Relaxor　ferroelectric　polymers　display　great　potential　in　capacitor　dielectric　applications　because　of　their　excellent　flexibility,　light　weight,　and　high　dielectric　constant.　However,　their　electrical　energy　storage　capacity　is　limited　by　their　high　conduction　losses　and　low　dielectric　strength,　which　primarily　originates　from　the　impact-ionization-induced　electron　multiplication,　low　mechanical　modulus,　and　low　thermal　conductivity　of　the　dielectric　polymers.　Here　a　matrix　free　strategy　is　developed　to　effectively　suppress　electron　multiplication　effects　and　to　enhance　mechanical　modulus　and　thermal　conductivity　of　a　dielectric　polymer,　which　involves　the　chemical　adsorption　of　an　electron　barrier　layer　on　boron　nitride　nanosheet　surfaces　by　chemically　adsorbing　an　amino-containing　polymer.　A　dramatic　decrease　of　leakage　current　(from　2.4　×　10−6　to　1.1　×　10−7　A　cm−2　at　100　MV　m−1)　and　a　substantial　increase　of　breakdown　strength　(from　340　to　742　MV　m−1)　were　achieved　in　the　nanocompostes,　which　result　in　a　remarkable　increase　of　discharge　energy　density　(from　5.2　to　31.8　J　cm−3).　Moreover,　the　dielectric　strength　of　the　nanocomposites　suffering　an　electrical　breakdown　could　be　restored　to　88%　of　the　original　value.　This　study　demonstrates　a　rational　design　for　fabricating　dielectric　polymer　nanocomposites　with　greatly　enhanced　electric　energy　storage　capacity.　©　2021　Science　China　Press