Capacity fade characteristics of lithium iron phosphate cell during dynamic cycle

As a key issue of electric vehicles, the capacity fade of lithium iron phosphate battery is closely related to solid electrolyte interphase growth and maximum temperature. In this study, a numerical method combining the electrochemical, capacity fading and heat transfer models is developed. The electrolyte interphase film growth, relative capacity and temperature change of lithium iron phosphate battery are obtained under various operating conditions during the charge-discharge cycles. The results show that the electrolyte interphase film thickness increases as the C rate rises and relative capacity decreases. The capacity loss is almost 19.7% when the C-rate rises from 0.5C to 2C after 2000 cycles. The thickness of electrolyte interphase film increases and relative capacity decreases when the ambient temperature goes up. A thicker negative electrode is adverse to the electrolyte interphase film growth, and leads to the increased relative capacity, while the influence of separator thickness can be negligible. The battery maximum temperature rises with increasing the C rate and initial temperature, which exceeds the safe upper limit when the ambient temperature increases to 318.15 K at 3C. By increasing the convective heat transfer coefficient, the maximum temperature can be reduced to the security value.