In situ generated MWCNT-FeF3·0.33 H2O nanocomposites toward stable performance cathode material for lithium ion batteries

Abstract

A hydrated iron(III) fluoride (FeF3·0.33 H2O) and hydrated multi-walled carbon nanotubes-iron(III) fluoride (MWCNT-FeF3·0.33 H2O) composites were prepared by a simple two-step method. Firstly, a wet chemistry reaction between iron(III) nitrate nonahydrate (Fe(NO3)3·9H2O) and ammonium fluoride (NH4F). The thermal decomposition of the mixture in the absence and presence of MWCNTs at 200 °C under argon atmosphere forms FeF3·0.33 H2O and MWCNT-FeF3·0.33 H2O. Powder X-ray diffraction, Raman spectroscopy, and scanning electron microscopy confirmed the formation of both FeF3·0.33 H2O and MWCNT-FeF3·0.33 H2O composites, with well-distributed hexagonal shape structure with particle size ranging from 500 to 650 nm. Cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and galvanostatic charge discharge (GCD) were performed to test MWCNT-FeF3·0.33 H2O composite cathode in half-cell using Li metal as counter and reference electrode and 1 M LiPF6 in mixture of organic carbonate electrolyte. It was found that the battery delivers a constant voltage of 2.95 V. CV results showed that MWCNTs-FeF3·0.33 H2O composite exhibits reversible and reproducible electrochemical conversion reactions, and stabilized solid–electrolyte interface during cycling. GCD profile displayed an irreversible lithiation/delithiation processes in the first cycle due to the decomposition of the electrolyte and the formation of SEI. However, specific charge capacity was at around 498 mAh/g (greater than commercial lithium cobalt oxide cathodes ~ 140 mAh/g) after 50 cycles with an average Coulombic efficiency of 95%. The excellent electrochemical performance makes from MWCNTs-FeF3·0.33 H2O a good candidate cathode material to replace conventional materials for LIBs in applications requiring high energy density and long cycling stability.