Lead-free　piezoceramics　with　a　temperature-insensitive　figure　of　merit　(FOM　=　d(2)/epsilon)　are　urgently　required　to　build　a　new　generation　of　piezoelectric　energy　harvesters　(PEHs)　that　can　be　used　for　environmental　protection　and　new　energy　applications.　Although　(K,Na)NbO3　(KNN)-based　ceramics　are　among　the　most　promising　lead-free　piezoelectric　candidates,　the　piezoelectric　charge　constant　(d(33))　and　dielectric　constant　(epsilon(r))　of　KNN　with　an　individual　orthorhombic　(O)　phase　exhibit　opposite　change　trends　in　a　certain　temperature　range,　resulting　in　FOM　with　poor　temperature　stability.　To　break　this　bottleneck,　a　diffuse　multiphase　coexistence　(DMC)　strategy　is　proposed　to　realize　a　temperature-insensitive　FOM.　By　constructing　a　DMC-featured　orthorhombic-tetragonal　(O-T)　phase　boundary　associated　with　a　hierarchical　domain　configuration,　the　temperature-driven　synergistic　variation　of　d(33)　and　epsilon(r)　was　realized　in　the　0.965(K0.48Na0.52)NbO3-0.035(Bi0.5Li0.5)ZrO3　(KNN-BLZ)　system.　Benefiting　from　an　excellent　temperature-insensitive　FOM,　the　power　density　of　the　cantilever　beam-type　PEH　produced　by　KNN-BLZ　obtained　a　record　value　of　865　mu　W　cm(-3)　at　80　degrees　C,　which　was　superior　to　the　reported　value　of　approximately　380　mu　W　cm(-3)　for　KNN-based　PEHs　measured　at　room　temperature.　These　results　pave　the　way　for　applications　of　KNN-BLZ　piezoceramics,　and　also　greatly　impact　our　understanding　of　the　strong　correlations　between　the　thermal　stability　of　DMC　structure　and　temperature-dependent　energy-harvesting　properties.