Local Polarization Unit Engineering Enables Ultrahigh Energy Density in NBT-Based High-Entropy Ceramic Capacitors

Dielectric energy storage capacitors play a pivotal role in pulsed power systems. Herein, we demonstrate a breakthrough in dielectric energy storage by engineering ​local polarization units in high-entropy multilayer ceramic capacitors (MLCCs). By incorporating equimolar Ba²⁺/Sr²⁺ dual cations, we precisely smoothen the phase transition and stabilize a nanoscale phase-coexistence state in an NBT-based matrix, which simultaneously retain robust local polar units while disrupting long-range domain order. This unique configuration, validated by atomic-resolution HAADF-STEM and phase-field simulations, enables a high reversible polarization and breakdown strength. The optimized MLCCs achieve an ultrahigh recoverable energy density of 18.2 J cm⁻³ with 91% efficiency, coupled with exceptional thermal stability and fatigue resistance. This work establishes a general design paradigm for high-entropy dielectrics for energy storage by controlling local polarization configurations.