Tuesday, April 07, 2015

New aluminum battery from Stanford University

Workers at the Chemistry Department at Stanford University published a paper on an aluminum-based battery: "An ultrafast rechargeable aluminum-ion battery," in the April 6 advance online edition of the journal Nature. The cathode to the aluminum anode is graphite.

Link: http://phys.org/news/2015-04-ultra-fast-aluminum-battery-safe-alternative.html#jCp


Lithium-ion batteries have been a boon for the modern world -- they've replaced the heavier, single-use alkaline type in everything from wristwatches to jumbo jets. Unfortunately, these rechargeable cells are already struggling to keep up with our ever-increasing energy needs. But a new type of aluminum-ion battery developed at Stanford University is not only less explode-y than lithium, but also can be built at a fraction of the price and recharges completely in just over a minute. Best of all, "Our new battery won't catch fire, even if you drill through it," Stanford chemistry professor Dai Hongjie boasted in a recent release.

Unlike earlier aluminum batteries, which generally failed after only about 100 recharge cycles, Stanford's prototype can cycle more than 7,500 times without any capacity loss -- 7.5 times longer than your average li-ion. The aluminum-ion cell isn't perfect (yet) as it can only produce about 2 volts, far less than the 3.6V that lithium-ion an muster. Plus aluminum cells only carry 40 watts of electricity per kilogram compared to lithium's 100 to 206 W/kg power density. "Improving the cathode material could eventually increase the voltage and energy density," said Dai. "Otherwise, our battery has everything else you'd dream that a battery should have: inexpensive electrodes, good safety, high-speed charging, flexibility and long cycle life. I see this as a new battery in its early days. It's quite exciting."


link: http://www.engadget.com/2015/04/06/stanfords-battery-charges-in-one-minute/?ncid=rss_truncated

work by Stanford chemistry professor Dai Hongjie

ArsTechnica gave some details which put the work in better perspective:


The electrolyte the researchers used was a solution of aluminum trichloride dissolved in an organic solvent that also contained chlorine. During charge/discharge cycles, electrons were donated to form AlCl4- and Al2Cl7- ions. This chemistry did not take advantage of the three electrons that aluminum has to donate, so it doesn't represent much of an improvement over lithium. In any case, these ions could slip in between layers of the cathode material—a process called intercalation—at which point they could hand over their spare electrons.

As for the cathode, the researchers decided to experiment with various forms of carbon. Graphite itself doesn't work especially well, as its structure tends to get destroyed by the intercalation of ions. So the authors tried a different form of graphite (pyrolytic graphite) that has cross links between the different sheets of carbon in the material. This graphite added structural strength, but it slowed down the process of intercalating ions so much that the charging and discharge rates were limited.


The reaction of graphite, AlCl3, and chlorine is known.


United States Patent and Trademark Office has granted patent no. 8,956,978, on February 17, 2014, to The Board of Trustees of the Leland Stanford Junior Univerity (California), titled as "Semiconductor device, method for manufacturing semiconductor single-walled nanotubes, and approaches therefor"

Inventors: Dai; Hongjie (Cupertino, CA), Zhang; Guangyu (Palo Alto, CA), Qi; Pengfei (Palo Alto, CA)
Assignee: The Board of Trustees of the Leland Stanford Junior Univerity (Palo Alto, CA)

According to the abstract released by the U.S. Patent & Trademark Office: "Nanotube devices and approaches therefore involve the formation and/or implementation of substantially semiconducting single-walled nanotubes. According to an example embodiment of the present invention, substantially semiconducting single-walled nanotubes couple circuit nodes in an electrical device. In some applications, semiconducting and metallic nanotubes having a diameter in a threshold range are exposed to an etch gas that selectively etches the metallic nanotubes, leaving substantially semiconducting nanotubes coupling the circuit nodes."


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