Harnessing electrochemistry with Earth-abundant materials

TSJ Science and EnvironmentBy Rylan Bledsoe

All over the world people are changing the climate of the energy industry. National figures show the installed price per watt of solar energy is dropping. Yet, major energy companies are not adopting renewable energy sources at substantial rates. Many communities still rely on fossil fuels because industry officials have not gained confidence in storage and distribution of clean energy technologies. Skeptics of solar and wind power ask, “What happens if the Sun doesn’t shine when we need the energy? How do we re-engineer the grid to accept intermittent energy sources?”

To store large amounts of excess energy in small spaces, we often turn to electrochemical storage: batteries. Most common batteries contain hazardous chemicals such as lead and lithium that may leach into the environment after use and typically have a lifetime of only a few years. Batteries with high energy densities also use rare metals that will simply never be abundant enough to be reasonable for mass energy demands. In the same way solar cells generate energy from Earth-abundant silicon, energy storage must also have its sustainable counterpart.

Chemical metallurgist Donald Sadoway argues that he may have the perfect solution to our energy storage woes. An MIT research scientist and educator, Sadoway is excited to introduce the liquid metal battery. Not only does his invention use Earth-abundant materials, it is more energetically dense than all other batteries on the market. Tesla Motors recently released the Powerwall household unit which uses expensive lithium ion cells and holds roughly 10 kilowatt-hours (kWh), costing $3,500. A comparable-sized unit of Sadoway’s technology could store more than double the energy at a fraction of the price. It would also foreseeably last much longer as a result of its stable chemistry.

The concept uses two components: metal alloy (Mg-Sb) and a mixture of metallic salts. When electrically stimulated by an energy source, magnesium atoms begin to flow out of the alloy and through a layer of molten salt, forming pure liquid magnesium on top. Once thoroughly energized, the liquid metal resting on top serves as an anode, and on bottom a cathode, separated by a molten salt electrolyte.

At first glance, this method seems like it would be hot and dangerous, and indeed, the battery chemistry must operate at high temperatures, 700–1300 degrees F. Consider however, if properly insulated, this heat can be contained or used to fuel other passive systems.

Remember, the goal is to produce mid to large-scale energy storage. You will never see a liquid metal battery in your cell phone, but with the right insulating refractory material, the simplicity and affordability of this battery’s chemistry could make it a reasonable option for many homes, businesses and communitiesespecially in areas without access to rare earth elements. The project has drawn the attention of big names like Bill Gates and has generated $13 million in capital. Sadoway’s company, Ambri Inc. is currently sending out prototype models with a 35 kW-hr capacity and is still working to build a sales pipeline for 2016 and beyond. Visit ambri.com for more information.

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