Long Life with Ultrahigh Capacitance Flexible Electrode At Practical Mass Loading For Battery Supercapacitor Hybrid

Abstract Designing economic and bio‐degradable flexible electrodes with industry‐standard mass loading (>10 mg cm ⁻² ) poses significant challenges for stable and durable energy storage devices. In this report, an endeavor is made to design flexible and bio‐degradable laboratory filter paper‐based electrodes for eco‐friendly and pocket‐friendly flexible battery supercapacitor hybrids (BSHs) via a combination of electroless and electrodeposition techniques. Filter paper (FP) is made conductive by electroless deposition of NiB‐layer (Ni/NiB‐FP) on which high mass loadings of nickel iron phosphide active material (4.5 to 17 mg cm ⁻² ) are deposited via electrodeposition method for the development of NiFeP@Ni/NiB‐FP flexible electrodes. The developed NiFeP@Ni/NiB‐FP electrode (17 mg cm ⁻² ) undergoes electrochemical activation by surface reconstruction to achieve ultrahigh areal capacitance of 37.5 F cm ⁻² (18.75 C cm ⁻² , 2220 F g ⁻¹ ) at 5 mA cm ⁻² as battery type electrode with exceptional rate capability (90.6% at 30 mA cm ⁻² ) and ultrastable cycling retaining 37.4 F cm ⁻² at 5 mA cm ⁻² even after continuous cycling for 1329 h (≈55 days). As a proof of concept, a tandem device with four flexible paper‐based BSH cells in series is demonstrated to achieve stable operational voltage up to 6 V. Practical applicability is showcased by powering a panel with 50 LEDs (each rated 1.6 V), a small fan, a digital calculator and a digital thermometer while measuring the body temperature highlighting the versatility for for diverse applications.