Enhanced rate capability and cycle stability of Ti₂C MXene for sodium storage through an aniline molecules welding strategy

MXenes obtained significant attention in the field of energy storage devices due to their characteristic layered structure, modifiable surface functional groups, large electrochemically active surface, and regulable interlayer spacing. Nonetheless, the self-restacking and sluggish ions diffusion kinetics performance of MXenes during the alkali metal ions insertion/extraction process severely impedes their cycle stability and rate capability. This paper proposes an aniline molecule welding strategy for welding p-phenylenediamine (PPDA) into the interlayers of Ti₂C through a dehydration condensation reaction. The welded PPDA molecules can contribute pillar effect to the layered structure of Ti₂C. The pillar effect effectively maintains the structural stability during the sodium ions insertion/extraction process and effectively expands the interlayer spacing of Ti₂C from 1.16 to 1.38 nm, thereby enhancing ions diffusion kinetics performance and improving the long-term cycle stability. The Ti₂C-PPDA demonstrates outstanding Na⁺ storage capability, exhibiting a specific capacity of 100.2 mAh·g⁻¹ at a current density of 0.1 A·g⁻¹ over 960 cycles and delivering a remarkable rate capability 81.2 mAh·g⁻¹ at a current density of 5 A·g⁻¹. The study demonstrates that expanding interlayer spacing is a promising strategy to enhance the Na⁺ storage capacity and improve long-term cycling stability, which provides significant guidance for the design of two-dimensional Na⁺ storage materials with high-rate capability and cycle stability.