OK, I found a short article about Form Energy and their proposed solution for Energy Storage.  It is another entry into the field of sulfur batteries.

"Chiang was experimenting with a new technology, making rechargeable batteries out of sulfur instead of lithium, resulting in incredible cost savings. Chiang’s early lab results for the sulfur batteries indicated they could store energy over longer durations for a tenth of the cost of lithium ion batteries. "

More information about this, although not all that much information, is found in an article linked below:

https://www.engine.xyz/founders/formenergy/