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Flexible and Stretchable Fiber for Energy Harvester and Supercapacitor

Flexible and Stretchable Fiber for Energy Harvester and Supercapacitor
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Flexible and stretchable yarn-based energy harvester and storage system are needed for existing and emerging wearable applications. commercial energy device was rigid and heavy form, thus, lightweight yarn/fiber or fabric type energy device have been needed. the research plan can be grouped into three parts: 1) Multi-direction stimuli mechanical fiber nanogenerator, 2) achieving stretchability in tensile direction by coiling and noncoiling structure, and 3) fiber type biocompatible supercapacitor for storaging electric energy from mechanical nanogenerator. At first, in order to achieve multi-direction stimuli flexible fiber type mechanical nanogenerator, PVDF-TrFE electrospun mats which has piezoelectric property are introduced. Flexible two-ply piezoelectric yarn-type generator using an electrospun polyvinylidenefluorideco- trifluoroethylene (PVDF–TrFE) mats and a commercially available silver-coated nylon fiber. By rolling the silvercoated nylon fiber into the electrospun PVDF–TrFE mats as the inner electrode, the two-dimensional piezoelectric PVDF–TrFE mats were easily transformed into a one-dimensional fiber. Then silver-coated nylon fiber rolled in PVDF–TrFE was plied with another similar fiber to make a flexible two-ply piezoelectric yarn. The overall fabrication processes of the flexible two-ply piezoelectric yarns were simple and have a high application potential. The flexible two-ply piezoelectric yarn can generate up to 0.7 V in compression and 0.55 V in tension. The yarn retained the piezoelectric performance in various shapes, such as a sewn structure. In addition, the piezoelectric performance was sensitive to velocity and pressure. Another strategy for multi-direction stimuli flexible fiber type mechanical nanogenerator is formed as core-shell structure. We have developed highly flexible piezoelectric fibers consisting of electrospun PVDF–TrFE mats, silver coated nylon, CNT sheets, and SEBS. The fibers were fabricated by a simple rolling and coating method. The fibers are robust and can be plied, coiled, knotted, sewn, and woven without damage. The individual flexible piezoelectric fiber shows piezoelectric voltage outputs to 2.6V in lateral compression and up to 1.4V during longitudinal extension. For second goal, in order to develop the reversibly stretchable fiber and yarn piezoelectric nanogenerator without performance loss, coil structured yarns or fibers structure are introduced. The stretchable coiled piezoelectric fibers are made by using a inserted twist to flexible piezoelectric fiber. This coil structure enables highly elastic piezoelectric nanogenerator without help of any elastomeric substrates. Dramatic improvement in tensile stretchability and conventional design in real application can be achieved by a core-shell structure in which fiber electrodes are microscopically buckled. New type of stretchable and weavable triboelectric fibers with microdiameter dimensions is introduced. The stretchable triboelectric fibers can be reversibly stretched up to 50% in tensile direction while generating voltage output proportional to the applied tensile strain. The reversible distance change induced by the Poisson’s ratio difference between the core fiber (silver-coated nylon/ polyurethane) and the shell (wrinkled polyvinylidene fluoride-co-trifluoroethylene/carbon nanotube layer) during tensile deformation is the key working principle for electrical generation. Owing to exceptional structural stability, the stretchable triboelectric fibers show high performance retention after 10,000 times repeated stretching/releasing cycle. For third goal, new functionality of biocompatible and implantable energy storage device to store electric energy is newly proposed. In order to achieve a biocompatible and implantable fiber-based electrochemical devices, The fiber supercapacitor were fabricated in a biscrolling process that trapped poly(3,4-ethylenedioxythiophene) : poly(styrenesulfonate) (PEDOT:PSS)/ferritin nanoclusters within multiwalled carbon nanotube (MWNT) sheets that provide mechanical strength and electrical conductivity. In addition, the supercapacitor was biocompatible because the MWNT sheet was coated with biocompatible materials such as PEDOT:PSS and ferritin. The areal capacitance of the PEDOT:PSS/ferritin/MWNT fiber supercapacitor was 32.9 mF/cm2 in a phosphate buffered saline solution, and the areal energy density was 0.82 mWh/cm2; these values are 52 times higher than for guest-free MWNT yarn. The supercapacitor operated well in a mouse and exhibited excellent biocompability : the capacitance was maintained above 90% in the mouse after eight days.
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