Asymmetry between charge and discharge during high rate cycling in LiFePO₄ - In Situ X-ray diffraction study

Asymmetric behavior of structural changes during charge and discharge of C-coated LiFePO₄ has been investigated using synchrotron based in situ XRD. C-coated LiFePO₄ undergoes phase transformation from triphylite to heterosite during charge and vise versa during discharge. However, it is observed that the phase transformation of C-coated Li_1-xFePO₄ during discharge is more difficult to be complete than that during charge. At 2C rate, the phase transformation from heterosite to triphylite was hardly observed during discharge while the complete phase transformation was observed in the previous charge. This indicates that the degree of the phase transformation completeness depends on the direction of the phase transformations.