Influence of Polymer Polarity on Ion Transport in Polymer Electrolytes

Polymer electrolytes are materials that could improve the safety and performance of lithium-ion and -metal batteries. Despite their promising attributes, such as high shear modulus and electrochemical stability, they tend to have sluggish ionic transport. Several properties have been shown to improve ionic transport, including host segmental dynamics. Recently, we showed that host polymer polarity, measured by the dielectric constant, is also an influencing factor in ionic transport. We found that higher polarity polymers more effectively break up ionic aggregates, which reduces correlated ionic motion. However, our study focused on polymers with a narrow dielectric constant range (~3–7), which prohibited a general understanding of the extent to which improving polarity could improve ionic transport.

In this work, we turn to a coarse-grained simulation model with which we explore a wide range of polymer polarities and simultaneously explore the influence of polymer molecular weight and salt concentration. We show that ionic transport maximizes at intermediate polarity due to a competition between reduced ionic aggregation and slowed polymer dynamics. We demonstrate that ionic transport only couples to molecular weight and salt concentration once a threshold polarity is exceeded.