Nissan Leaf was the first mass-produced electric vehicles (EV) using lithium -ion batteries (LiB). Most of the first generation (Gen 1) battery packs have been retired after approximately 10 years of operation, and some of them are repurposed to build battery energy storage systems (BESS). However, the health condition of the battery packs at the time of retirement, the battery aging trajectory, and the service life in second-life application are unclear. To answer these questions, this paper conducts a comprehensive study on the retired Nissan Leaf Gen 1 batteries. First, over 100 retired battery packs were investigated to evaluate their state of health (SOH). Secondly, a battery aging test was conducted on two battery cells which completed 7380 aging cycles. Lastly, the battery aging trajectory was analyzed. The result shows that although most retired Nissan Leaf Gen 1 battery packs have only 60 %-67 % remaining capacity, they can operate 12-20 years in second life. Whole-battery-pack utilization is preferable due to good battery consistency. A retired battery pack with a cost of $1000 can generate a $16,200 value in its second life, suggesting a good return on investment (ROI).
