Effect of Duty Cycle on the Lifetime of Single Crystal LiNi_0.5Mn_0.3Co_0.2O₂/Graphite Lithium-Ion Cells

Abstract

The effects of different duty cycles, involving mixtures of charge-discharge cycling and open-circuit storage segments, on the lifetime of single crystal NMC532/graphite cells were studied. Charge-discharge cycling was performed at C/3 with open circuit storage times of 0, 12, 84, 180 h or 3 months applied at upper cutoff voltages (UCV) of 4.1, 4.2 and 4.3 V. Testing was made at 40 °C for a period of 2.5 years. Cells tested to the same UCV showed similar capacity loss and impedance growth with time, independent of the ratio between the time spent cycling or in storage. Differential voltage analysis showed that the vast majority of the capacity loss stemmed from lithium inventory loss at the negative electrode with little or no loss of active materials. The thickness of the pouch cells after testing increased with the fraction of time spent cycling and the amount of gas generated in the cells increased with fraction of time spent in storage at the UCV. These results show that cycled and stored cells age differently, even though a similar capacity fade rate was observed in the first 2.5 years of cell life, which may cause different failure modes at the end of cell life.

Lithium-ion Differential Thermal Analysis Studies of the Effects of Long-Term Li-ion Cell Storage on Electrolyte Composition and Implications for Cell State of Health

“…2 are not due to electrolyte composition changes for the cells stored at 4.2 V and below. This is in agreement with the work of Cheng et al 9 which showed the main reason for capacity loss in cells of this type at 40 °C was Li inventory loss. Particularly, Cheng et al found that varying the storage time between cycles caused cells to lose capacity and gain impedance at similar rates with respect to time, but for different underlying reasons.…”

“…8 Cheng et al found that including an open circuit voltage hold at top of charge between C/3 cycles caused the cells to fail over far fewer cycles, but at similar rates with respect to time, and for different underlying reasons. 9 Further, Ecker et al investigated the relationships between capacity loss and open circuit voltage calendar aging against SOC, finding that storage at increased SOC led to increased degradation, with 100% SOC leading to dramatically faster capacity loss than even 95% SOC. 4 They also showed that storage at 50 °C caused significantly accelerated capacity loss, even when storing cells at 50% SOC.…”

Long-Term Study on the Impact of Depth of Discharge, C-Rate, Voltage, and Temperature on the Lifetime of Single-Crystal NMC811/Artificial Graphite Pouch Cells

“…Numerous publications examined the impact of cycling conditions on the cycle life of various cell chemistries. [8][9][10][11][12][13][14][15][16][17] For example, it has been demonstrated that charging at higher currents and/or lower temperatures induced Li plating, 11,12 and a large body of work agrees that capacity fade increases with SOC and/or DOD. 14,16,17 In addition to cycle life, studies on the impact of temperature and SOC on calendar life of NMC/Graphite cells have been carried out in various commercial cell formats.…”

Review—“Knees” in Lithium-Ion Battery Aging Trajectories

“…While the exact mechanisms leading to LAM deNE are challenging to pinpoint exactly without extensive destructive analysis, LAM can often be identified via differential capacity analysis. 43,44,50,51 However, we note that active material loss from well-made, graphitic negative electrodes cycling under "reasonable" conditions is often low in practice, 4,[58][59][60] so this effect may be most pronounced for cells with poorly made negative electrodes and/or cells with appreciable silicon content in the negative electrode. Furthermore, since negative electrode active material loss must outpace lithium inventory loss for this mechanism to occur, and since the rate of lithium inventory loss is more sensitive to high temperatures (∼40 °C) than active material loss, 4,60 this mechanism is more likely to occur at lower temperatures than higher temperatures.…”