The issue with cars is less efficiency, but more energy density. Li-ion is just at the point where it's energy dense enough to use in cars, and e.g. Tesla vehic

The issue with cars is less efficiency, but more energy density. Li-ion is just at the point where it's energy dense enough to use in cars, and e.g. Tesla vehicles are considered very heavy. Any new battery tech needs to be at least as energy dense as li-ion if it's going to work in vehicles.