Enhanced Discharged Energy Density Capability and High Efficiency of Heterostructure P(VDF‐HFP) With Lead‐Free BNKT Nanocomposites

Dielectric polymer‐based nanocomposites with well‐designed and controlled interfaces are essential for effective energy storage and energy conversion. However, achieving high energy density in nanocomposites often leads to low discharge energy efficiency due to increased dielectric loss and leakage current. Consequently, improving energy density while maintaining high efficiency in dielectric capacitors poses a challenge for polymer nanocomposites, especially when using the dispersion casting method. In this study, a two‐phase composite with improved energy storage capacity and reduced energy dissipation was created by mixing poly(vinylidene fluoride hexafluoropropylene) (P(VDF‐HFP)) with lead‐free Bi 0.5 (Na 0.8 ‐K 0.2 ) 0.5 TiO 3 (BNKT) ceramics. The P(VDF‐HFP) composite with 5 wt% BNKT demonstrated the highest discharge energy density, outperforming pure P(VDF‐HFP) under identical electric field conditions. This composite exhibits higher maximum polarization and remnant polarization relative to pure P(VDF‐HFP), accompanied by a reduction in loss density at low BNKT concentrations. The P(VDF‐HFP) composite with 5 wt% BNKT demonstrated a high energy storage density of 1.18 J/cm 3 at a low‐moderate electric field of 130 MV/m and excellent efficiency, achieving 82.1% at 40 MV/m. By optimizing the microstructure, the interfacial bonding between lead‐free BNKT and P(VDF‐HFP) polymer chains was strengthened, resulting in significant enhancements in polarization, charge density, dielectric loss reduction, and breakdown strength. These improvements contribute to the enhanced energy storage performance of the ferroelectric polymer nanocomposite.