Design and Fabrication of CsSnI3 Electrodes with 2D Perovskite (BA2SnI4)-Enhanced PVDF-HFP Gel Polymer Electrolytes for Advanced Solid-State Supercapacitor Devices

In this study, a novel symmetric solid-state supercapacitor was fabricated by integrating lead-free CsSnI3 perovskite electrodes with a 2D Ruddlesden-Popper (BA2SnI4)-reinforced PVDF-HFP/NaPF6 gel polymer electrolytes (GPEs). Composite GPEs were prepared via a solution-casting method with varying BA2SnI4 contents (0-20 wt.%) to enhance ionic conductivity, mechanical flexibility, and interfacial stability. Among the prepared samples, the optimized PNPS3 electrolyte containing 15 wt.% BA2SnI4 exhibited the highest ionic conductivity of 1.12 mS cm–1 and lowest bulk resistance (92 Ω), attributed to the formation of efficient ion-hopping pathways and reduced polymer crystallinity. The structural analyses confirmed the successful incorporation of layered BA2SnI4 nanosheets and the formation of highly crystalline orthorhombic black-phase CsSnI3 electrodes. With an energy density of 25.8 Wh kg–1, a power density of around 500 Wh g–1, a low IR drop (0.042 V), an equivalent series resistance of 4.8 Ω and a charge transfer resistance of 12.6 Ω, an optimized symmetric CsSnI3/PNPS3/CsSnI3 devices produced a high specific capacitance at 186 F g–1 at 1 A g–1. After 5000 cycles, the device showed outstanding cycling stability, maintaining 92% with its initial capacitance with a coulombic efficiency of >97%. The composite electrolyte membrane sustained over 1000 bending cycles, confirming its mechanical robustness for flexible applications. The enhanced electrochemical performance is attributed to the synergistic coupling between conductive CsSnI3 electrodes and the layered BA2SnI4-reinforced polymer matrix, which promotes rapid Na+ transport, stable interfaces and suppressed degradation. For next-generation energy storage devices, this work offers an efficient method for developing flexible, high-energy-density and eco-friendly solid-state supercapacitors.