The batteries (a battery is a bunch of cells) actually are made to be resistant. Be it firewalls between the cells, fuses, fire retardant, exhaust systems, BMS for thermal management etc.

The cells it’s just the nature of the chemistry and form.

The pouch cells used in many EVs are actually more fire prone than the cells used in a Tesla or Rivian. They are very easy to puncture, so in an accident or from manufacturing defects their fire risks are higher. They’re also larger in format and each cell contains more energy, resulting in a risk of more fire if something goes bad.

Prismatic and cylindrical cells are less fire prone and IMO should be the only choices. I wouldn’t be surprised if pouch cells were deemed unfit for vehicles far in the future, but probably not before the industry moves away from them naturally. Many have already announced moving away from pouch cells. One of the reasons they’re used in cars today is there was excess pouch manufacturing capacity compared to prismatic/cylindrical. The existing OEMs had to cobble together a battery supply chain with very few options.

Then the chemistry is important too. Lithium iron phosphate cells are more tolerant and less likely to have thermal runaway than the NCA or NMC (nickle coblat aluminum / nickle manganese cobalt), but their power density is lower, so you aren’t making long range vehicles (or semis with good range) today. LiPo cells are prismatic as well due to the nature of how they are made, so less fire risk from chemistry, and less risk from battery cell form.

Sodium Ion are even less likely, but it’ll be well over a decade before you make more than a commuter car with those, if ever. Toss them in a cheap to build car though and we can make a really great and cheap commuter vehicle in the near future.

Edit: more details.