The secret sauce in their high-temperature batteries? Liquid components that naturally settle into distinct layers because of their different densities -- the same trick any good bartender uses to whip up eye-catching cocktails and shots.
Variability is among the biggest problems with renewable energy. When the sun sets, the renewable power source drops off and that can create problems for grid operators trying to maintain a steady electricity supply. Grid-scale energy storage made from cheap and abundant materials could solve the variability problem and make renewable energy a viable source of power.
The researchers use two molten materials to form the positive and negative poles of the battery. An electrolyte layer, which allows charged particles to cross through as the battery is being charged or discharged, is located in between. Each layer is composed of readily available and inexpensive materials, according to a statement from Donald Sadoway, the John F. Elliott Professor of Materials Chemistry at MIT.
The research team combined magnesium for the negative electrode on the top layer, a salt mixture containing magnesium chloride for the electrolye or middle layer, and antimony for the positive electrode on the bottom layer. A detailed analysis of this formulation was published recently in the Journal of American Chemical Society.
According to Sadoway, the battery delivers current as magnesium atoms lose two electrons, which become magnesium ions that travel through the electrolyte to the other electrode. Once they've arrive, they reacquire two electrons and become ordinary magnesium atoms, which form an alloy with antimony. To recharge, the battery is connected to a source of electricity, which pushes magnesium out of the alloy and across the electrolyte, where it joins the negative electrode, according to the MIT News Office.
The team has been able to scale up their experiments, beginning with batteries the size of a shot glass. They're now testing the concept on a six-inch wide battery with 200 times the power-storage capacity of the original.
Others have researched liquid-battery storage systems. According to Sadoway, the team is the first to produce a practical, functional storage system using this approach.
Sadoway, along with fellow team member and MIT Materials Processing Center Research Affiliate David Bradwell, has founded startup Liquid Metal Battery Corp. to commercialize the technology. The two professors are shown in the photo to the right observing one of their test batteries. The battery, is located inside the metal cylinder.
The company still must solve a number of problems before their liquid batteries will be commercially viable, including electrolyte evaporation and the corrosion and oxidation of components. Cost is another ever-present issue that could prevent this successful lab experiment from becoming a practical and accessible solution for utilities.
Photo: Flickr user comedy_nose, CC 2.0