Interface engineering of calligraphic ink mediated conformal polymer fibers for advanced flexible supercapacitors

Abstract

Bio-based fibers with excellent mechanical and electrochemical properties are crucial to construct high-performance fiber-shaped electrochemical supercapacitors (FESCs) for wearable applications. However, the available biofiber electrodes suffer greatly from the drawbacks of serious interface stability and mechanical durability. Herein, a novel interface engineering strategy was developed to simultaneously promote the mechanical and electrochemical properties of seaweed-derived alginate fibers for organic–inorganic–organic composite fiber electrodes. Utilizing calligraphic ink as a conformal interlayer, a universal scaffold with a hierarchical core–shell structure was formed for sufficiently depositing pseudocapacitive molecules on alginate fibers, which not only boosted the interface stability and mechanical durability, but also resulted in a pathway for effective electrolyte infiltration and accelerated ion diffusion and transfer. As expected, the conformal composite fiber electrode demonstrates an excellent areal capacitance of 1025.6 mF cm⁻² and an ultrahigh mechanical strength of 321 MPa (17 times vs. GO-based composite fibers). The as-assembled symmetrical FESC device shows a high energy density of 5.49 μW h cm⁻², surpassing most of the state-of-the-art symmetric FESCs based on synthetic fibers. This study provides a universal interface engineering strategy to promote the energy density of FESCs without sacrificing the mechanical strength, which is desirable for sustainable portable and wearable electronics.