Ceramic dielectrics are reported with superior energy storage performance for applications, such as power electronics in electrical vehicles. Recoverable energy density (Wrec) of ~ 4.55 J cm-3 with η~90% is achieved in a lead-free relaxor BaTiO3-0.06Bi2/3(Mg1/3Nb2/3)O3 ceramics at ~ 520 kV cm-1. These ceramics may be co-fired with Ag/Pd, which constitutes a major step forward towards their potential use in the fabrication of commercial multilayer ceramic capacitors. Compared to stoichiometric Bi(Mg2/3Nb1/3)O3 doped BaTiO3 (BT), A-site deficient Bi2/3(Mg1/3Nb2/3)O3 reduces the electrically heterogeneity of BT. Bulk conductivity differs from grain boundary only by one order of magnitude which, coupled with a smaller volume fraction of conducting cores due to enhanced diffusion of the dopant via A-site vacancies in the A-site sublattice, results in higher breakdown strength under electric field. This strategy can be employed to develop new dielectrics with improved energy storage performance.

Electrical homogeneity is vital in optimising energy storage performance in BiFeO₃–BaTiO₃–xBi(Li_0.5Nb_0.5)O₃ ceramic multilayer capacitors, giving rise to high recoverable energy density ∼13.8 J cm⁻³ under electric field ∼950 kV cm⁻¹ and fatigue resistance behaviour.