Co ²⁺ -intercalated 3D Nb ₂ CT _x /CNTs flexible film via roller-wetting for superior lithium-ion storage

Abstract Conventional flexible MXene films are predominantly fabricated via vacuum filtration, which inevitably suffers from concentration polarization, strict size limitations, and structural brittleness at high mass loadings. To address this issue, we introduced carbon nanotubes (CNTs) as interlayer spacers, leveraging their high conductivity and mechanical strength. The flexible and self-supporting composite films Nb ₂ CT _x /CNTs with layered porous structures were prepared by roller wetting method and freeze-drying techniques. The porous architecture effectively inhibited the restacking of Nb ₂ CT _x nanosheets and provided numerous active sites. Furthermore, a Co ²⁺ -intercalated composite (Co@Nb ₂ CT _x /CNTs) was fabricated through electrostatic adsorption and thermal annealing. The resulting electrode material demonstrated a larger specific surface area, multiplied reactive sites, and a decreased charge transfer resistance. Owing to the synergistic effects, the Co@Nb ₂ CT _x /CNTs electrode achieved a marked enhancement in performance, exhibiting a high specific capacity (300.2 mAh g ⁻¹ at 0.05 A g ⁻¹ ) coupled with robust cyclic stability (229.6 mAh g ⁻¹ retained after 2000 cycles at 2 A g ⁻¹ ). In addition, its remarkable mechanical flexibility suggests potential applicability in flexible energy storage devices.