Influences of graphite electrode on degradation induced by accelerated charging-discharging cycling in lithium-ion battery

To investigate the effects of degradation on the Li-ion battery (LIB) during fast charging-discharging under various ambient temperatures, the structural changes and elemental distributions were investigated on the graphite electrode between pristine and degradation (Cell capacity < 50%) samples in LIB under room temperature (RT, 25 degrees C) and low temperature (LT, 0 degrees C) ambient using scanning electron microscope (SEM), transmission electron microscope (TEM), and time of flight-secondary ion mass spectrometry (ToF-SIMS). We focused our studies on the structural changes and element distributions via cross-section image for graphite electrode, which were cycled during fast charging-discharging under RT and LT (0 degrees C), respectively. The TEM results show that the surface of graphite in case of LT (0 degrees C) was only changed to amorphous state with cracks on the surface (approximate to 10 mu m thickness) partially, whereas the graphite of RT was not changed. Also, ToF-SIMS results confirm that the inhomogeneously concentrated elements of Li, F, and P originated from LiPF6 electrolyte were observed on the graphite surface only in the case of LT (0 degrees C). Our measurement results are expected to contribute to revealing the degradation mechanism during fast charging-discharging cycling under LT (0 degrees C) ambient.