Ultrahigh energy storage with superfast charge-discharge capability achieved in linear dielectric ceramic

Ceramic capacitors designed for energy storage demand both high energy density and efficiency. Achieving a high breakdown strength based on linear dielectrics is of utmost importance. In this study, we present the remarkable performance of densely sintered (1–x)(Ca0.5Sr0.5TiO3)-xBa4Sm28/3Ti18O54 ceramics as energy storage materials, with a measured energy density (Wrec) of 4.9 J/cm3 and an ultra-high efficiency (η) of 95% which is almost optimal in linear dielectric that has been reported. To unravel the underlying mechanisms, we conducted a systematic investigation on the influence of adding paraelectric Ba4Sm28/3Ti18O54 (BST) on both microstructure and macroscopic electrical properties of Ca0.5Sr0.5TiO3 (CST). Notably, the addition of BST effectively reduces the grain size of CST. The conduction mechanism is primarily governed by grain boundaries, where high-density grain boundaries act as barriers to charge carrier transport due to their elevated resistivity. Moreover, the activation energy associated with grain boundaries increases with rising resistivity, implying a lower concentration of free vacancies within these regions. The increased barrier height for oxygen vacancy migration at grain boundaries compensates for the grain boundary defects, thereby resulting in enhanced breakdown strength. This characteristic offers a substantial advantage in terms of thermal and frequency stability (25–175 °C, 1–100 Hz). This work introduces a candidate material with outstanding comprehensive energy storage properties.