Re-delocalization of localized d-electrons in VO₂(R)-VS₄ hetero-structure enables high performance of rechargeable Mg-ion batteries

Rechargeable Mg-ion batteries (MIBs) have attracted much more attentions by virtue of the high capacity from the two electrons chemistry. However, the reversible Mg²⁺ diffusion in cathode materials is restricted by the strong interactions between the high-polarized bivalent Mg²⁺ ions and anionic lattice. Herein, we design and propose a hetero-structural VO₂(R)-VS₄ cathode, in which the re-delocalized d-electrons can effectively shield the polarity of Mg²⁺ ions. Theoretically, the electrons should spontaneously transfer from VS₄ to VO₂(R) through the interfaces of hetero-structure due to the lower work function value of VS₄. Furthermore, the internal electrons transfer lead to the electronic injection into VO₂(R) from VS₄ and the partially broken V-V dimers, indicating the presence of lone pair electrons and charge re-delocalization. Benefiting from the shield effect of re-delocalized electrons, and the weakened attraction between cations and O/S anions enables more S²⁻-S₂²⁻ redox groups to participate the electrochemical reactions and compensate the double charge of Mg²⁺ ions. Accordingly, VO₂(R)-VS₄ hetero-structure exhibits a high specific capacity of 554 mA h g⁻¹ at 50 mA g⁻¹. It is believed that the charge re-delocalization of cathode extremely boost the Mg²⁺ ions migration for the high-capacity of MIBs.