Ti₃C₂T_x MXene Conductive Layers Supported Bio-Derived Fe_x−1Se_x/MXene/Carbonaceous Nanoribbons for High-Performance Half/Full Sodium-Ion and Potassium-Ion Batteries

Owing to their cost-effectiveness and high energy density, sodium-ion batteries (SIBs) and potassium-ion batteries (PIBs) are becoming the leading candidates for the next-generation energy-storage devices replacing lithium-ion batteries. In this work, a novel Fe_x−1Se_x heterostructure is prepared on fungus-derived carbon matrix encapsulated by 2D Ti₃C₂T_x MXene highly conductive layers, which exhibits high specific sodium ion (Na⁺) and potassium ion (K⁺) storage capacities of 610.9 and 449.3 mAh g⁻¹ at a current density of 0.1 A g⁻¹, respectively, and excellent capacity retention at high charge–discharge rates. MXene acts as conductive layers to prevent the restacking and aggregation of Fe_x−1Se_x sheets on fungus-derived carbonaceous nanoribbons, while the natural fungus functions as natural nitrogen/carbon source to provide bionic nanofiber network structural skeleton, providing additional accessible pathways for the high-rate ion transport and satisfying surface-driven contribution ratios at high sweep rates for both Na/K ions storages. In addition, in situ synchrotron diffraction and ex situ X-ray photoelectron spectroscopy measurements are performed to reveal the mechanisms of storage and de-/alloying conversion process of Na⁺ in the Fe_x−1Se_x/MXene/carbonaceous nanoribbon heterostructure. As a result, the assembled Na/K full cells containing MXene-supported Fe_x−1Se_x@carbonaceous anodes possess stable large-ion storage capabilities.