For grid scale storage Li-Ion is a transitional technology at best. It sees interest right now because it's quick to deploy (unlike the much cheaper pumped hydro), and because so much money had been pumped into Li-Ion research and production that other battery technologies have a hard time competing.

If it turns out people don't need all the cycles out their car battery then there's value in capturing that, but new large scale installations will move to other technologies over the next decade or two.