Freeze-assisted Tape Casting of Vertically Aligned MXene Films for High Rate Performance Supercapacitors

Conventional electrode preparation techniques of supercapacitors such as tape casting or vacuum filtration often lead to the restacking or agglomeration of two-dimensional (2D) materials. As a result, tortuous paths are created for the electrolyte ions and their adsorption onto the surfaces of the active materials can be prevented. Consequently, maintaining high rate performance while increasing the thickness of electrodes has been a challenge. Herein, a facile freeze-assisted tape-casting (FaTC) method is reported for the scalable fabrication of flexible MXene (Ti3C2Tx) supercapacitor electrode films of up to 700 μm thickness, exhibiting homogeneous ice-template microstructure composed of vertically aligned MXene walls within lamellar pores. The efficient ion transport created by the internal morphology allows for fast electrochemical charge–discharge cycles and near thickness-independent performance at up to 3000 mV s−1 for films of up to 300 μm in thickness. By increasing the scan rate from 20 to 10,000 mV s−1, Ti3C2Tx films of 150 μm in thickness sustain 50% of its specific capacitance (222.9 F g−1). When the film thickness is doubled to 300 μm, its capacitance is still retained by 60 % (at 213.3 F g−1) when the scan rate is increased from 20 to 3000 mV s−1, with a capacitance retention above 97.7% for over 14,000 cycles at 10 A g−1. They also showed a remarkably high gravimetric and areal power density of 150 kW kg−1 at 1000 A g−1 and 667 mW cm−2 at 4444 mA cm−2, respectively. FaTC has the potential to provide industry with a viable way to fabricate electrodes formed from 2D materials on a large scale, while providing promising performance for use in a wide range of applications, such as flexible electronics and wearable energy storage devices.