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_0.5Na_0.5TiO₃ (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 ΔP 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.