Constructing fluorinated triphenyl in carbonate copolymers toward flexible high energy-storable dielectric films with enhanced thermal resistance

The rapid development of distributed power grids and hybrid electric vehicles has driven the search for new dielectric polymers with enhanced capacitive performance and thermal resistance to replace conventional biaxially oriented polypropylene (BOPP). In this study, we present a series of novel polycarbonate dielectric films prepared through fluorinated triphenyl copolymerization. A self-synthesized fluorinated triphenyl benzene was introduced to produce low-cost and large-scale producible polycarbonate films. Both experimental and first-principles calculation results demonstrate that the incorporation of triphenyl improves the energy storage density of the polymer films while maintaining excellent energy storage efficiency, even at high temperatures. The addition of strongly electronegative fluorophenyl to the pendant of the main chain enhances the polymer's dipole moment, thereby achieving high energy storage density. Moreover, the introduction of large-volume sterically hindered phenyl groups increases the conformational transition energy barrier of the polymer, leading to higher glass transition temperatures (160.5 °C-178.7 °C). This improvement can increase the glass transition temperature of the polymer by up to 21 % compared to bisphenol A polycarbonate while maintaining good flexibility. Additionally, the inclusion of electronegative fluorophenyl groups in the polymer creates trap sites, resulting in low dielectric loss (≤0.0048) and high charge-discharge efficiency. Experimental shows that the film still maintains an efficiency of 97.3 % and a discharge energy density of 6.14 J/cm3 at 500 MV/m and room temperature, 91.8 %/0.87 J/cm3 @150 °C and 200 MV/m, while the current commercial BOPP film fails completely at this temperature. In summary, the fluorinated triphenyl carbonate we prepared provides a new possibility for replacing BOPP.