Sodium-potassium alloy is a room temperature liquid metal that could unlock a high-voltage flow battery. Source: Antonio Baclig/Stanford University

New flow battery technology from Stanford University may aid in developing a rechargeable battery able to store renewable power created through wind or solar sources.

Until now the kinds of liquids that could produce electrical current in this type of battery have either been limited by the amount of energy they could deliver, have required extremely high temperatures or used very toxic or expensive chemicals.

The researchers tested sodium and potassium, which when mixed form a liquid metal at room temperature, as the fluid for the electron donor side of the battery. Theoretically, this liquid metal has at least 10 times the available energy per gram as other candidates for the negative-side fluid of a flow battery.

A ceramic membrane composed of potassium and aluminum oxide was designed to keep the negative and positive materials separate while allowing current to flow. The membrane and liquid metal advances together more than doubled the maximum voltage of conventional flow batteries, and the prototype remained stable for thousands of hours of operation. This higher voltage means the battery can store more energy for its size, which also brings down the cost of battery production.

The ceramic membrane selectively prevents sodium from migrating to the positive side of the cell. However, this type of membrane is most effective at temperatures higher than 200° C. To develop a room-temperature battery, the researchers experimented with a thinner membrane, which successfully boosted the device’s power output and showed that refining the membrane’s design is a promising path.

The research is published in Joule.