Dual‐Anion‐Vacancy Engineering in MXene: Unlocking Quantum Confinement, Charge Compensation and Shielding Effects for Ultra‐Stable Mg ²⁺ /Li ⁺ Ions Storage

ABSTRACT Designing cathode materials that can synergistically store ions with significantly different charge densities and ionic radii poses a critical challenge in the ongoing development of Mg 2+ /Li + hybrid batteries (MLHBs). MXene‐based materials with vacancy defects offer promise, yet conventional monovacancy strategies cannot balance capacity and reaction kinetics. Herein, an innovative dual‐anion (Se, O) vacancy engineering strategy is proposed and constructed a quantum dot (QD) Ti 3 C 2 MXene heterostructure (QD@V Se,O ‐Ti 3 C 2 ). Benefiting from (i) the quantum confinement effect induced by QD TiO 2 , which modifies the electronic band structure and improves interfacial charge transfer, (ii) dual‐anion vacancies that establish a complementary charge environment, providing electrostatic shielding to lower Mg 2+ diffusion barriers and facilitate charge compensation, and (iii) in situ formed TiSe 2 layers combined with strong Se─C bonds, which ensure rapid ion/electron transport and maintain structural integrity. The QD@V Se,O ‐Ti 3 C 2 cathode delivers an ultra‐high capacity (705 mAh g −1 at 50 mA g −1 ) and outstanding cycling stability with 70% capacity retention after 2300 cycles at 1000 mA g −1 . The synergy among quantum‐confined, charge compensation and shielding effects, and interfacial electronic structure achieved unprecedented Mg 2+ /Li + co‐adsorption stability and rapid kinetics. This work establishes a new paradigm of QD‐enhanced multi‐anion vacancy engineering for next‐generation multivalent‐ion batteries.