All-Organic Cross-Linked Polysiloxane-Aromatic Thiourea Dielectric Films for Electrical Energy Storage Application

The development of high-power-density energy storage devices and systems calls for high-dielectric-constant (high-k) polymer films with low dielectric loss. Aromatic polythiourea attracts many interests because of its low dielectric loss and high beakdown strength, whereas the high brittleness significantly limits its application as dielectric films. In this report, flexible high-k films were successfully fabricated by cross-linking aromatic thiourea oligomers with allyl glycidyl ether grafted poly(methylhydrosiloxane) (PMHS). Siloxane segments of PMHS improve the flexibility of the cross-linked dielectric films, and the grafted glycidyl ether side groups of PMHS provide highly polarizable building blocks. Because of the high dipole moment (4.89 D), aromatic thiourea endows the dielectric films with a high dielectric constant. Microphase separation morphology was found within the film, and the self-assembly into layered lamellae contributed to the scatter of high-energy-charge carriers. As a result, the dielectric films exhibit reduced dielectric loss tangent and suppressed leakage current density with a high dielectric constant of above 6, a promissing energy density of 3.15 J/cm3 and a high efficiency of above 87% under an electric field of 350 MV/m.