Mapping of Lithium-Ion Battery Electrolyte Transport Properties and Limiting Currents with In Situ MRI

Given the electrochemical modelling and control systems challenges facing lithium-ion batteries in extreme operating conditions, such as low temperature and high C-rate, it is important to understand the transport dynamics in a polarized cell with large electrolyte concentration gradients. To this end, a combination of conventional magnetic resonance imaging (MRI) experiments and MRI experiments coupled with pulsed-field gradient NMR for diffusion measurements were performed on an in situ lithium-ion cell operating at a variety of temperatures and current densities. The aim was to quantify the electrolyte transport parameters with spatial resolution. Some progress was attained towards this aim, and the necessary framework for future studies along this direction was developed; however, it was determined that in order to accurately quantify the transference number, a very accurate measurement of the concentration gradient is necessary when the polarization is large. It was also observed that limiting current behavior in the electrolyte at low temperature arises as a consequence of diffusion limitation on the anodic side, rather than ion depletion on the cathodic side. The framework developed herein may be useful not only for electrochemical model validation, but potentially also comprehensive electrolyte transport characterization, should the identified experimental limitations be overcome.