This serves as a follow up to India's discovery of a an Iron Ion battery that is literally cheaper than lithium and lasts longer...
I think where you're coming from is likely something like this Lithium battery steals the press thunder from the Iron ion battery. It's likely the Lithium battery will be used in portable, vehicle applications and if it actually has any benefit the Iron would could be used to store surplus electricity for the grid.
Iron might be the future for some energy storage applications (e.g. home batteries) but can't compete for other applications (e.g. Automotive).