Let's not flatten it. Different materials have different externalities. And are available in different places with different levels of human rights and environmental protections

Sodium is better than lithium in that respect. But both are MUCH better than hydrocarbons.

The amount you need for driving a car for 3 years is several kg vs tonnes. And you can recycle the battery but you can't recycle the oil you burned.

That's why I'm not particularly harsh on lithium externalities. Let's get the low-hanging fruits first before we focus on nuances.

Seawater contains less than 1ppm of lithium (compared to 300-7k ppm in brine). There are zero commercial facilities to produce lithium from sea salt. It's not even a notable byproduct from other seawater-based processing facilities