Transition Metal (Co, Ni, Fe) Selenides by Selenization of Gallic Acid based MOFs used as Na-Ion Battery Anodes

Abstract

Sodium-ion batteries (NIBs) are gaining momentum, thanks to the increasing demand for energy storage devices and the abundant reserves and low sodium cost. Transition metals are well-established materials due to their high conductivity and electrochemical activity. In this work, metal selenides (MSe_x) (M: Ni, Co, Fe) are obtained by facile selenization in a single step of transition gallic acid based metal organic frameworks (MOFs) under Ar flow at 600 °C. As the powders undergo selenization, the resulting MSe_x particles are encapsulated within the amorphous carbon network formed by the decomposition of the gallate ligand. The microstructures are examined by HR-TEM analyses and the characteristic interplanar spacing of each transition metal selenide is measured and found to coincide with the XRD pattern. Meanwhile, the specific surface areas were measured as 121, 152, and 155 m²/g for CoSe₂, NiSe and FeSe, respectively. The resulting NiSe/C, CoSe₂/C and FeSe/C nanomaterials are tested as NIB negative electrodes and are shown to have a capacity of 315, 312, and 363 mAh/g, respectively, after 100 cycles at a current density of 100 mA/g while Na-ion diffusion coefficients (D_Na+) are calculated in the range of 10⁻¹⁰–10⁻⁷ cm²/s by galvanostatic intermittent titration (GITT) technique.