Revealing the Phase-Transition Dynamics and Mechanism in a Spinel Li4Ti5O12 Anode Material through in Situ Electron Microscopy.

Spinel Li4Ti5O12 is considered as a promising anode material for long-life lithium-ion batteries because of the negligible volumetric variation during the insertion and extraction of Li ions. Phase transition is an inevitable process during the migration of Li ions, and the transition process and mechanism need detailed investigation down to the atomic scale. In this study, we investigated the behavior and mechanism on the phase transition of Li4Ti5O12 through in situ transmission electron microscopy (TEM). It has been found that the spinel-structured Li4Ti5O12 was gradually transformed to a rock salt structure under electron beam irradiation. A sharp interface with an epitaxial relationship was observed between the transformed rock salt phase and the parent spinel phase. Furthermore, the heterostructure with different crystal structures of Li4Ti5O12 has been precisely tailored with electron beam irradiation. Our detailed in situ TEM results and theoretical calculations led to unprecedented level on the understanding of phase-transition mechanism in Li4Ti5O12. This study demonstrates a possible approach to precisely engineer the crystal structure of materials and to realize a well-designed heterostructure in electrode materials.