Three-Phase Transition of Spinel Li<sub>4</sub>Ti<sub>5</sub>O<sub>12</sub> with a Dense Single-Particle Microelectrode\nin Li-Ion Batteries

Spinel\nLi<sub>4</sub>Ti<sub>5</sub>O<sub>12</sub> is a well-known\ntwo-phase anode material, which can deliver a large specific capacity\nover a wide voltage window, and the kinetics of the two-phase boundary\nis very important to the electrochemical properties. In this work,\na dense Li<sub>4</sub>Ti<sub>5</sub>O<sub>12</sub> single-particle\nmicroelectrode is prepared by the transient electric-arc heating,\nand its electrochemical properties are measured over a wide voltage\nwindow in Li-ion batteries, which delivers an ultralow-potential discharge\nplateau. According to electrochemical, in situ electrochemical impedance\nspectroscopy, Raman, and optical results, an unsymmetrical core–shell\nmodel is proposed as discharging through the α/γ two-phase\ntransition and charging through the α/β two-phase transition,\nin which the Li-ion insertion into the two-phase interface is switched\noff for the β phase at a low potential and switched on for the\nγ phase at an ultralow potential. Therefore, this study provides\nnew insights into the electrochemical behaviors of spinel Li<sub>4</sub>Ti<sub>5</sub>O<sub>12</sub> and sheds light on some other two-phase\nmaterials, such as olivine LiFePO<sub>4</sub> and spinel LiCrTiO<sub>4</sub>.