Liquid batteries could increase viability of renewables

The technology uses high temperature batteries whose liquid components naturally settle into distinct layers because of their different densities. The three molten materials form the positive and negative poles of the battery, as well as a layer of electrolyte in between. All three layers are said to be composed of materials that are abundant and inexpensive. "We explored many chemistries looking for the right combination of electrical properties, abundant availability and differences in density that would allow the layers to remain separate," said researcher Donald Sadoway. "We found a number of promising candidates." One such combination made up of magnesium, a salt mixture containing magnesium chloride and antimony, would operate at a temperature of 700°C, Sadoway says. "In this formulation, the battery delivers current as magnesium atoms lose two electrons, becoming magnesium ions that migrate through the electrolyte to the other electrode. There, they reacquire two electrons and revert to ordinary magnesium atoms, which form an alloy with the antimony. "To recharge, the battery is connected to a source of electricity, which drives magnesium out of the alloy and across the electrolyte, where it then rejoins the negative electrode." Over the past three years, Sadoway and his team have gradually scaled up their experiments and have now progressed to using 6in wide cells with 200 times the power storage capacity of previous versions. The researchers are now working to optimise all aspects of the system, including the containers used to hold the molten materials. They are also looking at ways of insulating and heating them, as well as ways of reducing the operating temperature to help cut energy costs. While others have researched similar liquid battery systems, Sadoway says he and his team are the first to produce a practical, functional storage system using this approach. He is now working with a liquid metal battery company to help bring the technology to commercialisation. "If this technology succeeds," Sadoway concluded, "it could be a game changer for renewable energy."