High performance Na-doped lithium zinc titanate as anode material for Li-ion batteries

Abstract

A series of Li_2−xNa_xZnTi₃O₈ (x = 0, 0.05, 0.10, 0.15, 0.20) are prepared for the first time by a simple solid state method. Upon Na-doping, Rietveld refinement reveals that Na⁺ takes the 8c tetrahedral sites shared with Li⁺ and Zn²⁺ in the structure. Due to the larger ionic radius of Na⁺ than that of Li⁺, an increased disorder degree of ion locations in the structure is induced by Na doping. Furthermore, the lithium ion diffusion tunnel is also expanded after Na doping. Thus, higher lithium ion diffusion coefficient can be observed for all the Na-doped Li₂ZnTi₃O₈ samples. However, phase analysis shows that high Na-doping content can result in the formation of impurity in the as-obtained titanates. Besides, the existence of too many Na ions in the spinel also decreases the structural stability. Therefore, Na-doping with low dose is beneficial to improve the electrochemical performance of Li₂ZnTi₃O₈. Electrochemical evaluations show that Li_1.95Na_0.05ZnTi₃O₈ has the best lithium storage property among all the Li_2−xNa_xZnTi₃O₈. It can be found that Li_1.95Na_0.05ZnTi₃O₈ can deliver a reversible capacity of 267.3 mA h g⁻¹ after 50 cycles. This finding can provide an experimental support to synthesize high performance Ti-based materials by Na doping.