Novel molten metals (aluminium)-based battery offers low-cost, long-lasting storage for the grid

A novel rechargeable battery developed at MIT could one day play a critical role in the massive expansion of solar generation needed to mitigate climate change by midcentury. Designed to store energy on the electric grid, the high-capacity battery consists of molten metals (including molten aluminium) that naturally separate to form two electrodes in layers on either side of the molten salt electrolyte between them. Tests with cells made of low-cost, Earth-abundant materials confirm that the liquid battery operates efficiently without losing significant capacity or mechanically degrading-common problems in today's batteries with solid electrodes.

The MIT researchers have already demonstrated a simple, low-cost process for manufacturing prototypes of their battery, and future plans call for field tests on small-scale power grids that include intermittent generating sources such as solar and wind.

The ability to store large amounts of electricity and deliver it later when it's needed will be critical if intermittent renewable energy sources such as solar and wind are to be deployed at scales that help curtail climate change in the coming decades. Such large-scale storage would also make today's power grid more resilient and efficient, allowing operators to deliver quick supplies during outages and to meet temporary demand peaks without maintaining extra generating capacity that's expensive and rarely used.

MIT scientist Sadoway relied on aluminum smelting to develop the battery. Aluminum smelting is a huge-scale, inexpensive process conducted inside electrochemical cells that operate reliably over long periods and produce metal at very low cost while consuming large amounts of electrical energy. Sadoway thought of running the smelter in reverse so it gives back its electricity.

Subsequent investigation led to the liquid metal battery. Like a conventional battery, this one has top and bottom electrodes with an electrolyte between them. This novel approach provides a number of benefits. Because the components are liquid, the transfer of electrical charges and chemical constituents within each component and from one to another is ultrafast, permitting the rapid flow of large currents into and out of the battery. When the battery discharges, the top layer of molten metal gets thinner and the bottom one gets thicker. When it charges, the thicknesses reverse. There are no stresses involved, notes Sadoway. "The entire system is very pliable and just takes the shape of the container." While solid electrodes are prone to cracking and other forms of mechanical failure over time, liquid electrodes do not degrade with use.