Millions of electric cars are coming. What happens to all the dead batteries?

Source - https://usgreentechnology.com/recycling-reusing-electric-car-batteries/

A few years back I remember reading an article comparing the initial energy deficit that a rechargeable made for a hybrid car like a Prius compared to a Hummer (a stereotypically environmentally unfriendly vehicle). 

I haven't been able to find that article which - from my admittedly distant memory - stated that a Prius would have to be driven for a year and a half before it made up the initial energy deficit from the purification of elements in its rechargeable battery allowed it to catch up to a Hummer which took less energy to source its components.

I have, however, found a couple of articles that address similar concerns around the battery problem with electric vehicles. Creating batteries - particularly modern, high performance batteries - requires sourcing easily oxidized elements such as lithium, purification that requires massive amounts of energy output. Those batteries, sadly, aren't eternal and eventually have to be replaced and recycled. 

And there's the rub. What to do with those batteries once they're spent?

• From Science.org "A Dead Battery Dilemma: with millions of electric vehicles set to hit the road, scientists are seeking better battery recycling methods"
• From Wired.com "Cars Are Going Electric. What Happens to the Used Batteries?"