Saturday, September 1, 2012

Clean Energy With a Pinch of salt

A sodium-ion battery being developed in Australia is set to increase solar energy use and reduce our dependence on fossil fuels, according to researchers.

Although bulkier than commonly used lithium batteries, sodium-ion batteries will be cheaper, less toxic, and more environmentally friendly, said Manickam Minakshi, a chemistry and mineral scientist at Murdoch University, in Perth Australia.

“Our water-based sodium-ion battery has shown excellent potential for affordable, low-temperature storage,” he said.

Better batteries

Other batteries used for renewable energy storage – such as molten salt or molten sulphur – only work at high temperatures, making them expensive and impractical. Also, like lead-acid batteries, they are very corrosive and environmental pollutants, which aren't problems with sodium-ion batteries, said Minakshi.

The Murdoch team is now moving towards large-scale commercialisation, and the future could see these batteries connected to solar panels in every home. “This is a very exciting time,” said Minakshi.
The new sodium-ion battery has particular potential when coupled with the green power of solar energy. Widespread use of power from solar panels is limited because there are periods known as ‘non-generation’ times, when power cannot be produced. These include, for example, overcast weather or night-times.

Power in the dark

“Using solar energy panels to get power will only make sense when you can store the power when the Sun’s not shining,” said Stephen Thurgate, vice-president of program development partnerships at Sydney’s Macquarie University.

Murdoch’s new sodium-ion batteries could have applications in small networks with their own battery systems or ‘smart grids’ that use information and communication technology to reduce dependence on centralised power stations, said Thurgate.

While commonly used rechargeable lithium batteries have a higher voltage, making them more suitable for transport and vehicular power sources, they come with a lot of issues, said Minakshi.

Sodium: cheap and abundant

Lithium, for example, is more expensive and far less abundant than sodium in the Earth’s crust.
Another advantage of sodium-ion batteries is that they have a higher density, meaning they are able to store more energy for their weight. Combined with their low costs, they could open up affordable green energy to the developing world.

Lithium and sodium share similar chemical properties, but the sodium ion is 2.5 times the size of lithium, and a big challenge for the Murdoch researchers was finding a ‘host material’ for these large ions.

“Ions travel out of the cathode and into the anode to form a current,” said Minakshi. “As an imperfect analogy, you can think of them as mesh filters that ions pass through. We had to find materials with larger gaps in their mesh.”

Paving a path for alternative energy technology

Murdoch’s new development doesn’t spell the death of the lithium battery, which is still ideal for transportation because of its lighter weight, said Danielle Meyrick, deputy dean of the School of Chemical and Mathematical Sciences. “Sodium is slightly heavier and is much more suitable for stationary energy storage applications [such as] industry,” she said.

The sodium-ion technology could also enable the use of renewable energy in households, moving away from traditional energy generation sources.

“This kind of battery facilitates security of supply and continuity of electricity supply to households," said Meyrick. “It facilitates storage in times when there’s no sunlight, when there’s no wind, [and] when there’s no snow.”

Although there is more research to be done on finding the optimum scale of the battery and cell size, Thurgate said the findings were promising.

“The fact that [sodium-ion batteries are] based on readily available materials, that it’s an aqueous solvent [water-based] – so there’s no fear of the thing being flammable – [and] the fact the energy density is very high... are all great,” she said.

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