Investigation of Pre-conditioning Strategies that Enable State-of-Health Improvement for A Remanufactured Li-Ion Battery in Automotive Circular Economy Applications 2018-01-0444

Implementing and optimizing the sustainability of vehicles that contain embedded electrochemical energy storage have recently been afforded more attention in research due to legislative requirements and cited benefits from circular economy activities. The State-of-Health (SoH) for a traction battery system that prematurely failed can be restored through circular economy activities such as remanufacturing. To enable these circular economy activities, the ability to introduce a new or graded cell or module into a series string to replace the weakest cell or module in a battery module or pack is vital. However, very little is understood about the optimal strategy that will lead to maximizing the lifetime of the most aged cell or module in the new string and predict the expected lifetime of the repaired or remanufactured battery system. The aim of this research is to assess whether aged lithium-ion cells in series, with some of the aged cells replaced with new cells, have an optimized pre-conditioning strategy to ensure the weakest cell’s life is prolonged. Three modules with six 18650 cells in series have been evaluated to determine the optimal replacement strategy for an energy storage unit albeit cell or module in series for in-use life extension activities. Results highlight that it is possible to significantly reduce the degradation of the weakest cell in a repaired string of series cells. Reduction of circa 4% in aging of the weakest cells is reached with bottom pre-conditioning, while an increase in degradation of the new cell is only 2.5% relative to the worst case scenario. Additionally, the authors show that the energy capacity of the string pre-conditioned at the top reduces the most during cycling of the three strings. Based on these experimental results, an optimal pre-conditioning strategy for circular economy activities for electric vehicle traction battery systems is proposed.