Combined density functional theory and molecular dynamics analyses on Lithium/Sodium ion interaction and diffusion in gel polymer electrolytes with poly-vinylidene fluoride scaffold, propylene carbonate/Ionic Liquid solvent, and perchlorate salt

• Published in: Materials today communications 2023-12, Vol.37, p.107311, Article 107311
• Main Authors: Sarkar, Ranjini, Kundu, Tarun Kumar
• Format: Article
• Language: English
• Subjects: Density Functional Theory; Diffusivity; Electrochemical stability; Gel polymer electrolytes; Li- and Na-ion battery; Molecular Dynamics; Non-covalent interactions; PVDF; Transference numbers
• ISSN: 2352-4928; 2352-4928
• DOI: 10.1016/j.mtcomm.2023.107311

Choice of a proper electrolyte is very crucial to enhance the overall performance of a metal-ion battery. In this work, dispersion corrected density functional theory and classical molecular dynamics simulations are carried out to explore the metal ion (Li+ and Na+) interaction and diffusion through polyvinylidene fluoride (PVDF)-based gel polymer electrolytes. Four types of polymer/solvent/salt electrolyte systems are investigated considering PVDF scaffold for each case, and conventionally used propylene carbonate and rarely used, albeit cheaper, ionic liquid [BMIM][ClO4] as solvent, along with metal perchlorate salts LiClO4 and NaClO4. Inter-unit interactions within the electrolyte clusters, electrolyte uptake, and electrochemical stability of the electrolytes are explained by gas-phase DFT analyses, considering the polymer/solvent/salt components in 1:1:1 molecular ratio. Diffusion of the ions and ionic conductivity of the electrolytes are explored by MD simulation referring to two different size and time scales. From the DFT-based non-bonding interaction analyses, metal ions are found to exhibit strong non-covalent interactions with the adjacent O and F atoms, where the O atoms are parts of PC and [ClO4]- ions, and F atoms are from the PVDF chains. [BMIM]+, [ClO4]-, and PVDF are found to interact through weak van der Waals type hydrogen bonds. Both DFT and MD calculations suggest that, Li+ and Na+ ions are primarily coordinated with [ClO4]- ions. Dynamics studies confirm that for PVDF/IL/salt, total ionic conductivity is predominated by [BMIM]+ and [ClO4]-, exhibiting lower metal ion diffusivity as compared to PC-containing electrolytes. For both Li- and Na-ion systems, owing to the availability of higher number of charge carriers, electrolytes containing ILs show higher ionic conductivity compared to those containing PC as the solvent. [Display omitted] •Combined DFT and MD-based study is performed for gel polymer electrolytes (GPE) for Li- and Na-ion batteries.•The properties of [BMIM][ClO4] are compared with conventional solvent PC within PVDF-supported GPE.•Li+ and Na+ interactions with GPE components are demonstrated based on DFT calculations.•Li+ and Na+ diffusion through the electrolytes is studied using MD simulation.•Total ionic conductivity of IL-containing GPEs is found to be higher than PC-containing GPEs.