All-solid-state wire-shaped micro-supercapacitors: A microfluidic approach to core-shell structured bacterial cellulose-GN/PPy fibers

The one-dimensional (1D) wire-shaped micro-supercapacitors (micro-SCs) hold great structural advantages of low mass/volume with promising applications in wearable electronics. All-solid-state wire-shaped micro-SCs, characterized by their lightweight, high capacitance, flexibility, and robust mechanical stability, have been developing in a promising direction of energy storage devices. These 1D fiber-shaped supercapacitors can be independently operated or woven into various shapes, accommodating diverse applications. Despite their potential, the complexity of their preparation processes, especially the continuous fabrication process, remains a significant challenge. This study introduces a novel microfluidic technique for synthesizing core-shell structured fibers using bacterial cellulose (BC) and graphene (GN) with a polypyrrole (PPy) coating. Utilizing BC as a scaffold and GN for enhanced electrical properties, this method ensures uniformity in fiber structure and stability in the PPy shell. Employing a solid-state H₃PO₄/PVA gel as the electrolyte, the developed micro-SCs demonstrated exceptional electrochemical performance, evidenced by a high specific capacitance of 162 mF cm⁻², an energy density of 96.5 mW h cm⁻², and superior cycling stability with 95.11 % capacitance retention after 5000 cycles. This work contributes to the fabrication of filament electrodes inspired by the microfluidic strategy, which allows one to design the unique architecture of core-shell structured BC-GN/PPy fibers for the construction of micro-SCs in high performance wearable electronics.