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Some lithium ion batteries are plagued with, well, physical problems. Some of the mechanical effects are manifest as batteries that get very hot. Others swell, especially when overcharged, as has been noted by many authors (see here, for example). But seldom has the physical effects of lithium ion movement been demonstrated as dramatically as in this brief video produced by researchers at the Pacific Northwest National Lab.
Investigators at the DOE’s Environmental Molecular Sciences Lab on the PNNL grounds have been observing nanowires composed of tin oxide rapidly change shape and deform when carrying lithium ions. According to a story from PNNL, the wires fatten by a third and stretched 250 percent!
“Nanowires of tin oxide were able to withstand the deformations associated with electrical flow better than bulk tin oxide, which is a brittle ceramic,” said Chongmin Wang, a materials scientist at the lab. “It reminds me of making a rope from steel. You wind together thinner wires rather than making one thick rope.”
Wang, PNNL chemist Wu Xu and Jianyu Huang (Center for Integrated Nanotechnologies, Sandia National Lab) built a small battery with lithium cobalt oxide as the anode and a cathode composed of a single tin oxide nanowire. They then used a special TEM to image the nanowire while charging the battery.
Apparently, the ions cause a reaction front to move through the nanowire creating a moving “Medusa zone” or cloud of dense dislocations. These dislocations are nucleated and absorbed at the moving front.
Wang and the others say the nanowire begins as a crystalline state but the ions convert the tin oxide into a glassy state. They think the amount of accumulated deformation might provide a clue as to why some of these battery materials wear down. However, they also note that tin oxide nanowires perform better than bulk tin oxide cathodes.
“We think this work will stimulate new thinking for energy storage in general. This is just the beginning, and we hope with continued work it will show us how to design a better battery,” says Wang in the release.
There is good article about this in the Dec. 10 issue of Science.