High-Energy Li-Ion Cells: Impact of Electrode Ageing on Second Life Viability

High energy cells embedding Nickel-rich and silicon-doped graphite are promoted because they allow electric vehicles to increase their range. We study the ageing of such cells, aiming to reuse them in a second life application. Assuming that second life depends on what they experienced during their first life, we submit 26 fresh cells to 6 different ageing protocols, before a less demanding second life ageing. We find that initial cycling at 0 degrees C and calendar ageing at 45 degrees C are leading to the shortest second life. We also find that this originates in the resistance of negative electrodes, thanks to symmetrical coin cell impedance measurements. Dismantling of the cells reveals that lithium plating induced pore clogging is responsible of the fast second life capacity fade. Thanks to differential voltage analysis measurements, we also show that this mechanism affects the positive electrode facing the clogged zones. Conversely, we could not show any correlation between the silicon phase degradation and second life longevity. In addition, the increase of the charge transfer resistance of positive electrodes protects the cells by preventing the spread of lithium plating. Diagnosis and sorting of aged cells must thus rely on resistance measurements.