First principles modeling of nanoparticle–polymer surface functionalizations for improved capacitive energy storage

Abstract

Low energy density is the principle obstacle for widespread adoption of dielectric capacitors for large-scale energy storage, and in polymer–ceramic nanocomposite systems the root cause is dielectric breakdown at the nanoscale interface. Interfacial effects in composites cannot be observed directly, due to the long-range effects of the surrounding media and the internal nature of the defects, so we need to relate quantities we can calculate to macroscale properties. We demonstrate in silico a novel approach to evaluate surface coatings for dielectric polymer nanocomposites to determine their effect on electrical breakdown a priori. We look at the electric field at the interface of barium titanate nanoparticles, in a general way, using first principles of density functional theory. The calculated induced electric field of several surface functionalized polymer–ceramic nanocomposites, chosen based on their wide range of different chemical features, shows that 7-octenyltrimethoxysilane will have the most increased ultimate breakdown voltage. We also compare two previously used metrics for quantifying breakdown in composite materials, polarizability and band gap and discuss their limitations. Experimental results should be used to further refine our model because functionalization position is critical to the induced electric field, but this position is difficult to definitively determine computationally because of steric and other effects present in real systems. Combined with experimental inputs, our new approach could be used to dramatically reduce the cost and the number of experiments needed to find new composite materials.