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

Abstract 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 BaTiO 3 ‐based lead‐free films. Our lead‐free composition of simple (1‐ x )BaTiO 3 ‐ x CeO 2 (0.0 ≤ x ≤ 0.5) contains only four elements (Ba, Ti, Ce and O). The incorporation of stiff and insulating CeO 2 nanocomposites within BaTiO 3 matrix could disrupt the long‐range‐ordered micrometer‐size domains into short‐range‐ordered nanodomains. This disruption suppresses hysteresis and delays polarization of BaTiO 3 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 CeO 2 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 BaTiO 3 or even linear SrTiO 3 dielectrics.