Complete utilization of electrochemically active materials while maintaining the high areal/volumetric packing density is a goal to be achieved in miniaturized supercapacitor devices, which therefore display both high volumetric and areal energy density. Although critical, it is usually challenging to achieve this goal by optimizing the electrode architecture. Dense packing of active materials maximizes the volumetric capacitance but also results in sluggish diffusion of the electrolyte. Structurization of the electrode by forming large pores creates a pathway for electrolyte penetration but reduces the volumetric energy density. Here, densified electrodes with hierarchical porous architecture at the nanoscale are reported, which provide an alternative solution. Worm-like expanded titanium carbide MXene powders are produced in highly viscous reaction media and assembled by mechanical compression. The expanded morphology of the MXene powders translates into a buckling microstructure in the electrodes, resulting in 28.2 ± 4.1% porosity mainly in the form of nanosized pores. At the sub-nanometer scale, the diffusion of electrolytes is enhanced in interlayer space of the bended lattice with pillared intercalants. These hierarchical structural features lead to both high areal and volumetric capacitance (11.4 F cm-2 coupled with 770 F cm-3 ) in hundred-micrometers-thick electrodes, which inspires the design of high-performance electrochemical energy storage devices.
Keywords: mechanical compression; powder materials; structural stability; supercapacitors; titanium carbide MXene.
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