This Small Business Innovation Research (SBIR) Phase II project aims to develop a core-shell nanoparticle architecture with metal nanoparticles as the high capacitance core, and polymers as the shell. The nanoparticles will be entrained in a broad spectrum of host polymers via a novel approach to produce high dielectric-constant films with minimum dielectric loss. To scale up this process without losing the unique and valuable properties of core-shell nanoparticles, a wet chemistry route with laser for selective polymerization will be utilized to coat each metal nanoparticle with a polymeric shell.
The broader/commercial impact of this project will be the potential to provide high-dielectric constant nanoparticles for the development of nanocomposite to meet future energy storage needs of supercapacitors. Currently, commercially available supercapacitors either have too low power or energy density or are too expensive to manufacture. This project is expected to enable the fabrication of ultra high energy storage capacitors by providing high energy and power density in a cost-effective manner.
This project is focused on the development of a nanodielectric architecture based on metal-polymer core-shell nanoparticles. The effective permittivity of this nanocomposite structure is expected to be much higher than that of the parent polymer and without compromising on its dielectric strength. Nanocomposites, made of metallic nano-sphere particles embedded into polymers, which can be incorporated into standard capacitor manufacturing processes, is a forceful and influential concept for producing high dielectric constant films with minimum loss of the dielectric strength. Originally, the approach was thought to be very risky, as loss of the capacitor breakdown strength might be a factor. However, Phase I feasibility was a success, which allowed us to proceed further without losing priority. The nanoparticles will be entrained in a broad spectrum of host polymers, in a very innovative way that outperforms currently sought nanodielectrics. Scaling up this technology without losing its unique and valuable properties can be accomplished through a wet chemistry route using laser for selective UV polymerization, where each metal nanoparticle is coated with a polymeric shell, thus converting the process to a continuous flow to form super-capacitor slabs. The initial achievements included: fabrication of capacitors using silica-coated Silver (Ag) nanoparticles, fabrication of capacitors using PVP-coated Ag nanoparticles, characterization of capacitor slabs fabricated from Ag-SiO2 core-shell nanoparticles, optimization of minimum required polymer quantity and fraction of loading (FOL). We have achieved the enhancement of the effective dielectric constant of the nanodielectrics by a factor of about 6 (k> 40) using Ag nanoparticles dispersed in PVP, representing a good match with the k value of 58, as predicted by percolation theory. An optimized method was designed to increase the k value and also to strengthen the cross link between the nanocomposite solution and the Si wafer. The LCR characteristics were measured for a range of frequencies from 20 Hz to 10 MHz and exhibited less than 20% degradation over that range. The measured breakdown voltage was >156 V/µm. After a new procedure was implemented to increase the FOL of nanoparticles in the polymer, by using very lower concentration of nanoparticles the FOL in a polymer matrix was increased up to about 0.08 %, without agglomeration of nanoparticles. Devices fabricated with the new FOL were tested and exhibited k value close to 70. We fabricated and characterized packaged capacitor prototype devices. In order to promote collaborations with potential commercial vendors, working nanocapacitor prototype devices have been fabricated and tested. Results showed that after dicing, there was significant increase in the capacitance of individual chips. The reason for the increase in the capacitance from bulk to single chip conditions has not been investigated, however the most significant changes that might result in the increase of the capacitance is possible reduction of the surface leakage currents and modification of the electric field distribution. Because of the spin coating process limitations and apart from the tasks planned in the original proposal, we have decided to initiate the exploration for employment of a polymer printing technique using Drop-on-Demand (DoD) type inkjet printers. The preliminary results of the initial experiments on the application of the Jet ink printing technology for nanocapacititor fabrication are not conclusive. Further optimization of a large variation of nanosolution parameters, as well as printer regimes is necessary. However, due to the high potential of this technology for the development of the giant-K nanocapacitors for energy storage applications, this work will have to continue.
