Lithium-Ion Solvation Shell in Polyvinylidene Difluoride-Based Quasi-Solid Electrolytes from Ab Initio Molecular Dynamics Simulations

The development of high-performance lithium-metal batteries has long been at the forefront of energy technologies, with the electrolyte often being the limiting factor directly affecting the performance and safety of the battery. Among solid electrolytes, polyvinylidene difluoride (PVDF)-based electrolytes have attracted increasing attention due to their mechanical properties and wide electrochemical stability. However, there is growing evidence that the ionic transport in PVDF-based electrolytes requires the presence of a liquid solvent (DMF). This study uses ab initio molecular dynamics (AIMD) simulations to explore the role of the solvent in Li+ solvation and diffusion mechanisms across this quasi-solid electrolyte (QSE). AIMD simulations of liquid LiFSI-DMF and the extended LiFSI-DMF-PVDF system underline the weak interaction between Li ion and PVDF and show that the solvation structure of Li+, with DMF and bis(fluorosulfonyl)imide (FSI-) ions solvating Li+ ions, is not affected by the presence of the polymer. Conversely, a weak interaction between the FSI- anion and the polymer chains is observed. The Li+ solvation shell is dynamic, which can effectively influence the diffusion through the QSE. These insights represent a step forward in understanding the diffusion mechanism of Li-ion in PVDF-based electrolytes and can be used for the rational design of novel electrolytes.