The　development　of　lead-free　dielectric　ceramics　with　temperature　insensitive　high　discharge　energy　density　(W-dis)　and　high　energy　efficiency　(n)　are　highly　demanded　for　the　practical　applications　in　energy　storage　capacitors.　In　this　work,　we　have　designed　and　fabricated　the　NaNbO3　modified　Na0.5Bi0.5TiO3-K0.5Bi0.5TiO3　(NBT-KBT-xNN)　relaxor　ferroelectrics.　The　addition　of　metastable　antiferroelectric　NN　into　the　NBT-KBT　matrix　leads　to　enhanced　relaxor　behavior　and　improved　breakdown　strength.　As　a　result,　the　x　=　0.4NN　specimen　not　only　showed　optimal　inte7grated　energy　storage　properties　with　a　large　W-dis　of　1.7　J/cm(3)　and　eta　of　90%　under　a　moderate　electric　field　of　150　kV/cm,　but　also　exhibited　superior　temperature　stability　with　the　variation　of　W-dis　within　+/-　15%　and　eta　more　than　80%　from　-50　degrees　C　to　150　degrees　C.　All　these　properties　indicate　that　NN　modified　NBT-KBT　ceramic　was　a　promising　candidate　for　the　practical　application　of　energy　storage　capacitors.　(C)　2020　Elsevier　B.V.　All　rights　reserved.