Design of High‐Entropy Relaxor Ferroelectrics for Comprehensive Energy Storage Enhancement

Abstract For an ideal electrostatic energy storage dielectric capacitor, the pursuit of simultaneously high energy density and efficiency presents a formidable challenge. Typically, under an applied electric field, an increase in energy density is usually accompanied with a deteriorated energy storage efficiency due to the escalated hysteretic loss, which is harmful to the reliability of the capacitor. Thus, a well‐balanced performance of improved energy density and maintained high efficiency is highly demanded. In this work, a structure with amorphous phases embedded in polycrystalline nanograins using the entropy tactic, leading to a higher transport barrier of carrier is constructed. Hence, the hysteretic loss is largely suppressed at a high electric field and the high polarization is still sustained in the high‐entropy film. Consequently, an ultrahigh energy density of 139.5 J cm⁻³ with a high efficiency of 87.9%, and a high figure of merit of 1153 are simultaneously achieved in the high‐entropy Ba₂Bi₄Ti₅O₁₈‐based relaxor ferroelectric. This work offers a promising avenue in materials structure design for advanced high‐power energy storage applications.