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Researchers solve dendrite problem, boost Li-ion performance

Pic: Tour Group/Rice University

Rice University scientists have created a rechargeable lithium metal battery which is said to have three times the capacity of commercially available lithium-ion batteries. The improvement is ascribed to resolving the dendrite problem, which can cause the battery to fail and, in the worst case, to explode.

In the Rice battery, lithium is stored in what is said to be a seamless hybrid of graphene and carbon nanotubes – essentially a 3D carbon surface that provides abundant area for lithium to inhabit. This design is claimed to approach the theoretical maximum for storage of lithium metal, while resisting the formation of dendrites.

The team found that when the new batteries are charged, lithium metal coats the carbon hybrid anode evenly. “Lithium-ion batteries have changed the world,” said lead researcher James Tour. “But they’re about as good as they’re going to get. [Batteries] won’t last any longer until new technology comes along.”

According to Tour, the anode’s ‘nanotube forest’ has low density and high surface area, with plenty of space for lithium particles to ‘slip in and out’ as the battery charges and discharges. Lithium is distributed evenly, spreading the current carried by ions in the electrolyte and suppressing the growth of dendrites.

In tests, the anode material had a storage capacity of 3.351Ahr/g, said to be close to the theoretical maximum and 10 times that of Li-ion batteries, Tour said. The low density of the nanotube forest means lithium can coat all the way down to the substrate, making maximum use of the available volume.

To test the anode, the Rice lab built full batteries with sulphur-based cathodes that retained 80% of their capacity after more than 500 charge-discharge cycles – equivalent to two years of normal mobile phone use. Imaging the anodes after testing showed no sign of dendrites and, to the naked eye, anodes were dark when empty of lithium metal and silver when full.

“Many people doing battery research only make the anode, because to do the whole package is much harder,” Tour contended. “We’re producing these full batteries, cathode plus anode, on a pilot scale, and they’re being tested.”

Author
Graham Pitcher

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