Cost is influenced by demand. To put this in perspective about 60 TWh of electricity is used globally per day. About 1 TWh of lithium batteries were produced last year.
Even if every country tried to provision just one day of storage, that would cause a massive spike in demand that would inevitably drive up prices. Not to mention it would make EVs more expensive which would have its own negative consequences for emissions reductions.
Alternatively: the spike in demand will result in a similar spike in production capacity, leading to overall lower prices due to better economies of scale.
Battery costs have declined by 99% in three decades. Solar isn't much different. Demand for both have exploded during that time period.
Besides, the current battery storage tech is just a side-product of the EV revolution. If grid battery storage becomes the main solution we'll undoubtedly see cheaper and easier-to-scale alternative tech like iron redox flow batteries be adopted. Bulky, lossy, impossible to transport? Don't care - it's cheap!
If necessary, we’ll switch to sodium chemistry for stationary storage if needed based on commodity input prices. With that said, incredible amounts of both lithium and sodium are cost effectively available today to achieve net zero.
https://www.rethinkx.com/faq-and-mythbusting/myth-there-is-n...
https://x.com/mzjacobson/status/2046604942203658512
https://www.youtube.com/watch?v=XKBTnj1nTWo