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 Ba 2 + /Sr 2 + 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.