10.1021/am405150c.s001 Qi Liu Qi Liu Hao He Hao He Zhe-Fei Li Zhe-Fei Li Yadong Liu Yadong Liu Yang Ren Yang Ren Wenquan Lu Wenquan Lu Jun Lu Jun Lu Eric A. Stach Eric A. Stach Jian Xie Jian Xie Rate-Dependent, Li-Ion Insertion/Deinsertion Behavior of LiFePO<sub>4</sub> Cathodes in Commercial 18650 LiFePO<sub>4</sub> Cells American Chemical Society 2014 Commercial 18650 LiFePO 4 CellsWe LiFePO 4 Cathodes cycling conditions mechanism nonequilibrium lithium insertion LiFePO 4 phase operando synchrotron XRD LiFePO 4 LiFePO 4 cathode FePO 4 phase voltage plateau rate capability 2014-03-12 00:00:00 Journal contribution https://acs.figshare.com/articles/journal_contribution/Rate_Dependent_Li_Ion_Insertion_Deinsertion_Behavior_of_LiFePO_sub_4_sub_Cathodes_in_Commercial_18650_LiFePO_sub_4_sub_Cells/2315041 We 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 LiFePO<sub>4</sub>/C cells under realistic cycling conditions. The results indicate a nonequilibrium lithium insertion and extraction in the LiFePO<sub>4</sub> cathode, with neither the LiFePO<sub>4</sub> phase nor the FePO<sub>4</sub> phase maintaining a static composition during lithium insertion/extraction. On the basis of our observations, we propose that the LiFePO<sub>4</sub> 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 LiFePO<sub>4</sub> in commercial cells.