All‐Organic Polystyrene‐Based Copolymer Dielectrics for Superior High‐Temperature Charge Energy Storage with Robust Stability

Enhancing dielectric constant and breakdown field strength simultaneously, and exploring the design strategy of high charge energy storage properties at high-temperature environments are the core problems in thin film dielectrics. In this paper, γ-methyl-α-methylene-γ-butyrolactone (MeMBL) and styrene (St) are randomly copolymerized by free radical emulsion polymerization to obtain dielectric films with high energy density. The introduction of MeMBL units containing highly polar groups (ester groups as well as lactone rings) not only improves the dielectric constant and T_g of the copolymer but also creates trap sites for the capture of free charge carriers. The homogeneously distributed trap sites can effectively trap free space charges and thus significantly suppress the conduction under high electric fields and improve the breakdown strength under high temperatures. When utilized for dielectric energy storage, Poly(St-co-MeMBL) can achieve a discharge energy density of 8.08 J cm^-3 at room temperature. Even at 150 °C, Poly(St-co-MeMBL) can still provide a discharge energy density of 4.69 J cm^-3 with a charge/discharge efficiency of 88%. Moreover, Poly(St-co-MeMBL) dielectric films present excellent robustness and long-term working stability over 10³ charge-discharge cycles. The proposed design concept presents a novel way of manufacturing linear dielectric materials for high-temperature energy storage and electronics.