软包锂离子电池循环异常膨胀的改善研究

Analysis and improvement on abnormal cycle swelling for Li-ion polymer cell

运用交流阻抗谱(electrochemical impedance spectroscopy,EIS),激光厚度扫描,计算机断层扫描(computed tomography,CT),扫描电子显微镜(scanning electron microscope,SEM)&能谱仪(energy dispersive spectromete,EDS)和不同SOC极片界面分析对电芯的循环膨胀失效进行了研究。EIS表明,循环厚度异常和电芯SEI膜偏厚有关;激光厚度扫描和CT表明电芯厚度异常来源于电芯头尾部起翘和内部极片间隙。SEM&EDS表明起翘的区域可能存在较厚的SEI膜和析锂。不同SOC下的极片界面分析表明,阳极极片屋檐区域存在更高的SOC,当电芯满充时候,该区域会出现析锂。研究及验证结果表明电芯头尾部起翘,是由电芯内部阳极屋檐区域,偏弱的电极界面和特殊的锂离子传递路径叠加引起了析锂和SEI膜增加的失效模式。降低电芯充电倍率,提高锂离子在阳极的迁移速率可以有效解决该循环膨胀问题。

The failure of lithium ion batteries swelling was investigated by EIS,laser thickness scanning,CT,SEM&EDS and interface analysis of different SOC.EIS shows that the abnormal cell swelling is related to the thicker SEI film;laser thickness scanning and CT show that the abnormal cell swelling comes from the top and bottom turnup of cell or gap inside electrodes.SEM&EDS show that anode overhang area may exist thicker SEI film and lithium precipitation.Interface analysis of different SOC shows that the overhang area exists higher SOC,and this area may precipitate Li-ion when cell is full-charging.The research results show that the bulging of the top and the bottom of cell is caused by the lithium precipitation and S EI film contributed by weak electrode interface and special lithium ion transfer path in Overhang areas.Reducing cell charge rate and increasing Li-ion migration rate in anode will solve the cycle swelling problem effectively.