High-Temperature　dielectric　Bi0.5Na0.5TiO3(BNT)-based　relaxors　near　a　morphotropic　phase　boundary　are　developed　with　excellent　energy　storage　performance.　Random　distribution　of　polar　nanoregions　induced　by　composition　modulation　would　disrupt　the　ferroelectric　long-range　dipolar　alignment　and　weaken　the　coupling　between　the　ferroelectric　domains,　yielding　slender　and　deferred　polarization-electric　field　hysteresis　loops　with　relatively　high　saturation　polarization.　The　reversible　nano-domain　orientation　and　growth　in　relaxors　under　a　delayed　electric　field　result　in　negligible　remnant　polarization　and　advantageous　energy　storage　properties.　Simultaneously,　superior　recoverable　energy　storage　density　and　efficiency　are　gained,　significantly　surpassing　the　state-of-The-Art　dielectric　energy　storage　materials　under　similar　moderate　electric　fields.　Vacancies,　defect　dipole　behavior,　and　structural　evolution　that　relied　on　an　electric　field　and　temperature　are　discussed　to　disclose　the　underlying　mechanism　associated　with　phase　transition.　Even　thermal　stability　and　large　electrostrictive　strain　with　low　hysteresis　are　achieved　in　elevated　temperatures.　These　features　demonstrate　the　promising　candidates　for　dielectric　energy-storage　application　and　provide　a　strategy　in　designing　relaxors.　©　2022　American　Chemical　Society.　All　rights　reserved.