Silk-inspired stretchable fiber-shaped supercapacitors with ultrahigh volumetric capacitance and energy density for wearable electronics

Inspired by the naturally occurring silk, in this work, a novel parallel-like fiber-shaped supercapacitor (PFSS) was developed by using two silk-derived fiber electrodes. The ternary electrode, PANI@F-MWCNT@silk, was prepared by decorating raw silk yarn with 13 wt% of carboxyl-functionalized multi-walled carbon nanotube (F-MWCNT) and 16 wt% of polyaniline (PANI), which were utilized as a conductive interlayer and a pseudocapacitive wrapping layer, respectively. In a three-electrode configuration, the PANI@F-MWCNT@silk showed a large area-normalized capacitance of 95.5 mF cm(-2), and an ultrahigh volumetric capacitance of 63.7 F cm(-3) at 0.1 mA (0.1 mA = 5.3 mA cm(-2) and 3.5 A cm(-3)), which were obviously higher than numerous polyester fiber electrodes, and also comparable to or even better than many metal wire electrodes reported so far. The symmetric parallel-like all-solid-state supercapacitor device based on PANI@F-MWCNT@silk demonstrated an attractive capacitive performance with a high energy density of 1.22 mWh m(-2) at a power density of 127 mW m(-2). Moreover, benefiting from the extraordinary mechanical properties of silk, this ternary electrode exhibited a very large elongation of 33% with a high tensile strength of 225 MPa, and the silk-inspired PFSS could maintain more than 80% of its initial capacitance under an applied strain of 20%, suggesting a superb capacitive stability against deformations. Notably, the proposed fibrous substrate, which has abundantly existed in nature, may open up a new strategy to develop high-efficiency fiber-shaped power storage devices for wearable electronics.