Regulating interlayer spacing with pillar and strain structures in Ti3C2 MXene layers by molecular welding for superior alkali metal ion storage

An ion insertion type in two-dimensional (2D) materials has attracted extensive attention making 2D materials as promising energy storage materials. However, the interlayer spacing plays a key role in the design of 2D materials with fast ions de-intercalation dynamics and high-rate capability. Here, an unprecedented and convenient organic molecular welding approach was proposed to controllably tune different interlayer spacings in Ti3C2 MXene layers, resulting in pillar and strain-xDA-Ti3C2 structures by a dehydration condensation reaction between diacid molecules (HOOC(CH2)nCOOH) and -NH2 functionalized Ti3C2 layers. The xDA molecules can not only tighten the adjacent layers acting as ropes during the ion insertion process but also pillar the adjacent layers when ion extraction process was used to stabilize the Ti3C2 structure by suppressing the volume change. Furthermore, the interlayer spacing of xDA-Ti3C2 can be controllably tuned from 1.03 to 1.45 nm by choosing xDA with different lengths and controlled interlayer spacings of 1.35 and 1.38 nm can be achieved for the best rate capability of insertion/extraction processes with the superior diffusion coefficient of 4.6 × 10−7/2.8 × 10−8 cm2/s in Li+/Na+ batteries, respectively.