Synthesis and characterization of Na_2Ti_6O_(13) and Na_2Ti_6O_(13)/Na_2Ti_3O_7 sodium titanates with nanorod-like structure as negative electrode materials for sodium-ion batteries

摘要

In this work, we report microwave assisted hydrothermal synthesis of monoclinic sodium titanates with either tunnel or with mixed tunnel/layered structure. Single phase Na_2Ti_6O_(13) and mixed phase Na_2Ti_6O_(13)/ Na_2Ti_3O_7 titanates were studied by electrochemical measurements with cyclic voltammetry, impedance spectroscopy and galvanostatic cycling. SEM images revealed that all the synthesized materials consist of rods with widths in the range of tenths to hundreds nanometers. XRD analysis was used for determination of the phase composition and crystallite size. It was shown that mixed phase electrode material reveals higher capacity and wider active voltage range but has also lower cycling stability. The insertion potential of layered titanate Na_2Ti_3O_7 is much lower than in the case of Na_2T_(16)O_9 and the specific capacity of mixed titanate in the first cycle is double the capacity of pure Na_2Ti_6O_9. Although presence of layered titanate contributed to high specific capacity in early cycling, it allowed a considerable decrease in specific capacity at higher numbers of cycles.