Defective Ti2Nb10O27.1: an advanced anode material for lithium-ion batteries.

To explore anode materials with large capacities and high rate performances for the lithium-ion batteries of electric vehicles, defective Ti2Nb10O27.1 has been prepared through a facile solid-state reaction in argon. X-ray diffractions combined with Rietveld refinements indicate that Ti2Nb10O27.1 has the same crystal structure with stoichiometric Ti2Nb10O29 (Wadsley-Roth shear structure with A2/m space group) but larger lattice parameters and 6.6% O(2-) vacancies (vs. all O(2-) ions). The electronic conductivity and Li(+)ion diffusion coefficient of Ti2Nb10O27.1 are at least six orders of magnitude and ~2.5 times larger than those of Ti2Nb10O29, respectively. First-principles calculations reveal that the significantly enhanced electronic conductivity is attributed to the formation of impurity bands in Ti2Nb10O29-x and its conductor characteristic. As a result of the improvements in the electronic and ionic conductivities, Ti2Nb10O27.1 exhibits not only a large initial discharge capacity of 329 mAh g(-1) and charge capacity of 286 mAh g(-1) at 0.1 C but also an outstanding rate performance and cyclability. At 5 C, its charge capacity remains 180 mAh g(-1) with large capacity retention of 91.0% after 100 cycles, whereas those of Ti2Nb10O29 are only 90 mAh g(-1) and 74.7%.