Improving High-Rate and Long-Life Cycling of Li4Ti5O12 Anode by Dual Doping of Cd2+ and Ge4+

Abstract

A kinetically favored Cd²⁺ and Ge⁴⁺ dual-doped lithium titanate (Li₄Ti₅O₁₂) anode material is designed for lithium-ion batteries (LIBs). Rietveld refinement reveals that introducing a 0.05 wt.% of Cd²⁺ at Li(8a) and Ge⁴⁺ at Ti(16d) sites brings no structural change in the spinel Li₄Ti₅O₁₂. Scanning transmission electron microscopy (STEM) identifies Cd²⁺ and Ge⁴⁺ are homogenously doped in the Li₄Ti₅O₁₂ lattice. High-resolution powder diffraction (HRPD) confirmed that Cd²⁺ and Ge⁴⁺ doping in Li₄Ti₅O₁₂ brings expansion in the lattice, field emission scanning electron microscopy (FE-SEM) shows the reduction in the particle size due to of Cd and Ge in the LTO lattice, and X-ray photoluminescence spectroscopy (XPS) confirms the partial reduction of Ti⁴⁺ to Ti³⁺ ions on the surface of 0.05-Cd-Ge-LTO electrodes to the pristine LTO. Furthermore, the 0.05-Cd-Ge-Li₄Ti₅O₁₂ electrode exhibits a superior rate performance and delivers a discharge capacity of ≈169.1 mAhg⁻¹ at 0.1 current rates. It is worth mentioning that, the 0.05-Cd-Ge-Li₄Ti₅O₁₂ electrode brings outstanding cycling stability in Li⁺ half-cell, having a capacity retention of 98.79% after 300 cycles at 2C. This proves that dual-doping of Cd²⁺ at Li(8a) and Ge⁴⁺ at Ti(16d) sites in the Li₄Ti₅O₁₂ lattice is an effective approach to obtain superior electrochemical performance as anode material in LIBs.