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Polymer Dielectrics with Simultaneous Ultrahigh Energy Density and Low Loss

Polymer dielectrics are highly desirable in capacitor applications due to their low cost, high breakdown strength, and unique self‐healing capability. However, existing polymer dielectrics suffer from either a low energy density or a high dielectric loss, thereby hindering the development of compact, efficient, and reliable power electronics. Here, a novel type of polymer dielectrics simultaneously exhibiting an extraordinarily high recoverable energy density of 35 J cm−3 and a low dielectric loss is reported. It is synthesized by grafting zwitterions onto the short side chains of a poly(4‐methyl‐1‐pentene) (PMP)‐based copolymer, which increases its dielectric constant from ≈2.2 to ≈5.2 and significantly enhances its breakdown strength from ≈700 MV m−1 to ≈1300 MV m−1 while maintaining its low dielectric loss of <0.002 and high charge–discharge efficiency of >90%. Based on a combination of the phase‐field method description of mesoscale structures, Maxwell equations, and theoretical analysis, it is demonstrated that the outstanding combination of high energy density and low dielectric loss of zwitterions‐grafted copolymers is attributed to the covalent‐bonding restricted ion polarization and the strong charge trapping by the zwitterions. This work represents a new strategy in polymer dielectrics for achieving simultaneous high energy density and low dielectric loss.