Molten salt synthesis of nano-sized Li4Ti5O12 doped with Fe2O3 for use as anode material in the lithium-ion battery

Abstract

A single-phase Li₄Ti_5−xFe_xO₁₂ (x = 0, 0.1, 0.2, 0.3) with spinel structure has been synthesized in LiCl–KCl molten salts with a stoichiometric molar ratio of 4 : 5 : x/2 : 20 LiOH·H₂O, TiO₂, Fe₂O₃, LiCl–KCl (x = 0, 0.1, 0.2, 0.3). The effects of Fe₂O₃ on the phase structure, morphology and particle size of Li₄Ti₅O₁₂ were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscope (TEM) equipped with energy dispersive spectroscope (EDS). The electrochemical performances of the Li₄Ti_5−xFe_xO₁₂ were characterized by charge/discharge curves, electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). The results show that Fe₂O₃ homogenously distributes in the crystal lattice of Li₄Ti₅O₁₂ and slightly increases the lattice parameters due to Fe³⁺ ion doping. The addition of 0.1 molar ratio Fe₂O₃ to Li₄Ti₅O₁₂ reduced the average particle size of Li₄Ti₅O₁₂ from 1 μm to about 200 nm. The obtained Li₄Ti_4.8Fe_0.2O₁₂ was used as anode material for a lithium-ion battery, presenting the capacity of 173.7 mA h g⁻¹ at 0.2 C—approaching the theoretical capacity of Li₄Ti₅O₁₂ (175 mA h g⁻¹)—and giving a capacity of 103.4 mA h g⁻¹ at 10 C, much larger than the value of pure Li₄Ti₅O₁₂ (28.7 mA h g⁻¹). This is well explained by the EIS and CV results.