A battery usually hides its nastiest chemistry from view. Inside many rechargeable systems, useful energy moves through liquids that are strongly acidic, alkaline, flammable, corrosive, or difficult to discard. The battery works, until the same chemistry that made it powerful begins to eat away at its parts.
A team in China and Hong Kong has now built a very different kind of battery. Its electrolyte is a neutral water-based solution of magnesium and calcium salts, chemically close to the brines used to coagulate tofu. In tests, the device ran for 120,000 charge cycles, used nonflammable ingredients, and met several disposal safety standards, the researchers in China report.
It is not ready to replace the battery in your phone. But it points toward a cleaner kind of battery for the place where longevity matters most: the electric grid.