The surface of pure Li4Ti5O12 was modified with CaF2 via a chemical co-precipitation method followed by calcination at 400 degrees C for 5 h in order to study the reaction mechanism of the fluoride modification process. X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) were used to confirm the structure and morphology of the material. After the modification, the structure of Li4Ti5O12 was unchanged, as F- ions reacted with Ca2+ ions to form CaF2 instead of reacting with Li4Ti5O12. A consecutive CaF2 coating layer was not formed on the surface of Li4Ti5O12; instead, many microscale CaF2 crystals stacked on the Li4Ti5O12 particles. The stacked CaF2 crystals could not only reduce electrode polarization, but also partially suppress reductive decomposition, resulting in the formation of a thinner SEI film, thereby reducing resistance of the SEI film (R-sei) and the charge-transfer resistance (R-ct), both of which were beneficial to the electrochemical performance of Li4Ti5O12. The 2 wt% CaF2-modified Li4Ti5O12 exhibited a superior rate capacity, with discharge capacities between 0 and 3 V of 227.8, 215.8, 207.6, 190.6, 180.2, and 157.6 mAh g(-1) at rates of 0.2, 0.5, 1, 3, 5, and 10 C (1 C = 250 mAh g(-1)), respectively. Moreover, the 2 wt% CaF2-modified Li4Ti5O12 showed a discharge capacity retention of 96.7% after 125 cycles at a rate of 3 C, higher than that of pure Li4Ti5O12 (94.4%), which was due to the fact that CaF2 modification enhanced the capability of the material to resist HF attack during the discharge/charge processes. (C) 2017 Elsevier B.V. All rights reserved.