The idea has been kicking around for a while because it's superficially appealing.

Benefits:

- you can store huge amounts of energy in relatively cheap tanks

- because the + and - storage are physically separate, self discharge can be very low

- those two make it appealing for long term storage

Downsides:

- reagents end up being some combination of expensive (vanadium), poisonous, corrosive, etc. resulting in safety overhead

- requires specialized plumbing. This is very expensive. Ultimately this is the issue with nuclear as well, every joint requires careful inspection

- does not scale down nicely to house sizes

- ultimately likely to get economically lapped by incremental improvements to lithium or sodium battery chemistry

- the charge/discharge cell requires a liquid/liquid membrane separator which can exchange charge; these tend to have lifetime issues.