Sub‐Nanowires Boost Superior Capacitive Energy Storage Performance of Polymer Composites at High Temperatures

Abstract Polymer dielectrics with high breakdown strength ( E b ) and high efficiency are urgently demanded in advanced electrical and electronic systems, yet their energy density ( U e ) is limited due to low dielectric constant (ε r ) and high loss at elevated temperatures. Conventional inorganic fillers with diameters from nano to micrometers can only increase ε r at the cost of compromised E b and U e due to their poor compatibility with polymer matrix. Herein, hydroxyapatite (HAP) sub‐nanowires with a diameter of ≈0.9 nm are incorporated in polyetherimide (PEI) matrix to form HAP/PEI sub‐nanocomposites. ε r and E b of the composites are concomitantly enhanced with only 0.5 wt.% of HAP sub‐nanowires, leading to high U e of 5.14 (@150 °C) and 3.1 J cm −3 (@200 °C) with efficiency of 90% and high‐temperature stability up to 3 × 10 5 charge‐discharge cycles at 200 °C. Microstructural analysis and molecular dynamics simulations indicate that the sub‐nanowires with comparable diameter as polymer chains induce enormous interfacial area, substantially increase mobility of polymer chains and form dense traps for charge carriers. This work extends the current research scope of polymer‐inorganics composite dielectrics to the sub‐nano‐level incorporation and provides a novel strategy for fabricating high performance polymer dielectrics at elevated temperatures.