Lithium-ion batteries power many of today’s electric vehicles and nearly all portable electronics because they cram a lot of energy into small, lightweight packages. But they depend on flammable liquid organic electrolyte solutions to shuttle ions between the electrodes, and those liquids pose a small but potentially serious fire hazard. Scientists have been examining nonflammable solid electrolytes as alternatives. Most of the ones tested have ion conductivity values too low for practical use. Furthermore, the materials leave little room for improvement via chemical customization. To address these shortcomings, the Massachusetts Institute of Technology’s Elise M. Miner, Sarah S. Park, and Mircea Dincă developed a method for loading lithium, magnesium, and aluminum halides into a copper-based metal-organic framework (MOF), which can be tuned by altering the organic linkers. The team found that the MOFs exhibit high ionic conductivity for Li+ and roughly record-tying values for Mg2+ (J. Am. Chem. Soc. 2019, DOI: 10.1021/jacs.8b13418). Optimizing the size and polarity of MOF pores may lead to inherently safe magnesium-ion batteries that benefit from twice as much charge-capacity associated with divalent ions, the team notes.