Structural and electrochemical study of the reaction of lithium with silicon nanowires |
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| Authors: | Candace K Chan Riccardo Ruffo Seung Sae Hong Robert A Huggins Yi Cui |
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| Affiliation: | 1. Department of Chemistry, Stanford University, Stanford, CA, USA;2. Department of Materials Science, University of Milan-Bicocca, Milan, Italy;3. Department of Applied Physics, Stanford University, Stanford, CA, USA;4. Department of Materials Science and Engineering, Stanford University, Stanford, CA 94305, USA |
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| Abstract: | The structural transformations of silicon nanowires when cycled against lithium were evaluated using electrochemical potential spectroscopy and galvanostatic cycling. During the charge, the nanowires alloy with lithium to form an amorphous LixSi compound. At potentials <50 mV, a structural transformation occurs. In studies on micron-sized particles previously reported in the literature, this transformation is a crystallization to a metastable Li15Si4 phase. X-ray diffraction measurements on the Si nanowires, however, show that they are amorphous, suggesting that a different amorphous phase (LiySi) is formed. Lithium is removed from this phase in the discharge to form amorphous silicon. We have found that limiting the voltage in the charge to 70 mV results in improved efficiency and cyclability compared to charging to 10 mV. This improvement is due to the suppression of the transformation at low potentials, which alloys for reversible cycling of amorphous silicon nanowires. |
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| Keywords: | Lithium-ion battery Silicon nanowire Anode Phase transformation |
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