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Superior Batteries Get Closer To Reality

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Posted February 17, 2016

Today’s lithium-ion batteries could soon be a thing of the past with researchers claiming to have overcome major shortcomings of lithium metal and lithium air batteries.

"Traditional" lithium-ion battery packs like this one in Nissan Leaf are practical for short distance commutes. However, more advanced technologies are required to make electric vehicles suitable for longer travels.  Image credit: Tennen-Gas via Wikimedia, CC BY-SA 3.0

“Traditional” lithium-ion battery packs like this one in Nissan Leaf are practical for short distance commutes. However, more advanced technologies are required to make electric vehicles suitable for longer travels. Image credit: Tennen-Gas via Wikimedia, CC BY-SA 3.0

Rechargeable lithium metal batteries—capable of higher energy storage than lithium-ion batteries—could not qualify for commercial use earlier due to the problem of dendrite growth on their negative electrode.  Cornell University researchers have proposed a novel nanostructured membrane as the solution to this problem, making lithium metal batteries safer and more efficient for use in portable devices like laptops and smartphones.

Lithium metal batteries, when recharged, spontaneously grow treelike bumps called dendrites on the surface of their negative electrode. Over many hours of operation, these dendrites grow to bridge the gap between the negative and positive electrodes, causing short-circuit.

Current practice for checking the growth of these dendrites involves use of a mechanically strong barrier like ceramic separator between the electrodes. The relative non-conductivity of such barriers, however, means the battery must be operated at a very high temperature–300 to 400 degrees Celsius, in some cases. Also, given their high brittleness, the battery is prone to failure when the barrier cracks.

Cornell team proposes the use of nanostructured membranes with pore dimensions below a critical value to stop the growth of dendrites in lithium batteries at room temperature. Lead researcher Lynden Archer, a chemical and biomolecular engineering professor, credits graduate student Snehashis Choudhury with identifying the polymer polyethylene oxide as particularly promising. The idea was to take advantage of ‘hairy’ nanoparticles, created by grafting polyethylene oxide onto silica to form nanoscale organic hybrid materials, to create nanoporous membranes.

“Instead of a ‘wall’ to block the dendrites’ proliferation, the membranes provided a porous media through which the ions pass, with the pore-gaps being small enough to restrict dendrite penetration,” Choudhury said. “With this nanostructured electrolyte, we have created materials with good mechanical strength and good ionic conductivity at room temperature.”

Lithium air batteries—another promising lithium-ion rival—can store electricity at up to five times the energy density of lithium-ion batteries but are difficult to recharge. University of Illinois (UIC) researchers have come up with a new prototype powered by a surprising chemical reaction that may solve these batteries’ biggest drawback. The findings were reported in the Jan. 11 issue of Nature.

In lithium air batteries, the metallic lithium of the anode, or positive terminal, reacts with oxygen from the air, forming lithium peroxide. Versions tested to date have stored and released energy from lithium peroxide—an insoluble substance that clogs the battery’s electrode.

Battery scientists at the U.S. Department of Energy’s Argonne National Laboratory claim to have developed a prototype that produces only lithium’s superoxide, not peroxide, as the battery discharges. Unlike troublesome lithium peroxide, lithium superoxide easily breaks down again into lithium and oxygen, thus offering the possibility of a battery with high efficiency and good cycle life. The Argonne group designed the battery to consume one electron rather than two and produce the superoxide, said UIC’s Amin Salehi-Khojin, assistant professor of mechanical and industrial engineering.

Written by Uma Gupta, Contributing Author for Technology.Org

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