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

Abstract

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.

Keywords

• Mg-ion batteries
• Cathode
• Charge delocalization
• Electronic structure
• Heterostructure