Cd-Doped Li_4-xCd_xTi₅O₁₂ (x = 0.20) as a High Rate Capable and Stable Anode Material for Lithium-Ion Batteries

Li₄Ti₅O₁₂ (LTO), an excellent anode for lithium-ion batteries (LIBs), suffers from low electronic conductivity, limiting its high-power rate application. An aliovalent metal ion doping strategy that tunes the electronic/ionic conductivity can mitigate this issue. In this work, we investigated a series of Cd²⁺ dopings on the Li_4-xCd_xTi₅O₁₂ (x = 0, 0.05, 0.10, and 0.20) anode material by considering its effect on structural and electrochemical performance in Li- and Na-ion batteries. Combined Rietveld refinement and X-ray absorption spectroscopy (XAS) analysis explicitly identified Cd²⁺ doping into the Li(8a) tetrahedral site of the cubic spinel LTO structure. According to high-resolution powder diffraction (HRPD), scanning electron microscopy (SEM), 4-point probe, and X-ray photoelectron spectroscopy (XPS), an increase in Cd²⁺ doping from 5 to 20% at the Li (8a) site in the LTO results in a reduction in particle size, an expansion of lattice, an increase in conductivity, and an increase in Ti³⁺ content to Ti⁴⁺ ratio. High-resolution scanning transmission electron microscopy (HR-STEM) confirms that cadmium ions are interstitially doped in the LTO structure. Compared to the pristine LTO electrode in the Li half cell, the Li_3.80Cd_0.20Ti₅O₁₂ (Cd0.20-LTO) electrode showed a significant improvement in capacity at high rates and excellent cycling performance. The improvement in performance for Cd0.20-doped LTO is a consequence of the reduction in the diffusion path and the faster Li-ion kinetics. Therefore, this Cd-doped LTO series of electrodes demonstrates advantageous features for Li-ion battery systems.