Understanding Capacity Recovery Behavior Using Long-Term Stored Pouch Cells

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Commercial lithium-ion batteries often experience capacity and power degradation when stored for extended periods after production. Interestingly, the reduced capacity can be partially recovered over time when the cells are cycled again, a phenomenon known as capacity recovery. However, it is difficult to separate the analysis of capacity recovery from the capacity decay during recycling. Additionally, the widely accepted explanation for capacity recovery, the passive anode effect (PAE), focuses solely on the lithium inventory within the overhang anode site. To address these challenges, we studied large-capacity LiNi0.4Co0.3Mn0.3O2/graphite pouch cells that were stored for 4 years. During recycling, the capacity gradually recovered over 120 cycles, and this fully recovered capacity was maintained for up to 500 cycles, indicating minimal additional capacity decay during recycling. Our investigation also highlighted the significant impact of breakdown and thinning of the calendar-aged solid electrolyte interphase (SEI) on the entire anode site, affecting both capacity and power recovery beyond just the PAE. Furthermore, by integrating both the PAE and breakdown of the calendar-aged SEI into a life prediction model, we were able to predict the capacity recovery behavior for up to 1000 cycles under various operating conditions. This comprehensive approach provides insights into understanding and predicting the long-term performance of lithium-ion batteries, particularly in relation to storage-induced capacity degradation and subsequent recovery during cycling.