Taking The Ion Out Of Lithium-ion To Increase Power Storage

Lithium-ion batteries are everywhere because today's technology allows them to hold the most electricity of any other portable power source. But they could hold more if they ditched the ion in the battery's anode and used only lithium.

But lithium alone makes for an unstable battery - until today. Stanford University researchers say they've taken a major step toward developing a lithium-only device that could hold up to four times the power of comparably sized lithium-ion batteries. Their research was published July 27 in the journal Nature Nanotechnology.

"You might be able to have cell phone with double or triple the battery life or an electric car with a range of 300 miles that cost only $25,000 - competitive with an internal combustion engine getting 40 mpg," said team member Steven Chu, the Nobel laureate and former U.S. energy secretary who recently returned to Stanford.

Under today's technology, a battery's key components include the anode, a negative pole from which electrons flow to a device such as car or a smart phone, and the cathode, where the electrons return to the battery, completing the electrical circuit. Between them is a solid or liquid electrolyte containing positively charged lithium ions that shuttle between the anode and the cathode.

Today's anodes are made of graphite or silicon, but they don't hold as much of a charge as pure lithium. But during use, the material in an anode tends to expand during charging. Silicon and graphite don't expand very much, but the Stanford team says the growth of lithium in an anode is "virtually infinite" and uneven, causing bulges and eventually cracks on the battery's exterior.

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That allows lithium ions to escape, forming microscopic branchlike growths called dendrites, which short circuit the battery and limit its longevity.

Further, pure lithium reacts negatively with the electrolyte, depleting it and further shortening the battery's life. Finally, contact between an anode and an electrolyte generates heat, and sometimes even fire or an explosion, and therefore are unsafe, as demonstrated by recent battery fires in batteries in Boeing Dreamliners and Tesla electric cars.

So the Stanford team built a layer of interconnected carbon domes - "nanospheres" resembling a honeycomb - to cover anodes made of pure lithium. This layer is only 20 nanometers, or billionths of a meter, thick, yet it keeps the lithium from reacting with the electrolyte. And it's flexible, so it can keep insulating the lithium as it expands and contracts during charge and discharge.

If the Stanford research pans out, it would achieve the "Holy Grail" of batteries, according to Yi Cui, a professor of material science and engineering and the team leader. "[Pure lithium] is very lightweight and it has the highest energy density," he said. "You get more power per volume and weight, leading to lighter, smaller batteries with more power."

By Andy Tully of Oilprice.com