Binder-free WS2 nanosheets with enhanced crystallinity as a stable negative electrode for flexible asymmetric supercapacitors

Tungsten disulfide (WS2) has been emerging as an attractive electrode material for supercapacitors because of its intrinsically layered structure and high capacitance. Unfortunately, most of the currently developed WS2-based electrodes suffer from poor conductivity and fast capacitance fading. In this work, we demonstrated that the durability of WS2 nanosheets can be remarkably boosted via improving their crystallinity and the first example of using these WS2 nanosheets as a high-energy and stable negative electrode for flexible asymmetric supercapacitors (ASCs). Electrochemical results reveal the WS2 nanosheets with enhanced crystallinity were able to deliver an excellent durability with more than 82% capacitance retention after 10 000 cycles and an areal capacitance of 0.93 F cm−2 at 4 mA cm−2. Importantly, when using the as-prepared WS2 nanosheets as a negative electrode, a flexible and stable ASC device with an extraordinary volumetric energy density of 0.97 mW h cm−3 is obtained. This work affords new opportunities to use WS2 nanostructures and other 2D TMDs in constructing high-performance energy-storage devices.