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

The self-stacking of MXenes-Ti3CN 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-Ti3CN (1,4-PDEA-Ti3CN) by grafting rigid and flexible 1,4-phenylenediacetic acid (1,4-PDEA) into the amino-functionalized Ti3CN interlayers. The rigid and flexible 1,4-PDEA contributes to a pillar effect in the layered structure of Ti3CN, which is benefit to prevent the self-stacking and maintain a stable 2D layered structure. As a result, the interlayer spacing of Ti3CN 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 cm2 s−1 after point-to-point 1,4-PDEA grafting. The 1,4-PDEA-Ti3CN 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-Ti3CN 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.