PolyPlus lthium air and lithium seawater

What's the best battery chemistry after lithium ion batteries? PolyPlus Battery is working on lithium air and lithium seawater batteries which could extend electric vehicles' driving range to 500 miles. In a demonstration, PolyPlus puts a battery in water to generate a current. If it proves out as hoped, it says the energy density of its technology will rival liquid hydrocarbons.