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Piezoelectric nanogenerators, harvesting energy from mechanical stimuli in our living environments, hold great promise to power sustainable self-sufficient micro/nanosystems and mobile/portable electronics. BaTiO3 as a lead-free material with high piezoelectric coefficient and dielectric constant has been widely examined to realize nanogenerators, capacitors, sensors, etc. In this study, polydimethylsiloxane (PDMS)-based flexible composites including BaTiO3 nanofibers with different alignment modes were manufactured and their piezoelectric performance was examined. For the study, BaTiO3 nanofibers were prepared by an electrospinning technique utilizing a sol-gel precursor and following calcination process, and they were then aligned vertically or horizontally or randomly in PDMS matrix-based nanogenerators. The morphological structures of BaTiO3 nanofibers and their nanogenerators were analyzed by using SEM images. The crystal structures of the nanogenerators before and after poling were characterized by X-ray diffraction. The dielectric and piezoelectric properties of the nanogenerators were investigated as a function of the nanofiber alignment mode. The nanogenerator with BaTiO3 nanofibers aligned vertically in the PDMS matrix sheet achieved high piezoelectric performance of an output power of 0.1841 μW with maximum voltage of 2.67 V and current of 261.40 nA under a low mechanical stress of 0.002 MPa, in addition to a high dielectric constant of 40.23 at 100 Hz. The harvested energy could thus power a commercial LED directly or be stored into capacitors after rectification.

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Lithium-sulfur (Li-S) batteries are in the spotlight because their outstanding theoretical specific energy is much higher than those of the commercial lithium ion (Li-ion) batteries. Li-S batteries are tough competitors for futuredeveloping energy storage in the fields of portable electronics and electric vehicles. However, the severe "shuttle effect" of the polysulfides and the serious damage of lithium dendrites are main factors blocking commercial production of Li-S batteries. Owing to their superior nanostructure, electrospun nanofiber materials commonly show some unique characteristics that can simultaneously resolve these issues. So far, various novel cathodes, separators, and interlayers of electrospun nanofiber materials which are applied to resolve these challenges are researched. This review presents the fundamental research and technological development of multifarious electrospun nanofiber materials for Li-S cells, including their processing methods, structures, morphology engineering, and electrochemical performance. Not only does the review article contain a summary of electrospun nanofiber materials in Li-S batteries but also a proposal for designing electrospun nanofiber materials for Li-S cells. These systematic discussions and proposed directions can enlighten thoughts and offer ways in the reasonable design of electrospun nanofiber materials for excellent Li-S batteries in the near future.or conducting coagulation bath) is placed against the capillary. A thin polymer fiber membrane is deposited on the collector. The electrospun nanofibers have big potential for developing the outstanding energy storage systems due to their high surface area and excellent surface-to-volume ratio which can offer numerous active sites and controllable porous structure to buffer the huge volume changes during battery cycling and infiltrate the electrolyte. [18] Electrospun nanofiber membranes possess high porosity, large specific surface area, and controllable pore size, which will block "shuttle effect" of polysulfides and enhance the wettability for electrolytes. [19] Electrospinning technique and carbonization process are facile to manufacture freestanding nanofiber fabrics with controllable porous architecture and outstanding electrical conductivity. Electrospun porous nanofibers can come into a reservoir-like matrix for the reserve of active materials. First, the hierarchical pores in electrospun porous nanofibers can improve the reactive S reaction sites and block soluble polysulfides, thereby decreasing the "shuttling effect" of polysulfides during the electrochemical cycling. Second, electrospun porous fibers have excellent physical and mechanical properties, outstanding architecture, and superior electrical conductivity, which can enhance the transfer of Li-ions and electrons, endowing extraordinary electrochemical performance of the whole battery system. [20] Figure 2 shows phase and morphological evolutions of the electrospun nanofibers. By combining the electrospinning and other treatment (thermal, chem...

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As one of the essential components for flexible electronics, flexible electrochemical energy storage (EES) has garnered extensive interests at all levels of materials, devices, and systems. The successful implementation of high‐performance flexible EES devices relies on exploring of suitable electrode/electrolyte materials that have both superior electrochemical and mechanical properties. For this function, one‐dimensional electrospun nanofibers have emerged as a class of promising building blocks for the key components of flexible EES devices. In this overview, the fundamental principles and technical advances of electrospinning are examined, for both their successes and challenges in controllable fabrication of nanofibers with the desirable chemical compositions, micro/meso‐/nanostructures, and therefore resultant properties. The advances in applications of electrospun nanofibers for various key flexible EES devices are critically looked into, including those in supercapacitors, metal‐ion batteries, and metal‐air batteries. The existing challenges and prospects of these electrospun nanofiber‐based flexible EES are discussed, aiming to inspire continued efforts in developing the optimal high‐performance and low cost flexible EES devices for long‐awaited practical applications.