Novel high-entropy relaxors with ultrahigh energy-storage efficiency and density

•A high Wrec = 7.3 J/cm3 is obtained in BT-based ceramics by “high-entropy” strategy.•The highest η = 94.3 % reported so far has been achieved in BNBSCTN ceramics.•The correlation between four effects and energy storage performance is emphasized. One of the major problems in ceramic capacitors is that their limited energy storage density (Wrec) and efficiency restrict the development in cutting-edge energy storage applications. In this paper, the non-equimolar ratio high-entropy ceramics are designed using the “entropy” strategy based on the traditional ferroelectric BaTiO3. Ultimately, the superparaelectric region of BaTiO3 is extended successfully, forming the local polymorphic distortion structure and realizing the transformation of ferroelectrics-relaxor ferroelectrics. Here, the outstanding Wrec of 7.3 J/cm3, the excellent ξ of 214.71 J/kV·m2, and the highest energy storage efficiency (η = 94.3 %) in high-entropy ceramics are obtained under moderate electric fields, indicating a breakthrough progress in energy storage applications of high-entropy relaxor ferroelectrics. Additionally, our work compared performance across multiple dimensions using measurement parameters, giving readers a more comprehensive reference.