3D printed inks of two-dimensional semimetallic MoS2/TiS2 nanosheets for conductive-additive-free symmetric supercapacitors

Abstract

The semimetallic 1T′ and 1T phases of two-dimensional (2D) transition metal dichalcogenides (TMDs) have been attracting considerable attention as promising materials for electrochemical technologies owing to their intrinsic electrical conductivity and exceptionally high ion-intercalation properties. Achieving the 1T′ phase of MoS₂ in high concentration and preserving it during device operation are still pressing challenges as the phase is metastable. Herein, we demonstrate 3D printed electrodes of 1T′/1T MoS₂/TiS₂ nanosheets for microsupercapacitors. The highly concentrated water-based inks of exfoliated 1T′/1T MoS₂/TiS₂ nanosheets were suitable for the printing of 3D architectures with arbitrary geometry, micron-sized features and spatial uniformity. Such architectures are used as microsupercapacitor electrodes which exhibit an areal capacitance of 448.16 mF cm⁻² at a current density of 0.1 mA cm⁻². TMD-based microsupercapacitors with high-mass loading (up to 100 mg cm⁻²) 3D electrodes also exhibited excellent cycling stability and coulombic efficiency over 100 000 cycles, while retaining the 1T′ phase. Overall, the high mass loading of the printed electrode and the conductivity and the geometry of the electrodes contribute to achieving energy and power density (3.89 μW h cm⁻² and 250 μW cm⁻², respectively) which are prime amongst those of the TMD-based supercapacitors. This work demonstrates the possibility of formulating and processing inks of 2D TMDs without conductive additives, paving the way towards the manufacturability of electrically conductive device components based on metastable materials.