Mechanism of the effect of carbon coating on high temperature cycle performance of LiFePO4

To investigate mechanism of carbon coating on the high. temperature cycle performance of widely used LiFePO4/graphite batteries, two types of LiFePO4 cathode material with different carbon coating degrees were prepared. According to characterization results from X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), powder resistance, and coin cell, two types of LiFePO4 were almost identical with respect to the crystal structure, particle size, and specific capacity. Then LiFePO4/graphite pouch cells were prepared and cycled at 1C under 60 degrees C. It turns out that carbon coating can improve capacity retention from 80.4% to 84.9% after 1 251 cycles. The capacity improvement for polarization capacity and thermodynamic capacity account for 76% and 24%, respectively. This demonstrates that the mechanism of carbon coating is to reduce the polarization capacity loss by forming integrated conducting networks. In contrast, carbon coating can not inhibit Fe dissolution directly. Instead, it may be an indirect interaction through the reduction of moisture.