Speaker
Neelima Paul
Description
Aging in 18650-type NMC/C cells, produced under commercial conditions, has
been experimentally characterized by *in situ* neutron diffraction and electrochemical
analysis. The comparison of discharge capacity of an uncycled cell with
that of a cell which has undergone 1000 cycles under ambient conditions, shows a
capacity fade of 21% on cycling. Neutron diffraction of the uncycled and cycled
cell, in their charged state, shows a reduction in the weight fraction of the LiC6
phase as well as an increase in the weight fraction of the LiC12 phase on aging,
from which a cyclable lithium loss corresponding to a capacity loss of 23% can
be extracted. In spite of this large capacity loss, both the anode and cathode
materials are scrutinized to be structural stable and no evidence of active material
loss is observed in the evaluation of these neutron diffractograms. Thus,
other aging mechanisms could be excluded from these measurements, within the
experimental accuracy of the method. A physico-chemical aging model, which
attributes capacity fade solely to loss of cyclable lithium in the growth of a continuous
solid electrolyte interface (SEI) film on the anode surface, is developed
to reconsider aging contributions. This model is first validated by reproducing
the obtained experimental aging and voltage profiles which confirms cyclable
lithium loss into SEI layer growth as the sole aging mechanism. It also predicts
a reduction or shift in x = 0:18 for anode stoichiometry LixC6 (0 < x < 1), for
the cycled cell. This is in good agreement with the anode stoichiometry shift of
x = 0:20 for the cycled cell as obtained from neutron diffraction experiments.
Primary author
Co-authors
Prof.
Andreas Jossen
(TUM)
Frank Kindermann
(TUM)
Jonas Kiel
(TUM)
Ludwig Kraft
(TUM)
Dr
Oleksandr Dolotko
(Heinz Maier-Leibnitz Zentrum (MLZ), Technische Universität München (TUM),)
Ralph Gilles
Simon Erhard
(TUM)
