Unveiling the Synergic Roles of Mg/Zr Co-Doping on Rate Capability and Cycling Stability of Li4Ti5O12

Li4Ti5O12 (LTO) has attracted great interest as an anode material due to the zero strain during Li+ insertion and extraction. But the intrinsic ionic diffusion coefficient and electronic conductivity are very poor. Herein, a strategy of Mg2+ and Zr4+ co-doping has been proposed to modulate the crystal structure and improve the electrochemical performances. More importantly, the synergic roles of Mg/Zr co-doping has been unveiled based on the analysis of X-ray diffraction, Neutron powder diffraction, X-ray photoelectron spectroscopy, and electrochemical measurements. Firstly, Mg-Zr co-doping expands the lattice parameter, cell unit volume and even Li-O bond length, which reduces Li+ migration barrier and benefits to Li+ insertion/extraction. Secondly, Ti-O shrinkage induced by Mg-Zr co-doping enhances the structure stability and subsequently the cycle performance. Thirdly, Mg-Zr co-doping promotes more Ti4+/Ti3+ which facilitates electron conductivity. Moreover, Mg-Zr co-doping also decreases the polarization and charge transfer impedance. Li3.8Mg0.2Ti4.9Zr0.1O12 delivers a discharge capacity of 180.5, 150.7, 110.4 and 78.9 mAh/g at 0.2C, 1C, 5C and 10C, respectively. Moreover, the capacity retention is greatly increased from 57.9% of LTO to 98.59% at 10C after 500 cycles. (C) 2019 The Electrochemical Society.