18650型柱状锂离子电池的容量衰减机理

摘要

The mechanism for capacity fading of 18650 lithium ion full cells under room-temperature (RT) is discussed systematically.The capacity loss of 18650 cells is about 12.91％ after 500 cycles.The cells after cycles are analyzed by XRD,SEM,EIS and CV.Impedance measurement shows an overall increase in the cell resistance upon cycling.Moreover,it also presents an increased charge-transfer resistance (Rct) for the cell cycled at RT.CV test shows that the reversibility of lithium ion insertion/extraction reaction is reduced.The capacity fading for the cells cycled can be explained by taking into account the repeated film formation over the surface of anode and the side reactions.The products of side reactions deposited on separator are able to reduce the porosity of separator.As a result,the migration resistance of lithium ion between the cathode and anode would be increased,leading the fading of capacity and potential.%研究18650商业化锂离子全电池在常温条件下的容量衰减机理.结果表明,经过500次循环后,18650柱状电池的容量衰减率为12.91％;对经循环后的电池采用XRD、SEM、EIS和CV进行表征.电化学交流阻抗图谱表明,随着循环的进行,电池的电阻特别是电荷转移电阻逐渐增加;同时,循环伏安测试表明,在循环的后期,电池的锂离子脱嵌可逆性能下降,导致容量衰减.这是因为,在正、负极材料界面处发生电解液与电极材料副反应,反复形成固态电解质界面膜.同时,副反应产物沉积一部分沉积在隔膜上,堵塞隔膜孔,阻碍锂离子的穿梭.因此,锂离子在正负极间的移动阻力增大,导致电池的容量衰减和电位衰减.