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

Abstract

MXenes are promising 2D-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 in 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. The Ti3C2-BTCA exhibits a reversible capacity of 182.30 mAh g-1 at a current density of 0.1 A g-1 after 2000 cycles, and maintained a reversible capacity of 77.9 %. Moreover, the sodium diffusion coefficients of Ti3C2-BTCA are 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. The 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.