The commercial Li4Ti5O12 is co-modified using Mg2+ and F⿿ via a co-precipitation method with the purpose of understanding the reaction mechanism of the fluoride modification process. For comparison, the commercial Li4Ti5O12 is also modified using Mg2+ and F⿿, respectively. After the co-modification process, F⿿ reacts with Li4Ti5O12 chemically to generate new impurity phase such as anatase TiO2, rutile TiO2 and LiF, while Mg2+ forms MgO coating layer on the Li4Ti5O12 particles. The capacity and rate capability of the Li4Ti5O12 have been improved after the 1wt% Mg2+ and F⿿ co-modification. The charge capacity of the Mg2+ and F⿿ co-modified Li4Ti5O12 at 0.5C, 1C, 3C, 5C and 10C rate in the range of 0 ⿼3V is 234.1, 218.6, 200.8, 182 and 148mAh g⿿1, respectively. Meanwhile, the electrolyte reduction decomposition on the Li4Ti5O12 was suppressed after the co-modification process, thereby enhancing the cycling performance of the Mg2+ and F⿿ co-modified Li4Ti5O12. In particular, the 3 wt% Mg2+ and F⿿ co-modified Li4Ti5O12 keeps 74.5% charge capacity after 200 cycle charge-discharged test at a high rate of 5C, which is higher than the commercial Li4Ti5O12 (58.7%).