<p>Dielectric materials are indispensable in modern electronics owing to their rapid polarization response and excellent thermal stability. However, their widespread application is often constrained by limited energy storage density. A promising approach to overcome this limitation in Bi_0.5Na_0.5TiO₃ (BNT)-based systems involves introducing relaxor ferroelectric phases into the materials, which can produce pinched hysteresis loops beneficial for energy storage. In this study, the incorporation of the relaxor ferroelectric end member Sr_0.7Bi_0.2TiO₃ into BNT-based thin films effectively reduces the ferroelectric-to-relaxor phase transition temperature and stabilizes an ergodic relaxor ferroelectric state at room temperature. This structural modification promotes low-field polarization switching and enhances high-field polarization response, while retaining comparable remnant polarization. As a result, the expanded polarization response leads to a significant improvement in energy storage density, reaching up to 49&#xa0;J/cm³ in the developed thin films. This work highlights the strategic use of ergodic relaxor ferroelectrics as an effective route for enhancing energy storage performance in ferroelectric materials.</p>