Molecular Mechanisms Driving the Performance of Single-Ion Conducting Polymer Electrolytes in Lithium-Based Batteries

Single-ion conducting polymer electrolytes (SICPEs) hold great potential for the next-generation batteries due to their high safety, fast charging capability, and high energy density. However, their practical application is hindered by the low ionic conductivity (IC). The addition of plasticizers has been shown to effectively enhance IC, although the underlying molecular mechanisms remain unclear. In this study, we employed atomistic molecular dynamics simulations to examine the impact of ethylene carbonate (EC) on lithium-ionic conductivity in a modified polyethylene terephthalate (mPET)-based SICPE. Our simulations reproduced experimental IC values and revealed a similar IC trend with varying EC concentrations, including a notable transition at 50 wt % EC. This enhancement in IC appears to be associated with increased EC diffusion and the preferential coordination of the lithium ions with the oxygen atoms in EC. Analysis of the local oxygen coordination environment around lithium ions further explains the IC transition observed at 50 wt % EC. These findings provide insights into the molecular mechanisms by which EC enhances IC in mPET-based SICPEs, primarily through changes in the local oxygen environment surrounding lithium ions. This study contributes to the design of improved SICPEs with plasticizers, supporting advancements in lithium-ion battery technology.