Ultrahigh energy-storage dielectric ceramics via synergistic polymorphic nanodomain and defect design

Dielectric capacitors are critical for advanced energy storage due to their ultrahigh power density and rapid charge-discharge rates. However, their application is limited by the low energy density. Here, we design a BaTiO3-(K0.5Na0.5)NbO3-(Bi0.5Na0.5)Ti0.9Zr0.1O3 solid-solution system through synergistic polymorphic nanodomain engineering and defect optimization. By engineering polymorphic nanodomains with coexisting rhombohedral, orthorhombic, tetragonal, cubic nanodomain in 1.0–2.0 nm size and defect design with reduces oxygen vacancy concentration and forms defect complexes, we achieve an ultrahigh energy density of 18.7 J cm⁻3 with remarkable efficiency of 92.1% in multilayer ceramic capacitors, along with excellent cycling stability (>107 cycles) and thermal stability (