I’ve always found flow batteries to be exciting because of the scalability and the reusability of the materials that you flow from the tanks through the cell. The problem with lithium is “the membrane that separates the two electrodes must allow for quick passage of lithium ions during charging and discharging”, which is a problem that I hope to be working on soon, actually. LiFePO4 intercolation into solid electrodes has been studied and presented as an almost gamebreaking implementation of lithium iron phosphate, but the efficiency can certainly increase from a solid lattice, to say, a porous membrane. That problem is mentioned in the article: “delivers that power is 10,000 times slower than conventional flow batteries”. But this is one of the hot topics going around right now- stay tuned!