Study on the possibility of diagonal line rule in elemental doping effects in Li4Ti5O12 by mechanochemical method

Li4Ti5O12 (LTO) were doped with the same group element (Zr4+), diagonal elements (Nb5+ and W6+), and same period element (V5+) of titanium, respectively, to quantitative doping effect and explore the possibility of diagonal line rule in doping. It is conducive to synthesis doping Li4Ti5O12 with excellent properties by the ammonia-assisted mechanical ball-milling method (AAMBM). Through systematic experimental comparison, Li4Ti4.95Nb0.05O12 (LTNO) exhibits finer particle, higher specific surface area, narrower band gap, and more excellent electrochemical performance compared to others, since Nb and Ti have similar ion polarization ability, standard electrode potential, and the conjugable outer electron arrangement (Nb 4d45s1 whose 5 s electrons can be delocalized to d orbits to form half full orbit state). Particularly, LTNO shows the highest initial first discharged capability up to 151 mAh g−1 and the capacity retention of 90% at 5 C rate after 300 cycles, indicating both outstanding high-rate discharge performance and cycling stability. The doping factor was proposed to roughly quantify their doping effect of Zr4+, Nb5+, V5+, and W6+, by using the ratio of specific capacity values of doped LTO and pure LTO after 500 cycles at 5 C, which are 1.2, 1.86, 1.05, and 1.08, respectively.