基于内阻增加和容量衰减双重标定的锂电池健康状态评估

State of health estimation of Li-ion battery based on dual calibration of internal resistance increasing and capacity fading

锂电池健康管理对推动其广泛应用具有重要意义。立足锂电池应用现状,为解决复杂工况下健康状态估算困难、精度低等问题,以三元锂电池为研究对象,建立二阶RC等效模型对电池的工作特性进行表征,从内阻增加及容量衰减两方面分析健康状态变化。考虑荷电状态对内阻的影响,采用标定荷电状态,在放电情况下分为0~1 s及1~10 s两区间分析其内阻变化;并以温度为参量,扩大测量区间,更精确地反映不同温度下容量衰减。实验结果表明,在0~1 s内,锂电池健康状态同荷电状态并无关系;1~10 s内,锂电池健康状态下降速率同荷电状态呈反比;且在不同温度下的完全放电实验表明,实验用锂电池在25℃下健康状态最为优良。表明二阶RC模型能够较好地对锂电池健康状态进行估算,收敛速度快且跟踪效果好,基于内阻增加的健康状态估算误差控制在1.0%以内、基于容量衰减的健康状态估算误差控制在0.8%以内,有利于完善锂电池健康状态评估方法,推动锂电池应用。

The management of the state of health(SOH)and life prediction of Li-ion batteries are of great significance to promote their wide application.In this paper,on the basis of the situation of application of Li-ion batteries,to remedy the real-time estimation difficulty and low precision under various working conditions,a ternary Li-ion battery is taken as the research object,a second-order RC equivalent circuit model is established to characterize the operating characteristics of the battery,and the performance of the Li-ion battery is studied and analyzed on the basis of the experiments under various working conditions.The changes in the state of health were analyzed from two directions:internal resistance increase and capacity fading.The effect of the state of charge(SOC)on internal resistance is considered.The SOC is calibrated under discharge conditions,and the change of internal resistance is analyzed from 0 to 1 s and 1 to 10 s,respectively.We established the corresponding calculation formula of the evaluation method on the basis of the internal resistance increase of the Li-ion battery and determined the changes of state of health under different initial SOCs in two time ranges.The temperature is taken as a parameter,and the measurement interval is extended to reflect the capacity fading at different temperatures more accurately by multiple full charging and discharging experiments.We also established the corresponding mathematical formula of the state of health on the basis of capacity fading for the Li-ion battery and obtained the changes in the battery's state of health at different temperatures.The experimental results show that within 0—1 s,there is no relationship between the state of health of the Li-ion battery and the initial SOC.Within 1—10 s,the decline rate of the state of health is inversely proportional to the initial SOC.The complete discharging experiments at different temperatures show that the Li-ion battery has the best health condition at 25℃,so the test battery should be operated at this temperature as far as possible.It is indicated that the second-order RC equivalent circuit model can estimate the state of health of Li-ion batteries very well;the convergence rate is fast,and the tracking effect is good.The state of health estimation errors based on internal resistance increase and capacity fading are controlled within 1.0%and 0.8%,respectively.Improving the state of health estimation method helps promote the applications of Li-ion batteries.