The effect of sodium and niobium co-doping on electrochemical performance of Li4Ti5O12 as anode material for lithium-ion batteries

Na+- and Nb5+-co-doped Li3.98Na0.02Ti4.98Nb0.02O12 (NaNbLTO), the anode material for lithium-ion batteries, is synthesized by simple solid-state reaction route at 850 degrees C for 12 h. Na+ is introduced into the main structure to expand the lattice, while Nb5+ increases the electronic conductivity through the reduction of some of Ti4+ ions to Ti-3. The anode material is explored by X-ray diffraction (XRD), field emission scanning electron microscope (FESEM), and electric conductivity measurements. XRD patterns and FESEM images demonstrates that Na+ and Nb5+ co-doping do not alter the cubic spinel structure, the morphology, and the particle size of the Li4Ti5O12. Electric conductivity measurements reveal that the Na+- and Nb5+-co-doped NaNbLTO exhibits a higher electronic conductivity than the un-doped Li4Ti5O12 (LTO), Na+-doped Li3.98Na0.02Ti5O12 (NaLTO) and Nb5+ -doped Li4Ti4.98Nb0.02O12 (NbLTO). It is found that the discharge capacity of NaNbLTO is higher than those of the un-doped LTO, Na+-doped NaLTO, and Nb5+ -doped NbLTO at 0.1 C, 0.5 C, and 1.0 C current rates, which demonstrates the considerable synergic effect of Nb5+ and Na+ co-doping on improving the electrochemical performances of LTO. As evidence, NaNbLTO is a promising anode material for lithium-ion batteries.