Interfacial Engineering of Iodine-Polymer-Carbon Hybrid Cathodes for High-Energy Zn//I₂ Microbatteries

Miniaturized energy-storage devices with high energy density, fast charge-storage kinetics, and long-term durability are essential for next-generation on-chip electronics. Among various candidates, zinc-iodine (Zn//I₂) microbatteries (MBs) are attractive owing to their intrinsic safety, low cost, and rapid iodine redox chemistry. Herein, a printed coplanar Zn//I₂ MB is developed using a cathode-confined iodine strategy, in which redox-active iodine is immobilized within a rationally engineered polyaniline (PANI) and activated-carbon (AC) (I₂@AC-PANI) composite cathode framework. The synergistic AC-PANI architecture enhances iodine utilization, charge-transfer kinetics, and electrochemical reversibility, resulting in improved capacity, rate capability, and cycling stability. Through a combination of ex situ spectroscopic analyses, electrochemical measurements, self-discharge studies, and density functional theory (DFT) calculations, stronger interactions between iodine species and the AC-PANI framework are identified, together with enhanced charge-transfer characteristics compared with AC alone. As a result, the coplanar Zn//I₂ microbattery delivers an areal energy of 36.35 µWh cm^-2 at an areal power of 50 µW cm^-2 and retains 86.4% of its initial capacity after 2000 cycles. This work demonstrates that cathode-confined halogen chemistry combined with AC-PANI engineering provides an effective strategy for developing high-performance coplanar microbatteries and offers a promising route toward safe, integrable, and durable microscale energy-storage systems.