A Novel Phase of Li15Si4 Synthesized under Pressure |
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| Authors: | Zhidan Zeng Qingfeng Zeng Nian Liu Artem R. Oganov Qiaoshi Zeng Yi Cui Wendy L. Mao |
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| Affiliation: | 1. Department of Geological Sciences, Stanford University, Stanford, CA, USA;2. Center for High Pressure Science and Technology Advanced Research (HPSTAR), Shanghai, China;3. Science and Technology on Thermostructural Composite Materials Laboratory, International Center for Materials Discovery, School of Materials Science and Engineering, Northwestern Polytechnical University, Xi'an, Shaanxi, China;4. Department of Materials Science and Engineering, Stanford University, Stanford, CA, USA;5. Department of Geosciences, State University of New York, Stony Brook, NY, USA;6. Center for Materials by Design, Institute for Advanced Computational Science, State University of New York, Stony Brook, NY, USA;7. Moscow Institute of Physics and Technology, Dolgoprudny City, Moscow Region, Russian Federation;8. International Center for Materials Discovery, Northwestern Polytechnical University, Xi'an, Shanxi, China;9. Photon Science and Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, CA, USA |
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| Abstract: | Li15Si4, the only crystalline phase that forms during lithiation of the Si anode in lithium‐ion batteries, is found to undergo a structural transition to a new phase at 7 GPa. Despite the large unit cell of Li15Si4 (152 atoms in the unit cell), ab initio evolutionary metadynamics (using the USPEX code) successfully predicts the atomic structure of this new phase (β‐Li15Si4), which has an orthorhombic structure with an Fdd2 space group. In the new β‐Li15Si4 phase Si atoms are isolated by Li atoms analogous to the original cubic phase (α‐Li15Si4), whereas the atomic packing is more efficient owing to the higher Si? Li coordination number and shorter Si? Li, Li? Li bonds. β‐Li15Si4 has substantially larger elastic moduli compared with α‐Li15Si4, and has a good electrical conductivity. As a result, β‐Li15Si4 has superior resistance to deformation and fracture under stress. The theoretical volume expansion of Si would decrease 25% if it transforms to β‐Li15Si4, instead of α‐Li15Si4, during lithiation. Moreover, β‐Li15Si4 can be recovered back to ambient pressure, providing opportunities to further investigate its properties and potential applications. |
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| Keywords: | evolutionary metadynamics high pressure Li‐ion batteries Li15Si4 silicon anodes |
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