Two-Level Biomimetic Designs Enable Intelligent Stress Dispersion for Super-Foldable C/NiS Nanofiber Free-Standing Electrode

Due to the lack of in-depth understanding about the folding issues of the electronic materials, it is a huge challenge to prepare a super-foldable and highly electrochemical faradic electrode. Here, inspired from from the fully nimble structures of cuit cocoons and cockscomb petals, with two-level biomimetic design, for the first time we prepared a super-foldable and electrochemically functional freestanding cathode, made of C-fiber@NiS-cockscomb (SFCNi). In virtue of its nimble biomimetic structures, SFCNi can remarkably sustain over 100,000 times, repeated true-folding without composite fibers fracture, functional matters detachment, conductivity degradation, or electrochemical performance change. The main mechanism behind these behaviors was disclosed by Real-time scanning electron microscopy and mechanical simulations, on the folding process. Results unveil that the cockscomb-like NiS with atomic thickness can deform freely due to the need of bending, and the cuit-cocoon-like SFCNi can generate an “ ε-shape ” folding structure at the crease. Such a smart self-adaptive deformation capability can effectively reduce the effect of stresses and local excessive deformations, so that the chemical bonds can preserve their interaction, and the material won’t fracture. This subtle and exceptional mechanical behavior realizes a super-foldable property. The two-level biomimetic design strategy is a novel method for fabrication of super-foldable composite electrodes and integrated multi-functional super-foldable devices. Graphical abstract