Study on operating mode cycle performance of lithium ion power battery with natural graphite and LiFePO_4

The variation rules of capacities and internal resistances of lithium ion power battery with LiFePO4 electrode were studied at different temperatures and simulated levels of the operating mode cycle to develop reasonable cycle life evaluation and testing methods. The results show that after 72 815 cycles,equivalent to corresponding vehicle driving for 8.0×104 km,capacity fade and the increase of DC internal resistance are 5.6% and 9.6% respectively at 25 ℃ and 100% simulated level. During the operating mode cycling,the capability fade of lithiation-delithiation is mainly attributed to the cathode of battery,although the anode also has a certain extent fade. The increasing of impedance of SEI film (solid dielectric phase interfacial film) and charge transfer resistance is obvious.