Nonlinear Cycling Aging of a Commercial 18650 Lithium Ion Cell

The capacity and power loss are usually observed when lithium ion batteries were cycled or stored, however, the degradation mechanisms and their correlation with cell performance fade are not only dependent on the cell chemistry but also on the cell design and manufacture technique. The capacity loss diagnosis and the lifetime prediction for LIBs are still critical issues for large format applications. Commercial 18650 lithium ion cells containing a composite cathode of LiNi0.5Mn0.3Co0.2 (NMC) and LiMn2O4 (LMO) and graphite anode with a nominal capacity of 2.15 Ah were used in this study. Although the aging behavior of the battery comprised with LiNi1/3Mn1/3Co1/3O2/LiMn2O4 composite cathode and graphite anode cycled between 4.2 and 2.8V had been studied with an incremental capacity technique and suggested that there are two stages of capacity fade with first stage mainly caused by the loss of inventory (LLI) and further suffered from loss of active material (LAM) in positive electrode in the second stage [1, 2]. The results of capacity retention study within the voltag e range between 4.2 and 2.75V by following the manufacturer’s suggestion and charging the cells with CC-CV mode with 0.5C rate (cut-off at 0.04C) and discharging at 0.5, 1.0, and 2.0C rates, respectively, shown in Fig.1 (a), manifest that the cells cycled at higher discharge rate exhibit longer cycle life than that cycled at 0.5C. It is contrary to the generally accepted notion that high C-rate will accelerate cell aging. However, the expected tendency can be observed when cells were cycled between 4.2 and 3.0V (Fig. 1 (b)). From the results incremental capacity analysis (ICA) for the charge/discharge curves of the cells discharged at 1.0C rate with lower cut-off voltage of 2.75 and 3.0V, respectively, the redox peaks at around 3.53V, those relates with the amount of active graphite, decreases abruptly after 300th cycle where the accelerated capacity fade occurs for cell cycled between 4.2 and 2.75V.That suggests the accelerated capacity loss can be caused by loss of anode material instead of cathode material in additional to the continued loss of lithium inventory that can be observed from the shifting of the peak at around 3.53V to higher voltage and lowering of the peak at about 3.69V (Fig. 2). In order to understand the non-linear capacity fade when cells were cycled between 4.2 and 2.75V, post-mortem studies with XRD, SEM, ICP, and capacity retention for the electrodes obtained from fresh, 200 cycled, and aged cells will be performed for comparison with those of the cells cycled within 4.2 and 3.0V to support the results obtained from ICA. Reference [1] M. Dubarry, C. Truchot, M. Cugnet, B.Y. Liaw, K. Gering, S. Sazhin, D. Jamison, C. Michelbacher, Journal of Power Sources, 196 (2011) 10328-10335. [2] M. Dubarry, C. Truchot, B.Y. Liaw, K. Gering, S. Sazhin, D. Jamison, C. Michelbacher, Journal of Power Sources, 196 (2011) 10336-10343. Figure 1