Fortunately other chemistries are making their way down the learning curve lithium's been on, and after a few moment reflection it would be astounding if the same types of storage that are optimal for mobile consumers also happen to be optimal for grid balancing, as daily grid balancing can be done pretty reasonably with a c rating[0] of about .2 or even .1, and as long they aren't so heavy they need to be placed on massive foundation piles, weight is not really a factor. Just need to make it as cheap as possible.
[0] battery c rating is what fraction of the battery can discharge in 1 hour https://wikibattery.org/en/wiki-us/battery/charging-rate-cha...