Na+ and Zr4+ co-doped Li4Ti5O12 as anode materials with superior electrochemical performance for lithium ion batteries

摘要

Na ~(+) and Zr ~(4+) co-doped lithium titanates with the formula Li _(4? x ) Na _( x ) Ti _(5? x ) Zr _( x ) O _(12) ( x = 0, 0.01, 0.03, 0.05, 0.10, 0.15 and 0.20) were successfully synthesized via a solid-state reaction in air. XRD analysis indicates that Na ~(+) and Zr ~(4+) co-doping does not change the spinel structure of Li _(4) Ti _(5) O _(12) and the lattice parameter slightly increases with the enhancement of doping amount. Smaller particle size and larger BET surface areas are obtained for Na ~(+) and Zr ~(4+) co-doped Li _(4) Ti _(5) O _(12) samples. The four-point probe method and electrochemical impedance spectroscopy (EIS) results demonstrate that the Na ~(+) and Zr ~(4+) co-doped Li _(4) Ti _(5) O _(12) samples possess higher electrical conductivity and smaller charge transfer resistance compared with undoped Li _(4) Ti _(5) O _(12) , resulting in improved electrochemical performance. Particularly, Li _(3.97) Na _(0.03) Ti _(4.97) Zr _(0.03) O _(12) exhibits the best rate capability and cycling stability. Even at 20C, it delivers a discharge capacity of 140 mA h g ~(?1) , and after 100 cycles at 10C, 97.7% of its initial capacity is retained.