Achieving high overall energy storage performance of KNN-based transparent ceramics by ingenious multiscale designing

Dielectric capacitors show significant advantages of faster charge-discharge time over solid oxide fuel cells, Li-ion batteries, and electrochemical capacitors and have been considered the best candidates for next-generation high-performance pulsed power systems. Considering the advantage of the feasibility of efficient multifunctional coupling, which meets the integration trend of electronic devices and relies on the excellent transmittance of KNN-based ceramics, we chose KNN-based systems in this work. (1 − x)(K_0.5Na_0.5)NbO₃-xBa_0.9Ca_0.1Zr_0.15Ti_0.85O₃ ceramics were fabricated by employing conventional solid state technology, and as expected, the substitution of Ba/Ca by K/Na in the A-site and the substitution of Zr/Ti by Nb in the B-site strongly decreased the leakage current of pristine KNN. By multiscale designing, a W_rec of 7.83 J cm⁻³ with an η of 81.02%, which has huge advantages over both BCZT-based systems and KNN-based systems, was finally achieved when the x equals 0.30, and such an excellent energy storage performance was caused by both high maximum polarization and high large electric breakdown strength. According to their microstructure characterization, the former was caused by the existence of high polarization boundaries induced by the lattice mismatch between the two phases, and the latter was proved by the combined effect of conductive mechanism transition and interface engineering. In addition, relatively high energy storage frequency stability, thermal stability, and polarization fatigue endurance were also obtained, and the charge-discharge behavior indicated their potential in practical applications. The work offered a new concept for designing energy storage capacitors with high overall performance.