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

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.