A continuously graded fluorination interface for significantly strengthening the dielectric energy storage of polymer...

Surface modification represents a mainstream strategy for enhancing the energy storage abilities of polymer dielectrics, and decades of research mainly adopted the precept of constructing isolated deep traps to suppress electron injection from the electrode. However, especially at high temperatures and in strong electric fields, electrons can still traverse isolated deep traps by the quantum tunneling effect, limiting performance enhancements. Here we introduce a self-promoting fluorination diffusion reaction, breaking through traditional manufacturing limits to construct a continuously graded fluorination interface layer featuring linear deep traps on the film surface. While an electron may tunnel through an isolated deep trap, the probability of it successively tunneling through linear deep traps decays exponentially, effectively suppressing long-range electron injection. Meanwhile, the incorporation of highly electronegative fluorine further synergistically suppresses electron injection and transport within the continuously graded fluorination interface layer. Finally, the fabricated fluorinated polypropylene film achieves exceptional discharge energy densities of 3.30 and 2.01 J cm^-3 at high temperatures of 120 °C and 130 °C, respectively, coupled with an efficiency of over 90%, and it also presents fine self-healing abilities and a large enhancement in cycle life. This work offers a novel theoretical basis and structural design paradigm toward high-energy-density polymer dielectrics for harsh environments.