Stanford Researchers Report Battery Breakthrough

A research paper published in Sunday's online edition of Nature Nanotechnology could signal the beginning of a revolution in battery technology. The paper, 'Interconnected Hollow Carbon Nanospheres for Stable Lithium Metal Anodes,' was published by a team of researchers from Stanford University that have been working on developing an anode made of pure lithium.

A pure lithium anode has been referred to as the 'holy grail of battery science.' The discovery could lead to longer-lasting cell phones and electric cars capable of traveling longer distances.

The Lithium Standard

All batteries have three basic components: an electrolyte, which sits between a negatively charged anode and a positively charged cathode. Current battery technology works by allowing positively charged ions to collect on an anode made of materials such as silicon or graphite. In existing lithium-ion batteries, lithium is present in the electrolyte as the source of electrons, which are discharged by the anode and received by the cathode.

An anode of pure lithium would be the ideal design and result in an enormous boost in efficiency.

'Of all the materials that one might use in an anode, lithium has the greatest potential. Some call it the Holy Grail,' said Yi Cui, a Stanford University professor of Material Science and Engineering and leader of the research team. 'It is very lightweight and it has the highest energy density. You get more power per volume and weight, leading to lighter, smaller batteries with more power.'

However, a pure lithium anode has so far been impossible to build due to challenges presented by lithium's physical properties. Like all anode materials, lithium ions expand as they gather during charging. But lithium's expansion is 'virtually infinite' compared with the expansion experienced by other materials. That expansion causes cracks and pits to form on its outer surface, allowing the lithium ions to escape and form structures known as dendrites on the surface of the anode. The dendrites then short circuit the battery and shorten its life.

To overcome those limitations, researchers built a protective layer of interconnected carbon domes that sits on top of the lithium anode surface, dubbed 'nanospheres' by the researchers. The coating resembles a honeycomb that is flexible, uniform and chemically unreactive, protecting the anode from chemical reactions with the electrolyte.

Cheaper, Longer, Better

The development represents an enormous step forward toward commercialization, according to the researchers. In practical terms, the discovery could yield enormous cost savings for electronics devices in which the battery usually represents the majority of the cost and weight.

'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 costs only $25,000 -- competitive with an internal combustion engine getting 40 mpg,' said Steven Chu, a former U.S. Secretary of Energy and Nobel laureate and member of the Stanford research team.

'Battery life has been managed to date by a combination of chipset efficiencies, software intelligence and the growth in the size of smartphones,' said Nick Spencer, senior practice director at ABI Research. 'The battery technology itself hasn't improved in many years.'

The increased density that a pure lithium battery would provide would lead not only to greater battery life, but also design flexibility for wearable electronics, making that market much more viable, Spencer said.

Battery anxiety also affects smartphone usage, with many handsets shutting down all functions except voice and text when devices fall below 20 percent or 10 percent battery life, according to Spencer.

'Improved battery life would also increase developer options in terms of application design, which are constrained by batteries to date,' he added.

According to Cui, the technology could find its way to the market soon.

'We're close and this is a significant improvement over any previous design,' Cui said. 'With some additional engineering and new electrolytes, we believe we can realize a practical and stable lithium metal anode that could power the next generation of rechargeable batteries.'


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