 400 cycles. Ex situ characterizations of the post-cycled electrodes revealed that both the transition metal ions and the organic ligands contributed to the high reversible specific capacity. The polyhedral nanorods electrodes held the metal-organic skeleton together throughout the battery operation, although in a somewhat different manner than the pristine ones. This further substantiated that some MOF nanostructures are more appropriate than others for stable lithiation/delithiation processes. State-of-the-art CR2032 full cells showed that a high capacity of 86.8 mAh g (1) that was retained after 100 cycles (herein, the capacity for the full cell was calculated based on both the weight of the anode and the cathode, and the charge-discharge rate was 0.25C), when commercial LiFePO4 powders were used as the cathode. (C) 2017 Elsevier Ltd. All rights reserved.