Post mortem analysis of ageing mechanisms in LiNi0.8Co0.15Al0.05O2 – LiNi0.5Co0.2Mn0.3O2 – LiMn2O4/graphite lithium ion batteries

Abstract

The influence of storage temperatures on the ageing mechanisms of 60 Ah cells consisting of a blended cathode and a graphite anode are investigated. The post mortem analysis reveals that the capacity loss of the cells stored between 25 °C and 60 °C can be mostly assigned to a loss of mobile lithium during storage caused by side reactions on the surface of the anode, such as growth of the solid-electrolyte interphase. The loss of active lithium causes a relative shift of anode curve and cathode curves in full cell, as evident from the three-electrode measurement. Increasing storage temperature from 25 °C to 40 °C leads to a minor increase in loss of active lithium, while an increase in storage temperature to 60 °C leads to a more severe increase in loss of active lithium. The capacity of cathode decreases slightly when the cells are stored at 40 °C and 60 °C, however, it is found that the capacity loss of the cathode does not affect the capacity loss of the full cell. On the other hand, the graphite anode shows excellent storage stability. The capacity loss of the graphite anode is not found for all aged cells reported here.