A novel “point-to-point” 1,4-phenylenediacetic acid grafting of Ti3CN enhances sodium storage stability

The self-stacking of MXenes-Ti 3 CN limits the accessibility of nanochannels , reduces the ion diffusion kinetics, and hinders its application in alkali metal ion storage field. This study proposes a point-to-point mortise and tenon joining strategy to fabricate a composite structure of 1,4-phenylenediacetic acid-Ti 3 CN (1,4-PDEA-Ti 3 CN) by grafting rigid and flexible 1,4-phenylenediacetic acid (1,4-PDEA) into the amino-functionalized Ti 3 CN interlayers. The rigid and flexible 1,4-PDEA contributes to a pillar effect in the layered structure of Ti 3 CN, which is benefit to prevent the self-stacking and maintain a stable 2D layered structure. As a result, the interlayer spacing of Ti 3 CN is expanded from 1.20 to 1.46 nm and the Na + diffusion coefficient is improved from 1.16 × 10 −6 to 1.99 × 10 −6  cm 2  s −1 after point-to-point 1,4-PDEA grafting. The 1,4-PDEA-Ti 3 CN achieves a reversible discharge specific capacity of 202.3 mAh g −1 at a current density of 0.1 A g −1 after 770 cycles. Even at a high current density of 5 A g −1 , the 1,4-PDEA-Ti 3 CN still possesses a reversible discharge specific capacity of 137 mAh g −1 and it still maintains the high specific capacity of 256.1 mAh g −1 when the current density comes back to 0.1 A g −1 . This point-to-point mortise and tenon joining strategy provides a novel approach for designing other 2D energy storage materials with long cycle stability and high-rate capability.