CAES -- compressed air -- is quite mature. Until recently it was considered to have insufficient round-trip efficiency, but that doesn't matter so much anymore. Again, there are numerous interesting variations, including pumping air into a vessel anchored to the sea floor via a pipe from an onshore compressor, and others where heat of compression is banked and added back when extracting power, for better efficiency.
In Chile, a big air liquification system is under construction. In principle this is similar to compressed air storage, but without need for pressure vessels. LN2 can be shipped, and is industrially useful directly.
A float can be attached to a cable looped through a pulley at the sea floor, and winched down from on shore. This, like several other undersea systems, would work scaled down to local utility size.
There are numerous projects preparing to push hydrogen into underground cavities, in some cases cavities natural gas was recently extracted from.
A UK company has a system with a thousands-of-tons weight winched up and down in a disused mineshaft. There are a great many disused mineshafts worldwide. They can often be used to keep compressed air or hydrogen in at the same time.
Ammonia may be synthesized electrically, and stored or shipped in liquid form under light pressure. Ammonia is massively useful industrially, so synthesis equipment would be idle only when stocks are being drawn down.
Form is building out factories to make iron-air batteries.
Ultimately, we will end up using a few that turn out to be cheapest, or otherwise (e.g. ammonia, LN2) valuable. We just don't know which those will be. We do know that Energy Vault, a publicly traded pump-and-dump scheme, will not be among them.