H 2 O-Mg 2+ 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 Mg 2+ migration kinetics and structural collapse of the cathode materials. Here, an H 2 O-Mg 2+ waltz-like shuttle mechanism in the lamellar cathode, which is realized by the coordination, adaptive rotation and flipping, and co-migration of lattice H 2 O molecules with inserted Mg 2+ , leading to the fast Mg 2+ migration kinetics, is reported; after Mg 2+ extraction, the lattice H 2 O molecules rearrange to stabilize the lamellar structure, eliminating structural collapse of the cathode. Consequently, the demo cathode of Mg 0.75 V 10 O 24 ·nH 2 O (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 H 2 O provides a novel strategy to develop high-performance cathodes for MIBs as well as other multivalent-ion batteries.