there’s not enough lithium on this planet to store enough energy for like half of europe nevermind entire world
you know how to do this the right way? use pumped-storage hydropower. need more? build more, then dump power into heaters (or better yet heat pumps) on demand from grid since fossil fuel heating will be replaced anyway. (we’re nowhere close to this, but it can sink a lot of energy quickly while not using it at some other times)