Strong Ti₃ C₂ T_x MXene-Based Composite Films Fabricated through Bioinspired Bridging for Flexible Energy Storage...

Flexible energy storage device is one of the most critical components as power source for wearable electronics. The emergence of MXenes, a growing family of 2D nanomaterials, has demonstrated a brand-new possibility for flexible energy storage. However, the fabrication of MXene films with satisfactory mechanical, electrical, and electrochemical reliabilities remains challenging due to the weak interlayer interactions and self-restacking of MXene sheets. Sequential bridging of polydopamine/polyethyleneimine-functionalized (PDA/PEI)-coated MXene sheets to induce synergistically covalent and hydrogen binding connections of MXene-based films is demonstrated here. By interrupting self-hydrogen bonding and π-π stacking interactions, the introduction of long-chain PEI can not only inhibit the massive aggregation of PDA, but also improve the continuity of the interconnection network of PDA/PEI between MXene layers. Hence, the as-prepared MXene/PDA/PEI composite film displays high mechanical strength (≈366 MPa) which achieves 12-fold improvement compared with pure MXene film, as well as superior energy storage capability (≈454 F g^-1  at 5 mV s^-1 ) and rate performance of ≈48% at 10 000 mV s^-1 . This modulation of inserted polymer between MXene layers can provide an avenue for assembling high performance MXene films, and can even be extended to the fabrication of other 2D platelets for varied applications.