Liquids containing a flowing network of nanoscale particles could make batteries cheaper to manufacture, and thereby reduce the cost of using large amounts of solar and wind power.

Conventional batteries are far too expensive to store hours of electricity from large solar power plants or wind farms for use when the sun isn’t shining or the wind isn’t blowing. But the networked nanoparticles could enable a cheaper new type of battery called a flow battery.

Today, the total amount of wind and solar power is small, and existing fossil fuel plants can make up for any shortfalls. But renewable energy is growing quickly, especially in places such as California, and existing infrastructure might not be enough to support them and keep the lights on. Batteries are cleaner than fossil fuel plants, and can also respond to changes in the sun and wind far faster than fossil fuel plants can.

With conventional batteries, the materials that store energy and the equipment for getting electricity in and out of them are packaged in one container. In flow batteries, the materials that store energy are liquids that can be kept in large tanks and pumped into a relatively small device that either extracts the power or recharges the liquid.

Increasing the energy storage capacity of a flow battery is cheap and easy—just build bigger tanks. However, the materials used in flow batteries now are relatively expensive, and researchers are looking for cheaper alternatives (see “New Battery Material Could Help Wind and Solar Go Big” and “Startup EnerVault Rethinks Flow Battery Chemistry”).

With some alternatives, it is difficult to get charge in and out of the materials; electricity is extracted only from the part of the materials that comes in direct contact with a flat metal plate. The nanoparticle network creates paths for electricity to flow throughout the liquid. This makes it possible, for example, to get from five to six times more energy out of an experimental type flow battery made of lithium and sulfur. The nanoparticle network was developed in the lab of Yet-Ming Chiang, a professor of materials science at MIT.

Nanoparticles have long been used in conventional batteries with solid electrodes, but what distinguishes the new development is having a nanoparticle network form in a liquid, and maintain electrical connections even as that liquid flows.

The U.S. Department of Energy estimates that for batteries to be economical, they need to cost less than $100 per kilowatt-hour, and need to last a decade or more. Such batteries cost hundreds of dollars per kilowatt-hour now. Chiang says it could be possible to build batteries that cost less than $100 per kilowatt-hour with the nanoparticle networks, but the researchers haven’t yet demonstrated that they can be recharged enough times to last a decade.