Unlocking Unprecedented Gravimetric Capacitance in Thick Electrodes Through Conformal Densification of Robust MXene Hydrogels

Transition metal carbides/nitrides (MXenes), with intrinsic high density and pseudo-capacitance, along with the capability for liquid-phase assembly mediated by highly tunable colloidal chemistries, are promising candidates for developing thick electrodes toward high-energy devices. However, the manufacture of high-performance thick MXene electrodes faces fundamental challenges, including nanosheet restacking, 3D structural collapse, and surface oxidation. Here, a robust MXene gelation strategy induced by aniline (ANI) and hydrochloric acid is proposed, producing a skeleton-reinforced hydrogel that enables conformal densification via capillary shrinkage with minimal active site loss. During gelation, ANI absorbs onto MXene surfaces and polymerizes, simultaneously reinforcing the 3D network through covalent bonding while forming temporary hydrophobic layers to protect active sites. Subsequent thermal treatment effectively removes the surface-bound ANI and its oligomers, restoring the active sites for capacitive energy storage. At a thickness of 225 µm, the resulting electrode achieves a record gravimetric capacitance (395 F g⁻¹) among reported MXene electrodes over 40 µm, even surpassing that of a 7 µm MXene film, and delivers a high areal capacitance of 16.1 F cm⁻². This work provides a new insight for assembling robust MXene architectures toward practical MXene-based devices.