Novel organic molecular bridging strategy in Ti3CN interlayers towards stable and rapid sodium ions storage

Abstract

MXenes is considered as one of the most potential sodium ions storage materials due to its superior metallic conductivity, abundant surface functional groups, extensive specific surface area, and tunable interlayer spacing. Nevertheless, its practical application is hindered by severe volumetric expansion/shrinkage and slow sodium ions diffusion during sodium ions insertion/extraction process. Herein, a novel organic acid molecules bridging strategy is reported to stabilize layered structure and adjust the interlayer spacing of Ti₃CN, which is realized by bridging organic acid molecules (named as TOAA) into Ti₃CN interlayers (named as Ti₃CN-TOAA) to form strong amido (HNC=O) bonds. The carbonyl groups of TOAA molecules can not only provide active sites for sodium ions storage, but also inhibit volumetric expansion/shrinkage by providing strain/pillar effects within the Ti₃CN interlayers, achieving stable and rapid sodium ions storage. Consequently, the interlayer spacing of Ti₃CN-TOAA (1.42 nm) is enlargered compared with that of Ti₃CN (1.22 nm), while the sodium ions migration barrier of Ti₃CN-TOAA is reduced by 0.09 eV Ti₃CN-TOAA demonstrates superior cycling stability (the capacity retention remains at 83.2% after 2000 cycles at 0.5 A g^-1) and rate capability (2.5 times the capacity of pristine Ti₃CN at 5.0 A g^-1). Significantly, the Ti₃CN-TOAA||AC sodium ions capacitor (SIC) exhibits excellent cycling stability, retaining 79.3% of its capacity after 8000 cycles at 1.0 A g^-1. This work presents a novel approach to achieving stable and rapid sodium ions storage by stabilizing layered structure and adjusting interlayer spacing.