Diacid Molecules Welding Achieved Self-Adaption Layered Structure Ti3C2 MXene toward Fast and Stable Lithium-Ion Storage

Ti3C2 has been considered as a potential material for lithium-ion storage because of its abundant surface terminals, excellent metal-like conductivity, and modifiable layered structure. However, the Li+ diffusion rate in interlayer is limited by the small interlayer spacing determined by the van der Waals forces. Herein, the dehydration condensation reaction between amino-functionalized Ti3C2 (Ti3C2-NH2) and maleic acid (MA) molecules was utilized to enlarge the interlayer spacing of Ti3C2. The MA molecules were successfully welded into interlayers of Ti3C2 by HN–C═O bonds (namely, chemical welding) and MA chemical welded Ti3C2 (MA-Ti3C2) with self-adaption layered structure were obtained. The MA molecules can contribute double effects to the layered structure of Ti3C2, and they act as chains to remit the volume change during Li+ insertion and serve as pillars to enhance the structure stability during Li+ extraction. The MA-Ti3C2 exhibits an interlayer spacing of 1.28 nm, a fast Li+ diffusion rate (1.4 × 10–8 to 5.8 × 10–7 cm2 s–1), and improved Li+ storage performance. The MA-Ti3C2//AC lithium-ion capacitor (LIC) demonstrates an excellent energy density of 102.5 Wh kg–1 at 200 W kg–1 and cycle stability with 76.3% at 1.0 A g–1 after 1000 cycles. This novel chemical welding delivers an effective perspective for modifying the layered structure, enhancing the structure stability, and achieving fast Li+ diffusion and high-rate capability of two-dimension materials.