Metastable Structure for Ultra‐Sustainable, High Capacity and Kinetics‐Enhanced Magnesium‐Ion Battery

ABSTRACT Cost‐effective magnesium ion batteries (MIBs) offer a promising new pathway for next‐generation large‐scale energy storage, and yet its development is largely hindered by the severe polarization, limited rate capability, and poor cycling stability, where the challenges are largely rooted in the sluggish kinetics of Mg 2+ storage. Here, we report a metastable phase evolution strategy that enables high‐performance Mg 2+ storage by leveraging Ti‐modulated VS 4 (T‐VS 4 ), demonstrating a structurally soft and yet dynamically adaptive lattice, which are among the preconditions for the metastable phase formation. Metastable Mg x T‐VS 4 is formed during the initial Mg 2+ intercalation, significantly facilitating the subsequent Mg 2+ migration, favoring multi‐electron redox reaction, and enhancing the charge transfer kinetics. Impressively, the T‐VS 4 cathode demonstrates exceptional Mg 2+ storage performance with a high specific capacity (205.4 mAh g −1 at 50 mA g −1 ), excellent rate capability (up to 1000 mA g −1 ), and long‐term cycling stability (over 3000 cycles). This work exemplifies a new metastable phase engineering approach as the design paradigm for breaking kinetic limitations in MIBs, offering a novel avenue toward next‐generation energy storage systems.