The use of copper as the current collector for the negative electrode has particular reliability and safety implications. At very low cell voltages (usually approximately 1 V for the cell), the potential at the copper current collector increases to the point where copper will begin to oxidize and dissolve as copper ions into the electrolyte. On subsequent recharge, the dissolved copper ions plate as copper metal onto negative electrode surfaces, reducing their permeability and making the cell susceptible to lithium plating and capacity loss. Usually, once a severe over- discharge event has occurred, cell degradation accelerates: once the negative electrode has become damaged by copper plating it will no longer be able to uptake lithium under “normal” charge rates. In such an instance, “normal” charge cycles cause lithium plating, which result in a greater loss of permeability of the surfaces. Ultimately, over-discharge of cells can lead to cell thermal runaway.
From FPRA, the ExPonent report to Fire Research....
Out of my depth... But is this a precursor to the program of replacements? What would be the metric that alerts to the need to get the battery off the a/c ASAP?
Temperature logging? Inability to "take" a charge? What was the urgency in the replacement program? Reported is "over discharge". How many times and what was rhe evidence? What was the condition of the battery at removal? Any evidence of damage, potential hazards to continued presence onboard?
Certainly not "routine"......