Optimized molecular interactions significantly enhance capacitive energy storage in polymer blends at 150 °C

Dielectric polymers with capacitive energy storage capabilities are essential for advanced electronics and electrical systems. However, a persistent challenge lies in enhancing their energy density at elevated temperatures. Despite the exploration of high-glass transition temperature (T_g) polymers with superior dielectric-thermal stability, they face limitations in terms of low dielectric constant (ε_r) and reduced breakdown strength (E_b) under heightened temperatures. Here, we propose a blending strategy through synergistic design of intra-molecular structures and inter-molecular interactions between polyurea and polyetherimide (PEI), achieving simultaneously enhanced ε_r and E_b at elevated temperatures. The molecular structures of polyureas were initially designed to determine the optimal polyurea species for blending with PEI. The meticulously balanced polymer blend exhibits a significantly increased ε_r, alongside superior dielectric-thermal stability up to 150 °C. Additionally, the distinct electrostatic potential between polyurea and PEI contributes to an enhanced E_b. As a result of combined enhancement in ε_r and E_b, the blended polymer exhibits an ultra-high energy density of 9 J cm⁻³ at 150 °C, while maintaining a remarkable energy efficiency of 93%. These outstanding energy storage characteristics surpass those of state-of-the-art dielectric polymers, underscoring the substantial potential of blended polymers for high-temperature energy storage applications.