Researchers at Perth’s Murdoch University have developed a water-based sodium-ion battery that they say shows “excellent potential” to solve one of the renewable energy industry’s greatest challenges: cheap and reliable power storage for intermittent resources like wind and solar.

“To provide power at non-generation times, excess energy needs to be stored in batteries, but storage technologies now being considered, such as molten salt or molten sulfur, work at high temperatures, making them expensive and impractical,” said Senior research fellow and project leader Dr Manickam Minakshi. “Our water-based sodium-ion battery has shown excellent potential for affordable, low-temperature storage.”

The team from Murdoch’s School of Chemical and Mathematical Sciences tested various metals and phosphates to produce a cost-effective battery with high energy density made from manganese dioxide and a novel olivine sodium phosphate.

Dr Minakshi says sodium appealed as a key ingredient because, while its chemical properties are similar to lithium, it’s a good deal cheaper and far more abundantly available. The main challenge it presented, he says, was to find material for cathodes and anodes capable of accommodating sodium’s ionic size, which is 2.5 times larger than that of lithium.

“Ions travel out of the cathode and into the anode to form a current. 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,” Dr Minakshi said. The team eventually found success with manganese dioxide as the cathode, and a olivine sodium phosphate as the anode.

The resulting battery, says Dr Minakshi, is a safe, cost-effective battery with high energy density, with “excellent potential for large-scale use, including storing energy from wind turbines and solar farms for later feeding into local electricity grids, as well as use in industry.”

But the use of sodium-ion aqueous technology in the pursuit of cheaper and more reliable clean energy storage isn’t original to the Murdoch Uni team. Aquion Energy, a US company spun out of Carnegie Mellon University in Pittsburgh, has a promising-looking version on the theme, with its Aqueous Hybrid Ion (AHI) battery, which is targeted for commercial release in 2013.

The company – headed up by Carnegie Mellon professor of materials science and engineering Jay Whitacre, and previously known as 44 Tech – won $5 million in DoE funding for its “new type of sodium-ion battery” back in 2009, as part of a $620 million government package for improving the US electricity grid.

Back then, Technology Review reported that the start-up’s battery technology promised to be “particularly useful for storing large amounts of electricity cheaply – something that will be essential for making renewable energy the primary source of energy in the US, rather than just the supplemental source it is now.”

As Technology Review has since reported this February, Aquion Energy has this year selected a site for its first (reportedly fully funded) factory – “a sprawling former Sony television factory near Pittsburgh” – and says production capacity will be “hundreds” of megawatt-hours of batteries per year. The company says it initially hopes to make batteries for under $300 per kilowatt-hour, which can be recharged 5,000 times and could last for over a decade in situations in which they’re charged once a day.

Of course, the Murdoch University team’s technology – which differs from the Aquion battery mainly in its “quite novel” use of a phosphate-based anode – is a little less advanced than Aquion’s. Dr Minakshi told RenewEconomy in a telephone interview that work was needed on extending the battery’s cyclability, having achieved 100 power cycles only in the lab so far, with the battery able to last 12 hours at a time if run at an average current rate.

But like Aquion, Minakshi and Co hope that their salt and water derived battery technology might allow some of the world’s 1.4 billion people without electricity to get it – and perhaps to get it without having to hook up to the grid. Minakshi says that while they have no cost estimates at this stage, their batteries will “definitely be cheap,” and will be used for stationary applications, like smart grids and utility-scale. renewables plants.

The next step for the Perth team, he says, is to look for a potential commerical partner. So far, funding for the project has come from the Australian Research Council Discovery Project, through the University. “Our research has reached the stage where we’re ready to move beyond our lab towards larger-scale commercialisation,” said Manikshi. “This is a very exciting time.”