Non-Uniform Aging of Commercial NMC/Graphite Lithium-Ion Batteries

Non-uniform aging of commercial NMC/Graphite lithium-ion batteries

Abdulrahim Ayoub¹, Abdilbari Mussa², Maria Varini²

¹ Department of Chemical Engineering, The City College of New York, CUNY, New York, NY 10031, USA

² School of Chemical Engineering, Division of Applied Electrochemistry, Royal Institute of Technology, Stockholm, Sweden

Lithium ion batteries are well-established energy storage systems with high power and energy density. In the past few years, rechargeable lithium ion batteries have played a major role in automotive applications; however, many obstacles remain in long-term performance and durability. Decrease in capacity and/or a rise in impedance leads to electrode aging, thus, dramatically degrading the batteryÕs performance.

Herein, aging of commercial NMC/Graphite battery is investigated in (i) calendar aged cells, stored at 22^oC for approximately a year, (ii) cycled cells, cycled at +4C/-1C between 10-90% SOC. Further, electrochemical analysis was done on different positions within the electrode layer to study aging as a function of position, namely edge and center. In this study, electrochemical impedance and capacity measurements were the methods of choice used to characterize aging.

Calendar and cycled aged cells displayed differences in capacity fade and impedance rise. Specifically, the cycle-aged cells showed more pronounced losses, likely associated with the growth/formation of the solid-electrolyte interface(SEI) and the loss of cyclable lithium. Considering the edge and center of the same electrode layer, variations in capacity and impedance were also noticed, possibly caused by an un-even current distribution along the electrode.