Donald Sadoways battery startup Ambri seems to finally be breaking through commercially, so I'm quite optimistic about them. It was quiet for a while but now there seems to be commercial progress: https://ambri.com/news/
They had a partnership with NEC Energy Solutions which then left the integration business about 9 months later, so that was probably a business setback. I'm still hopeful that they get a chance to scale with projects like data centers and municipal electric utilities.
The first systems will go into the field as 40 kWh trial systems to demonstrate their effectiveness and operation. The pilot battery for Terra-Scale, which will be one of these trial systems, will be installed late 2021. A larger 1 MWh commercial-scale trial system will be installed in late 2022. Volume production will then start in 2023, at which time Ambri will build battery systems that are available in 1 MWh blocks and have discharge rates of 4 hours or longer.
https://www.greentechmedia.com/articles/read/storage-integra...
Edit: This recent Real Engineering piece updates their current business situation: https://www.youtube.com/watch?v=-PL32ea0MqM
https://teitimes.com/teaser/2021-02/#pf7
The first systems will go into the field as 40 kWh trial systems to demonstrate their effectiveness and operation. The pilot battery for Terra-Scale, which will be one of these trial systems, will be installed late 2021. A larger 1 MWh commercial-scale trial system will be installed in late 2022. Volume production will then start in 2023, at which time Ambri will build battery systems that are available in 1 MWh blocks and have discharge rates of 4 hours or longer.