ZSW study finds combination of high-rate and low-temperature cycling increases hazard risks for Li-ion cells
30 October 2014
A team from Zentrum für Sonnenenergie- und Wasserstoff-Forschung (ZSW) in Germany reports in a paper in the Journal of Power Sources that the interaction of high-rate and low-temperature cycling increases the safety hazard for Li-ion batteries.
In an earlier study (Waldmann 2014), also reported in the Journal of Power Sources, the team had identified two temperature-dependent aging mechanisms in Li-ion batteries. In that that study, they cycled the cells at temperatures ranging from -20 °C to +70 ˚C at a rate of 1 C until the discharge capacity fell below 80% of the initial capacity. For 25 ˚C and below, they found that they dominating aging mechanism was lithium plating on the anode; for temperatures above 25 °C, the cathodes showed degeneration and the anodes were increasingly covered by SEI layers.
In the more recent study (Fleischammer 2015), they aged the cells (as in the earlier study, commercial cells with LixNi1/3Mn1/3Co1/3O2/LiyMn2O4 blend cathode, a carbon/graphite anode and a PP/PE/PP tri-layer separator) by high-rate and low temperature cycling, leading to (i) mechanical deformation of the jelly roll and (ii) lithium plating on the anode.
The differences in the safety behavior between un-aged and aged high-power 18650 lithium-ion cells were investigated at the cell and material level by Accelerating Rate Calorimetry (ARC) and Simultaneous Thermal Analysis (STA).
The results show a strong influence of the aging history on the safety behavior. While cycling at high current does not have a strong influence on the cell safety, lithium plating leads to a significant increase of heat formation during thermal runaway and thus to a higher hazard of safety.
—Fleischhammer et al.
Resources
Meike Fleischhammer, Thomas Waldmann, Gunther Bisle, Björn-Ingo Hogg, Margret Wohlfahrt-Mehrens (2015) “Interaction of cyclic ageing at high-rate and low temperatures and safety in lithium-ion batteries,” Journal of Power Sources, Volume 274, Pages 432-439 doi: 10.1016/j.jpowsour.2014.08.135
Thomas Waldmann, Marcel Wilka, Michael Kasper, Meike Fleischhammer, Margret Wohlfahrt-Mehrens (2014) “Temperature dependent ageing mechanisms in Lithium-ion batteries – A Post-Mortem study,” Journal of Power Sources, Volume 262, Pages 129-135 doi: 10.1016/j.jpowsour.2014.03.112
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