The aim of this study is to determine the evolution of chemical, morphological and mechanical properties of a polyethylene separator under two different ageing conditions: calendar ageing and fast charge cycling in 18650 LFP/G batteries systems. Its porosity is evaluated by Helium pycnometry, its mechanical properties by tensile test. Surface chemical composition is also investigated by X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. Surface state is observed by scanning electronic microscopy (SEM) and by atomic-force microscopy (AFM). Electrochemical performances are analyzed by impedance spectroscopy and C-rate tests to investigate the consequences of the separator ageing. Safety tests are also performed by overcharge in an Accelerating Rate Calorimeter (ARC) and by in-situ dendrites growing in coin cells.
First results show a decrease of the separators porosity after calendar ageing which causes a decrease of the cell performances at high capacity rate. A deposit is observed on the extreme surface. A mechanistic model of ageing will be proposed which integrate a porosity gradient and an evolution in time.