Nano-enhanced polymer composites for energy storage applications

Polymer nanocomposites containing high dielectric permittivity ceramic particles embedded into a dielectric polymer represent promising candidates to overcome the limitations of monolithic materials in both energy storage and energy conversion. Indeed, monolithic materials are hitting a plateau in terms of high energy storage capabilities due to the trade-off between the dielectric constant, the dielectric loss and the dielectric breakdown. Since ceramics have high dielectric constant but low dielectric breakdown, while polymers have high dielectric breakdown and low loss but low dielectric constant, the strategy of simply filling a polymer with ceramic particles will only yield incremental and limited success. In this study, we investigate the effect of adding commercial metal oxide nanoparticles, TiO ₂, to a ferroelectric polymer on the dielectric constant, breakdown, ferroelectric behavior and energy density of the system; specifically, we focus on impact of the particles size, aspect ratio, and interaction with the polymer dipole. We find that at a very low TiO ₂ content, namely 4.6vol%, the energy density increased by more than 400% as compared to the pristine polymer, with an enhancement in both the dielectric constant and the dielectric breakdown while the dielectric loss remained in the same range as that of the pure polymer. We also investigate the mechanism for this large improvement and demonstrate that the high aspect ratio particles have a planar distribution in the nanocomposite film, resulting in a low local field, and therefore a high dielectric breakdown.