Defect-Mediated\nFormation of Oriented Phase Domains\nin a Lithium-Ion Insertion Electrode

The\nperformance and robustness of electrodes are closely\nrelated\nto transformation-induced nanoscale structural heterogeneity during\n(de)lithiation. As a result, it is critical to understand at atomic\nscale the origin of such structural heterogeneity and ultimately control\nthe transformation microstructure, which remains a formidable task.\nHere, by performing in situ studies on a model intercalation electrode\nmaterial, anatase TiO<sub>2</sub>, we reveal that defectsboth\npreexisting and as-formed during lithiationcan mediate the\nlocal anisotropic volume expansion direction, resulting in the formation\nof multiple differently oriented phase domains and eventually a network\nstructure within the lithiated matrix. Our results indicate that such\na mechanism operated by defects, if properly harnessed, could not\nonly improve lithium transport kinetics but also facilitate strain\naccommodation and mitigate chemomechanical degradation. These findings\nprovide insights into the connection of defects to the robustness\nand rate performance of electrodes, which help guide the development\nof advanced lithium-ion batteries via defect engineering.