Structural and electrochemical properties of Gd-doped Li₄Ti₅O₁₂ as anode material with improved rate capability for lithium-ion batteries

Pristine and Gd-doped Li₄Ti₅O₁₂ (LTO) in the form of Li_4-x/3Ti_5-2x/3Gd_xO₁₂ (x = 0.05, 0.10 and 0.15) were prepared by a simple solid-state reaction in air. The structural and electrochemical properties of the as-prepared powders were characterized using X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS), scanning electron microscopy (SEM), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). XRD revealed that only a small amount of the dopant can enter the lattice structure of LTO; excessive addition beyond x = 0.10 resulted in a discrete Gd₂O₃ impurity phase. The Gd doping did not change the spinel structure and electrochemical reaction process of LTO. The average particle size of as-prepared samples ranged between 0.5 and 1.5 μm. The Gd-doped materials showed much improved rate capability and specific capacity compared with undoped LTO. In particular, Li_4-x/3Ti_5-2x/3Gd_xO₁₂ (x = 0.5) exhibited the best rate capability and cycling stability among all samples. Beyond this doping level, however, Gd₂O₃ impurity phase in the LTO led to adverse electrochemical performance. The rate capability of the anode material made from the modified powder is significantly improved when discharged at high current rates due to the reduced charge transfer resistance and fast lithium insertion/extraction kinetics.