All-MXene (2D titanium carbide) solid-state microsupercapacitors for on-chip energy storage

On-chip energy storage is a rapidly evolving research topic, opening doors for the integration of batteries and supercapacitors at the microscale on rigid and flexible platforms. Recently, a new class of two-dimensional (2D) transition metal carbides and nitrides (so-called MXenes) has shown great promise in electrochemical energy storage applications. Here, we report the fabrication of all-MXene (Ti3C2Tx) solid-state interdigital microsupercapacitors by employing a solution spray-coating method, followed by a photoresist-free direct laser cutting method. Our prototype devices consisted of two layers of Ti3C2Tx with two different flake sizes. The bottom layer was stacked large-size MXene flakes (lateral dimensions of 3-6 mm) serving mainly as current collectors. The top layer was made of small-size MXene flakes (similar to 1 mm) with a large number of defects and edges as the electroactive layer responsible for energy storage. Compared to Ti3C2Tx micro-supercapacitors with platinum current collectors, the all-MXene devices exhibited a much lower contact resistance, higher capacitances and better rate-capabilities. Areal and volumetric capacitances of similar to 27 mF cm(-2) and similar to 357 F cm(-3), respectively, at a scan rate of 20 mV s(-1) were achieved. The devices also demonstrated excellent cyclic stability, with 100% capacitance retention after 10 000 cycles at a scan rate of 50 mV s(-1). This study opens up a plethora of possible designs for high-performance on-chip devices employing different chemistries, flake sizes and morphologies of MXenes and their heterostructures.