Ultra-conductive Se-terminated MXene Nb2CSe2 via one-step synthesis for flexible fast-charging batteries

Transition-metal carbides and/or nitrides (MXenes) with versatile surface functional groups have captured considerable attention for fast-charging energy storage owing to their adjustable electronic structure and surface characteristics. However, conventional MXenes might be hampered by the complex preparation process and the limited conductivity due to the O-containing surface groups. Herein, the novel Se-terminated niobium carbide MXene (Nb2CSe2) with a “TMD+MXene”-like structure was successfully synthesized through a one-step “vapor-active” method, which could largely simplify the preparation with no need for acid etching, and improve the yield up to ∼99 wt.%. Nb2CSe2 exhibits high conductivity (7.14 × 104 S m−1) over 2000 times higher than the conventional MXene Nb2CTx (T = O/OH/F). Nb2CSe2 delivers a superior high-rate capacity of 270 mAh g−1 at 10 C and 170 mAh g−1 at 50 C, outperforming most of the reported MXenes-based materials (generally < 200 mAh g−1 at 10 C). It also shows a long cycling lifespan of over 6,500 cycles at 25 C without distinct decay. Moreover, the as-obtained flexible Nb2CSe2/CNTs paper retains stable conductivity when bending and spreading over 10,000 times. The one-step method in this work to construct the ordered chalcogen terminations may break new ground on the rational design of MXenes-based electrodes toward fast-charging energy storage.