磷酸铁锂高温循环性能的改善

Improvement of high temperature cycling performance of LiFePO_(4)

磷酸铁锂结构稳定、循环性能优异,但是随着主机厂家对质保要求的不断提升,磷酸铁锂仍面临着高温循环性能不能满足客户要求的情况。以磷酸铁锂正极锂离子电池为研究对象,分别对比了基础电解液体系和改善电解液体系[在基础电解液中添加二氟二草酸硼酸锂(LiODFB)]对电池高温循环性能的影响。对循环后的电池采用直流内阻(DCIR)、电化学交流阻抗谱(EIS)、dQ/dU(恒定的电压间隔内电池容量的变化)曲线等无损分析方式进行数据对比,结果表明改善电解液体系电池的电荷转移阻抗进一步降低。通过对电池进行解剖,对两种电解液体系的电池极片进行了厚度分析、X射线衍射(XRD)分析、扫描电镜(SEM)分析、电感耦合等离子体发射光谱(ICP)元素分析等,结果表明改善电解液体系的电池在抑制负极表面副反应、减少正极铁溶出方面具有明显的效果,因此电池的高温循环性能更好。

LiFePO_(4)has stable structure and excellent cycle performance,but with the continuous improvement of the quality assurance requirements of the host manufacturer,LiFePO_(4)still faces the situation that the high-temperature cycle performance can not meet the requirements of customers.Taking LiFePO_(4)cathode lithium-ion battery as the research object,the effect of the basic electrolyte system and the improved electrolyte[adding lithium difluorodioxalate borate(LiODFB)to the basic electrolyte]system on the high-temperature cycle performance of the battery were compared.The non-destructive analysis methods such as DC internal resistance(DCIR),electrochemical AC impedance spectroscopy(EIS),dQ/dU(change of battery capacity in constant voltage interval)curve were used to compare the data of the recycled battery.The results showed that the charge transfer impedance of the battery with improved electrolyte system was further reduced.Through the dissection of the battery,the thickness analysis,X-ray diffraction(XRD)analysis,scanning electron microscope(SEM)analysis and inductively coupled plasma emission spectroscopy(ICP)element analysis of the battery electrode sheets of the two electrolyte systems were carried out.The results showed that the battery with improved electrolyte system had obvious effects in inhibiting the side reactions on the surface of the negative electrode and reducing the dissolution of positive iron,so the high temperature cycle performance of the battery was better.