I very skeptical that lithium-ion batteries are the end game for huge-scale energy storage.

Lithium-ion batteries are the "hot" energy storage. Efficient, powerful, and very light, but also expensive great for a laptop or a car, not so great for massive-scale "cold" storage.

Simpler things like flywheels, compressed air, reverse hydro, other cheaper battery types all seem like more plausible options.