W6+ & Br- codoped Li4Ti5O12 anode with super rate performance for Li-ion batteries

We report a novel Li4Ti5-xWxO12-xBrx (x = 0.025, 0.050 and 0.100) anode material simultaneously doped with W6+ and Br- ions prepared by a simple solid-state reaction in air, aiming to significantly improve electrical conductivity of Li4Ti5O12. Our theoretical calculation predicts that codoping with W6+ on the Ti4+ site and Br- on the O2- site can remarkably narrow down the band gap, and thus facilitate the electron transport in the lattice of LTO. The comparative experiments prove that W & Br-codoped LTO exhibits higher electrical conductivity compared with undoped LTO as expected, thus leading to improved rate capability and specific capacity. Particularly, Li4Ti5 xWxO12 xBrx (x = 0.05) exhibits the best rate capability and cycling stability with an outstanding capacity retention of 88.7% even at 10 C rate after 1000 cycles. This codoping strategy with high valence transition metal and halide ions holds promise to be applied to other insulating cathode materials suffering from inferior electrical conductivity.