Unraveling the Mg²⁺/Li⁺ dual-ion co-intercalation mechanism in 3D MXene heterojunctions for enhanced Mg/Li hybrid ion battery performance

Rechargeable Mg/Li hybrid ion batteries with Mg²⁺/Li⁺ double-salt electrolytes and safe Mg anodes are a viable option for large-scale energy storage. Nevertheless, achieving the desired reasonable electrochemical performance remains a great challenge due to the capacity limitations of conventional Li-intercalation cathodes. To mitigate this limitation, the 3D oxygenated MXene Ti₃C₂@CoS₂/FeS₂ (denoted as o-Ti₃C₂@CoS₂, o-Ti₃C₂@FeS₂) with both dual-storage mechanism and multidimensional structure to achieve the desirable storage capacity is engineered. Benefiting from the formation of special structure and interfacial chemical bonds Ti–O–Co/Ti–O–Fe, as well as the electronegative o-Ti₃C₂ weaken the Co–S/Fe–S bonds, the o-Ti₃C₂@CoS₂ cathode exhibits superior capacity up to 425 mAh g⁻¹ at 100 mA g⁻¹ and overwhelming advantageous ultra-long life over 2,400 cycles at 500 mA g⁻¹. Simultaneously, the o-Ti₃C₂@FeS₂ also displays a high-rate capability, outstanding cycling stability, and fast diffusion kinetics. Furthermore, the conversion reaction of Mg²⁺/Li⁺ co-intercalation and the charge storage mechanism during cycling are thoroughly clarified by systematic ex-situ characterizations and theoretical computations. This study reveals the influence of MXene electrode structure on the importance of electrochemical performance and provides guidance for the future design of high-performance MXene materials for energy storage applications.