High Energy Storage Efficiency and Exceptional Recoverable Energy Storage Density Achieved in KNN-based Ceramics via Entropy Engineering

Dielectric capacitors possess significant advantages in terms of fast charge and discharge. Therefore, they are recognized as the most promising candidates for the next generation of high-performance pulsed power systems. Nevertheless, achieving ultra-high recoverable energy storage density (W_rec) along with ultrahigh efficiency (η) poses a significant challenge. This challenge hinders the miniaturization and integration of cutting-edge energy storage devices. In this study, a high-entropy strategy is utilized to construct ultrafine grains (submicron). These grains feature a compact microstructure, enhanced electrical homogeneity, a wider bandgap, and polar nanoregions (PNRs). Such properties lead to an improved breakdown strength, a delay in polarization saturation, and enhanced relaxation behavior. As a result, the KNN-0.15 ceramic exhibits a recoverable energy density value of 6.36 J∙cm^-3 and an efficiency of 84% at an electric field strength of 580 kV∙cm^-1. Furthermore, the ceramic capacitor showcases a power density of approximately 436.5 MW∙cm^-3 and a discharge energy density of around 4.3 J∙cm^-3 at 160°C. Notably, its variability remains below 3% across a broad temperature range from 20 to 160°C. These achievements are propelling the field forward, aiming to develop more practical and powerful dielectric materials for energy storage.