From first to second life of lithium-ion batteries study

International audience; Second life of lithium-ion batteries is under investigation because it could be economically and environmentally profitable. However, the second life longevity of electric vehicles aged cells depends on aging parameters, as well as the state of health (SOH) shift point between first and second life. In this study, it has been set to 80 %, and two different cycling temperatures applied to two different references of 18650-format cells were tested as a first life aging. Periodical electrochemical check-ups allowed the monitoring of pulse resistance,incremental capacity analysis and electrochemical impedance spectroscopy. At the end of their first life, some cells were dismantled for visual and SEM inspections. It revealed in numerous cases the occurrence of lithium plating at the negative electrode, especially after aging at low temperature. Thicknesses, weights and electrochemical measurements of both electrodes confirmed this observation. Accelerated rate calorimetry (ARC) indicated the thermal safety degradations induced by the lithium plating. Similar aged cells were kept for a softer second life aging, with a reduced cycling rate. The over-aging longevity appeared to be depending on the first life, i.e. on the degradation mechanism. The occurrence of lithium plating seems to be tolerable only if its extension is limited.