Enhancing the rate performances of Li4Ti5O12 by Mo4+ doping and MoO2-Mo dispersed on the surface

Abstract

Li4Ti5O12 is considered as a promising anode material because of its high safety and excellent cycling stability. However, its practical application is limited due to the poor rate performances. This problem can be effectively compensated by introducing highly conductive materials and/or doping. Herein, Mo4+ doped Li4Ti5O12/MoO2-Mo composites were prepared by the simple solid-state method under a reducing atmosphere with MoO3 as an additive. MoO3 is reduced to MoO2 and Mo mixture under the heating atmosphere. From the results of XRD after cell refinement, it is inferred that only a small part of Mo4+ ions are doped into the lattice of lithium titanate. XRD, STEM, EDS mapping and XPS reveal that particles with a size of only tens of nanometers adhered to the surface of lithium titanate should be MoO2/Mo mixture. The electrochemical results of EIS and CV show that the modified sample display a lower charge transfer resistance and a larger diffusion coefficient of lithium ions as a result of the combined effects of Mo4+ doping and interfacial modification. Compared with pristine Li4Ti5O12 prepared under the same atmosphere, the modified Li4Ti5O12 exhibits a capacity of approximately 140 mAh·g−1 under a high current density of 1.7 A·g−1, which is about 20 mAh·g−1 higher than the former one. And the modified Li4Ti5O12 has better capacity retention after 500 cycles at 5 C, which may be related with the surface modification.