A New Method for Measuring Transference Number Using Raman Spectroscopy

Abstract

The successful use of lithium metal as the negative electrode in high-energy density batteries is dependent on the effective suppression of dendritic growth during charging.1 A key electrolyte property for mitigating dendritic growth is the transference number, which describes the movement of one ion in relation to the other ions in solution.2 Traditionally, the agreed method for measuring the transference number has been the Hittorf method,3 but with the requirement of a large volume of electrolyte and the difficulty of separator inclusion, it does not imitate a real battery application. The popular polarisation methods including the so-called Bruce-Vincent method4 and the pure Electrochemical Impedance Spectroscopy method5 addresses this problem by including separators and only using small amounts of electrolyte. However, these methods assume ideality, which can often lead to the incorrect value of transference number especially at high concentrations or using ionic liquid electrolytes.We propose a new method for measuring the transference number, using Raman Spectroscopy, which closely imitates a real cell by the inclusion of a separator and does not assume ideality. We believe this facile and powerful new experiment is implementable in both academia and industry to understand how novel electrolyte’s transference number is influencing the concentration gradient and also dendrite growth.