Role of Negative Electrode Porosity in Long-Term Aging of NMC//Graphite Li-Ion Batteries

Electrochemical energy storage associated to renewable energy sources requires devices with very long lifespan. In this work we simulated the long-term aging of Li(Ni 2/5 Mn 2/5 Co 1/5 )O 2 (NMC)//graphite lithium-ion batteries by standardized accelerated aging tests in tough storage and cycling conditions. Aging mechanisms taking place at the graphite electrode/electrolyte interface were characterized by X-ray Photoelectron Spectroscopy (XPS) and Electrochemical Impedance Spectroscopy (EIS). Besides usual aging processes commonly admitted, we highlight the role of electrode porosity. A model is proposed to describe the electrical behavior of the electrodes taking into account the influence of electrochemically blocking pores. The blocking effect of pores is believed to be caused by confinement of Li 2 CO 3 and/or gaseous CO 2 inside the narrow pores, which do not allow lithium ions to diffuse and insert into graphite. In these pores, lithium can only participate to SEI growth which decreases the capacity by lithium consumption.