Ultrahigh Efficiency and Robust Energy Density in Simple Barium Titanate‐Based Lead‐Free Films via Nanocomposite Approach

Relaxor ferroelectric (RFE) films represent promising candidates for high-performance energy storage applications for miniaturized electronic devices and power systems. However, achieving substantial energy storage performance always involves complex component or structural design. Herein, we employed a nanocomposite approach to obtain ultrahigh-efficiency and robust energy density in simple BaTiO₃-based lead-free films. Our lead-free composition of simple (1-x)BaTiO₃-xCeO₂ (0.0 ≤ x ≤ 0.5) contains only four elements (Ba, Ti, Ce and O). The incorporation of stiff and insulating CeO₂ nanocomposites within BaTiO₃ matrix could disrupt the long-range-ordered micrometer-size domains into short-range-ordered nanodomains. This disruption suppresses hysteresis and delays polarization of BaTiO₃ films. Combined with the enhanced breakdown strength, this formulation yielded an ultrahigh efficiency of ≈90% and a robust energy density of 45 ± 3 J cm^-3 at CeO₂ contents of x = 0.3 and 0.4. Meanwhile, these two films with x = 0.3 and 0.4 exhibit superior frequency (50 Hz to 2 kHz) and thermal stability (20 °C to 120 °C), demonstrating stable energy storage performance. The proposed strategy opens up a new avenue for designing high-performance nanocomposite films by incorporating stiff secondary phase embedded in BaTiO₃ or even linear SrTiO₃ dielectrics.