image: In the center can be seen the schematic diagram of the Mo 4d orbitals splitting manner and Mg2+ diffusion in o-MoO2.8F0.2, c-MoO2.4F0.6, and o-c MoO2.8F0.2/MoO2.4F0.6 heterostructure. Art by Liqiang Mai.
Credit: ©Science China Press
Rechargeable magnesium batteries (RMBs) hold significant promise for next-generation energy storage, owing to their low cost, high volumetric capacity (3833 mA h cm⁻³), and dendrite-free formation. However, the strong electrostatic interactions between polarized Mg²⁺ ions and the host lattice can result in sluggish electrochemical reaction kinetics, severely hindering their development. Therefore, the pursuit of advanced cathode materials that enable rapid ion and charge transfer is indeed of utmost urgency. Recently, extensive efforts have been dedicated to overcoming this issue, such as enlarging interlayer spacing through the preintercalation of molecules or ions, shielding the strong polarization of Mg²⁺ by introducing H2O molecules, and reducing binding forces by doping with anions of higher polarizability. Unfortunately, the improvement in magnesium storage is often inadequate in these designed electrodes, as the regulation of electronic conductivity and ionic diffusivity remains uncoordinated.
In response to this challenge, for the first time, the research team led by Professor Liqiang Mai from the Wuhan University of Technology (WUT) proposed an electron injection strategy for modulating the Mo 4d-orbital splitting manner and first fabricate a orthorhombic/cubic phase MoO2.8F0.2/MoO2.4F0.6 (o-c MoO2.8F0.2/MoO2.4F0.6) heterostructure to achieve efficient magnesium ion storage. The electron injection strategy induces a slight Jahn–Teller distortion in MoO6 octahedra and reorganizes the Mo 4d orbitals, resulting in a partial phase transition. This transition leads to the formation of the o-c MoO2.8F0.2/MoO2.4F0.6 heterostructure. The o-MoO2.8F0.2 generates molybdenum vacancies, which unlock the inactive basal plane of the layered crystal structure, thereby shortening the ion diffusion length (L) along the b-axis and ac plane within the crystal frameworks. Meanwhile, c-MoO2.4F0.6 activates the previously blocked crystal structure, enhancing ion diffusivity (D) in the materials. Consequently, the o-c MoO2.8F0.2/MoO2.4F0.6 heterostructure is meticulously designed by integrating o-MoO2.8F0.2 and c-MoO2.4F0.6, which effectively reduces Mg²⁺ diffusion time (t) from two perspectives (t ≈ L²/D). In addition, the designed heterostructure possesses an abundant built-in electric field, which simultaneously enhances electron transfer and ion diffusion in the crystal frameworks. Therefore, it pushes forward the orbital-scale manipulation for designing more advanced dual-phase heterostructure cathode materials.
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See the article:
Electron-injection-engineering induced dual-phase MoO2.8F0.2/MoO2.4F0.6 heterostructure for magnesium storage
https://academic.oup.com/nsr/article/11/8/nwae238/7712495
Journal
National Science Review