Enhanced energy storage density and discharge efficiency in potassium sodium niobite-based ceramics prepared using a new scheme

The development of lead-free ceramics with high recoverable energy density (W_rec) and high energy storage efficiency (η) is of great significance to the current energy situation. In this work, a new scheme was proposed to improve the W_rec and η of potassium sodium niobate ((K, Na)NbO₃, abbreviated as KNN) lead-free ceramics. Doping Bi elements in KNN ceramics to form a second phase (K₂BiNb₅O₁₅) can reduce the grain size and form Schottky-like contact. Meanwhile, the hybridization between the Bi 6p and O 2p orbitals can enhance the maximum polarization (P_max). So the K_1-3xBi_xNa_0.5NbO₃-1 mol%CuO ceramics was proposed to improve the W_rec of lead-free ceramics. A large W_rec (2.89 J/cm³) and dielectric breakdown strength (DBS) (300 kV/cm with a thickness of 0.2 mm) were achieved for K_0.14Bi_0.12Na_0.5NbO₃-1 mol%CuO ceramics. The high W_rec was supposed to benefit from low remnant polarization (P_r), high Ps and DBS of ceramics. In addition, a large η (80%) was simultaneously achieved for K_1-3xBi_xNa_0.5NbO₃-1 mol%CuO ceramics, which is superior to mostly reported lead-free bulk ceramics. The results show that K_1-3xBi_xNa_0.5NbO₃-1 mol%CuO ceramics have a good application prospect in the field of energy storage, and provide a new scheme for the preparation of lead-free ceramics with high energy storage density and high conversion efficiency.