Giant Capacitive Energy Storage in High‐Entropy Lead‐Free Ceramics with Temperature Self‐Check

Abstract Considering the large demand for electricity in the era of artificial intelligence and big data, there is an urgent need to explore novel energy storage media with higher energy density and intelligent temperature self‐check functions. High‐entropy (HE) ceramic capacitors are of great significance because of their excellent energy storage efficiency and high power density (P_D). However, the contradiction between configurational entropy and polarization in traditional HE systems greatly restrains the increase in energy storage density. Herein, the contradiction is effectively solved by regulating the octahedral tilt and cationic displacement in ABO₃‐type perovskite HE ceramics, i.e., (1‐x)[0.6(Bi_0.47Na_0.47Yb_0.03Tm_0.01)TiO₃‐0.4(Ba_0.5Sr_0.5)TiO₃]‐xSr(Zr_0.5Hf_0.5)O₃ (BNYTT‐BST‐xSZH). Combining the tape‐casting process and cold isostatic pressing, the optimal BNYTT‐BST‐0.06SZH ceramic displays a large recoverable energy storage density (10.46 J cm⁻³) at 685 kV cm⁻¹ and a high P_D (332.88 MW cm⁻³). More importantly, due to Tm/Yb codoping, abnormal fluorescent negative thermal expansion and excellent real‐time temperature sensing are developed, thus the application of fault detection and warning in high‐voltage transmission line systems is conceptualized. This study provides an effective strategy for enhancing the polarization of energy‐storing HE ceramics and offers a promising material for overcoming the problems of insufficient capacitor density and thermal runaway in terminal communication.