The effects of chlorotrifluoroethylene (CTFE) units on the dielectric and energy storage properties of P(VDF-CTFE)

Polyvinylidene fluoride-based ferroelectric polymers are favoured in the field of advanced high-energy-storage dielectric capacitors due to their strong spontaneous polarisation and high dielectric constant (ε_r). It has been confirmed that the ferroelectric behaviour and energy storage performance can be regulated by copolymerising polyvinylidene fluoride with bulky monomers such as chlorotrifluoroethylene, and hexafluoropropylene. Past research based on these copolymers mostly focused on the preparation of composites, yet with limited discussion on the effect of copolymer composition. In this work, a series of P(VDF-CTFE) films with different chlorotrifluoroethylene contents were fabricated through a solution-casting method. The introduction of bulky chlorotrifluoroethylene units can tune the polymer crystal structure and crystallinity, alter the state of polymer chains and the response of dipoles to electric fields, and lead to dramatic changes in dielectric properties, breakdown strength (E_b), and energy storage density (U_e). As a result, the copolymer with a chlorotrifluoroethylene content of 15 wt% obtained the best overall performance, and the U_e reached 16.73 J/cm³ at 650 kV/mm. This work provides a basis for the optimisation of the properties of polyvinylidene fluoride-based ferroelectric polymers and the development of high U_e dielectric.