• Lithium is lighter.

A 144 volt system with 200 AH (that's quite peppy and will take you a long way between charges) will have around 720 lbs worth of lithium batteries. Compared with 1500 lbs or so of lead.

• Lithium likes speed.

Freeway driving won't intimidate your lithium electric car batteries; no matter what kind of motor you've got in your electric car, lithium will keep bringing the amps. They're pretty tolerant of rapid charging and discharging. The "lead foot tax" is less of an issue.

• LiFePO4 is tolerant of deeper discharge.

This might be one of the best qualities of lithium. Another benefit to switching from lead to lithium - aside from weight loss - is the DOD (depth of discharge) that lithium batteries will tolerate. Lead batteries shouldn't be taken below 50% DOD. So lithium not only has a higher energy density, but it has a deeper use of stored energy. Basically AH to AH, lithium will always provide more useable energy than lead.

• lithium salt mining

Lithium mining is environmentally gentle and human friendly.
According to an NPR special on electric cars on the process of lithium is not mined at all, but rather comes naturally in a salt form that is found out in the open in South America (The "Salar" in Bolivia), sun-dried by locals, and trucked to its destination. No miners trapped underground, no fracking, no toxic waste.