A Battery Made of Molten Metals

Estimated reading time: 11 minutes

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 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.

A decade ago, the committee planning the new MIT Energy Initiative approached Donald Sadoway, MIT’s John F. Elliott Professor of Materials Chemistry, to take on the challenge of grid-scale energy storage. At the time, MIT research focused on the lithium-ion battery — then a relatively new tech­nology. The lithium-ion batteries being developed were small, lightweight, and short-lived — not a problem for mobile devices, which are typically upgraded every few years, but an issue for grid use.

A battery for the power grid had to be able to operate reliably for years. It could be large and stationary, but — most important — it had to be inexpensive. “The classic academic approach of inventing the coolest chemistry and then trying to reduce costs in the manufacturing stage wouldn’t work,” says Sadoway. “In the energy sector, you’re competing against hydrocarbons, and they’re deeply entrenched and heavily subsidized and tenacious.” Making a dramatic shift in power production would require a different way of thinking about storage.

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