磷酸铁锂电池开路电压曲线特性分析

Characteristic Analysis of Open Circuit Voltage Curve of LiFePO4 Battery

为揭示磷酸铁锂电池开路电压曲线特性,以静置法获取磷酸铁锂/石墨电池荷电状态(SOC)与开路电压(OCV)关系曲线,研究了活性材料、电池类型、SOC调节方向及静置时间、电池容量衰减、负极掺硅及预锂化对SOC-OCV曲线的影响,并采用扣式和软包电池分析了正极和负极对SOC-OCV曲线的影响以及60%SOC附近电压阶跃的原因。结果表明:磷酸铁锂和石墨活性材料种类变更,存储和充放电循环,造成电池容量降低,负极嵌锂量减少,电位上升,SOC-OCV曲线向右移动。负极掺硅后,电位上升,SOC-OCV曲线向右移动。方型电池与软包电池的SOC-OCV曲线一致,不受电池类型影响。受电压迟滞效应影响,放电SOC-OCV曲线低于充电SOC-OCV曲线,但随着静置时间的增加,放电SOC-OCV曲线上升,充电SOC-OCV曲线降低,两者趋向重合。负极预锂化使负极电位降低,SOC-OCV曲线向左移动。全电池SOC-OCV曲线主要由负极决定,60%SOC附近OCV阶跃主要受石墨发生2L到2阶相变的影响。研究结果提高了对磷酸铁锂电池OCV曲线的认识,可为动力电池开发提供科学参考。

In order to reveal the open circuit voltage(OCV)curve characteristics of lithium iron phosphate(LiFePO4)battery,the relationship curves between state of charge(SOC)and OCV of LiFePO4/graphite batteries were obtained by method of rest.The influences of active material,battery type,SOC adjustment direction and rest time,battery capacity fading,anode mixed with silicon and pre-lithiation on the SOC-OCV curves were studied.The influence of cathode and anode on SOC-OCV curve,and the reason of voltage step near 60%SOC were analyzed by using coin cells and soft pouch batteries.The results show that the change of lithium iron phosphate and graphite active materials,storage and charge-discharge cycles can lead to the fading of battery capacity,causing the reduction of lithium amount in anode,the rise of anode potential,and ultimately the SOC-OCV curve moves to right.After mixed with silicon,the anode potential rises,and the SOC-OCV curve moves to right.The SOC-OCV curve of prismatic battery is consistent with soft pouch battery,and independent of the battery type.Due to the voltage hysteresis effect,the curve of discharging SOC-OCV is lower than charging SOC-OCV.However,with the increase of rest time,the curve of discharging SOC-OCV increases while the charging SOC-OCV decreases,and the two curves tend to coincide.Pre-lithiation of anode can reduce the potential,and make the SOC-OCV curve shift to left.The SOC-OCV curve of the battery is mainly determined by anode,and the OCV step occured in near 60%SOC is mainly affected by the phase transition of 2L to 2 stage in the process of lithium intercalation.The research results improve the understanding of OCV curves of LiFePO4 battery,and can provide scientific reference for the development of power batteries.