Effect of Zn2+ and F− Co-Modification on the Structure and Electrochemical Performance of Li4Ti5O12 Anode Material

Zn 2 + and F − ions are successfully used to modify pure Li 4 Ti 5 O 1 2 via a co-precipitation method followed by calcination at 400 ∘ C for 5 h in an Ar atmosphere in order to further investigate the reaction mechanism of the fluoride modification process. Zn 2 + and F − co-modified Li 4 Ti 5 O 1 2 samples are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and electrochemical measurements. After the modification process, no ZnF 2 coating layer is formed on the surface of Li 4 Ti 5 O 1 2 , instead, F − ions react with Li 4 Ti 5 O 1 2 to generate a new phase, composed of a small amount of anatase TiO 2 , rutile TiO 2 , LiF, and Zn 2 + ions are suspected to form a ZnO coating layer on Li 4 Ti 5 O 1 2 particles. The electrolyte reduction decomposition is suppressed in Zn 2 + and F − co-modified Li 4 Ti 5 O 1 2 due to the ZnO coating layer. 1 wt.% Zn 2 + and F − co-modified Li 4 Ti 5 O 1 2 exhibits the best rate capability, which leads to a charge capacity of 236.7, 227.8, 222.1, 202.7, 188.9 and 150.7 mAh g − 1 at 0.2C, 0.5C, 1C, 3C, 5C and 10C, respectively, between 0 V and 3 V. Furthermore, 1 wt.% Zn 2 + and F − co-modified Li 4 Ti 5 O 1 2 exhibits 96.0% charge capacity retention at 3C rate after 200 cycles, which is significantly higher than that of pure Li 4 Ti 5 O 1 2 (78.4%).