Intercalation-Induced Amorphization Boosts Aqueous Magnesium-Ion Storage

The design of aqueous battery cathode materials that can store divalent ions with high capacity and satisfactory reversibility is of great technical importance and challenge. Here, we report that divalent Mg²⁺ storage is facilitated by an intercalation-induced amorphization of vanadate electrode materials. Electrokinetic analyses and in situ synchrotron X-ray diffraction and absorption spectroscopy collectively demonstrate that vanadate layered materials (Li-V₃O₈) undergo a structural transformation to amorphization induced by Mg²⁺ intercalation, and a reversible restoration of crystalline structure upon Mg²⁺ deintercalation. Debye scattering simulations suggest that intercalation-induced turbostratic disorder, especially random rotations, translational shifts, oscillatory motions, or varied interlayer spacing of adjacent V-O molecular layers, could be responsible for the observed amorphization. The highly distorted local structure, in turn, facilitates Mg²⁺ intercalation across the vanadate electrode materials, responsible for nearly 3/7 of the total Mg²⁺ ions intercalated. The study presented reveals an intriguing relationship between ion transport and the reversible amorphization-to-crystallization dynamics it induces, opening a paradigm for designing advanced aqueous battery electrodes.