Controllable Synthesis of Atomically Thin Type-II Weyl Semimetal WTe2 Nanosheets: An Advanced Electrode Material for All-Solid-State Flexible Supercapacitors

Compared with 2D S-based and Se-based transition metal dichalcogenides (TMDs), Te-based TMDs display much better electrical conductivities, which will be beneficial to enhance the capacitances in supercapacitors. However, to date, the reports about the applications of Te-based TMDs in supercapacitors are quite rare. Herein, the first supercapacitor example of the Te-based TMD is reported: the type-II Weyl semimetal 1Td WTe2. It is demonstrated that single crystals of 1Td WTe2 can be exfoliated into the nanosheets with 2-7 layers by liquid-phase exfoliation, which are assembled into air-stable films and further all-solid-state flexible supercapacitors. The resulting supercapacitors deliver a mass capacitance of 221 F g(-1) and a stack capacitance of 74 F cm(-3). Furthermore, they also show excellent volumetric energy and power densities of 0.01 Wh cm(-3) and 83.6 W cm(-3), respectively, superior to the commercial 4V/500 mu Ah Li thin-film battery and the commercial 3V/300 mu Ah Al electrolytic capacitor, in association with outstanding mechanical flexibility and superior cycling stability (capacitance retention of approximate to 91% after 5500 cycles). These results indicate that the 1Td WTe2 nanosheet is a promising flexible electrode material for high-performance energy storage devices.