Nanoscale Engineering of Lithiated Nanowires for Battery Electrodes

Engineers at the University of California-San Diego have discovered a new method for growing lithium on heterostructures made of germanium and silicon.

Nanowires are a hot topic right now in battery research, often made of silicon or germanium, because their high surface area provides more room for the ion (usually lithium) to bind, increasing the maxmium potential energy density of the battery.  Higher energy density means, at the same wattage, the battery can last longer.  Concerning transportation, energy density is the key factor preventing batteries from making inroads more quickly into the market (other than price) – we as a society demand to be able to go more then 100 miles without needing to recharge.

So nanowires in battery anodes are a potential gamechanger.  Silicon seems especially promising due to its earthly abundance and ability to hold much more graphite per area compared to standard graphitic anodes.  But a major issue with nanowires has been diffusion through the nanowire itself.

This paper has appeared to find a remedy for this.  By coating germanium nanowires with a layer of silicon, Liu and colleagues show that lithium no longer wants to diffuse into the nanowire, known as lithiation, but rather creates a layer that grows along the axis of the nanowire.  This makes a clear lithium layer completely separate from the germanium nanowire, important in battery chemistry to keep the anodes functioning properly.

Cool stuff, and exciting to see where other great minds take this technology for new battery architecture!  And there’s even a cool YouTube video created by the authors that show the lithiation along the axis occuring!  They darker rod at the beginning is the silicon-coated germanium nanowire, and the gray that starts to take over is the lithium lithiating (doing what it does best!)

The developers do not have a singular purpose in mind for the new nano-architecture, but it appears this structure could help control lithium volume expansion which can often lead to cracks and device breakdown in batteries.  Even more potentially groundbreaking, this method of growing lithium could open the way for completely new geometries for battery architecture.

References

ResearchBlogging.org

Liu Y., Liu X.H., Nguyen B.M., Yoo J., Sullivan J.P., Picraux S.T., Huang J.Y. & Dayeh S.A. (2013). Tailoring Lithiation Behavior by Interface and Bandgap Engineering at the Nanoscale, Nano Letters, 13 (10) 4876-4883. DOI:

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