Why not go the opposite direction entirely?

Grid scale batteries would be better served by Nickel-Iron batteries with pumped electrolyte. They don't have a fire risk like Li-ion and can be discharged to 0% without damage. The downside is the electrolyte needs changing frequently (daily to weekly) but for a grid scale battery bank, that isn't an issue, just trickle through new electrolyte at a constant rate.

It's not a solution for vehicles or portable devices, but for big batteries we shouldn't be looking at solid state.