Low temperature performance of graphite and LiNi0.6Co0.2Mn0.2O2 electrodes in Li-ion batteries

Low temperature (LT) behavior of graphite/LiNi0.6Co0.2Mn0.2O2 (NCM622) cells prepared with low loading or LL (thinner electrodes prepared with low loading and packing density) and high loading or HL (thicker electrodes prepared with high loading and packing density) were investigated. The cells were prepared as half coin cell, full coin cell, and full pouch cell to identify the main factors that limit LT operations of lithium ion batteries. All the cells were tested at −32 °C, and the capacity retention at LT was compared to the capacity retention at room temperature (RT). The Li+ insertion kinetics was analyzed by electrochemical impedance spectroscopy. The LL electrodes showed a lesser charge transfer resistance (R ct) than that shown by the thicker electrodes at LT. The diffusion coefficients of Li+ calculated via the galvanostatic intermittent titration technique (GITT) in graphite and NCM622 electrodes prepared with LL and HL at RT were in the range of 10−8 cm2/s but decreased to the range of 10−13 and 10−11 cm2/s at −32 °C, respectively. GITT results confirmed that the capacity loss at LT, with increased electrode loading, arose from the limitation of Li-ion diffusion within the electrode.