Anisotropic Amorphization and Phase Transition in Na₂ Ti₃ O₇ Anode Caused by Electron Beam Irradiation

Na₂ Ti₃ O₇ is considered one of the most promising anode materials for sodium ion batteries due to its superior safety, environmental friendliness, and low manufacturing cost. However, its structural stability and reaction mechanism still have not been fully explored. As the electron beam irradiation introduces a similar impact on the Na₂ Ti₃ O₇ anode as the extraction of Na⁺ ions during the battery discharge process, the microstructure evolution of the materials is investigated by advanced electron microscopy techniques at the atomic scale. Anisotropic amorphization is successfully observed. Through the integrated differential phase contrast-scanning transmission electron microscopy technique and density functional theory calculation, a phase transition pathway involving a new phase, Na₂ Ti₂₄ O₄₉ , is proposed with the reduction of Na atoms. Additionally, it is found that the amorphization is dominated by the surface energy and electron dose rate. These findings will deepen the understanding of structural stability and deintercalation mechanism of the Na₂ Ti₃ O₇ anode, providing new insight into exploring the failure mechanism of electrode materials.