Conductive and highly compressible MXene aerogels with ordered microstructures as high-capacity electrodes for Li-ion capacitors

Assembling two-dimensional (2D) materials into functional three-dimensional (3D) structures can enable their use in a wide variety of applications. For energy storage devices, 3D electrodes with high ionic and electronic transport properties and decent mechanical properties are expected to prompt the fabrication of the next generations of devices with high energy and power densities. Herein, we report a simple, efficient, and scalable process based on unidirectional freeze casting to fabricate ordered and porous 3D aerogels from 2D Ti3C2Tx MXene flakes. The fabricated aerogels show excellent mechanical, electrical, and electrochemical properties. Our studies show that the processing conditions significantly affect the properties of MXene aerogels. The electrical conductivity and mechanical properties of fabricated aerogels directly correlate with their structural features. The mechanical test results showed that MXene aerogels with ordered structures could withstand almost 50% of strain before recovering to their original shape and maintain their electrical conductivities during continuous compressive cycling. As electrode materials for lithium-ion capacitors, the fabricated aerogels delivered a significantly high specific capacity (~1210 mAh/g at 0.05 A/g), excellent rate capability (~200 mAh/g at 10 A/g), and outstanding cycling performance. We believe that the MXene aerogels with ordered structures have promising properties for a broad range of applications, including energy storage devices and strain sensors.