Comparative analyses of MIL-88B(Fe) and MIL-100(Fe) metal organic frameworks as active anode materials for Li ion batteries
D. Pukazhselvan, Carlos M. Granadeiro, Francisco J.A. Loureiro, A.L. Shaula, Sergey M. Mikhalev, Gil Gonçalves, Duncan P. Fagg
Abstract
Two Fe based metal organic framework (MOF) nanorod structures, MIL-88B(Fe) and MIL-100(Fe), were synthesized and their performance as working electrodes for Li ion half-cell batteries was evaluated under identical testing conditions. It was found that MIL-88B(Fe) provides a charge / discharge capacity of 468 mAh/g at the current density of 100 mA/g, which is over 3 times higher as compared to that of MIL-100(Fe) under the same conditions. Nevertheless, after an impressive charge / discharge capacity in the first few cycles, a slow capacity degradation was noticed in the case of the MIL-88B(Fe) material. Energy dispersive spectroscopy (EDS) and Fourier transform infrared (FTIR) spectroscopy results suggest that capacity degradation may be due to strained metal coordination in the MIL-88B(Fe) network. In contrast, despite moderate charge / discharge capacity such issues are identified to be minimal in the case of MIL-100(Fe). Electrochemical impedance spectroscopy (EIS) analyses suggest that ohmic and polarization resistance are smaller for MIL-88B(Fe) as compared to MIL-100(Fe) (both cycle 1 and 100). This makes MIL-88B(Fe) an attractive anode over MIL-100(Fe) for Li ion batteries, but stability issues remain a concern with MIL-88(B)Fe.