The reaction mechanism of the Mg2+ and F− co-modification and its influence on the electrochemical performance of the Li4Ti5O12 anode material

• The reaction mechanism of Mg2+ and F− co-modification is studied.
• F− reacts with LTO to form new impurity phase, such as anatase TiO2, rutile TiO2 and LiF.
• Mg2+ forms a coating layer on the LTO particles.
• 1 wt% Mg2+ and F− co-modified LTO exhibits excellent capacity and rate capability.
• The Mg2+ and F− co-modified LTO samples also present outstanding cycling performance at a high rate of 5C.

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 ∼3 V 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%).

After the modification process, F− reacts with LTO 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 1 wt% Mg2+ and F− co-modified Li4Ti5O12 has a higher capacity than commercial Li4Ti5O12 at different C-rates in the range of 0 ∼ 3 V. The MgO coating layer could prevent the electrolyte reduction decomposition on the Li4Ti5O12 particles. Therefore, the cycling performance of the Mg2+ and F− co-modified Li4Ti5O12 and Mg2+ modified Li4Ti5O12 at a high rate of 5C are greatly improved.Figure optionsDownload as PowerPoint slide