Lithium batteries seem to be mainstream now, offering high energy density, high output current capability.
Stepping down the periodic table there are alkali metals with greater electronegativity than Lithium: sodium and potassium, etc.
So why not sodium and potassium batteries. Can't these offer higher energy density, higher current output? Is the reactivity just so great that the chemistry can't be engineered to provide a practical battery? Or are the safety issues just too great?