Ultrahigh Energy Charge–Discharge Efficiency in Olefinic Elastomer with POSS Cage‐Linking Construction

Abstract Polymer dielectrics with intrinsic breakdown strength and fast release cycle are promising candidates in energy conversion and embedded power systems. However, the charge–discharge efficiency and dielectric reliability of polymer film should be further enhanced urgently based on the depression of energy loss. In this study, the sulfhydryl group modified polyhedral oligosiloxanes (SH‐POSS) nanoparticle, and the sulfhydryl‐functionalized POSS serves as crosslinking site through reacting with the unsaturated double bond in poly(styrene‐butadiene‐styrene) (SBS) block copolymer. The dielectric constant ( ɛ ′) of composite retains stable tendency over wide testing frequency, e.g. ɛ ′ = 1.79 at 10 6 Hz and ɛ ′ = 1.73 at 15 GHz for 5 wt.% composite. With the presence of cage particles as crosslinking sites, the viscoelastic hindrance becomes weak, resulting in the descending dissipative force between inter‐chains, which contributes to the depression of hysteresis loss under field on‐off cycle. The charge–discharge efficiency of 5 wt.% film reaches 97.5% at 450 MV m −1 , and the current composite exhibits outstanding stability with 10 5 cycles at 100 °C and 100 MV m −1 . These results indicate that the proposed method effectively balances low dielectric constant with high insulation that demonstrates broad prospects in energy storage/conversion of microelectronic packaging and stretchable electronics.