不同放电倍率磷酸铁锂电池循环性能研究

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

磷酸铁锂电池的容量、能量、内阻和开路电压是其性能的重要指标,也是涉及电池管理系统设计的重要参数.这些特性均与电池充放电倍率紧密相关.通过对40℃下不同放电倍率的LiFePO_4锂离子电池的容量、能量、交流阻抗和开路电压等循环性能试验,研究不同放电倍率循环下以上特性的变化规律.结果表明,电池放电容量与放电倍率间满足幂函数规律;高倍率下循环,电池容量衰减更快;在循环过程中,放电倍率对电池的欧姆阻抗和电化学阻抗的影响程度不同,欧姆内阻受倍率影响很小,电化学阻抗则随着放电倍率升高,增加越快;另外,在循环后期,放电倍率越高,开路电压下降越快;大电流下,电池放出能量降低,产热增加,老化加快,寿命降低.

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 LiFePO4battery at different discharge rates was tested at40℃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.