Department of Mechanical Engineering, Purdue School of Engineering and Technology, Indiana University-Purdue University , Indianapolis, Indiana 46202, United States.
ACS Appl Mater Interfaces. 2014 Mar 12;6(5):3282-9. doi: 10.1021/am405150c. Epub 2014 Feb 24.
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 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.
我们进行了同步辐射高能 X 射线衍射（XRD）的原位实验，以非侵入式、实时监测在实际循环条件下商业 18650 LiFePO4/C 电池中的动态化学和结构变化。结果表明，在 LiFePO4 正极中存在非平衡的锂离子嵌入和脱出，在锂离子嵌入/脱出过程中，LiFePO4 相和 FePO4 相都没有保持静态组成。基于我们的观察，我们提出 LiFePO4 正极在整个平坦电压平台范围内同时经历两相反应机制和双相固溶反应机制，这种双相固溶行为强烈依赖于充放电速率。所提出的双相固溶机制可以解释 LiFePO4 在商业电池中出色的倍率性能。
