<p>This study explores an efficient encapsulation strategy to improve the dielectric insulation properties of epoxy (EP) composites. The integration of different concentrations of BST@SiO₂ into the EP matrix markedly enhances the overall performance of the composites, particularly under high-temperature conditions and diverse electric fields. The core–shell structure, where barium strontium titanate (BST) particles are coated with an insulating silica shell, serves to reduce DC electrical conductivity, prevent space charge accumulation, and improve DC breakdown strength. The silica coating restricts the movement of charge carriers, while the positive temperature coefficient (PTC) characteristics of BST further enhances insulation properties by transitioning to an insulative state near the Curie temperature. The electrical double-layer effect in the composite helps to suppress excessive charge injection through Coulombic repulsion, preventing the formation of high local electric fields, which are often a direct cause of electrical breakdown. This mechanism ensures higher breakdown strength by delaying the occurrence of critical local fields. The encapsulated BST@SiO₂ particles provide improved thermal stability, contributing to the composite’s ability to retain superior dielectric properties at elevated temperatures. The reported methodology for fabricating these nanocomposites offers valuable insights into developing EP-based materials with enhanced insulation properties, particularly for high-performance applications.</p>