High Entropy Design Tailored Local Chemical Coordination in Lead‐Free Dielectrics Toward Superior Capacitive Energy Storage

Abstract Continuous advances in pulsed power technologies demand dielectric capacitors that concurrently deliver ultrahigh power density, efficiency, and environmental friendliness/stability in practice. However, conventional dielectric ceramics struggle to meet these requirements owing to the inherent trade‑offs among dielectric polarization, hysteresis loss, and breakdown strength. Herein, the lead‐free ferroelectric relaxor of Bi 0.5 Na 0.5 TiO 3 is adopted as a prototypical framework and implement high‐entropy design. Through the synergistic of maximizing the A‐site ions radius mismatch (Li + , Ba 2+ ), the combination of polar ions (Bi 3+ , Ti 4+ ) and spatial ions with large ionic radius (Ba 2+ ), the local polar configuration is precisely tailored. Polar fluctuations and multiphase nanodomains are formed, resulting in strong local polarizability and significantly reduced polarization switching barriers. Consequently, the entropy‐engineered ceramics are endowed with outstanding energy‐storage performance, characterized by an outstanding recoverable energy density of 16.1 J cm −3 and an exceptional efficiency reaching 84.5% simultaneously under an applied electric field of 77.5 kV mm −1 . Negligible performance degradation within 150 °C, along with a cycling stability of 10 8 cycles, ensures its application potential. The findings provide critical insights and a robust design paradigm for next‑generation dielectric materials in pulsed‑power energy‑storage applications.