A BATTERY able to match the output of those used in cellphones from 1/20th of their electrode area may have you dreaming of more talk time.
But putting it in your pocket would be a bad idea – it’s full of molten metal. Instead, its inventors hope it will provide much-needed storage capacity for electricity grids.
Grid-scale batteries would boost efficiency by allowing solar energy to be used at night, for example, or excess power from a nuclear plant to be stored for later.
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Engineers led by at the Massachusetts Institute of Technology were inspired by the way aluminium is smelted using electricity. They created a similar but reversible process that can either consume or release energy.
Their batteries are simply tanks filled with three separate layers of liquid at 700 °C that float on top of one another: the top one is molten magnesium, the bottom antimony and the one in between a salt containing magnesium antimonide, a dissolved compound of the two metals.
When the battery is being charged, magnesium antimonide in the middle layer breaks down into the pure elements and so the upper and lower layers deepen. Discharging the battery reverses the process and releases electrons to provide power. Once heated up to its operating temperature, the battery generates enough heat on its own to keep the liquids molten.
A small prototype provided up to 20 times as much current as a lithium-ion battery – the kind used in portable devices and electric cars – from the same area of electrode, says team member Luis Ortiz. The materials used are much cheaper than lithium (91av, 12 December 2009, p 23), making scaling to up to grid scale feasible, he says.
“Cost-effective storage is the holy grail of the electricity grid,” says Matthew Nordan, a specialist in clean technology at venture-capital firm in Cambridge, Massachusetts, who has not invested in the technology.
The MIT team calculates that a battery the size of a shipping container could deliver a megawatt of electricity – enough to power 10,000 100-watt light bulbs – for several hours.
“A battery the size of a shipping container could deliver a megawatt of electricity”
