Based on the troubleshooting threads we see aroudn here, and others around the internet, the problem is not whether the cells are energy dense or not. A fire that starts is already burning and it wont' matter if the cells had a few percent (or even a few dozen percent) more energy in them than others.
Cell chemistry (which might be different for the higher density cells; I don't know) might make some difference to which cells actually ignite on their own, but actual fire causes aren't always from cells themselves.
As I see it, the problems are:
Cheap packs that are built of literal garbage cells taken out of service for reasons, that should have been recycled for materials but instead were reused.
Construction that doesn't protect cells from shorting to each other or interconnects, and doesn't protect wiring from pinches, insulation failures, disconnects, etc.
Battery Management Systems that don't. Frequently no balancers, no status info, insuffiicnet protections / limits, etc. No protections against a failure of the FETs to turn off the input or output. No protections against tampering by the user bypassing them, etc.
No environmental protections, unsealed casings (if any casing at all!), etc.
Then there are users that "fix" cell problems in otherwise well-designed packs by bypassing the BMS, or they replace a non-broken BMS with one that ends up not having the protections that the original did, so now cells experience excursions outside their ability to handle, and damage occurs, leaving them vulnerable to starting a fire.
Regulation can't stop this part. Well, it could, but only by truly draconian measures.
Speculation below:
To really eliminate all the above issues, they'd have to eliminate all manufacture and sale and use of generic BMS and generic battery packs (including DIY), worldwide. Requiring closed systems that require manufacturer-specific and model-specific BMS that communicate with the EV system, and eliminate the abilty of anyone to repair their own system, instead requiring any battery problem to discard the old one (making more hazardous waste that will never get properly recycled), and replace it with a new one from that specific manufacturer.
When they dont' make them anymore (which because of corporate "greed" will be soon, and often), for various models, the entire EV will have to be scrapped, as the regulations would have to eliminate all generic parts from the supply chain, worldwide, in order to prevent the ability to use any potentially unprotected battery.
(the regulations could insist on a standard so that all the battery packs could be interchangeable, electrically and communication-wise, so at least it wouldn't generate all the scrapped EVs the typical corporate methods would).
Regulations would have to be made making all DIY EVs and hacking illlegal with harsh penalties, or else the risk would remain of users bypassing protections or building their own unprotected packs, etc.
EV adoption would necessarily go down as costs for them skyrocket to probably many times what they cost now.
Etc.
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