Paradoxical Role of Structural Degradation of High-Nickel Layered Oxides and Electrode Crosstalk in Capacity Retention upon Storage of Lithium-Ion Batteries

Batteries undergo both active cycling and prolonged idle storage throughout their lifespan. While degradation mechanisms induced by cycling and their mitigation techniques have been deeply studied, the specific effects of storage without cycling remain largely underexplored. Notably, battery performance also sees a unique decline over time, contingent on the state-of-charge (SoC) when the batteries are at rest. Capacity decline during SoC70 storage primarily arises from electrode slippage and Li inventory loss in a full cell. This is accompanied by a minor structural breakdown of Ni-rich layered oxide cathodes. Conversely, SoC100 storage leads to a more pronounced structural impairment of Ni-rich cathodes and pronounced side reactions. Intriguingly, these severe side reactions curb the Li inventory loss, electrode slippage, and the reduction of full-cell capacity during SoC100 storage. In addition to standard degradation processes, such as Li/Ni cation mixing, the formation of surface reconstruction layers, and the emergence of exhausted phases, cathodes stored at SoC100 displayed an unexpected contraction of interlayer spacing during post-storage cycling, highlighting the atypical effects of storage. Based on the mechanisms of capacity reduction highlighted in this study, we propose strategies to counteract the aging caused by storage. This research offers valuable perspectives for refining battery production and management to enhance their calendar lifespan.