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

Abstract

Na⁺ and Zr⁴⁺ co-doped lithium titanates with the formula Li_4−xNa_xTi_5−xZr_xO₁₂ (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 Zr⁴⁺ co-doping does not change the spinel structure of Li₄Ti₅O₁₂ 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 Zr⁴⁺ co-doped Li₄Ti₅O₁₂ samples. The four-point probe method and electrochemical impedance spectroscopy (EIS) results demonstrate that the Na⁺ and Zr⁴⁺ co-doped Li₄Ti₅O₁₂ samples possess higher electrical conductivity and smaller charge transfer resistance compared with undoped Li₄Ti₅O₁₂, resulting in improved electrochemical performance. Particularly, Li_3.97Na_0.03Ti_4.97Zr_0.03O₁₂ 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.