Lithium batteries are currently the belle of the battery ball. They have a lot going for them, including high energy storage for their weight and the ability to charge and recharge many times before losing much capacity.

But we’re all familiar with the drawbacks, too. Lithium-ion batteries pose a fire risk, and the lithium and cobalt used in them aren’t the most abundant elements, which makes things more expensive.

Plenty of other possible battery chemistries could compete with lithium, but getting them to live up to their theoretical potential is difficult. Zinc, for example, performs admirably in your non-rechargeable alkaline batteries, and it could theoretically make a safer and cheaper rechargeable one—with a water-based electrolyte rather than a flammable organic one. This hasn’t happened, though, and the reason becomes apparent if you throw the batteries under a microscope.