Achieving ultrahigh energy storage efficiency in local-composition gradient-structured ferroelectric ceramics

Although relaxor dielectric ceramic capacitors possess attractive features for high-power energy storage, their low energy storage efficiency (η) induces the dissipation of energy in the ceramics, thus significantly increasing their temperature and deteriorating their breakdown strength and lifetime in practical applications. Here, a new strategy for designing local-composition gradient-structured grains was proposed to improve the energy storage efficiency performance under a high-intensity electric field. To verify the applicability of the proposed strategy, the 0.9(K0.5Na0.5)NbO3–0.1Bi(Zn2/3Nb1/3)O3 relaxor-ferroelectric solid solution was employed for the experimental procedure. The gradient distribution of Zn from the grain interior to the grain boundary was achieved through the meticulous manipulation of different element diffusion behaviors. The resulting local-composition gradient structure could improve the relaxation behavior, while enhancing their dynamic response to external electric fields, thus decreasing dielectric nonlinearity and remarkably improving η performance under a high-intensity electric field. As a result, the η value of the ceramics decreased by a marginal extent until the electric field reached 326 kV cm−1, with a minimal variation of <±1.5%, demonstrating substantially higher performance than that of the well-studied lead-free nonlinear dielectric ceramics. Furthermore, by alleviating the local electric field concentration near the grain boundary, the unique structure could enhance the intrinsic breakdown of the dielectric material. Finally, through the proposed strategy, the optimum energy storage properties were obtained, namely, a high recoverable energy density of 4.01 J/cm3 and an ultrahigh energy efficiency of 97.1% at 326 kV cm−1. The proposed highly effective local-composition gradient-structured design offers a new paradigm for improving the energy storage efficiency of dielectric ceramic capacitors.