H2O‐Mg2+ Waltz‐Like Shuttle Enables High‐Capacity and Ultralong‐Life Magnesium‐Ion Batteries

Mg‐ion batteries (MIBs) are promising next‐generation secondary batteries, but suffer from sluggish Mg2+ migration kinetics and structural collapse of the cathode materials. Here, an H2O‐Mg2+ waltz‐like shuttle mechanism in the lamellar cathode, which is realized by the coordination, adaptive rotation and flipping, and co‐migration of lattice H2O molecules with inserted Mg2+, leading to the fast Mg2+ migration kinetics, is reported; after Mg2+ extraction, the lattice H2O molecules rearrange to stabilize the lamellar structure, eliminating structural collapse of the cathode. Consequently, the demo cathode of Mg0.75V10O24·nH2O (MVOH) exhibits a high capacity of 350 mAh g−1 at a current density of 50 mA g−1 and maintains a capacity of 70 mAh g−1 at 4 A g−1. The full aqueous MIB based on MVOH delivers an ultralong lifespan of 5000 cycles The reported waltz‐like shuttle mechanism of lattice H2O provides a novel strategy to develop high‐performance cathodes for MIBs as well as other multivalent‐ion batteries. Universal Mg2+‐H2O waltz‐like shuttle mechanism: the lattice H2O molecules in the lamellar structure of Mg0.75V10O24·nH2O (MVOH) coordinate and co‐migrate with Mg2+ during discharging, meanwhile, they adaptively rotate and even flip to assist the migration of Mg2+, which facilitates the Mg2+ migration kinetics. After Mg2+ extraction, the lattice H2O molecules rearrange as supporting pillars to stabilize the lamellar structure of MVOH.