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 Mg 2+ /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 Ti 3 C 2 @CoS 2 /FeS 2 (denoted as o-Ti 3 C 2 @CoS 2 , o-Ti 3 C 2 @FeS 2 ) 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-Ti 3 C 2 weaken the Co–S/Fe–S bonds, the o-Ti 3 C 2 @CoS 2 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-Ti 3 C 2 @FeS 2 also displays a high-rate capability, outstanding cycling stability, and fast diffusion kinetics. Furthermore, the conversion reaction of Mg 2+ /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.