Molten sodium battery energy storage

Can mesh membrane pave the way to mass molten salt ESS deployment?

A team of scientists from Massachusetts Institute of Technology announced this month that they have developed a new separator for molten sodium batteries. The new technology could pave the way for cheaper grid-scale molten sodium battery energy storage.

Molten sodium batteries currently use a ceramic as a battery membrane, but the material is fragile and brittle. The separator developed by the MIT team uses steel mesh with a titanium nitride solution coating, which retains the functionality of the ceramic membrane without its brittleness.

The team’s leaders, professor Donald Sadoway and postdoctorates Brice Chung and Huayi Yin, think that the new battery technology could be suitable for grid-scale stationary energy storage installations. The scientists also state that the new separator membrane could be compatible with other molten-electrode technologies such as sodium-sulfur or sodium/nickel-chloride, potentially revealing new battery design opportunities.

The use of molten salt as an electrolyte has been around since the thirties and the second world war, however the fragility of the delicate ceramic membranes made breakages common and drove up battery costs — the technology never found a place in the mass-market. A steel mesh membrane could bring costs down enough, and make such batteries tough enough, to make them again worth a look.

Lead researcher Sadoway stated that the chemistry was best-suited to large stationary applications where cost was the driving factor rather than size or weight — utility-scale facilities are the obvious choice.

According the US Energy Storage Association, molten salt or NaS batteries have been deployed at several sites across the world, including 190 locations in Japan. They have been used for large-scale energy storage, Japan’s largest such site is a 34 MW/245 MWh facility while the largest NaS storage system in the world is a 360 MW installation located in Chile, which came online early last year.

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