Unraveling capacity recovery behavior of 78 Ah pouch cells after long-term storage for EVs: Passive anode and calendar-aged SEI effects

Abstract

The unavoidable long-term storage after production can result in capacity and power fading in commercial lithium-ion batteries. Remarkably, the decreased capacity is partially and gradually recovered when the stored cells are cycled again, known as capacity recovery. However, it is challenging to analyze the capacity recovery phenomenon independently from the capacity decay during re-cycling. Moreover, the most well-known explanation for capacity recovery, the passive anode effect (PAE) is only focus on the lithium inventory inside the overhang anode site. To address these issues, the large-capacity LiNi0.4Co0.3Mn0.3O2/graphite pouch cells stored for 4 years is used. Typically, throughout the re-cycling, the capacity is gradually recovered up to 120 cycles, and the fully recovered capacity was maintained up to 500 cycles, indicating that additional capacity decay by re-cycling was almost suppressed. Also, we clearly reveal the impact of breakdown and thinning of the calendar-aged solid electrolyte interphase (SEI) on the whole anode site influences both capacity and power recovery, not just limited to the PAE. Furthermore, by combining both the PAE and breakdown of the calendar-aged SEI into a life prediction model, the capacity recovery behavior for up to 1000 cycles under various operating conditions can be predicted.