Do you have any link for the claim that overcharging can produce cyanide?

I have never heard such a thing and all the articles that I have seen about overcharging concluded that such batteries are much safer during overcharging than other kinds of batteries, the worst case effect being battery swelling.

In normal conditions, even during overcharging there are no obvious chemical reactions that could produce hydrogen cyanide.

For instance, at

https://pubs.acs.org/doi/10.1021/acsenergylett.4c02915

it is said that cyanide release can happen only at temperatures above 300 Celsius degrees. Such temperatures cannot be reached in normal conditions.