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The development of eco-friendly, quasi-solid-state bio-polymer hydrogel electrolytes has become one of the challenging issues in energy storage. The assembly of safer devices has still been the key to be addressed for safety reasons. The present work reports the synthesis of bio-polymer electrolytes using sodium carboxy methyl cellulose (C)/citric acid (CA) support, which was further intercalated by Hibiscus sabdariffa (H), at various fractions. Stable and scalable blends were produced, and the ion transport was effectively enhanced via insertion of H, which occurred through Na + and H 3 O + ions from the corresponding "host and guest", where no external salt as ion source was inserted. The results showed that H in the hydrogel improved the ionic conductivity while maintaining the homogeneity and electrochemical stability. CCAH was coated on the carbon composite electrodes, and the devices were assembled, followed by experimental analysis under ambient conditions. The device exhibited excellent charge/discharge performance over 10,000 cycles with a specific capacitance of 442 F g −1 . In addition, the device offers a superior energy density of 72 W h kg −1 at a power density of 331 W kg −1 . Using non-toxic quasi-solid-state bio-polymer electrolyte hydrogels in devices may pave the way for safe usage in emerging wearable electronics and energy storage systems.

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The quasi-solid-state electrolytes for flexible energy storage devices have indicated a great advancement during the last decade. However, further progress is still required to resolve non-flammability issues, high ionic conductivity, as well as electrochemical stability. Herein, we designed a new complex gel electrolyte with glycerol (Gly)/boric acid (BA) to address the non-flammability and maintained high conductivity by doping with potassium hydroxide (KOH). The Gly/3KOH/3BA combination was the optimum composition in terms of stability as well as hierarchical array for improved ionic conductivity to 2.9 × 10–3 S cm–1. Flexible electrochemical double-layer supercapacitors were assembled by using carbon composite electrodes, and the device provided a specific capacitance of 327 F g–1 at 1 A g–1. A remarkable cyclic stability of 93.4% capacitive performance is maintained after 10,000 cycles. The device indicated a specific energy of 45.4 W h kg–1 at a power of 920 W kg–1. Highly flexible devices constructed by using boron-incorporated gel electrolytes can provide a new strategy to assemble flexible devices for wearable electronics.