磷酸铁锂电池循环初期衰减快原因分析及性能改善

Cause analysis of early cycling attenuation of LiFePO_(4) battery and its performance improvement

磷酸铁锂电池由于循环性能优异、价格相对低廉、安全性能有保障等诸多优势而备受青睐。磷酸铁锂电池循环曲线的特点是前面衰减很快,到中后期变得平缓。为了挖掘磷酸铁锂电池更长寿命的潜在能力,以磷酸铁锂/石墨电池为研究对象,对衰减较快的前期循环进行了研究,并依据研究结果提出了改善建议。与三元类(NCM)电芯比较,正极材料的首效差异造成磷酸铁锂材料循环衰减快于三元材料,并通过电感耦合等离子体发射光谱(ICP)、X射线衍射(XRD)等手段证实了这一理论。采用电感耦合等离子体发射光谱(ICP)、能谱(EDS)和差式扫描量热分析(DSC)等多种手段对固体电解质界面(SEI)膜进行了表征,证明磷酸铁锂前期衰减快的原因主要是活性锂的消耗,而损失的活性锂主要用于修复破坏的SEI膜。最后提出一系列改善措施,即通过改善负极颗粒的OI值(活性材料取向指数)、负极涂覆量、负极胶的溶胀、正极比表面积等,可以减缓磷酸铁锂电池前期的衰减速率。

LiFePO_(4)battery is highly favored for its′excellent cycling performance,relatively low price and high stability.The cyclic curve faded rapidly in the early stage,and flattened out in the middle and late stages.In order to explore the potential capacity of LiFePO_(4)battery for longer service life,LiFePO_(4)/graphite battery was taken as the research object to study the early cycle with fast decay,and suggestions for improvement were put forward based on the research results.Compared with the ternary(NCM)cell,the differences of initial efficiency of the anode material caused the cycle attenuation of LiFePO_(4)material to be faster than that of the ternary material.This theory had been confirmed by means of inductively coupled plasma emission spectroscopy(ICP),X-ray diffraction(XRD),etc.The SEI films were characterized by inductively coupled plasma emission spectroscopy(ICP),energy dispersive spectroscopy(EDS)and differential scanning calorimetry(DSC).It was proved that the main reason for the fast decay of LiFePO_(4)in the early stage was the consumption of active lithium,and the loss of active lithium was mainly used to repair the damaged SEI film.Finally,the decay rate of the LiFePO_(4)battery in the early stage could be slowed down by improving the OI value of the negative particles,the coating amount of the cathodes,the swelling of the negative gel,and the specific surface area of the anodes.