Interface ion-exchange strategy of MXene@FeIn₂S₄ hetero-structure for super sodium ion half/full batteries

Herein, a well-designed hierarchical architecture of bimetallic transition sulfide FeIn₂S₄ nanoparticles anchoring on the Ti₃C₂ MXene flakes has been prepared by cation exchange and subsequent high-temperature sulfidation processes. The introduction of MXene substrate with excellent conductivity not only accelerates the migration rate of Na⁺ to achieve fast reaction dynamics but provides abundant deposition sites for the FeIn₂S₄ nanoparticles. In addition, this hierarchical structure of MXene@FeIn₂S₄ can effectively restrain the accumulation of MXene to guarantee the maximized exposure of redox active sites into the electrolyte, and simultaneously relieve the volume expansion in the repeated discharging/charging processes. The MXene@FeIn₂S₄ displays outstanding rate capability (448.2 mAh g^-1 at 5 A g^-1) and stable long cycling performance (428.1 mAh g^-1 at 2 A g^-1 after 200 cycles). Moreover, the Na_y-In₆S₇ phase detected by ex-situ XRD and XPS characterization may be regarded as a "buffer" to maintain the stability of the Fe-based components and enhance the reversibility of the electrochemical reaction. This work confirms the practicability of constructing the hierarchical structure bimetallic sulfides with the promising electrochemical performance.