Comprehensive study of the aging knee and second-life potential of the Nissan Leaf e+ batteries

Aging knee may induce rapid degradation of lithium-ion batteries (LIBs) and pose safety risks. It is crucial to study the battery aging knee and find solutions to address it. In this light, this study focuses on the comprehensive aging characterizations of the Nissan Leaf third generation (Gen3) LIBs to elucidate their aging trajectories. Twenty-four battery cells were divided into six groups and cycled at different working conditions, i.e., voltage, current, and temperatures. The test result shows that the batteries tend to reach the aging knee around 75 % state of health (SOH). Then, we improved the working conditions after the knee point to mimic second-life operation. Key findings show that the aging knee can be stopped by improving the working conditions. The battery capacity degradation slowed down to about 4 % per 1000 cycles, projecting a second-life potential of 4000–6000 cycles between 75 % and 50 % SOH. Post-mortem analysis indicated that negative electrode failure is the cause of aging knee and gas generation. The impact of working conditions on the battery aging is analyzed. Based on the analysis, we propose strategies for both the first and second life operations of LIBs to improve battery life and avoid the aging knee. •Battery aging knee can be avoided by improving the operating conditions.•The second life window after the knee point is 75 %∼50 % SOH.•The estimated second life is 4000∼6000 cycles and 11–16 years.•The graphite exfoliation on the anode is the reason of aging knee.