Bringing Molten Batteries to Large-Scale Energy Storage
A newly formulated liquid based battery may be supplying us grid power in the near future.
A team of researchers at MIT have developed a molten metal battery that can operate at 500C. This lower operating temperature makes it much more likely that these batteries can be manufactured and operated at a grid-storage scale.
Batteries require positive and negative electrodes which are isolated by a separator to keep the electrode materials physically apart but electrically or ionically connected so charge can pass between the electrodes during the charge and discharge processes. The molten metal battery developed by MIT professor Donald Sadoway and his colleagues is constructed of metals and salts all held in liquid form by elevated temperature.
Until this recent effort the required temperatures exceeded 700C. Their research and testing efforts have netted a 200C reduction which opens up construction material selection, reduced heating energy consumption, and allows considerably longer material life.
The electrodes are molten antimony-lead and lithium with a salt mixture separator. When heated to 450C the two electrodes and the separator self-organize into layers and remain separated due to their densities and immiscibility (like oil and water).
Storage: The Biggest Challenge in Renewable Energy
As more of our grid power is supplied by renewable sources, the variability of these sources becomes more problematic. This is because large systems like classic power plants cannot be near-instantly ramped up and down to match the minute to minute variations in wind and sunlight.
Presently, the only useful form of national electrical grid storage is pumped storage, which consists of hydro plants using reversible turbines backed by reservoirs.
Unfortunately, pumped storage faces its own challenges. There are environmental impacts demanded by the enormous areas that need to be dedicated to the task. The required geography for a successful pumped storage site means that this form of energy storage can only be placed in locations that don’t necessarily match the locations actually needing the electrical energy storage. That means more transmission costs which reduce overall storage efficiency.