Unveiling the Interlayer–Intralayer Cooperative Diffusion Mechanism in Bimetallic Layered Cathodes for Rechargeable Magnesium Batteries

Rechargeable Mg batteries are promising candidates for large-scale energy-storage applications; however, the scarcity of viable cathode materials and sluggish Mg²⁺ diffusion kinetics severely hinder their application. While layered compounds exhibit exceptional potential for guest-ion intercalation, existing research predominantly focuses on optimizing intralayer diffusion, with the critical role of interlayer diffusion in Mg-storage remaining underexplored. Herein, two-layered Cu₂MoS₄, designated as CMS-L (sole intralayer diffusion channels) and CMS-V (intralayer/interlayer diffusion channels), were synthesized and comparatively evaluated as Mg-storage cathodes. Benefiting from unique three-dimensional ion-transport tunnels, CMS-V delivers superior Mg-storage performance compared to CMS-L, achieving a high reversible capacity of 210 mAh g^-1 at 100 mA g^-1, excellent rate capability (98 mAh g^-1 at 2 A g^-1), and outstanding cyclability with 77% capacity retention after 500 cycles. Mechanism analyses reveal Mg²⁺ intercalation reactions dominate in both compounds, while the covalent-like nature of the Mo-S bond ensures the structural stability of the MoS₄ cluster during Mg²⁺ insertion/extraction. Theoretical computations confirm that the vertically aligned interlayer tunnels in CMS-V significantly reduce diffusion barriers, enabling rapid ion transport via an interlayer-intralayer cooperative diffusion mechanism. This work underscores the importance of multidimensional ion-transport pathway engineering in optimizing Mg-storage kinetics and offers valuable theoretical insights for designing advanced RMB cathode materials.