The fatigue of commercial lithium ion batteries after long-term cycling at two different temperatures and
cycling rates is investigated. The cells are opened after cycling and post-mortem analysis are conducted.
Two main contributions to the capacity loss of the batteries are revealed. The loss of active lithium leads
to a relative shift between anodes and cathodes potentials. A growth of the solid electrolyte interface
(SEI) on the anode is determined as well as the formation of lithium fluoride species as an electrolyte
decomposition product. Those effects are reinforced by increasing cycling rates from 1C/2C (charge/
discharge) to 2C/3C as well as by increasing cycling temperatures from 25 C to 40 C. The other
contribution to the capacity loss originates from a fatigue of the blended cathodes consisting of
LiNi0.5Co0.2Mn0.3O2 (NCM), LiNi0.8Co0.15Al0.05O2 (NCA) and LiMn2O4 (LMO). Phase-specific capacity losses
and fatigue mechanisms are identified. The layered oxides tend to form microcracks and reveal changes
of the surface structure leading to a worsening of the lithium kinetics. The cathode exhibits a loss of
manganese at 40 C cycling temperature. Cycling at 40 C instead of 25 C has the major impact on
cathodes capacity loss, while cycling at 2C/3C rates barely influences it.
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