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Synergistic Degradation Mechanism in Single Crystal Ni-Rich NMC//Graphite Cells

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paragon-plus: 5245930 
Fiamegkou, Eleni; paragon-plus: 6735118 
Gott, James A.; paragon-plus: 6206810 
Wang, Heng; paragon-plus: 6735121 
Temprano, Israel; paragon-plus: 1806052 


Oxygen loss at high voltages in Ni-rich NMC//graphite Li-ion batteries promotes degradation, but increasing evidence from full cells reveals that the depth of discharge choice can further accelerate aging, i.e., synergistic degradation. In this Letter, we employ cycling protocols to examine the origin of the synergistic degradation for single crystal Ni-rich NMC//graphite pouch cells. In regimes where oxygen loss is not promoted (V < 4.3 V), a lower cutoff voltage does not affect capacity retention (after 100 cycles), despite significant graphite expansion occurring. In contrast, when NMC surface oxygen loss is induced (V > 4.3 V), deeper depth of discharge leads to pronounced faster aging. Using a combination of post-mortem analysis and density functional theory, we present a mechanistic description of surface phase densification and evolution as a function of voltage and cycling. The detrimental impact of this mechanism on lithium-ion kinetics is used to explain the observed cycling results.


Publication status: Published


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American Chemical Society
Faraday Institution (FIRG044)
Faraday Institution (FIRG060)
Faraday Institution (FIRG024)