A Size-Dependent Sodium Storage Mechanism in Li<sub>4</sub>Ti<sub>5</sub>O<sub>12</sub> Investigated by a Novel Characterization Technique Combining in Situ X‑ray Diffraction and Chemical Sodiation Xiqian Yu Huilin Pan Wang Wan Chao Ma Jianming Bai Qingping Meng Steven N. Ehrlich Yong-Sheng Hu Xiao-Qing Yang 10.1021/nl402263g.s001 https://acs.figshare.com/articles/journal_contribution/A_Size_Dependent_Sodium_Storage_Mechanism_in_Li_sub_4_sub_Ti_sub_5_sub_O_sub_12_sub_Investigated_by_a_Novel_Characterization_Technique_Combining_in_Situ_X_ray_Diffraction_and_Chemical_Sodiation/2368255 A novel characterization technique using the combination of chemical sodiation and synchrotron based in situ X-ray diffraction (XRD) has been detailed illustrated. The power of this novel technique was demonstrated in elucidating the structure evolution of Li<sub>4</sub>Ti<sub>5</sub>O<sub>12</sub> upon sodium insertion. The sodium insertion behavior into Li<sub>4</sub>Ti<sub>5</sub>O<sub>12</sub> is strongly size dependent. A solid solution reaction behavior in a wide range has been revealed during sodium insertion into the nanosized Li<sub>4</sub>Ti<sub>5</sub>O<sub>12</sub> (∼44 nm), which is quite different from the well-known two-phase reaction of Li<sub>4</sub>Ti<sub>5</sub>O<sub>12</sub>/Li<sub>7</sub>Ti<sub>5</sub>O<sub>12</sub> system during lithium insertion, and also has not been fully addressed in the literature so far. On the basis of this in situ experiment, the apparent Na<sup>+</sup> ion diffusion coefficient (D<sub>Na+</sub>) of Li<sub>4</sub>Ti<sub>5</sub>O<sub>12</sub> was estimated in the magnitude of 10<sup>–16</sup> cm<sup>2</sup> s<sup>–1</sup>, close to the values estimated by electrochemical method, but 5 order of magnitudes smaller than the Li<sup>+</sup> ion diffusion coefficient (D<sub>Li+</sub> ∼10<sup>–11</sup> cm<sup>2</sup> s<sup>–1</sup>), indicating a sluggish Na<sup>+</sup> ion diffusion kinetics in Li<sub>4</sub>Ti<sub>5</sub>O<sub>12</sub> comparing with that of Li<sup>+</sup> ion. Nanosizing the Li<sub>4</sub>Ti<sub>5</sub>O<sub>12</sub> will be critical to make it a suitable anode material for sodium-ion batteries. The application of this novel in situ chemical sodiation method reported in this work provides a facile way and a new opportunity for in situ structure investigations of various sodium-ion battery materials and other systems. 2013-10-09 00:00:00 Li 4Ti system sodium insertion behavior solution reaction behavior chemical sodiation method XRD ion diffusion kinetics Li 4Ti Investigated ion diffusion coefficient Novel Characterization Technique sodium insertion Chemical SodiationA novel characterization technique Li 4Ti