Energy　storage　capacitors　are　valued　for　their　high　power　density　and　ultrafast　discharging　rates,　positioning　them　as　promising　candidates　for　advanced　electronic　systems　and　pulse　power　technologies.　This　study　developed　a　KBT-based　solid　solution　composed　of　K0.5Bi0.5TiO3,　Na0.5Bi0.5ZrO3,　K0.5Bi0.5ZrO3,　and　Na0.5Bi0.5TiO3,　located　near　a　morphotropic　relaxor　boundary.　This　configuration　results　in　a　perovskite　host　with　both　high　structural　entropy　and　enhanced　polarization　capability.　The　incorporation　of　Bi(Zn2/3Nb1/3)O3　not　only　modifies　the　dynamic　behavior　of　polar　nanoregions　but　also　increases　the　resistance　contribution　from　the　grain　boundary,　thereby　improving　the　electrical　breakdown　strength　Eb.　Optimal　polarization　behavior　and　energy　storage　performance　were　achieved　with　1.0　mol.%　Bi(Zn2/3Nb1/3)O3　addition,　resulting　in　a　large　field-induced　polarization　ΔP　of　55.3　µC/cm2,　a　high　recoverable　energy　density　Wr　of　6.52　J/cm3,　and　a　high　efficiency　η　of　80　%.　Overall,　this　work　proposed　a　design　strategy　for　developing　KBT-based　ceramics　for　energy　storage　capacitors.　©　2024　Elsevier　Ltd