Interesting. First the economic value of a 4 million mile would be at least 10x at the same energy density, the cost of Co and Ni likely would not be a barrier. Solving the environmental and human issues would of course have to be addressed. If a commercially viable solution becomes likely no doubt investment in Co and Ni sourcing would follow.
I look forward to continuous improvement news.
By the way I have not heard of anyone experimenting with the surface shape (groves, pins, fins) enabled by new gen 3D printers. Just playing around, Likely the current flow is currently not well controlled (lumpy?) but perhaps could be if E fields and current flow are shaped for an optimal density pattern. I am retired and young engineers way more tools to optimize designs. Fun to watch the evolution.