A Semi-Empirical Capacity Fade Model for Li-NCA Cathode

Abstract

Lithium Nickel-Cobalt-Aluminum (NCA) is a popular cathode material for Li-ion cells due to its high energy density and moderate cost. Cycling experiments confirmed that the cathode capacity fade is the dominant capacity fade mechanism [1] in such cells. Electron energy loss spectroscopy (EELS) and X-Ray Absorption Fine Structure (XAFS) analysis of the aged LiNCA particles exhibit the formation of a NiO type layer, which is inactive to Li intercalation, at the surface of the particles. Estimated amount of this inactive layer is found to match with the capacity loss of the cell. Therefore, a physics based model with one empirically determined parameter has been constructed for this reaction and it has been implemented on Li-ion battery electrochemical model [3]. The model predicts the relative capacity of a Li-NCA cell cycles at different temperatures with high accuracy (Fig.1). For constant current condition, a simple closed form solution for the capacity fade has been derived and validated. On extension this model can effectively predict the remaining useful life.