Interface-engineering-enhanced energy storage performance of (Na_0.8K_0.2)_0.5Bi_4.5Ti₄O₁₅/Bi₄LaTi_3.5Mg_0.5O₁₅ multilayer film capacitors

Dielectric capacitors are vital components in advanced electrical power systems due to their high power density. However, how to improve their comparatively low energy density is still a major challenge. In this work, we designed a dielectric capacitor with a multilayer structure by inserting different numbers of ferroelectric (Na_0.8K_0.2)_0.5Bi_4.5Ti₄O₁₅ (NKBT) layers into relaxor ferroelectric Bi₄LaTi_3.5Mg_0.5O₁₅ (BLTM). Through the regulation of interface engineering, that is, the joint effects of electrical field amplifying, interlayer coupling, and block layer at the interface, enhancing the energy storage density and breakdown field in (NKBT/BLTM)_N capacitors. A giant energy density (W_rec) of 81.2 J/cm³ and a high breakdown electric field of 4074 kV/cm are achieved in capacitors with N = 4. Consequently, interface engineering can be promoted as a universal route to optimize the energy storage performance of dielectric capacitors.