Polymer gel electrolytes (GPEs) are an important class of materials used as electrolytes in lithium-ion batteries and supercapacitors. Poly (vinylidene fluoride) (PVDF) have been largely used as polymeric matrix to prepare GPEs due to its high porosity and low degree of crystallinity, which allows the retention of a large amount of liquid electrolyte. To understand ion transport, molecular dynamics (MD) is a tool that allows a microscopic point of view knowledge. In this work, polymeric systems of PVDF, with different concentrations of bis(trifluoromethylsulfonyl)imide [EMIM][FSI] were studied through MD simulations, which were performed by using the Gromacs suite package. Polymer electrolyte simulation systems were built by considering 50 chains of polymer and each chain of polymer had 18 repeating units. The amount of [EMIM][FSI] used was of 40, 55, 65 and 75 in wt.%. Pure IL and neat PVDF were also simulated. To calculate the glass transition temperature, NpT simulations were performed, in which the balanced systems were heated slowly. To neat PVDF the glass transition temperature obtained of 233.1 K is in good agreement with the literature (error around 0.4%). Ionic conductivities were calculated based on the Nernst-Einstein and Einstein-Helfand equations, an excellent agreement between experimental and simulation conductivity was observed for pure IL and the other systems reproduced the general trend of ionic conductivities reported experimentally. The structural analysis of the electrolytes showed that the interaction of the polymer with the ions occurs at specific sites, forming alternating layers of cations and anions. The ion transport mechanism was characterized and it was observed that IL passes through many different polymer solvation sites, indicating a rapid exchange coordination environment, characterizing the ion transport mechanism as a hopping between ion coordination sites.

Molecular dynamics simulations of polymer electrolytes based on poly (vinylidene fluoride) and ionic liquids

ACS Spring Meeting 2021

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