Balancing Polarization and Breakdown for High Capacitive Energy Storage by Microstructure Design

Abstract The compromise of contradictive parameters, polarization, and breakdown strength, is necessary to achieve a high energy storage performance. The two can be tuned, regardless of material types, by controlling microstructures: amorphous states possess higher breakdown strength, while crystalline states have larger polarization. However, how to achieve a balance of amorphous and crystalline phases requires systematic and quantitative investigations. Herein, the trade‐off between polarization and breakdown field is comprehensively evaluated with the evolution of microstructure, i.e., grain size and crystallinity, by phase‐field simulations. The results indicate small grain size (≈10–35 nm) with moderate crystallinity (≈60–80%) is more beneficial to maintain relatively high polarization and breakdown field simultaneously, consequently contributing to a high overall energy storage performance. Experimentally, therefore an ultrahigh energy density of 131 J cm −3 is achieved with a high efficiency of 81.6% in the microcrystal‐amorphous dual‐phase Bi 3 NdTi 4 O 12 films. This work provides a guidance to substantially enhance dielectric energy storage by a simple and effective microstructure design.