Bioceramic Ionic Conductor Enabling Multifunctional Hydrogel Electrolytes for Printable On‐Body Devices

ABSTRACT The rapid advancement of flexible electronics has imposed urgent need for lightweight, integrated, and biocompatible energy storage devices in wearable applications. Herein, bioceramic (hydroxyapatite, HA) ionic conductor is synthesized at kilogram scale via a simple ion‐exchange method using ZnCl 2 , effectively avoiding CaSO 4 •2H 2 O impurities. Zn‐doped hydroxyapatite (ZnHA) is then combined with gelatin to form a hydrogel electrolyte (ZnHA/Gel). The impurity‐free ZnHA provides additional Zn 2+ transport pathways that synergize with ion migration in the gelatin matrix, achieving a high ionic conductivity of 42.2 mS cm −1 . Moreover, the abundant hydroxyl groups on ZnHA promote Zn salt dissociation and Zn 2+ desolvation, suppressing side reactions such as hydrogen evolution and corrosion. Meanwhile, strong interactions between ZnHA and gelatin enhance the mechanical strength of the electrolyte and inhibit dendrite growth. As a result, the half cells operate stably for over 2800 h at 1 mA cm −2 /1 mAh cm −2 , while the full cells retain 90% of their capacity after 1000 cycles. Notably, the biomass‐derived components impart printability, degradability, recyclability, and biocompatibility to the electrolyte. Finally, flexible batteries were 3D printed and integrated with wearable sensor and LEDs to form an interactive system, demonstrating good potential for next‐generation flexible and on‐body electronic applications.