Enhanced Energy Storage Performance of Lead-Free Capacitors in an Ultrawide Temperature Range via Engineering Paraferroelectric and Relaxor Ferroelectric Multilayer Films

Industry has been seeking a thin-film capacitor that can work at high temperature in a harsh environment, where cooling systems are not desired. Up to now, the working temperature of the thin-film capacitor is still limited up to 200 °C. Herein, we design a multilayer structure with layers of paraferroelectric (Ba0.3Sr0.7TiO3, BST) and relaxor ferroelectric (0.85BaTiO3-0.15Bi(Mg0.5Zr0.5)O3, BT-BMZ) to realize optimum properties with a flat platform of dielectric constant and high breakdown strength for excellent energy storage performance at high temperature. Through optimizing the multilayer structure, a highly stable relaxor ferroelectric state is obtained for the BST/BT-BMZ multilayer thin-film capacitor with a total thickness of 230 nm, a period number N = 8, and a layer thickness ratio of BST/BT-BMZ = 3/7. The optimized multilayer film shows significantly improved energy storage density (up to 30.64 J/cm3) and energy storage efficiency (over 70.93%) in an ultrawide temperature range from room temperature to 250 °C. Moreover, the multilayer system also exhibits excellent thermal stability in such an ultrawide temperature range with a change of 5.15 and 12.75% for the recoverable energy density and energy storage efficiency, respectively. Our results demonstrate that the designed thin-film capacitor is promising for the application in a harsh environment and open a way to tailor a thin-film capacitor toward higher working temperature with enhanced energy storage performance.