Temperature and concentration dependence of the ionic transport properties of poly(ethylene oxide) electrolytes

Even though batteries operate at different temperatures depending on their use and state of charge, little work has been done to understand the effects of temperature on the ionic transport properties of the electrolyte. The temperature dependence of these properties is important for predicting how the performance of the battery will change as a function of temperature, along with gaining fundamental insights into the underpinnings of ion transport in these electrolytes. In this study we provide the first investigation of the effect of temperature on ionic conductivity, salt diffusion coefficient, transference number, and the thermodynamic factor of a model polymer electrolyte: lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) salt dissolved in poly(ethylene oxide) (PEO). These properties were measured at 70, 90, and 110 °C. As expected, we see monotonic increases in conductivity and diffusion with increasing temperature. Additionally, monotonic dependencies on temperature were obtained for the transference number and the thermodynamic factor. One presumes that concentration polarization decreases with increasing temperature due to more rapid ion transport. We use concentrated solution theory to predict concentration polarization in lithium-PEO/LiTFSI‑lithium symmetric cells and thereby quantify the effect of temperature on concentration polarization. •Electrochemical characterization as a function of temperature and concentration.•Negative values of the cationic transference number at all measured temperatures.•Modeling of concentration gradients at different temperatures and concentrations.