High-Entropy Engineered (Bi _0.2 Na _0.2 Ba _0.2 K _0.2 La _0.2 )TiO ₃ - <i>x</i> Ca(Hf _0.7 Zr _0.3 )O ₃ Lead-Free Ceramics for Superior Energy Storage Performance

Environmentally friendly dielectric ceramics with high energy storage are indispensable for advanced pulsed power capacitors, primarily due to their outstanding power density. Nevertheless, the relatively low energy storage performance (ESP) of these ceramics continues to limit their broader applications. Here, a series of lead-free (Bi 0.2 Na 0.2 Ba 0.2 K 0.2 La 0.2 )TiO 3 - x Ca(Hf 0.7 Zr 0.3 )O 3 high-entropy ceramics (abbreviated as BNBKLT- x CHZ HECs) was prepared based on a synergistic high-entropy design, aiming to achieve enhanced ESP. Remarkably, BNBKLT-0.15CHZ ceramics characterized by high configurational entropy (Δ S config ≈ 2.16 R) exhibit an ultrahigh recoverable energy density ( W rec ) of ∼6.77 J/cm 3 and an efficiency (η) of ∼86%. The enhanced Δ S config, as a consequence of introducing CHZ, results in a reduction of grain size from ∼0.89 μm at x = 0.00 to ∼0.32 μm at x = 0.20, along with an enhancement of the breakdown strength (BDS) from ∼200 kV/cm at x = 0.00 to ∼485 kV/cm at x = 0.15. Moreover, excellent frequency stability (<3.2%, ranging from 10 to 500 Hz), temperature stability (<6.4%, ranging from 25 to 140 °C), fatigue resistance (<4.0%, ranging from 1 to 10 5 cycles) and ultrafast discharge time (∼79 ns) are obtained in the optimal composition. The results demonstrate that the BNBKLT-0.15CHZ HEC has considerable potential for utilization in dielectric energy storage capacitors.