Laser-induced graphene electrode and eco-friendly chitosan–poly(ethylene)glycol–LiClO4 electrolytes for all-solid state flexible supercapacitors

Abstract

The growing global demand for flexible, safe, and sustainable energy storage systems has intensified research into advanced materials for next-generation electrochemical devices. In response to this need, the present study focuses on the preparation and characterization of a biopolymer blend electrolyte using chitosan (CS) and poly(ethylene)glycol 8000 (PEG) with lithium perchlorate (LiClO₄) incorporated for solid-state supercapacitor applications. The optimal blend composition of 70 wt% CS and 30 wt% PEG (named CP30) was subsequently doped with varying concentrations of LiClO₄ (10–50 wt%, named CPLxx, with “xx” representing the weight percentage) to enhance ionic conductivity. Electrochemical impedance spectroscopy (EIS) revealed a maximum room temperature ionic conductivity of 1.27 × 10⁻⁴ S cm⁻¹ for the CPL40 (70 wt% CS, 30 wt% PEG and 40 wt% LiClO₄) composition, attributed to improved segmental mobility and lithium-ion dissociation. Electrochemical stability up to 3.23 V was established via linear sweep voltammetry (LSV). Two solid state double layer capacitors were fabricated with this solid electrolyte, employing activated carbon and Laser-induced graphene (LIG) as symmetric electrodes. The activated carbon-based device demonstrated a maximum specific capacitance of 5.32 F g⁻¹ at 0.01 A g⁻¹, while the LIG-based device exhibited an areal capacitance of 18.83 mF cm⁻² at 0.02 mA cm⁻². Both systems showed good cycling stability, retaining 84.2% and 89.3% of their initial capacitance after 3000 charge–discharge cycles. Additionally, the LIG-based device maintained 97.8% capacitance retention after 500 mechanical bending cycles, underscoring its flexibility and electrochemical durability. The influence of electrode loading was carefully addressed to enable a fair and meaningful performance evaluation of the two systems. These findings collectively demonstrate the potential of CS–PEG–LiClO₄ biopolymer electrolytes integrated with carbon-based electrodes to realize eco-friendly and flexible all-solid-state supercapacitors.