Grid level battery storage is very likely moving to other chemistries. The only reason to use lithium is that it's the chemistry that's the most developed right now, but lithium-ion batteries do not fundamentally speaking have the best properties for grid storage. Lithium-ion is great for energy density, but that's not a critical requirement for the grid.

For grid storage I think molten metal makes the most sense. It's a technology that was developed to be ideal for grid storage from the start. Flow cell batteries might also make sense. And then there's other storage technologies like compressed air, pumped hydro, storing kinetic energy, storing thermal energy, etc.

http://news.mit.edu/2016/battery-molten-metals-0112 https://www.youtube.com/watch?v=NiRrvxjrJ1U