Si5-pentagonal rings and Y-shaped Si4 building blocks in Li32Si18 system: similarities with the crystalline Zintl phase Li12Si7

Abstract

Potential energy surface screening combined with density functional computations reveal that the Li₃₂Si₁₈ lowest energy structure consists of Si₄ Y-shaped and Si₅-pentagonal moieties, as observed in the crystalline Zintl-phase Li₁₂Si₇. The Li₃₂Si₁₈ system can be interpreted as an assembly of Li₁₀Si₄ (Si₄-Y) and Li₆Si₅ (Si₅-pentagonal) clusters, showing a clear growth pattern towards a material assembled from clusters. Chemical bonding analysis shows that the silicon atoms are strongly connected by covalent bonds, with a significant electron transfer from the lithium resulting in primarily electrostatic Li–Si interactions. This study establishes a structural relationship between Li–Si compounds at sub-nano, nano, and macro scales, which, together with the abundant literature on Zintl-phases of lithium silicides, may open new routes for materials design.