Electrochemical activity of Fe-MIL-100 as a positive electrode for Na-ion batteries

Abstract

Here we investigate the electrochemical activity of metal–organic frameworks (MOFs) as positive electrodes for Na-ion batteries in coin cell configurations. The performance of Fe-MIL-100 material is highly dependent on the choice of sodium salt source, and electrolyte system. The overall capacity fades over many cycles, however the high coulombic efficiency is maintained. This can be correlated with inaccessibility of active sites for Na intercalation, due to the increase of extra carbonaceous material inside the pores. Powder X-ray diffraction via synchrotron data and pair distribution function analyses of the as-made and cycled electrodes reveal the structure maintains the long-range order with progressive cycling. This finding suggests that careful consideration of all variables in battery components, and especially electrolyte selection can lead to greatly improved performances.