Nb₂CT_x MXene Anchored with Carbon Quantum Dots for Lithium-Ion Batteries

Nb 2 CT x is a candidate MXene material for lithium-ion batteries because of its advantages in ion movement, diffusion barrier, and average intercalation potentials. However, Nb 2 CT x nanosheets tend to self-restack when assembled into electrodes because of the strong van der Waals force between them. Electrodes with densely packed Nb 2 CT x nanosheets can limit the diffusion of Li-ions and impair their electrochemical performance. Here, carbon quantum dots (CQDs) are anchored on the Nb 2 CT x nanosheets by a hydrothermal reaction to expand the interlayer spacing and create abundant Li-ion transport channels. The CQD-Nb 2 CT x nanosheets have higher specific surface area (84 m 2 /g), more active sites, and more Li-ion diffusion paths, which can facilitate the transfer of Li-ions. The CQD-Nb 2 CT x electrode exhibits a high capacity of 334 mAh/g at 50 mA/g and good long-term cycling stability of 1000 cycles with 260 mAh/g at 1 A/g.