Why the LG ES is right, when it dismisses folded tab as the root cause for the Hyundai Kona's pack fire issue

I will explain why LG Energy Solution is right when it says that it is difficult to imagine that the root cause of the Hyunday Kona’s fire was a folded anode tab.

Dendriting

In general copper pieces laying on the active material are not a good thing – if you place Cu stipe on the cathode, the high electric potential leads to its dissolution into ionic form. The dissolved Cu ions then precipitate on the surface of the anode due to the low potential. However this material doesn’t retain its previous form: when it precipitate it forms dendrites which puncture separator leading to internal short circuit.

But if the Cu dissolves on the cathode side and precipitate on the anode side, it is obvious that folded tab laying on the anode’s active material cannot dissolve. The electric potential is simply too low there. On the anode side plating is the issue – not the opposite. The only case when this can happen is when the cell has been overdischarged, but this was not the case here.

So if folded anode tab cannot form dendrite, how it could damage the cell?

Mechanical damage

It could damage the separator mechanically. But the thickness of the Cu foil used in the cell is around 10um – too thin to puncture a separator (even if you fold it couple of times).

But let us imagine an extreme example: there is a tab burr issue, and this tab is folded. In theory it could damage the separator. But if this is the case, then this cell is subjected to 100% short-circuit inspection. Still, the leakage current may be so small that the short-circuit inspection will fail to detect that – this is exactly the reason why during the cell formation the self-discharging characteristic of the cell is closely monitored. If the voltage drop over period of time is over certain limit, then this cell is discarded.

Capacity loss

There is still one thing: if the anode’s tab is folded, then this anode doesn’t contribute to the cell’s overall capacity. This is important as the recommended C-rate is calculated by the design team with respect to the cell’s capacity, and it doesn’t change over time. So the same amount of current will act differently on the cell with folded tab. This may lead to the failure of the cell during high current charging-discharging, however – yet again the battery plant does 100% inspection of this characteristic. It is done during so called “power grading” when the cell is charged and discharged with the C-rate as high as 4.

All in all, in my opinion the folded tab issue could not lead to the fire of the cell and the root cause lays somewhere else.

Technical cleanliness is important!

However let’s assume that the Cu foil attached onto cathode surface, or some part of the machine failed and started to produce metal chips due to friction.

Will you be able to detect it in your battery plant?

If you say: “We are doing everything according to the VDA 19”, then the answer is “No”.