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

A series of Na x Li 4−x Ti 6 O 14 (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 Na 2 Li 2 Ti 6 O 14 and Na 4 Ti 6 O 14 and three multi-phase samples of Li 4 Ti 6 O 14 (Li 4 Ti 5 O 12 /TiO 2 ), NaLi 3 Ti 6 O 14 (Na 2 Li 2 Ti 6 O 14 /Li 4 Ti 5 O 12 /TiO 2 ) and Na 3 LiTi 6 O 14 (Na 2 Li 2 Ti 6 O 14 /Na 2 Ti 3 O 7 ) can be formed by using a stoichiometric ratio of starting materials based on the formula of Na x Li 4−x Ti 6 O 14 . Besides, different Na/Li atomic ratios in Na x Li 4−x Ti 6 O 14 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 Li 4 Ti 6 O 14 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, Na 4 Ti 6 O 14 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 Li 4 Ti 6 O 14 is the most potential lithium storage material among all the Na x Li 4−x Ti 6 O 14 samples.