Regulation of Micron‐Sized Rutile TiO ₂ With (111) Crystal Facet Dominated Enables High‐Capacity Magnesium Ions Storage

Abstract The reversible intercalation of multivalent Mg 2+ into electrode materials suffers from slow Mg 2+ diffusion, nanosizing electrode materials is a usually used method, while the higher surface area tends to cause electrode‐electrolyte interface side reactions. Here, through facet regulation engineering to enable efficient Mg 2+ storage in micron‐sized rutile TiO 2 is demonstrated without relying on nanostructuring, to expose specific facets to improve Mg 2+ intercalation. Especially, materials dominated by high‐energy (111) facets exhibit nearly twice the capacity of pristine material, demonstrating more efficient Mg 2+ intercalation. First‐principles calculations indicate that exposing the (111) and (110) facets can effectively open migration pathways and reduces the diffusion energy barrier of Mg 2+ , thereby improving electrochemical performance. Notably, the (111) facets dominated TiO 2 shows high reversible capacity of 196.8 mAh/g at 20 mA/g, and retains 119.2 mAh/g after 1623 cycles at 100 mA/g and 91.3 mAh/g after 2000 cycles at 1 A/g, suggesting its potential for energy storage systems. The time‐of‐flight secondary‐ion mass spectrometry (TOF‐SIMS) and atomic‐resolution scanning transmission electron microscopy (STEM) imaging jointly confirm the effective intercalation of Mg 2+ in the lattice. These findings highlight the potential of facet engineering to unlock hidden electrochemical activity in materials and offer a new approach to designing multivalent‐ion battery cathodes.