Grids

WSU researchers extend life of lithium ion batteries for electric vehicles

And strangely enough, it involves tiny tin “whiskers,” and something akin to a shave. “It’s caused many, many millions of dollars in failures of microelectronic devices over many, many decades,” Norton said of the growth of whisker-like structures that can lead to short circuits. “The earliest example that I found in the literature was radar problems back in the Second World War that were caused by tin whisker growth on the tin-plated electronics.”

A rechargeable lithium-ion battery is composed of two electrodes – the cathode and the anode – which are separated by an electrolyte. Lithium ions move from the cathode during charging, and are stored as energy by the anode. The reverse occurs during discharging to create an electric current.

Current lithium-ion batteries typically have anodes made from graphite, which only has about a third of the energy-storing capacity of tin. But the tin anodes suffer from whisker growth, which can short-circuit a battery.

Getting rid of the whiskers has consistently bedeviled engineers, including Norton and his team, which has worked on the problem for the better part of a decade.

But about 18 months ago, as Norton puts it, he decided to make lemonade from his lemons.

“We sort of turned the problem on its head,” he said. “We’ve got these interesting structures, so let’s find ways that we can use them, instead of looking at them as annoying structures.”

Norton set out to deliberately create the whiskers, but in a controlled way so they wouldn’t grow beyond their designed length. And he put a physical separator in the battery’s electrolyte, providing another layer of protection.

And the best thing about the new structures, called “nanoneedles,” is that producing them on a large scale should be cheap and easy through electroplating.

“It’s a process that’s been scaled up already,” Norton said. “So we didn’t have to reinvent the wheel in terms of a processing method. We’re using something that is a very cost-effective way of making these coatings.”

That also means battery manufacturers could simply replace their carbon-based anodes with Norton’s new tin-plated anodes, and avoid costly redesigns.

He said the university has already filed patent applications for the technology, and talks have started with commercial electroplating companies. If all goes smoothly, Norton estimated the higher-capacity batteries could start appearing in consumer electronics like phones, laptops and digital cameras in a year, and in electric car batteries in about four years.

www.wsu.edu/