Ultralight supercapacitors utilizing waste cotton pads for wearable energy storage.

Successful popularization of wearable energy storage devices lies in the exploitation of scalable fabrication technologies that are based on economically viable materials. Herein, we reveal that discarded cotton pads can be used as a cost-efficient substrate for the in situ polymerization of pyrrole and exhibited good mechanical flexibility, lightness, and high conductivity. To extend the applications of the resulting PPy-coated cotton pads (PCPs) to the supercapacitor field, a layer of MnO2 nanosheets was further decorated on the surface of PCPs (PCPs@MnO2) by a simple electrochemical deposition technique. The PPy coating not only improves the electrical conductivity of the cotton pads, but also increases the contact between the active materials and the cotton fibers. Amazingly, ultrathin (≈ 0.8 mm) flexible solid-state asymmetric supercapacitors (ASCs) using PCPs@MnO2 as the positive electrode and active carbon coated on PCPs (PCPs@AC) as the negative electrode display a high areal capacitance of 1.21 F cm-2 at 1 mA cm-2, and a high energy density of 6.8 mW h cm-3 at a power density of 11.2 mW cm-3, which can also be tailored and folded into various shapes with only slight capacitance fading. These findings demonstrate that the prepared advanced ultralight, flexible and renewable cotton pads hold great promise for practical application in wearable energy storage systems with high cost effectiveness and scalability.