Cheaper yes, but I don't think Lithium is that cheap, or ever will be. I think storage (even the expensive ones like pumped hydro) will become more useful over time to handle day/night issues. Probably even enough to handle 2-4 week variations in weather. However for seasonal weather storage is going to be too expensive compared to just building a more solar panels that we don't use in summer.

Of course once we have solar that we won't use in summer there will be programs to use that power. I suspect things like ore refining, steel mills, and the like: will start running in summer only. They will go offline in winter for maintenance. (Investors will make a ton of money buying in summer and selling in winter - as they already do for lots of other commodities that have seasonal aspects)

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.