Phase Engineering of MXene Derivatives Via Molecular Design for High-Rate Sodium-Ion Batteries

Since 2019, research into MXene derivatives has seen a dramatic rise; further progress requires a rational design for specific functionality. Herein, through a molecular design by selecting suitable functional groups in the MXene coating, we have implemented the dual N doping of the derivatives, nitrogen-doped TiO₂@nitrogen-doped carbon nanosheets (N-TiO₂@NC), to strike a balance between the active anatase TiO₂ at low temperatures, and carbon activation at high temperatures. The NH₃ reduction environment generated at 400 °C as evidenced by the in situ pyrolysis SVUV-PIMS process is crucial for concurrent phase engineering. With both electrical conductivity and surface Na⁺ availability, the N-TiO₂@NC achieves higher interface capacitive-like sodium storage with long-term stability. More than 100 mAh g⁻¹ is achieved at 2 A g⁻¹ after 5000 cycles. The proposed design may be extended to other MXenes and solidify the growing family of MXene derivatives for energy storage.