Realizing high energy density and efficiency simultaneously via sub-grain modification in lead-free dielectric films

Lead-free dielectric capacitors are widely used in electronic devices due to their extremely high charge-discharge rate and environmental friendly. However, the relative low energy density and poor thermal stability greatly hinders their application in high temperature. Herein, thin films of 0.85BaTiO₃-0.15Bi(Mg_0.5Zr_0.5)O₃ with columnar sub-grain structures are obtained by structural modification, which exhibit giant energy storage density 99.34 J/cm³, with energy storage efficiency 75.65% at room temperature. The improvement of energy density is realized through reducing the hysteresis loss, postponing saturation of the electric polarization and enhancing the dielectric breakdown strength simultaneously. Moreover, a good thermal stability and anti-fatigue properties are obtained in the temperature range from room temperature to 200 °C. The energy storage density can go up to 61.78 J/cm³ at 200 °C, which is much higher than those reported for other lead-free materials. Our results demonstrate that the columnar sub-grains can boost the domain dynamic and reduce leakage current, leading to an excellent energy storage performance in wide temperature range, which might also be applied to tailor the energy storage properties of other kind dielectric materials.