Electric Breakdown of Dielectric Polymers is Strongly Correlated to Mechanical Toughness.

Dielectric energy storage is critical for technologies demanding ultrafast discharging and pulse power, and preventing electric failure is paramount to the design and engineering of dielectric materials. Under high voltages current traverses the dielectric leading to electric breakdown, which is the primary failure mode of dielectrics. While intrinsic breakdown strength in perfect dielectrics can be predicted from quantum mechanics, failures in dielectric materials often occur under an electric field well below their intrinsic theoretical strengths, and the mechanism is still poorly understood. Here we show that electric breakdown of dielectric polymers is strongly correlated to their mechanical toughness. We reveal through in situ experiments that breakdown of polymers proceeds through nucleation and growth of cracking channels, suggesting a close connection between electric and mechanical failures. We demonstrate that the breakdown strength of polymers can be modulated by their tensile toughness, and there is a universal relationship between electric toughness and mechanical toughness. As a result, the breakdown strength for a wide range of polymers with mechanical and dielectric properties spanning two orders of magnitude can be reliably predicted, uncovering a dominant electromechanical breakdown mode that unifies mechanical and electric failures. Toughening strategies in enhancing dielectric strength can therefore be explored.