{"id":8374,"date":"2013-10-21T10:47:34","date_gmt":"2013-10-21T17:47:34","guid":{"rendered":"http:\/\/cafe.foundation\/blog\/?p=8374"},"modified":"2013-10-22T10:41:37","modified_gmt":"2013-10-22T17:41:37","slug":"breaking-up-isnt-so-hard-to-do","status":"publish","type":"post","link":"http:\/\/cafe.foundation\/blog\/breaking-up-isnt-so-hard-to-do\/","title":{"rendered":"Breaking Up Isn\u2019t So Hard to Do"},"content":{"rendered":"

A great deal of the research on lithium batteries goes into figuring out how to keep them together for the greatest number of charge-discharge cycles.\u00a0 \u00a0Unfortunately, the active compounds in these batteries that give the greatest energy storage capacity or power output, also tend to be those compounds that come unglued under stress.<\/p>\n

Taking high-resolution 3D movies with X-ray tomography<\/a> (somewhat like the CAT scans used on human subjects), researchers at the Swiss Light Source, a mecca for seeing the unseeable, have witnessed the expansion and contraction of the internal structure of lithium-ion batteries, while the batteries are operating<\/i>.<\/p>\n

\"text\"<\/a>

Particles of a tin oxide electrode experiencing structural changes during charging (1-2 – top row) and discharging (3-4 – bottom row). Illustration: Martin Ebner, Laboratory for Nanoelectronics, ETH Zurich<\/p><\/div>\n

Stanford University\u2019s Dr. Cui has explained that the expansion and contraction of batteries leads to their eventual failure, but until now, there has been no real-time observation of these internal reactions.\u00a0 Martin Ebner, a Ph.D. candidate at the Laboratory for Nanoelectronics\u00a0in the Department of Information Technology and Electrical Engineering (D-ITET) at\u00a0ETH (Eidgen\u00f6ssische Technische Hochschule)<\/a> and Professor Vanessa Wood, head of the Laboratory for Nanoelectronics at D-ITET, used “spectrally pure\u201d and intense x-rays to take a non-invasive look into the \u201ccomplex electrochemical and mechanical degradation\u201d leading to shortened battery life.<\/p>\n

\"Swiss<\/a>

Swiss Light Source – for seeing the unseeable<\/p><\/div>\n

ETH-Professor Marco Stampanoni, a faculty member at the Institute for Biomedical Engineering at D-ITET, runs the\u00a0tomographic x-ray<\/a>\u00a0microscopy beamline at the Swiss Light Source, the synchrotron facility at the Paul Scherrer Institute.\u00a0 Ebner and Wood had Stampanoni focus on batteries, acquiring high-resolution x-ray images that were later assembled into three-dimensional movies that show the flexing and disintegration of the crystalline strutures making up electrodes.\u00a0 Even better, researchers were able to quantify the relevant factors from the 15 hours of image collection.<\/p>\n

According to ETH, \u201cThe data illustrate that tin oxide (SnO) particles expand during charging due to the influx of lithium ions causing an increase in particle volume. The scientists demonstrate that material lithiation happens as a core-shell process, progressing uniformly from the particle surface to the core. The material undergoing this reaction expands linearly with the stored charge. The x-ray images show that charging destroys the particle structure irreversibly with cracks forming within the particles. \u2018This crack-formation is not random,\u2019 emphasizes Ebner. Cracks grow at locations where the crystal lattice contains pre-existing defects. During discharge, the particle volume decreases; however, the material does not reach its original state again; the process is therefore not completely reversible.\u201d<\/p>\n

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lithium particles fractured irreversibly<\/p><\/div>\n

For instance, an electrode that was originally 50 micrometers in one dimension may swell to 120 micrometers under charge.\u00a0 During discharge, it may contract to 80 micrometers, a permanent deformation causing the polymer binder to allow release of individual particles from the electrode.\u00a0 A loss that is repeated on every charge\/discharge cycle, and that lead to final battery failure.<\/p>\n

Researchers chose crystalline tin oxide as a model material because its transformations are also present in other materials, with insights providing, \u201cthe basis for developing new electrode materials and electrode structures that are tolerant to volume expansion.\u201d<\/p>\n

Wood thinks using amorphous or nanostructured materials instead of crystalline ones will provide opportunities to avoid this internal self-destruction. \u201cOn the quest for new materials, one must also bear in mind that they are only of industrial interest if they can be produced in large quantities at a low cost. However, amorphous and nanostructured materials offer a sufficient playground for innovation.\u201d<\/p>\n

Amorphous and nano-materials may offer economic advantages for development, being less expensive to process than crystalline structures overall.\u00a0 This quest for longer-lasting, less-costly battery materials alternatives will eventually pay off in reliable, affordable sources of energy storage.<\/p>\n

The team\u2019s work can be seen in, \u201cVisualization and quantification of electrochemical and mechanical degradation in Lithium ion batteries<\/a>,\u201d published online in Science Express<\/i>, 17th\u00a0October 2013.<\/p>\n