One of the primary problems with renewable energy, particularly wind and solar, is that power gets generated when the wind or sun is available, rather than when it's most needed. This problem would more or less disappear if the world could come up with a massive, cheap, long-lasting battery design that could be used to store power at grid-scale levels and feed it back out when required.
Lithium batteries are the current darlings (heh heh) of the electric vehicle and consumer electronics industries, due to their high performance, power density and light weight. But lithium is way too expensive a material for grid-scale storage, and when you're talking about making batteries for a whole city, size and weight are far less important than making something super cheap, safe and reliable that will last for as long as possible. All the better if it can be made out of common and easily available materials.
Good news, then, from MIT on this front, as a team of researchers has found a cheap, effective and durable way of resurrecting an old battery idea first documented 50 years ago.
The discovery centers around molten salt batteries such as sodium/sulfur or sodium/nickel chloride designs in which electrodes are kept at high temperatures to keep them in a molten state and allow charge to transfer between them.
Typically, the electrodes need to be kept separate by a special type of membrane that allows certain molecules through and keeps others separate. This has been successfully done in the past with a thin beta-alumina ceramic layer, but commercial use of these batteries has been limited by how fragile and brittle this ceramic layer is, and its tendency to shatter. Not the kind of thing you want to bet your city's power supply on.
The MIT team has discovered a different way of separating the electrodes, using a regular steel mesh coated with titanium nitride. Where the ceramic layer sorts molecules according to their physical size, using the size of holes in the porous ceramic material, the steel mesh uses its electrical properties instead to achieve the same result. And it's much more durable.
The steel mesh technique is applicable to a number of different molten-electrode battery chemistries, and while it doesn't help with small, lightweight battery designs like you'd see in an electric car or mobile phone, the researchers believe it could be a game changer for large-scale, low-cost, fixed-location energy storage.
Such an advance could allow cities to safely and easily ramp up the amount of renewables in its energy mix – and that's good news for everyone.
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