Highly flexible and high energy density fiber supercapacitors based upon spiral silk composite membranes encapsulation

Abstract Fiber supercapacitors (FSCs) have attracted great interest recently as promising energy storage devices for wearable electronics. As an important factor for wearable electronics, FSCs require high flexibility and energy density. The current encapsulation methods would dramatically increase the overall diameter of FSCs, reduce the flexibility and knittability/weavability. Herein, a new encapsulating strategy that gives rise to fine FSCs with an overall diameter of ≈1mm is proposed. In particular, the ultra-thin, soft and sufficient mechanical strength of the silk composite membranes are used as an encapsulating material for the first time. This endows FSCs with significant flexibility. Meanwhile, FSCs with higher electrochemical performance have been obtained through a tight spiral-winding encapsulating strategy. This gives rise to the 28% enhancement of electrochemical performance of the FSCs encapsulated using silk composite membranes than that FSCs encapsulated using the traditional plastic tube. Specifically, the corresponding asymmetric FSCs encapsulated with silk composite membranes exhibit excellent performances with respect to a high energy density (12.9 mWh cm−3 at 80 mW cm−3), remarkable bending stability (≈97.1% capacitance retention for 1000 bending cycles), superior to most state-of-the-art supercapacitors. Moreover, the energy storage device woven with 12 FSCs can easily drive a watch and 65 light-emitting diodes. This work demonstrates a new encapsulating design strategy in which the encapsulated FSCs can improve their electrochemical performance without sacrificing flexibility and weavability. In addition, the transparent and skin-friendly silk composite membranes expand the advantages of FSCs in wearable energy storage applications.