Rigid‐Flexible Polar Structures for Ultrahigh Energy Storage in Lead‐Free Multilayer Ceramic Capacitors

ABSTRACT Dielectric capacitors are essential components in advanced power electronics owing to their high‐power density and ultrafast discharge rates. However, the development of compact, high‐temperature electrical systems relies heavily on solving the severe energy dissipation and performance degradation of current dielectrics at elevated temperatures. Here, we demonstrate a rigid‐flexible polar structure in BiFeO ₃ ‐based lead‐free multilayer ceramic capacitors (MLCCs) that couples high‐energy storage performance with robust thermal durability. Guided by atomic‐resolution imagings and phase‐field simulations, we confirm the dynamic confinement of active polar nanodomains (the flexible component) within an invariant tetragonal matrix (the rigid framework). This fundamental structural decoupling flattens the local thermodynamic energy landscape for the nanodomains, facilitating low‐barrier polarization switching, while the tetragonal framework provides high resistance to thermal and electrical breakdown. Consequently, the fabricated MLCCs deliver a recoverable energy density ( W _rec ) of 21.58 J cm ⁻³ with an efficiency ( η ) of 91.3% under electric fields exceeding 1100 kV cm ⁻¹ at room temperature, and stably maintain W _rec of 10.85 J cm ⁻³ with an η of 90% at 150 °C. This structural paradigm offers a scalable pathway for designing high‐performance dielectrics for harsh‐environment power applications.