They currently use some of both NiMh and Li-ion. Toyota is notoriously conservative when choosing technologies. My guess is they still use a lot of NiMH because they have proven long-term reliability, more forgiving characteristics in harsh use, and they already have a lot of existing tooling to support them.
If there any single car that has made the general public comfortable with very expensive batteries in their car: it’s the Prius.
If there any single car that has made the general public comfortable with very expensive batteries in their car: it’s the Prius.