Enhancing the dielectric breakdown strength and energy density of solid-state polymeric capacitors by chain end manipulations*

The maximum energy density of a polymeric dielectric capacitor is limited by the breakdown of the dielectric material at high electric fields. Theoretically, it has been shown that chain ends contribute adversely to the electrical breakdown of polymer dielectrics. In this work, we experimentally demonstrate the role of chain ends indirectly and directly in the dielectric breakdown by using block copolymers (BCP) and cyclic polymer films respectively. The BCPs show an enhanced breakdown strength due to chain end segregation, resulting in energy densities of 5 J/cm³. For direct observation of the role of chain ends in the breakdown, we synthesized the cyclic polymers with high purity. The cyclic polymer films demonstrate ~50% enhancement in dielectric breakdown strength and as a result, the energy density in the cyclic polymer films increases by ~80% as compared to their linear counterparts. Interestingly, the cyclic polymer films show a higher refractive index and packing density as compared to their linear counterparts, which might be attributed to the elimination of chain end-based free volume. These insights into the structure-property relationship will help design next-generation polymeric energy storage materials and devices.