Manipulating fluorine induced bulky dipoles and their strong interaction to achieve high efficiency electric energy storage performance in polymer dielectrics

The pursuit of polymer dielectrics with elevated energy density frequently results in heightened energy loss, thereby hindering practical applications. To decouple the dependence of the high energy loss on the high energy storage performance, based on theoretical simulations, a bulky polar unit constructed from a fluorine atom substituted phenyl ring (4-FSt) is designed and copolymerized with methyl methacrylate (MMA). The fluorine atom is found to induce the dipole formation by deforming π-conjugated electrons distribution on the phenyl ring, which favors reversible polarization behaviors instead of conventional dipole orientation polarization under AC electric field and enhances the energy density of polymers. Meanwhile, the introduction of fluorine atoms possessing electron-withdrawing properties is confirmed to increase the electrons capturing ability and the dipole interactions, which significantly reduces the leakage conduction and orientation relaxation induced energy loss. As a result, the rather high energy discharging efficiency (over 88 %) could be finely maintained up to 825 MV m⁻¹, and a discharge energy density of 16.6 J cm⁻³ is obtained, which exhibits significant advances over the reported polymer dielectrics. This work presents the first practice to decouple the dependence of high energy storage and energy loss in polymer dielectrics by manipulating the fluorine effect.