Hierarchical Polar-Nonpolar Phase Architecture Enabling Excellent Lead-free Capacitive Energy Storage

Abstract

Dielectric capacitors are highly attractive for advanced power electronics owing to their ultrafast charge–discharge rate, high power density, and excellent reliability. Yet their application is hindered by the persistent trade-off between high recoverable energy density (Wrec) and high efficiency (η) owing to the inherent coupling in single-phase dielectrics, where stronger polarization generally comes at the expense of higher hysteresis and limited breakdown strength. Here, we present a polar-nonpolar hierarchical phase architecture design in BaTiO3–BiMg0.5Ti0.5O3-based ceramics to overcome this limitation by modulating thermodynamic spinodal decomposition. The polar Ba-rich phase provides large maximum polarization, while the non-polar Cd-rich precipitation with a large bandgap acts as a high-resistivity barrier that isolates polar regions and enhances the breakdown field. Atomic-scale electron microscopy analysis reveals that the nanoscale polar regions (~1–3 nm) with locally disordered configurations emerge in the ceramic, which lowers the energy barrier for domain switching and enables near-zero hysteresis losses. As a result, the optimized hierarchical composition achieves an ultrahigh efficiency of 92.8%, a high recoverable energy density of 9.7 J cm-3, an outstanding high figure of merit WF of 135 at 460 kV cm-1, along with excellent stability against temperature, frequency, and cycling, and fast discharge with a power density up to 185 MW L-1. This work demonstrates a robust design paradigm based on complementary dual-phase coexistence, offering fundamental insights and a practical pathway toward high-performance, lead-free dielectric capacitors.