Constructing mesyl triphenyl based polycarbonate copolymers for enhancing energy storage performance of flexible all-organic dielectric film

Given the advancements in electric vehicles and high-temperature power systems, there has been significant interest in high-temperature dielectric materials. Biaxially oriented polypropylene (BOPP) is widely employed in energy storage films due to the excellent dielectric properties. However, its limited thermal resistance constrains its use in high-temperature environments. In contrast, polycarbonate (PC) offers a high glass transition temperature (T_g ~ 150 °C), making it more suitable for elevated temperatures, but its relatively low dielectric constant (~3.0) hampers its energy storage density. To overcome this, we introduced the triphenyl-sulfone group into PC, for increasing the dielectric constant while further enhancing its glass transition temperature. Both simulation and experiments reveal that increasing sulfone-containing triphenyl amount is beneficial to the dielectric and energy storage performance. The inclusion of high polar sulfone group could enhance the dielectric constant of the polycarbonate film while improve the chain rigidity and thermal resistance. With a molar content of 50 %, sulfone-containing triphenyl polycarbonate copolymer displays a T_g of 216 °C as well as a dielectric constant of 4.2 (@50 Hz) without sacrificing the breakdown strength (E_b). A high discharge energy density (U_e) of 3.81 J/cm³ was achieved, 33 % higher than that of PC, with a high efficiency (η) exceeding 94 %. At room temperature and under 200 MV/m, the U_e reached 0.94 J/cm³, 1.8 times that of BOPP under the same conditions. Furthermore, the film demonstrated good operational stability, being recycled 10⁴ times at 200 MV/m both at room temperature and 120 °C, with good self-cleaning properties and showing no apparent performance degradation.