A Novel Phase of Li15Si4 Synthesized under Pressure. Issue 12 (14th April 2015)

• Record Type: Journal Article
• Authors: Zeng, Zhidan; Zeng, Qingfeng; Liu, Nian; Oganov, Artem R.; Zeng, Qiaoshi; Cui, Yi; Mao, Wendy L.
• Is Part Of: Advanced energy materials. Volume 5:Issue 12(2015:Jun.)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2015-04-14
• Subjects: Energy harvesting -- Materials -- Periodicals; Energy conversion -- Materials -- Periodicals; Energy storage -- Materials -- Periodicals; Photovoltaics -- Periodicals; Fuel cells -- Periodicals; Thermoelectric materials -- Periodicals; 621.31
• DOI: 10.1002/aenm.201500214
• Languages: English
• ISSNs: 1614-6832

Abstract

<abstract abstract-type="main" xml:lang="en"> <title> <x xml:space="preserve">Abstract</x> </title> <p>Li<sub>15</sub>Si<sub>4</sub>, 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 Li<sub>15</sub>Si<sub>4</sub> (152 atoms in the unit cell), ab initio evolutionary metadynamics (using the USPEX code) successfully predicts the atomic structure of this new phase (β‐Li<sub>15</sub>Si<sub>4</sub>), which has an orthorhombic structure with an <italic>Fdd2</italic> space group. In the new β‐Li<sub>15</sub>Si<sub>4</sub> phase Si atoms are isolated by Li atoms analogous to the original cubic phase (α‐Li<sub>15</sub>Si<sub>4</sub>), whereas the atomic packing is more efficient owing to the higher SiLi coordination number and shorter SiLi, LiLi bonds. β‐Li<sub>15</sub>Si<sub>4</sub> has substantially larger elastic moduli compared with α‐Li<sub>15</sub>Si<sub>4</sub>, and has a good electrical conductivity. As a result, β‐Li<sub>15</sub>Si<sub>4</sub> has superior resistance to deformation and fracture under stress. The theoretical volume expansion of Si would decrease 25% if it transforms to β‐Li<sub>15</sub>Si<sub>4</sub>, instead of α‐Li<sub>15</sub>Si<sub>4</sub>, during lithiation. Moreover, β‐Li<sub>15</sub>Si<sub>4</sub> can be recovered back to ambient pressure, providing opportunities to further investigate its properties and potential applications.</p> </abstract>