There’s a promising new entry in the race to build cheap batteries for storing energy from solar panels and wind turbines. Stanford researchers led by Yi Cui, a professor of materials science and engineering, have demonstrated a partially liquid battery made of inexpensive lithium and sulfur. Cui says the battery will be easy to make and will last for thousands of charging cycles.

Cui believes that the material and manufacturing costs of the battery might be low enough to meet the Department of Energy’s goal of $100 per kilowatt-hour of storage capacity, which the DOE estimates will make the technology economically attractive to utilities. Existing batteries can cost hundreds of dollars per kilowatt-hour of capacity, although several companies are working to commercialize cheaper ones (see “Ambri’s Better Battery” and “Battery to Take On Diesel and Natural Gas”).

The technology is a cross between a flow battery and an experimental type called a lithium-sulfur battery. In a flow battery, positive and negative liquid electrolytes are stored in swimming-pool-size tanks. The batteries are attractive because the amount of energy they store can be increased simply by expanding these tanks, without increasing the size of the electronic connections and other battery parts needed to extract the energy. But they require expensive ion membranes and large amounts of material.