Organism epidermis/plant-root inspired ultra-stable supercapacitor for large-scale wearable energy storage applications

Abstract

Wearable energy storage system must maintain robust electrochemical performance under severe mechanical and chemical deformations. Here, we demonstrate wearable supercapacitor system assembled with electrodes composed of one-step carbonized plant epidermis and gelatin based hydrogel electrolyte which possesses high electrochemical performance and superior reliability under ambient condition. The carbonized mulberry paper (MP) was used as an electrode to achieve improved volumetric energy density as well as mechanical-chemical reliability (e.g. mechanical toughness and acid resistance). Rationally designed active materials composed of vertically grown WO 3 NRs and reduced graphene oxide (rGO) anchored on MP, were employed for developing organism epidermis based supercapacitor. Such electrode exhibits high volumetric energy and power densities of 30.28 mWh cm −3 and 7.67 W cm −3 , retaining the volumetric capacitance of 96.0% even after 110,000 charge-discharge cycles. As the final step, we employed the gelatin based electrolyte with high ionic conductivity to solve evaporation and leakage problems of conventional electrolytes. Organism epidermis based supercapacitor integrated with hydrogel electrolyte showed high electrochemical performance and long-term stability under ambient condition even after exposure to acid, demonstrating its gareat suitability as a large-scale wearable energy storage system. We demonstrate wearable supercapacitor system assembled with electrodes composed of one-step carbonized plant epidermis and gelatin based hydrogel electrolyte which possesses high electrochemical performance and superior reliability under ambient condition. Organism epidermis based supercapacitor integrated with hydrogel electrolyte showed high electrochemical performance and long-term stability under ambient condition even after exposure to acid, demonstrating its great suitability as a large-scale wearable energy storage system. • We maximized areal and volumetric electrochemical performance (energy & power densities) and mechanical/chemical toughness through carbonized mulberry paper integrated with reduced graphene oxide (rGO) layer. Mulberry fibers inherently show excellent mechanical flexibility and acid resistance, since they have lower portion of lignin cellulose (~40%) compared with conventional paper fiber. However, electrochemically inactive mulberry fiber exhibits still low areal/volumetric energy densities and electrochemical reliability. Thus, we used carbonized mulberry paper as a substrate and electrode in this study, which was maximized for volumetric energy/power densities and mechanical/chemical toughness. • We have designed the plant-root inspired active materials structure with excellent electrochemical reliability and performances. Inspired from plant-root, we synthesized active materials structure by one-step reduction heat treatment, where WO 3 nanorods (NRs) vertically grow within the spaces of rGO and are anchored as strongly as plant-root on the carbonized mulberry fibers. The anchored structure can effectively maintain electrochemical performance and flexibility of carbonized paper by preventing delamination of WO 3 NRs even without protection layer. WO 3 NRs anchored carbonized mulberry paper (thickness 110 µm) with rGO layer exhibits volumetric capacitance retention of 96% for 110,000 cycles. In addition, maximum volumetric energy and power densities were increased to 30.28 mWh cm −3 and 7.67 W cm −3 (improvement of 220%). • Conventional liquid and gel-type electrolyte have critical issues including evaporation under ambient condition and leakage under mechanical bending-twisting deformation. Such problems are main causes of rapid electrochemical performance degradation. In our work, gelatin based hydrogel electrolyte extracted from porcine skin was integrated with electrode, in order to fabricate wearable energy storage system that is capable of operating in ambient conditions. The gelatin based hydrogel electrolyte can retain water contents and high ionic conductivity under ambient condition over 2 weeks. Ionic conductivity maintained 90.3% (228 mS cm −1 ) after two weeks of exposure to ambient condition, and the moisture content was maintained 98.0%. • We further extended organism epidermis based supercapacitor to large-scale application capable of operation in ambient condition. High hydrophilicity of mulberry paper enables the uniform deposition of precursor material for growth of WO 3 , i.e, WO 3 precursor, that is dispersed in the aqueous solution. As a result, GO and WO 3 precursor were uniformly deposited on large-area electrode with 9, 25, 49 cm 2 followed by carbonization, resulting in the fabrication of large-scale organism epidermis based supercapacitor.