Ultrahigh Energy Storage Density in Superparaelectric‐Like Hf(0.2)Zr(0.8)O(2) Electrostatic Supercapacitors

Electrostatic capacitors attract great interest in energy storage fields due to their advantages of high power‐density, fast charge/discharge speed, and great reliability. Intensive efforts have been placed on the development of high‐energy‐density of capacitors. Herein, a novel supercapacitor with Hf(0.2)Zr(0.8)O(2)/xAl(2)O(3)/Hf(0.2)Zr(0.8)O(2) (HAHx) is designed to improve the breakdown strength (E (b)) through optimizing Al(2)O(3) (AO) film thickness. Low‐temperature annealing is first proposed to enhance the polarization difference (P (m) −P (r)) due to the formation of dispersed polar nanoregions, which is called “superparaelectric‐like” similar to previous super‐paraelectric behavior of perovskite structures. As results, both large E (b) and P (m) −P (r) values are obtained, leading to an ultrahigh energy storage density of 87.66 J cm(−3) with a high efficiency of 68.6%, as well as a reliable endurance of 10(7) cycles. This work provides a feasible pathway to improve both the polarization difference and breakdown strength of HfO(2)‐based films by the combination of insulation insertion layer and low‐temperature annealing. The proposed strategy can contribute to the realization of high‐performance electrostatic supercapacitors with excellent microsystem compatibility.