I've been pleasantly surprised by the impressive recent results that multiple groups have gotten with potassium-based dual-ion batteries. The dual-ion battery s

I've been pleasantly surprised by the impressive recent results that multiple groups have gotten with potassium-based dual-ion batteries. The dual-ion battery stores both positive (in the anode) and negative (in the cathode) ions, which means that both electrodes can be made of carbon rather than metals. Storing negative ions in the cathode also eliminates the major hurdle with sodium-ion: the large Na+ ion doesn't like to be yanked out of the metal-oxide cathode's crystal lattice. I'm not sure why the best stability results I've seen have been with potassium, but anyway: 1500 cycles, 95% capacity retention: https://pubs.rsc.org/en/content/articlelanding/2017/ee/c7ee01535f/unauth https://pubs.rsc.org/en/content/articlelanding/2017/ee/c7ee0... 2000 cycles, "100%" capacity retention (degradation below measurement limits): https://onlinelibrary.wiley.com/doi/full/10.1002/adfm.202001440 https://onlinelibrary.wiley.com/doi/full/10.1002/adfm.202001... It's rare that I see a battery that meets the triple criterion of high stability (>>1000 cycles), cheap materials and high current efficiency (which in a large installation is also related to heat dissipation), but these seem to do it. The density is too low for vehicles, but fine for grids.