Flow batteries specifically are liquid, or more accurately fluid, there can be gas flow batteries, where the chemical sub-products are pumped in and out of the cells.

They tend to be large utility scale things that look like a chemical plant, correction, are a chemical plant with electrical storage as the product.

Liquid electrolyte batteries have been a thing from when batteries have been invented. But not much work has been done to really scale it up.

You might find the home made batteries of this guy interesting as well https://www.youtube.com/watch?v=eq7fR9ISuCw

It's not a new idea, they already exist.

A huge redox-flow battery is currently under construction in Switzerland https://www.swissinfo.ch/eng/climate-solutions/switzerland-b...