Phase composition and electrochemical performance of sodium lithium titanates as anode materials for lithium rechargeable batteries

A series of NaxLi4−xTi6O14 (0 ≤ x ≤ 4) are prepared by solid-state method and their structures, morphologies and electrochemical properties are compared by changing the Na/Li atomic ratio. It can be found that two single-phase samples of Na2Li2Ti6O14 and Na4Ti6O14 and three multi-phase samples of Li4Ti6O14 (Li4Ti5O12/TiO2), NaLi3Ti6O14 (Na2Li2Ti6O14/Li4Ti5O12/TiO2) and Na3LiTi6O14 (Na2Li2Ti6O14/Na2Ti3O7) can be formed by using a stoichiometric ratio of starting materials based on the formula of NaxLi4−xTi6O14. Besides, different Na/Li atomic ratios in NaxLi4−xTi6O14 also induce the morphology evolution shifting from round-shape to polyhedron-shape, and then to square-shape with the increase of Na content. Electrochemical tests show that Li4Ti6O14 delivers the highest charge capacities of 116 mAh g−1 at 100 mA g−1, 91.5 mAh g−1 at 200 mA g−1, 77.5 mAh g−1 at 300 mA g−1 and 66.9 mAh g−1 at 400 mA g−1 among five samples. For comparison, Na4Ti6O14 only reveals the reversible capacities of 38.6 mAh g−1 at 100 mA g−1, 30.2 mAh g−1 at 200 mA g−1, 24.8 mAh g−1 at 300 mA g−1 and 20.9 mAh g−1 at 400 mA g−1. It suggests that Li4Ti6O14 is the most potential lithium storage material among all the NaxLi4−xTi6O14 samples.