There is an increasing demand to improve the energy density of dielectric capacitors for satisfying the next generation material systems. One effective approach is to embed high dielectric constant inclusions such as lead zirconia titanate in polymer matrix. However, with the increasing concerns on environmental safety and biocompatibility, the need to expel lead (Pb) from modern electronics has been receiving more attention. Using high aspect ratio dielectric inclusions such as nanowires could lead to further enhancement of energy density. Therefore, this paper focuses on the development of a lead-free nanowire reinforced polymer matrix capacitor for energy storage application. Lead-free sodium niobate nanowires (NaNbO3) were synthesized using hydrothermal method, followed by mixing them with polyvinylidene fluoride (PVDF) matrix using a solution-casting method for nanocomposites fabrication. Capacitance and breakdown strength of the samples were measured to determine the energy density. The energy density of NaNbO3/PVDF composites was also compared with that of lead-containing (PbTiO3/PVDF) nanocomposites and previously developed Pb( )O3/PVDF composites to show the feasibility of replacing lead-containing materials. The energy density of NaNbO3/PVDF capacitor is comparable to those of lead-containing ones, indicating the possibility of expelling lead from high-energy density dielectric capacitors. 1. Introduction Electrical energy storage plays an important role in modern electronic devices such as stationary power systems, mobile devices, and pulse power applications [1]. The most common devices used for storing electrical energy are batteries and capacitors. Compared to batteries, capacitors typically have lower power density but can be charged/discharged very quickly and has a significantly higher range of operating voltage [2]. Currently, there are many types of capacitors in use, such as dielectric capacitors, electrolytic capacitors, and electric double layer capacitors (EDLC or supercapacitors) [3]. Among these, the dielectric capacitor is still the most widely used because of its low cost, easy processing capability, low dielectric loss, high operation voltage, and reliability. Within dielectric capacitors group, there are two main types of capacitors: polymer based and ceramic based [1]. Polymer-based capacitors are more widely used because of their high breakdown strength, lightweight, and easy processing capability [1]. To date, dielectric polymer film capacitors have been used for power electronics, power conditioning, and for pulse power
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