Non-polar nanocluster confinement engineering realizes high capacitive energy storage in Pb-free high-entropy relaxors.

Dielectric ceramic capacitors with ultrahigh power density have become indispensable in modern power electronics, yet the persistent challenge of achieving superior energy density with high energy efficiency remains a critical bottleneck for practical applications. Herein, we propose an effective non-polar nanocluster confinement strategy through phase-field simulation-guided design of high-entropy (Bi0.2Na0.2Ba0.2Sr0.2Ca0.2)(Ti1-xSnx)O3 lead-free relaxor ferroelectrics. The incorporation of Sn4+ ions with low ionic polarizability leads to the formation of localized non-ferroelectric perovskite units, which constitute robust non-polar nanoclusters, being further stabilized and rendered immobile against electric fields by the substantial local random fields inherent to the high-entropy configuration. Consequently, these engineered non-polar nanoclusters serve as effective pinning centers to impede the merging and growth of polar nanodomains under electric fields, thereby reconciling the inherent conflict between polarization enhancement and hysteresis reduction. The optimized composition (x = 0.06) exhibits a high recoverable energy density of ~18.5 J·cm-3 together with an ultrahigh energy efficiency of ~92.4% in multilayer ceramic capacitors, representing a competitive combination among lead-free counterparts. This approach not only establishes a viable paradigm for next-generation energy storage dielectrics but also provides fundamental insights for designing functional materials with tailored electrical properties.