E-beam irradiation of poly(vinylidene fluoride-trifluoroethylene) induces high dielectric constant and all-trans conformation for highly ionic conductive solid-state electrolytes

Abstract

Polymer matrices have limited abilities to dissociate lithium salts and transport ions, thus making most solid-state polymer electrolytes (SPEs) have extremely low ionic conductivities (10−7–10−5 S/cm) at 25 ℃. In this work, a high-energy electron-beam (e-beam) irradiation is applied to a poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)] SPE to improve the ionic conductivity. P(VDF-TrFE) easily shows pure all-trans (TTTT) conformation with all fluorine atoms located on one side of the carbon chain to provide an ion transport highway. E-beam irradiation keeps large amounts of TTTT conformation of P(VDF-TrFE) and produces –CF3 side groups, where the latter expands the interchain distance to split the large ferroelectric domains into nanosize to induce a unique relaxor ferroelectric behavior. This enhances the dielectric constant of the irradiated P(VDF-TrFE) from 15 to 20 and thus facilitates lithium salt dissociation. As a consequence, the ionic conductivity of the irradiated P(VDF-TrFE) SPE is increased from 5.8 × 10−5 to 1.6 × 10−4 S cm−1 at 25 ℃. The solid-state Li//Li symmetrical cell cycles for more than 3000 h at 25 ℃ without a short circuit. Furthermore, the solid-state LFP//Li cell cycles stably for more than 350 cycles with a capacity retention of around 91.3% at 1 C and 25 ℃. This study paves a new way to prepare high-performance SPEs by inducing high dielectric constants and abundant TTTT conformations through e-beam irradiation.

Keywords

• solid-state polymer electrolytes
• pvdf
• dielectric constant
• electron-beam irradiation
• all-trans conformation