The Development of Jelly Roll Deformation in 18650 Lithium-Ion Batteries at Low State of Charge

Abstract

In this paper, the origin of the jelly roll deformation in 18650 lithium-ion batteries is examined in more detail by combining volume expansion measurements, accelerated lifetime testing, and CT imaging. Based on the presented research, a theory is developed to determine the cause of the jelly roll deformation at low states of charge (0%–20% SOC). The diameter of the cell is increasing during ageing, which reflects the increase of the internal pressure. Continuously growing cover layers of chemical degradation explain the latter. It is concluded that for releasing internal pressure, the jelly roll starts to deform. This deformation accelerates the ageing processes by electrically isolating active material from the current collector and the formation of fresh SEI. In addition, the CT images are used to determine the time of the deformation. Conclusively, it is shown that the jelly roll deformation is driven by cyclic ageing. Due to the correlation of the mean diameter change and the capacity curve, the deformation of the jelly roll and thus the sudden cell death can be predicted by measuring the mean diameter change of the battery.

Production of high-energy Li-ion batteries comprising silicon-containing anodes and insertion-type cathodes

“…Note that the system-level design (e.g. shape/size of the cell, 21,700 vs. 18,650 cells 43 , 44 ) is equally important to the individual compartments, but its discussion is beyond the scope of this manuscript.

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Establishment of transition point in operating mode for Constant Current Constant Voltage (CC-CV) charging of Li-ion batteries

“…The End of discharge voltage for the battery was around 3.23V. Since, the battery may become chemically unstable when discharged beyond 3.2V [11], it was taken care that the discharge was stopped when the battery voltage reached 3.2V.…”

“…This experiment was conducted on a Li-ion battery of capacity 2000mAh with barely 2 charge cycles. The battery was subjected to 3 different rates of charging and they were discharged to a discharge cutoff voltage of 3.21V as beyond 3.2V the battery might be chemically unstable and its lifetime might be negatively affected [11,12,13]. Then the SoC was calculated by coulomb counting method using the equations 2 and 3 and the change in the point of mode transition was then noted for different charge rates.…”

“…The next important factor that determines the transition voltage of 4.2V is the age of the cell or the number of charge cycles that the cell has experienced. An average lithium-ion cell can have a charge cycle ranging from 100 to 1000 [11,12,13]. When dealing with lithium-ion batteries, the end of charge voltage is around 4.2V [14].…”

Piecewise-linear modelling with feature selection for Li-ion battery end of life prognosis

“…Similarly, properties of temperature profiles have demonstrated linear relationships with capacity [21], [22]. Other functions with demonstrated linear relationships with health are voltage regions [14], [23]- [25], internal stresses [17], [26] and combinations of impedances [27].…”