A Flexible and Safe Planar Zinc‐Ion Micro‐Battery with Ultrahigh Energy Density Enabled by Interfacial Engineering for Wearable Sensing Systems

Abstract Aqueous zinc‐ion micro‐batteries (ZIMBs) have attracted considerable attention owing to their reliable safety, low cost, and great potential for wearable devices. However, current ZIMBs still suffer from various critical issues, including short cycle life, poor mechanical stability, and inadequate energy density. Herein, the fabrication of flexible planar ZIMBs with ultrahigh energy density by interfacial engineering in the screen‐printing process based on high‐performance MnO 2 ‐based cathode materials is reported. The Ce‐doped MnO 2 (Ce‐MnO 2 ) exhibits significantly enhanced capacity (389.3 mAh g −1 ), considerable rate capability and admirable cycling stability than that of the pure MnO 2 . Importantly, the fabrication of micro‐electrodes with ultrahigh mass loading of Ce‐MnO 2 (24.12 mg cm −2 ) and good mechanical stability is achieved through optimizing the interfacial bonding between different printed layers. The fabricated planar ZIMBs achieve a record high capacity (7.21 mAh cm −2 or 497.31 mAh cm −3 ) and energy density (8.43 mWh cm −2 or 573.45 mWh cm −3 ), as well as excellent flexibility. Besides, a wearable self‐powered sensing system for environmental monitoring is further demonstrated by integrating the planar ZIMBs with flexible solar cells and a multifunctional sensor array. This work sheds light on the development of high‐performance planar ZIMBs for future self‐powered and eco‐friendly smart wearable electronics.