Surface Chemistry and Mesopore Dual Regulation by Sulfur‐Promised High Volumetric Capacity of Ti₃C₂T_x Films for Sodium‐Ion Storage

Abstract Electrochemical sodium‐ion storage has come out as a promising technology for energy storage, where the development of electrode material that affords high volumetric capacity and long‐term cycling stability remains highly desired yet a challenge. Herein, Ti₃C₂T_x (MXene)‐based films are prepared by using sulfur (S) as the mediator to modulate the surface chemistry and microstructure, generating S‐doped mesoporous Ti₃C₂T_x films with high flexibility. The mesoporous architecture offers desirable surface accessibility without significantly sacrificing the high density of Ti₃C₂T_x film. Meanwhile, the surface sulfur doping of Ti₃C₂T_x favors the diffusion of sodium ions. These merits are of critical importance to realize high volumetric capacity of the electrode material. As a consequence, as the freestanding electrode material for electrochemical sodium‐ion storage, the S‐doped mesoporous Ti₃C₂T_x film exhibits a high volumetric capacity of 625.6 mAh cm⁻³ at 0.1 A g⁻¹, which outperforms that of many reported electrodes. Moreover, outstanding rate capability and excellent long‐term cycling stability extending 5000 cycles are achieved. The work opens the door for innovative design and rational fabrication of MXene‐based films with ultrahigh volumetric capacity for sodium‐ion storage.