today’s flow batteries pump two different liquids through an interaction chamber where dissolved molecules undergo chemical reactions that store or give up energy. the chamber contains a membrane that only allows ions not involved in reactions to pass between the liquids while keeping the active ions physically separated. this battery design has two major drawbacks: the high cost of liquids containing rare materials such as vanadium – especially in the huge quantities needed for grid storage – and the membrane, which is also very expensive and requires frequent maintenance.

the new stanford/slac battery design uses only one stream of molecules and does not need a membrane at all. its molecules mostly consist of the relatively inexpensive elements lithium and sulfur, which interact with a piece of lithium metal coated with a barrier that permits electrons to pass without degrading the metal. when discharging, the molecules, called lithium polysulfides, absorb lithium ions; when charging, they lose them back into the liquid. the entire molecular stream is dissolved in an organic solvent, which doesn’t have the corrosion issues of water-based flow batteries.