Three-Phase Transition of Spinel Li₄Ti₅O₁₂ with a Dense Single-Particle Microelectrode in Li-Ion Batteries

Spinel Li4Ti5O12 is a well-known two-phase anode material, which can deliver a large specific capacity over a wide voltage window, and the kinetics of the two-phase boundary is very important to the electrochemical properties. In this work, a dense Li4Ti5O12 single-particle microelectrode is prepared by the transient electric-arc heating, and its electrochemical properties are measured over a wide voltage window in Li-ion batteries, which delivers an ultralow-potential discharge plateau. According to electrochemical, in situ electrochemical impedance spectroscopy, Raman, and optical results, an unsymmetrical core–shell model is proposed as discharging through the α/γ two-phase transition and charging through the α/β two-phase transition, in which the Li-ion insertion into the two-phase interface is switched off for the β phase at a low potential and switched on for the γ phase at an ultralow potential. Therefore, this study provides new insights into the electrochemical behaviors of spinel Li4Ti5O12 and sheds light on some other two-phase materials, such as olivine LiFePO4 and spinel LiCrTiO4.