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Rate-Dependent, Li-Ion Insertion/Deinsertion Behavior of LiFePO4 Cathodes in Commercial 18650 LiFePO4 Cells
journal contribution
posted on 2014-03-12, 00:00 authored by Qi Liu, Hao He, Zhe-Fei Li, Yadong Liu, Yang Ren, Wenquan Lu, Jun Lu, Eric A. Stach, Jian XieWe have performed operando synchrotron
high-energy X-ray diffraction (XRD) to obtain nonintrusive, real-time
monitoring of the dynamic chemical and structural changes in commercial
18650 LiFePO4/C cells under realistic cycling conditions.
The results indicate a nonequilibrium lithium insertion and extraction
in the LiFePO4 cathode, with neither the LiFePO4 phase nor the FePO4 phase maintaining a static composition
during lithium insertion/extraction. On the basis of our observations,
we propose that the LiFePO4 cathode simultaneously experiences
both a two-phase reaction mechanism and a dual-phase solid-solution
reaction mechanism over the entire range of the flat voltage plateau,
with this dual-phase solid-solution behavior being strongly dependent
on charge/discharge rates. The proposed dual-phase solid-solution
mechanism may explain the remarkable rate capability of LiFePO4 in commercial cells.