Version 2 2023-11-08, 20:16Version 2 2023-11-08, 20:16
Version 1 2023-11-06, 20:00Version 1 2023-11-06, 20:00
journal contribution
posted on 2023-11-08, 20:16authored byGalo J. Páez Fajardo, Eleni Fiamegkou, James A. Gott, Heng Wang, Israel Temprano, Ieuan D. Seymour, Matthew J. W. Ogley, Ashok S. Menon, Ifan E. L. Stephens, Muhammad Ans, Tien-Lin Lee, Pardeep K. Thakur, Wesley M. Dose, Michaël
F. L. De Volder, Clare P. Grey, Louis F. J. Piper
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.