Molecular Dynamics Simulations of Polymer-Ionic Liquid (1-Ethyl-3-methylimidazolium Tetracyanoborate) Ternary Electrolyte for Sodium and Potassium Ion Batteries

We have performed molecular dynamics (MD) simulations of 1-ethyl-3-methylimidazolium tetracyanoborate ([EMIM](+)[B(CN)(4)](-)) ionic liquid to investigate the impact of addition of Na+/K+[B(CN)(4)](-) salts and poly(ethylene oxide) (PEO6) on transport properties. These ternary mixtures are promising electrolyte materials for Na+-ion and K+-ion batteries as alternatives to the traditional Li+-ion ones. In addition, local structure was assessed through radial distribution functions. Our main findings are the following: (1) when compared to systems with larger amounts of Na+ and K+, it was observed that lower concentrations enhance the overall ionic conductivity and decrease viscosity; (2) Na+ and K+ cations prefer to be coordinated to the polymer chains rather than the [B(CN)(4)](-) anions; (3) transport properties are improved when PEO6 oligomers are included in the electrolyte medium but these improvements continue only up to an optimum amount of PEO6. Beyond this amount, further addition of PEO6 did not have any additional impact on transport properties.