A Prestretch‐Free Dielectric Elastomer with Record‐High Energy and Power Density via Synergistic Polarization Enhancement and Strain Stiffening

Abstract Dielectric elastomer actuators with high energy and power output, combined without pre‐stretching treatment to simplify device fabrication, are highly desirable for soft robotics. Here, different from most studies that focus on modifying elastomers such as polyacrylates and silicones, the study designs a prestretch‐free dielectric elastomer based on hydrogenated carboxylated nitrile butadiene rubber to reach a record‐high energy density (564 J kg⁻¹) and power density (5641 W kg⁻¹), ≈15 times greater than natural muscle and three times greater than the state‐of‐the‐art dielectric elastomers. This excellent performance arises from the synergistic polarization enhancement and strain stiffening overcoming the inherent trade‐offs between electrical and mechanical properties, simultaneously endowing the elastomer with an extremely high dielectric constant (ɛ_r = 17, 100 Hz), ultralow mechanical loss (tan δ_m = 0.04@1 Hz), and large electrical breakdown strength (105 V µm⁻¹). The assembled 40‐µm‐thick actuator lifts a 200‐g load with over 20% strain and maintains a stable power density of 4780 W kg⁻¹ for 50 000 cycles. Furthermore, the actuators demonstrate diverse applications, including serving as biceps artificial muscles to achieve a 90° rotation angle at a speed of 360°/s and actuating a soft robot carrying a load 20 times its weight. These findings provide a different approach for developing high‐performance dielectric elastomers to broaden their application in soft robotics.