Enhanced electrochemical properties of Mg2+ doped Li2Na2Ti6O14 anode material for lithium-ion batteries

A series of Mg2+ doped Li2Na2Ti6O14 in the form of Li2-xMgxNa2Ti6O14 (x = 0.0, 0.05, 0.1, 0.15, 2.0) are successfully synthesized via a solid-state method. Phase structure and surface morphology analyses show that all samples maintain high purity and low dose of Mg2+ doping does not change the crystal structure and surface morphology of Li2Na2Ti6O14. According to the Rietveld refinement result, it is known that Mg2+ takes the tetrahedral 8i sites shared with Li+ in the structure. Galvanostatic charge/discharge tests demonstrate that Li1.95Mg0.05Na2Ti6O14 exhibits higher reversible capacity (264.6 mAh g (1)) and better cycling performance (capacity retention of 82.7% after 50 cycles) than other materials. Even cycled at high current density of 500 mA g (1), Li1.95Mg0.05Na2Ti6O14 still provides the specific capacity of 167.4 mA g (1) after 100 cycles, indicating that low dose of Mg2+ doping can effectively improve the lithium storage capability of Li2Na2Ti6O14. The enhanced electrochemical properties are contributed to the improved electronic conductivity and ionic diffusion coefficient of Li2Na2Ti6O14 via Mg2+ doping. Besides, the lithiation/delithiation behavior of Li1.95Mg0.05Na2Ti6O14 is also studied by homemade in-situ X-ray diffraction device, which reveals that Li1.95Mg0.05Na2Ti6O14 exhibits high structural and electrochemical reversibility as lithium storage material. (C) 2016 Elsevier Ltd. All rights reserved.