A Flexible, Bioadhesive, and Breathable On‐Skin Battery Based on Silk Fibroin Hydrogel for Wearable Electronics

Abstract On‐skin electronics rely on flexible power sources for stable operation and comfortable wearing. However, the current materials and device designs of on‐skin batteries for human‐interface electronic systems suffer from inadequate adhesion and impermeability. In this work, a general design of a bioadhesive and breathable on‐skin flexible metal‐air battery is presented. By laterally loading a conducting polymer‐based cathode and a zinc anode onto a biocompatible silk fibroin ionic hydrogel electrolyte film, the battery exhibits good epidermal adhesions (shear strength exceeds 20 kPa and interface toughness exceeds 150 J m −2 ) and excellent sweat breathability (3 times greater than commercial 3 M breathable dressing). A singular battery can generate an open circuit voltage of up to 1.4 V and a power density of 72 µW cm −2 . It shows stable adhesion to the skin for five days, while simultaneously preserving epidermal respiratory function and facilitating natural skin movement. On‐skin integration of the battery array can be easily conducted to increase the electrical output. This battery design enhances the usability, comfort, and safety of wearable electronics, enabling new applications in healthcare, fitness tracking, and beyond.