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

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