Highly stretchable CNT/MnO2 nanosheets fiber supercapacitors with high energy density

Fiber-shaped supercapacitors (FSSCs) are promising devices in the wearable electronics because of their good flexibility, weavability, tiny volume and lightweight. However, the low stretchability and energy density limit their practical applications on wearable electronics requiring deformation and high energy density. It remains challenging to increase the energy densities of FSSCs without sacrificing their stretchability. Herein, we design and construct a wearable, stretchable and high-energy density CNT/MnO2 nanosheets FSSCs by wrapping the fiber supercapacitors on the spandex yarn. The CNT/MnO2 FSSCs show high stretchability up to 80%, ultrahigh capacitances of 685 mF cm−2 and energy density of 15.2 μWh cm−2. Furthermore, the CNT/MnO2 FSSCs have the good flexibility, stability and ultralong cycle life. In addition, we also develop the in situ characterization strategy to evaluate the structure evolution during the stretching process of the CNT/MnO2 FSSCs for better understanding the structure evolution of stretchable FSSCs. This work paves the way for the high-performance stretchable energy storage devices.