Résumé
The successful development of electrified vehicles is a key factor in the transition to a moreenvironmentally friendly transportation sector. Li-ion batteries, which are today’s choice to powerelectrified vehicles, have to fulfill more stringent requirements in terms of ageing and need advancedtools to study the interfaces evolution upon cycling. This work is thus focused on understanding theimpedance behavior of a commercial graphite-based negative electrode, which is used in a Li-ion batterydesigned for such vehicles. 3-electrode pouch cells were assembled with such negative electrode, a LMOlayeredoxide-based positive electrode, a Celgard1type separator soaked with a carbonate solvents-LiPF6mixture electrolyte and a LTO-based electrode as reference. Electrochemical Impedance Spectroscopymeasurements were performed at different cell states of charge and ageing times. The impedance of thegraphite-based anode is analyzed forfirst time with de Levie’s equation for porous electrodes. Theanalysis is supported by designed SEI layer formation experiments with vinylene carbonate and vinyleneethyl carbonate additives. The high frequency domain of the interfacial kinetic loop reflects porosityeffects and the graphite particles–composite matrix electric tranfer. The SEI layer and charge transferphenomena are reflected in the medium and medium to low frequency domains respectively, and theirimpedance contributions depend on the Li content of the graphite particles. Upon ageing, the interfacialimpedance of the graphite-based electrode should increase due to SEI layer growing. However, from 100%to 80% of battery capacity retention, the impedance decreases. Our analysis backed by post-mortemcharacterizations allows to assign this unexpected behavior to porosity rise and slight Mn-contaminationof the SEI layer.