This. We have electric engines pinned down. All that's missing from unlimited application of energy is better batteries and better power generation.
Look at it this way: Human endeavor consists of intelligent application of energy to mass. One of the three elements are close to being made trivial! It's very easy to get excited about batteries and renewable energy!
this is not that simple. the article claims that density is similar to lithium batteries, but it doesn't say what kind of density is it. the fact that it charges 20x as much may mean naught if it holds 1/20 energy per kg or per liter.
What do you mean "what kind of density"? "Similar to lithium batteries" means just that, if you have a lithium battery of a certain size, this will hold an amount of energy similar to that.
A 30% difference would still be classified as "similar", but this would still be a big deal since batteries are just borderline capable to provide electric cars with sufficient charge to be acceptable for most people. A battery that's 30% worse than the best current batteries would be unusable.
Energy density can be given in terms of mass or in terms of volume. In general, if a source of a new interesting battery technology does not describe which one they mean in a comparison, you can assume the worst, that is, that they are comparable to lithium-ion in joules/m^3 (at which lithium ion isn't actually that good).
