Rigid organic molecule pillared Ti₃C₂ towards high rate capability and fast sodium ion storage

MXenes are promising two-dimensional layered anode materials for rechargeable batteries due to their outstanding electrical conductivity, high specific surface area, and tunable surface functional groups. However, serious self-stacking of the layered structure and the sluggish sodium diffusion kinetics lead to inferior rate capability and cycling stability. Herein, an organic molecular pillaring strategy is reported to enlarge the interlayer spacing of Ti₃C₂ through a dehydration condensation reaction between the -COOH groups of 3,3',4,4'-benzene tetracarboxylic acid (BTCA) molecules and the -NH₂ groups of Ti₃C₂-NH₂, which enables rigid organic BTCA molecules to be chemically pillared into the interlayers of Ti₃C₂ (Ti₃C₂-BTCA). The rigid organic BTCA molecules not only play a dual role of pillar and strain effects in Ti₃C₂ layers, but also expand the interlayer spacing. Therefore, they can significantly enhance the rate capability and cycling stability of Ti₃C₂. Ti₃C₂-BTCA exhibits a reversible capacity of 182.3 mA h g^-1 at a current density of 0.1 A g^-1 after 2000 cycles and maintains a reversible capacity of 77.9%. Moreover, the sodium diffusion coefficient of Ti₃C₂-BTCA is 6.6 × 10^-7 cm² s^-1. Ti₃C₂-BTCA shows a relatively low sodium diffusion barrier and a high sodium diffusion coefficient compared with Ti₃C₂. Interlayer engineering based on the organic molecular pillaring strategy is significant and meaningful for expanding the interlayer spacing of Ti₃C₂. This work provides theoretical guidance and new perspectives for the development of Na⁺ storage materials with high-rate capability.