Accurate characterization of transference numbers in electrolyte systems

Efficient lithium-ion transport is pivotal for the battery advancement, and the transference number plays a central role in achieving this efficiency. In the literature, significant discrepancies in transference number values are often observed. For instance, in polymer electrolytes, notable inconsistencies in transference numbers exist even when the electrolyte chemistry, such as salt concentration and polymer molecular weight, is held constant. Therefore, conventional wisdom focusing on the material chemistry cannot explain these inconsistent results. Herein, we report a long-standing overlooked aspect: the discrepant transference number results can stem from the misestimation of parameters in measurement methodologies. Our analysis leverages the transmission-line-model applied to a polyethylene oxide electrolyte, allowing us to reevaluate traditional measurement methods. Through this reassessment, we not only uncover how the determination of measurement parameters can exert a significant influence on the attained transference number but also suggest a method to accurately characterize the transference number. Furthermore, we explore the origins of anomalous transference number and elucidate the impact of transference number on electrochemical impedance and direct-current polarization experiments. This research contributes vital insights into addressing critical challenges associated with transference number measurements in electrolyte systems, promoting the development of more efficient lithium-ion transport in battery technology.