Non-invasive diagnosis of solid electrolyte interphase and charge transfers resistances for degraded lithium-ion batteries

Abstract

Modeling the electrical behavior of cells is often complex because several parameters have to be determined simultaneously, which may lead to inconsistencies and inaccuracies. In the present paper, we modeled the “surface resistance” by using a method based on rules of dependence, already presented in the literature, which makes it possible to separate the contributions of the SEI (Solid Electrolyte Interphase) layer and the charge transfers as a function of the temperature and the current. A physical model is able to provide a consistent estimate of the surface resistance values at untested operating points. We transposed this model to NCA (LiNixCoyAl1−x−yO2) and NMC-622 (LiNi0.6Mn0.2Co0.2O2)/graphite+Si cells and we characterized them for different states of health (SOH). For a SOH of 87%, we found that the charge transfers resistance was multiplied at least by 5.8, while the SEI resistance was multiplied at least by 1.5. As the cell ages, the proposed model should be easier to recalibrate than lookup tables. For that, we propose two methods, one that provides more detailed and accurate results and one that is more practical from an engineering point of view.