Synergistic Design Strategies Breaking the Energy Storage Trade‐Off in Lead‐Free Dielectrics

Development of lead‐free dielectric capacitors with simultaneously high recoverable energy‐storage (ES) density ( W rec ) and breakdown strength ( E b ) is hindered by a fundamental constraint; although high E b permits large electric fields, conventional ferroelectrics suffer from premature polarization saturation, limiting further enhancement of W rec . We demonstrate a mechanism‐guided strategy for Bi 0.5 Na 0.5 TiO 3 (BNT)‐based relaxor ferroelectric ceramics, centered on optimized polar nanoregion (PNR) responses and delayed polarization saturation. Phase‐field simulations show that interconnected rhombohedral/tetragonal (R/T)‐related PNRs with appropriate size and dynamic responsiveness can be progressively activated under electric fields, enabling delayed polarization saturation, sustained Δ P growth, and low hysteresis loss. Guided by this mechanism, compositional disorder, R/T phase coexistence are integrated in the BNT‐based system to construct an optimized PNR landscape. The optimized multilayer ceramic capacitors deliver a record ES potential ( ξ = W rec / E b ) of 278 J kV −1 m −2 , together with a high W rec of 26.4 J cm −3 at 950 kV cm −1 and 89% ES efficiency. Atomic‐resolution microscopy confirms pronounced local chemical heterogeneity and coexisting R/T‐related PNRs, consistent with the optimized PNR response predicted by phase‐field simulations. These results establish a generalizable framework for overcoming the intrinsic ξ – E b trade‐off and advancing next‐generation high‐ W rec dielectric capacitors for ES and pulsed‐power applications.