FULL PAPER 1700214 (1 of 8) © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.mme-journal.de Enhanced Piezoelectric Performance of Electrospun Polyvinylidene Fluoride Doped with Inorganic Salts Bin Yu, Mengye Mao, Hao Yu,* Tao Huang,* Weiwei Zuo, Hongzhi Wang, and Meifang Zhu Dr. B. Yu, M. Mao, Prof. H. Yu, Dr. T. Huang, Prof. H. Wang, Prof. M. Zhu State Key Lab for Modification of Chemical Fibers & Polymer Materials No. 2999 North Renmin Road, Songjiang District Shanghai 201620, P. R. China E-mail: yuhao@dhu.edu.cn; t_huang@163.com Dr. B. Yu, M. Mao, Dr. T. Huang, Prof. W. Zuo, Prof. H. Wang, Prof. M. Zhu College of Material Science & Engineering Donghua University No. 2999 North Renmin Road, Songjiang District Shanghai 201620, P. R. China The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/mame.201700214. DOI: 10.1002/mame.201700214 The popular approach is to add nucle- ating agents and/or inductive agents to stretched PVDF molecules to increase the proportion of β phase. [22–24] Hybrid methods that make use of PVDF and nanostructured enhancers, [25] such as multi-walled carbon nanotube, [26,27] repre- sent another promising approach. In some previous work, inorganic piezoelectric nanoparticles have been added into PVDF solutions or melt to form composites with attractive properties for energy-harvesting devices. [28,29] However, the majority of researches to date has been based on heterogeneous additives. Agglomera- tion and particle size effects from adding such additives increase the difficulty of manufacturing the devices and influence their output performance. Moreover, PVDF treated with additives may require postpolarization treat- ments at high temperature and high electric field intensity to achieve piezoelectric functionality. The dispersion of additives in the polymer and postpolarization processing of piezoelectric components require complicated preparation technologies, which add to the components’ high cost and limit their com- mercial and practical applications. The effects of interfaces in these devices that result from the heterogeneous composition and postpolarization treatment limit the applications of sim- pler fabrication technologies. Hence, a homogeneous PVDF system, prepared without a postpolarization treatment, would allow low-cost simple manufacturing processes to be used. This advance would enable more widespread use of these devices. For fabrication of homogeneous PVDF systems electrospin- ning has been shown to promote piezoelectric crystals for- mation through in situ electric polarization and mechanical stretching. [30–32] Moreover, electrospinning is a convenient way to prepare flexible nanofiber mats with complex microstructures. In this work, we introduce a novel approach to prepare electrospun PVDF mat-based PENGs, with high piezoelectric performance, with inorganic-salts doping PVDF solutions without a posttreatment step. A range of different inorganic salts was tested and showed a variety of effects on the PVDF electrospinning precursor solutions. We categorized the effects of these different salts into three groups. The highest piezo- electric output voltage achieved in these PENGs represented an increase of seven times the performance of a device based on untreated nanofibers. These findings represent great pro- gress for PVDF as a piezopolymer applied in energy-harvesting and sensors. Piezoelectric A novel approach to preparing electrospun polyvinylidene fluoride (PVDF) nanofibers is proposed, with high piezoelectric performance. PVDF nanofibers are doped with inorganic salts without the use of any postpolari- zation treatment. Twenty-six salts are doped into the nanofibers and their piezoelectric properties are studied. The salts are classified into three groups based on their differing piezoelectric enhancement effects. A piezoelectric nanogenerator fabricated with an optimized electrospun PVDF nanofiber mat shows a piezovoltage seven times greater than that of a device based on undoped nanofibers. The simple and low-cost approach to fabricate these piezoelectric nanofiber mats may broaden the range of industrial applications of these materials in energy-harvesting devices and portable sensors. 1. Introduction A recent boom in portable energy-harvesting technologies [1–3] has generated great interest owing to the broad range of applica- tions that these devices may have in our daily life. Piezoelectric materials allow harvesting of low-frequency mechanical energy, which exists widely in the ambient environment. Piezoelectric nanogenerators (PENGs) [4–9] should be able to handle complex and volatile external environments, because of the full encapsu- lation to provide device stability. Commercially available polyvinylidene fluoride (PVDF) has been widely studied in micro-electric devices, including elec- tromechanical sensing [10–12] and energy harvesting devices [13–18] owing to its flexibility, light-weight, biocompatibility, and long- term stability. Current research is focused on enhancing the active piezoelectric crystal phases of this material, namely the β phase. [19–22] There have been several attempts to increase the β phase content of PVDF and to enhance its overall crystallinity. Macromol. Mater. Eng. 2017, 1700214