Study on cycling performance of lithium iron phosphate battery at different discharge rates

The capacity, energy, internal resistance and open-circuit voltage are key indicators to represent the performance of lithium iron phosphate battery and important parameters in battery management system (BMS) design as well.These characteristics are closely related to the charge and discharge rate. The cycling performance of the LiFePO₄ battery at different discharge rates was tested at 40℃ in terms of battery capacity, energy, AC impedance and open-circuit voltage to investigate their changing laws in the circulation of different discharge rates. The result shows that the relation between discharge capacity and discharge rate follows the rule of power function; battery capacity declines more quickly with a high rate of circulation; the discharge rate has different influences on ohmic impedance and electrochemical impedance of the battery in the course of circulation, that is, the ohmic impedance is little affected by the rate but the electrochemical impedance increases quickly with the rate rising; in addition, the higher the discharge rate, the faster the open-circuit voltage falls in the late cycle; the battery emits less energy, with its heat production increasing, burn-in accelerating and lifetime decreasing in a large current.