Electronic band and core-shell structure engineering enables ultrahigh energy storage in high-entropy ceramics

Relaxor ferroelectric ceramics are promising energy-storage candidates for high-power electronic systems owing to their high energy density and fast charge-discharge speed. However, achieving ultrahigh energy density still poses challenges due to the inherently inverted coupling relationship between polarization (P) and breakdown electric field (Eb). Here, we propose a high-entropy strategy to decouple polarization from breakdown electric field. The high-entropy design exerts a triple effect, which involves flattening electronic band to restrict the transport of charge carriers, driving the formation of core-shell heterostructure to suppress electrical breakdown, and stabilizing polymorphic polar phases to promote polarization rotation. The triple synergy effect led to an ultrahigh Eb and a maximized polarization disparity (ΔP = Pm - Pr). As a result, the high-entropy ceramics exhibit an ultrahigh recoverable energy density (Wrec) of 10.23 ± 0.99 J/cm3 and a satisfactory efficiency (η) of 85.44% ± 3.34%, alongside good cycling reliability and temperature stability. This work provides an innovative design paradigm for achieving excellent energy storage performance of dielectric capacitors. A high-entropy strategy combines flattened electronic bands, core–shell microstructures, and polymorphic polar phases to overcome the trade-off between polarization and breakdown electric field, achieving high energy storage performance in lead-free dielectric ceramics.