Stitchable supercapacitors with high energy density and high rate capability using metal nanoparticle-assembled cotton threads

Herein, we introduce a high-performance and highly flexible asymmetric supercapacitor that is prepared from metallic cotton threads coated with pseudocapacitive nanoparticles without the aid of carbon-based conductive materials. In this study, Au nanoparticles are layer-by-layer assembled on highly porous cotton threads using amine-functionalized molecular linkers in organic media for the preparation of metallic cotton threads that can store a large amount of pseudocapacitive nanoparticles. The highly porous metallic cotton threads exhibit exceptional electrical conductivity (∼2.1 × 10⁴ S cm^-1, resistance of ∼0.1 Ω cm^-1) and yet maintain the intrinsic flexibility of cotton. Using the same assembly method, Fe₃O₄ and MnO nanoparticles are deposited onto the metallic cotton threads to prepare the anode and the cathode, respectively, of the asymmetric supercapacitors, and furthermore, Au nanoparticles are periodically inserted between the pseudocapacitive multilayers to facilitate charge transport. The assembled all solid-state asymmetric supercapacitors with a unique structural design deliver a notable areal energy density of 80.7 μW h cm^-2 (at 172.5 μW cm^-2) and a power density of 3450.1 μW cm^-2 (at 53.7 μW h cm^-2), exceeding the performance of conventional thread-type asymmetric supercapacitors. We also emphasize that this energy performance can be further enhanced by increasing the number of metal and/or pseudocapacitive nanoparticle layers deposited.