They've tested the anode and the electrolyte, but they are still working on the final piece--the battery's cathode--using this same method.

FORBES: Breakthroughs

The spheres are then dissolved to leave a 3D-metal scaffold onto which a nickel-tin alloy is added to form the anode, and a mineral called manganese oxyhydroxide to form the cathode.

BBC: Super-powered battery breakthrough claimed by US team