Cycle life modeling and the capacity fading mechanisms in a graphite/LiNi 0.6 Co 0.2 Mn 0.2 O 2 cell

A 3.0 Ah pouch-type lithium-ion cell with a high energy density (200 Wh kg −1 ) was studied to establish a cycle life model of the battery. The cells consisted of graphite and LiNi 0.6 Co 0.2 Mn 0.2 O 2 electrodes, and they were cycled at 1 C over a 100 % depth of discharge at different temperatures (25, 35, and 45 °C). A semi-empirical cycle life model was developed using experimental data by adopting a simple time power law and Arrhenius kinetics. The cycle life model agreed well with the experimental data but featured a much higher power law factor (1.3) compared to the value of 0.5 associated with the general t 1/2 rule based on the rate of solid electrolyte interphase (SEI) growth. The capacity fading mechanisms that operated within the cells were investigated using electrochemical, physical, and chemical diagnostic methods. These results revealed that the loss of active lithium ions via SEI formation as well as electrode degradation, especially cathode degradation, was responsible for the capacity fading in the cells.