Harnessing In Situ Iodine Ionic Liquids for High Areal Capacity and Long Cycle Life Zn//I2 Solid Microbatteries

Abstract Zn‐ion microbatteries (MBs), distinguished by their simple fabrication process, low material costs, and high safety, are ideal candidates for powering microelectronic devices. Nevertheless, most Zn‐ion MBs face momentous performance challenges of limited areal capacity and insufficient cycling as a result of poor contact between the electrode and electrolyte. In this work, a liquid–solid electrode–electrolyte contact is designed by harnessing in situ generated iodine ionic liquids to produce Zn//I 2 solid MBs with unprecedented energy storage capabilities, even at temperatures as low as −20 °C. As a result, Zn//I 2 MBs demonstrate an ultrahigh capacity of 7.2 mAh cm −2 , energy density of 8.3 mWh cm −2 , and stable cycling for over 900 cycles with a Coulombic efficiency of 99.8% at room temperature. Even at −20 °C, the MBs still afford a capacity of 3.9 mAh cm −2 and an energy of 4.1 mWh cm −2 . Operando spectroscopic analysis and theoretical calculations are employed to track the evolution of ionic liquid electrodes upon electrochemical cycling. Moreover, such MBs are integrated into flexible Bluetooth sensor modules, thereby ushering in a bright future for powering microscale electronics.