Advanced cathode for synergistic anion-cation redox reactions in magnesium-ion batteries - A pathway to fast diffusion/reaction kinetics

The quest for efficient energy storage solutions has catalyzed interest in magnesium-ion batteries (MIBs), which utilize the nature of magnesium to achieve higher volumetric capacity, improved safety and cost advantages. However, significant challenges remain, including severe polarization caused by the high charge density of Mg2+ and limited ion diffusion in cathode materials. In this study, we present a strategic approach to address these challenges by doping vanadium tetrasulfide (VS4) with copper. This doping effectively expands the interlayer spacing, relieving steric hindrance to Mg2+ ion diffusion and introduces anion vacancies that serve as additional diffusion pathways. These vacancies promote simultaneous cation-anion redox reactions and facilitate multi- electron transfer during electrochemical processes. This enhancement of diffusion and reaction kinetics significantly boosts the overall electrochemical performance. Based on this, copper-doped VS4 (CVS) achieves a high discharge capacity of similar to 130 mAh g(-1) at a current density of 50 mA g(-1) and exhibits exceptional cycling stability, maintaining performance over 1000 cycles at 1 A g(-1) . This dual optimization of ion diffusion and redox kinetics offers a promising solution to the intrinsic challenges of MIBs and provides a basis for addressing similar limitations in other divalent ion systems.