All-in-one fiber for stretchable fiber-shaped tandem supercapacitors

Stretchable fiber-shaped supercapacitors (SFSSs) with high energy density and high-voltage output are becoming increasingly critical for powering wearable electronics. However, challenges still exist in the pursuit of combination of mechanical stretchability and excellent electrochemical performance due to the limitation of the fiber electrode. Here we circumvent these problems by developing a new type of “internal tandem” stretchable fiber-shaped supercapacitors based on high crystalline “all-in-one” polymer fiber. This polymer fiber has the combined properties of high conductivity, high flexibility, high specific capacitance and wide electrochemical window that can simultaneously function as electrical conductive wire and as energy storage electrode in an assembled device. The symmetric assembled tandem SFSS groups (T-SFSSs) are fabricated without the use of metal wire and additional welding connection showing tunable voltage output, tailored capacitance and outstanding stretchablility. The resulting T-SFSS assemblies consisting of 8 serially connected cells display high-voltage output of 12.8V, ultrahigh energy density of 41.1μWhcm−2 at power density of 3520μWcm−2 and remarkable stretchability of up to 400% without obvious capacitance degradation. This work provides a new family of flexible fiber electrode and novel concept designs of flexible power systems that could be threaded or integrated into wearable and portable electronics.