In lithium-ion battery research, sometimes promising-looking electrode materials fail inexplicably. Copper fluoride is one such material. Now, an experimental study reveals the chemical basis of CuF2’s shortcomings, a key step toward rendering that material and related ones useful for battery applications (J. Phys. Chem. C 2014, DOI: 10.1021/jp503902z). Most Li-ion battery research focuses on Li intercalation compounds, spongelike materials into which Li ions insert themselves as the battery is used to provide power. Metal fluorides, including FeF2 and NiF2, are attractive nonintercalating electrode candidates because they provide high charge capacity and capacity retention. But test batteries with electrodes made of CuF2, which is especially promising because of its high operating voltage and charge capacity, fail quickly. A team led by Xiao Hua and Clare P. Grey of Cambridge University and Stony Brook University, SUNY, now know why. On the basis of X-ray, NMR, and electrochemistry analyses, the team finds that during the first charge cycle, CuF2 dissolves in the liquid electrolyte producing Cu+ species. They consume LiF (at the other electrode) and prevent CuF2 from re-forming when the battery is recharged. Those problems might be avoided with protective electrode coatings or by using substitute electrolytes, the team suggests.