<p>Lead-free piezoelectric ceramics based on 0.94Bi₀.₅Na₀.₅TiO₃–0.06BaTiO₃–K₀.₅Na₀.₅NbO₃ (BNT–BT–KNN) were modified with varying amounts of B₂O₃ (0–2.0 wt%) to investigate the influence of sintering aid on their structural, microstructural, dielectric, ferroelectric, and energy storage properties. The ceramics were prepared via the solid-state reaction method and sintered at reduced temperatures owing to the fluxing effect of B₂O₃. X-ray diffraction confirmed a single perovskite phase with coexisting rhombohedral and tetragonal symmetries near the morphotropic phase boundary. Scanning electron microscopy revealed improved densification and grain growth at moderate B₂O₃ contents, while excessive doping led to grain-boundary phase formation. The 1.5 wt% B₂O₃ composition exhibited optimal performance, achieving a high piezoelectric coefficient (<i>d₃₃</i> = 210 pC/N) and enhanced dielectric constant and loss. At 1.0 wt% B₂O₃ achieved maximum energy storage efficiency (η = 87.5%). Ferroelectric measurements indicated that excessive B₂O₃ increased leakage current and reduced polarization, consistent with AC conductivity trends. These results demonstrate that controlled B₂O₃ addition is an effective strategy for tailoring the microstructure and enhancing the multifunctional performance of lead-free BNT–BT–KNN ceramics for eco-friendly piezoelectric and energy storage applications.</p>