This is a cathode made from nanoscale particles of crystalline copper hexacyanoferrate which has a lattice that nicely fits hydrated potassium ions. Very high charge and discharge rates. 40000 cycles and still 80% capacity. Projected to be cheap to mass produce.<p>The battery chemistry is cheaper than lithium ion, but also heavier for the same energy storage. Sounds like more than a few times heavier, but hard to tell from the article. In any event, aimed at grid storage, energy density isn't as important as for portable electronics.<p>The fly in the ointment is that they do not have a suitable anode terminal, but as researchers that just gives them something to work on.