Sequential Electrochemical Construction of Hierarchical LIG/PPy/MnO2 Microsupercapacitors with High Areal Capacitance and Device-Level Stability

Abstract

Achieving high areal energy storage in flexible microsupercapacitors while maintaining compatibility with direct planar patterning remains challenging, particularly when multiple pseudocapacitive components must be sequentially integrated without compromising electrode accessibility or device level performance. In this paper, we develop a sequential electrochemical construction strategy to integrate polypyrrole (PPy) and manganese dioxide (MnO2) directly onto interdigitated laser-induced graphene (LIG) electrodes without preformed composite powders, slurry casting, or polymer binders. Porous LIG serves as the conductive framework and current collector, followed by in situ PPy electropolymerization and subsequent MnO2 electrodeposition. Systematic control of LIG processing, PPy growth, MnO2 deposition, and gel electrolyte composition establishes a fabrication window that balances electrical conductivity, pseudocapacitive material loading, and structural accessibility while preserving the underlying porous LIG architecture. Stepwise LIG, LIG/PPy, and LIG/PPy/MnO2 controls exhibit the same performance hierarchy at both the individual electrode and complete device levels, demonstrating that the electrochemical gains introduced during sequential functionalization are retained after complete microsupercapacitor (MSC) assembly. The resulting LIG/PPy/MnO2 device delivers an areal capacitance of 621.2 mF cm–2 at 0.37 mA cm–2 and a maximum areal energy density of 55.22 μWh cm–2 at 0.1494 mW cm–2. Extended rate measurements further demonstrate continued electrochemical operation up to 5 mA cm–2 under substantially increased current demand. The device retains 97.04% of its flat state capacitance at 180° static bending, exhibits a device-to-device RSD of 2.29%, retains 94.5% capacitance after 60 days of ambient storage, and maintains 85.1% after 5000 GCD cycles. Series integration further extends the operating voltage from 0.8 to 2.4 V with predictable electrical scaling and enables three MSCs to power a red LED for approximately 183 s. These results establish a directly patterned and independently controlled approach for translating hierarchical pseudocapacitive construction into high areal energy storage, reproducible device performance, and scalable voltage output.